ISB conference 2005
Emergence of Gait
in Legged Systems
André Seyfarth
ISB conference Cleveland, 2005
Seyfarth: Emergence of gait
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ISB conference 2005
Emergence of Gait
in Legged Systems
André Seyfarth
Locomotion Laboratory
Friedrich-Schiller University, Jena
Seyfarth: Emergence of gait
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ISB conference 2005
Arrival at Cleveland
Jürgen
Seyfarth: Emergence of gait
Suzi
Hartmut
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ISB conference 2005
Models
• Springs
• Joints
• Segments
• Muscles
Robots
• Springs
• Screws
• Metal parts
• Servos
• Rubber
simple, fast, easy to understand
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ISB conference 2005
Central questions
What are the common design and
control principles of legged locomotion?
Internal Leg
Function
Seyfarth: Emergence of gait
Global Leg
Function
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ISB conference 2005
Central questions
What are the common design and
control principles of legged locomotion?
What are the movement primitives of
legged locomotion?
MECHANICS
Seyfarth: Emergence of gait
STABILITY
CONTROL
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ISB conference 2005
Outline
• Jumping for distance
2
• Stable operation of a segmented leg
3
• Generation of muscle activity
4
• Stable running with elastic legs
5
• From running to walking
6
• Exploration of simple legged robots
7
• Conclusions
1
Seyfarth: Emergence of gait
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ISB conference 2005
1
Jumping for distance
Seyfarth: Emergence of gait
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ISB conference 2005
Ground reaction force (N)
Dynamics of the long jump
m1
k
Seyfarth: Emergence of gait
Nonlinear
spring-damper
element
m2
time (ms)
Energetic losses
may increase
performance!
Seyfarth et al. (1999) J. Biomech.
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ISB conference 2005
Dynamics of the long jump
Is this model able to predict
jumping distance?
Is this model able to
predict maximum
jumping distance?
m1
k
Nonlinear
spring-damper
element
m2
Seyfarth et al. (1999) J. Biomech.
Seyfarth: Emergence of gait
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ISB conference 2005
Muscle operation in long jump
eccentric operation
Tendon compliance
(SE) shifts eccentric
muscle operation
(CE) into midstance
Seyfarth et al. (2000) J. Exp. Biol.
Seyfarth: Emergence of gait
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ISB conference 2005
Take home message
(long jump)
• The dynamics of long jump can well be
described by a simple two-mass model
• Energetic losses due to impacts and
eccentric muscle operation can improve
jumping distance
• Tendon compliance shifts eccentric
muscle operation into midstance
Seyfarth: Emergence of gait
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ISB conference 2005
2
Stable operation of a
segmented leg
Seyfarth: Emergence of gait
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ISB conference 2005
Control of a segmented leg
Idea
Global Leg
Function
Local Leg
Function
Seyfarth: Emergence of gait
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ISB conference 2005
Control of a segmented leg
Idea
Seyfarth: Emergence of gait
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ISB conference 2005
Control of a segmented leg
Idea
Seyfarth: Emergence of gait
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ISB conference 2005
Control of a segmented leg
3a
3b
3
2
1
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ISB conference 2005
Control of a segmented leg
Solutions
Seyfarth et al. (2001) Biol. Cybern.
Seyfarth: Emergence of gait
+
• Biarticular Structures (e.g. Muscles)
• Geometric Constraints (e.g. Heel pad)
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ISB conference 2005
Take home message
(internal leg stability)
• With three or more leg segments,
internal stability becomes important
• At certain leg length, symmetric joint
flexion becomes unstable
• Different safety strategies do exist to
resolve the intrinsic stability problem
Seyfarth: Emergence of gait
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ISB conference 2005
3
Generation of
muscle activity
Seyfarth: Emergence of gait
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ISB conference 2005
Generation of muscle activity
Positive Force
Feedback
Geyer et al. (2003) Proc.Roy.Soc.B.
Seyfarth: Emergence of gait
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ISB conference 2005
Generation of muscle activity
Seyfarth: Emergence of gait
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ISB conference 2005
Take home message
(positive force feedback)
• In hopping or running tasks, the
generation of extensor muscle activity
could be facilitated by positive force
feedback
• This control regime imitates spring-like
leg behavior and is robust with respect
to environmental changes
Seyfarth: Emergence of gait
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ISB conference 2005
4
Stable Running with
elastic legs
Seyfarth: Emergence of gait
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Spring Mass Running
PERIODICITY
fixed angle of
attack
SYMMETRY
fixed leg
stiffness
ELASTICITY
Seyfarth et al. (2002) J. Biomechanics
Seyfarth: Emergence of gait
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ISB conference 2005
Spring Mass Running
RETRACTION
Seyfarth et al. (2003) J. Exp. Biol.
Seyfarth: Emergence of gait
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ISB conference 2005
Spring Mass Running
Seyfarth & Geyer (2002) CLAWAR Meeting, Paris.
Seyfarth: Emergence of gait
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ISB conference 2005
Take home message
(spring mass running)
• For a given leg stiffness and angle of
attack, self-stable running can be
found.
• The stability of running is largely
increased, if leg retraction is applied.
Seyfarth: Emergence of gait
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ISB conference 2005
5
From Running
to Walking
Seyfarth: Emergence of gait
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ISB conference 2005
Spring Mass Walking
Geyer et al. (2005) ISB Conference
Seyfarth: Emergence of gait
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ISB conference 2005
Spring Mass Running &Walking
FY
RUNNING
stiffness k
stiffness 0
stiffness k
stiffness 0
YCOM
WALKING
stiffness k
stiffness 2k
stiffness k
stiffness 2k
mass m
mass m/2
mass m
mass m/2
FY SS DS
YCOM
POSTER #197
Seyfarth: Emergence of gait
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ISB conference 2005
Spring Mass Walking
Stable solutions
E
k
Seyfarth: Emergence of gait
0
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Spring Mass Walking
E=const.
