Download Simulation Based Design

Simulation-based design
to reduce metabolic cost
OpenSim for the Warrior Web, May 2013
Overview: Lecture + Hands On Exercise
1.  Generating and evaluating a muscledriven simulation of walking
2.  Metabolics 101
3.  Designing and evaluating devices to
reduce metabolic cost
4.  Next Steps:
a.  Heavily loaded walking simulations
b.  Finding help and resources
OpenSim for the Warrior Web, May 2013
10 Gait Cycle
Simulation Created
By Chand John
Muscle Activation
0
fully
deactivated
OpenSim for the Warrior Web, May 2013
1
fully
activated
Elements of a Musculoskeletal Simulation
OpenSim for the Warrior Web, May 2013
“Research Grade” Musculoskeletal Model
12 body segments
29 degrees of freedom1,2
92 musculotendon actuators1,2
Arms3 driven by torque motors
1
Delp, 1990
2 Anderson and Pandy, 2001
3 Holzbaur et al., 2005
OpenSim for the Warrior Web, May 2013
Simple Model for the Exercise
Torso + Right & Left Femur, Tibia, Foot
10 degrees of freedom
18 musculotendon actuators
No arms
OpenSim for the Warrior Web, May 2013
Experimental Data
•  Experimental Data Collection
–  Full body motion capture
measures kinematics
–  Force plate treadmill
measures ground reaction
forces
–  Electromyography (EMG)
measures muscle activity
•  Subject Specs
–  Speed: 1.2 m/s
–  Height: 1.8 m
–  Weight: 75 kg
Data collected by Chand John and Jill Higginson at the University of Delaware Neuromuscular Biomechanics Lab
OpenSim for the Warrior Web, May 2013
Generating the Simulation
Scale
IK
RRA
CMC
v
Fresi
v
Fgrf
Scale the
Generic Model1
Inverse
Kinematics
Residual Reduction
Algorithm2
1
Hamner et al., J Biomech, 2010.
et al., IEEE Trans Biomed Eng, 2007.
3 Thelen and Anderson, J Biomech, 2006.
2 Delp
OpenSim for the Warrior Web, May 2013
Computed Muscle
Control3
Computed Muscle Control Algorithm
x
OpenSim for the Warrior Web, May 2013
Residual and Reserve Actuators
Residual
Actuators
Reserve
Actuators
Lumbar
Hip
MZ
FX
Knee
Ankle
OpenSim for the Warrior Web, May 2013
Muscle Driven Simulation of Walking
fully
deactivated
fully
activated
OpenSim for the Warrior Web, May 2013
Part I: Explore the Model
10 minutes
1.  How many degrees of freedom does the model
have? How many muscles? How many bodies?
10 dof, 18 muscles, 12 bodies (feet welded)
2.  Do any muscles cross the lumbar joint?
No … we’ll probably need reserve moments at
the lumbar joint
3.  Which model (generic or subject-specific) do you
think has a lower BMI (body mass index)?
The subject-specific model … it is taller and
weighs less
OpenSim for the Warrior Web, May 2013
Part II: Simulate Unassisted Walking
15 minutes
1.  Which coordinate had the biggest tracking errors?
Max Knee Angle Tracking Error < 1 degree
2.  What is the maximum value of the residual forces
and moments? Why only “OK” forces?
FY Max = 21 N
No arms, “Large” CMC Time Window
Peak Power = 4 Watts (120 Watts for muscles)
3.  Why is the lumbar extension reserve so much
larger than the reserves for the hip, knee, and
ankle?
No muscles cross the lumbar joint
OpenSim for the Warrior Web, May 2013
Part II: Simulate Unassisted Walking
4. 
When do plantarflexor forces peak? What about the
dorsiflexors?
OpenSim for the Warrior Web, May 2013
Overview: Lecture + Hands On Exercise
1.  Generating and evaluating a muscledriven simulation of walking
2.  Metabolics 101
3.  Designing and evaluating devices to
reduce metabolic cost
4.  Next Steps:
a.  Heavily loaded walking simulations
b.  Finding help and resources
OpenSim for the Warrior Web, May 2013
How can we analyze metabolic cost?
Measure oxygen consumption from human
experiments
• 
• 
Physiologically accurate
Limited to available prototypes
• 
• 
Facility and labor intensive
Only gives a bulk measure of cost
Evaluate metabolic cost using
musculoskeletal simulations
• 
• 
• 
• 
Fast and inexpensive
Iterate and optimize design
parameters
Explore general principles
Requires a sophisticated
simulation environment
OpenSim for the Warrior Web, May 2013
Calculating Energy Consumption
E = hA + hM + hSL + w CE [W/kg muscle mass]
hA (u (t ), a(t ), rST , S ) : activation heat rate
· due to transport of calcium ions
hM (u (t ), a(t ), rST , S ) : maintenance heat rate
· due to actomyosin interaction
hSL (u(t ), a(t ), rST , S , vCE (t )) : shortening/lengthening heat rate
· separate calculations for fast- and slow-twitch fibers
w CE : mechanical work rate of the contractile element
1.  Umberger, B.R., Gerritsen, K.G.M., and Martin, P.E. (2003) A Model of human muscle energy expenditure. Computer Methods in
Biomechanics and Biomedical Engineering, 6(2):99–111.
