A longitudinal-torsional composite ultrasonic vibrator with thread grooves

The idea of employing slant grooves to achieve the conversion between the longitudinal vibration and the torsional vibration has been proposed for many years, however, comparative studies on the effectiveness of different forms of diagonal grooves are seldom reported. In this paper, a sandwich longitudinal-torsional (L&T) composite ultrasonic vibrator driven by a longitudinally polarized PZT stack is presented. Four diagonal grooves were equally distributed around the front mass of the vibrator for mode conversion purpose. The grooves can be machined either along thread curves or along straight lines. The influences of the thread grooves on the characteristics of the vibrator were compared with that of the straight grooves both numerically and experimentally. Modal, harmonic and transient analysis were conducted using a finite element model established in a commercial FEM software. Then, prototypes of a transducer and a pair of front mass with thread and straight grooves were manufactured for experimental purpose. The measurement results coincide with the FE simulation prediction. It indicates that although both types of grooves are able to convert the longitudinal vibration into L&T composite vibration, the thread grooves can achieve much larger torsional amplitudes. The present work provides useful information for engineers to make trade-offs between the two sorts of grooves at designing stage.