Design of Customizable Assistive Utensil Grip

A Major Qualifying Project Report submitted to the Faculty of the Worcester

Polytechnic Institute in partial fulfillment of the requirements for the Degree of

Bachelor of Science.

Kyle Fitzgerald

Adam Huber

Winton Parker

Date: April 27th, 2017

Advisors:

Professor Allen H. Hoffman

Professor Holly Keyes Ault

Disclaimer: This report represents the work of WPI undergraduate students. It has been

submitted to the faculty as evidence of completion of a degree requirement. WPI publishes these

reports on its website without editorial or peer review.

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Abstract

The objective of this project was to design an assistive utensil device to help individuals

with limited grip strength and range of motion in the completion of daily tasks. The list of

utensils applicable for use with the device includes forks, spoons, knives, pencils and

toothbrushes, but could be expanded with additional design efforts. There were three final

designs produced each with similar functional characteristics but employing different hand

positioning when holding the device. The main advantage of the developed devices is the

capability to customize multiple features for personal effectiveness and comfort. Feedback was

received from professionals in the rehabilitation field that confirmed the effectiveness of the

designs.

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Acknowledgements

Our team would first and foremost like to thank our project advisors Professor Allen

Hoffman and Professor Holly Keyes Ault for their guidance during this project. We would also

like to thank Professor Erica Stults for her help with rapid prototyping considerations for creation

of our prototypes. Lastly, our team would like to thank Melissa Berndt for her help with the

testing of our prototypes.

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Table of Contents Abstract ............................................................................................................................................ i

Acknowledgements ......................................................................................................................... ii

List of Figures ................................................................................................................................. v

List of Tables ................................................................................................................................ vii

1.0 Introduction ............................................................................................................................... 1

2.0 Background ............................................................................................................................... 4

2.1 The Human Hand .................................................................................................................. 4

2.2 Conditions that Diminish Hand Function ........................................................................... 19

2.3 Effect on Daily Life ............................................................................................................ 25

2.4 Assistive Devices ................................................................................................................ 27

2.5 Current Products ................................................................................................................. 28

2.6 Furthering Research ............................................................................................................ 31

3.0 User Requirements .................................................................................................................. 32

4.0 Design Specifications.............................................................................................................. 35

4.1 Critical Design Specifications ............................................................................................. 35

4.2 Important Design Specifications ......................................................................................... 36

5.0 Ergonomic Analysis ................................................................................................................ 38

5.1 Finger Engagement Diameters ............................................................................................ 38

5.2 Surface Area Contact .......................................................................................................... 39

5.3 Tapering of Handle ............................................................................................................. 40

5.4 Angle of Utensil in Hand .................................................................................................... 41

5.5 Optimal Extension of Utensil from the Hand ..................................................................... 42

6.0 Preliminary Design Concepts ................................................................................................. 45

6.1 Ergonomic Handle .............................................................................................................. 45

6.2 Utensil Interface .................................................................................................................. 52

6.3 Repositioning of Utensil in Hand ....................................................................................... 63

7.0 Complete Design Concepts ..................................................................................................... 68

7.1 Designs with Hex-Bit Insert/Gimbal Joint .......................................................................... 68

7.2 Designs with Locking Compression Case .......................................................................... 71

7.3 Design Elimination ............................................................................................................. 73

8.0 Functional Design Selection ................................................................................................... 75

8.1 Preliminary Prototyping ...................................................................................................... 75

8.2 Preliminary Prototype Testing Results ............................................................................... 78

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9.0 Revisions for Final Prototypes ................................................................................................ 87

9.1 Gimbal Joint Assembly ....................................................................................................... 87

9.2 Grip Modifications .............................................................................................................. 91

10.0 Testing of Final Prototypes ................................................................................................... 95

10.0 Final Prototype Survey Responses.................................................................................... 95

10.2 Final Prototype Survey Results and Analysis ................................................................... 97

11.0 Product Manufacturing Considerations ................................................................................ 99

12.0 Conclusion .......................................................................................................................... 105

13.0 Recommendations ............................................................................................................... 107

13.1 Grip Sizing ...................................................................................................................... 107

13.2 Material Considerations .................................................................................................. 107

13.3 Locking Mechanism Design ........................................................................................... 108

13.4 Potential Applications ..................................................................................................... 109

14.0 References ........................................................................................................................... 110

Appendix A: Hex-Bit Gimbal Joint Design Drawings ............................................................... 113

Appendix B: Handle Design Drawings....................................................................................... 117

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List of Figures

Figure 1: Tendons of the Hand (Mount, 2011) ............................................................................... 6

Figure 2: Thumb Muscles (Abbot, n.d.) ......................................................................................... 7 Figure 3: Joints of the Hand (Troy, 2010) ...................................................................................... 8 Figure 4: Radioulnar Deviation of the Wrist (J., 2012) .................................................................. 9 Figure 5: Flexion and Extension of the Wrist (J., 2012) ................................................................. 9 Figure 6: Extrinsic Forearm Muscles (Corcoran, 2012) ............................................................... 11

Figure 7: Grip Force Measuring Knife (McGorry, 2001) ............................................................. 12 Figure 8: Goniometer (Dahl, n.d.) ................................................................................................ 13 Figure 9: Scapula Range of Motion for Daily Tasks (Chadwick et al., 2005) ............................. 14 Figure 10: Hand to Target Paths (Beer et al., 2000) ..................................................................... 15 Figure 11: European Utensil Grip Style (How to Use a Fork and Knife, n.d.) ............................. 17

Figure 12: American Utensil Grip Style (How to Use a Fork and Knife, n.d.) ............................ 17

Figure 13: Ableware Universal Built-Up Handle (Universal Built-Up Handle, n.d.) .................. 28 Figure 14: OXO Good Grips Weighted Utensil Fork (Good Grips Weighted Utensils, n.d.) ...... 29

Figure 15: Norco Universal Cuff (Norco Universal Cuff, n.d.).................................................... 30 Figure 16: Finger Loop Dinner Fork (Finger Loop Utensils, n.d.) ............................................... 30 Figure 17: Shoulder Flexion and Abduction (Ahmad, 2016) ....................................................... 33

Figure 18: Elbow Flexion (Lee, 2014) .......................................................................................... 33 Figure 19: Wrist Flexion and Extension (Common Injuries, 2016) ............................................. 34 Figure 20: Finger Flexion and Extension (Clinical Gate, 2015) ................................................... 34

Figure 21: Thumb/Finger Force Overlap (Seo et al., 2008) ......................................................... 39 Figure 22: Optimal Handle Diameter Calculation (Seo et al., 2008)............................................ 39

Figure 23: Locked Fingers ............................................................................................................ 40

Figure 24: Spread Fingers ............................................................................................................. 40

Figure 25: Tapered Handle Distribution of Forces ....................................................................... 41 Figure 26: Gripping Axis of Hand (Hunt, n.d.) ............................................................................ 42

Figure 27: Short Shaft Precision Grip Range of Motion .............................................................. 43 Figure 28: Long Shaft Precision Grip Range of Motion............................................................... 43 Figure 29: Tapered Handle with Finger Grooves ......................................................................... 46

Figure 30: Pistol Grip.................................................................................................................... 47 Figure 31: Pistol Grip - Top View ................................................................................................ 47

Figure 32: Ball Grip ...................................................................................................................... 48 Figure 33: Fencing Grip ................................................................................................................ 48 Figure 34: Fencing Grip in Hand with Utensil ............................................................................. 49 Figure 35: Dual Finger Slot Grip .................................................................................................. 49 Figure 36: Button Snap Clips (Replacement V Clips, n.d.) .......................................................... 52

Figure 37: Interlocked Tubes with Button Snap Clip ................................................................... 53 Figure 38: Upgraded Button Snap Clips with Enlarged Button Heads ........................................ 53

Figure 39: Zip-Tie Locking Mechanism ....................................................................................... 54 Figure 40: Pelican Case (1200 Small Case, n.d.) .......................................................................... 55 Figure 41: Button Locking Mechanism Design; Base (1); Utensil (2); Button (3); Spring (4) .... 56 Figure 42: Button Release Mechanism - Unlocked (Left) and Locked (Right); Locking Groove

(5) .................................................................................................................................................. 57 Figure 43: Lock ............................................................................................................................. 58

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Figure 44: Key .............................................................................................................................. 58

Figure 45: Lock and Key - Unlocked Position ............................................................................. 59 Figure 46: Lock and Key - Locked Position ................................................................................. 59 Figure 47: Fork with Hex Insert.................................................................................................... 60

Figure 48: Magnetic Hex-Bit Screwdriver ................................................................................... 60 Figure 49: Pin Joint Swivel Mechanism; Rotation Axis (1); Upwards Rotation Stop (2);

Downwards Rotation Stop (3) ...................................................................................................... 63 Figure 50: Gimbal Joint Swivel; Central Ball Attached to Nail (1); Ball Housing (2); Utensil

Paths (3) ........................................................................................................................................ 64

Figure 51: Hex-Bit Insert/Gimbal Joint Assembly ....................................................................... 68 Figure 52: Utensil Head with Hex-Bit Extrusion ......................................................................... 69 Figure 53: Hex-Bit Gimbal ........................................................................................................... 69 Figure 54: Set Screw with Wing Nuts .......................................................................................... 70

Figure 55: Ball Grip with Hex-Bit Insert and Gimbal Joint ......................................................... 70 Figure 56: Pistol Grip with Hex-Bit Insert and Gimbal Joint ....................................................... 71

Figure 57: Tapered Grip with Hex-Bit Insert and Gimbal Joint ................................................... 71 Figure 58: Ball Grip with Locking Compression Case ................................................................. 72

Figure 59: Pistol Grip with Locking Compression Case .............................................................. 72 Figure 60: Tapered Grip with Locking Compression Case .......................................................... 73 Figure 61: 8mm Ball Lift Support (Lift Support Hardware, n.d.) ................................................ 75

Figure 62: Gimbal Joint Ball Grip; Hex-Bit Insert (1); Grip Halves (2); 1/4-20 Bolt (3); Full

Assembly (4) ................................................................................................................................. 76

Figure 63: Gimbal Joint Tapered Grip; Hex-Bit Insert (1); Grip Halves (2); 1/4-20 Bolt (3); Full

Assembly (4) ................................................................................................................................. 76 Figure 64: Gimbal Joint Pistol Grip; Hex-Bit Insert (1); Grip Halves (2); 1/4-20 Bolt (3); Full

Assembly (4) ................................................................................................................................. 77

Figure 65: Compression Pistol Grip; Cover (1); Hinge (2); Handle Base (3); Full Assembly (4);

Locations for Magnets (5) ............................................................................................................. 77 Figure 66: Gimbal Joint Assembly; Custom Hex-Bit Utensil Head (1); Gimbal Joint Cap (2);

Hex-Bit Gimbal Joint Insert (3);Inner Threaded Tube (4);Two 0-80 Fasteners (5) ..................... 88 Figure 67: Threaded Inner Tube ................................................................................................... 89

Figure 68: Gimbal Joint Cap ......................................................................................................... 90 Figure 69: Hex-Bit Gimbal Joint Insert ........................................................................................ 90

Figure 70: Custom Hex-Bit Utensil Head ..................................................................................... 91 Figure 71: Final Ball Grip Prototype ............................................................................................ 92 Figure 72: Final Ball Grip Prototype – Disassembled .................................................................. 92 Figure 73: Final Pistol Grip Prototype .......................................................................................... 93 Figure 74: Final Pistol Grip Prototype – Disassembled................................................................ 93

Figure 75: Final Tapered Grip Prototype ...................................................................................... 94 Figure 76: Final Tapered Grip Prototype - Disassembled ............................................................ 94

Figure 77: Dual Injection Process (Multi Shot, n.d.) .................................................................. 100 Figure 78: BASF Quick Cost Estimator for Injection Molding Thermoplastic Parts - Ball Grip

..................................................................................................................................................... 102 Figure 79: BASF Quick Cost Estimator for Injection Molding Thermoplastic Parts - Tapered

Grip ............................................................................................................................................. 103

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Figure 80: BASF Quick Cost Estimator for Injection Molding Thermoplastic Parts - Pistol Grip

..................................................................................................................................................... 104 Figure 81: Final Grip Prototypes; Pistol Grip (1); Ball Grip (2); Tapered Grip (3) ................... 105

List of Tables

Table 1: Finger and Thumb Joint Ranges of Motion ...................................................................... 8 Table 2: Ergonomic Handle Design Grading Table ..................................................................... 52

Table 3: Utensil Interface Grading Table ..................................................................................... 62 Table 4: Repositioning of Utensil Grading Table ......................................................................... 67 Table 5: Ball Grip Feedback Ratings ............................................................................................ 85 Table 6: Pistol Grip Feedback Ratings ......................................................................................... 85

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1.0 Introduction

In 2012 about 56.7 million Americans, nearly one fifth of the entire United States

population, reported a disability to the United States Census Bureau (US Census, 2012). Of these

56.7 million people, about 19.9 million reported that their disability caused a limitation in the use

of their hands, increasing the difficulty of grasping objects or using utensils. The effects of hand

disabilities can severely complicate the daily life of an individual. Numerous activities of daily

living, often referred to as ADLs, require the use of hands for completion. Simple tasks like

eating or brushing one's teeth can become a challenge with hand disabilities, negatively

impacting the daily life of the individual.

These disabilities can result from a multitude of conditions, ranging from physical

limitations caused by injury to loss of muscle strength and control as a symptom of neurological

disorders. For instance, some neurological disorders may cause weakness and poor muscle

coordination in the hand, which can lower workplace productivity and require the affected

person to modify their approach to ADL completion. A study published in 2012 from the

European Neuropsychopharmacology Journal showed that the costs that result from being

diagnosed with a neurological disorder can be severe, ranging from €200-€30,000 (about $225-

$33,600) per year in expenses. Sixty percent of these expenses were attributed to medical costs,

while 40% were credited to loss in productivity (McDonald et al., 2016). The simplest of tasks

can take much longer than before, and the fine motor skills and grip strength of the hand can

rapidly deteriorate as the disorder progresses.

