Temperature control scheme using hot-gas bypass for a machine tool oil cooler

Accurate temperature control that addresses heat generation is crucial given the development of high-accuracy high-speed machining process. Heat generation leads to a thermal error of machine tools. Therefore, developing high-accuracy machining without appropriate temperature control scheme is challenging. Machine tool coolers for forced convection cooling can effectively control heat generation. However, temperature control accuracy cannot be achieved because the temperature control scheme for machine tool oil cooler encounters nonlinear and time-varying problems with time delay characteristic. This study presents a novel temperature control scheme, namely, Proportional–integral–derivative (PID) control logic based on Smith predictive method. MATLAB simulation software was utilized to determine the specifications of outlet temperature control using hot-gas bypass scheme of high-precision oil cooler with refrigerant R-32. Simulation results revealed that the proposed control scheme present better temperature control accuracy than the traditional PID control. The proposed control scheme can also effectively solve the abovementioned problems through on-site experimental results. The steadystate error of the oil outlet temperature of the high-precision-type machine tool oil cooler can be controlled within 0.1 °C by using the proposed control hot-gas bypass scheme.