An improved thermal model for characteristics analysis of multi-link ultra-precision press system

In traditional models, only the effect of temperature change of bearings on the heat generation power and thermal contact resistance is considered. But the effect of bearing stiffness and flexibility of crank shaft on the heat generation power is often neglected, thereby impairing the accuracy of the thermal analysis. Therefore, a better thermal model is demanded to accurately analyse the thermal characteristics of a Multi-link ultra-precision press system (MLUPPS). By combining the effect of stiffness of bearing and flexibility of crank shaft on the heat generation power, an improved thermal model of MLUPPS was developed in this work. The model was based on as-derived kinematic and dynamic equations of Multi-link transmission mechanism (MLTM) and flexible dynamic model of crankshaft-bearing system. The dimension chain of thermal error is constructed to analyse the dimensional error between the slider and the work table at the position of Bottom dead point (BDP). The developed thermal model of MLUPPS and its analysis results from this model are in good agreement with the measurement results, and that is more accurate than the traditional one. The simulation results reveal that the maximum temperature rise of MLUPPS occurs at the crank shaft, and the dimensional error between the slider and the work table at the position of BDP is due to thermal expansion fluctuation before the generation and conduction of heat power reaches balance. The temperature rise and thermal error of MLUPPS under different rotation speeds, piling forces and bearing stiffness were also studied.