This limitation to productivity and daily life is not just spurred by neurological disease,

but can also be linked to other trauma. Hand and upper extremity injuries account for over 50%

of orthopedic surgeries according to the American Academy of Orthopaedic Surgeons (Jafarnia,

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2011). Hand and wrist injuries can take several weeks to recover and provide the individual with

replenished range of motion and grip strength. This process can take even longer if the injury

requires surgery or other forms of treatment. Even though treatment is readily available for many

of these conditions, some individuals may never fully return to their previous capabilities. For

example, carpal tunnel syndrome also affects the wrist and hand, and while corrective surgery is

available, patients can still feel pain and have reduced grip strength even with the aid of a brace

(NINDS, 2016). However, disease and injury are not the only situations that can cause a

reduction in hand and arm functionality, as muscle deterioration and poor grip strength can often

arise with old age.

It is therefore highly likely that during some point in the average person’s lifetime, they

will experience some sort of difficulty in controlling utensils or simple tools, regardless of the

source of the ailment. Even though therapy and corrective surgery are available for many of the

causes of hand or arm disability, they are not always effective at alleviating symptoms. There is

often a time period where devices can be used to aid in the day-to-day tasks that are impaired.

Many of these assistive devices are currently on the market; grips that help people with

disabilities more effectively use utensils—like forks and knives—are some of the most common.

However, these devices are not tailored to meet the needs of every individual and are generally

applied to specific conditions. They are rarely customizable to fit an individual grip pattern, and

may be clunky or difficult to use.

The purpose of this project is to design and construct a versatile, customizable utensil

grip to improve the experience of a user with diminished grip strength or limited range of motion

when engaging in ADLs that require the use of the arms and hands. The members of this MQP

team created a series of utensil grip devices that are applicable to a range of potential users,

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while allowing the device to be used with as many household items and for as many task

applications as possible. These products should be a cost-effective alternative to existing

assistive grips with the added capability of customization for the individual’s needs.

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2.0 Background

Before the design process could take place, our team needed to have a strong

understanding of the potential users of assistive utensil grips. While this is the overarching theme

of the background section, there are many specific fields that stem from the knowledge of these

potential users. The following section describes the functionality of the human hand, conditions

and disorders that can reduce hand functionality, how these reductions in hand capability have an

effect of daily life, and assistive devices currently on the market.

2.1 The Human Hand

The human hand is often regarded as one of the most differentiating factors between the

human race and other mammals. It is a marvel of anatomical engineering that has resulted from

millions of years of intricate evolution. “[The human hand] gives us a powerful grip but also

allows us to manipulate small objects with great precision. This versatility sets us apart from

every other creature on the planet” (McGavin, 2014). The extensive capabilities of the hand are a

culmination of several internal elements operating together. This section will discuss the

anatomy of the hand, its associated biomechanics, and the involvement of these biomechanical

properties in an individual's ability to complete everyday tasks.

2.1.1 Anatomy

An understanding of the hand’s anatomy is necessary in order to design an assistive grip.

The human hand can be divided into several components including the bone structure, muscles,

tendons, nervous system, and skin. The human hand and wrist consist of 27 bones, which are

classified as carpals, metacarpals, and phalanges. Eight carpal bones are present in the wrist,

organized in two rows with very limited motion between each bone. The hand has five

metacarpal bones each composed of a base, a shaft, a neck, and a head. Each of the four fingers

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is composed of proximal, middle, and distal phalanges, while the thumb has only proximal and

distal phalanges.

The muscles utilized by the hand are broken down into two groups: intrinsic and

extrinsic. Intrinsic muscles are found within the hand, while extrinsic muscles are located in the

forearms and control the hand through connecting tendons. The extrinsic muscles are further

divided into extrinsic flexors and extrinsic extensors. The intrinsic muscles are divided into four

groups: the thenar, hypothenar, lumbrical, and interossei muscles.

The nervous system of the hand is composed of three main nerve branches: the median,

ulnar, and radial nerves. Each of these nerves contains a motor component that is responsible for

movement and a sensory component that sends signals back to the brain. These sensory signals

are sent to the brain and perceived as the sensation of touch.

Finally, the skin of the top of the hand, called the dorsum skin, is attached to the muscles

and tendons of the hand by loose tissue that is thin and flexible. However, the skin of the palm is

very different; it is much thicker than the dorsum skin and is attached to the bones by stronger

fibers. Because of these qualities, it is better suited for tasks like grasping an item while

maintaining item stability (Wilhelmi, 2016).

2.1.2 Biomechanics

The impressive capabilities of the hand can be seen when the multiple internal

components function synchronously. The fingers of the hand have two main types of motion:

flexion and extension. Flexion of the fingers occurs when the fingers are brought towards the

palm to make a fist. This type of motion is used when the person attempts to grab an object, and

is accomplished by contracting the extrinsic flexor muscles on the palm side of the forearm.

These muscles are attached to flexor tendons and finger pulleys, which are used to enable the

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movement of the fingers (Figure 1). Each of the four fingers contains five annular pulleys and

four cruciate pulleys, while the thumb has two annular pulleys and one oblique pulley. Extension

of the fingers occurs when the fingers are brought away from the palm and are straightened,

made possible by the extrinsic extensor muscles positioned on the top of the forearm. These

extensor muscles pull the extensor tendons that are located on backside of the fingers to bring the

finger segments into alignment (Wilhelmi, 2016).

The intrinsic muscles are responsible for precise and individual movements of the

fingers. The interossei muscles control adduction and abduction of the fingers. A group of three

muscles called the hyperthenar muscles, located in the palm, control the movement of the little

finger. On the opposite side of the hand is a group of four muscles called the thenar muscles that

control the movement of the thumb (Figure 2). There are 8 muscles located in the hand and

forearm that control abduction, adduction, extension, flexion, and opposition of the thumb

(American Society for Surgery of the Hand, 2016).

Figure 1: Tendons of the Hand (Mount, 2011)

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There are four main joints involved in the movement of the hand: the radiocarpal joint,

the carpometacarpal joint, metacarpophalangeal joint, and the interphalangeal joint. The angles

for regular range of motion for each finger and the thumb joint can be seen in Table 1, while the

joints themselves are shown in Figure 3. The thumb’s main types of movement are flexion and

abduction. Abduction of the thumb occurs when the thumb is moved away from the palm, while

flexion occurs when the thumb is brought across the palm (Gulick, 2013). Generally, a smaller

range of motion in hand joints is necessary for gripping large objects while smaller grips require

a greater range of motion (McDonald et al., 2016).

Figure 2: Thumb Muscles (Abbot, n.d.)

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Table 1: Finger and Thumb Joint Ranges of Motion (Gulick, 2013)

Joint Normal Range of Motion

Radiocarpal 60-80° Flexion. 60-70° Extension.

Thumb CMC 70° Abduction. 45-50° Flexion.

Thumb MCP 75-90° Flexion.

MCP 90° Flexion.

IP 100° PIP Flexion. 80° DIP Flexion.

The human wrist provides additional angular degrees of freedom that allow for better

positioning of the fingers. Movement of the hand side to side at the wrist is known as radioulnar

deviation (Figure 4), while the up and down movement of the wrist is known as flexion and

Figure 3: Joints of the Hand (Troy, 2010)

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extension (Figure 5). Extension results in the fingers pointing upwards and flexion results in the

fingers pointing downwards if the palm is facing the ground.

The nervous system of the hand allows the brain to react to the movements and sensory

signals of the hand. The motor components of each of the three main nerves control different

aspects of the hand muscles. The median nerve is responsible for the pinch and fine precision

functions. The ulnar nerves are located in the muscles used for power grips and control their

contraction and relaxation. The radial nerve is associated with stabilization of the hand and the

position of the hand by innervating the wrist extensors (Wilhelmi, 2016).

Figure 4: Radioulnar Deviation of the Wrist (J., 2012)

Figure 5: Flexion and Extension of the Wrist (J., 2012)

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2.1.3 Grip Configurations

The biomechanics of the hand allow for a variety of configurations and angles of the

fingers and thumb. One the most important configurations that allows for the holding and

utilization of objects are grips. There are two main grip types that are used to manipulate objects,

commonly known as precision and power grips. A precision grip employs the smaller hand and

finger muscles to better control tools. Precision grips are generally used with writing or eating

utensils and involve a pinch between a few fingers and the thumb. This style of grip is limited in

strength but is optimal for finer movements. In contrast, power grips engage the forearm

muscles, which allows for much higher grip strength as all fingers and the thumb are wrapped

around the object within the palm. The muscles used during power grips are the flexor digitorum

profundus (FDP), flexor digitorum superficialis (FDS), lumbricales, palmer interossei, flexor

pollicis longus (FPL), opponens pollicis (OP), and the flexor pollicis brevis (FPB) (Figure 6). In

a power grip, the fingers are manipulated mostly by muscles located in the forearm through the

use of tendons (Gulick, 2013). This allows the fingers to exert much greater forces than if the

muscles that activate grip were located solely within the hand. An appropriate example of the

scale of these forces can be seen in the act of rock climbing where the individual can suspend

their entire body weight by just the tips of their fingers.

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Figure 6: Extrinsic Forearm Muscles (Corcoran, 2012)

2.1.4 Essential Hand Capabilities

When holding an object, there are three main abilities the user's hand must possess to use

the object in the desired way. These capabilities are grip strength, range of motion, and

coordination. Grip strength is required to keep the item in the hand. Range of motion in the arm

and finger joints are necessary to apply proper force in specific areas for stability and

maneuverability. Coordination in the nerves, muscles, and tendons must be present to ensure that

the components of the arm function together in a desired manner. These capabilities are

fundamental to the performance of the hand. If any of these capabilities are reduced or

eliminated, an item held by the hand may not be fully supported or usable in an effective way.

These three capabilities are discussed in more detail in the following sections.

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2.1.4.1 Grip Strength

Grip strength is an essential aspect of performing even the simplest of tasks. This hand

function is required for grasping, lifting, and moving items, and must not drop below a minimum

threshold in order to effectively complete specific tasks. For completion of ADLs, grip strength

is usually the first hand function that is employed by the individual.

A study performed by researchers at the Liberty Mutual Research Center for Safety and

Health in 2009 quantified the forces applied by a human hand during a variety of exercises. The

experiment attempted to simulate the cutting of meat using a kitchen knife by slicing certain

thicknesses of clay. Strain gauges were positioned on the sides of the knife handle to measure the

strain applied to the knife handle that resulted from the fluctuating amounts of applied grip force.

A power grip style was used to complete the task, and the knife used for the experiment is shown

in Figure 7 (McGorry, 2001).

Figure 7: Grip Force Measuring Knife (McGorry, 2001)

2.1.4.2 Range of Motion

When completing ADLs, the next step after grasping an object is to move the object in

question to its desired location successfully. Moving the arm from a position of rest to the

desired end location requires a certain range of joint motion and muscle mobility that varies for

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each section of the arm or hand. The shoulder, elbow, wrist, and fingers all must meet the

minimum range of motion requirements for task completion.

Range of motion is measured using a goniometer or other electromagnetic tracking

devices, which come in many forms (Figure 8). Different sizes of goniometers are used to

accurately measure the different joints of the body (Houglum et al., 2016).

Figure 8: Goniometer (Dahl, n.d.)

Each of the joints of the arm has different required ranges of motion to complete

activities of daily living. A study conducted by researchers at Delft University of Technology in

2003 measured the ranges of motion of the shoulders and elbows of 24 healthy adult females

when completing ADLs (Chadwick et al., 2005). The motions of scapula, humerus, and forearm

were recorded using an electromagnetic tracking device and calculated for the 5th and 95th

percentiles. In this study, the 5th percentile was considered to be the minimum required range of

motion to complete the ADL. Figure 9 shows a portion of the table of results from the

experiment, detailing the angular range of motion of the shoulder for the majority of people.

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Figure 9: Scapula Range of Motion for Daily Tasks (Chadwick et al., 2005)

As an example from this study, eating with a spoon requires a minimum range of 13.3° of

scapular laterorotation (also known as lateral rotation), which is defined as positive or upwards

rotation about the z-axis of the shoulder. The full table of results appears in the published study

(Chadwick et al., 2005). If this minimum range of motion is not met, along with the minimum

ranges of motion for other joint rotations, then eating with a spoon cannot be successfully

completed in a normal manner.

Without the ability to effectively move the muscles of the arm from the starting point to

the desired end point, the majority of ADLs would be very difficult if not impossible to

successfully accomplish; muscle mobility and range of motion are essential for task completion.

2.1.4.3 Muscle Coordination

The third essential hand and arm capability required for ADL completion is adequate

muscle coordination of the arms and hands. Muscle coordination is the ability of the body to

correctly combine force with spatial direction, determined by the brain, to move the muscle in an

intended manner. A reduction of this capability means the brain is unable to send the correct

neurological signals to move the muscles to perform a desired task.

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There are often changes in hand motion patterns in individuals who experience a

reduction of muscle coordination. In 2000, a study was published by researchers from

Northwestern University that correlated individuals with hemiparesis (weakness on one side of

the body) with a disruption of muscle coordination in the affected arm. The experiment mapped

the hand trajectories of 11 subjects when moving from a central position to 16 surrounding target

locations on a horizontal plane. Of the subjects, three of them had no existing conditions that

would affect the hand to act as the control group while the other eight subjects had been

diagnosed with hemiparesis. The results (Figure 10) show a longer path to each target with

greater deviation from a straight line in comparison to the control group. The shaded circles

represent the desired targets for hand placement, and the lines represent the paths followed by the

hands (Beer et al., 2000).

Figure 10: Hand to Target Paths (Beer et al., 2000)

This study demonstrates that while ADLs can sometimes still be completed without

standard muscle coordination, a lack of muscle coordination can make task completion more

difficult. Muscle coordination is necessary for performing activities of daily living in an efficient

manner, especially when fulfilling tasks that require the fine motor skills of the hand.

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2.1.5 Uses in Daily Tasks

The three essential hand capabilities discussed above play an integral role in everyday

tasks and objectives. These ADLs consist of the many self-care tasks completed nearly every day

by a typical individual. These tasks include, but are not limited to, bathing, dressing, cooking,

eating, grooming, and other household chores. For each ADL, hands almost always play an

essential role in their completion. To accomplish each task, the hand makes use of different

biomechanical operations for movement and force application. For the purpose of this project,

the use of household tools and utensils is the main focus.

