Abstract
Compliant constant force mechanisms (CFMs) output a constant force over a large range of displacement input and offer tremendous energy storage compared to mechanisms/material with linear or hardening responses. In this study, we present a graph-based sequential structural optimization framework to design CFMs with high energy storage capacity. In the framework, the constant force behavior with a zero preload is defined to be ideal, as this behavior offers the maximum energy storage given a force and displacement limit. A graph-based topology selection, followed by shape optimization is conducted to select designs with energy storage most similar to the energy of the ideal constant force relation. During the graph-based topology selection, the possible topologies are exhaustively listed, and then ranked based on their performance in energy storage capacity. The better performing topologies are selected as the initial shape of the following shape optimization. We present two design cases obtained from this framework. The obtained CFM designs through this framework has a higher energy similarity index compared to typical designs from literature (0.95 vs. 0.90) and they are experimentally validated. The constant force mechanisms developed through this study can be further applied in different robot/human-environment interfaces that benefit from both mitigating impact force and increasing energy storage.
