Development of Small-Footprint Large-Amplitude Tripod (three lambda) Mode Traveling Wave Generator

Abstract

The vibration characteristics of cylindrical stub vibrators without and with end flanges have been investigated by means of computer simulation and experiment, with the aim of generating a traveling wave of three lamda mode shape (i.e. of three crests and three troughs) along the circumference of both end faces to provide stable, non-rocking drive for ultrasonic micromotors. The FEA results revealed that the said mode shape can be realized with a short aluminum cylinder of 14 mm in OD, 12 mm in ID, and 10 mm in length and that its axial displacement amplitude can be significantly enhanced if end flanges of 0.5 mm in thickness and 18 mm in OD are incorporated. These results were verified experimentally with prototypes driven by twelve (12) PZN-PT single crystal active elements, which were arranged into 2 sets of 6 crystals each such that a travelling wave is generated at the end faces of the cylinder when two a.c. voltage signals of 90 degree phase difference were applied to respective sets of crystals. For the flanged cylinder, the traveling wave displayed relatively large axial displacement amplitude of 5 ?m when driven with ac voltage signals of 26 V at the resonance frequency of 70 kHz.