Precise position control of ultrasonic motors using three parameters high speed switching method

Abstract

The rotation speed of the ultrasonic motor depends on three parameters such as frequency, voltage and phase difference. In current mainstream drive circuits using a step-up transformer, ultrasonic motors are controlled frequency (rotation speed) by variable value, and voltage (rotation and stop) and phase difference (forward and reverse) by two values. The primary disadvantage of this drive system is that the control input value does not correctly correspond to the output value at extremely low rotation speeds, which prevents precise position control. In this research, we have achieved precise position control by controlling the frequency and voltage by variable values and the phase difference by two values as the control method. In order to realize this position control method, we developed a drive circuit that uses a direct digital synthesizer and a high voltage operational amplifier to generate a sine wave, in place of the step-up transformers typically used for drive circuits. By using these elements in the circuit, it is possible to control the three parameters (frequency, voltage and phase difference) of the output voltage applied to the ultrasonic motor with high speed response and accurate waveform. Using this control method and drive circuit, we performed precise position control within 2.424×10−6 rad. The features of the developed drive circuit and the control method for changing the three parameters are described.

Keywords

• ultrasonic motor
• precise position control
• piezoelectric element
• actuator
• step-up transformer direct digital synthesizer
• high voltage operational amplifier