Shape Change Through Programmable Stiffness

We present a composite material with embedded sensing and actuation that can perform permanent shape changes by temporarily varying its stiffness and applying an external moment. Varying stiffness is a complementary approach to actuator-chain based approaches that can be accomplished using a large variety of means ranging from heat, electric field or vacuum. A polycaprolactone (PCL) bar provides stiffness at room temperature. Heating elements and thermistors are distributed along the bar so that local regions can be tuned to a specific temperature/stiffness. Applying an external moment using two tendon actuators then lets the material snap into a desired shape. We describe the composite structure, the principles behind shape change using variable stiffness control, and forward and inverse kinematics of the system. We present experimental results using a 5-element bar that can assume different global conformations using two simple actuators.