Lubrication – Slide-bearing lubrication
Reexamination Certificate
2001-11-02
2002-09-17
Kim, Chong H. (Department: 3682)
Lubrication
Slide-bearing lubrication
C074S089440, C074S424710, C384S013000, C277S446000, C277S496000
Reexamination Certificate
active
06450295
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a feed screw device of a ball screw, square thread, etc. Particularly, the invention relates to a feed screw device that can automatically supply a lubricant over a long term.
A conventional ball screw, a kind of feed screw device, is described in Japanese Utility Model Unexamined Publication Nos. Hei 7-4952 and 6-47762, etc., for example.
This kind of ball screw comprises a spiral thread groove
50
a
made in the outer peripheral surface of a screw shaft
50
threadably engaging a spiral thread groove
51
a
made in the inner peripheral surface of a nut member
51
via a plurality of balls
52
, as shown in
FIG. 1
, for converting relative rotation of the screw shaft
50
to the nut member
51
into relative displacement in an axial direction of the nut member
51
via the balls
52
.
An annular recess
53
is formed in both end parts of the inner diameter face of the nut member
51
(in
FIG. 1
, only the right end is shown), and a sealing member
54
is mounted on the recess
53
.
The sealing member
54
is made from plastic containing a lubricant into a ring shape, and a projection
54
a
that can be fitted into the thread groove
50
a
of the screw shaft
50
projects from the inner peripheral surface of the sealing member.
A ring-like garter spring
55
is inserted in the circumferential direction between the outer peripheral surface of the sealing member
54
and the recess
53
of the nut member
51
. The garter spring
55
clamps down all the outer peripheral surface of the sealing member
54
toward the outer peripheral surface of the screw shaft
50
, that is, the sealing member
54
is pressed in the inner diameter direction.
Further, a tapped hole
56
radially penetrating the circumferential wall of the nut member
51
is made in the position of the recess
53
in the nut member
51
and a set screw
57
is fitted into the tapped hole
56
, thereby fixing the sealing member
54
to the nut member
51
.
The garter spring
55
sets the gap between the inner peripheral surface of the sealing member
54
and the outer peripheral surface of the screw shaft
50
to zero or less for preventing the lubricant filled in the ball screw from leaking to the outside and a foreign material from entering the ball screw from the outside.
Further, the lubricant exuding from the sealing member
54
decreases frictional resistance of the slide portion between the inner peripheral surface of the sealing member
54
and the outer peripheral surface of the screw shaft
50
, namely, slide torque and at the same time, is supplied to the thread groove
50
a
of the screw shaft
50
, the balls
52
, and the thread groove
51
a
of the nut member
51
.
However, for the conventional feed screw device of the structure as described above, the garter spring
55
needs to be inserted between the outer periphery of the sealing member
54
and the recess
53
of the screw shaft
50
so that a dimension error of the sealing member
54
is absorbed and that the inner peripheral surface of the sealing member
54
comes in sliding contact with the outer peripheral surface of the screw shaft
50
; it is feared that the outer diameter of the feed screw device may grow as large as the garter spring.
In the conventional structure, the sealing member
54
is pressed diametrically, so that it is abutted against the outer peripheral surface of the screw shaft
50
, thus the spring needs to be disposed on all the outer periphery of the sealing member
54
in the circumferential direction.
The inner diameter portion on the opposite side (portion not pressed by the garter sprint) to the side pressed by the garter spring
55
of the sealing member
54
in the axial direction apts to float-up with respect to the outer peripheral surface of the screw shaft and it is feared that a sufficient lubricant will not be supplied from the portion.
Some conventional feed screw devices comprise a spring inserted between the tip of the set screw
57
and the sealing member
54
in place of the garter spring
55
. However, the lubricant supply section is also pressed only diametrically, thus it is feared that the inner peripheral surface of the sealing member
54
may be placed out of contact with the outer peripheral surface of the screw shaft
50
or that the portion pressed by the set screw in sliding contact with the screw shaft may be worn on one side in portions shifted 90 degrees from the placement position of the set screw
57
, etc., for example.
Even if hardware for suppressing jump out of the sealing member
54
from the recess
53
is attached to the nut member
51
, the tapped hole
56
needs to be made in the nut member
51
and fixed by the set screw
57
to prevent accompanying rotation of the screw shaft
50
of the sealing member
54
in addition to the hardware; workability is poor.
Further, when the sealing member
54
has a part cut (for example, the sealing member
54
is made into c-shaped) because of attachment thereof, the inner peripheral surface of the sealing member
54
does not come in sufficient contact with the screw shaft
50
and it is feared that a sufficient lubricant will not be supplied from the sealing member
54
depending on the operating condition.
Known as another ball screw, a kind of conventional feed screw device, is a device wherein a space
204
between a screw shaft
201
and a ball screw nut
202
threadably engaged into the screw shaft
201
via a large number of balls
203
is filled with grease or lubricant, as shown in FIG.
2
. The ball screw is of seal type wherein an annular recess
205
is made in an end of the ball screw nut
202
and a sealing member
206
is fitted into the annular recess
205
to prevent powder dust, etc., from entering into the ball screw nut
202
.
By the way, to lubricate such a conventional ball screw device, normally grease or lubricant is supplied from a grease nipple
207
attached to the ball screw nut
202
to a ball circulation passage for lubricating a rolling element.
However, particularly when the ball screw device adopting such a lubrication system directly using lubricant or grease is used in a high-temperature environment or a environment wherein wood chips, etc., easily absorbing lubricants are existed, the filled lubricant or grease flows out to the outside, is exhausted fast, and must be again supplied repeatedly for a short term. Japanese Utility Model Unexamined Publication No. Hei 7-4952 is known as application relating to an oil-containing polymer lubrication ball screw to improve this point.
For the oil-containing polymer lubrication ball screw disclosed here, a lubricant supply member mounted on a ball screw nut is formed of lubricant-containing rubber or synthetic resin and the lubricant continuously exuding from the lubricant supply member is automatically supplied to a rolling element lubrication passage of the ball screw nut.
However, with the ball screw, as the lubricant supply member containing the lubricant runs with the ball screw nut while coming in contact with the screw shaft, the lubricant exudes from the contact part for lubrication; lubricant supplied to a guide rail is easily absorbed particularly in an environment wherein foreign materials such as wood chips easily absorbing lubricant are existed, and the lubricant can also be absorbed from the lubricant-containing polymer member; resultantly, it is feared that a lubrication failure may be invited.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a feed screw device for enabling a lubricant-containing member to come in uniform contact with an outer peripheral surface of a screw shaft without enlarging the outer diameter of the feed screw device and in a simple structure.
According to the invention, there is provided a feed screw device comprising a screw shaft, a nut member threadably engaging an outer periphery of the screw shaft, and a lubricant supply device being fixed to the nut member, coming in contact with the outer peripheral surface of the screw shaft, and having a
Kato Soichiro
Tsukada Toru
Kim Chong H.
NSK Ltd.
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