Design and Fabrication of a Bistable Unit Actuator with Multi-Material Additive Manufacturing

Bistable systems have two stable equilibrium states around which they can be perturbed. Bistability in a mechanical system requires large deformation, which is commonly accommodated by means of springs or soft joints. In this paper, the authors leverage the ability of advanced Additive Manufacturing (AM) technology that enables printing of materials of varying stiffness values to design and fabricate monolithic bistable unit actuators that maximize the stroke length. A Von Mises Truss (VMT) based bistable structure utilizing snap-through buckling behavior is designed and fabricated. By varying the material stiffness and length of the joints, the authors are able to adjust the activation forces while keeping the geometry constant. 56 specimens are fabricated and tested in tension and compression. Numerical simulation models are constructed and the results are found to correlate well with experimental data. The required activation force can be increased with a decrease in joint length or an increase in joint material stiffness.