Direct correction of thermo-elastic deformations

点击翻译按钮获取中文摘要

According to VDI/DGQ 3441 the production accuracy, the machining accuracy and the geometrical accuracy are a matter of concern for the majority of machine tools. The geometrical accuracy of a machine tool is the accuracy with that any position in the volume can be approached. It depends on the geometrical deviations between the axes and of the single axis itself. The cartesian deviations of the tool center point (TCP) from its required position can explicitly be described by a model of the kinematic chain and the errors defined in ISO 230-1.To increase the geometrical accuracy of machine tools their geometry is measured and corrected by the control system of the machine after the bringing into service. Under operating conditions, the measured errors are superposed by static, dynamic and non-steady thermo-elastic errors. The thermo-elastic errors represent up to 75% of the total error. The presented project focusses on these errors.Beside machine internal heat sources and sinks thermal influences of the environment induce heat flows into the structural components of the machine. Depending on the thermal material characteristics, such as heat capacity, mass distribution and position of the heat sources, an irregular and non-stationary temperature field is formed. Together with the elongation lengths, their elongation coefficients, the part structure, the position of the parts to each other and the type and installation of the position measurement system, deviations and inclinations of the machine structure result from this temperature field. Hence, the resulting TCP deviation is highly pose dependent.If high changes of the thermal state of the machine tool occur after the measurement, the errors can increase, leading to a higher deviation of the TCP from its required position. Subsequently the part quality decreases. A process actual measurement of the geometrical errors could help to deal with this problem. Measured machine errors are in the case of this proposal process actual, if they are acquired a few minutes before the final cut.Up to now, there is no state of the art technology available in science and industry that is able to measure the geometrical errors of small and medium machining centers process actually. The aim of the presented research project is the validation of such a measurement method. On top, a method for the direct compensation of the measured deviation shall be validated.