一种运动分岔并联机构的结构约束与运动模式分析
Structural Constraint and Motion Mode Analysis on Parallel Mechanism with Bifurcated Motion

为设计得到一种新型运动分岔并联机构,运用螺旋理论对其结构约束和运动模式进行分析,同时分析了输入选取。首先,研究了一种运动分岔单环闭链的运动特性,具有两种不同的单自由度转动和两自由度瞬时转动;其次,将运动分岔单环闭链与四自由度PPRR(P表示移动副，R表示转动副)串联支链相结合,得到一种具有无约束、存在一个约束力偶和一个约束力矢的3种不同结构约束的混联支链,并得到了混联支链在不同运动模式下的约束螺旋表达式;最后,利用3条相同的混联支链连接定平台和动平台,得到一种新型运动分岔并联机构,并讨论了其输入选取。研究结果表明,该运动分岔并联机构具有3T3R、3T、3R、2T1R和1T2R(T表示移动，R表示转动)共5种不同运动模式。
To obtain a new kind of parallel mechanism with bifurcated motion, the structural constraint, motion mode and input scheme are analyzed by using screw theory. The motion characteristics of a closed？？loop linkage with bifurcated motion is firstly analyzed. In different motion modes, the closed？？loop linkage with bifurcated motion has two kinds of single DOF(degree of freedom) finite rotational motions and one 2？？DOF instantaneous rotational motion. A kind of hybrid limb with bifurcated motion is then obtained by integrating the closed？？loop linkage with 4？？DOF PPRR(P？？prismatic pair, R？？revolute pair ) serial limb. The constraint exerted by the hybrid limb can switch among no？？constraint, a constraint couple, and a constraint force. The constraint screws associated with the hybrid limb in different motion modes are identified. Lastly, a kind of parallel mechanism with bifurcated motion is constructed with three identical hybrid limbs connecting the fixed base and moving platform, and the actuation scheme for the parallel mechanism is discussed. The result shows that the parallel mechanism has the ability to perform variable motion modes such as 3T3R, 3T, 3R, 2T1R(T？？translation, R？？rotation) and 1T2R