Statically balanced compliant two-port bistable mechanism

A unique click-clack tin-lid mechanism is analyzed here. This mechanism has the feature to be switched between its two stable states by applying forces along different lines of action at two different points, called ports here. The 3D click-clack tin-lid mechanism is modified to design a planar fully-compliant two-port bistable mechanism. By using the theory presented in this paper, a bistable mechanism can be designed to have a mechanical advantage. An analytical kinetoelastic model is used to explain the energy behavior of the mechanism and gain insights into applying it in practice. To account for varying loads experienced by the mechanism during switching, bistability is combined with static balancing. Such a mechanism is amenable to the design of an easy-chair to ease the suffering of arthritic and elderly users. Thus, a sit-to-stand easy-chair is designed where a small force applied on the armrest can gently propel and ease rising from it. Static balancing is implemented to partially compensate for the weight of the patient and to reduce the jerky motion arising from bistability. Furthermore, tuning parameters in static balancing enable adjustment for weights of different users of the chair.