Motor/guide contact evaluation of rectangular plate linear ultrasonic motors using power spectrum

Motor/guide contact evaluation is one of the most important processes to achieve high performances of linear ultrasonic motors. In this paper, a displacement power spectrum is proposed and investigated to evaluate the motor/guide contact of rectangular plate linear ultrasonic motors. First, the effect of the guide surface asperity on the motion of the linear ultrasonic motor is modeled as an elastic contact process, and then its effect on the motor displacement is illustrated with its power spectrum. Using a data acquisition board, LabVIEW software, a control circuit, and a laser displacement sensor, an experiment ring is set up. Assuming that the guide surface is smooth enough over short distances and there are asperities on the guide surface over long distances, the motor is controlled in long and short displacements in a to-and-fro repetitive motion, respectively. The power spectrum of the long distance displacement contains full of harmonics, while the power spectrum of the short distance displacement is mainly made of odd-numbered harmonics. Theory and experiment results prove that the pattern variation of the displacement power spectrum of motor can be used to evaluate the motor/guide contact.