Experimental verification and modeling of high-efficiency operation in lubricated ultrasonic motors

Ultrasonic motors (USMs) are typically driven under dry contact condition in order to obtain sufficient torque. Friction drive, however, induces friction loss and wear which limit motor efficiency and lifetime. On the other hand, the investigations of lubricating effect on USMs have been performed as a trial for solving the preceding problems. In this paper, we compared the characteristics of the hybrid transducer-type ultrasonic motor (HTUSM) in dry and lubricated conditions through simulations and experiments, and clarify that the motor performance can be drastically enhanced at high static preloads if appropriate lubricant is employed. The maximum transduction efficiency of the HTUSM was significantly enhanced from 28% in dry condition to 68% in lubricated condition. Both simulation and experimental results illustrated the desirable operating conditions for the USMs using lubricant.