Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2003-12-22
2004-12-28
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C277S547000
Reexamination Certificate
active
06835000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrathin-walled rolling bearing used, for example, in industrial robots, machine tools, medical instruments, and the like, and it also relates to a cage incorporated in such bearings.
2. Description of the Prior Art
FIG. 14
shows an example of a CT scanner device that is a kind of medical instrument. As shown in the same figure, in the CT scanner device, X-rays produced by an X-ray tube device
1
are radiated to a subject
4
through a wedge filter
2
for uniformizing their intensity distribution and a slit
3
for restricting said intensity distribution. The X-rays passing through the subject
4
are received by a detector
5
, where they are converted into an electric signal, which is then fed to an unillustrated computer.
Such parts as the X-ray tube device
1
, wedge filter
2
, slit
3
, and detector
5
in this CT scanner device are mounted on a substantially cylindrical rotary frame
8
rotatably supported on a fixed frame
7
through a bearing
6
, the rotary driving of said rotary frame
8
rotating the parts around the subject
4
. In the CT scanner device, the rotary motion of the mutually opposed X-ray tube device
1
and detector
5
around the subject
4
provides the projection data covering all angles in the examination cross-section of the subject
4
, and a tomographic image is obtained from a reconstructed program programmed in advance from these data.
In the CT scanner device, since the inner periphery of the fixed frame
7
is formed with a large diameter (about 1 m) to receive the subject
4
, a bearing that is very small in cross-sectional area for its diameter, or a so-called ultrathin-walled rolling bearing is used as the bearing
6
between the fixed and rotary frames
7
and
8
.
In the prior art, for ultrathin-walled rolling bearings used in CT scanner devices, split type cages are frequently used. Such type of cage
11
is of split construction, as shown in
FIGS. 15 and 17
, having a plurality of arcuate segments
12
annularly formed by being circumferentially joined together. In the prior art, as shown in FIGS.
17
(
a
) and (
b
) and
18
(
a
) and (
b
), each segment
12
is formed at its opposite ends with projection-shaped or recess-shaped fitting sections
13
and
14
, and such projection-shaped or recess-shaped fitting sections
13
and
14
are assembled, by fitting, to the recess-shaped or projection-shaped fitting sections
14
and
13
at the ends of the mating segment (see FIG.
19
). That is, as shown in
FIG. 20
, one (for example, projection-shaped) fitting section
13
of the segment
12
is radially pushed into the recess-shaped fitting section
14
of the mating segment
12
, whereby they are circumferentially engaged with each other to form a cage
11
(see, for example, Japanese Unexamined Patent Publications 2001-304266 (paragraph no. 0018, and
FIGS. 2 and 3
) and 2002-81442 (paragraph no. 0016, and FIGS.
3
and
4
). Each segment
12
is formed with a pocket
15
for receiving a ball.
In this connection, in the prior art, a proper interference is imparted to the fitting sections
13
and
14
of the segments
12
constituting the cage
11
and the mating segments
12
are joined, thereby forming an annular cage
11
. The segments
12
forming this cage
11
are generally injection moldings of resin, with the result that molding errors or the like causes the interference between the fitting sections to increase in some cases or decrease in other cases, sometimes resulting in rattling produced between the fitting sections
13
and
14
.
If the interference between the fitting sections
13
and
14
of the segments
12
increases as described above, the two fitting sections
13
and
14
tend to easily interfere with each other when one fitting section
13
is radially pushed into the mating fitting section
14
, so that smooth fitting of the two fitting sections
13
and
14
becomes difficult and the operating efficiency greatly lowers.
Reversely, if the interference between the fitting sections
13
and
14
of the segments
12
decreases to produce rattling, the cage
11
tends to easily change in shape from a right circle to a polygon, producing a radially inward or outward deviation between the adjacent segments
12
, the deviated segment
12
coming into contact with the raceway surface of the inner or outer member, generating abnormal sounds such as hammering sounds or vibrating sounds, and causing a rise in bearing torque.
Particularly in the CT scanner device, abnormal sounds of this type are likely to induce a stress in the subject
4
, making it strongly desired to lower the abnormal sound generating level Further, in the case where the rolling elements in the cage
11
are balls, a decrease in the clearance between the pocket
15
and the balls due to contraction deformation of the pocket
15
tends to restrain the balls in the pockets
15
, resulting in an increase in the bearing torque.
SUMMARY OF THE INVENTION
The present invention has for its object the provision of a cage adapted to suppress rattling in fitted-together segments and to improve operating efficiency in joining segments, and an ultrathin-walled rolling bearing having such cage.
The invention provides a cage composed of a plurality of arcuate segments, wherein the joining projection formed in the bonding section of one of adjacent segments is fitted in a joining recess formed in the bonding section of the other segment to thereby annularly bond the segments, said cage being characterized in that said joining projections and joining recesses have a tapered fitting surface, for example, a conical surface, as seen in a radial section, and joining is effected by closely contacting the two fitting surfaces. In addition, the radial dimension of the jointing projections and joining recesses may be made smaller than the radial dimension of the segments. Here, the above-mentioned “radial” means radial with respect to a circle defined by the segments when annularly bonded together.
In the cage of the invention, fitting the bonding sections of the segments along the radially tapered fitting surfaces, for example, conical surfaces, allows a change in interference between the joining projections and recesses due to molding errors or the like to escape radially of the cage in the fitting surfaces, so that rattling in the fitted state can be suppressed to realize a stabilized fitted state. Therefore, the function of the cage can be maintained stabilized for a long time, and the generation of abnormal sounds due to contact between radially deviated segments and the raceway surfaces of the inner and outer members can be reliably prevented. Assembly of the cage can be easily effected, efficient assembly being possible. It is desired that the segments constituting the cage of the invention be made of resin, such as PPS (polyphenylene sulfide).
In the above arrangement, the butt surface of the bonding section of one of adjacent segments is formed with a projecting engaging section while the butt surface of the bonding section of the other segment is formed with a recessed engaging section, and the two butt surfaces butt against each other; thus radial positional deviation of the cage can be reliably prevented by controlling the radial position of the segments; this serves as a slip-off prevention means.
A cage which is a target of the invention is annularly formed by circumferentially bonding a plurality of segments, has pockets for receiving rolling elements at circumferentially equispaced intervals, and is suitable for use in an ultrathin-walled rolling bearing whose ratio of the diameter of said rolling elements to the pitch circle diameter of the bearing is not more than 0.03.
The cage of said arrangement is adapted to constitute an ultrathin-walled rolling bearing by combining an outer member having a raceway surface in its inner periphery, an inner member having a raceway surface in its outer-periphery, and a plurality of rolling elements interposed between the racew
Hiramatsu Kengo
Tanimaru Takeshi
Arent Fox
Footland Lenard A.
NTN Corporation
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