System Design Review

Team Members: ◦ Pattie Schiotis – Team Manager (ME)

◦ Shane Reardon – Lead Engineer (ME)

◦ Dana Kjolner (EE)

◦ Robert Ellsworth (EE)

◦ Sam Hosig (CE)

◦ John Williams (CE)

•Faculty Guide: Dr. DeBartolo

Introduction

Work Breakdown Structure

Customer Needs

Engineering Specifications

Functional Decomposition

Concepts

Component Benchmarking

Risk Assessment

MSD I Project Plan

Lasting side effect of a stroke: foot drop ◦ Inability to dorsiflex the foot

Ankle Foot Orthotics (AFOs) currently used to aid dorsi-flexion. ◦ Passive devices don’t allow for movement when

walking on ramps and stairs

Foot is always pointed upwards

User will have no ability to either plantar-flex or dorsi-flex their foot

Side to side stability of the foot will be ignored

Worst case will be analyzed: ◦ 95 percentile male having heavy foot.

◦ Fast walker – gait cycle less than 1 second.

Device may not use air muscles as an actuation source

Primary Needs: Secondary Needs:

Safety

Portable ◦ Lasts all day without

charging/refueling

◦ Lightweight

◦ Tolerable to wear all day

Reliable

Accommodates Flat Terrain

Accommodates Special Terrain ◦ Stairs

◦ Ramps

◦ Obstacles

Comfortable ◦ Aesthetically Pleasing

Durable ◦ Water Resistant

◦ Corrosion Resistant

Salt & Environment

Biocompatibility

Convenient ◦ Easy to put on and take

off

Engineering

Specification

Number

Engineering Specification

Description

Units of

Measure

Preferred

Direction

Nominal

Value

Method of

Validation

Stems From Customer

Need

s1 torque on Foot N-m Up ≥±3.0 Test FT1,2,4,ST1,5

s2 system response time (sensing

terrain to actuating device) ms down <400 Test ST3

s4 predicts step down yes/no - yes Test ST1,2,4

s5 predict flat yes/no - yes Test FT1,ST5

s7 predicts ramp down yes/no - yes Test ST1,2,4

s10 allowable range of motion

between foot and shin degrees range 70 to 135 Test FT1,3,CF8,9,ST1

s12 untethered usage time hrs/steps up 8 hrs or

3000 steps P1,2,D1

s17 force to secure constraints N down < 80 Test C4

s18 force to remove constraints N down < 80 Test C3

s23 radius of edges/corners on AFO mm up 0.5 - S4,CF1,2

s24 weight of entire device kg down ≤3 Test FT6

s28 Operates in environment

temperature range °C range

-17.8 to

37.8

Component

Ratings D2

s31 Minimum life until failure steps up 5.5

million test D1

Mechanical Locking Method Uses a solenoid to unlock the heel which allows the foot to drop.

Mechanical Locking Method ◦ Mechanically restrict the foot from dorsi/plantar

flexing while in the air.

◦ Use gravity to help the foot plantar-flex as needed (stairs/ramps)

◦ Methods: 1. Use a solenoid to unlock the heel which allows the foot to drop.

2. Use a brake to unlock the heel which allows the foot to drop.

3. Ratcheting Device attached to ankle

Active Actuation ◦ Uses a linear actuator to force the foot into the

proper position.

◦ Methods:

Solenoid

Piezoelectric

Power Screw

Hybrid

Power Screw with electric motor

Hard Stop Two preset distances can be

moved back and forth using

a servo motor and screw.

