Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
1999-06-14
2001-09-04
Lorence, Richard M. (Department: 3681)
Machine element or mechanism
Gearing
Directly cooperating gears
Reexamination Certificate
active
06282971
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a ball screw particularly having a structure capable of circulating balls rolling in a loaded rolling passage formed between a screw shaft and a nut member by a return pipe fitted to the nut member.
One known example of such a ball screw is composed of a screw shaft to which a ball rolling groove is formed and a nut member to which a loaded ball rolling groove corresponding to the ball rolling groove formed to the screw shaft. These ball rolling groove and loaded ball rolling groove constitute, in combination, a loaded ball rolling passage in which balls are rolled. One and other ends of the loaded ball rolling passage are connected by a return pipe fitted to the nut member in a manner such that the ball rolling in the loaded ball rolling passage is scooped at the one end thereof by the return pipe and returned to the loaded ball rolling passage at the other end thereof. The ball screw having the above structure is shown, for example, in Japanese Utility Model Laid-open (KOKAI) Publication No. HEI 6-69502.
FIG. 9
shows one known example of the return pipe
1
having both opened ends, to which a pair of tongue pieces
2
a
,
2
b
are formed to be fittable into the loaded ball rolling passage. The balls, which have rolled in the loaded ball rolling passage formed to the periphery of the screw shaft, collide with the tongue pieces
2
a
,
2
b
and then are scooped thereby so as to be introduced into the return pipe
1
. The balls thereafter circulate through the return pipe
1
and then again return to the loaded ball rolling passage. Notches or cutouts
3
are also formed near the tongue pieces
2
a
,
2
b
at both the opened ends of the return pipe
1
for preventing the balls from interfering with the ball rolling groove formed to the screw shaft.
However, in recent years, it has been required to carry out a high feed operation of a machine tool or the like mechanism, and hence, to render the ball screw rotate ABL at a high rotating speed. In a case where the ball screw is used with an increased D/N value (which is a value obtained by multiplying a rotating number per one minute of the screw shaft by a rotating diameter of the ball), there are fears such that stress concentration will be liable to occur on root portions of the tongue pieces
2
a
,
2
b
due to repeated collision of the balls, which results in metal fatigue at these root portions, which are hence damaged.
SUMMARY OF THE INVENTION
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a ball screw capable of effectively scooping the balls without forming any specific ball scooping means such as tongue pieces to a return pipe.
This and other objects can be achieved according to the present invention by providing a ball screw comprising:
a screw shaft formed, on an outer peripheral surface thereof, with a spiral ball rolling groove;
a nut member having an inner peripheral surface on which a spiral loaded ball rolling groove corresponding to the spiral ball rolling groove of the screw shaft is formed, both the spiral grooves constituting a loaded ball rolling passage in combination when the screw shaft is fitted to the nut member;
a number of balls rolling in the loaded ball rolling passage; and
at least one return pipe having one end connected to one end of the loaded ball rolling passage and another end connected to another end of the loaded ball rolling passage so as to scoop the balls rolling in the loaded ball rolling passage at the one end of the return pipe and return the balls to the loaded ball rolling passage at the another one end of the return pipe, the return pipe having both end portions to which cutouts, each having a width gradually reduced, are formed.
In a preferred embodiment, the return pipe is disposed so that both the end portions thereof accord with a lead angle of the screw shaft. The return pipe is disposed so that both the end portions thereof are directed to a direction tangential to a track of the balls.
The width of the cutout is gradually reduced from the end portion of the return pipe towards the inside thereof.
The return pipe is formed with a pair of guide grooves to the inner surface so as to extend along the axial direction thereof.
According to the present invention of the characters mentioned above, since the cutouts are formed to both the ends of the return pipe so that the width of each cutout is gradually reduced, the balls rolling in the loaded ball rolling passage can be guided by both the sides of the cutout. And the balls guided by both the sides of the cutout are gradually led into the inside of the return pipe. According to this structure, the balls can be scooped smoothly without forming any specific portion for scooping the balls such as tongue pieces as in the conventional structure.
According to the preferred embodiment of the present invention, since both the ends of the return pipe are arranged so as to accord with the lead angle of the screw shaft, the balls can be scooped with the lead angle direction, i.e. ball advancing direction being maintained. It is therefore possible to prevent the strong impact from being applied to the return pipe when the balls are led into the return pipe. The maintenance of the ball advancing direction permits to carry out the smooth scoop of the balls without the balls being displaced to one side of the cutout, and the balls are smoothly scooped in a balanced condition.
Furthermore, since the balls can be scooped by the return pipe in the tangential direction, the balls can be smoothly scooped, thus also reducing the collision impact force to the return pipe.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.
REFERENCES:
patent: 2780943 (1957-02-01), Stump
patent: 4604911 (1986-08-01), Teramachi
patent: 5063809 (1991-11-01), Schlenker
patent: 5303607 (1994-04-01), Katahira
patent: 6089117 (2000-07-01), Ebina et al.
patent: 0857883A1 (1998-08-01), None
patent: 63-001852 (1988-01-01), None
patent: 5-27408 (1993-04-01), None
patent: WO98/12442 (1998-03-01), None
Ebina Shigeru
Shirai Takeki
Takeda Ryuji
Lorence Richard M.
THK Co. Ltd.
Young & Thompson
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