Functional biomimesis*

1
Functional biomimesis
Compliant Sagittal Rotary Joint
Active Thrusting Force
Cham et al. 2000
2
Example mapping from passive mechanical
properties of insects to biomimetic robot
structures
Study biological materials, components, and their
roles in locomotion.
Study Shape Deposition Manufacturing (SDM)
materials and components.
Models of material behavior and design rules for
creating SDM structures with desired properties
3
Example mapping from passive mechanical
properties of insects to biomimetic robot
structures
Study biological materials, components, and their
roles in locomotion.
Study Shape Deposition Manufacturing (SDM)
materials and components.
6
Data
Model
4
2
0
Force (mN)
-2
-4
-6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
position (mm)
Models of material behavior and design rules for
creating SDM structures with desired properties
4
Self-tuning is needed to adapt to changes
Velocity versus slope for different stride
frequencies
24 deg.
60
Sprawlita running on sloped track
Frequency 11 Hz
40
Velocity (cm/s)
20
Frequency 5 Hz
0
-10
0
10
20
slope
5
Biological approach

• Passive mechanical system and predominantly
  feed-forward control allow animal to run over
  rough terrain.
• Preflexes, augmented by reflexes and
  adaptation, account for changes in system and
  environmental conditions.
• The approach overcomes limitations of slow neural
  pathways, imperfect sensing, etc.

Task
Adaptation
FF model
model
Feed-Forward control
Learning
Reflex control
Command
signal
Mechanical
system
preflex
Environment
Sensory feedback
6
Adaptation in small biomimetic robots

• Use preflexes and open-loop motor control for
  robust, stable locomotion.
• Use simple, inexpensive sensors to detect changes
  in operating conditions.
• Use adaptation to tune the parameters of the
  open-loop system.

Feed-forward activation patternand timing
Command input
tripods
time
Mechanical system (actuators, limbs)
preflexes
Environment
Locomotion
Passivestabilization
7
Thrust timing for max. height
y
Contact Time
Ground Reaction Force
Height
Thrust
Time
y
tf
ttd
tc
tl
8
Effect of period for long thrust hopping
-3
x 10
2.5
Hop Height
Natural period tn 0.21 sec Thrust magnitude
F/mg 1.50 Damping z 0.20
2
1.5
1
0.5
0.15
0.2
0.25
0.3
0.35
0.4
Multiple Solutions
1
0.8
Eigenvalues
0.6
0.4
0.2
normal
0.15
0.2
0.25
0.3
0.35
0.4
unstable period-1
0
Velocity atactuation
-0.5
hop-settle-fire
-1
0.15
0.2
0.25
0.3
0.35
0.4
Period (ms)
9
Conclusions from 1 DOF model

• Maximum hop height occurs if thrust is initiated
  near maximum compression
• Stability requires thrust initiation before max.
  compression.
• For long thrust (vs natural period) thrust should
  begin before max. compression and end
  essentially at liftoff.
• Therefore, measuring the interval between thrust
  deactivation and liftoff is a good indicator of
  whether the stride period is tuned correctly.

10
Adaptation algorithm
Dtn1 Ki - Kp(Td - Tl Tv)
Td Deactivation Time
Tl Loss of Contact
Drift Trying to reduce activation frequency
Tv Const. offset between deactivation and
lift-off times
ON
piston activation
foot contact
OFF
0
20
40
60
80
100
120
140
160
180
200
time (ms)
Gait Period
11
Slope adaptation demonstration
12
Hopping with variable stiffness
(1)
(2)
fn sqrt(k/m)/(2pi)
(3)
Discussion Blue curve shows typical results
when maximum stroke length is constrained.Maximum
period-1 hop height (1) is followed by range of
non-period-1 hops (2) and then bylow amplitude,
stable period-1 behavior (3). At frequencies
below (1) hopping reverts to hop-settle-fire. J
. Karpick 08MAR06