中文摘要：

基于Tsai提出的3-UPU并联机构原型，设计了一种改进的新型3-UPU并联机构，并对其进行了约束奇异分析，从而提供了一种可以改善3-UPU机构奇异特性，使其尽量远离约束奇异的机构设计方法。首先，分析了3-UPU并联机构的末端约束螺旋系，并将约束螺旋矩阵的条件数作为机构发生约束奇异的衡量指标，从而量化了机构接近约束奇异位形的程度。当条件数无穷大时，约束矩阵严重病态，而此时所讨论的机构就发生约束奇异。然后，基于得到的约束图谱，选择最小值作为机构优化设计的目标，即：使机构的约束条件数保持在最小值附近。最后，分析讨论了改进型机构的奇异问题，结果表明，改进型3-UPU机构不容易发生奇异。

英文摘要：

Based on the prototype of 3-UPU parallel mechanism proposed by Tsai, an improved 3-UPU parallel mecha- nism with three translational motions was designed and its constraint singularity was evaluated, thus a design meth- od for improving the singularity characteristic of a 3-UPU parallel mechanism was created. First, through analysis of the terminal constraint wrench system of the 3-UPU parallel mechanism, the condition number of constraint wrench matrix was used as the measure of constraint singularity to perform the constraint singularity evaluation. When the condition number is infinity, the constraint matrix becomes ill-conditioned, and the discussed mechanism is con- straint singularity. Then, based on the obtained contour atlas of constraint condition number, the minimum value of condition number on the contour atlas was chosen as the design objective, namely, keeping the condition number in the area around the minimum value. Finally, the singularity of the improved 3-UPU parallel mechanism was ana- lyzed, and the result showed it had the better constraint performance and was far from constraint singularity