Mobility analysis of a hybrid mechanism based on POC equations and its kinematic

Abstract

Institutional innovation is a challenging task. For parallel mechanisms, a new type of branch structure and a new branch combination scheme can be considered as the innovative design of the topology of the parallel mechanism. At present, there are three main methods for the synthesis of parallel mechanisms, namely, displacement subgroup method, screw theory method and position and orientation characteristic (POC) equations. Degree of freedom analysis is an indispensable part of mechanism synthesis, and is also the foundation of mechanism kinematics. A 5 degrees-of-freedom (DOF) hybrid mechanism was researched in this paper based on a 3-DOF translational parallel mechanism with parallelogram linkage and 2-DOF serial mechanism. Firstly, the characteristics of this topology structure were introduced, and the mobility of the mechanism was analyzed by POC equations. Secondly, according to the space vector relation between the moving platform and the fixed base, the direct kinematics of parallel part were deduced via an analytical method and the inverse kinematics was performed by D-H method. Finally, In order to verify the efficiency of the kinematics algorithm, a set of given arguments about mechanism could be put into the kinematics algorithm to obtain the corresponding changes of displacements and the position of the moving platform. The error of the inverse and direct kinematics was analyzed by an example of machining a complex surface, which shows that the proposed algorithms are effective and have satisfactory computation precision.