Thermal error mechanism model and transient thermal characteristics analysis of direct-drive rotary axis transmission system of CNC machine tools

The direct-drive rotary axis is an important component of precision five-axis machine tools, and its transient thermal characteristics are crucial in improving machining accuracy. This study proposed a direct-drive rotary axis transmission system thermal error mechanism modelling method based on the theory of heat conduction and thermoelasticity. In contrast to traditional modelling methods, both the temperature field and thermal deformation are also mechanism models here. We first simplify the rotary axis moving parts into equivalent hollow cylinders and develop a mechanism model of the heating and cooling transient temperature field based on variable separation and eigenfunction expansion method. Then, based on the features that the direct-drive axis heat source and boundary conditions are approximately symmetrical about the central axis, a thermoelastic potential-based transmission system thermal error mechanism model is established. According to temperature rise and interference compressive stress, this model calculates thermal error. Both experimental and simulation results validate the accuracy of the proposed mechanism model in predicting actual temperature changes along with thermal error of the rotary axis in real time. This work lays the groundwork for active control or compensation of thermal errors in direct-drive rotating parts such as CNC machine tool turntables and spindles.