Active control of self-locking torque of traveling-wave ultrasonic motors using standing-wave operation

Abstract

This article presents a new approach to perform self-locking torque control of travelingwave ultrasonic motors. It is to engage the motor under standing-wave operation. At that mode, the motor constantly alternates between a "lock" state and a "float" state at high frequency. The self-locking torque is thus reduced. The basic operating principle of the motor is discussed. Theoretical derivation demonstrates that the voltage amplitude can be used as the control variable to manipulate the self-locking torque. Simulation is performed using an equivalent circuit analysis. Experiments have shown consistent results with simulation, and confirm the effectiveness of the method.