X-shaped frame double-bistable mechanism: Coupling between Two bistable modules sharing an X-shaped frame

Recent research has demonstrated the potential of multistable mechanisms for logic operations, shape morphing, and robot reconfiguration. This work proposes a novel fully compliant multistable mechanism called X-frame double-bistable mechanism (XD multistable mechanism), which consists of two bistable modules sharing a common X-shaped frame. The X-shaped frame has a limited stiffness, which leads to strong coupling between the two bistable modules. By tuning four main parameters of the mechanism, a variety of state switching behaviors are exhibited by six examples. The two motion paths of the mechanism were demonstrated through a kinetostatic model, and the path transition phenomenon was explained from an energy perspective. A bistable module demonstrates distinct mechanical properties when the state of another module undergoes changes. An anomalous transition phenomenon resulted from the coupling is also uncovered. The state switching behaviors and the anomalous transition phenomenon are further validated by experiments. The rich mechanical behaviors presented can effectively guide further design and application based on such multistable mechanisms.