A contact model of traveling-wave ultrasonic motors considering preload and load torque effects

The preload and load torque are two important operating parameters of traveling wave ultrasonic motors (TWUSMs), which have strong effects on the contact of stator and rotor. First, the effects of preload and load torque on vibrations of stator were investigated in this paper. A laser Doppler vibrometer was used to measure the vibration velocities of stator. According to the results, the vibration velocity curve of free stator is basically sinusoid. As the preload and load torque applied, the fluctuations in the peaks and troughs of the velocity curve are increased, which indicates that the movement trajectory of the particle on stator surface is changed. The stator amplitude is not the only parameter which represents the drive capability of stator. The drive capability of stator is also related to the movement trajectory of the particle on stator surface. Then, the preload coefficient and load torque coefficient were proposed. Using the two coefficients, the effective amplitude could be obtained. Finally, the contact model considering preload and load torque was established. The performances of the motor were analyzed using the proposed contact model and the calculated results shown good agreements to the measured values.