Ground Reaction Forces
A
Seyfarth: Emergence of gait
B
C
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ISB conference 2005
Walking and
Running with
Elastic Legs
Running
GAP
Speed vX
Walking
stiffness k
Seyfarth: Emergence of gait
angle of
attack 0
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ISB conference 2005
Take home message
(spring mass walking)
• In bipedal spring-mass model,
self-stable walking can be found.
• The model predicts the experimentally
observed force pattern.
• Running and walking are behaviors of
one and the same system.
Seyfarth: Emergence of gait
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ISB conference 2005
6
Exploration of simple
legged robots
Seyfarth: Emergence of gait
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ISB conference 2005
Our Approach
• Experiments
• Theory
• Simulations
• Robotics
Seyfarth: Emergence of gait
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ISB conference 2005
Experiments
Seyfarth: Emergence of gait
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ISB conference 2005
Robotics
Seyfarth: Emergence of gait
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ISB conference 2005
Hip Control
Seyfarth: Emergence of gait
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ISB conference 2005
Experimental Robotics
CPG
Seyfarth: Emergence of gait
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ISB conference 2005
Comparison with Biology
robot
Seyfarth: Emergence of gait
human
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ISB conference 2005
Human Walking & Running
walking
Seyfarth: Emergence of gait
running
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ISB conference 2005
Take-home message
(hip control)
• Sinusoidal hip oscillations applied to an
elastic leg may result in stable hopping
patterns
• Elastic joints are important to master
impacts and to keep control simple.
Seyfarth: Emergence of gait
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ISB conference 2005
Movement Direction
?
Seyfarth: Emergence of gait
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ISB conference 2005
Hopping direction?
High Speed
200Hz Rummel et al. (2005) ISB Conference
Seyfarth: Emergence of gait
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ISB conference 2005
Frequency
Bias Angle
?
Seyfarth: Emergence of gait
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ISB conference 2005
Hopping direction?
CPG
0
0.3
0
0.
3
0.
1
0
0.1
10
-0.2
0.
3
0
0
3
0.
-10
0.
1
0.3
-0.4
0
0.3
0.1
bias angle [deg]
v
0
0.
1
20
0.2
-0 .2
0.1
0
horizontal velocity [m/s]
-20
-0.6
2
6
4
oscillation frequency [Hz]
Seyfarth: Emergence of gait
8
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ISB conference 2005
Influence of Hip Retraction
v
CPG
FLEG
M = c (0 – )
Seyfarth: Emergence of gait
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ISB conference 2005
Take-home message
(movement direction)
Leg segmentation and motor frequency
defines preferred locomotion direction.
Leg compliance supported
by the hip action
Leg stiffness supported by
the hip action
Seyfarth: Emergence of gait
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ISB conference 2005
Leg Segmentation & Gait
Seyfarth: Emergence of gait
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ISB conference 2005
Leg Segmentation and Gait
Is walking just running with
double support phases?
Seyfarth: Emergence of gait
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ISB conference 2005
Leg Segmentation and Gait
WALK
Seyfarth: Emergence of gait
RUN
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ISB conference 2005
Leg Segmentation and Gait
GAS
Seyfarth: Emergence of gait
GAS
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ISB conference 2005
Leg Segmentation and Gait
(corresponds to GAS length)
Seyfarth: Emergence of gait
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ISB conference 2005
Passive Walking?
Cornell ankle-powered biped walking on a level surface
1
2
1
straight leg during stance
2
curved foot
Collins et al. Science 18 Feb 2005; 307: 1082-1085
Seyfarth: Emergence of gait
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ISB conference 2005
Compliant Walking
Seyfarth: Emergence of gait
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ISB conference 2005
Compliant Walking
HUMAN
ROBOT
Iida (2005) AMAM Conference
Seyfarth: Emergence of gait
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ISB conference 2005
Running & Walking
LEG FUNCTION RUNNING WALKING
KNEE AND ANKLE JOINT
↑↑
↑↓
ELASTIC ENERGY
HIGH
LOW
LEG COMPRESSION
FAST
SLOW
LEG ROTATION
FAST
SLOW
BI-ARTICULAR MUSCLE
SLOW
FAST
KNEE JOINT @ STANCE
↓+↑
↓+↑+↓
Seyfarth: Emergence of gait
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ISB conference 2005
Take-home message
(leg segmentation and gait)
Walking and running can be observed in
passive elastic legs with harmonic
oscillations at the hip.
In the three-segmented leg,
ankle and knee joint symmetry is
switched between running and walking.
Seyfarth: Emergence of gait
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ISB conference 2005
Conclusions
• Simple models and robots
can help to better understand
legged locomotion
• Selfstability is an effective tool
to identify movement patterns
with cheap control
• Walking and running can be
described as two behaviors of
the same mechanical system
Seyfarth: Emergence of gait
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ISB conference 2005
Thank you!
Locomotion Lab Jena
Hartmut Geyer · Heidi Knüsel
Fumiya Iida · Susanne Lipfert
Jürgen Rummel · Jan Michel
Elmar Dittrich
Research Partners
Prof. Reinhard Blickhan · Motion Science, Jena
Prof. Volker Dietz · ParaLab, Zurich
Prof. Hugh Herr · Biomechatronics Lab, MIT
Prof. Karl Th. Kalveram· University Düsseldorf
Supported by German Research
Foundation (DFG grant SE1042)
Seyfarth: Emergence of gait
Jena
www.lauflabor.de