中文摘要：

并联机构在高承载能力、高刚度和高精度等应用场合得到广泛应用．但并联机构工作空间较小、回转能力相对不足，其应用受到限制．本文提出一种三自由度2．P（4R）RR平面并联机构，其运动平台能够在360°范围内连续回转．基于螺旋理论，通过分析机构的运动螺旋和约束反螺旋确定机构自由度的类型，根据回转空间内奇异形成的原因，得出机构动平台在360°的回转空间范围内发生运动奇异和约束奇异的条件；通过分析机构在发生奇异位形时机构动平台的运动类型，讨论动平台奇异姿态对连续回转的影响以及能否跨越，研究机构各类奇异消除的必要性；分析增加冗余驱动后机构约束螺旋的变化，从而消除约束奇异，保证机构连续回转的可控性．

英文摘要：

Parallel mechanisms are widely used when large payload capability, high stiffness and fine precision are needed. However the smaller workspace and the lower rotational ability restrict their application. A 3-DOF planar 2-P（4R）RR parallel mechanism is proposed and the mobile platform of the mechanism can rotate to and fro in the range of 360 ° continuously. Based on screw theory, the DOF type of the 2-E4R）RR the mechanism is confirmed by analysis of the kinematic screws and constraint screws. In the rotational range of 360 o, the conditions that produce kinematic singularity and con- straint singularity are obtained according to the reason to form singularities. The discussions that the singularities influence on the continuous rotation and whether the orientation of singularities can be stepped over when the motion types of the mobile platform are developed. So the necessity to eliminate the singularities is studied. Adding a redundant actuation to the 2-E4R）RR the mechanism, the new constraint screws show the elimination of the constraint singularity which improves the controllability for the continuous rotation.