Some of the most commonly used tools in households today are eating utensils.

Depending on the type of food being consumed, utensils are generally held in a precision grip.

This grip primarily uses the intrinsic muscles of the hand for stabilization and control. In the case

of using a fork to consume solid food, the majority of extremity movement occurs from the

elbow to the hand. The two main techniques for eating with a fork are known as the European

style and the American style.

In the European style (Figure 11), the fork is placed in the left hand with the prongs

facing down as the index finger stretched down the backside of the fork with the thumb

supporting from beneath. The middle finger traps the end of the fork against the palm. Using this

style, the process of eating begins with the extension of the forearm to pierce the solid food.

Supination of the forearm rotates the food toward the face and flexion of the elbow and wrist

bring the fork to the mouth.

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Figure 11: European Utensil Grip Style (How to Use a Fork and Knife, n.d.)

In the American style (Figure 12), the fork is generally held in the right hand with the

prongs facing upwards between the thumb on the top and two fingers as side and bottom

supports. As the fork is tilted downward toward the food the forearm is slightly pronated. The act

of either scooping or piercing the solid with the fork is a result of simultaneous supination of the

forearm and ulnar deviation of the wrist. Once the solid food is on the fork, flexion of the elbow

brings the fork to the mouth. A very similar sequence of motions occurs when eating liquid food

but with a smoother transition of movements in order to keep the liquid within the spoon.

Figure 12: American Utensil Grip Style (How to Use a Fork and Knife, n.d.)

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During the team’s analysis of a healthy individual eating solid food with an American

grip, the angles of the wrist and elbow were recorded at their extremes to gather the approximate

angular range of motion. It was found that the extremes occurred when the individual was

piercing or scooping food and when the individual transferred the food to the mouth. As the

individual was picking up food from the plate, the flexion/extension angle of the elbow and the

wrist were 84° and 38°, respectively. When the individual was transferring the food to their

mouth, the flexion/extension angle of the elbow and the wrist were 65° and -10°, respectively.

These results gave a 19° range of motion for the elbow and a 48° range of motion for the wrist.

Another daily use of hand biomechanics can be seen during the process of brushing one’s

teeth. Generally, the toothbrush is held in a power grip with the majority of the movement

coming from the shoulder and the elbow. The orientation of the individual’s joints is different

when brushing the front of the teeth than when brushing the back molars. An analysis of a

healthy individual brushing their teeth was conducted, with the range of angles experienced by

the wrist recorded. The wrist allows for two planes of rotation, radioulnar deviation and

flexion/extension. The angles of the wrist on these two axes were measured as the individual

brushed their front teeth and their back molars, giving the extremes of angular range of motion

for this activity. As the individual brushed their front teeth, the radial deviation was 42° and

flexion was 37°. When brushing the back molars, the ulnar deviation was 8° and extension was

32°. This gives the approximate range of motion for radioulnar deviation and flexion/extension

as 50° and 69°, respectively. Radial and ulnar deviation are shown in Figure 4, and wrist flexion

and extension are shown in Figure 5 in Section 2.1.2.

With many daily tasks such as the ones above, specified grip strength, ranges of motion

for components within the arm, and muscle coordination are necessary. While muscle

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coordination can be difficult to quantify, a minimum level is still required for ADL completion.

Some tasks require more force or muscle exertion than others, while others may require great

flexibility movement to complete them comfortably. In all ADLs, a certain level of coordination

between the brain and the muscles is necessary to perform the correct movement and force

application. This creates a combination of both physical and neurological abilities that allow an

individual to perform tasks. The following section will discuss specific conditions in which this

duality of abilities can be restricted, thus resulting in the increased difficulty of completing daily

tasks.

2.2 Conditions that Diminish Hand Function

The extensive capabilities made possible by the biomechanics of the human hand can be

disrupted by a wide range of diseases and other conditions. Ranging from conditions as simple as

hand and wrist injury to severe neurological disorders, these ailments can target many

components of the hand’s anatomy, including the musculoskeletal and nervous systems. This

section provides an encompassing summary of conditions that may contribute to a reduction of

the three hand characteristics that are the focus of this project: diminished grip strength, reduced

range of motion/mobility of the hands and arms, and a lack of muscle coordination.

Although there are many disorders that can affect hand functionality, the conditions

described in this section encompass a broad range of symptoms that can diminish the

functionality of the human hand. While each of these conditions may have several different

symptoms influencing a variety of bodily functions, they all have some effect on an individual's

hand or arm function.

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2.2.1 Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic Lateral Sclerosis, also known as Lou Gehrig’s Disease or simply ALS, is a

fatal neurological disorder that deteriorates the strength of the muscular system. This disease is a

rapidly progressive disease, meaning that symptoms develop very quickly as the disease begins

to spread. Individuals with ALS will rapidly encounter muscle weakness and eventual failure,

starting with weakness and twitching in the arms, hands, legs, and swallowing muscles. Those

affected will quickly lose the ability to speak and easily communicate, and typically die within 3-

5 years of diagnosis, due to lung failure (National Institute of Neurological Disorders and Stroke

[NINDS]).

ALS sufferers can encounter diminished grip strength, reduced range of motion, and a

lack of muscle coordination. As the muscles of the body begin to fail, all three fundamental hand

characteristics will not be able to perform at a level suitable for task performance and

completion. While there is a relatively short period of time where the hands and arms can still be

effectively used, it is important to those with ALS that independence regarding daily activities

can be retained for as long as possible.

2.2.2 Multiple Sclerosis

Multiple Sclerosis (MS) is another neurological disorder that affects the muscular system

and, while it can be less severe than ALS, may cause a much broader range of potential

interruptions to daily life. It can be difficult to diagnose MS, as symptoms can often fluctuate on

a day-to-day basis. Often, doctors may be able to diagnose MS as symptoms start, yet sometimes

it can take months or even years of incorrect diagnoses to accurately pinpoint the condition

(NINDS).

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Grip strength and muscle coordination are both impacted by the onset of multiple

sclerosis. While MS can cause partial paralysis in some severe cases, it is often simply a

breakdown of muscle tissue in the fingers that can diminish grip strength. One of Multiple

Sclerosis’ many possible symptoms also includes a decrease in coordination and muscle response

time. Although MS can especially affect muscle coordination in the legs, impacting balance and

gait, the coordination of the arms and hands should also be considered for the effective

completion of ADLs (NINDS).

2.2.3 Cerebral Palsy (CP)

Another example of a non-fatal neurological disorder is Cerebral Palsy (CP), which does

not affect every individual the same way, similar to MS. While some individuals may require

assistance with ADLs, some can function without the aid of a caregiver or assistive devices and

treatments (NINDS). It is important to note that CP, unlike ALS or MS, is a birth defect and

therefore not a progressive disease. Those affected by CP are affected as children, which is not

necessarily the case for individuals with ALS or MS.

Cerebral Palsy can induce spasticity in affected individuals, which causes stiff muscle

tone and exaggerated reflexes. Performing a task when afflicted with spasticity can increase the

time needed to complete the task due to the exaggeration of arm reflexes, which affects the

mobility of the arm muscles (NINDS). The stiffer muscle tone can cause a decrease in the range

of motion of the shoulder, elbow, wrist, and finger joints as the muscles remain in a constantly

contracted state. When the arm muscles are continuously being contracted, the range of motion is

decreased as the ligaments are pulled taut and joints do not bend as fluidly as joints not affected

by spasticity. Another common symptom of individuals affected by CP is ataxia, which is a

distinct lack of muscle coordination when performing voluntary movements (NINDS). If ataxia

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affects the arm and hand muscles, it can be very difficult for the individual to move an object

from its start to end point. The signals sent from the brain to the arm and wrist muscles in an

unaffected individual are clearly transmitted and the task is easy to complete. Ataxia does not

allow these signals to transmit in a clear and efficient manner, although the individual still

comprehends what actions are needed to complete the task in question.

2.2.4 Carpal Tunnel Syndrome

One of the most common types of a neurological disorder of the upper extremity is carpal

tunnel syndrome. Carpal tunnel is an affliction that occurs when the median nerve in the forearm

becomes constricted at the wrist, causing numbness or tingling in the wrist and hand, and can be

very painful. This condition can develop over time due to overuse or may be caused by sudden

wrist trauma, and occurs most often in adult women, (NINDS).

The flexion of fingers can become an issue for individuals with carpal tunnel syndrome,

causing a reduction in grip strength. As the median nerve of the wrist becomes inflamed, forming

a fist and closing the fingers may be difficult, especially around smaller objects. This

inflammation can be very painful and can constrict the tendons and ligaments of the wrist that

normally give the hand its wide range of motion and dexterity. Reductions in the hand and wrist

ranges of motion and mobility may become further obstructed if a bulky corrective brace is used

as a treatment option.

2.2.5 Stroke

Another common neurological condition is stroke. Strokes can be both ischemic,

meaning there is a blockage of a blood vessel supplying blood to the brain, or hemorrhagic,

meaning there is internal bleeding in the brain. Stroke sufferers can endure numbness, muscle

weakness, or even paralysis on portions or an entire side of the body (NINDS).

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In cases of partial or complete paralysis, the affected body regions will be severely

limited, and hand and arm use can decrease or even completely fail when affected. Even if

paralysis is not an apparent symptom, grip strength can still be reduced through muscle weakness

in hand and wrist. The neurological signal from a brain that has experienced a stroke can be

delayed and the muscle response time is often skewed when compared to responses in a healthy

brain. With a skewed muscle response time, coordination can cause issues for the individual to

perform ADL's involving the use of the hands.

2.2.6 Arthritis

One of the most prominent conditions that affect hand function is arthritis. Arthritis is a

collective term for what can actually be several different types of joint pain, stiffness, or disease.

There are many different forms of arthritis, including osteoarthritis and rheumatoid arthritis, and

these conditions as a collective whole affect nearly 50 million Americans over the age of 18

(Cooper, 2007). Arthritis can target any of the body’s joints including the hips, the knees, and the

finger joints, breaking down the cartilage within those joints and sometimes resulting in harmful

bone formation.

Arthritis causes issues with grip strength due to difficulties during flexion of the fingers.

For example, osteoarthritis patients have difficulty creating a fist as joint tissue has degenerated

and range of motion is limited. Without the ability to adequately form a fist, individuals

experiencing symptoms of osteoarthritis cannot effectively use many utensils and tools. In both

rheumatoid and osteoarthritis, the range of motion in the finger joints is reduced due to

degeneration of the joint tissue, and the ability to clench the finger muscles to the hand is

impaired (Marchand, 2017).

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2.2.7 Old Age

Conditions affecting the musculoskeletal system that aren’t caused by sudden trauma or

chronic conditions are often attributed to old age. After age 60, there is a "rapid decline in hand-

grip strength, by as much as 20-25%" due to decreasing muscle mass (Carmeli, Patish, &

Coleman, 2003). It is therefore highly probable that hand functionality will decline as age

increases for a majority of the population.

The aging process also provides an explanation for reduced grip strength in people as

they grow older. As age increases a loss of muscle tissue, called atrophy, is common and is part

of the reason for an overall decreased body mass. Muscle fibers begin to shrink, and the flexible

muscle tissue reproduces at a slower rate and is replaced by a “tough fibrous tissue...most

noticeable in the hands” (MedLine Plus). Individuals will also often experience limitation in

muscle movement in both ranges of motion and speed. With aging, joint tissue begins to

breakdown, causing stiffness and inflammation. Such symptoms can be caused by overuse over

time or more severe conditions like arthritis, which affects nearly 50% of adults aged 65 years

and older (Arthritis Foundation).

2.2.8 Injury

Injury can also cause a breakdown in hand function, and can cause complications that

extend from weeks to even months at a time; in some cases, full hand functionality may never

return. These injuries can range from chronic pain due to overuse to impairment as a result of

sudden trauma like a broken bone.

Many injuries, including sprains, breaks, or even simple overuse of the region, can mimic

the inflammation and pain of arthritis and carpal tunnel syndrome and cause a similar reduction

in grip strength. Some injuries can also limit the individual's range of motion, especially

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shoulder, elbow, and wrist injuries. For example, an individual with a rotator cuff injury in the

shoulder may not be able to lift their arm past a certain level without experiencing pain.

2.3 Effect on Daily Life

Individuals affected by any of the previously listed conditions will experience a wide

range of symptoms associated with each ailment. Each of these conditions will affect at least one

of the three essential hand capabilities discussed in this project, and each of these capabilities can

affect the progression and completion of ADLs. The focus of this project concerns the use of the

hand, wrist, and arm to grasp and successfully use small objects, while minimizing the effective

grip strength and ranges of motion needed for task completion where possible. While it does not

intend to alleviate the effects that reduced muscle coordination may have on an individual, this

project does aim to help individuals with reduced grip strength and range of motion to complete

activities of daily living. Activities using the hands that are especially impacted by a reduction of

these three capabilities can include, but are not limited to: utilization of eating utensils (spoons,

forks, and knives), toothbrushes, writing utensils, and small handheld tools. One of the most

simply understood ADLs is the process of using a utensil to eat.

For example, when eating with a fork, the user must be able to complete a series of stages

before they can eat the food. These include the four stages shown below, amongst many more

before the task of eating using the aid of a utensil can be completed.

Grasping the fork

Moving the fork from its rest position to pick up food

Bringing the fork to/depositing food in the mouth

Bringing the fork back to its rest position

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These four stages are only some of many, but these stages encompass the use of the arms,

wrists and hands. Each stage employs one of the three essential hand capabilities addressed for

this project and the symptoms are often crucial for each stage.

As the fork is moved from place to place during the task of eating, a minimum level of

muscle coordination and response time is necessary to move the fork where the individual

intends. Those affected by CP, MS, or stroke may have difficulty completing these stages of

motion, as the neurological response needed for the muscle movements of the arm and hand may

be slowed or skewed. Although these individuals may possess the physical strength and range of

motion necessary to eat with a fork, they may not be able to adequately control the muscles they

need to perform the task. Alternatively, people that are afflicted by only physically limiting

conditions like carpal tunnel syndrome, arthritis, or old age may have perfect muscle

coordination, but are unable to complete desired tasks. For example, if a person is affected by a

condition such as carpal tunnel or arthritis, the hand may not be able to meet the minimum angle

of flexion to form a grip around a utensil. The wrist and the elbow are both required for moving

the fork from its rest position to pick up food, while the shoulder is also necessary to bring the

fork from its rest position to the individual’s mouth and back. If these joints have a range of

motion that is too low the individual may not be able bring the fork to the mouth from the rest

position.

