Non-contact R-test is used for the dynamic measurement of five-axis machine tools. However, due to the spherical curvature, calculating the spherical center displacement (SCD) by using the non-contact R-test is challenging and inefficient. Thus, in this paper, an efficient calculation method based on multiple Gaussian process regression (GPR) is proposed to calculate the SCDs of the continuous trajectory by using the non-contact R-test. In the proposed method, first, the transformation matrix is constructed to roughly calculate the SCD. Second, the measurement error caused by the spherical curvature is solved and compensated by using the GPR model. Next, the threshold is set to remove some of the set points and reconstruct GPR to improve the model accuracy. Finally, the transformation matrix and the GPR model are outputted to calculate the SCDs of the continuous trajectory. We constructed a micro S trajectory to verify the proposed method. Experimental results showed that compared with the neural network method, the proposed method achieves higher model accuracy with shorter model construction time and improves the calculation efficiency by 99%.
Strong shear force developed in the lubrication film in the high-speed spindles will resulting high temperature rise and expanding the mandrel, which would arouse safe servicing problem. This study aimed to address the temperature rise issue in spindles through the use of substitutes in the spindle bearing material. To this end, we developed a spindle with a water-lubricated ceramic hydrodynamic and hydrostatic journal bearing. To support the selection of ceramic materials for the water-lubricated journal bearing, we initially performed application-oriented tests; to this end, the water absorption and porosity among alumina, silicon nitride, and silicon carbide were considered. To investigate the performance, and particularly the temperature characteristics of the hybrid bearing, a water-lubricated ceramic hydrodynamic and hydrostatic bearing test rig was designed to include temperature sensors. At the test rig, the radial clearance was measured for solving the temperature distribution of the bearing during the simulation. The experimental results helped verify that the water temperature increased by approximately 0.7°C as the rotation speed increased from 1200 rpm to 5400 rpm without an external radial load. The increase in temperature with and without radial load under a rotation speed of 3600 rpm was compared, and the results revealed a difference of 0.14°C. This indicates that the developed ceramic bearing improves the thermal stability of the spindle which shows its potential for industrial application in machine tools or other high rotation speed machines.
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