Patent ID: 7278332

Claim:
A linear motion device comprising: a linear motion body externally fitted onto a shaft and making a relative linear motion along the shaft; a plurality of balls retained in a rolling element groove formed in an inner surface of the linear motion body, and rolling between the rolling element groove and the shaft; a circulating path formed in the linear motion body and for circulating the balls from one end side of the rolling element groove to the other end side thereof; and separators interposed among the balls; wherein each of the separators has contact surfaces each contacting with the ball and having a concave surface like an offset Gothic arch, a ratio f p =r p /D w of a curvature radius r p of the concave surface to a ball diameter D w is in a range of from 0.53 to 0.67, a ratio Γ=A p /D w of an offset A p of the Gothic arch to the ball diameter D w is in a range of from 3.486×10 −1 f p −1.743×10 −1 to 3.390f p −1.700, and a ratio θ=d/D w of an outer diameter d of the separator to the ball diameter D w is in a range of from 0.65 to 0.85, or each of the separator has concave surfaces each contacting with the ball, the concave surface being a conical surface shape with an apex angle α of 64° to 140°, and a ratio θ=d/D w of an outer diameter d of the separator to the ball diameter D w is in a range of from 0.65 to 0.85; wherein the linear motion device is charged with grease containing base oil and thickener, the base oil being 50-500 mm 2 /s in kinematic viscosity at 40° C., the thickener being contained at 3-40% by mass with respect to whole mass of the grease so that worked penetration defined by JIS K2220 is 220-395.