High speed hydrostatic spindle

Abstract

An integrated spindle and motor unit includes a housing containing both the spindle shaft and motor with hydrostatic bearings around the front and rear of the spindle shaft. The hydrostatic bearings utilize high pressure oil, preferably in the range of 1,200-1,500 psi and provide good load bearing capacity and increased stiffness for improved cutting accuracy when cutting within the full range of cutting speeds. The present spindle unit is designed to be run at high speeds. The front and rear hydrostatic bearing pads are closely axially spaced along the spindle shaft so that the dynamic stiffness of the spindle is increased to avoid resonant vibrations even at high speed operation thereof. The spindle unit incorporates a sealing system utilizing a series of non-contacting seals including a labyrinth seal and aerostatic floating ring seals which keeps bearing oil in the spindle. The aerostatic ring seals have air restrictor openings therein to create an aerostatic air film that also keeps the rings concentric with the spindle shaft even though the spindle shaft is tilted in a nutator. A permanent magnet (PM) motor is integrated with the spindle with the rotor of the motor on the spindle shaft carrying the permanent magnets rotating within the stator of the motor which is attached in the spindle housing. The PM motor herein can provide high levels of power, e.g., at least 100 hp at the tool head, even in the short span provided by the short spindle shaft. At high speeds the bearing fluid may be pumped by viscous pumping from the radial bearing pockets. To counter such viscous pumping, small low pressure pockets are provided with low pressure oil to fill the high pressure pockets with oil.