| 摘要 |
PROBLEM TO BE SOLVED: To provide a means for reducing polar moment of inertia of a screw shaft of a ball screw device. SOLUTION: The screw shaft is provided with: a spiral shaft raceway groove formed in an outer circumference face; and a nut with a nut raceway groove confronting against the shaft raceway groove formed in an inner circumference face, wherein the shaft raceway groove and the nut raceway groove are screwed and fit via a plurality of balls and the nut is moved in a shaft direction of the screw shaft by rotating the screw shaft. A collection hole consisting of two or more shaft centers CL and a parallel long hole is provided between a shaft center CL of the screw shaft and a root diameter Db of a shaft raceway groove, and a rotation center of gravity of the collection hole is approximately aligned with the shaft center CL. COPYRIGHT: (C)2007,JPO&INPIT
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