中文摘要：

以3PUS-S（P）球面变胞并联机构为研究对象。机构由动平台、静平台、3条PUS支链和1条中间S（P）变胞支链组成，具有2个构态，即构态1（正常构态）和构态2（变胞构态）。构态1时，动平台相对静平台具有3个转动自由度，等效于三自由度球面机构；构态2时，动平台具有1个额外的径向移动自由度。首先，运用矢量代数法，建立机构运动学位置逆解模型；其次，在位置逆解模型的基础上，建立求解机构工作空间的约束条件；最后，以实物样机为研究对象，采用边界搜索法确定该机构的工作空间，为机构进一步的分析与应用奠定基础。

英文摘要：

We analyzed a 3PUS-S （P） parallel spherical metamorphic mechanism which consists of a moving platform, a base plate, three PUS legs and one middle S（P） leg. This mechanism has two configurations： the 1st normal configuration and the 2nd metamorphic configuration. The moving platform has three revolute degrees of freedom which is equivalent to spherical joint and extra translational freedom in the direction of radius. Firstly, the kinematic constraints pos of itional inverse solution equations are established based on the vector algebra method. Then the workspace are built based on the inverse kinematic solution. Finally, the boundary of workspace, on the basis of the study of real mechanism is determined with the boundary search method.