Modal truncation to vibration analysis of stator in ultrasonic motor

The active controls of structures are always realized by controlling a few major modes. The assumed modal method can be used to establish a low-order motion equation to reduce modes, but it is difficult to find a suitable assumed mode for the entire system. Moreover,although the solution precision of the finite element method is higher, the greater number of freedom degrees can affect the subsequent computation efficiency. Based on the finite element analysis on the vibration mode of the stator in an ultrasonic motor,this paper presents a modal truncation method to reduce the dimension of the finite element model and to reserve the special modes. By taking a stator in the travelling rotory ultrasonic motor TRUM as an example,the ANSYS Parametric Design Language(APDL) is used to recognize the working mode automatically, to extract the electrical parameters of equivalent circuit model and to calculate the mechanical and electrical responses simulatively. The dynamic properties of the structure are simulated and tested with a laser Doppler vibrometer. Comparing with experiment results of the working mode frequency, the relative error is 9.1% to the assumed modal method, and 0.3% to the finite element method. For the stable response, the relative error between the observation and the calculation of the modal truncation method is 3%. It is shown that the acquisition method of modal parameters is effective and the modal parameters reflect the actual motion state of the free stator more precisely than that of the assumed modal method.