Development of stage mechanism with high damping capacity for high-precision positioning

The stage, using new mechanism called viscous-elastic unit, is proposed to improve accuracy and acting time of positioning, and the effects are examined experimentally. In this mechanism, a stage is supported by flexure hinges, and damping force is given by squeeze film of silicon oil instead of conventional sliding friction. When the stage moves for a long distance, a supporting part of the viscous-elastic unit slides along a guide, and maximum damping force is limited by sliding friction. In this paper, the viscous-elastic units have been added to a conventional one-axis stage mechanism driven by a ball screw. Positioning has been carried out with a closed-loop control system using a laser measurement system. The experimental results indicate that the viscous-elastic unit can reduce the peak more than 20 dB on Bode diagram, and this system is capable of positioning the stage with an error less than 10 nm in 350 ms acting time, when the mass of stage is 18 kg and moving distance is 20 mm.