The Geometric Error Sensitivity Analysis And Total Differential Kinematics Solution For CNC Multi-axis Machine Tools

Multi-axis NC machine tool has arbitrary accessibility in the processing space, whichis beneficial to improve manufacture quality and efficiency. In recently years, thelarge-scale multi-axis NC machine tools are widely used in manufacture of largepropellers, wind turbine blades, etc. Geometric error is the main factor of static error toeffect manufacture precision, which contains manufacture, assembly error and plasticdeformation of motion parts. Especially for large multi-axis CNC machine tool, because oflarge-travel of each motion axes, the effect on accuracy is more significant.Due to the defect of existing post-processing algorithm which is only suitable for aspecific type of multi-axis NC machine tool, a generalized post-processing method thatfits arbitrary configuration is presented. It derives a general kinematic model frommulti-body kinematics, and then describes the spatial relationship between adjacent cutterlocations (CL) as total differential. This method transforms the complicated reversekinematics problem into solving linear equations of increments of each axis. Incomparison with the conventional methods, experiment on a specific machine tool showsthat the total differential post-processing method has the attributes of being bettergeneralized, more accurate, and with faster computing speed.As it is difficult to solve the kinematic model with geometric errors, the currentmethods is geometric method.So the kinematic solution method with geometric errorsbased on the principle of iterative is proposed. The machine model, that is considered withthe geometric error, has many variables and the kinematic model is nonlinear, thereforethe results are difficult to be obtained. Based on iteration theory, establish respectively thekinematic model with geometric error and non-geometric error. Through the forward andinverse kinematics solution, correct the axis value of the solutions and intermediate cutterlocation points datas, closer and closer to the ideal value. In addition, it has proofed theconvergence of the algorithm. It shows that algorithm has good convergence.As large complex surface machine has many error components that is difficult tomeasure and solve,the orthogonal experiment method was proposed, which was used to analyse primary and secondary factors of geometric errors.By using this method,make aanalysis of the effect of geometric error in order to simplifie the solution and measurement.The identify method is measuring each axis of machine tool base on laser tracker, thenusing the least square method to fit the axis, as a result the coordinate system of each axiscan be built. The geometric error of machine tool can be gained by analysis of thecoordinate system.