A Shear-Mode Ultrasonic Motor Using Potassium Sodium Niobate-Based Ceramics with High Mechanical Quality Factor

概要

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(K,Na)NbO3–LiNbO3–CuO lead-free piezoelectric ceramics that show a high mechanical quality factor $Q_{\text{m}}$ were synthesized and used as a drive element of an ultrasonic motor. The $Q_{\text{m}}$ of the (K,Na)NbO3 ceramic could be enhanced by chemical modification using Li and Cu as well as microstructure control to obtain ceramics with fine grains. The grain size dependence of the $Q_{\text{m}}$ was consistent with a model based on the formation of internal bias field to stabilize the domain structure. A shear mode was used to drive the ultrasonic motor because the piezoelectric $d_{31}$ and $d_{33}$ constants of the ceramics were not sufficient for the motor applications. A shear-mode motor driven with four piezoelectric ceramic plates was developed using the lead-free ceramics with a high $Q_{\text{m}}$ of 1400, a high $d_{15}$ of 207 pC/N, and a high $k_{15}$ of 0.72. The highest revolution speed of 486 rpm was achieved at 34.5 kHz with the input voltage of approximately 180 Vp–p (peak to peak).
2008-09-25