一種以周向傳遞之脊緣波致動的超音波馬達

Abstract

本研究研發一種以周向脊緣波驅動的超音波馬達，碟型定子的外側圓周上設一脊緣，強化定子的扭轉剛性。以雙相交流電激發定子底部的壓電圓環，產生兩組振幅相同、相位差90度的撓曲駐波。兩者經建設性干涉成行進波，沿著定子外側脊緣作周向傳遞，藉摩擦力驅動轉子。依兩組駐波的相位領先或落後，改變馬達的轉動方向。 碟型定子的外側脊緣設有30度斜角齒梳，放大行進波的振幅。以定子的外徑、厚度及脊緣高度為設計參數，採用有限元素法進行數值模擬，依據模態隔離的程度，選擇撓曲模態F(1,3)作為定子的激振模態。另以定子表面粒子的橢圓運動軌跡比值為目標函數，決定定子的最佳幾何尺寸。本研究實驗量測超音波馬達原型機的性能曲線。表面鍍一層鐵氟龍耐磨材料之不鏽鋼轉子的最大轉速達101.6 rpm，最大扭矩為8.16 mN-m，具有高扭矩、低轉速、輸出穩定及靜音的特性。

This thesis presents the development of an ultrasonic motor (USM) driven by circumferential ridge waves traveling along a disc-shaped stator. A stiffening ridge is provided around the outer periphery of the stator to reinforce its torsional rigidity. The piezoelectric annular disc adhered under the stator is excited by two sets of alternating voltages to generate two equal-intensity standing waves with 90 degree phase difference. Both standing wave modes interfere constructively with each other to induce a traveling wave whose direction can be switched by phase lag or lead between these modes. A number of projectors with 30 degree inclined surfaces deposit on the outer ridge to enlarge the amplitudes of traveling flexural waves. Design parameters of the stator including its outer diameter, thickness and height of the ridge are selected. Numerical analysis on dynamic response of the USM was carried out by use of finite element method. Based on modal separation results of the stator, the flexural mode F(1, 3) was considered to drive the USM. The optimal design has another objective seeking to maximize the aspect ratio of elliptical trajectory for the motion of a particle on the contact interface. The performance of a USM prototype was measured experimentally. The USM with stainless steel rotor coated by a wear resistant material, Teflon, achieves the maximum revolution speed and torque up to 101.6 rpm and 8.16 Mn-m, respectively. The presented USM has merits of high torque at low speed, stable output and quiet performance.