Grip strength is required throughout each of the four stages, and may be the most basic

yet most crucial symptom affected by neurological and physical conditions. Without a minimum

level of grip strength, the fork cannot be held throughout the stages of this ADL, and therefore

will hinder the performance of the activity. It is important to note that the minimum level is not

simply the level of force required to hold the fork, but rather to hold the fork with the additional

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burden of food while the fork is in motion. There are many other ADLs that require the use of

the hands, but without adequate control over grip strength, range of motion, and/or muscle

coordination, many of these tasks will be difficult to complete.

2.4 Assistive Devices

The disruption of specific hand biomechanics results in dysfunctional movements of

muscles, tendons, and joints. Daily tasks can become much more difficult and take longer for

someone with reduced hand function. For example, those afflicted by many diseases discussed

previously reported difficulty in eating, preparing food, brushing teeth, writing, and using other

hand tools. These actions all require fine motor skills from the fingers as well as overall grip

strength to hold the necessary tool securely. Standard versions of these tools often have grips that

don’t account for diminished hand strength or reduced hand mobility, making it difficult for

someone suffering from these symptoms to use the tool.

Assistive devices can give the user the opportunity to counteract the symptoms that occur

as a result of neurological or physical conditions. These devices attempt to bring the

functionality of the affected individual as close as possible to the functionality of an unaffected

individual. Assistive devices can range from simple grips that can reduce the necessary grip

strength for specific tasks to complex electromechanical wheelchairs.

Due to their complex biomechanics, the hands can be affected in a multitude of ways.

When grip strength, range of motion, or muscle coordination is decreased, ADLs like eating or

using basic utensils can be directly affected. The most common assistive devices for hands

include grips that are easier to hold and control or utensils that are reconfigured for ease of

control. There is already a very extensive existing market for assistive tools, which accommodate

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for a wide range of users who require assistive devices. A few existing products are described in

the following section.

2.5 Current Products

The Ableware Universal Built-Up Handle (Figure 13) targets those with diminished grip

strength and is marketed towards individuals with arthritis. This product is applicable primarily

for eating utensils. The handle provides a larger diameter textured gripping surface in addition to

the option of using a comfortable power grip for the utensil. The switch to a power grip allows

the user to employ extrinsic muscles in the forearm for improved grip strength that is not

available when using a precision grip. The handle also provides a larger contact surface between

the hand and the utensil. This, along with added friction from the texture, gives the user better

control and manipulation of the utensil.

Figure 13: Ableware Universal Built-Up Handle (Universal Built-Up Handle, n.d.)

Another popular product is the OXO Good Grips Weighted Utensil Fork (Figure 14).

This product is weighted with an extra 6 oz. for tremor reduction. The rubber material and

enlargement of the grip make it easier for the user to hold the utensil. One of the most significant

aspects of the product is the ability to bend the shaft of the utensil. This allows the user to

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customize the angle of the fork in relation to the handle. Although the bending of the utensil

requires significant effort, it can reduce the necessary bending in the wrist when bringing food to

the mouth. However, once the optimum angle is found for each user, it does not necessarily have

to be adjusted again. If the utensil adjustment requires too much effort, a caregiver would be able

to help as well.

Figure 14: OXO Good Grips Weighted Utensil Fork (Good Grips Weighted Utensils, n.d.)

The Norco Universal Cuff (Figure 15) eliminates any grip strength required to hold

utensils by strapping them to the hand. This product is ideal for individuals with minimal to no

gripping capabilities. Standard eating utensil shafts can be inserted into a pocket on the palm side

of the strap. The strap can be loosened or tightened to the hand with the Velcro strap that is

secured on the reverse of the palm, ensuring that the utensil cannot be dropped. The device

places the utensil in the power grip position, which reduces the fine motor control that is

otherwise available in precision style grips.

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Figure 15: Norco Universal Cuff (Norco Universal Cuff, n.d.)

The Finger Loop Dinner Fork (Figure 16) is designed to accommodate users with arthritis

who experience little grip strength. The product contains a loop attached to the shaft for the

thumb to provide additional leverage when eating. It also secures the utensil to the user’s hand

through more contact points than standard utensils. In addition, the loop decreases the possibility

of dropping the utensil while in use.

Figure 16: Finger Loop Dinner Fork (Finger Loop Utensils, n.d.)

These products attempt to mitigate specific symptoms through the adjustment of required

hand biomechanics. The modification of the grip, for instance, can lead the individual to engage

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more muscles when grasping for improved stability. The price range for these and similar

products varies between $10 and $30, making them relatively affordable for the public. Overall,

the currently available assistive devices allow individuals with reduced hand function to decrease

stress and pain during daily tasks like eating.

2.6 Furthering Research

While there are many assistive devices available for symptoms that diminish hand

function, many do not completely address the needs of the user. Most often, assistive devices

adopt the philosophy of ‘one size fits all’ and do not accommodate for the individual user, which

can result in user dissatisfaction. Our group spoke with a hand therapist who claimed that the

biggest drawback in the available products in the assistive device market was the distinct lack of

customizable options (Marchand, 2016). The absence of personally customizable tool grips in the

current market opens the door for innovation in this area of study. Our team of students attending

Worcester Polytechnic Institute has taken the initiative to investigate product inadequacies with

the intent to develop new grip designs that better serve the user with an emphasis on personal

customizability.

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3.0 User Requirements

The user requirements illustrate what abilities a typical user of the designed product must

have. Should the user lack all of these abilities, the product will not be as effective for that

individual. The target user for this product is an individual who has trouble or may require

assistance using the following items:

For the purpose of eating or preparing meals:

Fork

Knife

Spoon

For the purpose of maintaining personal hygiene:

Toothbrush

Razor

For the purpose of writing:

Pen

Pencil

In order to successfully use the listed items, a minimal range of motion necessary to

complete daily tasks was measured on an able bodied individual for each major joint in the arm.

As the able bodied individual completed common daily tasks with the items, the maximum angle

experienced by each joint during the motion was recorded. This benchmark for mobility details

the physical capabilities that the user should have for successful completion of tasks with the

listed items. Each range of angles was measured from the neutral position with the arm at the

individual’s sides with palms facing inwards and fingers fully extended.

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The user should have an angular range of shoulder motion of 55º to the side of the body

(abduction) and 55º to the front of the body (flexion) (Figure 17).

Figure 17: Shoulder Flexion and Abduction (Ahmad, 2016)

The user should have an angular range of elbow motion of 90º (flexion) (Figure 18).

Figure 18: Elbow Flexion (Lee, 2014)

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The user should have an angular range of motion of 20º in both wrist flexion and

extension (Figure 19).

Figure 19: Wrist Flexion and Extension (Common Injuries, 2016)

The user should have an angular range of motion of 45º for each joint in the finger

(flexion) (Figure 20).

Figure 20: Finger Flexion and Extension (Clinical Gate, 2015)

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4.0 Design Specifications

These design specifications were developed to help determine the effectiveness of each

design. The specifications are divided into critical and important categories with the former

being of greater importance to the design.

4.1 Critical Design Specifications

1. This device must be able to hold a fork, a spoon, a toothbrush, a pencil, and a pen.

o The limits set here apply to a large range of utensils that are commonly used

inside and outside one’s home. It is important for our grip to accommodate these.

2. This device must allow the user stable manipulation of the tools used with this device, in

order to allow the consumption of solid and liquid foods.

o Eating solid and liquid foods is one of the most common ADLs. Stability and

manipulation of the food is important to keep it on the utensil during its path to

the mouth.

3. This device must allow the user to utilize power and precision grips.

o Different tools require different grip configurations for best effectiveness. A

toothbrush may require a power grip, while an eating or writing utensil may need

a more precise grip.

4. This device must allow the user to customize the grip for their own comfort.

o Every user’s hand is different, by allowing grip customization the user can avoid

uncomfortable finger or hand positioning on the handle.

5. This device must not permanently deform when subjected to temperatures below 180°F.

o The highest temperature the product will most likely encounter daily would be in

a dishwasher, 180°F is the highest temperatures most dishwashers can reach, and

deformation below this temperature would make the product unusable after being

cleaned in a dishwasher.

6. This device must not deteriorate/deform when washed in a dishwasher.

o Dishwashers are commonly used to wash flatware; degradation in a dishwasher

would limit washing options for users.

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7. This device must be food-safe and non-toxic.

o The device will be usable with or around food and can’t present a toxic risk to

users.

8. This device should weigh less than 100 grams.

o The device should weigh about the same or less than existing assistive devices

that aim to provide a solution to similar symptoms. For example, the Ableware

Built-Up Handle weighs 75 g without a utensil inserted, and 100 g on average

with a utensil inserted.

9. This device must not break if dropped from a height of 5 feet.

o The device will most likely not be placed in places higher than shoulder height

shelves (generally about 5 feet), and will mostly reside on tables or in waist-

height drawers.

10. This device must not contain any sharp edges.

o The device will not be safe if it can cut the user’s hand when handled.

4.2 Important Design Specifications

11. This device should be available in a wide range of colors

o The device will be more appealing to customers if it is aesthetically pleasing to a

larger base of people.

12. This device should not increase the angular range of motion within joints of the arm,

wrist, and hand necessary for tasks like eating

o Most users will experience the same or less range of motion in their joints as a

result of their ailments. It is important to ensure that the users do not have to

extend their extremities past typical angular limits when normally conducting the

specific task.

13. This device should be indistinguishable from a regular utensil or tool from a maximum

viewing distance of 10 feet

o The grip should be a low profile device that the user is comfortable to use in a

public setting without drawing attention.

14. This device should have a maximum length of 6 inches

o The device should be able to be transported in the user's pocket or small handbag.

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15. This device should cost less than $20 to manufacture the final product

o Many current products have a market price ranging from $10-$15 on average,

meaning the production cost and cost of all product inputs should ideally range

from $5-$10 maximum per product. For this project, the customizability adds

another factor to both the material and manufacturing input stages, therefore

raising the price of production.

16. The prototypes for this project should cost less than $750 to produce.

o This is the provided budget for our three-person MQP team. This will cover all

material, hardware, and rapid prototyping costs.

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5.0 Ergonomic Analysis

An investigation in hand ergonomics was necessary to increase the quality of potential

design solutions. As a result, further research was conducted to develop a better knowledge base

surrounding grip characteristics and locking mechanisms.

5.1 Finger Engagement Diameters

Research that was conducted helped to create a range of grip diameters that would be

optimal for each finger. For the index and middle finger, the grip diameter that allows for the

highest grip strength was approximately 40 mm. This information was acquired from research

from the University of Michigan, Ann Arbor (Seo et al., 2008). The experiment’s objective was

to “investigate relationships between grip forces, normal forces, contact area for cylindrical

handles, handle diameter, hand size, and volar hand area. The main result of the research was

that the greatest grip strength is achieved when the middle finger tip and the thumb fingertip

overlap (Figure 21) so the normal forces of these fingers are directly opposite to the palm. The

researchers also produced an equation that gives the optimal diameter for a cylindrical grip

(Figure 22). Calculations were performed using Air Force data for hand sizes and the team

performed these calculations on one of its members and the results were both 40mm. This led the

team to include a 40 mm diameter dimension for the index and middle fingers in most of the

designs.

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Figure 21: Thumb/Finger Force Overlap (Seo et al., 2008)

Figure 22: Optimal Handle Diameter Calculation (Seo et al., 2008)

5.2 Surface Area Contact

Additional conclusions from the University of Michigan study (Seo et al., 2008) were

that a good design would maximize surface area contact between the hand and the grip.

Maximizing surface area contact reduces pressure from the normal force because pressure is

ratio of the normal force magnitude divided by the contact area. Reducing pressure would

decrease discomfort for the person holding the grip. One strategy to increase surface area contact

is to spread the fingers apart, allowing material between the fingers. With the sides of the fingers

locked together (Figure 23) there is less contact with the grip in comparison to the fingers spread

apart (Figure 24).

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Figure 23: Locked Fingers

Figure 24: Spread Fingers

5.3 Tapering of Handle

Additional findings from the University of Michigan study helped us conclude that

tapered handles were easier to hold. This idea can be seen in the design of cups. Most cups have

a smaller diameter towards the bottom than the top instead of taking a cylindrical form. The

tapered grip helps to conform to the hand's natural resting position, requiring less grip strength

from the fingers to secure. In addition, tapered handles divert the force from purely frictional

forces, seen in a cylindrical grip, to both frictional and vertical support force (Figure 25). This

information led to the tapering of most of the design handles.

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Figure 25: Tapered Handle Distribution of Forces

For the index and middle fingers, the distance between where the second segment of the

finger and the palm contact the grip is 40mm approximately. The ring finger and pinky finger

grips have incrementally smaller values. This information was acquired from a study done that

relates the diameter of a grip to the absolute force applied by specific fingers (Blackwell et al.,

1999). The results were that each muscle that is used to hold the grip should be at its optimal

length, especially the finger muscles. The conclusion of the study was that grips should not be

uniform in diameter but should vary at each finger so the finger is at its optimal length to provide

its greatest absolute force output.

5.4 Angle of Utensil in Hand

The angle orientation in which the utensil is held, in comparison to the grip axis of the

hand (Figure 26), determines the range of motion of the wrist necessary to complete the task. In

eating liquid food with a spoon for instance, carrying the spoon to the mouth requires rotation in

other joints to maintain the orientation of the spoon as it translates from the bowl to the mouth,

without rotating and spilling. In order to keep the movement of the spoon purely translational,

the wrist must accommodate for the movements of the arm to keep the hand level.

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Figure 26: Gripping Axis of Hand (Hunt, n.d.)

