Design of a flexure-based constant-force XY precision positioning stage

This paper presents the design of a new flexure-based XY precision positioning stage with constant force output. Its uniqueness lies in the reduction of driving force for achieving a large stroke output and the realization of a constant force output without using a force controller. By combining the bistable beams and positive-stiffness leaf flexures, a zero-stiffness mechanism is devised. An analytical model of the stage is established and verified by conducting finite-element analysis. The structure parameters are designed for the requirements of range, stiffness, and payload capabilities. A prototype stage is fabricated for experimental studies. Results show that the developed stage delivers a constant force of 29 N and a constant-force motion range of 700 mu m along with less than 1% motion coupling in each working axis. The stage possesses a good motion repeatability, which indicates a hysteresis width lower than 1.5% of the maximum force. Multiple motion tests reveal that the stage has less than +/- 1 N float of the constant force. Moreover, sensitivity analysis results indicate that the machining errors of the in-plane width and inclined angle of the bistable beams are the main reasons which cause the discrepancy between simulation and experimental results.