Efficient Computation of Large Deformation of Spatial Flexure-Based Mechanisms in Design Optimizations

Abstract

Design optimizations of flexure-based mechanisms take a lot of computation time, in particular when large deformations are involved. In an optimization procedure statically deformed configurations of many designs have to be obtained, while finding the statically deformed configuration itself requires tens to hundreds of load step iterations. The kinematically started deformation method (KSD-method) [1] computes deformed configurations fast by starting the computation from an approximation. This approximation is obtained by allowing the mechanism only to move in the motion-direction, based on kinematic equations, using data of the flexure joints in the mechanism. This is possible as flexure based mechanisms are typically designed to be kinematically determined in the motion directions. In this paper the KSD-method is extended such that it can also be applied without joint-data, such that it is not necessary to maintain a database with joint-data. This paper also shows that the method can be used for mechanisms containing joints that allow full spatial motion. Several variants of the KSD method are presented and evaluated for accuracy and required computation time. One variant, which uses joint-data, is 21 times faster and shows errors in stress and stiffness below 1%, compared to a conventional multibody analysis on the same model. Another variant, which does not use joint-data, reduces the computation time by a factor of 14, keeping errors below 1%. The KSD-method is shown to be helpful in design optimizations of complex flexure mechanisms for large range of motion.