Abstract: A new type of 4-degree-of-freedom(4-DOF) 3T1R parallel mechanism—2PPaPaR parallel mechanism was proposed, which had the characteristics of simple structure, symmetrical configuration, large workspace, high positioning accuracy and good dexterity, and might be widely used in sorting, handling and packaging operations. The number and types of DOF of the mechanism were verified based on the screw theory. By analyzing the configuration, the forward and inverse kinematics solution modules were obtained based on the closed-loop vector method, and were validated by calculating examples of forward and inverse solutions. With the inverse kinematics as the constraint conditions, the reachable workspace and the possible workspace shapes were discussed based on numerical method. The Jacobian matrix was established by analyzing the input and output velocity characteristics of the mechanism. Then the singularity of the mechanism was analyzed, and several typical singular configurations were given. Finally, taking the three performance evaluation indicators of reachable working space, positioning accuracy and operability degree as the objective function, the particle swarm algorithm was used to optimize the design of the geometric dimensional parameters. Compared with the original mechanism, it is discovered that the kinematic performance of the optimal mechanism is significantly improved, which provides reference for the subsequent prototype constructions.

Key words:  , parallel mechanism, performance indicator, particle swarm algorithm, optimal design

摘要： 提出了一种新型的四自由度3T1R并联机构——2PPaPaR并联机构，该机构具有结构简单、构型对称、工作空间大、定位精度高、灵巧度好等特点，可广泛应用于分拣、搬运以及包装等操作中。基于螺旋理论验证了该机构自由度的数目和种类，通过对其构型进行分析，基于闭环矢量法求得运动学正逆解模型，并利用正逆解算例进行了验证，以运动学逆解作为约束条件，基于数值法计算出该并联机构的工作空间。对机构的输入和输出速度特性进行分析，建立了机构雅可比矩阵，并基于此分析了该机构的奇异位形，给出了几种典型的奇异构型。以可达工作空间、定位精度和可操作度三种性能评价指标为目标函数，采用粒子群算法对机构几何尺寸参数进行优化设计，对比发现，优化后机构的运动性能有了明显的提高，从而为后续样机搭建提供了参考。 

关键词: 并联机构, 性能指标, 粒子群算法, 优化设计