提出一种新型3-UPU对称并联机构，其动、定平台始终关于中间平面对称，该机构具有两个转动自由度和一个移动自由度。运用螺旋理论对机构的自由度性质及运动特性进行分析，证明该机构动平台可以绕对称平面内的任意一条轴线或任意点发生连续转动，说明该机构不存在“伴随运动”，这为机构的求解及控制提供了很大的便利。同时，该机构还具有一个沿对称面法线方向的移动自由度，动平台沿该自由度方向也可以发生连续的移动。针对此机构的结构特点，用两个角度参数就可以方便、直观地表示出动平台的姿态信息。推导该并联机构的位置正、反解，并分析其工作空间，可以看出该机构的正反解都具有解析解，且表达式较为简单，方便后续的深入研究。该机构具有较大的工作空间，能够满足一般的工作需要。
A novel 3-UPU symmetrical parallel mechanisms is proposed, whose base and moving platform are always symmetrical about a middle plane. It has two rotational and one translational (2R1T) degrees of freedom (DOFs). The mobility and motion characteristics of this mechanism are studied by using the screw theory. And it has been approved that the moving platform can rotate continuously about a fixed axis or fixed point, which can be chosen freely on the middle plane. Therefore this mechanism has no parasitic motion, which will bring much convenience to the kinematics analysis and controlling. Meanwhile, it also has a translational DOF along the normal of the middle plane, and the moving platform can realize continuous translation along this direction. Based on the structure characteristics of this mechanism, the orientation of moving platform can be represented by two angle parameters, which is very convenient and visual. The forward and inverse solutions are derived and the analytical solutions are obtained which is very simple and make it easy for further study. The workspace is analyzed, which is large enough for ordinary requirement.
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