Study On The Error Separation Of CNC Machine Tools Based On Curved Surface Topography Information Of Workpieces

The issue concerning about CNC machine tools is an important factor influencing the machining accuracy. To make sure how each error occurs in machine tool’s machining process, is quite pivotal to establish an error model and to compensate the errors of machine tool. In the process of machining a machine tool, every error would no doubt reflect on the surface of workpiece, weather it is a static one or a dynamic one, finally forming surface profile error. Based on the analysis of the curved surface topography information of workpiece, this paper is a research of relative fields concerning to error separation of CNC machine tools. Firstly, measuring curved surface topography of workpiece. Secondly, through the analysis of the curved surface topography information of workpiece, the calculation of the reverse cutter location point. Thirdly, take the information of motion model of machine tool while machining, the theoretical digital model of workpiece, the theoretical tool paths and other factors into consideration to separate the surface profile errors. Lastly, separate the machine tool’ geometric error, thermal error and dynamic error, and compare the errors out of detecting of machine tool. The results of separating are basically consistent with actual detection.Analyze the generation of the error sources of CNC machine tools while machining, there we take five-axis machine tool of RTTTR as example, to analyze the ideal movement of CNC machine tools while machining, and to establish homogeneous coordinate transformation matrix’ Axis Motion of each axis in ideal situation and the relationship among them. Besides, analyze the generation approach of tool paths, to the processing of complex surfaces, here to take curved surface topography while machining workpiece and how the surface dynamic tool path generated, to solve the influence of machining to performance of workpiece’s curved surface and reduce the machining error. At the same time, analyze the actual machining movement of machine tool to get the error element of each axis motion and their homogeneous coordinate transformation matrix and the error motion matrix of machining movement of machine tool. Finally, combine the ideal machining movement of machine tool with the actual machining movement of machine tool to get the the comprehensive model of machining movement of CNC machine tools.Measure the surface of workpiece through three coordinate measuring machine, do data processing of workpiece’s curved surface topography with Geomagic Studio software to get whole point cloud data of workpiec, then use Geomagic Qualify software create features of the workpiece’s curved surface topography information, and to alignment with the theoretical workpiece’s CAD model, and to conduct 3D comparing analysis and 2D comparing analysis, finally attain the curved surface topography information of actual workpiece, namely, the deviation between the theoretical coordinate values of workpiece curved surface’s point cloud, the actual coordinates values, each point and the actual coordinates values.Based on the curved surface topography’s information of workpiece, then, using reverse algorithm of cutter contacting point and cutter contacting point to determine the cutter contacting point and cutter location point of workpiece’s point cloud. Then, according to the above efforts to establish error model of machine tool based on cutter contacting point vector chain, making this model able to get errors of machine tool on each cutter contacting point. Then get the relationship between the above relationship to attain the space accumulation reaction and its law of the next cutting point. Finally, provide timely quantity basis for error compensation of machine tool.Based on the curved surface topography information of workpiece and the error model of machine tool based on cutter contacting point vector chain,to establish six dimensional error model based on the workpiece surface’s cutter contacting point, and to separate each error of machine tool, then to get machine tool’s geometric error, thermal error, dynamic error, and to use the double-ball-bar and laser interferometer to detect each error of machine tool to verify if the separating method is correct.