Can we explain reduced gravity trends without springs? S. Javad Hasaneini, Chris J.B. Macnab, John E.A. Bertram, and Henry Leung {s.j.hasaneini, cmacnab, jbertram, leungh}@ucalgary.ca, University of Calgary, Canada O BSERVATIONS • Metabolic power in running decreases with gravity faster than in walking. • Previous explanation (Farley and McMahon [1]) based on elasticity in running vs. poten- tial/kinetic energy exchanges in walking 0 1 2 3 4 0 25 50 75 100 Cost of Transport (metabolic) (J/Kg/m) Gravity (% g) Walk V=1 m/s Run V=3 m/s B IPED M ODEL W ITHOUT S PRINGS • Realistic mass distribution • Periodic gaits: walking, and running • Extended double support is allowed in walking • Dynamic optimization finds the gaits • Cost function: mechanical COT = positive work step length×body mass • Step length and step frequency are free • Optimizations simulate reduced gravity in two ways: • ’hip-lift’ (constant upward force, like experi- ment) • ’reduced-g’ (reduced g on all body parts) Actuated Hips Feet stay flat Actuated Compound Ankle Linear Actuators M ODEL P REDICTIONS (E NERGETIC C OST ) • Model predictions consistent with observations • Cost cross-overs even without springs • The energetics is determined by the balance be- tween the stance and swing leg works for mini- mum net cost. • ’Hip-lift’ and reduced-g optimizations give almost identical results. • Springs decrease the cost of running, improving the estimates of cross-over gravity levels. 0.00 0.05 0.10 0.15 0.20 0.25 0 25 50 75 100 Gravity (% g) Cost of Transport (mechanical) (J/Kg/m) Walk V=1.1 m/s Walk V=1.6 m/s Run V=3.3 m/s R EFERENCES [1] C.T. Farley, and T.A. McMahon, “Energetics of walking and running: insights from simulated reduced-gravity experiments,” J. Appl. Physiol., 73(6): 2709-2712, 1992. [2] A.D. Kuo, “A simple model of bipedal walking predicts the preferred speed-step length relationship,” J. Biomech. Eng., 123(3): 264-269, 2001. K INEMATICS Experiment 0.5 0.9 1.3 1.7 0 25 50 75 100 Run V=2.2 m/s Walk V=1.1 m/s Gravity (% g) Step Length (1/ Leg Length) Model Prediction 0.0 0.5 1.0 1.5 2.0 2.5 0 25 50 75 100 Run V=3.3 m/s Walk V=1.1 m/s Gravity (% g) Step Length (1/ Leg Length) • For walking and running: decreased g results in increased step length. • Step length predictions for ’hip-lift’ are slightly shorter than for reduced-g. • Optimizations under-estimate step length. • An extra cost term for fast leg swing (e.g. force/time) improves step length estimates [2]. R EDUCED G RAVITY S IMULATOR ( CONSTANT UPWARD FORCE ) The reduced gravity apparatus based on zero-rest-length springs: Harness’ Height Adjusting Winch Treadmill Rolling Trolley Lever Spring Loading/Unloading and Zero-Rest-Length Spring Adjusting Winch Force (Gravity) Adjusting Grids Cable Force Transducer Level Line Cable Cable Designed by Andy Ruina F INAL C OMMENTS • Experimental results support model predictions • The optimization here predicts energetic and kine- maytic trends without using springs: running more affected by gravity than walking • Main determinant in optimization: trade offs be- tween leg swing and stance costs. • Some optimization details: • Some trends are explicable with collision an- gles. • Optimization in running shows constant cost per step as gravity is reduced = ⇒ COT ∝ g. O PEN Q UESTIONS • How would springs change these results? • Besides energy efficiency, what is the role of passive compliance in biological locomotion? A CKNOWLEDGMENT Thanks to Prof. Andy Ruina for his technical sup- port and suggestions.
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
-
Can we explain reduced gravity trends without springs?