5.5 Optimal Extension of Utensil from the Hand

To continue with the example of the spoon, the head of the spoon must be placed at an

optimal distance from the grip. The length of shaft that connects the grip to the head of the

utensil affects the amount of movement necessary by the wrist as well as the rest of the arm. To

describe an extreme example, if the shaft of the spoon were a foot long, the user would have to

move their hand one foot from the bowl in order to place the head of the spoon in the liquid, thus

extending their arm farther than if the shaft of the spoon was an inch long. In a precision grip

however, the longer the shaft the utensil, the less movement in the fingers is required to move the

head of the spoon around the hand (Figures 27 and 28).

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Figure 27: Short Shaft Precision Grip Range of Motion

Figure 28: Long Shaft Precision Grip Range of Motion

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In both of these cases, the smallest range of motion in the hand or arm is optimal since

one of the conditions the team is addressing is the lack of mobility during task completion. For

our designs, we approximated both the angle of the utensil and shaft length by placing a utensil

in the hand at different positions and attempted to eat with each position. The average of the

most comfortable angles and shafts lengths was used in our final designs.

45

6.0 Preliminary Design Concepts

After conducting further research on the characteristics of assistive grips, it was

concluded that the final designs would be broken down into three main aspects: an ergonomic

handle, a user-friendly utensil interface, and the ability to adjust the utensils’ position in the

hand. For each aspect there are multiple sub-designs accompanied by a description. Then a

grading rubric for each aspect was created to detail the criteria on which each design was graded.

Finally, scores for each design were assigned for each criterion and assembled in a table.

6.1 Ergonomic Handle

Preliminary sketches were created for five different handle designs. These designs were

created to maximize the user’s ability to manipulate the utensil. The handle should maximize

contact to provide stability, be lightweight, and be the correct size to help the user but not attract

attention in public. These handle concepts were then formed from oven-hardening clay to test

their functionality and comfort.

6.1.1 Tapered Handle with Finger Grooves

This design would be held in the hand with a power grip, similar to some existing eating

utensil handles, although the shape of the handle would better conform to the human hand

(Figure 29). The index finger will wrap around the top groove, while the middle finger makes

contact with the second groove, and so on. Separate grooves for each finger, in contrast to a

purely cylindrical surface, would create a more ergonomic feel since the handle would fit better

with the pads of the fingers when in a power grip position. When the device is held in the hand,

the index finger will have an optimal distance of 40 mm from the palm. The tapering of the

handle also conforms to the natural position of clenched fingers when the hand is closed as a fist,

46

as opposed to a constant-diameter cylindrical surface, with the average diameter being larger at

the top than at the bottom.

Figure 29: Tapered Handle with Finger Grooves

6.1.2 Pistol Grip with Index Finger Extension

This design is held in a similar manner to how a person grips a pistol (Figure 30). The

middle, ring, and little finger are placed around the handle of the grip with each finger gripping

around a progressively smaller diameter from middle to little finger. The grip for the middle

finger has an approximate diameter of 40 mm and the grip for the little finger has an approximate

diameter of 34 mm. Fingers are placed in the grooves of the handle to better conform to the

user's grip. At the top of the handle, the design allows the index finger to be outstretched along

the side of the device. The thumb is outstretched on the same plane as the index finger on the

other side of the device (Figure 31), and this top section is modeled to fit the curve of the palm

and index finger. Although only shown designed for use in the right hand, simply mirroring the

geometry would allow for left hand usage.

47

Figure 30: Pistol Grip

Figure 31: Pistol Grip - Top View

6.1.3 Ball Grip

This design takes the form of a ball with a diameter of approximately 40 mm, with a short

protruding shaft to accompany any utensils (Figure 32). This shape can be manipulated and

easily repositioned in the hand and does not lock the user into holding the grip in a single

orientation. With the freedom to position the Ball Grip in many orientations, the user is able to

choose the position that is the most comfortable and effective for the desired task. The overall

size of the grip increases the amount of contact with the hand when compared to standard

utensils but can still be concealed within the hand.

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Figure 32: Ball Grip

6.1.4 Freeform Fencing Grip

The shape of a fencing handle inspired this grip. The palm is positioned parallel to the

ground with the fingers wrapped down around the grip. The thumb is outstretched along the grip

pointing at the utensil and away from the body, while the two protrusions on the grip increase

surface contact between the hand and the grip (Figure 33). One protrusion is located between the

thumb and the palm of the hand, while the other protrusion is placed between the index and

middle fingers. More protrusions could be added to the grip in order to create more surface

contact if it would better suit the user’s needs. The utensil shaft is placed parallel to the thumb.

For clarity, Figure 34 shows the grip with a utensil being held.

Figure 33: Fencing Grip

49

Figure 34: Fencing Grip in Hand with Utensil

6.1.5 Dual Finger Slot Grip

The approximate shape of this grip is a 4-inch long cylinder that has two finger holes for

the user’s index and middle fingers to pass through as it is held in a power grip (Figure 35). The

cylinder would be tapered with varying diameter for each finger, while the diameter of the grip

for the middle finger is 40 mm. Two finger slots are added to this design to increase surface

contact with the device, while also preventing the user from dropping the device. The increase in

surface area decreases pressure on the hand, which reduces discomfort. Each finger hole would

be about 30mm (1.2 inches) in diameter, which would allow 99% of people to pass all of their

fingers through (Dreyfuss, 1973).

Figure 35: Dual Finger Slot Grip

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6.1.6 Handle Grading

The handles were analyzed using three different criteria: volume, indistinguishability

from standard utensils, and surface contact with the hand. Each of these criteria was weighted on

importance and shown with the handle’s score in Table 2. The volume of each handle was

calculated using the water displacement method. The volume was used as a grading criterion

because the material had not been selected at this stage so volume was a way to compare the

weight differences of the handles assuming at the handles were made of the same material in the

final design. They were graded using the following criteria:

Volume of Handle (without utensil)

1. > 170 cm3

2. 131-170 cm3

3. 91-130 cm3

4. 51-90 cm3

5. <50 cm3

The criterion of the handle being indistinguishable from standard utensils is used because

these distances are the difference between someone noticing the utensil from across the table or

from across the restaurant. We decided that less than two feet was an accurate estimate for the

width of a dinner table. Then the different distances would be from different tables around the

restaurant. People will use a grip that is more discrete in public rather than one that draws

attention to them. The distances were graded based on the following criteria:

Indistinguishable from Standard Utensils

1. Is distinguishable from standard utensils from >10 ft.

2. Is distinguishable from standard utensils from 8 ft.

3. Is distinguishable from standard utensils from 6 ft.

4. Is distinguishable from standard utensils from 4 ft.

5. Is distinguishable from standard utensils from < 2 ft.

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The criterion of surface contact with the hand is used because the grip will be more easily

manipulated and easier to grasp as the amount of contact with the hand increases. If the handle is

just barely resting in the fingertips (a low percentage of surface area contact), it will be much

harder to grip and use when compared to something that can rest in the palm and be firmly

grasped (a higher percentage of surface area contact).

Surface contact was measured by first taking a picture of the tester’s hand for a base

reference. Then the handles had paint applied to them, after which the tester gripped the handle.

After releasing the handle, paint was seen on the tester’s hand where it made contact and pictures

were taken for analysis. Surface contact was graded using the following criteria:

Surface Contact with Hand

1. < 20% of hand surface area in contact with grip

2. 21-40% of hand surface area in contact with grip

3. 41-60% of hand surface area in contact with grip

4. 61-80% of hand surface area in contact with grip

5. > 80% of hand surface area in contact with grip

The following decision matrix lists the three criteria with their weights and scores for each

design. The Tapered Grip, Pistol Grip, and Ball Grip were selected for further testing based on

their higher scores. The Fencing Grip received a score that was close to the Ball Grip due to the

complexity of the shape of this handle. Fencing handles are generally customized to the user’s

hand. A handle that is universal for more users is a better design for a commercial product so this

handle was eliminated.

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Table 2: Ergonomic Handle Design Grading Table

Ergonomic Handle

Weight Tapered Handle

Pistol Grip

Ball Grip

Fencing Grip

Finger Slot Grip

Volume 5 4 4 5 5 3

Indistinguishable from Standard Utensils

3 4 4 5 3 2

Surface Contact with Hand

5 5 5 2 3 4

TOTAL 13*5=65 57 57 50 49 41

6.2 Utensil Interface

The utensil interface is the part of the device where the utensil is inserted into the handle.

Six different utensil interfaces were designed to provide the user with the ability to change

utensils. This process was designed to be simple, easy, and require a minimal number of steps.

6.2.1 Button in Slot Snap Clips

This locking mechanism consists of two interlocking hollow cylinders. The inner cylinder

would have a spring button clip (Figure 36) placed inside with the buttons protruding from two

coaxial holes. These buttons would lock the inner cylinder within the outer cylinder through

aligned holes. A cross sectional view of the two cylinders locked by the spring button clip can be

seen in Figure 37.

Figure 36: Button Snap Clips (Replacement V Clips, n.d.)

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Figure 37: Interlocked Tubes with Button Snap Clip

This original concept was improved to better suit the needs of the intended users. The

forces required to precisely compress the buttons may be difficult for an individual with arthritis

for example. To make compressing the buttons easier the heads of each button were enlarged

(Figure 38). This widening of the buttons would distribute the necessary force to a larger area of

the user's fingers, reducing discomfort.

Figure 38: Upgraded Button Snap Clips with Enlarged Button Heads

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6.2.2 Zip-Tie Insert

The device would be used with specially made utensils or tools that have grooves on one

end, similar to those seen on common household zip-ties. Another set of grooves are located on

the inside of the handle, angled to face the opposite direction as the grooves on the utensil

(Figure 39). The utensil is inserted until it is locked in position, after which it cannot be directly

removed because these oppositely facing grooves lock when pulled against each other and do not

allow movement. The device contains a release trigger that, when pulled back, works as a lever

to pull the grooves located in the device upward in a clockwise direction away from the grooves

on the utensil. This releases the utensil because the two sets of grooves are no longer in contact.

Figure 39: Zip-Tie Locking Mechanism

6.2.3 Compression Lock

The compression lock design uses a similar approach in securing items as a Pelican Case

(Figure 40). The material on both inside surfaces of the case is compressible. As the case is

closed around the item within, the material deforms around the object, keeping it secure. This

idea would be applied to existing utensils; however, the head of the utensil would remain outside

the case with the handle secured within.

55

Figure 40: Pelican Case (1200 Small Case, n.d.)

6.2.4 Button Release Mechanism

This type of utensil locking mechanism features an internal assembly, where only the

release button and utensil can be viewed on the exterior of the grip. The full internal assembly is

shown in Figure 41. While unable to be used with existing utensils as shown, this locking

mechanism could be modified to incorporate the use of existing utensils. The mechanism

consists of a base (1) with a slot wide enough to accommodate the tail end of the custom utensil

(2), a button (3) that extends from outside the grip surface to depress a spring (4). The base (1) is

shown here as its own component for clarity, but would be part of the handle itself, with only

cuts made to incorporate slots for the utensil, button and spring system, and to provide a suitable

protrusion on which the spring would rest.

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Figure 41: Button Locking Mechanism Design; Base (1); Utensil (2); Button (3); Spring (4)

This device works by depressing the button far enough until the utensil can be either slid

in or slid out of the device. As shown in Figure 42, the end of the utensil is T-shaped. When the

button component is depressed, the slot in the base is wide enough for the entire utensil to be

inserted or removed. When the button is released, the spring pushes the locking groove (5) of the

button component into place, ensuring the utensil does not move out of place. For the success of

this locking mechanism, a spring with a relatively low spring constant is beneficial, to eliminate

the need for excessive force to press the button.

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Figure 42: Button Release Mechanism - Unlocked (Left) and Locked (Right); Locking Groove (5)

This device can be easily incorporated into many designs, is easy to use, and easy to

manipulate. However, it requires some small parts that may be difficult to repair if broken, and

requires custom utensils.

6.2.5 Lock and Key Design

This Lock and Key design incorporates a utensil locking within the handle of the device.

Two parts are required: the grip handle "Lock" (Figure 43) and the utensil "Key" (Figure 44).

The entire assembly can be viewed where the utensil key is in an unlocked position and a locked

position in Figures 45 and 46, respectively. The cuts made within the handle allow the key to be

inserted to a depth of 50 mm, stopped, rotated 90 degrees clockwise, stopped, then pushed down

another 5 mm to lock in place.

58

Figure 43: Lock

Figure 44: Key

59

Figure 45: Lock and Key - Unlocked Position

Figure 46: Lock and Key - Locked Position

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6.2.6 Magnetic Hex Bit Insert

This locking mechanism has a magnet at the base of the shaft that pulls and holds the

inserted utensil in place. The end of the utensil would have a hexagonal cross section at the end

(Figure 47). The design behind this locking mechanism between the utensil and the handle would

be the same as the locking mechanism used with interchangeable screwdriver bits (Figure 48).

The end of the hexagonal insert would have to be made from a material that is magnetic. This

hex shaped slot would also allow for existing screwdriver bits to work with the device. Although

the main purpose for this device is to be used with eating utensils, toothbrushes, and writing

utensils, modifying. the design for existing screwdriver bits could additionally expand the

device’s capabilities.

Figure 47: Fork with Hex Insert

Figure 48: Magnetic Hex-Bit Screwdriver

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6.2.7 Locking Mechanism Grading

The locking mechanisms were analyzed using three criteria: number of moving parts,

necessary connection steps, and compatibility with existing utensils. Each of these criteria was

weighted on importance and shown with the locking mechanism’s score in Table 3. The first

criterion is number of moving parts. The rationale for this criterion comes from the fact that the

more moving parts a utensil insertion interface has, the harder it will be to manufacture or repair.

