Conceptual design and parameter optimization of a variable stiffness mechanism for producing constant output forces

Abstract

A variable stiffness mechanism is of great significance for simplifying the control scheme of a robot for a polishing process, which requires that the mechanism complies with the displacement variation along its axial axis while keeping the output force constant. To meet this demand, this paper addresses the design and optimization of a variable stiffness mechanism for producing constant output forces. The conceptual design of the variable stiffness mechanism is introduced, which is based on the principle of varying the effective length of a leaf spring. Then, the stiffness model of the mechanism is derived based on Euler-Bernoulli beam theory, in which the small sliding displacement of the leaf spring that affects the effective length is specifically addressed. For parameter optimization, a nonlinear multiobjective optimization problem is formulated to achieve a larger range of stiffness variation and higher transmission efficiency. Utilizing the optimized design parameters, a finite element analysis model and a prototype of the variable stiffness mechanism are developed. The effectiveness of the proposed stiffness model and the validity of the designed variable stiffness mechanism are demonstrated by numerical simulations and experimental studies.