Efficiency improvement of hybrid transducer-type ultrasonic motor using lubricant

Ultrasonic motors have hit a bottleneck caused by low efficiency and short life, which limits their applications to some niche areas. We believe that lubrication is a promising candidate to solve these problems. In this paper, we clarify, both analytically and experimentally, that the performance of the hybrid transducer-type ultrasonic motor (HTUSM), including the transduction efficiency, can be drastically improved at large static preloads if appropriate lubricant is applied. First, simulation was performed using an equivalent circuit in dry and lubricated conditions, and the HTUSM characteristics were shown to be more desirable at high static preloads in the lubricated condition than in the dry condition. Then, we experimentally investigated the mechanical performance of the HTUSM, verifying the effect of improving the motor performance at high preloads using lubricant, which was in good agreement with the simulation results. The maximum transduction efficiency of the HTUSM was significantly enhanced from 28% in the dry condition to 68% in the lubricated condition.