並聯式機構在實際的機台設計中，零件多為複雜的幾何形狀，若是加工精度要求不足會導致加工誤差，誤差反應至零件實際尺寸與輪廓上，使得真實機構參數產生變異。此外，零組件間具有嚴謹的幾何約束條件，如連桿兩端萬向關節之兩軸若互相平行，可達到末端效應器之純平移運動，但組裝過程中難免留下組裝誤差，無法達成機台理想約束條件而影響末端效應器之運動行為。因此本論文將針對應用於五軸工具機的3-UPU平移並聯式機構建立誤差模型，並探討各項誤差影響定位精度之敏感度。
　　本文首先介紹具變化連桿長度之3-UPU型並聯式機構，以及將萬向接頭獨立為兩旋轉軸之3-RRPRR型，並根據機構參數定義以空間向量法與D-H表示法推導順逆向運動學，再利用雅可比矩陣之條件數定義可操控性指標來評估機構之操控性能。接著，以實際工程圖標註之幾何公差作為製造誤差來源對3-UPU型並聯式機構建立誤差模型，分別探討機構參數變異量對組裝可行性與各連桿迴路端點位置之影響。最後，透過敏感度分析瞭解各公差對於端點位置之影響權重，進而調配關鍵公差項之公差等級以改善端點位置偏移情形。

As the parallel kinematic manipulators (PKM) are designed for the machine tools, the complex shapes of machine elements are challenging to produce precisely. The actual sizes and forms of each part may deviate from nominal parameters through the manufacturing tolerances. In addition, the behavior of the end-effector is controlled by the strict geometric condition between parts. However, the assembly errors will be inevitably left to cause the position and orientation errors of the end-effector. Therefore, a translational 3-UPU PKM applied to five-axis machine tool was investigated in this paper. The error model of PKM was built and the sensitivity analysis was conducted to decide the influential parameters on positioning accuracy of the end-effector.
This paper first introduced a 3-UPU parallel kinematic mechanism with variable-length links. Based on the 3-UPU configuration, the universal joints could be separated into two revolute joints, which was corresponding to the 3-RRPRR mechanism. After defining the structural parameters of two mechanisms, the inverse and forward kinematics were derived through vector algebra and Denavit-Hartenberg method. Furthermore, the Jacobian matrix was obtained by the formula of inverse kinematics. The dexterity index was determined by the condition number of Jacobian matrix to evaluate the control characteristic of mechanisms. Then, the error model of a 3-UPU which contained the manufacturing geometric tolerances was established for investigating the influence of the actual design parameters on assembly condition and positioning of links’ endpoints. Finally, the sensitivity analysis was completed to determine the critical tolerances which significantly affected the deviation of positioning. Through modifying the tolerance grade of critical terms, the improvement on the accuracy of links’ endpoints could be evaluated.

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