42%

0.152H

Fw

NmmkgsmHFwankleM 636.1)868.1)(152.0)(42.0)(4.1(/8.9)152.0%)(42(/ 2

lbfNcm

Nm

l

TF 25.1150

3.3

636.1If our actuator is 1.5” (3.3 cm) behind

ankle joint:

Anthropometric Data for male, 95 percentile: •Stature=1.868 m •Foot Weight=1.4 kg

θ=20°

cmly 28.1)20sin(3.3sin

Dorsi-flexion:

Plantar-flexion:

cmly 33.2)45sin(3.3sin

Total stroke=3.61 cm In 0.4s, we need 9 cm/s

Solenoid Electro-Mechanical Piezoelectric

Actuation Force 30 lbs 22 lbs 100N

Stroke 1.1 cm >4.4 cm micro-meters

Speed <100 ms 10 cm/s -

Power Consumption 92V, 7.2 A (moving), 0.08 A (holding) 12VDC, 5 A 100 V

Pros Cons

Mechanical Locking

• Low Power Consumption • Can hold the foot up in the

event of an electrical failure • Uses Gravity to position the

foot

• Can only hold the foot in a position that it has been

• Needs a Large voltage spike to trigger the solenoid

Active Actuation

• Can move the foot to any location needed

• Can be designed to hold the foot up under failure

• Large amount of energy required

• Slow response time • Heavy

Hard Stop • Low Power Consumption • Capable of counter-acting

large amounts of plantar-flexion force

• Difficult to create failsafe

• Slow response time • Does not reset it self

when the toes need to be pointed up

Concepts

A B C D

Mechanical

Locking

Active

Actuation Hard Stop

Passive Device

Selection Criteria Weight Rating Weighted

Score Rating

Weighted

Score Rating

Weighted

Score Rating

Weighted

Score

Safety 20% 2 0.4 1 0.2 1 0.2 1 0.2

Portable 15% 2 0.3 0 0 3 0.45 3 0.45

Reliable 15% 2 0.3 3 0.45 1 0.15 2 0.3

Accommodates Flat Terrain 15% 2 0.3 1 0.15 1 0.15 1 0.15

Accommodates Special Terrain 15% 3 0.45 1 0.15 2 0.3 0 0

Comfortable 8% 1 0.08 0 0 2 0.16 1 0.08

Durable 8% 1 0.08 1 0.08 2 0.16 2 0.16

Removability 4% 2 0.08 2 0.08 3 0.12 2 0.08

Total Score 1.99 1.11 1.69 1.42

Rank 1 4 3 2

Continue? Yes No No N/A

Bounces infrared light off terrain to determine distance

10 cm to 80 cm range

Worst case power consumption per sensor is 0.00176 kWhr

Output from -0.3 to +0.3 volts

Highly accurate within operational ranges

Low cost (~$15)

https://www.sparkfun.com/products/242

A Far A Normal A Close

B Far

Mid Stride,

Down

Slope/

Stairs

Mid Stride,

Normal

Terrain

Mid Stride,

Up Slope/

Stairs

B

Close

Foot

Planted,

Down

Slope/

Stairs

Foot

Planted,

Normal

Terrain

Foot

Planted,

Up Slope/

Stairs

Sensor A

Sensor B

Terrain

Nonlinear response Reflective ratio of

materials is mostly irrelevant

Static position

Concerns about irregular terrain types

https://www.sparkfun.com/products/242

Predicts what type of terrain we are walking on

Calculates where in the gait cycle we are Has some modeling that improves

performance of predictions

NEED TO CHANGE Need to be able to fully implement in C Error checking for invalid states Nothing is done at run-time

Micro controller needs: ◦ Interface with two IR sensors and possible angle

senor

ADC

◦ Control actuation method

PMW or Digital I/O

◦ Other considerations

Must run on battery power for at least 8 hours

Must be able to simulate system in “real time”

Must be able to fit on orthotic

Must be able to export data to sd card if needed

Power From Micro Controller and Sensors

Device Time

(Hours) Current

(A) Voltage

(V) Power

(mWhr) Total Power (mWhr) IR Sensors 8 0.03 5 1200 2400 Micro C. 8 3.00E-04 5 12 12

