中文摘要：

本文旨在解决非过约束4自由度并联机构综合这一机构学难题．在总结已有的4自由度并联机器人综合结果的基础上，结合运动子群的概念和螺旋理论的方法，技术性地解决了约束数目和支链数目之间存在的矛盾．利用解析的手段给出了一套全新的非过约束对称4自由度并联机构设计方法．定义了一系列便于综合该机构的概念，分析了该类机构必须具有的拓扑结构，得出两种类型的该类并联机构．给出了满足设计条件的运动副组成情况及空间装配条件，最后给出了典型机构的设计范例．

英文摘要：

Structural synthesis for 4-DOF non-overconstrained parallel manipulators, an open problem in the field of mechanism, is solved. Current structural synthesis methods of 4-DOF parallel manipulators are summarized, and the conflict between the number of constraints and limbs is technically solved using the concept of kinematics group and screw theory. A new method is presented for designing 4-DOF non-overconstrained symmetrical parallel manipulators through an analytical process. Some concepts are defined to make the structural synthesis efficient and convenient. Topological structures necessary for this kind of mechanism are analyzed, and two parallel mechanisms of such kind are obtained. The configurations and spatial assembly conditions of all possible kinematic pairs are provided. Finally, some typical mechanisms are given as design examples.