Stryker Interaction Design Workshop September 7-8, January 2006 Functional biomimesis * Compliant Sagittal Rotary Joint Active Thrusting Force *[Cham et al. 2000]

Stryker Interaction Design Workshop September 7-8, January 2006 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 Example: mapping from passive mechanical properties of insects to biomimetic robot structures stiff material viscoelastic material

Stryker Interaction Design Workshop September 7-8, January 2006 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 Hysteresis Example: mapping from passive mechanical properties of insects to biomimetic robot structures position (mm) Force (mN) Data Model

Stryker Interaction Design Workshop September 7-8, January Velocity (cm/s) Frequency = 5 Hz Frequency = 11 Hz Sprawlita running on sloped track uphilldownhill slope Self-tuning is needed to adapt to changes Velocity versus slope for different stride frequencies 24 deg.

Stryker Interaction Design Workshop September 7-8, January 2006 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. Mechanical system FF model Task Environment Adaptation model Reflex control Sensory feedback Learning Command signal Feed-Forward control preflex

Stryker Interaction Design Workshop September 7-8, January 2006 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. Mechanical system (actuators, limbs) Environment Feed-forward activation pattern and timing Command input Locomotion preflexes Contact Senso r Adaptation model Passive stabilization time tripods No encoders, gyros, tachometers... No tedious calibration No fancy filtering No sophisticated closed-loop control.

Stryker Interaction Design Workshop September 7-8, January 2006 maximize: Thrust timing for max. height Time tftf t td tctc tltl Thrust Height Ground Reaction Force T T on y y Contact Time

Stryker Interaction Design Workshop September 7-8, January 2006 Hop Height Natural period:  n = 0.21 sec Thrust magnitude: F/mg = 1.50 Damping:  = x Period (ms) Multiple Solutions Velocity at actuation Eigenvalues Effect of period for “long thrust” hopping “normal” unstable period-1 hop-settle-fire 1 2 3

Stryker Interaction Design Workshop September 7-8, January 2006 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.

Stryker Interaction Design Workshop September 7-8, January time (ms)   n+1 = Ki - Kp(Td - T l + Tv) “Drift” Trying to reduce activation frequency Td Deactivation Time T v Const. offset between deactivation and lift-off times T l Loss of Contact piston activation foot contact Gait Period ON OFF Adaptation algorithm Lag Period (ms) (T d - T l )

Stryker Interaction Design Workshop September 7-8, January 2006 Slope adaptation demonstration

Stryker Interaction Design Workshop September 7-8, January 2006 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 by low 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)