Koji Kosaka

Highly Reliable Piezoelectric Actuator for Precision Stage System

A highly reliable nonresonant ultrasonic motor (NRUSM) made of cylindrical piezoelectric material is proposed in this paper. The high reliability is characterized by long lifetime and no outer gas in the vacuum environment, which are ensured by not using stack adhesives as the source of the gas emission. Positioning and tracking accuracy was better than below ±2 nm. The structural design is discussed in terms of the application to a high-speed high-precision stage system which has stable response to frequent biases without interference from resonant phenomena and the required mechanical strength.

Ultra-precision stage control based on friction model of non-resonant ultrasonic motor

This paper presents a friction model-based ultra-precision stage control that introduces the non-resonant ultrasonic motor (NRUSM). At first, the friction characteristic is experimentally evaluated as a function of the stage position. Next, the friction model is adopted for the proposed continuous-pass tracking control design, and then the efficiency of the model-based control is verified by positioning experiments. Finally, measuring the time variation of the static friction characteristics, the on-line identification method for the control system is proposed.

Variable Forgetting Factor-Based Friction Compensation Method of Precision Stages

This paper presents the nonresonant ultrasonic motor (SPIDER)-driven precision stage control based on an adaptive identification method with a variable forgetting factor (VFF). SPIDER-driven stage has a strong non-linearity due to the frictional drive mechanism. Focusing on the VFF, dynamical change of frictional property is detected. Therefore, fast and precise friction compensation can be performed based on the VFF. The validity of both the identification and compensation methods is verified through experiments

VARIABLE FREQUENCY CONTROL FOR SPIDER-DRIVEN ULTRA-PRECISION STAGES

Abstract This paper proposes a variable control method of drive frequency for the SPIDER-driven precision stage. Control performances such as positioning accuracy and maximum velocity strongly depend on the drive frequency. At first, the identification experiments of the SPIDER with different drive frequency are carried out. Next the gain-scheduled control strategy for the variable frequency control, considering the variation rate of the frequency is introduced. Finally, simulations and experiments are performed in order to verify the efficiency of the proposed control method.