Electroactive Soft Bistable Actuator With Adjustable Energy Barrier and Stiffness

A soft bistable actuator can generate high-speed motion between two prescribed stable positions, which is very useful for boosting the actuation of soft robots. Generally, the stroke of such an actuator is completely determined once the design is finalized, which prohibits its applications in robots that perform multiple tasks. In the current work, a bistable actuator with adjustable characteristics is proposed by exploring its strain energy landscape, in which the energy barrier is manipulatable via electroactive twisted and coiled polymer fibers. As such, the actuator can operate in either bistable or postbistable mode, both of which exhibit adjustable stiffness. A kinetostatic model that combines the chained beam constraint model and the mechanics of electroactive materials is established to characterize the actuator design. Experimental results validate the kinetostatic model and the behaviors of the actuator. As a robotic demonstration, a gripper that is formed by two actuators is prototyped, and it exhibits an adjustable load capacity (up to 6.5 times its weight under a 3 V voltage).