Transient analysis of bar-type ultrasonic motors

In this paper, analysis of the dynamics of the ultrasonic motors is introduced. Though static characteristics have in the past been clarified, the dynamic characteristics were still unclear. For the purpose of realizing high speed control of ultrasonic motors, we analyzed the dynamic characteristics through measurement and numerical simulation. Among the different types of ultrasonic motors, we focused on bar-type ultrasonic motors and first measured the step response using a laser doppler velocimeter (LDV). We measured changing the input parameters and showed the relationship between input parameters and delay, overshoot of the rotational speed of the rotor. Next, we established a mathematical model of the bar-type ultrasonic motor. In our model, we approximated the stator as a rigid disc and torsional spring. We set the discrete spring at the contact area between rotor and stator, and simulated considering stick-slip at the contact area. The results of numerical simulation matched that of the measurements qualitatively and we clarified the dynamics of the contact condition and friction force at the contact area.