Medical Robotics - uniroma1.itvenditt/didattica/mr/16_Exoskeletons.pdfVendittelli: Medical Robotics...

Medical Robotics Marilena Vendittelli

Exoskeletons: introductory concepts and applications

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Vendittelli: Medical Robotics - Exoskeletons

Upper-extremity exoskeletons and Intelligent Assist Devices

! Human power augmentation for manipulation of heavy and bulky objects, and reduction of risk of MS disorders.

! Mostly used in industrial sites : The user feels, as a natural feedback, scaled-down of the load actual weight.

! Can filter and decrease the forces transferred from a device to handle, and follow a particular trajectory.

! Designed based primarily on impedance control schemes relying on human-machine interaction forces

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Upper/Lower-extremity exoskeletonsIn the early 60’s the US Defense Department started successive projects of “powered suit of armor” development to increase soldiers’ lifting and carrying capabilities. Hardiman (General Electric & Cornell).

“The idea of humanoid robots has arisen from the desire to help handicapped persons”

M. Vukobratovic

Yagn’s running aid (1890) is perhaps the first device resembling an exoskeleton (never built)

In late 60’s, Vukobratovic and Hristic developed active orthoses for paraplegic at the Mihajlo Pupin Institute, in Belgrade.

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Biomechanics of walking

Biomedical measures in the sagittal plane are fundamental for exoskeleton design.

At low speed, the exoskeleton must mainly add power at the hip, dissipate power at the knee (brake or damper), store and release energy at the ankle (passive elastic).

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DARPA Program Exoskeletons

“EHPA Exoskeletons for Human Performance Augmentation”, started in 2001, followed by the “Army Program Executive Office Soldier (PEO Soldier) in 2008.

- 3 institutions demonstrated working exoskeletons - Berkeley Exoskeleton (BLEEX)- Sarcos Exoskeleton - MIT Exoskeleton

- Other institutions made advances in “enabling” technologies such as portable power supply.

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BLEEX (UC Berkeley)

- First version actuated by bidirectional linear hydraulic cylinders

- Energetically autonomous (hybrid hydraulic-electric power supply)

- 7DOFs in each leg, only 4 actuated : Hip, knee, ankle flex/extention + hip abd/adduction. Other joints spring-loaded

- Active balance control but the wearer must provide a forward guidance force to direct the system during walking.

- Sensors: - 8 encoders + 16 linear accelerometers- Foot switch sensor + pressure sensor at the foot- 8 single-axis force sensor associated to each actuators - 1 inclinometer

- Second generation with electric motors.

- Walking velocity : 0.9m/s with 75kg, 1.3m/s without load

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Bleex control scheme (Kazerooni 2008)

Case of a 1DoF exoskeleton leg in swing configuration (no contact with the ground)

- The human force on the exoskeleton cannot be measured in a robust and repeatable way (contact points location and force direction vary).

- In the absence of gravity, the dynamic behavior of the exoskeleton is described by:

- If the actuator is closed-loop stabilized (large gain), or non-back-drivable (large transmission ratio) the sensitivity S is small (small exoskeleton response)

- Objective : Increase S through feedback but without measuring d

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v =Gr + SdActuator

Human

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The control scheme of BLEEX

Case of a 1DoF exoskeleton leg in swing configuration (no contact with the ground):

- Feedback loop from the exoskeleton only. No sensor on the pilot or the exoskeleton interface with the pilot.

€

SNEW =vd

=S

1+GC

- However, any negative feedback from the exoskeleton leads to

- Classically, one wants to minimize the sensitivity of the closed-loop system to external forces (disturbances). For an exoskeleton, the reasoning is opposite.

- Strategy: use the inverse of the exoskeleton dynamics as a positive feedback controller so that the loop gain be slightly less than 1:

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SNEW ≤ S

€

SNEW =vd

=S

1−GC

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C = (1−α−1)G−1

€

(α =10⇒ SNEW =10S)with

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Case of a 1DoF exoskeleton leg in swing configuration (no contact with the ground):

- Finally, denoting by H(v) the (unknown) pilot impedance:

- This control scheme works well if the system model G is well identified: No force-sensor but low robustness to parameter variation.

