Functional biomimesis *

Stryker Interaction Design Workshop

September 7-8, 20051January 2006

Functional biomimesis*

CompliantSagittalRotary Joint

ActiveThrusting

Force

*[Cham et al. 2000]



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 creatingSDM structures with desired properties

Example: mapping from passive mechanical properties of insects to biomimetic robot structures

ServoMotor

Roachleg

Displacement InputForce Output

stiff material

viscoelasticmaterial



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 creatingSDM structures with desired properties

Hysteresis loop@10Hz

Example: mapping from passive mechanical properties of insects to biomimetic robot structures

-0.5-0.4-0.3-0.2-0.10 0.10.20.30.40.5-6

-4

-2

0

2

4

6

position (mm)

Forc

e (m

N)

Data

Model



0

20

40

60

-10 0 10 20

Velo

city

(cm

/s)

Frequency = 5 Hz

Frequency = 11 HzSprawlita running on sloped track

uphilldownhill slope

Self-tuning is needed to adapt to changes

Velocity versus slope for different stride frequencies

24 deg.



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.

Mechanicalsystem

FF model

Task

Environment

Adaptationmodel

Reflex control

Sensory feedback

Learning

Commandsignal

Feed-Forward control

preflex



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.

Mechanicalsystem

(actuators, limbs)

Environment

Feed-forward activation pattern

and timing

Command input

Locomotion

preflexesContactSensor

Adaptationmodel

Passivestabilization

timetripods

•No encoders, gyros, tachometers...•No tedious calibration•No fancy filtering•No sophisticated closed-loop control.



maximize:

Thrust timing for max. height

Time

tfttd tc tl

Thrust

HeightGround ReactionForce

T

Ton

y

y

Contact Time



Hop Height

Natural period: n = 0.21 sec

Thrust magnitude: F/mg = 1.50

Damping: = 0.20

0.15 0.2 0.25 0.3 0.35 0.4

0.5

1

1.5

2

2.5

x 10-3

0.15 0.2 0.25 0.3 0.35 0.4

0.2

0.4

0.6

0.8

1

0.15 0.2 0.25 0.3 0.35 0.4-1

-0.5

0

Period (ms)

Multiple Solutions

Velocity atactuation

Eigenvalues

Effect of period for “long thrust” hopping

1

2

3

“normal”

unstable period-1

hop-settle-fire1

2 3



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.



0 20 40 60 80 100 120 140 160 180 200

time (ms)

n+1 = Ki - Kp(Td - Tl + Tv)

“Drift”Trying to reduce

activation frequency

TdDeactivation

Time

Tv Const. offset between deactivation and lift-off times

TlLoss ofContact

piston activationfoot contact

Gait Period

ON

OFF

Adaptation algorithm

100 140 180 220 260 3000

50

Lag

Period (ms)

(Td - Tl)



Slope adaptation demonstration

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.



Hopping with variable stiffness

(1)(2)

(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

fn = sqrt(k/m)/(2*pi)

Functional biomimesis *

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