2.  Umberger, B.R. (2010) Stance and swing phase costs in human walking. Journal of the Royal Society Interface, 7(50):1329–1340.
OpenSim for the Warrior Web, May 2013
Calculating Energy Consumption
•  Key variables:
–  Activation
–  Muscle mass
–  Fast/slow
twitch fiber
ratio
–  Aerobic vs.
Anerobic
–  Fiber velocity
OpenSim for the Warrior Web, May 2013
Metabolic Probes in OpenSim
Model
CMC
Probe
Set
States
Probe
Reporter
•  Variable to set when adding new probes
–  Slow/Fast Twitch Ratio
•  Use defaults for everything else
•  Probes work with Forward Tool and Analyze Tool
(value only)
OpenSim for the Warrior Web, May 2013
Probe
Results
Part III. Explore Metabolics of Unassisted
Walking
15 minutes
1.  What is the metabolic energy consumed for one
walking trial?
960 Joules; 9.8 J/kg/s or Watts/kg
2.  For which parts of the gait cycle is the total rate
of metabolic energy consumption highest?
Early Stance/Push Off
3.  Why are there differences between force
production and metabolic cost?
Soleus is acting concentrically (doing positive
work) in late stance, which increases energy
consumption
OpenSim for the Warrior Web, May 2013
Part III. Explore Metabolics of Unassisted
Walking
OpenSim for the Warrior Web, May 2013
Overview: Lecture + Hands On Exercise
1.  Generating and evaluating a muscledriven simulation of walking
2.  Metabolics 101
3.  Designing and evaluating devices to
reduce metabolic cost
4.  Next Steps:
a.  Heavily loaded walking simulations
b.  Finding help and resources
OpenSim for the Warrior Web, May 2013
Example Assistive Device: Ankle Spring
Plantarflexion Torque (Nm)
Spring Torque vs. Gait Cycle
75
0
0
% Gait Cycle
100
k = 10 Nm when dorsiflexion > 5 degrees
OpenSim for the Warrior Web, May 2013
Assistive Device: Path Spring
Path Spring Tension vs. Gait Cycle
Tension (N)
625
175
0
% Gait Cycle
k = 10,000
OpenSim for the Warrior Web, May 2013
100
Part III. Simulate Walking with Assistive
Devices
15 minutes
1. 
Which device reduced metabolic cost and by how much?
2. 
Path Spring; 2.6% Reduction
How do the devices affect the ankle muscles in early to mid
stance (gastroc, soleus, tib ant)?
3. 
How do the devices affect iliopsoas and soleus in late stance
and swing?
4. 
Are there any significant changes in residuals, reserves, or
tracking errors?
OpenSim for the Warrior Web, May 2013
Soleus Metabolic Rate
OpenSim for the Warrior Web, May 2013
Tibialis Anterior Metabolic Rate
OpenSim for the Warrior Web, May 2013
Iliopsoas Metabolic Rate
OpenSim for the Warrior Web, May 2013
Part III. Simulate Walking with Assistive
Devices
15 minutes
1. 
Which device reduced metabolic cost and by how much?
2. 
Path Spring; 2.6% Reduction
How do the devices affect the ankle muscles in early to mid
stance (gastroc, soleus, tib ant)?
3. 
How do the devices affect iliopsoas and soleus in late stance
and swing?
4. 
Are there any significant changes in residuals, reserves, or
tracking errors?
Minimal changes
OpenSim for the Warrior Web, May 2013
Overview: Lecture + Hands On Exercise
1.  Generating and evaluating a muscledriven simulation of walking
2.  Metabolics 101
3.  Designing and evaluating devices to
reduce metabolic cost
4.  Next Steps:
a.  Heavily loaded walking simulations
b.  Modeling active devices and other components
c.  Finding help and resources
OpenSim for the Warrior Web, May 2013
Next Steps: Modeling Your Device
OpenSim Model Structure
Model
Body
Joint
Constraint
Force
Controller
OpenSim for the Warrior Web, May 2013
Modeling Your Device: Forces
Force
Prescribed
function of time
PathSpring
Bushing
Contact
function of state
Actuator
External Force
PathActuator
PointActuator
function of control
TorqueActuator
CoordinateActuator
Muscle
OpenSim for the Warrior Web, May 2013
Why the #!%@ isn’t
OpenSim working?
OpenSim for the Warrior Web, May 2013
OpenSim Resources
• 
Key Online Resources:
• 
GUI Resources:
• 
Scripting Help:
• 
Developer Help:
– 
– 
– 
– 
– 
– 
Support Portal with Search Box
Users Guide
Examples and Tutorials
User Forum
Best Practices Guides
Doxygen
–  Context-Sensitive Help in the Tools
–  Property Editor for Property Descriptions
–  XML Browser
–  Examples
–  Online Documentation
–  methodsview()
–  Developer’s Guide
–  Developer’s Wiki
–  Explore the Source
OpenSim for the Warrior Web, May 2013