Abstract
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 23.9 kHz 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 0.3 μm, the rotational speed was 4 rpm. 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 0.8 μm for a rotor revolution was reduced to within ±0.1 μm.
