An Approach to Force-Feedback Control with Traveling Wave Ultrasonic Motor

The traveling wave ultrasonic motor is considered for use in haptic devices where feedback forces are required, particularly in force-feel systems where a certain input— output relation is desired between the applied torque and the response. Owing to some of its unique characteristics, there are circumstances where the ultrasonic motor may be considered an appealing alternative to the more standard DC motor. However, the two types of motors are significantly different in their principles of operation, and are not necessarily interchangeable for all applications. The ultrasonic motor is limited in that the torque cannot be arbitrarily controlled under external loading. Moreover, direct control of the motor torque is difficult due to the complex nature of the contact mechanics. To accommodate these limitations, we investigated a method of model reference force-feedback control, in which the interaction torque is used as the reference source. Experimental results demonstrated that the closed-loop system is able to approximate simple second-order behavior, thus approximating the feel of a spring and damper.