| It is of important significance to improve machine tool’s geometric accuracy on the condition that none of machine tool components is changed. Based on multi-body system kinematics theory, the universal topological structure model of workpiece to tool for multi-axis CNC machine tools is established, and the geometric error measurement and identification methods of translation axis and rotation axis are researched systematically. On these bases, the geometric error compensation is realized in combination with software programming technique, and machine tool’s geometric accuracy is improved. The key contents are shown as follows:(1)Based on multi-body system kinematics theory, the universal topological structure model of multi-axis CNC machine tools was builded and the error parameter definition of movement axes in the kinematic chains of tool and workpiece was unified. On these bases, the ideal transformation matrix and actual one for the motion of the tool relative to workpiece were derived, according to multi-axis machine tools with arbitrary structure. Also, the universal modeling of geometric error for the machine tool with RTCP/RPCP function was carried out.(2)On the basis of present ten-line displacement method, the identification methods of the pitch error, yaw error and roll error were improved on the combination of actual measuring paths. The ten-line displacement method applied to translation axes both driving tool and workpiece was mainly researched, and the identification of21geometric error parameters for translation axis was completed.(3)A new rotation axis error’s measurement and identification method based on the actual position and orientation of ball bar was proposed. It had generality and all of6geometric error parameters for rotation axis could be identified. Also the rotation axis error’s identification accuracy could be improved in consideration of actual ball-bar position and orientation in the measurement process, meanwhile removing eccentric error for clamping ball bar and translation axis’error. The error formulas of this method were applicable to the whole rotation axis’s travel by building a rotatable measurement coordinate system that rotated following the rotation axis, and it could avoid error values’flounce when rotation angle crossed over the quadrant.(4) Based on VC++6.0, a geometric error compensation software of multi-axis CNC machine tools was developed. It aimed at realizing geometric error modeling, identification and compensation of multi-axis CNC machine tools by calling Matcom C++matrix library to express the transformation matrixs between adjacent bodies of machine tools, and by establishing the function library of matrixs’valuation, the algorithm library of interpretating RTCP/RPCP function and calculating rotation angles.(5)A controlling radius of cutter axis vector was set to solve the mutation problem of one rotation axis’s angle after software error compensation, which was caused by the other closed to0degree. Whether the two rotation axes’angles should be compensated was decided by the controlling radius. It made the program not deal with those cutter axis vectors with minimal rotation angles and directly output the original angles.With the geometric error measurement and identification methods proposed in this paper, the error measurement experiments of translation axis and rotation axis were carried out on DMU100T five-axis CNC machine tool and32geometric error parameters were identified. Then the geometric error compensation software was used to establish geometric error model and compensate the NC code of blade test part. Finally, the theory of geometric error modeling, identification and compensation was proved to be correct by designing a comparing experiment and analyzing the contour error of two blade surfaces respectively machined by the original NC code and compensated NC code. |
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