Comprehensive thermal compensation of the servo axes of CNC machine tools

Abstract

The disadvantages of the common thermal error compensation methods were analyzed. Based on the analysis, we report the concept of the comprehensive thermal error (CTE) of the servo axes of CNC machine tool. The total CTE was divided into the thermal expansion error (TEE) in the stroke range and the thermal drift error (TDE) of origin, and their sources and effects on workpieces were analyzed. Furthermore, models for TEE and TDE were established. The model for TEE derived from the heat production, conduction, and convection theory predicted the thermal field of a screw and the thermal errors of servo axes in real time. The model for TDE was established by the multiple linear regression method. The experiments were carried out on a vertical machining center. The simulation and experimental results indicate that a high accuracy stability can be achieved with error compensation, even when the moving state is changed. To visualize the effect of error compensation with naked eyes, a special machining process was designed for a rectangular workpiece. The machining results confirm that the proposed models provide a high accuracy stability and robustness.