Design of Four-Bar-Mechanism Stability Using Over-Constraint

This paper presents a new concept and method to design mechanisms’ stability using over-constraint. The designs involve the use of parametric Computer-Aided Design (CAD) software to synthesize a mechanism’s geometry in order to achieve a design’s specific bistability requirements. This method ensures a stable position without the need of a hard-stop. There are two main initial design considerations that need to be met in this analysis. First, both (first and second) state of the mechanism should be chosen and should represent the mechanism’s desired stable positions. The first state is the position that the mechanism was manufactured or assembled at, whereas the second state is the position at which the mechanism is toggled to. The second consideration is the assumption that the magnitude of the joints’ torsional spring stiffness is small i.e. living hinges. The main idea is to attach a Potential Energy Element (PEE), such as a spring or a compliant link, to the four-bar mechanism such that it is unstretched in both stable positions and has to deform (stretch or compress) during the motion between stable states. This approach seems to allow the designer considerable freedom in amount of motion between stable states and in the amount of force required to toggle between stable states.