Dynamic and static characteristics of a hydrostatic spindle for machine tools

The objective of this work is to study the static and dynamic behavior of a shaft supported by hydrostatic bearings. The hydrostatic bearing consists of a thrust bearing and a radial bearing fed by orifice restrictors. The radial bearing consists of six rectangular symmetry oil pockets that have the same depth; the thrust bearing consists of eight fan-shaped oil pockets. Static and dynamic modeling was performed in order to investigate the effect of the eccentricity ratio on the film thickness, stiffness and deformation of a spindle system. In the first step, the deformation of the spindle caused by the parameter change is studied according to a static model. In the second step, the vibration response caused by the eccentricity is analyzed with a dynamic model. In the third step, the effect of imbalanced vibration on the machining accuracy is analyzed; the imbalance-induced force in two directions is derived from the dynamic results. This research shows that the location and stiffness of the bearing affect the machining accuracy to a high degree.