Reconfigurable Soft Actuators That Can Hold a Load

Ideally soft machines could instantly take on any arbitrary shape, and then hold that shape with zero power consumption and with a high blocking force. Soft materials however often imply low load-bearing abilities, and multi-DOF shape reconfiguration is generally achieved using many actuators, complicating design and control.<br/>I present three solutions developed in my lab towards reconfigurable actuators, combining soft actuators and phase change polymers. In the first two device, the shape holding, but also the direction of the shape change, is dynamically set using a film of shape memory polymer (SMP) covered with addressable heaters, that enable local reversible change of stiffness. By layering this SMP film with a single large dielectric elastomer actuator, we can obtain complex shapes and much higher blocking force than what the DEA can deliver. By combining the addressable SMP film with liquid metal coils in an elastomer substrate, we created a multi-segment finger where each joint can be independently bent or twisted using electromagnetic forces, and then latched into place, requiring no power to hold any given position.<br/>The SMP devices offer high holding forces, but require up to tens of seconds to cool. The third type of soft actuator is based on electroadhesion, allowing for millisecond scale response, shear forces of over 100 kPa, and simple adaptation to complex shapes. I will contrast the performance limitations of the above-mentioned soft actuators, and illustrate use cases in grippers and manipulation.