Tsubaki Nakashima Co., Ltd.

Soichiro Ohga

Hidemi Horimoto

Hiroyuki Takagi

Hirouyki Takagi

A ball screw device utilizes spacers having concave ball-contacting surfaces with distributed protrusions or dimples. Balls having needle-like recesses may also be used. The spacers are provided in two thicknesses, and the relative numbers of the thinner and thicker spacers are selected in order to ensure retention of the spacers in their proper positions, while providing a small clearance between the balls and spacers to avoid fluctuations or sharp increases in dynamic torque.

Method for inserting balls and spacers into ball screw device

A ball screw comprising a screw shaft made of steel and having a thread groove on outer peripheral surface, a ball nut made of steel and having a thread groove opposing the thread groove on inner peripheral surface, a return tube attached on the ball nut and a plurality of balls inserted between the two thread grooves and and in the return tube As the balls, steel balls made of bearing steel and ceramic balls made of silicon nitride are disposed alternately at a given ratio. Diameter Dc of the ceramic ball is set to a value smaller than diameter Ds of the steel ball so that contact stress acted on contact surfaces of the ceramic ball and the two thread grooves and will be equal to contact stress acted on contact surfaces of the steel ball and the two thread grooves and

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Nara-ken, Japan

Soichiro Ohga