- The upper feedback loop stabilizes the overall system (pilot + exoskeleton)

Human loop

Exoskeleton loop

- The lower feedback loop is positive, potentially destabilizing

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d=-H(v)



Extension to the complete exoskeleton

- Abduction-adduction control at the hip decoupled from the control of flexion-extensions in the sagittal plane

- Three gait phases associated to three dynamical models:

Example of the singe support phase

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M(θ) ˙ ̇ θ +C(θ, ˙ θ ) ˙ θ + P(θ ) = T + d

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θ = (θ1,...,θ7)T T = (0,T1,...,T6)

T

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T = ˆ P (θ) + (1−α−1)[ ˆ M (θ) ˙ ̇ θ + ˆ C (θ, ˙ θ ) ˙ θ ]

- If the estimates are accurate and sufficiently large, the force felt by the pilot is minimal (transparency)

€

α

- When the abduction/adduction angles vary only the value of

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P(θ)

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needs to be modified.


From the same technology: Phenix

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• a modular exoskeleton allowing the user to independently put on and remove each piece• only two actuators at its hip• weighs 12.25kg (27 lbs)• 1.1 miles/hour (0.5 m/sec) has been clocked by a Phoenix user; the maximum speed depends on the individual user

• autonomy: 4 hours continuously or 8 hours intermittently• marketed in Europe by Meccanica per I'Elettronica e Servomeccanismi s.p.a. (MES)

video


WEAR (Sarcos Research Corporation)

- Joints actuated by rotary hydraulic actuators

- Energetically autonomous (own power supply)

- Force sensing between the wearer and the robot used for control

- Few information has been made public (DOF, control scheme, sensors, power supply)

Impressive results :

- wearer standing on one leg while carrying another person on the back

- 1.6m/s with 68kg on the back and 23 kg on the arms

- walking through 23 cm of mud, twisting, squatting,…

Wearable Energetically

Autonomous Robot

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MIT Exoskeleton

- Quasi-passive concept aiming at exploiting the passive-dynamics of human walking. No actuator for adding power at the joint

- Relies on the control of energy storage/release through spring-loaded joints and dampers at the hip, knee and ankle.

- Sensory information : strain gages at the shin and a potentiometer at the knee joint

- 11.7kg and only 2W of energy for the knee damper control.

Results :

- 36kg load at 1m/s, 80% of payload transferred to the ground

- However 10% increase of walking metabolic cost compared to walking with the same load in a standard backpack (increase of mass, inertia and added kinematic constraints that modify the human dynamics)

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Until 2008 no one has yet demonstrated an exoskeleton that reduces the metabolic cost of transport when compared to the load-carriage with a standard backpack.


Other lower-limb exoskeleton projects started during the 90’s

HAL 3 (Hybrid Assistive Leg)Univ. Tsukuba by Pr. Y. Sankai- For augmentation & rehabilitation- Elec. motors with harmonic drive- Hybrid control system

RobotKnee by Yobotics.- Assist stair climbing during load carrying tasks- Linear Series Actuators- Use of CoP and Ground reaction force

Nurse Assisting Exoskeleton Kanagawa Inst. of Techno.- Direct-drive pneumatic actuators- Knee control via Force Sensing Resistors- No mechanics at the front

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HERCULE (CEA List – DGA 2001 )

- Electric actuators

- 2 actuated axes per leg (hip and knee)

- Li-ion Batteries (4 hours autonomy at 4km/h)

- Load weight 40kg

- Transfer of the load to the ground

- Controlled by the wearer natural movements

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From passive to active orthoses

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Passive Orthoses, FES, Hybrid Orthoses

Hybrid orthoses FES + HKAFO

- Delays muscle fatigue- Muscle effort lighter systems- Better trajectory control (brake, spring-brake, hip constraining mechanism)- DC motors or pneumatic.

AFO KAFO, HKAFO- Mechanical structure that locks or limits the joints movement during the stance phase

- Energy demanding (43% more than a wheelchair) and low functional efficiency

RGO (Reciprocating Gait Orthoses) : The flexion power of one hip is used to extend the opposite one

FES (Functional Electro Simulation) + uses the muscle as natural actuator

+ strong functional and psychological benefits - difficult control of joint trajectory

- rapid muscle fatigue

€

⇒

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Robotics mobility training devices

Locomat (Paracare Univ. of Balgrist Zurich) Lopes (Univ. of Twente)

- Exoskeleton + treadmill + support (arm bars + body harness)- Selective control of gait functions during rehabilitation- Efficiency, reduction of physical load on both the therapist and the patient

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Early full-lower limb active orthoses

Mihailo Pupin Inst., (Vukobratovic et al 74).- Pneumatic actuators for the hip, knee and ankle flex/ext + ab/adduction at the hip- Execution of gait pattern via an “electronic diode” function generator- Piezo-ceramic force sensors in the shoes- Last version with DC motors for portability

Visconsin exoskeleton (Seireg et al 1968 81).- Flex/ext at the hip and knee actuated by battery powered rotary hydraulic actuators,- DC motor driving an hydraulic pump. - Remaining DoF passive or spring-loaded - Autonomy except for off-board computer- Open-loop trajectory following with crutches

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HAL-5 (2001 )

- Developed at Tsukuba Univ., by Y. Sankai, today commercialized by Cyberdyne.

