雙模態耦合的三角形超音波馬達

Abstract

本研究提出一種嶄新設計之雙模態耦合驅動的超音波馬達，主要特徵是在三角形定子的側邊或角端處作水平開槽，減弱定子的縱向剛性，使定子的縱向與扭轉共振頻率重合。定子的各邊黏貼方形壓電陶瓷材料，電極部份分割為A、B相 兩塊區域，施加兩組相位差90度的交流電壓於電極，可激發定子的縱向與扭轉共振模態，使得定子接觸點突起作橢圓形軌跡運動，定子與轉子間的摩擦力驅使轉子旋轉。切換相位的領先與落後，可控制轉子的旋轉方向。本研究以有限元素分析探討三角形定子的高度、厚度、水平開槽長度及位置等幾何尺寸對定子特定模態自然頻率的影響，達成優異的模態隔離，並探討定子與轉子的接觸力學行為，估算超音波馬達轉速與扭矩的性能曲線。本研究製作及測試三個馬達原型機，定子的材質為鋁合金，轉子為不鏽鋼。其中最佳設計的操作頻率為19.59kHz，原型機三的最大轉速為142rpm，最大扭矩3.17N-cm。若將原鋁合金定子的突起改為鋼球，接觸區域由線接觸變為點接觸，馬達的最大扭矩提升至4.239N-cm，有效提升馬達的輸出性能。本研究設計、製作的馬達具低轉速、高扭矩、穩定輸出及靜音的特性。

This thesis presents a novel design of dual mode coupled ultrasonic motor, which is driven by the fundamental longitudinal mode and torsional mode of the stator. The triangular tube-like stator is machined with horizontal slot in each side or at each corner to form a flexible structure with appropriate weakness in its axial stiffness. It results that the longitudinal mode has reduced resonant frequency very close to that of the desired torsional mode. The PZT4 element with two segmented electrodes is adhered to each peripheral surface of the stator. Two ac signals with 90 degree phase difference are applied to the electrodes to excite both vibration modes. Every contact point undergoes an elliptical trajectory in response to a harmonic excitation of the coupled modes, which are used to drive the ultrasonic motor via frictional force between both rotor and stator. The revolution direction of the rotor can be controlled by switching phase lag or lead. Excellent modal separation was achieved by modifying the geometric parameters, such as height, thickness of the triangular stator and length, location of the slots, according to the calculated natural frequencies of the stator by using finite-element analysis. The contact mechanics between both rotor and stator are explored and is used to estimate the T-N curves of the present ultrasonic motor. Three prototypes of the presented ultrasonic motor were fabricated and tested. The stator and rotor are made of aluminum alloy and steel, respectively. In the best design, the operating frequency is 19.59 kHz. The maximum revolution speed is 142 rpm without payload, and the maximum measured torque is 3.17 N-cm. To reduce the wear, an embedded steel ball is used to replace the line contact bump on the stator and to form a point-like contact. It follows that the output torque promotes to 4.239 N-cm. The presented ultrasonic motor has advantages of high torque at low speed, stable output and quiet performance.