A novel symmetrical 3-CRCR/RPU parallel mechanism was proposed.Based on the modified Kutzbach-Grtübler formula and the screw theory,it is concluded that the mechanism has four degrees of freedom.The vector equation was established according to the conditions of geometric constraint.The kinematic positive and inverse solutions were gained in form of analytical solutions.The velocity and acceleration of the parallel mechanism were analysed,which was based on the kinematic inverse solution.The mechanism had no singularity and partially decoupled by analyzing Jacobian matrix.A simulation model was established by ADAMS software to verify the correctness of the kinematics model.The workspace was given according to the conditions of each joint constraint,and the conclusion was obtained,that α-β-z configuration space of the mechanism was similar to oblique hexahedron.Finally,the influences of the structural parameters on the workspace were studied.The overall performance distribution of the mechanism under different structural parameters was studied based on the improved global performance index ηJ,which provides the basis for the optimization of the mechanism's spatial trajectory planning and structural design.%提出一种新型对称3-CRCR/RPU并联机构,借助修正的Kutzbach-Grübler公式,结合螺旋理论进行分析,该机构具有4个自由度.根据几何约束条件列写矢量方程,以解析解形式给出该机构的运动学正解和逆解,基于逆解对机构速度和加速度进行分析,对机构雅可比矩阵分析知,该机构不合奇异位形且部分解耦.应用ADAMS软件建立仿真模型,验证运动学模型的正确性.根据机构各关节限制约束条件给出其工作空间,得出机构具有类斜六面体的α-β-z位姿子空间.最后,研究机构结构参数对工作空间的影响,并基于改进后的全局性能指标ηJ研究不同结构参数下机构整体性能分布,从而为该机构的空间轨迹规划、结构设计的优化问题提供参考.
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