- 15kg, battery powered, electric motors with harmonic drive to power hip, knee, and ankle flexion/extension joints

- Hybrid control system- Cybernetic Voluntary control : Low bio-electrical signals appearing on skin surfaces when a movement is attempted are used to trigger power units

- Robotics autonomous control : walking pattern

- Crutches needed for stabilization

- Can carry up to 40 kg on the arms and increase the leg press capability from 100kg to 180kg

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ReWalk (2007 )

- ARGO Medical Technologies – Israel- Electric motors, 8h autonomy- Control by upper-body tilting (AP) and leaning (ML)- Upper-body tilt sensors- Actuation of hip and knee flex/ext - Spring-loaded ankle joints- Walker or crutches required for stability - Possibility to walk (2.2km/h), on level ground or slopes and climb stair.

Claire Lomas walking the 2012 London’s Marathon

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video


eLEGS EKSO 2010-11

- Developed by Univ. of California and Berkeley Bionics based on the know-how developed in the BLEEX project

- Two axes actuated per leg (hip + knee) with electric motors + spring-loaded joint at the ankle

- IMU used to the determine absolute arm position

- Force sensor in the crutch

- Control of straight walking + stand-up/sit-down

- 20kg, 3.2 km/h, 6h battery autonomy

- In the process of being certified for medical use

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Other Lower-limb orthoses with crutches

MINA 3 (Florida IHMC - NASA)- Brushless DC motors + harmonic drive providing compliance- Similar to ReWalk - Sensory substitution interface at the tongue and abdomen for COP, ground reaction forces, joint position, torques

INDEGO (Vanderbilt Univ. Nashville + Parker Eng. )

- Brushless DC motors- Hip and knee flex/ext- used with a standard AFO stability + preclude foot drop - Light and modular- Sitting, standing, walking

WPA (Nagoya Univ.) - 6 actuated joints (hip knee ankle) ; adaptable 1.6m to 1.9m- Interface with the walker- The user moves the walker, the opposite leg is moved by WPAL - Pressure & acceleration sensors

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REX – Bionics (Aukland New-Zealand 2010-)

- No need for crutches, robust balance control even in single support free hands

- Electric actuation : hip : flex/ext + abd/add ; knee: flex/ext ; ankle: dorsi/plantar + ever/inv

- 38kg, Max Payload 100kg; 1.45m to 1.95m ; 0.12 km/h, 2h battery autonomy

- Stand-up/sit down, walk on flat or sloping surfaces, steping, turning, going up/down stairs

- Control via pad and joystick - network of 29 micro-controllers (reactivity + smoothness)€

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EMY (CEA List – Leti 2013 )

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video


Transparency through the CEA actuator- Back drivable, low friction- limited inertia, good ratio weight/power- Enables torque-based control without sensors- Silent but flexible - Enables free motion when enhancing power while adapts assistance to users with reduced strength

EMY (CEA List – Leti 2013 )

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V0 (March 2013)- 20 DoF, 7Dof at the arm (ABLE) + 3 at the leg- automatic cyclic walking- no balance control- deported electronics- no onboard energy supply- simulation framework based on XDE

V1 (January 2014)- New arms 4 DoF (compact size & low weight)- Same legs as for V0- Active harness system

V2 (2015-16)- Balance control- Active hip ab/adduction control- Onboard electronics and batteries

EMY Versions

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-EEG-based Interface

- Only lower body control - Hip : flex/extension + ab/adduction - Knee: flexion/extension - Ankle: dors/plantarflexion

- Mainly devoted to rehabilitation- No clear information about the control

Another BCI project at TU Delft

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Toward soft exoskeletons

- Less than 10kg, no rigid element- Pneumatic muscles- Comfortable, ease the wearer to perform natural movements

Robot suit and Muscle suit, Univ of Tokyo, CEATEC Exosuit Wyss Inst. Harvard Univ.

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Medical Robotics - uniroma1.itvenditt/didattica/mr/16_Exoskeletons.pdfVendittelli: Medical Robotics...

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