研究了一种变结构并联机构,这类机构的上、下平台通过4条结构相似的支链连接,各支链上均有一移动副,根据输入选取原则,该运动副适合作为驱动副。机构动平台可具备4个空间自由度。连接支链与上、下平台的运动副采用万向节（U副）,由于其拓扑结构的多样性,不同构型下动平台可具有多种空间自由度组合形态。考虑机构的实用性,运用螺旋理论并采用增加约束支链的方法,系统的综合了机构的2T2R和3T1R构型。建立了机构的位置关系方程,利用求导法得到了机构的雅克比矩阵,研究了不同构型下机构的奇异位形,并提出了免初始奇异和全局奇异的措施。%In this paper, a variable structure parallel mechanism that moving and fixed platforms are linked with four limps possessing is studied. It is feasible that prismatic pairs are selected as driver in each limp based on choice principle of input. Through integration analysis, the moving platform should be provided with 4 spatial DOFs. The universal joints are used to connect limps to moving and fixed platforms, whereas moving platform may obtain many forms of spatial DOFs for various topological structures. Considering practicability of this class of mech- anism, 2T2R and 3T1R configurations are deduced by screw theory and adding limp. The positional equation and the Jacobian maxim are built, and singular position is researched in different configurations. Finally the method of avoiding initial and global singularity is proposed in order to provide a guide for path planning algorithm.
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