S. Javad Hasaneini, Chris J.B. Macnab, John E.A. Bertram, and Henry Leung{s.j.hasaneini, cmacnab, jbertram, leungh}@ucalgary.ca, University of Calgary, Canada
OBSERVATIONS
• Metabolic power in running decreases withgravity faster than in walking.
• Previous explanation (Farley and McMahon[1]) based on elasticity in running vs. poten-tial/kinetic energy exchanges in walking
0
1
2
3
4
0 25 50 75 100
Cos
t of
Tra
nspo
rt
(meta
bol
ic)
(J/K
g/m
)
Gravity (% g)
Walk
V=1 m/s
Run
V=3 m/s
BIPED MODEL WITHOUT SPRINGS• Realistic mass distribution• Periodic gaits: walking, and running• Extended double support is allowed in walking• Dynamic optimization finds the gaits
• Cost function: mechanical COT = positive workstep length×body mass
• Step length and step frequency are free• Optimizations simulate reduced gravity in two
ways:
• ’hip-lift’ (constant upward force, like experi-ment)
• ’reduced-g’ (reduced g on all body parts)
Actuated
Hips
Feet stay flat
Actuated
Compound
Ankle
Linear Actuators
MODEL PREDICTIONS (ENERGETIC COST)• Model predictions consistent with observations
• Cost cross-overs even without springs
• The energetics is determined by the balance be-tween the stance and swing leg works for mini-mum net cost.
• ’Hip-lift’ and reduced-g optimizations give almostidentical results.
• Springs decrease the cost of running, improvingthe estimates of cross-over gravity levels.
0.00
0.05
0.10
0.15
0.20
0.25
0 25 50 75 100
Gravity (% g)
Cos
t of
Tra
nspo
rt
(mech
anic
al)
(J/K
g/m
)
Walk
V=1.1 m/s
Walk
V=1.6 m/s
Run
V=3.3 m/s
REFERENCES
[1] C.T. Farley, and T.A. McMahon, “Energetics of walking and running: insights from simulated reduced-gravity experiments,” J.Appl. Physiol., 73(6): 2709-2712, 1992.
[2] A.D. Kuo, “A simple model of bipedal walking predicts the preferred speed-step length relationship,” J. Biomech. Eng., 123(3):264-269, 2001.
KINEMATICSExperiment
0.5
0.9
1.3
1.7
0 25 50 75 100
Run
V=2.2 m/s
Walk
V=1.1 m/s
Gravity (% g)
Ste
p Leng
th (
1/ L
eg
Leng
th)
Model Prediction
0.0
0.5
1.0
1.5
2.0
2.5
0 25 50 75 100
Run
V=3.3 m/s
Walk
V=1.1 m/s
Gravity (% g)
Ste
p Leng
th (
1/ L
eg
Leng
th)
• For walking and running: decreased g results inincreased step length.
• Step length predictions for ’hip-lift’ are slightlyshorter than for reduced-g.
• Optimizations under-estimate step length.
• An extra cost term for fast leg swing (e.g.force/time) improves step length estimates [2].
REDUCED GRAVITY SIMULATOR (CONSTANT UPWARD FORCE)The reduced gravity apparatus based on zero-rest-length springs:
Harness’ Height
Adjusting Winch
Treadmill
Rolling
Trolley
Lever
Spring
Loading/Unloading and
Zero-Rest-Length Spring
Adjusting Winch
Force (Gravity)
Adjusting Grids
Cable
Force Transducer Level Line
Cable
Cable
Designed by Andy Ruina
FINAL COMMENTS• Experimental results support model predictions
• The optimization here predicts energetic and kine-maytic trends without using springs: runningmore affected by gravity than walking
• Main determinant in optimization: trade offs be-tween leg swing and stance costs.
• Some optimization details:
• Some trends are explicable with collision an-gles.
• Optimization in running shows constant costper step as gravity is reduced =⇒ COT ∝ g.
OPEN QUESTIONS• How would springs change these results?
• Besides energy efficiency, what is the role ofpassive compliance in biological locomotion?
ACKNOWLEDGMENTThanks to Prof. Andy Ruina for his technical sup-port and suggestions.
Related Documents
