一类两转动自由度完全解耦的三支链两转一移并联机构

Three-branch 2R1T fully-decoupled parallel mechanism with two rotational degrees of freedom

提出了含恰约束支链两转一移3自由度并联机构(2R1T)两转动自由度完全相互解耦的两个充分条件,设计得到了两转动自由度完全解耦的2R1T并联机构RRU-UUR-RPR和RPU-UPR-RPR,采用螺旋理论对机构自由度性质进行了分析,得到机构两条连续转动轴线的分布。然后建立机构输入位移与位姿输出之间的映射模型,根据转动自由度完全解耦的数学描述,分析得到该机构两转动自由度是完全解耦的。最后比较分析了该类机构与其他两转一移三支链并联机构含有的被动单自由度运动副数目,该类机构含有的被动运动副数目仅为8,易于实现高结构刚度的目标,具有广阔的应用前景。

In this article,for the 2 R1 T fully-decoupled three-degree-of-freedom parallel mechanism with constraint branches,two sufficient conditions for the full decoupling of two rotational degrees of freedom are identified;the 2 R1 T fully-decoupled parallel mechanism RRU-UUR-RPR and RPU-UPR-RPR with two rotational degrees of freedom are developed.The mobility of these mechanisms is analyzed by means of the screw theory,and the distribution of two continuous rotational axes is obtained.Then,the mapping model between the mechanism’s input displacement and its output pose is established.According to the mathematical expression of the fully-decoupled rotational degree of freedom,it is found that the two rotational degrees of freedom of the mechanism are fully decoupled.Finally,the comparative analysis is conducted on the number of the passive singledegree-of-freedom joints contained in this mechanism and the other three-branch 2 R1 T mechanisms,and the number for this mechanism is eight,which ensures a high standard of structural rigidity.Thus,this mechanism has a wide scope of application.