The Study On Parallel Mechanisms With Planar Branch And Couple-constrained Wrench

Because of the special structural defects of the spherical joint in the parallel mechanism such as its too small rotation angle and bearing high pressure but poor performance under tension,which make the most important performance indicators including position and posture workspace and stiffness characteristics become severely restricted,these disadvantages affect the application and popularization of parallel mechanism in practice.This paper focuses on the idea of transforming spherical joint in the parallel mechanism.Due to revolute joint's large rotation angle and withstanding large loads regardless of tension or compression,it is possible to make a mechanical synthesis by means of a planar closed-loop sub-branch that only includes revolute joint and prismatic joint,and then the kinematics and dynamic performance of the parallel mechanism are improved.Because of the utilization of planar closed-loop sub-chains,it will complicate the analysis of mechanisms,for example the analysis about degree of freedom and constraint,and even it leads to a condition that is different from the previous situation,which the coupling constraint exists.Therefore,this paper is devoted to solving the problems.The main contents of this paper are as follows:Synthesis and experimental synthesis of new parallel mechanism with planar closedloop branch.First of all,according to the actual requirements,the synthesis objectives will be listed as a basis for institutional integration;and then a class parallel mechanism of planar closed-chain sub-chain branches with 4-,5-,6-degree of freedom will be put forward by transforming spherical joints into revolute joints to synthesize.Finally,some typical experimental prototypes of the above-mentioned mechanism are built by means of experimental synthesis to verify the correctness of the integrated mechanism.Two parallel mechanisms with planar closed-loop sub-chain branches were analyzed.First of all,two parallel mechanisms with planar branches are designed,and the formulae are derived for inverse position.Secondly,the variable-step boundary search method for the mechanisms with larger correlations between the branches is proposed.Then it is concluded that the constraints of this kind of mechanisms are different with the different constraints of the pose,and then the models of kinematics,statics and dynamics of the two mechanisms are obtained.Finally,a 2UPR-R+3SPU mechanism simulation model is built,and the derived formulae are verified by the numerical examples.Three parallel mechanisms with planar closed-loop sub-chain branches were analyzed.Firstly,according to the respective characteristics of these three mechanisms,the each inverse position models is established,and the workspace is obtained according to the variable-step search method,and from the results,the shape effects of the planar branches and single-chain branches on the workspace can be seen;The constraint nature of planar closed-loop branching on moving platform is deeply analyzed,and the conclusion that the kind of mechanism constraint has the coupling relation force is obtained.Then the unified Jacobian matrix and Hessian matrix of the mechanism are obtained,then the static and dynamic models of the mechanism are deduced.Finally,the simulation model is established for(2UPR-R)mechanism as an example,and the theoretical model is verified by numerical examples.The control platform system of 2UPR-R+SPS+SP parallel mechanism was built and experimental research was carried out.First,the experimental platform of 2UPRR+SPS+SP mechanism is built;then by using VB language for the two time development of CAD software,the trajectory planning software experimental platform is written,and by utilizing motion control card based,the preparation of the motion control part is completed.Finally,the application software of the laboratory experiments is carried out to study the motion control,and the derived theory is validated.