相較於電磁式馬達，球形壓電馬達在設計上具有結構簡單、體積小等特點，實現多自由度驅動有其先天優勢，對於日益蓬勃發展的機器人科技來說是一大助力。然而目前球形壓電馬達的實際應用尚不普遍，其中一個主要原因為轉子旋轉軸向的控制方法並未有統一形式，大多與不同的系統設計而有所不同，既有的文獻中也較少針對軸向控制方法進行探討。為此本研究以力矩基本定義作為靈感並以全向輪(Mecanum wheel)的設計概念作為發想，提出由四個獨立壓電致動元件所組成的全新球形壓電馬達系統設計。在此系統中每一個壓電致動元件皆透過電極配置的方式切換兩種振動模態，可單獨驅動使轉子繞其對應軸旋轉作為基本軸向；接著利用力矩向量合成法便可產生多個不同的旋轉軸向。本文先闡述軸向控制的方法及原理，以單致動元件的驅動特性為基礎，再透過向量疊加的方式推導雙致動元件驅動下的多種合成軸向範圍，進而分析所設計球形壓電馬達系統如何達成全軸向旋轉之目標。實驗結果顯示旋轉軸向與理論推導完全一致，成功驗證所提之力矩向量合成軸向控制法可使輸出轉子以多個軸向進行旋轉。除此之外，本文亦利用向量合成的方式分析致動元件於不同驅動電壓下轉子輸出的轉速關係，藉此計算致動元件的驅動電壓參數並進行開迴路軸向控制實驗探討。

Comparing to the electromagnetic motors, the spherical piezoelectric motors have the advantages of simpler structure, more compact size, and easier implementation of multiple DOF motion in recent robot technologies. However, the use of spherical piezoelectric motors is still rarely seen in practical industrial applications and commercial products. The primary difficulty lies in the fact that the orientation manipulation of rotors is highly dependent on the design of various kinds of spherical motors and a unified version of orientation control method has not been reported yet. In light of this, the current study proposes a novel spherical piezoelectric motor system design using the idea of Mecanum wheel and torque vector synthesis. The proposed system is composed of four independent piezo actuating elements, in which two vibration modes can be implemented and switched to generate different rotor orientations in each actuating element through the technique of electrode configuration. These basic rotor orientations are then expanded to a great number of new orientations with the different combinations of piezo actuating elements and the technique of torque vector synthesis. The study first introduces the principle of orientation generation with a single piezo actuating element and then derives all the possible rotor orientations through the proper integration of torque vector synthesis and two piezo actuating elements. Based on the derived results, the goal of omnidirectional orientation can be achieved using our proposed system design. Experiments show that the orientation results are greatly consistent with the theoretical ones, demonstrating the effectiveness of the proposed omnidirectional orientation generation method. Furthermore, a preliminary study on open loop orientation control using the idea of vector synthesis is also conducted for future reference.

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