含有混合运动支链的无耦合2R1T并联机构型综合研究

Type Synthesis for Uncoupled 2R1T Parallel Mechanism with Hybrid Kinematic Branch

摘要:

针对并联机构运动学耦合性强和转动能力弱等问题，本文提出了一种含有混合运动支链的无耦合2R1T并联机构型综合方法。根据机构输出运动特性，利用螺旋理论构建了运动等效分支基础结构形式，即PRR分支。通过引入1条等速比分支运动链，构造运动等效的混合分支运动链，并基于位移流形理论实现了等速比分支运动链结构综合，获得诸多新型混合支链。根据分支驱动力螺旋理论确定单开链分支驱动力螺旋、主动运动螺旋和非主动运动螺旋形式，根据连接度不同完成了单开链分支结构综合。根据建立的分支装配条件，实现了具有期望运动特性的2R1T并联机构型综合和创新设计。最后，对所综合的PRRRR/(PR-RURU)-R并联机构进行了自由度、运动学及转动性能分析，结果表明该机构可实现二维转动、一维移动，雅可比矩阵为对角阵，而动平台2个姿态角转动范围分别达103.48°和125.24°，因此该机构为三自由度2R1T无耦合并联机构，且具有良好的转动能力，从而验证了所提出型综合方法的正确性与可行性。

Abstract:

Aiming at the problems of strong motion coupling and weakly rotational capability of parallel mechanism, a type synthesis method for uncoupled 2R1T parallel mechanisms with a hybrid kinematic branch was proposed. Based on the output kinematic characteristics of the mechanism, the basic structure of the kinematical equivalent branch, namely the PRR branch, was constructed by using the screw theory. By introducing a constant-velocity-ratio branch, the hybrid kinematic branch with equivalent motion was built. Structural synthesis of the constant-velocity-ratio branches was completed in terms of the displacement manifold theory, and many new hybrid branches were obtained. The forms of the actuation wrench screw, actuated twist screws and unactuated screws of single-open branch were determined according to the actuation wrench screw theory. Then structural synthesis of the single-open branches was realized by means of the different branch connectivity. Based on the branch assembly conditions, type synthesis and innovative design of the 2R1T parallel mechanism with the desired kinematic characteristics were completed. Finally, analysis of degree of freedom, kinematics and rotational capability of the new PRRRR/(PR-RURU)-R parallel mechanism were performed. The results showed that the mechanism was capable of two-dimensional rotation and one-dimensional translation, its Jacobian matrix was a diagonal form, and the rotational ranges of two orientation angles of the moving platform reached 103.48° and 125.24°, respectively. Therefore, the mechanism was a 3 DOF 2R1T uncoupled parallel mechanism with well rotational capability. The correctness and feasibility of the proposed type synthesis method were verified.