Soft Pneumatic Actuator with Bimodal Bending Response Using a Single Pressure Source.

Deformation behavior of soft pneumatic actuators (SPAs) can mechanically be preprogrammed into their architecture during design. To date, the majority of SPAs rely on a unimodal bending design. This paper develops a method of including a bimodal design into the deformed state by means of a bilinear material that replaces the conventional strain limiter. With a simple increase in pneumatic pressure, it is possible to have distinctly different deformation directions in one actuator. While inflating at low pressures, the actuator has a preferential deformation direction. As the pressure continues to increase, this preferential deformation direction changes due to a change in the stiffness of the strain limiter. An example of this behavior is demonstrated by an actuator that initially bends in one direction, but then gradually changes direction in plane as the pressure continues to increase. Three different physical actuators were manufactured, tested, and correlated with preliminary numerical models. The physical and numerical models exhibited the desired bimodal behavior, although at different pressures. Furthermore, it was possible to alter the pressure at which this transition occurs by changing the crimp ratio of the embedded bilinear material.