A digital position controller of travelling wave ultrasonic motors

Ultrasonic motor offers great advantages for industrial applications due to its excellent intrinsic properties. However, when load torque is applied, a dead-zone occurs in the control input. Therefore, a digital controller is adopted for ultrasonic motor. The state quantities, such as acceleration, speed and position, are needed to apply the digital controller for position control. Yet, rotary encoder causes quantization errors in the speed information. To overcome these problems, this paper presents a digital position control method for ultrasonic motor. The state variables for digital controller are estimated by a Variable Structure System observer. Furthermore, a small, low cost and fast response digital controller is designed by using a micro computer that is essential in embedded system for the developments of industrial equipments. Effectiveness of the proposed method is experimentally verified.