Research On Intercepted Feedback Method For Thermal Error Compensation Of NC Machine Tools

During the machining process of the NC machine tool, inevitably disturbed by the friction heat and the change of ambient temperature, the actual location of cutting tools deviates from the location specified by the program, resulting thermal deformation and affecting the machining accuracy. Therefore, thermal error compensation is one of the key technologies to ensure the accuracy of precision machining.Based on multiple linear regression method, a theoretical basis of development of the temperature compensation system is established by deriving mathematical model of temperature field for CNC machine tools.An intercepted feedback compensation method of thermal error of CNC machine tool is researched in this paper. According to the data from temperature sensors, based on the relation model of temperature - geometry, the pulse equivalent which is transformed from the thermal error caused by temperature change, will be inserted into the feedback loop servo system to increase or decrease the position feedback pulse automatically, so as to achieve thermal error compensation.A real time pulse compensation circuit with low time delay and low costs is designed. Method of determine the compensation pulse width constrained by the minimum period of the feedback pulse from the NC machine tool is studied, so that not only the orthogonality of the feedback pulse kept up, but also that compensation process is done within 1/4 cycle of the position feedback pulse.Moreover, this paper also includes the intercepted feedback thermal error compensation system consisting of some advanced parts, such as the highly integrated MCU, single-bus digital temperature sensor and etc. This system can be directly embedded in the original CNC machine tool position feedback pulse loop, without any change of original hardware or software, which has broad application prospects, because it directly upgrades a normal CNC into the one with thermal error compensation function.The experimental platform for compensation system is established, and the intercepted feedback compensation method for the thermal error compensation is proven. The results show that compensation results meet the design requirements.