Characteristic Analysis Of Two Kinds Of 3-dof Kinematically Identical Parallel Manipulators

Parallel manipulators(PMs)with two rotational and one translational(2R1T)degrees of freedom(DOFs)have caused widespread concern in academia and industrial field because of its great application prospect in engineering institutions,but this kind of mechanism configurations which can be applied to the engineering practice are less.This paper mainly studies kinematically identical manipulators(KIMs)for two kinds of 2R1 T PMs,this class of manipulators generated from the original manipulator have identical kinematics with the original one,but there are differences in the structure.Compared with the original one,the KIMs may have some better performance in some respects.In this paper,we take the asymmetric 3-PRS mechanism as research objects,and derived six different forms of the Jacobian matrix from the asymmetric 3-PRS Jacobian matrix based on the application of matrix elementary transformation theory,and get 6 mechanisms which have identical kinematics with the 3-PRS mechanism.The concept of transmission wrench screw,power coefficient and virtual output motion screw are introduced,based on this three concepts,the concept of constraint transmission index is introduced.Comparative analysis on constraint performance with constraint transmission index among the nonredundant constraint KIMs has been done.It is found that the constraint performance of nonredundant constraint KIMs is independent of the movement of the mechanism platform along the Z direction,only with the attitude of the mechanism.Seven KIMs for the RPS+SPS+SP PM are derived based on matrix elementary transformation theory.It is found that the constraint performance of this class of mechanism have relation with the movement of the mechanism platform along the Z direction,comparative analysis on constraint performance of nonredundant constraint KIMs with Z as 3 different numerical values are studied.Rotation axes of a class of 3-PRS KIMs and a class of RPS+SPS+PS KIMs have been analyzed,the instantaneous axes distribution of the two classes of mechanisms is obtained,and the continuous rotating shaft of the two classes of mechanisms are discussed.The prototype of the KIMs and the experiment based on prototype are developed.First of all,the processing design process of some required prototype parts are introduced,and the selection of motor,hooke joint,ball joint and control system are completed;then the process of prototype assembly are introduced and prototype assembly are completed;Finally,experimental process are introduced and the experiment shooting,experimental result record,experiment operate are completed.