Total Power 2412 80% Efficiency 2894

Solenoid Power Usage for Option 1 Watts per step Time per step mWhr / step

40 0.5 5.5

ID Risk Item Effect Cause Like

liho

od

Seve

rity

Imp

ort

ance

Action to Minimize Risk Owner

1

Foot failing in down position User would trip and fall Sensor unable to detect terrain

or send faulty readings 2 3 6

Software fail safe, if no data is

sensed will fail in natural position

Engineering

Lead

2

Actuator malfunction 1 2 2

System free to move if actuator

breaks

Engineering

Lead

3

Structural failure, orthotic unable

to support equipment 1 3 3

Large enough factor of safety Engineering

Lead

4

Spring Yielding/Buckling

1 2 2

Structural modification, mechanical

prevented action

Engineering

Lead

5

Power supply

3 2 6

Before system runs out of power,

lock in normal state. Warning signal

included

Electrical

Engineers

6

Scheduled deadlines not met Timeline falls behind, other

deadlines change

Personal conflicts: time

management, overloads schedule,

illness

3 2 6

Communication among members to

know each other’s schedules,

understand critical path, seek help

when needed

Team

Manager

7

Material acquisition delay Prototype cannot be built and

tested

Long lead times, parts not ordered

on time

1 2 2

Contact with vendors, determine

parts with long lead times, order by

week 7

Team

Manager

8

Incorrect material handling Overload system capabilities Misuse of supplies

2 2 4

Responsible team members in

charge of their components.

Understand system capabilities and

specifications

Engineering

Lead

9

Unable to meet customer

specifications

Project failure, unhappy

customer

Weight of device too heavy

2 3 6

Be cautious of component weights

when creating detailed design

Engineering

Lead

10

Device contains sharp edges, harms

the users 1 3 3

Ensure all points of contact will not

harm user, no pressure points

Mechanical

Engineers

11

Memory overflow Device would go into an error

state

Not enough memory on the micro

controller and associated memory

systems 2 2 4

Ensure enough memory is available

on micro controller

Computer

Engineers

ID Task Name Complete (%) Completetion Goal

When Completed

Issues/Comments

1 Define Project 2 Review customer needs 90% 10/2/2012 Review after concepts selected 3 Review customer specifcations 90% 10/2/2012 Review after concepts selected 4 Finalized functional decomposition 100% 9/21/2012 9/21/2012 5 Determine work breakdown structure 100% 10/5/2012 9/28/2012 changes after systems review 6 Observe walking patterns at naz clinic 100% 9/24/2012 9/24/2012 7 Concept Generation 8 Create benchmark matrix 90% 9/28/2012 9 Define components 100% 9/14/2012 9/28/2012

10 Establish system possibilities 100% 9/14/2012 9/21/2012 11 Create system comparions (Pros and Cons) 100% 9/28/2012 10/2/2012 12 Develop Proposed Design 13 Assign team member specific jobs 100% 9/21/2012 9/21/2012 Proposed design approval 14 Develop psedeocode 100% 9/28/2012 9/28/2012 15 Review previously developed sensor code 100% 9/28/2012 9/28/2012 16 Feasibility analysis 80% 10/2/2012 17 Compile Systems Design Review 18 Schedule review 100% 9/25/2012 9/28/2012 19 Create risk assessment 100% 10/2/2012 10/2/2012 20 Create review report out 95% 9/28/2012 21 Develop project schedule 90% 10/2/2012 22 Part Selection 23 Select components 40% 10/12/2012 24 Create budget breakdown 0% 10/12/2012 Need component specifications 25 Detail component information (specs, vendor) 5% 10/19/2012 26 Purchase parts 0% 10/26/2012 relient on specs 24-26 27 Detailed Design 28 Create BOM 0% 10/19/2012 29 Update risk assessment on going 30 Verify design output 0% 10/23/2012 31 Finalize system architecture 0% 10/16/2012 32 Prepare drawings, schematics, and flow charts 0% 10/26/2012 33 Identify critical design path 0% 10/12/2012 34 Document design changes (if any) 0% 11/10/2012 35 Test Plan 36 Determine component testing 0% 10/26/2012 37 Create testing guide/SOP 0% 11/3/2012 38 Estimate resource requirements 0% 11/10/2012 39 Create data collection sheets 0% 11/10/2012 40 Additional Tasks 41 Update EDGE on going

1. Scope of project is to design a modified AFO that includes: Energy storage medium

Foot rotation device

Terrain sensing system

Microcontroller

2. We will focus on a detailed design following the “Mechanical Locking Mechanism” concept.