A locking mechanism that only requires the user to insert a utensil (this may be either one

moving part or none at all) is much easier to make, use, clean, and repair than a locking

mechanism that has several relatively small moving parts (as these moving parts must fit inside a

utensil grip). The number of moving parts was graded using the criteria below:

Moving Parts

1. 5 or more moving parts

2. 4 moving parts

3. 3 moving parts

4. 2 moving parts

5. 1 or fewer moving parts

The criterion for necessary connection steps was used because ideally, it would only take

a user one step to connect the utensil to the device. As the number of connection steps increases,

the overall complexity of the device also increases. More connection steps would increase the

total time and effort needed to use the device, which is not a desirable trait. The number of

necessary connection steps was graded using the criteria below:

Necessary Connection Steps

1. 5 or more connection steps

2. 4 connection steps

3. 3 connection steps

4. 2 connection steps

5. 1 connection step

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The criterion of compatibility with existing utensils was used because a grip that uses

standard existing utensils would reduce the cost of the product because the consumer would not

need to buy adapted utensils. It would also make the device more convenient if the user could

just transport the device to a restaurant without any extra components and use the flatware

provided. The compatibility of the grip using existing utensils was graded using the following

criteria:

Compatible with existing utensils

1. Not usable with existing utensils

5. Usable with existing utensils

Table 3 shows the decision matrix using the three criteria with their weight and overall scores

for each locking mechanisms. The compression case and the magnetic hex bit were selected for

further testing based on their significantly higher grades.

Table 3: Utensil Interface Grading Table

Utensil

Interface

Weight

Button

Snap

Clip

Zip

Tie

Insert

Compression

Case

Button

Release

Lock

and

Key

Magnet

Hex Bit

Moving Parts 3 4 3 4 3 5 5

Necessary

Connection

Steps

5 4 4 3 3 1 5

Compatibility

with Existing

Utensils

4 1 1 5 1 1 1

TOTAL 12*5=60 36 33 47 28 24 44

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6.3 Repositioning of Utensil in Hand

The ability for the utensil to change orientation allows the device to help users with

various disabilities. Two different systems were designed for this part of the design. One allows

planar motion in two directions while the other allows motion in three directions for the utensil.

6.3.1 Pin Joint Swivel

This design would allow the user to adjust the orientation of the utensil within an angular

range in one plane. The mechanism that would create this angular movement would be located

within the handle (Figure 49). To change the angular position of the utensil, the user would

simply pull the shaft of the utensil from position to position and rotate it about the central axis

(1). There are two possible locations for the utensil to be locked into position; one stop directed

upwards along the gripping axis (2) and another position slightly further than perpendicular to

the gripping axis (3). Resistance can either be applied or removed to lock or unlock the

movement of the utensil.

Figure 49: Pin Joint Swivel Mechanism; Rotation Axis (1); Upwards Rotation Stop (2); Downwards Rotation Stop (3)

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6.3.2 Gimbal Joint Swivel

This design would allow the user to adjust the orientation of the utensil within a spherical

range of angles. The mechanism that would create this spherical movement would be located

within the handle (Figure 50). This mechanism is composed of a central ball (1) that is attached

to the utensil, which is seen as a nail in the figure. A housing (2) is placed around the ball (1) to

keep it in position but allow rotation. Paths for the utensil (3) are cut in the housing to determine

how the utensil will be able to move or rotate. There are two possible paths in which the utensil

can be locked. To change the angular position of the utensil, the user would simply pull the shaft

of the utensil from position to position. Resistance can either be applied or removed to either

lock or unlock the movement of the utensil. While the complexity of this mechanism is greater

than the Pin Joint Swivel, it would allow for a greater number of utensil positions.

Figure 50: Gimbal Joint Swivel; Central Ball Attached to Nail (1); Ball Housing (2); Utensil Paths (3)

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6.3.3 Repositioning of Utensil in Hand Grading

The repositioning of the utensil in the hand was analyzed using four criteria: range of

usable angles, applicable with different utensils, moving parts, and necessary steps to reposition.

Each of these criteria was weighted on importance and shown with their score in Table 4. The

range of usable angles was used because the ability to change the position of the utensil allows

the user to apply the assistive device to more tasks that require different utensil orientations. If

the utensil is only usable in specific locations, the number of orientations is limited to the

number of locations. The number of orientations can be expanded with a design that allows

continuous locations within a range of rotation about a single pivot point creating a greater

number of orientations in which the user may want to use the utensil. The number of orientations

can further be expanded if the design allows rotation about two or three axes. The range of

motion of the utensil was graded using the criteria below:

Range of Usable Angles

1. Usable in specific positions (1 Dimensional)

3. Usable in a range of positions on a single plane (2 Dimensional)

5. Usable in a range of positions in multiple planes (3 Dimensional)

The criterion of number of applicable utensils was used because the device would ideally

be able to be used with a wide variety of utensils. The fork is the most common eating utensil

with a small range of motion required for its use. Additional eating utensils use more complex

motions or require greater force. For example, the toothbrush needs to be turned 180 degrees to

get the top and bottom teeth. The writing utensil needs to be held facing down vertically, unlike

eating utensils, which are held horizontally. The knife requires the user to apply a force to press

down on the food that is being cut and maintain this force while the knife is being moved

66

forward and backward to cut the food. Number of applicable utensils was graded using the

criteria below:

Number of Applicable Utensils

1. Works with a fork

2. Works with a fork and spoon

3. Works with 3 utensils

4. Works with 4 utensils

5. Works with spoon, fork, knife, writing utensil, and toothbrush

The criterion for number of moving parts was used since more moving parts within the

utensil interface makes the device harder to repair if broken, and more likely to break in the first

place. Number of moving parts was graded using the criteria below:

Moving Parts

1. 5 or more moving parts

2. 4 moving parts

3. 3 moving parts

4. 2 moving parts

5. 1 or fewer moving parts

The criterion for necessary steps to reposition the utensil was used because changing the

position of the utensil should be as simple as possible. Fewer steps decrease the time needed to

change the position of the utensil and make the utensil simpler to use. Necessary steps to

reposition the utensil was graded using the criteria below:

Necessary Steps to Reposition

1. 5 or more reposition steps

2. 4 reposition steps

3. 3 reposition steps

4. 2 reposition steps

5. 1 reposition step

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Table 4 shows the decision matrix with the four criteria, their weights, and overall scores for

each repositioning design concept. The gimbal joint swivel was selected for the prototypes

because it received the highest grade.

Table 4: Repositioning of Utensil Grading Table

Repositioning of

Utensil in Hand Weight Pin Joint Swivel

Gimbal Joint

Swivel

Range of Usable Angles 4 3 5

Applicable with Different

Utensils 5 4 5

Moving Parts 2 1 3

Necessary Steps to Reposition 4 5 3

TOTAL 15*5=75 54 63

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7.0 Complete Design Concepts

From the design selection in Section 6.0, the best concepts from each sub-design section

were identified. These top sub-designs were combined to create six main design concepts. The

solid models generated for each design were only created to show the integrated concepts and do

not represent a fully dimensioned or final design.

7.1 Designs with Hex-Bit Insert/Gimbal Joint

The first three designs incorporated the gimbal joint and the hexagonal bit locking

mechanism into the three selected handle geometries. These designs each have four main parts;

the handle geometry, the hex-bit gimbal, the utensil, and a locking set screw. An assembly

without the handle can be seen in Figure 51 with the utensil seen in red, the hex-bit gimbal in

blue and the set screw in green.

Figure 51: Hex-Bit Insert/Gimbal Joint Assembly

These designs require custom utensils (Figure 52) with a hexagonal extrusion after the

head in order to connect to the hexagonal slot of the hex-bit gimbal. The hex-bit gimbal (Figure

53) is essentially a ball connected to a hexagonal slot. The ball portion is inserted into a socket

69

that is incorporated into the geometry of the handle, creating the gimbal joint that allows for the

rotational manipulation of the utensil. The gimbal joint must also be lockable to prevent the

utensil from moving once in the desired position.

Figure 52: Utensil Head with Hex-Bit Extrusion

Figure 53: Hex-Bit Gimbal

A simple compression screw (Figure 54) was incorporated to allow the user to unlock and

lock the gimbal joint when needed. As the setscrew is twisted, the end of the screw is

compressed against the ball in the socket, locking it in place and preventing any unnecessary

utensil movement during use. In these preliminary concepts the handle geometry has internal

threads for the setscrew. The set screw also has wing nut like tabs for ease in locking and

unlocking the gimbal joint.

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Figure 54: Set Screw with Wing Nuts

In creating the solid models and integrating the gimbal joint assembly with the handle

geometries, flaws in the sub-design combination were easily noticeable. In the Ball Grip design

(Figure 55), for instance, the wing nut tabs would make it more difficult for the individual to use

the grip. For this specific case the knob could have a lower profile as to not interfere with the

user’s grip. The Pistol Grip and Tapered Grip designs are shown in a similar configuration in

Figures 56 and 57, respectively.

Figure 55: Ball Grip with Hex-Bit Insert and Gimbal Joint

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Figure 56: Pistol Grip with Hex-Bit Insert and Gimbal Joint

Figure 57: Tapered Grip with Hex-Bit Insert and Gimbal Joint

7.2 Designs with Locking Compression Case

The last three design were a combination of the top handle geometries with the

compression case geometry. This locking mechanism uses the geometry of the handle to close

and lock around existing utensils, holding them in place. A compressible material is placed on

the inside surfaces of the case mechanism to help secure the utensil. The incorporation of the

compressing case for the Ball Grip, Pistol Grip, and Tapered Grip can be seen in Figures 58, 59,

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and 60, respectively. In each of these designs, the area that has the compressible material is

shown by the grid extrusion. Again, these designs are simply to show the concept of the sub-

design integration in order to highlight potential design flaws.

Figure 58: Ball Grip with Locking Compression Case

Figure 59: Pistol Grip with Locking Compression Case

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Figure 60: Tapered Grip with Locking Compression Case

7.3 Design Elimination

After initially designing the combinations of the secondary sub-designs, it became

apparent that a few of the design concepts above would not function properly if manufactured.

For example, in the design that combines the compression case with the Ball Grip, the utensil

would most likely protrude from the opposite end of the grip. This is due to the fact that the ball

will be around 2 inches long so it fits in the hand whereas most eating utensils are about 7 inches

long. This would interfere with the user's hold on the Ball Grip in many positions, making it

much less effective. If the user were to only insert the end of the utensil in order to keep it from

protruding from the back of the grip, the head of the utensil would be at an unnaturally long

distance from where utensils are typically held. Attempting to eat in this orientation would result

74

in awkward motions and would be less effective for most users. For this reason, the Ball Grip

with the compression case locking mechanism was eliminated.

The second design that was eliminated was the Tapered Grip with the compression case

locking mechanism. In considering how most users would load utensils it was determined that

they would typically place the utensil with one hand on the compressible material when the

handle is open, while holding the grip in the other hand. The hand holding the grip would most

likely be oriented so that when the user closes the grip, their hand will already be in the intended

power grip orientation. When closing the grip in this way, the back, hinged surface would be in

contact with the palm. This would create the potential for the skin of the palm to be caught in this

hinged edge, harming the user. This was not seen as an issue for the Pistol Grip with the

compression case since the hand would not be in contact with the hinge edge when closing the

top. For these reasons, the remaining four designs were prototyped in the next stage.

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8.0 Functional Design Selection

This section details the preliminary prototyping of the six design concepts presented in

Section 7.0 and the selection process used to choose the final design concepts. After the

preliminary prototypes were 3D printed, as described in Section 8.1, five tests were administered

to able-bodied college students to gain insight and feedback as to how the designs could be

improved. Careful analysis of the feedback was performed to make changes to the designs of the

final devices.

8.1 Preliminary Prototyping

Since the oven-baked prototypes (shown in Section 6.0) were simply to show concept

and did not include ergonomic dimensions, the designs were modeled in SolidWorks and 3D

printed out of ABS plastic using a Stratasys uPrint SEPlus rapid prototyping machine. In order

to assemble the prototypes with the gimbal inside the handle, the handle geometries were split

and matching holes and pegs were incorporated to join the two pieces. To test the effectiveness

of the gimbal joint, 8mm ball lift supports like the one shown in Figure 61, originally intended

to assist in holding up car hoods, were used instead of manufacturing our own part consisting

of a ball connected to a hexagonal slot. The lift supports also contained a short threaded rod

protruding from one end.

Figure 61: 8mm Ball Lift Support (Lift Support Hardware, n.d.)

76

A connecting piece with a hexagonal slot to represent the magnetic hex-bit locking

mechanism was modeled and 3D printed. This part was then threaded onto the end of the lift

support. For the three gimbal joint prototype assemblies (Figures 62, 63, and 64), the

unassembled parts include the hex bit insert (1), the two halves of the grip (2) that enclose the

threaded ¼-20 locking bolt (3). In the gimbal joint ball grip device, the bottom half of the grip

includes the ¼-20 bolt (3). The full devices are shown on the right side of the images (4).

Figure 62: Gimbal Joint Ball Grip; Hex-Bit Insert (1); Grip Halves (2); ¼-20 Bolt (3); Full Assembly (4)

Figure 63: Gimbal Joint Tapered Grip; Hex-Bit Insert (1); Grip Halves (2); ¼-20 Bolt (3); Full Assembly (4)

77

Figure 64: Gimbal Joint Pistol Grip; Hex-Bit Insert (1); Grip Halves (2); ¼-20 Bolt (3); Full Assembly (4)

The compression pistol grip prototype was assembled differently. Shown in Figure 65,

this prototype had a cover (1) that could be clamped onto an existing utensil about a hinge (2).

The utensil would rest between the cover (1) and the handle of the device (3) to hold it in place.

The full assembly is shown on the right (4). Although not shown here, the system would be held

closed through the use of magnets attached to both the cover and the handle at two spots (5).

Figure 65: Compression Pistol Grip; Cover (1); Hinge (2); Handle Base (3); Full Assembly (4); Locations for Magnets (5)

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Two of the designs were immediately eliminated after the assembly of the initial

prototypes. The design with the compression case locking mechanism integrated into the pistol

grip was eliminated after attempting to use multiple utensils, since the force generated by the

compressible material on the utensil would be inconsistent and determined by the size of the

utensil. The opening designed into the prototype had a square cross sectional area with 10 mm on

each side and worked well for a pencil, however a larger or smaller utensil would have varying

compression forces, rendering some utensils unusable. The Tapered Grip with the gimbal joint

was initially eliminated since it was very difficult to use writing utensils in the power grip

configuration. However, the Tapered Grip was revived later in this project with its application

being geared primarily towards eating utensils. This left only the Ball Grip and Pistol Grip with

the gimbal joint mechanism to be used in the preliminary testing.

