摘 要
　　迴路與分支缺陷為機構在尺度合成過程中，最常發生的缺陷問題。機構於尺度合成後，若機構在各指定通過位置之組合構形位於不同的迴路上，則此合成結果具有迴路缺陷。若機構在各指定通過位置之組合構形，雖然位於同一迴路上，但是卻位於不同的分支上，則此合成結果具有分支缺陷。
　　本文之目的在於探討平面六連桿機構之迴路與分支特性，進而提出適合平面六連桿機構之迴路與分支辨識準則。平面六連桿機構依輸入桿與固定桿之選定，可由Watt與Stephenson運動鏈衍生九型機構。利用四連桿組之耦桿點曲線、雙連桿、運動倒置、等效連桿組、傳動角連續性、包絡線理論與死點構形之幾何特徵等機構學基本原理，本文提出可行的方法進行各型機構之迴路與分支特性的分析與辨識。針對五種Stephenson型機構的死點構形位置分析及迴路與分支辨識，均可藉由SIIIB4型機構之位置分析閉合解與四種死點構形幾何特徵分析而得；針對四種Watt型機構的死點構形位置分析及迴路與分支辨識，均可藉由WIB4型機構之位置分析閉合解與四種死點構形幾何特徵分析而得。文中亦探討各類型機構，對應於單一耦桿點曲線所存在之最多迴路數目、分支數目與死點構形數目，以及對應於單一迴路所存在之最多分支數目。
　　本文所提出之迴路與分支辨識方法，將可用於各型平面六連桿機構尺度合成時，避免迴路與分支缺陷的形成。

Abstract
　　Branch and Circuit defects are the major problems encountered in the process of dimensional synthesis of mechanisms. A synthesized mechanism is said to have circuit defect if the assembly configurations of all specified positions do not fall on the same circuit. If the assembly configurations of all specified positions fall on the same circuit, nevertheless, fall on the different branches, the synthesized mechanism is said to have branch defect.
　　The main purposes of this work are to study the characteristics of circuits and branches of planar six-bar mechanisms, and to propose suitable criteria for circuit and branch identification of the mechanisms. There are nine types of six-bar mechanisms obtained by assigning the input and ground links on the Watt and Stephenson kinematic chains. Based on the fundamental concepts of coupler curve of four-bar linkage, dyad, kinematic inversion, equivalent linkage, continuity of transmission angle, theory of envelope, and geometric feature of dead-center configuration, feasible criteria are proposed for the analysis and identification of circuit and branch of planar six-bar mechanisms. The position analysis of dead-center configuration and identification of circuit and branch of five Stephenson mechanisms are obtained according to the closed form solution of SIIIB4 mechanism and four types of geometric features of dead-center configurations. The position analysis of dead-center configuration and identification of circuit and branch of four Watt mechanisms are obtained according to the closed form solution of WIB4 mechanism and four types of geometric features of dead-center configurations. The possible maximum number of circuits, branches, and dead-center configurations corresponding to a coupler curve of four-bar linkage and that of branches corresponding to a circuit are discussed for each planar six-bar mechanism.
　　The method proposed in this study for circuit and branch identification of each planar six-bar mechanism can be applied for the dimensional synthesis of planar six-bar mechanisms without branch and circuit defects.

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