On topology design of compliant constant output/input force mechanisms with contact interactions

Abstract

We seek monolithic topologies for constant output (CoFM) and input (CiFM) force mechanisms using topology optimization. We capture large displacements, buckling, contact interaction between members and external surfaces, and importantly, interaction of the mechanism with flexible workpieces to accurately simulate force transfer. Features of constant force characteristics, e.g., magnitude(s) of the desired force(s), range of input displacement over which slope of the force–displacement curve is near zero, and distance between workpiece and the mechanism are controlled individually. Two constant output and constant input force mechanisms each, are synthesized using stochastic optimization ensuring ready manufacturability. We observe that (a) accurate modeling of the mechanism-workpiece interaction is important. (b) Fixed external surfaces may not necessarily contribute to contact force characteristics though interesting alternative solutions are possible in their presence. (c) It behooves to model self contact between members than to reject viable solutions wherein members intersect in intermediate configurations. We finally fabricate the synthesized mechanisms and find that the desired constant force characteristics are by-and-large retained qualitatively, even when the mechanisms may undergo plastic deformation.