Dimensional Synthesis And Trajectory Planning Of 6-dof Reconfigurable Parallel Machine

Based on traditional Stewart parallel platform,combined the robotic technology with machine tool technology,a novel reconfigurable parallel machine was obtained.Its mechanism owns six degree of freedom,in which the mobile plate and the fixed plate are connected by three branches,which are in the same structure.Each branch is composed of two mobile links,and the moving links are connected by a composite hinge that composed of one prismatic pair and one rotating pairs.The mechanism of the parallel machine can realize transformation among the configurations of 3-UPS、2-UPS-URS、2-URS-UPS and 3-URS flexibly.It has characteristics of high stiffness to weight ratio,fast response,large workspace,great flexibility and strong adaptability.In this dissertation,the dimensional synthesis and trajectory planning were studied,the six degree-of-freedom reconfigurable parallel machine taken as a research object.The contents of this dissertation were divided into the following parts:Firstly,the background of this subject was introduced,the history and development status of parallel machine at home and abroad was briefly described,and researches on the workspace,dimensional synthesis and trajectory planning towards parallel machine were summarized.Secondly,the results of analyses about mechanism configuration,degree of freedom,inverse displacement and other aspects,which were done by workmates in our team were declared.Furthermore,based on the result,kinematic velocity performance analysis was carried out by taking the method of kinematic influence coefficients,the velocity Jacobian matrix of the mechanism of the parallel machine was obtained,which provides a theoretical basis for the dimensional synthesis and trajectory planning.In addition,dimensional synthesis was carried out.Based on theoretical basis of inverse displacement,factors of link length,kinematic pair and radial scale of links were taken into consideration,according to pose transformation in this parallel machine,the mathematical model that reflecting the pose of mobile plate was established,and the mathematical relationship between the scale of the branch link and the workspace of the parallel machine was obtained.The effect of the dimensional change of links on workspace of the mechanism of parallel machine was discussed,under the constraint of the corresponding scale relation between two links.Equation to calculate workspace of the mechanism of the machine was established by using the polar coordinate searching method,and workspace of some examples was calculated.Finally,trajectory planning was studied.According to the result of dimensional synthesis,the parallel machine with the largest workspace was selected and the model was established.In the trajectory planning,the cutter location was taken as the locus reference point,and the angular displacement of each driver corresponding to the cutter location was solved through the inverse displacement.The angular displacement is fitted by using the quintic polynomial interpolation method,and the corresponding interpolation function was obtained,and as the input of each driver to realize the trajectory planning,one example was given.