Integrated Servo-Mechanical Design of a Fine Stage for a Coarse/Fine Dual-Stage Positioning System

Abstract

Traditionally, the coarse and fine mechanical stages within a dual-stage positioning system are designed separately without consideration about their control performance in dual-stage integration. In this paper, a flexure-based Lorentz motor fine stage is designed concurrently with a simple PID controller to perform the dual-stage positioning, based on the existing coarse stage. The design of fine stage is carried out using a proposed integrated servo-mechanical design approach, where various specifications are considered and formulated as constraints in an optimization problem. Through the approach, both the plant modal parameters and controller parameters of fine stage are concurrently solved. It demonstrates that through suitable mechanical plant design, the fine stage can fulfill various control specifications by only using a simple PID controller, e.g., to compensate sensitivity peak, maintain stability, etc. Meanwhile, the proposed design approach also ensures certain open-loop positioning performance and the decoupling property of coarse/fine stages. The prototype of designed fine stage is fabricated, and experimental investigation indicates that the sensitivity peak is effectively reduced from 14.5 dB of coarse stage to 7.1 dB in the dual-stage system, and the fine stage is able to achieve submicrometer accuracy. The maximal tracking error is also reduced significantly from about 20 μm via the coarse stage to less than 2 μm through dual-stage positioning.