A Pseudo-Rigid-Body Model Approach for the Design of Compliant Mechanism Springs for Prescribed Force-Deflections

Compliant mechanism springs offer a variety of benefits for applications where nonlinear force responses are desired. Designing a compliant mechanism spring with a prescribed force response is a unique challenge with many design variables. This paper introduces a method, based on the Pseudo-Rigid-Body Model (PRBM) for large beam deflections, to synthesize three- and four-link compliant mechanisms that exhibit prescribed force-deflection responses. The designer prescribes the target force-deflection curve, the number of links the spring is to have, and bounds for the spring’s link lengths and torsional spring constants. The method uses a genetic algorithm routine to search for promising designs and a direct search method to further refine the configuration to achieve the desired force-deflection curve. Experimental results illustrate the methods ability to generate springs whose force-deflection curves approximate the target curves. The results also suggest that inclusion of more complex configurations may lead to more accurate designs. It is shown how the method can be used to design springs that closely mimic the behavior of zero-free-length springs, and a discussion of how the method can be extended to design springs that behave similarly to pre-tensioned springs is presented.