An Adjustable Magnetic Preloading and Stepping Controlled Piezoelectric Traveling-Wave Ultrasonic Micromotor

A piezoelectric traveling-wave ultrasonic micromotor at the millimeter scale with adjustable magnetic preloading and precise stepping control is proposed. This micromotor consists of a well-designed annular stator of 4 mm in diameter and an innovative rotor preloading mechanism using magnetic attraction, which is first achieved in such a small system. With adjustable magnetic preloading and 10-V AC actuating voltage, the maximum speed reaches 9900 rpm and a maximum torque of 37.0 μNm is obtained. Stable startup characteristic and accurate stepping control are also achieved. The minimum stepping angle of the micromotor is 10°, and the deviation is less than 7%. An approximately linear relationship between the stepping angles and preloading forces is proved as well. Therefore, the adjustable magnetic preloading provides a completely new access for the increased torque generation and precise motion control for the micromotor.