Kinematic Calibration Of 3RPS Parallel Mechanism Based On Five-axis Hybrid Machine Tool

The machining of complex curved surface components as blade,the development trend of it is high efficiency,high precision,and high surface quality.To cater to all of these requests,5-DOF hybrid machine tool emerged with the advantages of large working scope,high structural quality stiffness and light end quality.The leading reason why 5-DOF hybrid machine tool couldn't be applied into practice widely is the low terminal accuracy of parallel mechanism(PM).As the best way to improve the end precision of PM,kinematic calibration got focused by researchers worldwide.Based on comprehensive analysis of relevant literatures in this field,the terminal accuracy issue of 3RPS PM in 5-DOF hybrid machine tool is studied systematically in theory and experimental verification as well for its geometrical error source.The research on the associated motion,inverse and forward position solution is carried out respectively.On the basis of the structure constraint characteristics of 3RPS PM,the associated motion gets deduced in an analytic way.A conclusion that the end-associated displacement and angle in edge of working space are larger than in central region is obtained by simulating.By transforming the inverse position solution into the absolute length of each driven bar,the inverse position solution is analyzed in an analytic way.A conclusion that the motion of end along or around any independent coordinate axis is the result of all the chain's driven parameters in a non-linear mapping way get verified by simulating.By replacing the forward position solution with the solution of non-linear equations,the correlation and derivation of it get carried out by the means of numerical analysis,which reduces the complexity of analytic computation.The mapping relationship between end pose error and geometrical error source is studied theoretically.Based on the spatial closed-loop vector method,the mapping equation between end pose error and each chain's 9 geometrical error elements is formulated.To assure that all the error elements can be calibrated,the 27 geometric error elements were simplified as a combination of 21 independent geometric error elements by decoupling.The mapping model between the 6 dimension end pose error and 21 independent geometric error elements is constructed.A conclusion that end pose error is larger in the edge area of the workspace get achieved by simulating.The method of geometric parameter identification and the compensation strategy of end pose error are studied theoretically and verified by simulation.A parameter identification method based on the subset of end pose error gets proposed.The optimal combination of the subsets is selected,which helps to avoid of the detection of the complete set of end pose information.With the corner error of the end around X?Y independent axes,the parameter identification model is constructed,and the problem of missing rank of the identification matrix gets solved.By scatering the observation configuration on the edge of working space,the signal-to-noise ratio of observational information get improved.The robustness of parameter's identification result gets improved by the principal element weighted iterative method.By simulating,A consulution that the maximum identification error of 17 geometric error elements is reduced from 80%to 20%gets verified.Based on the working characteristics of the 5-DOF hybrid machine tool,the compensation strategy is analyzed for the end pose error,and the feasibility of it get testified by simulating.The effectiveness of the proposed theoretical research get testified by experiment on the 3RPS parallel mechanism of the 5-DOF hybrid machine tool.The relative zero get calibrated by using a dial indicator,and the accuracy of home returning get measured as well.With a laser displacement sensor,the calibration of abosolute zero get achieved by constructing the relative increment between z-axis of end and three of Actuators with the genetic algorithm.By contrasting the position/angle positioning error of the end,the validity of the absolute zero calibration get verified.By using a two-axis inclinometer,the geometric error elements are identified based on the angle error of the end around X and Y axes.The effectiveness of the geometric error calibration is verified by the position error of the end along the Z axis and the angle positioning error around the X axis at different positions.