Post on 11-Jul-2015
Is Motion Capture-Based Biomechanical Simulation
Valid for HCI Studies? Study and Implications
Myroslav Bachynskyi
Antti Oulasvirta
Gregorio Palmas
Tino Weinkauf
Saarbrücken
http://resources.mpi-inf.mpg.de/biomechanics
There are more opportunities in HCI for gestural and full body controls
Larger design spaceMore freedom for interface design
Traditional interfaces
Modern interfaces
Physical ergonomics is very important for the success of an interface
Gorilla arm Trapezius fatigueJoint stress
Traditional ergonomics instruments are too expensive, invasive or cumbersome
Goniometers QuestionnairessEMG (Surface
Electromyography)Needle EMG
SubjectiveUnreliable
CumbersomeNot accurate
Limited
Only surface musclesCross-talk
Unreliable in dynamics
Too invasiveOnly expert useHard to move
Motion-capture based biomechanical simulation allows “looking inside the body”
Optical motion capture (MoCap) Biomechanical simulation
Biomechanical simulation produces wide range of inside-body ergonomics indices
– Moments
– Forces inside joints
1. Model Scaling
2. Inverse Kinematics
3. Inverse Dynamics
4. Static Optimization
Output for observable movement:
Further processing
• Physical work
• Energy expenditure
• Fatigue index
• Per muscle:– Force exerted
– Activation by neural system
• Per joint:– Angles
MoCap data
Subject weight
Performance and ergonomics measured within single experiment synchronously
Single HCI experimentwith MoCap recording Performance of movements:
speed, accuracy, throughput
Ergonomics of movements: Joint angles and momentsMuscle forces and activationsEnergy expenditure
Synchronized in time and registered in 3D movement space
Our goal is to adapt biomechanical simulation for HCI scenarios
Select HCI task Record MoCap Simulate Analyze the data
Another HCI task
Medicine and sports:• Educated experimenters• Model fine-tuned to subject• Goal: highly focused analysis• Focus on lower body, gait and run
HCI:• Non-expert experimenters• No fine-tuning of the model• Multiple user groups• Overview of movement space• Upper extremity and full-body• Specific types of movements
Is it valid for HCI?
Sources of error:• Marker mapping• Marker drift• Suit drift• Marker trust• Model scaling• Mass distribution• Muscle properties• Activation optimality ?
Upper extremity model with muscles must be validated for HCI tasks
HCI Biomechanics
[Honglun2007]
[Du2007]
[Chang2007]
Bio
mec
han
ical
co
vera
ge
Simple ergonomics toolsintegrated with MoCap
Biomechanical simulationwith EMG for muscles
Complete biomechanical simulation
[This paper]
Moment at joint [Lloyd2003]
Muscle activations [Hamner2010]
[Pronost2011]
3 muscles and specific movement [Daly2011]
8 muscles and whole space movements
[This paper]
Bio
mec
han
ical
co
vera
ge
The paper reports 2 experiments
Study 1: Applicability across HCI tasks
Study 2: Validity against EMG data
Small movements Finger and arm
Full body
Run simulations and qualitatively inspect outputs
EMG
Simulation
Correlation as similarity measure?
EMG data
Predictions
Setup
PhaseSpace Impulse
Force plate OpenSim and Full-Body model
Main results
1. The simulation is successful for movements larger than 4cm
Failure Partial success Success
Hand model
2. Problems caused by strong users
Extremely fast movements Inverse Kinematics Static Optimization
3. Dynamic contact forces require external force measurements
Movement Without external forces the model is up in the air fixed onto pelvis
Correct simulation
Incorrect simulation
Part of parachute harness to fix pelvis
4. Large muscles are better predicted
Good
Bad
5. Fast movements are better predicted
Good
Bad
FastMediumSlow
6. Large individual differences due to age, gender and anatomy
Good
Bad
Conclusions
Biomechanical simulation is valid for the following HCI scenarios
• Movements longer than 4cm
• No extreme angles
• No strong participants
• Recording of external forces, if present
• Focus on bigger muscles
• Longer and faster movements
Possible improvements and future work
• Computed Muscle Control should produce better results than Static Optimisation
• Small finger movements may be successful with more comprehensive motion capture
• Simple-to-use index of muscular fatigue needs to be developed based on biomechanical simulation
Despite the restrictions, biomechanical simulation CAN be effectively applied for a wide range of HCI tasks
Select HCI task Record MoCap Run the simulation Analyze the data
Another HCI taskhttp://resources.mpi-inf.mpg.de/biomechanics
Is Motion Capture-Based Biomechanical Simulation Valid for HCI Studies?
Study and Implications
http://resources.mpi-inf.mpg.de/biomechanics
Myroslav Bachynskyi
Antti Oulasvirta
Gregorio Palmas
Tino Weinkauf
Saarbrücken