Ultra thin type rolling bearing and cage therefor

Details Ultra thin type rolling bearing and cage therefor Ultra thin type rolling bearing and cage therefor

2000-05-19

2002-04-09

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S504000, C384S506000, C384S537000

Reexamination Certificate

active

06367980

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an ultra thin type rolling bearing for use in an industrial robot, a machine tool, medical equipment or the like and a cage for such a rolling bearing.
FIG. 8
shows a CT scanner, an example of one kind of medical equipment. As shown, in the CT scanner, an X ray generated by an X ray tube assembly
20
is directed upon an object
23
through a wedge filter
21
to equalize the intensity distribution and a slit
22
to restrict the intensity distribution. The X ray passed through the object
23
is received by a detector
24
, converted into an electrical signal and transferred to a computer which is not shown. Elements such as the X ray tube assembly
20
, wedge filter
21
, slit
22
and detector
24
are mounted on an approximately cylindrical, rotary pedestal
27
supported rotatably around a stationary pedestal
26
through a bearing
25
, and driven to rotate by the rotary pedestal
27
around the object
23
. In the CT scanner, the rotating movement around the object
23
of the X ray tube assembly
20
and the detector
24
opposing to each other results in projection data covering all the angles at every point within a cross section of the object
23
to be examined, and a cross sectional image is obtained based on these pieces of data using a pre-programmed reconstruction program.
In the CT scanner, the inner circumferential surface of the stationary pedestal
26
has a large opening to let the object
23
therein (approximately 1 m in diameter), and therefore a so-called ultra thin type rolling bearing having a cross section significantly small relative to the diameter is used for the bearing portion
25
between stationary pedestal
26
and rotary pedestal
27
. Among such ultra thin type rolling bearings, a so-called combination angular contact ball bearing formed by combining two angular contact ball bearings X and Y as shown in
FIG. 9
is used, particularly when such a bearing is used at a high rotating speed of about 120 rpm or higher. The combination angular contact ball bearing as shown is a so-called back-to-back arrangement having the two angular contact ball bearings X and Y with their back faces (faces which can receive the thrust load) in contact with each other, and pressurizing force is allowed to act upon in the direction in which the outer ring
31
(outer member) of one bearing X and the inner ring
32
(inner member) of the other bearing Y face each other, so that appropriate preload is applied to the inside of the bearings for use.
According to the conventional device, the outer annular body
33
is threadedly secured to one pedestal (the rotary pedestal
27
, for example), and inner annular body
34
is threadedly secured to the other pedestal (the stationary pedestal
26
, for example). Each outer rings
31
of the two bearings X and Y is engaged to the inner circumferential surface of the outer annular body
33
, while each inner ring
32
of the two bearings X and Y is engaged to the outer circumferential surface of the inner annular body
34
, so that the rotary pedestal
27
is rotatably supported. A presser member
36
is secured to each of one end side of inner annular body
34
and the other side of outer annular body
33
, using a fastening screw
35
, and the presser members
36
press the end surfaces of the outer ring
31
and inner ring
32
, and the end surfaces on the opposite side are received by shoulder portions
33
a
and
34
a
provided at the outer annular body
33
and inner annular body
34
, respectively, so that preload is applied to the inside of the bearings.
In the conventional ultra thin type rolling bearing for the CT scanner as described above, a cage
4
′ of resin is used. The resin cage
4
′ is of a separate type cage formed into an annular shape by connecting a plurality of segments
40
′ having a circular cross section as shown in FIG.
10
(
a
), and in the conventional device, recessed or raised engaging portion
44
a
′,
44
b
′ are formed at the ends of each segment
40
′ as described in FIG.
10
(
b
), and the recessed or raised engaging portion
44
a
′,
44
b
′ is engaged to raised or recessed engaging portion
44
b
′,
44
a
′ at the segment end to be coupled therewith, so that they are engaged with each other in the circumferential direction to couple each segment
40
′.
The conventional ultra thin type rolling bearing for the CT scanner is assembled with a large number of parts including the outer and inner annular bodies
33
and
34
, presser members
36
, in addition to the bearing parts such as the outer rings
31
and inner rings
32
as described above. Since such a large number of parts are necessary, the precision of each part would be added up to lower the entire precision, and therefore, strict precision control is demanded for each part. Furthermore, since the bearing portion is extremely thin, if the deviation from circular is even slightly deviated than allowed for the inner and outer annular bodies, the bearing ring bends along the shape, which adversely affects the performance of the bearing, and therefore the outer and inner rings should also be finished with high precision. As a result, the part and assembly cost for the conventional bearings has been increased and there is a strong demand for cost reduction.
Also in the conventional resin cage, segments are coupled with their recessed and raised engaging portions as described above, but the engagement between the recessed and raised engaging portions can be loose depending upon the formation error at the time of forming the resin. In this case, individual segments tend to shift toward the inner and outer diameter sides, which may cause oscillation when the rotating speed is increased. In order to solve this problem, the recessed and raised engaging portions should be formed with high precision but realizing this requires much work including correction of forming molds, which pushes up the cost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to reduce the number of parts and reduce the manufacturing cost as a result. Another object of the present invention is to securely and less costly prevent the coupling portions of a separate type cage from being shifted in the circumferential and radial directions.
In order to achieve the above-described objects, an ultra thin type rolling bearing according to the present invention includes an outer member having a double row raceway surface in which a rolling element rotates at its inner circumferential surface, an inner member provided on the inner circumferential side of the outer member, formed of an annular member and an engaging member engaged at the outer circumference of the annular member with an axial clearance with respect to the annular member, and provided with raceway surfaces in which rolling elements rotate at respective outer circumferential surfaces of the annular member and the engaging member, rolling elements inserted in two rows between the outer and inner members and having a diameter whose ratio relative to a pitch circle diameter is 0.03 or less, and a preloading means for pressurizing the engaging member to reduce the axial clearance for preloading.
Alternatively, the ultra thin type rolling bearing may include an outer member having a double row raceway surface in which a rolling element rotates at its inner circumferential surface, an inner member provided on the inner circumferential side of the outer member, formed of an annular member and a pair of engaging members engaged at the outer circumference of the annular member with an axial clearance therebetween, and provided with raceway surfaces in which rolling elements rotate at respective outer circumferential surfaces of both engaging members, rolling elements inserted in two rows between the outer and inner members and having a diameter whose ratio relative to a pitch circle diameter is 0.03 or less, and a preloading means for pressurizing one engaging member to re

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