Compliant Constant Output/ Input Force Mechanisms- Topology Optimization with Contact

TL;DR

This paper develops topology optimization methods for designing monolithic force mechanisms with constant output or input force characteristics, considering complex interactions and validating the designs through fabrication and testing.

Contribution

It introduces a comprehensive synthesis approach capturing all deformation aspects and interactions, enabling the design of manufacturable constant force mechanisms with customizable features.

Findings

Synthesized mechanisms retain constant force characteristics after fabrication.

External surfaces are not always necessary for constant force behavior.

Force characteristics can vary with workpiece shape and material changes.

Abstract

We synthesize monolithic topologies of constant output (CoFM) and input (CiFM) force mechanisms. During synthesis, we capture all possible aspects of member deformation including finite displacements, buckling, interaction between members, their interaction with external surfaces, and importantly, interaction of the mechanism with flexible workpieces to capture force transfer in true sense. 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 via novel objectives proposed herein. Two of the constant output and constant input force mechanisms each, are synthesized using stochastic optimization ensuring ready manufacturability. We observe that presence of external surfaces may not be required for singlepiece mechanisms to attain constant force characteristics. However, interesting solutions are possible if mutual contact is permitted. We also note that desired force characteristics may not remain the same with alteration in the workpieces shape and (or) material properties. We finally fabricate and test the synthesized mechanisms and find that the desired constant force characteristics are by and large retained.