中文摘要：

基于螺旋理论，分析了一种新的3-PSS并联机构的运动特性。首先将该机构的一个分支拆分成两个串联机构，分别建立了动平台的螺旋运动方程；接着根据结构特点，找到机构的运动约束关系；再根据反螺旋理论中的运动和约束力的关系，得出该机构始终受到三个线性无关的力偶约束力，最终从理论上证明3-PSS并联机构只能有三个平动自由度。结论极大地简化了该机构的其它特性分析，同时该方法对其它少自由度并联机构运动特性分析具有一定借鉴意义。

英文摘要：

3 -PSS mechanism was analyzed based on the screw theory. First one offset of the mechanism was split into two serial mechanism, and two screw kinematic equations were given. Second the kinematic constraint was found according to configuration. At last a constraint from three linearly independent anti - screw moments was shown to act on the moveable platform of the 3 - PSS mechanism, which then could move only in three - translation direction. The conclusion can simplifier the analysis of 3 - PSS other characteristics, and the method has some reference for other deficient dof mechanism.