Design of the Bistable Compliant Four-bar Linkage with Changing the Position of the Flexible Limb

Bistable mechanisms have two distinct stable positions that can move from one of these situations to other by a small stimulus. These stable positions, as well as the movement between them, have increased the use of these mechanisms in devices such as valves, switches, and etc. This bistable behavior is the result of the storage and release of the potential energy. Therefore, it is obvious that these mechanisms must have one or more flexible links or joints. In this paper, flexible members are modeled, using torsional springs based on the pseudo-rigid-body-model (PRBM). The existence of one flexible member is sufficient for bi-stability of the four-bar linkage. However, with changing the location of this flexible member as the input, the output, or the coupler link (or changing the location of equivalent torsional spring), various conditions are generated for the design of a four-bar linkage, which is discussed in this study. The results show that in all cases (the crank-crank, the crank-rocker, the rocker-crank, and the rocker-rocker), the equivalent torsion spring should not be connected to a smaller link in order to create a bistable four-bar linkage.