本研究使用速度分析的圖形法以尋找3PPSR並聯式機械手臂的正向奇異位置。推導出驅動器靜止情況下活動平台的速度關係式，當活動平台的 速度不必為零的情況，即是發生正向奇異位置的條件。本文並利用這條件找出數種3PPSR並聯式機械手臂的正向奇異位置，並探討在此位置活動平台可能的瞬間運動。並與利用Jacobian矩陣尋找正向奇異位置的方法作比較。 It is shown in this thesis that direct singular positions of parallel manipulators may be determined by using graphical method for velocity analysis. The 6-DOF 3PPSR parallel manipulator is used as an example for graphical analysis. The moving platform’s velocity under zero actuating speeds is obtained. Direct kinematic singularity happens when this velocity is nonzero. Several direct singular positions are found in this thesis. It is shown that moving platform’s instantaneous motion at a direct singular position can also be found. The method of determining direct singular positions of this particular manipulator by using Jacobian matrix is also discussed.