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 mu Nm is obtained. Stable startup characteristic and accurate stepping control are also achieved. The minimum stepping angle of the micromotor is 10 degrees, 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.