Effect of Damping Factor Variation on Eigenfrequency Drift for Ultrasonic Motors

Experimental studies reveal that the eigenfrequency of stator is increasing along with the growing preload. However, the inherent mechanism is obscure and the equivalent physical model is not investigated especially. By description variation of preload equivalently, the oscillatory differential equation at constrained boundary is established with the introduced parameters of damping factor and stiffness coefficient. With the characteristic parameters of piezoelectric vibrator measured by an impedance analyzer, mechanical quality factors are acquired and values of loss factor and stiffness coefficient are calculated. As the vibration mode of stator is high order, the finite element model is optimized to decrease the computational error. With loss factor and stiffness coefficient as the input parameters, the computed eigenfrequencies based on the equivalent physical model is sensitive to the variation of boundary conditions, which promotes the computational accuracy relating to the adjustable preload.