The contact problem of hard contact materials linear ultrasonic motors

Hard contact materials, such as AL(2)O(3) ceramic, have been used widely to improve motion accuracy of linear ultrasonic motors (LUSM). Nevertheless, experimental results show that, for this kind of LUSM, the contact frequency between the stator and the slider is far less than the frequency of the driving signals, which prevents the vibration energy of the stator from being utilized fully. However, almost all existing theoretical models assume that the stator and slider will come into contact in each driving signal cycle, which lead to the great difference between the theoretical results and the actual situation. In order to solve this problem, theoretical analysis and experimental investigation on the micro-impact processes of hard contact materials linear ultrasonic motors (HLUSM) are conducted in this research. Some parameters, which are closely related to the contact state, have been investigated through modelling the high frequency micro-amplitude contact behaviour on the contact interface in normal direction. It is found that the stiffness of the stator supporting spring, the high frequency vibration amplitude of the driving tip and the low-frequency response amplitude of the stator centre of mass (COM) are important factors affecting the contact frequency. Simulation and experimental results show that increasing the value of the stiffness of the stator supporting spring and decreasing the amplitude of the low-frequency response of stator COM can improve the contact frequency. Moreover, experimental results show that the output power of the linear ultrasonic motor is effectively improved in the ideal contact state. The efficiency is improved by approximately 50 %.