To surely restrain the generation of an air hammer caused by the compressibility of air.
A spindle 14 is rotatably supported to a housing 12 via porous air bearings 26-29. The spindle 14 is connected to a motor rotary shaft 44 of an electric motor 38. The housing 12 has air passages 30-33 exhausting air introduced from an air supply port 34 from an exhaust port 36 via the porous air bearings 26-29. The porous air bearings 26 and 27 are constituted as radial berings. The porous air bearings 28 and 29 are constituted as thrust bearings. A flange 16 of the spindle 12 has pockets 50 and 51 introducing and storing air flowing in a bearing clearance and air passing through the porous air bearings 28 and 29, an air exhaust passage 52 introducing air stored in the pockets 50 and 51 to the outside of the bearings, and orifices 54 and 55 adjusting flow rates of air passing through the air exhaust passage 52.
TAKAHASHI ATSUSHI
KOBAYASHI NAOYA
Katsuro Tanaka
Shinji Oga
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