Error Modeling And Experimental Research On A 2-DOF Parallel Kinematic Machine Tool

While the parallel kinematic machine tool(PKMT)theoretically has the advantages of high stiffness and high accuracy,its performance isn’t ideal in practical industrial application.This paper mainly focusses on the mechanism analysis,error modeling and error measurement of a 2-DOF(Degree of Freedom)multi-function PKMT developed by ourselves with precision analysis as a guide.The main content of this study is as follows:(1)Fistly,the kinematics and dynamics analysis of a 2-DOF mechanisms are solved,and a complete mapping relationship model of "joint force-joint movement-end movementload force-joint internal force"was established,and the workspace analysis based on the forward kinematics model,and the inverse dynamics analysis based on Lagrange method and the positive dynamics analysis based on Newton Euler method.(2)Secondly,the error model of the 2-DOF PKMT is established based on screw theroy.On the basis of a kinematic exponential product model,the axial error of joint is equivalent to the hypothetical generalized joint screw so that the error twist was established.The position and orientation errors of the tool coordinate system were respectively equivalent to the screw motion of the translation joint and the revolute joint,so that the error model of the 2-DOF mechanisms was established,which provieds the basis for the analyses and comparisons of end trajectory affected by joint error model subjected to gravity and the motion process respectively,and the corresponding numerical simulation is carried out.At the same time,the error model based on vetor method of the 2-DOF mechanism is established and the mapping relationship between component parameters and terminal errors was analyzed.(3)Thirdly,a kind of CNC platform for 2-DOF multi-function PKMT based on industrial PC and PCI motion control card is proposed which take the forward and inverse kinematics model into the CNC system so that the precise point-to-point movement control is realized.At the same time,the interpolation algorithm of linear and circular trajectory is designed.(4)Last but not least,2 kind of experiments are conducted in this paper.First,the vertical vernier caliper is used to measure the vertical orientation precision of the 2-DOF PKMT under different initial structure parameters,and the precision is improved remarkably by optimizing the structure parameters.The other experiment is the general precision measurement method of the parallel machine tool’s translation axis by ten-line method.Basis that,an analysis of precision of parallel machine tool is conducted.