Strained Elastic Surfaces with Adjustable-Modulus Edges (SESAMEs) for Soft Robotic Actuation

For robots to interact safely with humans and travel with minimal weight, low-density packable actuators are sought. Electronically-driven active materials like shape memory wire and other artificial muscle fibers offer solutions, but these materials need a restoring force. Moreover, if joint bending is required, the actuators must exert a bending moment around the joint. In this paper, we model the three-dimensional shapes of strained elastic surfaces with adjustable-modulus edges (SESAMEs), then implement SESAMEs by machine embroidering shape memory alloy wire onto stretched elastic fabric, showing a path to lightweight actuators that exert bending forces and have built-in restoring forces. SESAMEs start out planar, and upon release from the plane take on three-dimensional shapes thanks to the balance between bending energy in the boundary and strain energy in the elastic surface. The elastic creates both a restoring force to bring the boundary back to its original shape after actuation, and an out-of-plane structure for applying a bending moment. We demonstrate SESAMEs' properties as soft robotic actuators individually and in arrays, and coupled to flexible plastic frames during the planar fabrication process as bending actuators to switch bistable mechanical structures.