6-Axis ultraprecision positioning mechanism design and positioning control

Abstract

Recently, the positioning accuracy level employed for some of precision products has reached the level of sub-micron. Optical devices, precision machine tools, and semiconductor manufacturing machines are the typical examples. For instance, one of the core technologies of step and repeat lithography systems, such as optical reduction projection aligners and electron beam exposure systems, is in their ultra precision wafer positioning. In this thesis, a 6-axis piezo-driven flexure pivoted micro-motion stage is developed as an aligner for step and repeat lithography systems. This study also presents a computer-based method that automatically generates equations of motion for flexure hinge mechanisms and solves them numerically to predict static and dynamic characteristics of the hinge mechanisms. This modeling method is general, easy to use, and helpful to optimize the stage design and to control the position and orientation of the stage with a high precision and high speed. In addition, various types of manufacturing imperfection arising during the machining for the hinge mechanism are presented and also motion errors caused by them are quantitatively predicted using the proposed modeling method. The design and analysis of a 6-axis stage using the proposed computer-based modeling method are presented including an optimal design procedure for a XYθ stage with a large yaw ($θ_z$) motion. It is also presented that the performance of the flexure hinge mechanism is heavily influenced by the selection of design parameters such as hinge thickness, hinge radius, hinge width, lever length ratio, etc. In particular, a mathematical formulation of the optimization problem is described and solved using a sequential quadratic programming(SQP) method. The performance prediction of the designed XYθ stage is verified via experiments. Actual experiments demonstrate that the simulated model can predict a desired motion with a deviation of less than 5% from the experimental results...