Closed-Loop Control of an XYZ Micro-Stage and Designing of Mechanical Structure for Reduction in Motion Errors

Abstract

This paper presents a compact XYZ micro-stage driven by an impact driving mechanism. A moving body is translationally actuated along the X-, Y-, and Z-axes in millimeter-scale range and with nanometer-scale resolution. Cr–N thin-film strain sensors are integrated into the micro-stage for closed-loop positioning. Closed-loop control is also carried out. The motion errors in six degrees of freedom are also investigated for this micro-stage. It is clarified by analysis of finite element method that rotational motion errors around the driving axis are caused by torques due to tensions from the elastic hinges of micro-stage. The mechanical structure of XYZ micro-stage to cancel out the torque generated is proposed and the second prototype is fabricated. Although the rotational motion error is successfully suppressed in the second prototype, a rotational motion error of more than 0.1° remains due to remaining torque and assembly error of the elastic hinges. Then, in order to reduce the rotational motion error, the prototype is designed in which the location of elastic hinges is single-layered. By designing a mechanical structure in which torque is suppressed, all rotational motion errors are successfully reduced to less than 0.05° in the prototype with single-layer hinges.