关键词: 约束螺旋理论, 机构型综合, 对称并联机构;两自由度并联机构

Abstract:

The spatial symmetrical parallel mechanisms with 2-DOF were sorted into two classes firstly, i.e. Type 2Ryz 2-DOF parallel mechanism with two rotations about y-and z- axes in the plane of fixed platform and Type 1Rz1Tz 2-DOF  parallel mechanism with one rotation about z-axis and one translation along z-axis. The limb constraint system and the mechanism constraint system of the two kinds of parallel mechanism were enumerated with the geometrical conditions which guaranteed the combined effects of all the limb constraint screws equal to the desired mechanism constraint system. Then, the type synthesis for the two classes of 2-DOF spatial symmetrical parallel mechanisms were performed  systematically with the constraint screw synthesis theory, and the structure of the mechanisms were obtained, which could continuously realize the required rotations about the two axes in the base or rotation about the normal of the base plane and translation along it. The structures of limbs of the mechanisms as well as their constraint characteristics were gained also. The types of lower-mobility symmetrical parallel mechanism are expanded into 11 from 9, and their synthesis methodologies are also provided; all of these makes the type synthesis perfect.

Key words: constraint screw theory;type synthesis of mechanism;parallel mechanism with symmetrical structure;2-DOF parallel , mechanism