Design of High-Performance Triple-Axis Cross Pivots

Abstract

Cross-axis flexural pivots are increasingly implemented in mechanical systems due to their high precision and wide range of motion. However, designing high-performance pivots in terms of low-axis drift, low rotational stiffness, and low values of maximum stress remains a challenging task. In fact, these features often behave antagonistically to each other. In this paper, the design of a novel family of high-performance cross-axis pivots is presented. The compliant joints are obtained by the composition of two crossing flexible elements with initially curved axis, and of one auxiliary flexure with straight axis. Two different arrangements, that depend on the constraints layout, are proposed. Chained beam constraint model and nonlinear finite element analysis are implemented for the analysis of the kinetostatic response of the pivots. The effects of initial curvature and orientation of the flexures on axis drift, stiffness, and maximum stress, are investigated and reported in the form of design maps. A global performance index, that embodies the above-mentioned features and captures the overall kinetostatic behavior of the pivot, is introduced. The design maps and the global index serve as key tools for the design procedure, giving insight into the antagonistic issue and leading to the determination of the best tradeoff solutions that meet the application requirements. An experimental campaign is conducted to compare the performance improvement of triple-axis pivots with respect to a benchmark double-axis joint, and to validate the design method.