Control Performance of Compact Manipulator Driven with Traveling-Wave-Type Ultrasonic Motor.

Abstract

Ultrasonic motors have been developed on the basis of a new concept. One of these ultrasonic motors is a traveling-wave-type ultrasonic motor(USM). USM does not have any solenoid coils, but has a stator that is an elastic-object-bonded piezoelectric element, and a rotor pressed on the stator. Traveling ultrasonic waves are generated in the stator, the vibration energy of which is transferred to the rotor through the frictional force. USM has some advantages such as compact size, light weight, and high torque in the low speed range. Then USM may be applicable to construct a direrct-drive manipulator with compact size and light weight. In this study, a compact-size robot manipulator is manufactured and controlled. USM is generally driven by the analog driving method. The fatal fault of the analog driving method is the discontinuity between control input and rotational speed, which makes it impossible to control the motor stably in the low speed range. Then, if the manipulator is controlled for the step desired input, it vibrates at the final desired position. To solve this problem, the PWM driving method is employed to drive USM. It enables stable control in the low speed range. Also the amplitude of vibration at the desired position can be decreased. Positioning and trajectory control with the PWM driving method are made on the robot manipulator. The results of this paper can assure the suitability of ultrasonic motors for constructing compact-size robot manipulators.