A study on temperature dependence of an ultrasonic motor for cryogenic environment

In this study, we have examined the temperature dependence of an ultrasonic motor for a cryogenic environment. When we use an ultrasonic motor at low temperatures, thermal stress is induced at the ultrasonic transducer owing to the difference in temperature. Thus, the preload for the transducer needs to be regulated for a cryogenic environment. By finite element method (FEM) analysis, we have simulated the thermal stress at piezoelectric elements of the transducer. We have designed the transducer consisting of a body and a nut made of SUS304, and a bolt made of titanium. We have fabricated and evaluated the transducer at temperatures from 4.5 to 293 K. To evaluate the temperature dependence of the relationship between the preload and the thermal stress, we have measured the clamping torque and admittance. The optimal clamping torque shows a low-temperature dependence from 4.5 to 293 K. We have also evaluated the performance of an ultrasonic motor of the transducer. The ultrasonic motor can be driven at temperatures from 4.5 to 293K without the regulation of the preload of the transducer.