Type Synthesis and Analysis of a New Class of Bifurcation 3T2Rv Parallel Mechanisms With Variable/Invariable Rotational Axes

Since the parallel mechanism has many advantages, such as high strength, high precision and so on, many industrial applications require mechanisms with three-dimensional translational and two-dimensional rotational motion (3T2R), 3T2R parallel mechanisms are widely studied. The direction of the first rotation axis is invariant for the existing 3T2R parallel mechanism, and the direction of the second rotation axis is changeable only with the first rotation axis, while the first and second rotation axes themselves are invariant. Based on bifurcation 1Rv parallel mechanisms with a variable/invariable rotation axis, a new 3T2Rv parallel mechanism with two variable/invariable rotational axes is proposed by using finite screw theory. The assembly condition and actuation scheme of this kind of 3T2Rv parallel mechanism are analyzed. The novel bifurcation 3T2Rv parallel mechanism consists of four motion modes: the invariable-invariable axis motion mode, invariable-variable axis motion mode, variable-invariable axis motion mode, and variable-variable axis motion mode. Compared with the traditional fixed axis mechanism, the variable axis mechanism can produce posture changes in other directions in the process of posture adjustment of the mechanism. The 3T2Rv mechanism with two variable axes rotation proposed in this paper can meet the assembly requirements of the third dimensional rotation that the traditional fixed axis 3T2R mechanism can not complete. The existing 3T2R parallel mechanism with two invariable rotation axes is extended to the bifurcation 3T2Rv parallel mechanism with two variable/invariable rotation axes.