In order to compensate the measurement errors of the on-machine measurement system caused by the XY worktable error accurately under the influence of multiple factors, the structural characteristics of the XY worktable are analyzed in detail. The dynamic positioning error model of the XY worktable motion components such as the grating measurement systems, the ball screw assemblies, the guide rail system manufacturing errors and the friction forces under the influence of the above factors are established, and the theoretical model of the dynamic positioning error of the XY worktable is derived. It can be seen from the analysis process that the main factors affecting the dynamic positioning error are the movement speed of the worktable, the weight of the workpiece to be measured, the installation position of the workpiece and the friction force. The actual model parameters are substituted into the theoretical model to calculate the dynamic positioning error of the worktable under different influencing factors by using the technical indicators of the experimental platform. From the analysis of calculation results, it can be seen that the dynamic positioning error is the smallest when the moving speed of the worktable is 12 mm/s, and this velocity is defined as the best measuring speed,which lays a good theoretical foundation for improving the dynamic machining accuracy of machine tools and the measurement accuracy of on-line measurement system.
KEYWORDS: Convection, 3D modeling, Thermal modeling, Finite element methods, Lithium, Temperature metrology, 3D metrology, Analytical research, Spindles, Head
In order to reduce the additional influence of the thermal-force coupling deformation of the Computerized Numerical Control(CNC)machine tools bed based on the grating measurement, the concept of the thermal-force coupling deformation critical point in the direction of the grating installation line of the machine bed is proposed. In order to accurately determine the thermal-force coupling deformation critical point of the machine bed, the BV75 CNC machine tool is taken as an example. The factors that cause the deformation of CNC machine bed are analyzed by using material theory, thermos-elastic and nonlinear thermal deformation theory. According to the actual structure size of the machine tool ,a 3D model is established. The heat sources and load conditions of the machine bed deformation are theoretically analyzed, and the finite element thermal- force coupling analysis of worktable is carried out. The deformation critical point in the direction of grating installation line of machine tool bed is determined by theoretical modeling and finite element analysis. Under loading single heat source, the multi heat sources and the different size and position load, the comparison experiments of the thermal deformation of the machine bed and the zero shift errors of the grating measurement are carried out. The experimental results show that the bed thermal deformation is the main source of the grating additional error, and the workpiece loading position will cause the bed deformation. The position of thermal-force coupling deformation critical point is different from the thermal deformation critical point. The zero position and the indication error of the grating can be reduced by fixing the grating on the thermal-force coupling deformation. An accurate grating error prediction compensation model can be established, which is use for the subsequent error compensation of the on-machine measurement system of the CNC machine tools.
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