高階周向波式蝶型超音波馬達的研發

Abstract

本文提出一以高階周向撓性波驅動的碟型超音波馬達，馬達定子形狀類似於內徑具有圓管突起的環形碟片，鋁合金碟片下方黏貼一佈有雙相電極的PZT-4壓電圓環。應用雙相致動原理，將兩組相位差90o 的相等振幅駐波，合成為沿著定子周向波傳的指向性行進波。馬達定子的(1, 3)模態與鄰近的共振頻率有較寬的模態隔離，被選為驅動超音波馬達的模態。定子與轉子間有三個接觸點，可避免轉子轉動時發生晃動。馬達定子上的行進波最大振幅與轉子的轉速成正比，定子的扭曲剛性需保證提供馬達適當的扭矩。本研究以馬達定子的內徑、內側圓管脊緣高度為設計參數，尋求提供馬達高轉速及扭矩的設計。超音波馬達原型機的內徑設為18 mm，內側圓管脊緣高度分別為4、5、6 mm，實作還包括壓電圓環厚度正負方向的極化。實驗以阻抗分析儀及雷射都卜勒干涉儀量測馬達定子的共振頻率，(1, 3)模態約為37 kHz，設為馬達的操作頻率。馬達定子與轉子間的預壓力愈大，轉子的轉速會愈趨減緩。

This thesis proposes a disc-typed ultrasonic motor (USM) driven by a higher order circumferential ridge waves around its inner stiffened circular ring. The motor stator is made of an aluminum alloy disk supported at its outer edge and a PZT-4 annular disk with segmented dual phase electrodes. A directional traveling wave is formed from constructive interference of two equal-intensity standing waves induced by those transducers using dual sinusoidal excitations in 90 degree phase difference. The circumferential mode (1, 3) is selected to drive the USM since it has the widest modal separation from its adjacent resonant frequencies and provides three contact points to get rid of wobble motion happened to the rotor. The maximum amplitude of circumferential displacement is proportional to the revolution speed. The motor stator is required to have enough torsional rigidity to support output torque. A good design of USM has an optimal compromise between revolution speed and output torque. The inner radius and height of the stiffened circular ring are considered as two design parameters for optimal design. The prototypes having inner radius of 18 mm and the heights of inner rings of 4, 5, 6 mm were developed in this study. The fabrication includes opposite direction poling in thickness of PZT-4 annular disks. The resonant frequency of mode (1, 3) measured by impedance analyzer and laser Doppler vibrometer is around 37 kHz, which is used to be the operating frequency for the USM. The revolution speed decreases with the increase of pre-stress exerted by the rotor against the stator.