Simulating Balance Recovery Responses to Trips Based on Biomechanical Principles

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Simulating Balance Recovery Responses to Trips
Based on Biomechanical Principles

• Takaaki Shiratori1,2
• Rakié Cham3

Brooke Coley3 Jessica K. Hodgins1,2
3
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2
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Physical Simulation for Human Characters
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Steady-state behaviors.
Reactive responses required.
1 http//lh6.ggpht.com/_UAku2WOHdSE/SlP6lTodsMI/A
AAAAAAADOU/BFQRfrvySDM/
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Reactive Response to Trips
Biomechanical Principles
Motion capture data
Simulation
4
Prior Work

• Synthesize reactive responses.

Simulation-based method
Kudoh et al., 2002
Zordan et al., 2002
Macchietto et al., 2009
Komura et al., 2004
Not applicable to tripping.
Not for human characters.
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Strategies
Push-off reaction
Elevating strategy
Push-off reaction
Strategy selection
Lowering strategy
Eng et al. 1994, Schillings et al. 2000,
Pijnappels et al. 2004, 2005
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Push-off Reaction
Pijnappels et al. 2005

• Ground reaction force vector passes anteriorly to
  the COM.

Reduce forward angular velocity.
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Arm Motions

• Increase moment of inertia to reduce angular
  acceleration.
• Arm ipsilateral to tripped leg
• moves in sideward direction.
• Arm contralateral to tripped leg
• moves in forward direction.
• Protect head/chest.

Roos et al. 2008, Pijnappels et al. 2008
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Capturing Tripping Motion

• Subjects must not know when/where tripping occurs.

Harness
Trip machine
Trip slide
Semi-rigid shoe
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Motion Capture Dataset
Elevating
Lowering
Elev.-DS Elev.-FL Lower.-DS Lower.-FL
subjects 4 3 4 3
Speed m/s (SD) 1.15 (0.146) 1.44 (0.0751) 0.942 (0.191) 1.44 (0.232)
Elev.-DS Elev.-FL Lower.-DS Lower.-FL
subjects 4 3 4 3
Speed m/s (SD) 1.15 (0.146) 1.44 (0.0751) 0.942 (0.191) 1.44 (0.232)
Faster walking speeds tend to lead to Flight
Phase.
(DS double support FL flight phase)
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Human Model
Create a 3D skin model from 400 optical
markers. ? Calculate mass and moment of inertia
from volume.
42 DOFs in total
Park and Hodgins 2006
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Controller Overview

• Finite state machine with Proportional Derivative
  (PD) servo.

Elevating
Leading leg contacts ground.
Yes
Muscle activities start.
No
Clearance
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.
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Controller for Tripping Reactions
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Clearance
Collision
Lowering
Simulation initialization
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Baseline walking
• Playback of motion capture data.
• Simulation
• Initialized with tripping forces just before trip
  occurs.

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Controller for Tripping Reactions
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Clearance
Collision
Lowering
Simulation initialization
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.
Vertical sine function Fore-aft Gaussian
function
Observed tripping forces.
Pijnappels, et al., 2004
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Controller for Tripping Reactions
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Clearance
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Support leg
• Control attitude of upper body.
• Swing leg
• Moving forward like walking.
• Target angles motion capture data of walking.

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Controller for Tripping Reactions
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
Muscle activities start.
No
Clearance
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.
Support knee
0 tripping instant
Ralston et al. 1976
Schillings et al. 2000
Pijnappels et al. 2005
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Controller for Elevating Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
Muscle activities start.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.
Support leg Push-off reaction Extend all
joints. Compensation torque to ankle for COM.
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Controller for Elevating Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
Muscle activities start.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.
Swing leg Clear the obstacle. Target
angles motion capture data.
Motion capture
Simulation
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Controller for Elevating Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Leading leg
• Extended for touchdown.
• Target angles
• motion capture data.
• Trailing leg
• Start flexion.

Motion capture
Simulation
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Controller for Elevating Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Leading leg
• Control attitude of upper body.
• Trailing leg
• Move forward for the next step.

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Controller for Elevating Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.
COM starts falling.

• Leading leg
• Extended for the next step
• Target angles
• motion capture data.
• Trailing leg
• Control attitude of upper body.
• Keep extension.

Motion capture
Simulation
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Controller for Elevating Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Leading leg
• Control attitude of upper body and extend knee.
• Trailing leg
• Control attitude of upper body .
• Plantar-flex ankle for the next step.

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Controller for Elevating Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Leading leg
• Control attitude of upper body.
• Trailing leg
• Move forward for the next step.

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Controller for Lowering Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
Muscle activities start.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Swing leg (tripped)
• Extended for touchdown immediately.

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Controller for Lowering Strategy
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
Tripped leg touches ground.
COM starts falling.

• Swing leg (tripped)
• Extended for touchdown immediately.
• Support leg (non-tripped)
• Leaves ground after swing leg touchdown.
• Clear the obstacle.

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Control of Arm Motion
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Start reaction.
• Timing 100 msec
• Target angles
• motion capture data.

Pijnappels et al. 2008
Motion capture
Simulation
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Control of Arm Motion
Elevating
Yes
Muscle activities start.
Leading leg contacts ground.
No
Collision
Lowering
Leading leg contacts ground.
Tripped leg touches ground.
COM starts falling.

• Back to motion in normal walking.

Motion capture (walking)
Simulation
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Simulation Result

• Elevating strategy with double support.
• Input walking speed 1.0 m/s

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Simulation Result

• Elevating strategy with flight phase.
• Input walking speed 1.4 m/s

Elevating
Lowering
DS
FL
DS
FL
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Simulation Result

• Lowering strategy with double support.
• Input walking speed 0.75 m/s

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Simulation Result

• Lowering strategy with flight phase.
• Input walking speed 1.1 m/s

Elevating
Lowering
DS
FL
DS
FL
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Comparison with Motion Capture Data

• Elevating strategy with flight phase.

Pitch deg
Pitch deg
Time sec
Time sec
-0.5
0
0.5
1.0
Hip
Knee
tripping instant simulation
result motion capture data
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Comparison with Motion Capture Data

• Elevating strategy with flight phase.

Foot trajectory
Pelvis
tripping instant simulation
result motion capture data
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Quantitative Comparison

• Root mean square errors
• Unit deg/frame (frame rate 120 Hz)

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Discussion

• Recovery with multiple steps.

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Discussion

• Better contact model
• Many force plates.
• Larger marker set for feet.
• More precise model of tripping forces.

Push-off reaction
Tripping forces.
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Summary

• Controllers for strategies of balance recovery
  responses to trips.
• Graphics
• Integrate walking controllers.
• Other reactive responses.
• Biomechanics application
• Answer what if questions.
• Improve training and rehabilitation systems.

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3
1 http//www.youtube.com/watch?vLVStmLCoH30
2 http//www.yamakai.org/profiles/marriott.html
3 http//www.treadmilladviser.com/landice-l7-reh
abilitation-treadmill.html
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Acknowledgements

• Adam Bargteil for help with calculating mass and
  moment of inertia.
• Moshe Mahler for rendering animation.
• Justin Macey for the human model.
• Subjects for participation in the experiments.
• NSF -0540865 Quality of Life Technology
  Engineering Research Center
• F31 AG025684-03 NIH Ruth L. Kirschstein Award
• Autodesk for Maya donation.