A Tristable Actuator for a Bidirectional Crawling and Falling-Rebootable Robot

Tristable actuators can achieve state retention without energy input and switch states when the external energy reaches the jump threshold. Among many designs, a tristable actuator that can switch between two stable states without passing through the third state is highly beneficial for multimode robots. In this work, a design scheme of a novel tristable actuator is proposed under the inspiration of tristate gate circuit. Switching between any two of the three stable states in such a tristable actuator is realized when we orthogonalize two bistable structures that can be driven by artificial muscle materials. A kinetostatic model using the chained beam constraint model is established to characterize the actuator design. Experimental results validate the kinetostatic model and the effectiveness of the actuator. To demonstrate the functionality, a robotic crawler combining two tristable actuators is prototyped, which is capable of functions of bidirectional crawling as well as an in-situ reboot to locomotion after a fall, by utilizing the tristable switching feature.