The MIT Leg Lab: From Robots to Rehab.

The MIT Leg Lab: From Robots to Rehab

State Of The ArtState Of The ArtFlex-FootOtto Bock C-Leg

State of the Art: State of the Art: Prosthetist defines knee dampingProsthetist defines knee damping

Otto Bock C-Leg

The MIT Knee: A Step The MIT Knee: A Step Towards AutonomyTowards Autonomy

Virtual Prosthetist

Virtual Biomechanist

How The MIT Knee Works:How The MIT Knee Works:MechanismMechanism

How The MIT Knee Works:How The MIT Knee Works:SensorsSensors

Knee PositionAxial ForceBending Moment

Measured Local to Knee Axis (no ankle or foot

sensors)

Amputee can use vertical shock system

Goal: Early Stance Flexion & Goal: Early Stance Flexion & ExtensionExtension

How the MIT Knee Works: How the MIT Knee Works: Stance ControlStance Control

Stance Control: Three StatesStance Control: Three States

Stance Flexion & Stance Extension– A variable hydraulic damper– Damping scales with axial load

Late Stance– Minimize damping

Toe-Loading to trigger late-stance zero damping is automatically adjusted by system

Stance Flexion

Goal: Control Peak Flexion Angle & Goal: Control Peak Flexion Angle & Terminal ImpactTerminal Impact

How the MIT Knee Works: How the MIT Knee Works: Swing ControlSwing Control

0

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1 6 11 16

Number of steps taken

Max

imum

sw

ing-

flex

ion

angl

e (d

egre

es)

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Swin

g-fl

exio

n da

mpi

ng

valu

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rbit

rary

uni

ts)

Swing Control: FlexionSwing Control: Flexion

Swing Control: FlexionSwing Control: Flexion

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0.0 0.5 1.0 1.5 2.0 2.5

Speed (m/sec)

Ang

le (d

egre

es)

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0.0 0.5 1.0 1.5 2.0 2.5Speed (m/sec)

Ang

le (d

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Swing Phase: ExtensionSwing Phase: Extension

Extension damping adaptation Stage one:

– Map tc versus impact force

– Apply appropriate damping Stage two:

– Control final angle while minimizing impact force 0

0.5

1

1.5

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0 0.5 1 1.5 2 2.5Velocity (m/s)

Time

(s)

Foot Contact Time

The MIT Knee In Action

Human Knees Human Knees Brake Brake andand Thrust Thrust

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1

-1

Pow

er (

W/K

g)

Percent Gait Cycle

Human Ankles are Smart Springs

Variable stiffnessfoot-anklesystems

Leg stiffness control in walking and

running humans

Human Ankles are PoweredHuman Ankles are Powered

Future of O&P Leg Systems: Future of O&P Leg Systems: Intelligent Application of PowerIntelligent Application of Power

• Greater Distance & Less Fatigue

• Natural Gait - Dynamic Cosmesis

• Enhanced Stability

• Increased Mobility

Human Rehab: A Road Map Human Rehab: A Road Map to the Futureto the Future

Better Power Systems and Actuators

Series-Elastic ActuatorsSeries-Elastic Actuators(Muscle-Tendon)(Muscle-Tendon)

Controlling Force, not Position

Weight: 2.5 lbs.Stroke: 3 in.Max. Force: 300 lbs.Force Bandwidth: 30 Hz

• Nearly autonomous

• Controllable

• Swam 0.5 body length per second

Biomechatronics GroupBiomechatronics GroupHybrid RobotsHybrid Robots

Human Rehab: A Road Map Human Rehab: A Road Map to the Futureto the Future

Improved Walking Models

Low Stiffness Control: Virtual Model Low Stiffness Control: Virtual Model Control LanguageControl Language

• Passive walkers work using physical components

• Q: Can active walker algorithms be expressed using physical metaphors?

• A: Yes, and they perform surprisingly well

Virtual Assistive Devices for Legged Virtual Assistive Devices for Legged RobotsRobots

Troody

Science Technology What are the biological

models for human walking?

Virtual Model Control

Active O&P Leg Systems

Human Rehab: A Road Map Human Rehab: A Road Map to the Futureto the Future

Distributed Sensing and Intelligence

Virtual Prosthetist

Virtual Biomechanist

User Intent

CollaboratorsCollaborators

Leg LaboratoryGill Pratt

Biomechatronics GroupRobert Dennis (UM)Nadia Rosenthal (MGH)Richard Marsh (NE)

Spaulding Gait LaboratoryCasey KerriganPat Riley

Sponsors

•Össur

•DARPA

•Schaeffer Foundation

SummarySummary

Advances in the science of legged locomotion, bioactuation, and sensing are necessary to step towards the next generation of O&P leg systems