Lubrication – Lubricators – Liquefiers
Reexamination Certificate
1998-06-25
2001-04-17
Fenstermacher, David (Department: 3682)
Lubrication
Lubricators
Liquefiers
C074S089100, C074S424830, C074S459500
Reexamination Certificate
active
06216821
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a lubricating apparatus for a ball screw, and more particularly to a lubricating thread capable of supplying a lubricant to a ball screw for a long time.
A ball screw is a mechanism for converting rotational motion into linear motion. In the ball screw, a plurality of balls are interposed between a screw shaft having a thread groove on an outer periphery thereof and a ball nut having a thread groove on an inner periphery thereof opposed to the screw shaft thread groove. The ball nut is moved axially by rotating the screw shaft.
A lubricant such as a grease is normally applied to a portion between the thread groove and the ball, thereby preventing the thread groove and the ball from abrading and heating because of the friction between the thread groove and the ball. However, the effectiveness of the grease in reducing the friction is quickly diminished by such factors as temperature, moisture, foreign material and abrasion, such that it is necessary to periodically add additional lubricant. Therefore, apparatuses for supplying additional lubricant have been designed.
However, such supplying apparatuses are typically expensive. Moreover, because it is necessary to provide a piping for supplying oil to the apparatus, additional costs are incurred. Further, these apparatuses are inconvenient in that it is necessary to inspect and maintain the supplying apparatus.
By comparison, it has also been suggested to dispose a polymer member containing a lubricant between the screw shaft of the ball screw and the ball nut. The polymer member is designed so that the lubricant gradually oozes out of the polymer member over a long period of time. Thus, the thread groove and the ball remain lubricated as a consequence of the lubricant oozing out of the polymer member containing the lubricant even after the lubricating function of the grease initially applied to the thread groove is diminished. Accordingly, such a device is substantially maintenance-free.
There are still problems with using the polymer member described above. By way of illustration,
FIG. 15
is a cross sectional view which shows a ball screw using a polymer member containing a lubricant as described above. In
FIG. 15
, a cylindrical ball nut
2
is disposed around a screw shaft
1
. A polymer member
10
containing a lubricant is disposed between an inner peripheral surface
5
a
of an annular recess portion
5
formed on an end surface of the ball nut and an outer peripheral surface of the screw shaft
1
. The polymer member
10
acts as a seal to seal grease within the ball nut
2
.
A garter spring
15
is fitted into an outer peripheral surface lob of the polymer member
10
. With the garter spring
15
radially pressing the polymer member
10
into the thread groove
1
b
of the screw shaft
1
at a fixed pressure, suitable contact with the screw shaft
1
is maintained and good lubrication is maintained even when the inner peripheral surface of the polymer member
10
is abraded.
FIG. 16
is a cross sectional view of the ball screw of
FIG. 15
taken along a line XVI—XVI.
FIG. 17
is an enlarged cross sectional view of the ball screw of
FIG. 15
taken along a line XVII—XVII.
In
FIG. 16
, the polymer member
10
includes an upper half portion
10
c
and a lower half portion
10
d,
each formed in a substantially half cylindrical shape. In the upper half portion
10
c
and the lower half portion
10
d,
all of the inner peripheral portions are in close contact with the outer peripheral portion of the screw shaft
1
. A gap A is formed between the upper half portion
10
c
and the lower half portion
10
d.
Comparing
FIG. 16
with
FIG. 15
, it will be recognized that a convex portion
10
a
of the polymer member
10
is disposed in such a manner as to be in close contact with the outer peripheral portion of the thread groove
1
b
of the screw shaft
1
. As shown in
FIGS. 16 and 17
, when the convex portion
10
a
of the polymer member
10
is in close contact with the thread groove
1
b
and the screw shaft
1
oscillates relative to the cylindrical ball nut
2
, the lubricant attached to an inner portion of the thread groove
1
b
is scraped out to the stroke end of the screw shaft
1
by a sliding convex portion
10
a
of the polymer member
10
. In fact, as shown in
FIG. 16
, when an end portion (a portion facing to the gap A) of the convex portion
10
a
comes in close contact with the thread groove
1
b
without any gap, there occurs a so-called scraper effect, that is, the end portion scrapes out the lubricant attached to the thread groove
1
b
to the gap A. The lubricant scraped out to the gap A is hardly used for lubricating.
Thus, the amount of the lubricant essentially supplied to the thread groove is decreased because of the shape of the polymer member
10
containing the lubricant. In an application wherein the ball screw supports a large load, not enough lubricant will remain to lubricate the ball screw, such that there is a risk of abnormal abrasion and early breakage of the thread groove and the ball.
SUMMARY OF THE INVENTION
The present invention is made by taking the conventional problems into consideration, and an object of the invention is to provide a lubricating apparatus for a ball screw which can sufficiently lubricate the ball screw even when large loads are supported.
The above-mentioned object can be attained through the use of a lubricating apparatus for a ball screw according to the present invention, wherein a polymer member containing a lubricant is disposed between a ball nut and a screw shaft such that the polymer member is mainly in slidable contact with an outer diameter portion of the screw shaft and is mounted to at least any one of both ends of the ball nut and a space including a ball not-passing space in an inner portion of the ball nut. Accordingly, the polymer member does not scrape off the lubricant attached to the thread groove when the screw shaft oscillates relative to the cylindrical ball nut, such that the lubricant attached to the thread groove can be effectively maintained.
In addition, in accordance with the present invention, the above-mentioned object can also be achieved through the use of a lubricating apparatus for a ball screw in which a polymer member containing a lubricant is disposed between a ball nut and a screw shaft such that the polymer member is in slidable contact with only an outer diameter portion of the screw shaft and is mounted to at least any one of both ends of the ball nut and a space including a ball not-passing space in an inner portion of the ball nut. Accordingly, the polymer member does not scrape off the lubricant attached to the thread groove when the screw shaft oscillates relative to the cylindrical ball nut, such that the lubricant attached to the thread groove can be effectively maintained.
Further, in accordance with the present invention, the above-mentioned object can also be achieved through the use of a lubricating apparatus for a ball screw including a polymer member containing a lubricant which is disposed between a ball nut and a screw shaft such that the polymer member is slidably contactable with an outer diameter portion of the screw shaft and is mounted to at least any one of both ends of the ball nut and a space including a ball not-passing space in an inner portion of the ball nut, the polymer member being partially engaged with a portion of the surface of thread groove formed on the screw shaft adjacent to the outer diameter portion of the screw shaft but disengaged from the bottom surface of the thread groove.
Further, in combination with any of the foregoing, the polymer member is preferably separated into a plurality of sections in a circumferential direction, or a slit is provided along a radial direction, so that an inner diameter size thereof is made larger than an outer diameter of the screw shaft. The gap thus formed between the outer diameter portion of the screw shaft and the polymer member containing the lubricant further enhances the retention o
Ideta Osamu
Miyaguchi Kazuo
Namimatsu Ken
Yabe Toshikazu
Fenstermacher David
Marshall O'Toole Gerstein Murray & Borun
NSK Ltd.
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