8.2 Preliminary Prototype Testing Results

Tests were conducted with five able-bodied individuals to acquire further feedback from

five individuals outside of our design group about the two remaining 1st-order prototypes

(Figures 62 and 63 in Section 8.1). For this preliminary testing period, a fork and a pencil utensil

head were available for manipulation by the participants. The five participants included three (3)

male students aged 18-25 and two (2) female students aged 18-25. None of the five individuals

had any deficiencies relative to the three essential hand capabilities that are the focus of this

project, explained in Section 2.1.4. The tests were used to establish a baseline of information

regarding the effectiveness of the devices and to highlight any previously unrecognized potential

design issues.

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Each individual was allowed to freely manipulate and comment on the devices, following

a set of test protocols:

Individuals were given 5 minutes to freely manipulate the grips. This included, but was

not limited to, simulating eating and writing motions, detaching and reattaching different

utensil heads, or writing with the pencil attachment on provided paper.

After the participants manipulated each grip, they were asked a series of applicable

questions about both daily task completion and personal opinion.

At the end of the testing period, each participant was also asked to rate each device on a

given scale for functionality, comfort, and public use.

During the testing period, any comments made by the participants were recorded as

“other comments” in the questionnaire.

The questions asked of each participant are shown in section 8.2.1 of this report. The purpose

of the questionnaire was to gain insight into which daily activities require the use of different

types of utensils, as well as to understand the potential market for our products. The most useful

information that the questions were designed to obtain was to note any drawbacks of the devices,

so that our team could modify the designs to better fit the needs of the user.

After the testing was completed, the team reviewed the feedback from the questionnaire,

finding that the open comments section was particularly helpful. Careful consideration was taken

throughout the duration of the testing scenarios to pay attention to even the simplest details or

comments the participants would make about any of the grips. Multiple choice questions were

useful, but they also showed that when asked to certain demographics, as the answers will either

not be helpful or always be the same. The open comment section was much more useful for this

preliminary testing scenario.

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8.2.1 Preliminary Testing Questionnaire

Task Completion Questions

1. Which of the following tasks that require a spoon do you complete most frequently on a

daily basis?

a. Eating frozen foods, such as ice cream

b. Eating foods that have a thick composition, such as yogurt

c. Eating foods that are liquid with solid chunks, such as cereal or beef stew

d. Eating foods that are thin and liquid, such as tomato soup

e. Other: ____________________

2. Which of the following tasks that require a fork do you complete most frequently on a

daily basis?

a. Eating foods that require a ‘stabbing motion’ such as salad or meat

b. Eating foods that require a spindling motion such as spaghetti

c. Eating foods that require a scooping motion such as rice or peas

3. Which of the following tasks that require a knife do you complete most frequently on a

daily basis?

a. Cutting of food

b. Spreading (butter, jam, peanut butter, etc.) onto foods

4. Which of the following writing utensils do you use most frequently on a daily basis?

a. Pen

b. Pencil

c. Thin marker (ex. Sharpie)

d. Thick marker (ex. Whiteboard marker)

e. Other: ____________________

Opinion Questions

1. Of the values below, what would be the maximum price that you would be willing to pay

for this assistive utensil grip device?

a. Less than $10

b. $10-19

c. $20-29

d. $30-39

e. $40 or greater

2. Where would be the most convenient place for you to buy this device?

a. Local Store

b. Online

c. Catalog

d. Television

e. Other: ______________

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3. What feature of the device do you think is the most helpful for you, and why?

4. Would you use this device outside of your home?

a. If not, why?

5. What aspect(s) of this device, if any, would you change?

a. How would you change it?

6. Do you have any other comments on our device?

8.2.2 Multiple Choice Responses and Analysis

The results of the multiple choice questions for the five testing sessions are detailed

below.

Task Completion Questions

1. Spoon- One (1) participant answered B: yogurt. Four (4) participants answered C: cereal

or stew.

2. Fork- All five (5) participants answered A: salad or meat.

3. Knife- All five (5) participants answered A: cutting of food.

4. Writing Utensil- Three (3) participants answered A: pen. Two (2) participants answered

B: pencil.

Opinion Questions

1. Maximum Price- All five (5) participants answered C: $20-29.

2. Purchase Location- Two (2) participants answered A: Local Store. Three (3) participants

answered B: Online.

The feedback from the six multiple choice questions did not have much variation across

the testing participants; only three of the questions had more than one answer selected by the

participants. However, it gave our team several valuable insights.

According to the responses given in this section, a final version of our prototypes would

have to be able to withstand the forces and motions that are congruent with actions such as

consumption of cereal, consumption of solid foods using a fork, using a knife in a cutting

motion, and application of force on a writing utensil like a pen or pencil. These responses also

gave our team insight into potential market considerations, including a general price range and

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different means of purchase. Any future marketing opportunities for a similar product could

follow the patterns shown from these responses to judge the best means of sale.

It is important to note that the individuals performing these tests were able-bodied

individuals who had no need for assistive devices. Additionally, these participants were all

young; between the ages of 18 and 25. Therefore, their responses may be skewed towards this

demographic, which would not necessarily be the target audience for a product like this.

Feedback from multiple choice questions would be much more valuable for a demographic more

consistent with the target audience. However, the open responses that came at the end of the

multiple choice questions provided much more valuable feedback for our team.

8.2.3 Open Comment Responses and Analysis

The results of the open comment questions from the five participants are detailed below.

Not all responses are recorded here if they were repeated across participants.

1.) What feature of the device do you think is the most helpful for you, and why?

a.) Ball Grip: Easy to change position in hand. The end from which the utensil

protrudes makes it easy to manipulate the utensil.

b.) Pistol Grip: Fits better in the palm. The ability to wrap your hand around the grip.

2.) Would you use this device outside of your home? If not, why not? (This section will

only detail the “no” answers for simplicity. All five participants stated that they would

use the Ball Grip outside of their home if necessary, while only four stated that they

would use the Pistol Grip outside their home).

a.) Ball Grip: Would use, but would feel strange using at a nice restaurant.

b.) Pistol Grip: No. It is awkward and too obvious.

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3.) What aspect(s) of this device, if any, would you change? How would you change

them?

a.) Ball Grip: Increase size, feels a little small. Bottom heavy. Make the grip-able

protrusion longer.

b.) Pistol Grip: Can only use it with right hand. Extend grip downwards, pinky keeps

slipping off when holding.

4.) Do you have any other comments on our devices?

This section was varied in the level of comments. Some comments were specific to

individual grips, while others applied to all of the grips. The most useful/most common

comments are shown below; these comments were useful for creation of the final prototypes for

this project, as well as manufacturing considerations in the future.

General:

Make gimbal attachment shorter/longer if necessary for different users.

Offer different sizes for the grips.

Ensure that the locking mechanism for the gimbal joint doesn’t protrude too far

from the grip itself.

Ball Grip:

Too small and bottom heavy.

Hard time unscrewing the locking mechanism.

Pistol Grip:

Somewhat resembles a firearm at quick glance, would be wary to take into public.

Somewhat top heavy.

Many of the participants wished to see the Ball Grip increase in size, and we were

cautioned that the utensil attachment piece may protrude too far from the grip, which does not

allow the user to have the highest amount of control possible. When attached to the Pistol Grip

for example, the utensil head protruded over 4 inches from the device to the tip of the utensil,

and about 2 inches from the device to the beginning of the utensil head. The Pistol Grip is

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designed to be held in a precision grip. This does not provide the user with an ideal amount of

control, as manipulation is not very precise when the item they try to control is several inches

from their fingertips. Every participant recommended that we offer different sizes for the grips if

the designs were to reach a production stage. When redesigning these parts for the final

prototype stage, these main points were the focus of the redesign efforts.

8.2.4 Post-Testing Feedback

The results of the feedback from the five participants are detailed in this section.

Question 5 was not asked because all of the preliminary designs were manufactured using ABS

plastic. Each of the participants was asked to rate each category on a 1-5 scale, 1 being the worst

and 5 being the best. The post-testing feedback rating questions are shown below.

Post-Testing Feedback Ratings

Functionality

1. Task Performance: On a scale of 1-5, how well does the device help you perform the

required task?

2. Utensil Attachment: On a scale of 1-5, how well does the utensil attach and detach from the

device?

Comfort

3. Position in Hand: On a scale of 1-5, how well does the device fit in your hand?

4. Weight: On a scale of 1-5, how well are you able to handle the weight of the device?

5. Material: On a scale of 1-5, how comfortable is the material of the device? *

Public Use:

6. General Use: On a scale of 1-5, how well could you see yourself using this device in

public?

7. Size: On a scale of 1-5, how well could this device be discreetly transported, like in a

handbag or coat pocket?

8. Shape: On a scale of 1-5, how well could the device resemble a standard eating utensil?

*This question was not asked during this testing period, as there was no material yet chosen for

the grip handles.

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Ball Grip

Table 5: Ball Grip Feedback Ratings

Ratings

Question 1 2 3 4 5

Task Performance – Pencil XX XX X

Task Performance – Fork X XX XX

Utensil Attachment XXXXX

Position in Hand X XX XX

Weight X XXXX

Material (not asked) - - - - -

General Use XXXX X

Size XXXXX

Shape X XXX X

Pistol Grip

Table 6: Pistol Grip Feedback Ratings

Ratings

Question 1 2 3 4 5

Task Performance – Pencil XX XX X

Task Performance – Fork X X XXX

Utensil Attachment XXXXX

Position in Hand XX XXX

Weight X XXXX

Material (not asked) - - - - -

General Use X XXX X

Size X XX XX

Shape X XXX X

Analysis

In the category of task performance, where we asked participants to rate the utensils on how

well they allowed the individual to perform the intended task, there was a wide range of

responses. It is important to note that each of the five individuals held the two devices in

different manners. For the most part, the Pistol Grip has a generally universal means of holding

the grip, but the Ball Grip was freely held in a variety of ways. Some participants enclosed the

Ball Grip within their hand, wrapping their fingers around the device while the bottom of the

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grip (the side furthest from the utensil) rested in their palms. Others used the Ball Grip similar to

how one would hold a pen or pencil, with their thumb and index finger wrapped around the

cylindrical protrusion and the rest of the device not enclosed in their hand. Depending on how

each person naturally held the devices, their responses varied for both task performance and

comfort.

While the tests provided accurate data, some of the feedback from this section will not

necessarily be the same if these tests were performed by a group closer to our target consumer

base (older, less able-bodied, etc.). The weight and general use categories were harder for these

participants to answer, as they often said it was “difficult to visualize a need for these products”

when they had no use for the devices. Any young, able-bodied individual would have no trouble

lifting these devices, but using these devices in public would “most likely be embarrassing.”

After the completion and analysis of the preliminary prototype testing, it was determined that

there were several changes that had to be made for the next stage of prototypes.

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9.0 Revisions for Final Prototypes

The existing designs were altered as a result of the feedback generated by the testing of

the first round prototypes.

9.1 Gimbal Joint Assembly

Preliminary testing of the initial prototypes revealed that one of the greatest issues was

properly securing the ball within the gimbal joint. In the initial prototypes, the socket for the

gimbal joint was designed into the handle’s geometry. However, after multiple uses this socket

deformed. The deformation was a result of the set screw locking the ball against the inside of the

socket. The locking force exceeded the compressive yield strength of the handle’s ABS plastic,

expanding the socket and reducing functionality. In some cases, the section of the handle

securing the gimbal joint failed completely from compression, destroying the gimbal joint and

yielding the prototype unusable. A new design requirement was created, stating that the locking

mechanism should not fail over multiple loading cycles. A multi-part assembly was designed to

better withstand these locking forces and increase the number of locking cycles before part

failure. This new design consists of five parts and can be seen in Figure 66; the custom hex-bit

utensil head (1), the gimbal joint cap (2), the hex-bit gimbal joint insert (3), the inner threaded

tube (4), two 0-80 fasteners (5), and the set screw (not pictured).

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Figure 66: Gimbal Joint Assembly; Custom Hex-Bit Utensil Head (1); Gimbal Joint Cap (2); Hex-Bit Gimbal Joint Insert

(3);Inner Threaded Tube (4);Two 0-80 Fasteners (5)

The first part of the assembly (Figure 67) is a threaded inner tube with threads for a set

screw and half of the gimbal joint socket. The threads would be tapped into the smaller inner

diameter hole with the large diameter hole allowing for a close fit tolerance with a ¼-20 set

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screw. This part also includes a cut that allows the utensil to be rotated perpendicular to the

setscrew on one side and 0-80 threaded holes to connect the next part; the gimbal joint cap.

Dimensioned drawings of each of these parts can be seen in Appendix A.

Figure 67: Threaded Inner Tube

The gimbal joint cap (Figure 68) completes the rest of the gimbal joint socket and is

fastened to the top of the threaded inner tube. As a result, the locking force from the set screw is

distributed to the two 0-80 fasteners rather than the handle material as seen in the first

prototypes. The gimbal joint cap was designed to have a greater coverage over the ball, which

sacrifices some range of motion to better prevent the possibility of the ball coming out of the

socket during locking. The hex-bit gimbal joint insert (Figure 69) was redesigned to reduce the

length by about 25 mm (1 inch) in comparison to the initial prototypes. This was a result of

feedback gathered from the first round of prototype testing, which stated that the end of the

utensil was too far from the handle, making the use of the grip awkward for some users. In

addition, the hex bit gimbal was adjusted to accommodate 6 mm diameter magnets. These

magnets would create the force holding each interchangeable utensil within the hexagonal cut.

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Figure 68: Gimbal Joint Cap

Figure 69: Hex-Bit Gimbal Joint Insert

The end utensil, modeled as a fork head (Figure 70), was designed with a hexagonal

protrusion at the base that locks in place within the hexagonal slot. A separate magnet was

attached to the base of the utensil to hold the utensil in the hex bit insert during use but allowing

easy removal of the utensil when changing to another. The full assembly (Figure 66) shows each

part as they are connected to each other, including fasteners. The only part omitted from the

figure is the set screw, which would be inserted from the base of the inner tube.

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Figure 70: Custom Hex-Bit Utensil Head

9.2 Grip Modifications

Modifications to the three grip geometries were based on feedback from the preliminary

prototype testing. The main addition to each grip was a slot for the gimbal joint assembly to be

inserted and locked within the grip. For the Ball Grip, the most significant adjustment was

increasing the diameter of the ball portion from 40 mm to 50 mm since most respondents

suggested a slightly larger size for greater comfort. The Pistol Grip was lengthened to provide

more space for the middle, ring, and pinky finger. Finally, a slot was created in each handle to

allow the utensil to rotate a complete 90 degrees in one direction from the inner tube central axis.

