半径方向運動誤差補正可能な非接触超音波モータの開発  [in Japanese] Development of Non-contact Ultrasonic Motor with Motion Error Compensation in Radial Direction  [in Japanese]

超音波帯域で励振される円筒状ステータの面内振動たわみ進行波によってロータを非接触支持すると同時に, 気体の粘性によってロータを非接触で回転させることのできる非接触超音波モータを構築し, 基礎特性を測定した. また, ロータの半径方向運動誤差を測定し, リアルタイムで圧電素子への印加電圧を補正することで, 半径方向運動誤差を低減させ, 回転軸系の高精度化を行った.

Real-time motion error correction of a rotor driven by a non-contact ultrasonic motor (non-contact USM) was achieved. The rotor is installed in the cylindrical stator with a small gap designed to have a resonance frequency of 23.9kHz at the 8th flexural mode of vibration. The multi-layered piezoelectric actuators excite the flexural wave traveling in the circumference direction. The ultrasonic vibration produces a sound field to levitate the rotor and the traveling wave induces near-boundary streaming to rotate the rotor by viscous force. Herein, we report the experimental performance of the non-contact USM. When the amplitude of the flexural vibration was 0.3μm, the rotational speed was 4rpm. The rotational speed and starting torque were proportional to the vibration amplitude. The staring performance of rotational speed was consistent (time constant=2 sec) for various vibration amplitudes, hence the rotational torque is independent of the rotational speed and the resistance forced on the rotor is governed by viscosity. In addition, the non-contact USM allows contact-free micro positioning of the rotor by control of the deformations of the piezoelectric actuators. A PI controller was constructed to compensate the detected motion error of rotor in the radial direction. As a consequence, the motion error of 0.8μm for a rotor revolution was reduced to within ±0.1μm.