Research On Robust Compensation Technologies Of The Machine Tools' Thermal Error

Thermal error was the key factor to degrade the accuracy of the machine tool. It has been reported that thermal errors account for 40-70% of the total errors arising from various error sources. The accuracy of the workpiece produced on metal-cutting machine tools is largely influenced by the thermal error. With the fast development of the modern industry, the demand for high-speed/high-precision machine tools is rapidly increasing. How to realize the effect compensation of the thermal errors and keep the machining progress reliability and stability at the same time were the urgent technique needed solved at the present.Thermal error modeling, measurement and compensation were the three components of the thermal error compensation and control system. In practical machining progress, the complex working condition, abnormal malfunction of the measurement system and error compensation might cause the undetermined factors, such as machine structure vibration, which would disturb the system inevitably and influence reliability and stability of the thermal compensation and control system. On the other hand, the present domestic thermal error compensation systems were usually applied out of the CNC system. So the effect of the compensation was reduced and the application and extension were restricted greatly. Surrounding "Facing embedded integrated machine tool thermal error compensation and control system", this paper emphasized to solve two problems:the first was the robust compensation control of the machine tool thermal error; the second was the embedded integrated machine tool thermal error compensation and control system.To solve the problem on the robustness of the thermal error compensation and control system, the FEM technique was first used to qualitative analyze the transient and stable response of the thermal deformation to different working condition and temperature rise aiming at the machine thermal characterize in the complex working condition. And the changing law of the machine thermal characterize according to the working condition parameters was analyzed.Then to analyze the effect of the changing working condition on the machine thermal characterize, the experiment research of the thermal error in different working conditions were developed and the relationship between the temperature rise and the thermal error in changing working conditions was analyzed. And the characteristic working condition parameters (server speed, main spindle speed and environment temperature), which affected the machine thermal characterize, were determined. The traditional modeling manner which mapping the relationship between the temperature and the thermal error directly was broke through, the present method induced the characteristic working parameters into the thermal error model. A mix parameters LS-SVM machine thermal error predicting model which has strong robust characterize to changing working condition was developed.To solve the unstable problem of the thermal error compensation and control system caused by the abnormal malfunction of the measurement system and realize the online fault diagnose and self-repair in the measurement system, the online fault diagnose and self-repair method based on the temperature domain characterize of the machine tool was developed. The presented method induced the hypothesis testing and D-S proof theory arithmetic to accurately diagnose the abnormal malfunction sensor. And the linear regressive model was used to self-repair the abnormal data. So the measuring system could be continuously running without disruption in the abnormal conditions and keep the continuity and security of the thermal error compensation and control.To solve the problem on the real time compensation of the thermal error, the embed compensation method in CNC was analyzed. A embed feedforward thermal error compensation was developed. At the same time, To solve the problem on the machine vibration caused by the thermal error compensation, the compensation stability of the real time thermal compensation which was embedded into the kernel interpolation layer was analyzed. Stability constrained error compensation control arithmetic was developed and the arithmetic realized the stable compensation control on the position dependent and the position independent thermal error.At last, to solve the problem how to embed integrate thermal error compensation and control system in the CNC, the HUST-8 CNC system which was based on the fieldbus was analyzed. With the support of second development integrate platform in this CNC system, the measurement and modeling parts of the thermal error compensation and control system were developed and integrated with the CNC system through the fieldbus technique. At the same time, the real time thermal error compensation model was merged together deeply by the insert technique in the kernel interpolation layer.All studied thermal error compensation and control technique were tested in practical experiment.The experiments results verify the efficiency of the developed embedded integrate thermal error compensation functional.