Abstract: At present, bimodal ultrasonic motor (USM) applied to large displacement actuation and nanometer positioning control uses combination control of the actuation’s modes, namely AC actuation mode, pulse actuation mode and the DC actuation mode. This paper proposes a novel single wavelet actuation pattern of bimodal USM, which can realize step control with the stepping distance adjusted. A wavelet actuation wave is composed of 8 sinusoidal voltage waves of 39.6 kHz, whose maximum triggering frequency is up to 5 kHz. In a positioning control application, the grating with 20?m pitch was selected as the displacement measurement sensor. The fast subdivision formula of mutual compensation functions developed by the author was used as the grating nanometer measurement tool. With the control algorithm of measurement and actuation sequence, the maximum stepping distance of bimodal USM was 2?m and the maximum actuation speed of the stage reached 10mm/s. The experimental results indicate that when the wavelet actuation parameters are properly chosen, nanometer actuation resolution and nanometer positioning accuracy can be reached.

Key words: bimodal USM, wavelet actuation, positioning control
, stepping distance, grating measurement, resolution