A comprehensive analysis of factors affecting the accuracy of the precision hydrostatic spindle with mid-thrust bearing layout

This paper investigates the influence of rotor coaxiality error on spindle accuracy under different operating conditions in the precision hydrostatic spindle with a mid-thrust bearing structure. Firstly, a linearized model of rotor dynamics equation with five degrees-of-freedom is established based on Newton’s law of motion and angular momentum principle. Then, by solving the Reynolds equation and the flow continuity equation using the mathematical perturbation method, the steady and transient pressure distribution functions of the hydrostatic bearings are obtained; subsequently, the stiffness and damping coefficient matrices of the spindle are determined. Furthermore, the linearized stiffness and damping coefficients are substituted into the rotor dynamics equation to obtain the instantaneous acceleration of the rotor, and the motion trajectory of the rotor is solved iteratively by the Euler method. Finally, the paper studies the influences of different rotor coaxiality, rotating speed, cutting load, oil supply pressure, and oil film clearance on dynamic characteristics, amplitude amplification factor, and radial runout of the spindle by computer simulation. The simulation results show that the spindle runout is more sensitive to rotor coaxiality error and oil film clearance.