Control method of a spherical ultrasonic motor

In this paper, we propose a control method for controlling an arbitrary orientation of a rotor of a spherical ultrasonic motor (SUSM) by using a magnetized rotor and Hall devices. The arbitrary orientation of the magnetized rotor is determined by detecting the output voltage of the magnetic pole axis measured by Hall devices embedded in the center of each stator. The sensing method offers a size reduction for the entire structure as well as giving the rotor room to move in a wider range, since there is no restriction from geometry constraints of sensor devices, such as rotary encoders or potentiometers. We describe a method for detecting the arbitrary orientation of the magnetized rotor and the magnetization method of the rotor. The experimental results show that the magnetic field generated around the rotor is equally distributed, and confirm the validity of the proposed control method.