Design and Performance Study of a Compliant Mechanism Capable of Achieving Dual-Range Constant Force Output

A compliant constant-force mechanism (CCFM), known for its frictionless, contact-free operation and inherently constant output, is typically limited to a single force range, restricting its adaptability to multi-task applications. To address this problem, in this study, we propose a dual-stage compliant constant-force mechanism (DSCCFM) that delivers a continuous dual-range constant-force output within a monolithic structure. The design integrates a Z-shaped beam with a bistable beam and a bistable rhombic beam, thereby forming the DSCCFM. By integrating the pseudo-rigid-body model (PRBM) with the chained-beam constraint model (CBCM), a theoretical model of the DSCCFM is established. Using a finite-element response surface model and multi-objective genetic algorithm (MOGA) optimization, the constant-force stroke was improved by approximately 38% over the initial design. The experiments confirm stable outputs of 6.72 N and 21.91 N across the 2-5.8 mm and 11.6-14.8 mm ranges, respectively. The DSCCFM effectively supports multi-stage force execution, cell gripping, and micro/nano-scale manipulation.