All of the handle designs appear in Figures 71 through 76. Dimensioned drawings of the handle

designs appear in Appendix B.

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Figure 71: Final Ball Grip Prototype

Figure 72: Final Ball Grip Prototype – Disassembled

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Figure 73: Final Pistol Grip Prototype

Figure 74: Final Pistol Grip Prototype – Disassembled

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Figure 75: Final Tapered Grip Prototype

Figure 76: Final Tapered Grip Prototype - Disassembled

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10.0 Testing of Final Prototypes

Once the final prototypes were manufactured, they were critiqued by professionals in the

rehabilitation field. Occupational Therapists (OT) and Certified Occupational Therapy Assistants

(COTAs) from three different facilities analyzed each grip. In total, the grips were tested by six

OTs and two COTAs from Whittier Rehabilitation Hospital, one OT from Behavioral Concepts,

Inc., and one OT from Knollwood Nursing Center. The OT from Behavioral Concepts, Inc.

worked in pediatrics whereas the other 9 professionals worked with adults.

10.0 Final Prototype Survey Responses

After evaluating each device, the professionals answered a survey that asked the

following questions for each of the three grip designs.

Survey Questions:

1. What are the desirable features of the device?

2. What are the drawbacks/deficiencies of the device?

3. Would you use this device with your patients?

4. Why or why not?

5. Do you have any other comments on this device?

Survey Responses:

Ball Grip

What are the desirable features of the device?

Easy to hold

Gross grasp/grip

Lightweight

No sharp or pointed objects near the grip

Simple to use correctly/safely for patients

The size is good for kids, maybe for stoke patients it would be good also

L or R hand use

Great for use with patients with patients with high contractures of fingers

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What are the drawbacks/deficiencies of the device?

Need a decent amount of grip strength to grip/control

Weight

Slippery

Would you use this device with your patients?

Why or why not?

Yes (10/10)

Stroke or spinal cord injury with low hand grasp

Yes, if necessary

I would try it with children

Pistol Grip

What are the desirable features of the device?

Utilizes index and thumb

Good angle for people with wrist flexion issues

Comfort grip

Angle and shape

Wrist comfort when using

The weight of it is good

Great for patients with fixed contractures that limit other grasp patterns.

What are the drawbacks/deficiencies of the device?

Shape is slightly excessive if there is already a 90-degree angle from ball and socket

Pinch grasp feels awkward

You would need a different device for left hands

More specific type of patient to use this on

Could use a longer or extended grip

Could be a little lighter

A bit awkward to manipulate

Would you use this device with your patients?

Why or why not?

Yes (8/8)

Yes, if applicable

I would need a specific patient to trial this device

Yes, if low wrist function

It depends on the circumstances, I would try it

2 did not answer

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Tapered Grip

What are the desirable features of the device?

The grip feels natural

Finger grooves

Simple to use

Style

Hand grasp

Weight is good

What are the drawbacks/deficiencies of the device?

Heavy

Could be a little lighter for arthritis patients

‘There are similar shaped built up utensils out there although this may be better, it might

be harder to sell”

Would you use this device with your patients?

Why or why not?

Yes (7/7)

3 did not answer

Yes, the grip would allow increased control with self-feeding

10.2 Final Prototype Survey Results and Analysis

The most desirable features written by the professionals for all three grips were the ability

to adjust the position of the utensil based on the needs of the patient and the easy process of

switching the utensil. The Ball Grip seemed to be the most favorable grip according to the

professionals. This grip is a unique design and is very different from the current products as

stated by one OT who said “I really like this design. I haven’t seen this type of grip used yet, it

would be a nice addition.” The Pistol Grip is a good grip for wrist flexion and grip strength

limitations due to the way it utilizes the index finger and thumb. However, it was noted by

several respondents that the Pistol Grip would require a specific patient with certain symptoms in

order for the grip to be beneficial. It also would need to be manufactured in both left and right

hand versions. The Tapered Grip’s finger grooves seemed to be the best feature according to the

professionals. One OT claimed it was “the best one because it’s the most natural.” However,

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another OT said, “there are similar shaped built up utensils out there. Although this may be

better, it might be harder to sell,” which would reduce the marketability of the grip as a

commercial product.

The overall results of the survey showed that the gimbal joint is the best feature on all of

the designs. Some of the answers were omitted due to the locking mechanism failing after many

uses since the material used for the prototypes was not strong enough. There were no significant

deficiencies noted by the professionals that would interfere with the functionality of the product

with their patients. The common minor deficiencies that were noted addressed the device’s

weight and finish of the material being slippery. Two OTs asked if the grips were dishwasher

safe, which was taken into consideration when selecting a final material. Two other suggestions

were to add a Velcro strap for patients who cannot physically hold the grips and to make both

lightweight and weighted versions of the grips for different patient applications. An important

result from the responses was that no respondent said they simply would not try the devices with

their patients. This is significant since OTs are the professionals who suggest devices to their

patients for assistance in eating either at their homes or in long-term facilities.

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11.0 Product Manufacturing Considerations

Each of the final three designs contains six main parts aside from fasteners: the custom

utensils, the gimbal joint cap, the hex-bit gimbal connector, the threaded inner tube, the set

screw, and finally the handle geometry. The geometry of the handles is the main difference

between designs. Each of the other independent parts would have to be manufactured separately

and then assembled to create a functional product. This section discusses the potential

approaches that could be taken to manufacture each part.

Research was conducted on the various manufacturing processes that could be used to

produce the parts. The hex-bit gimbal, the threaded inner tube, and the gimbal joint cap should

be made out of metal and could be made using various methods including die casting, sheet

metal forming, and milling. The handle geometry should be made out of plastic to minimize

weight using 3D printing or injection plastic molding. The magnetic utensil end should be

manufactured using current flatware production methods but with a hexagonal protrusion added

to the end of the utensil head instead of a handle.

The gimbal joint assembly as shown in Figure 66, which includes the gimbal joint cap (2),

hex-bit gimbal joint insert (3), and the threaded inner tube (4), could be manufactured from

aluminum using machine milling processes. This method is suitable since the complex

geometries of the parts would be difficult to form from sheet metal and the larger tolerances and

defect rate of die cast parts would be inadequate. Also, since the parts would have to be drilled

for fasteners after the base shape is made, producing the parts in a single machine shop would be

the most time effective. Aluminum was chosen over plastic due to the strength of the material.

The components cannot deform after the metal set screw is repeatedly tightened to lock the

system. Aluminum was also chosen because of its low cost, durability, and low weight.

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For the custom utensils (1), the current utensil manufacturing process could be slightly

modified. The material should be a Ferritic stainless steel, which is magnetic so the utensil will

stay in the hexagonal slot. The most common Ferritic stainless steel used in cutlery is Grade 430

Stainless Steel because it is cheap and can be formed and welded easily. It would start as thick

coil and then manufactured into the shape of the utensil head. The head of the utensil should then

be welded to a hexagonal protrusion made from the same material.

For the set screw, the geometry should resemble a standard bolt with ¼-20 threads.

Features should also be added to the exposed end of the bolt to give the user a better grip and

provide greater locking force. In terms of the Ball Grip, the exposed end of the bolt should be

screwed into the lower half of the Ball Grip as seen in Figure 72. The set screw should also have

a rubberized tip to maximize holding power on the gimbal joint. The 0-80 fasteners (5) could be

purchased from another supplier.

The handles should be manufactured using a multi-component injection molding. A mold

surrounding the gimbal joint insert would be manufactured for each of the three grips. Molten

plastic would be injected into this mold and harden to make the final shape of the grip. The first

injection of material is a thermoset. Then the second injection would be a liquid silicon rubber

for improved grip (Figure 77).

Figure 77: Dual Injection Process (Multi Shot, n.d.)

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Liquid silicon rubber is used in the healthcare industry because it is bacteria-resistant and

hypoallergenic. Plastic injection molding was chosen over 3-D printing because of the high

production rate and low cost of the plastic injection molding process. 3-D printing is generally a

very time consuming and expensive process for these larger, composite-material parts.

The BASF Corporation cost estimator for injection molding thermoplastic parts was used

to get an estimated cost for the three grips (BASF, n.d.). Ultradur B 4500 FC was chosen as the

material because it is a general-purpose food contact plastic. The assumptions made were 10,000

parts per year, an average labor rate cost, and 20% overhead contingencies. The volume, wall

thickness, and projected area of the part were calculated from the CAD models and inserted into

the calculator. The calculated costs for the three grips are shown in Figures 78, 79, and 80. The

ball grip was calculated to be the least expensive grip with an estimated cost of $1.11, then the

tapered grip costing $1.17, and the pistol grip with an estimated price of $1.18. These estimated

prices are without the rubber coating added to the outside.

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Figure 78: BASF Quick Cost Estimator for Injection Molding Thermoplastic Parts - Ball Grip

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Figure 79: BASF Quick Cost Estimator for Injection Molding Thermoplastic Parts - Tapered Grip

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Figure 80: BASF Quick Cost Estimator for Injection Molding Thermoplastic Parts - Pistol Grip

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12.0 Conclusion

A set of three customizable assistive utensil grip devices were created and evaluated by

students and experts in the rehabilitation field. These grip devices allow users with limited grip

strength and range of motion to easily manipulate utensils, which they may not have been able to

do without the aid of these devices. Assistive eating utensils and other handheld devices

currently on the market are typically ‘one size fits all’. The devices that were designed in this

project can better accommodate a variety of users and conditions by allowing the users to

customize the type and orientation of the utensil attachments. The three grips created are shown

in Figure 81; the Pistol Grip (1) is shown on the left, the Ball Grip (2) is in the middle, and the

Tapered Grip (3) is on the right.

Figure 81: Final Grip Prototypes; Pistol Grip (1); Ball Grip (2); Tapered Grip (3)

The availability of three different handle geometries is a feature that can be selected by a

potential user for increased comfort and effectiveness. With each grip shape providing a different

hand orientation, the proper product can be selected to better address an individual’s condition.

Additionally, the interchangeable utensil heads bring a level of personal modification not seen

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with existing products. While some products on the market can be used with existing utensils—

such as the Ableware Universal Built-Up Handle (Figure 13)—the majority of available products

only provide the user with one option to use per device, and users are often required to purchase

additional devices for use with different handles. The grip devices created in this project can be

used with a large number of interchangeable utensil heads without the need for additional device

purchases.

The most significant customizability feature of these devices is the capabilities presented

by the gimbal joint. While the user of these products may have very limited range of motion in

the wrist, elbow, or even shoulder joint, the limitless orientations for the utensil head provided by

the gimbal joint will help increase the possibility of effectively completing daily tasks with just

one device.

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13.0 Recommendations

At this stage of development, the final designs and their respective prototypes were fully

functional. These recommendations include improvements to the design that can expand the

range of potential users by increasing customizability.

13.1 Grip Sizing

From analyzing feedback from both the initial and final rounds of prototype testing, there

was a common trend in the desire for different sizes for the handles, both bigger and smaller.

Some of the individuals who participated in the initial round of testing commented that the

devices were generally too small for their hands. Based on these responses, it would be

beneficial to offer a few sizes of grips to accommodate for individuals with different sized hands.

Except for the Ball Grip, these devices were difficult to design, as the contours do not

simply consist of straight lines and perfect arcs. Designing these parts relied on attempts to

mimic the shape of the human hand in different grip orientations, which made it challenging to

design without splines and more freeform shapes. A better modeling strategy could be used to

make it easier to scale different handle dimensions for various hand shapes and sizes.

13.2 Material Considerations

While the devices are functional and sturdy, the current prototype materials should not be

used for the final product. The threaded inner tube (Figure 68), gimbal joint cap (Figure 69), hex-

bit insert (Figure 70), and utensil head were printed using MED 610 plastic, while the outer grips

were printed with Vero White Plus plastic, all from the Objet260 Connex Rapid Prototype

machine. The locking mechanism of each of the devices uses ¼-20 threaded bolts.

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One of the difficulties encountered when adjusting the locking mechanisms on the

prototypes was that the plastic on the gimbal joint cap was not strong enough to withstand the

force applied by the threaded bolt on the hex-bit insert. Often, after multiple locking and

unlocking cycles, the hex-bit insert would push past the gimbal joint cap, rendering the locking

mechanism useless. For future manufacturing, it would be better to create the inner parts

(threaded inner tube, gimbal joint cap, and hex-bit insert) from metal to avoid the deformation

that is currently affecting the locking mechanism. In order to keep the overall weight of the

device to a minimum, aluminum or another lightweight yet strong metal may be a desirable

material to use.

13.3 Locking Mechanism Design

The locking mechanism of the three devices currently consists of the hex-bit insert, the

inner threaded tube, and the ¼-20 threaded bolt. With future iterations of this mechanism, simply

using a ¼-20 bolt is not ideal, as it can be hard to turn if the user lacks muscle coordination or

grip strength and is not aesthetically pleasing. Instead, it is recommended that a similar system

be used with a modified end that protrudes from the handle. Rather than having the bolt end

protruding from the grip handle, a design with fins that is easy to grasp and rotate could be

incorporated. This would require less force to lock the gimbal joint and could be more

aesthetically pleasing but would need to be designed in such a way as to not interfere with how

the user holds the handle.

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13.4 Potential Applications

For the prototyping and testing done during this project, only a fork head was designed

and created as a utensil attachment. However, the list of possible detachable utensil applications

is much more expansive, and can include the following:

1. Knife

2. Spoon

3. Personal care items (toothbrushes, razors, etc.)

4. Writing utensils (pens, pencils, etc.)

5. Small handheld tools (screwdrivers, wrenches, etc.)

The list of potential applications is more extensive, and would be for specific needs that

would vary on an individual basis. However, because the mechanism attachment design is

simple, only requiring a hexagonal protrusion and a magnetic base, any other specific utensils

would be simple to design and produce.

110

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Appendix A: Hex-Bit Gimbal Joint Design Drawings

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Appendix B: Handle Design Drawings

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