Machine element or mechanism – Gearing – Teeth
Patent
1998-05-20
1999-11-23
Herrmann, Allan D.
Machine element or mechanism
Gearing
Teeth
744248R, F16H 2522
Patent
active
059880074
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL BACKGROUND
The present invention relates to a ball screw unit comprising a screw shaft and a nut fitted about the screw shaft through a number of balls and more particularly to such type of ball screw unit that is provided with a ball circulating structure including change paths at both ends of the nut, respectively.
BACKGROUND TECHNOLOGY
Conventionally, it has been usual that the above type of ball screw unit is provided with a helical ball rolling groove formed on the outer peripheral surface of the screw shaft and a spiral load rolling groove formed on the inner peripheral surface of the nut so as to lie face to face with the ball rolling groove, a ball return path extending through the nut in the axial direction and change direction paths arranged at both ends of the nut so as to establish communication between both ends of the load ball path and both ends of the ball return path whereby the screw shaft and the nut can move relative to each other when a number of balls circulate through an endless circulation path formed of the load ball path, the ball return path and the change direction paths.
When the screw shaft and the nut move relative to each other, each of the balls which have rolled through the load ball path while bearing a load between the screw shaft and the nut comes out from the load ball path but in order to guide the ball to the ball return path by receiving the ball in each of the change direction paths, it is necessary to separate the ball from within the ball rolling groove of the screw shaft up to the outer peripheral surface of the screw shaft.
Conventionally, as a structure for separating each of the balls from the ball rolling groove of the screw shaft, it has been general that a tongue piece is inserted into the ball rolling groove at a position corresponding to the ball separating position and the ball which has come to roll in the ball rolling groove is caused to creep on the tongue piece thereby picking up the ball.
With such a ball separating structure, it is ideal to pick up the ball in the tangential direction of the ball rolling groove but in that case, the thickness of the tip of the tongue piece can not but be reduced so that there has been a problem that the strength and durability of the tip of the tongue piece are not sufficient in view of an impact which would take place at the time when the high-speed rolling ball runs on the tongue piece. On the other hand, there has also arisen another problem that when the thickness of the tip of the tongue piece is made large in consideration of the strength and durability of the tongue piece, a level difference takes place between the ball rolling groove and the tongue piece and a great impact is applied on the tongue piece at the time the ball runs on the tongue piece so that not only the tongue piece deforms due to a successive use thereof but also a collision sound generates every time when the ball runs on the tongue piece.
Meanwhile, as a means for separating the ball from the ball rolling groove of the screw shaft without using the above-mentioned tongue piece, there has been proposed a method in which the progressing direction of the ball rolled out from the load ball path is somewhat displaced with respect to the ball rolling groove of the screw shaft, the ball is separated up to the outer peripheral surface of the screw shaft by making use of the inner peripheral surface of the screw shaft and then, the ball is separated up to the outer peripheral surface of the screw shaft thereby picking up the ball within each of the change direction path (see U.S. Pat. No. 4,148,226).
FIGS. 13 and 14 show a ball screw unit disclosed in the above-mentioned United States Patent. This ball screw unit comprises a screw shaft 101 having a helical ball rolling groove 102 formed on the outer peripheral surface thereof, a nut 104 having on the inner peripheral surface thereof a helical load rolling groove 107 opposing to the ball rolling groove 102 and a ball return path 106 formed along the axis of the screw shaft 101, a pa
REFERENCES:
patent: 477642 (1892-06-01), Brunthaver
patent: 2724284 (1955-11-01), Anderson et al.
patent: 4074585 (1978-02-01), Richaud et al.
patent: 4148226 (1979-04-01), Benton
patent: 5154091 (1992-10-01), Bianco
patent: 5279175 (1994-01-01), Kasuga et al.
Herrmann Allan D.
THK Co. Ltd.
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