A Primal Treatise of Constant-Force, Compliant Segments and Mechanisms

Abstract

The evolution of constant-force mechanisms is propelled by a growing interest in being able to exert constant or near-constant force in various applications. Compliant mechanisms have recently received much attention in the design of constant-force mechanisms because of their several advantages, e.g. fewer parts, compact construct, natural energy storage, no backlash, among many others. There have been many research efforts in developing various techniques to design these mechanisms for applications in diverse fields. Several of these techniques require design optimization to generate a constant force over a desired range of motion. There is generally a lack of understanding of the mechanics of the generation of constant force. This paper presents the hypothesis that simple arrangements, such as a rigid link with a torsional spring, or compliant segments, under axial loading are capable of producing constant force. Three compliant segment types are considered herein: fixed-free, pinned-pinned, and fixed-guided beams under axial loading, to demonstrate that they can exert near-constant force, without the need for a design optimization. This paper further exemplifies that the proposed theory is the kernel to generating constant force by different mechanism configurations.