Ultrathin walled rolling bearing

Details Ultrathin walled rolling bearing Ultrathin walled rolling bearing

2001-04-24

2002-10-15

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S523000

Reexamination Certificate

active

06464397

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrathin walled rolling bearing for use in industrial robots, machine tools, medical equipment, and the like.
FIG. 5
illustrates an example of a CT scanner, a kind of medical equipment. As shown in the figure, in this CT scanner, an X-ray beam generated by an X-ray tube unit
20
is radiated toward a subject
23
via a wedge filter
21
for making the X-ray intensity distribution uniform, and a slit
22
for controlling the intensity distribution. The x-ray beam having passed through the subject
23
is received by a detector
24
, is thereby converted into an electric signal, and is fed to a computer (not shown). The constituent components including the X-ray tube unit
20
, the wedge filter
21
, the slit
22
, and the detector
24
are attached via a bearing
25
to a rotary platform
27
of substantially cylindrical shape rotatably supported by a stationary platform
26
. As the rotary platform
27
is driven to rotate, these components are rotated about the subject
23
. In the CT scanner, by driving the X-ray tube unit
20
and the detector
24
opposed to each other to rotate about the subject
23
, projection data of the slice planes to be examined in multiple view directions around the subject
23
can be acquired. Then, by execution of an image reconstruction program configured beforehand based on the acquired projection data, a tomographic slice image is obtained.
In this CT scanner, the inner peripheral surface of the stationary platform
26
has a diameter large enough to permit the insertion of the subject
23
(a diameter of approximately 1 meter). Therefore, as the bearing portion
25
provided between the stationary platform
26
and the rotary platform
27
, a bearing having a significantly small cross section relative to its diameter, i.e., a so-called ultrathin walled rolling bearing is used. As shown in
FIG. 6
, the ultrathin walled rolling bearing
25
is composed of an outer member
1
′ having in its inner periphery a raceway surface
1
b
′, an inner member
2
′ having in its outer periphery a raceway surface
2
b
′, a plurality of rolling elements
3
′ (balls are used in the illustrated example) interposed between the raceway surfaces
2
b
′ and
1
b
′ of the inner and outer members
2
′ and
1
′, and a cage
4
′ for circumferentially equally spacing the rolling elements
3
′.
Among ultrathin walled rolling bearings, such a large-diameter bearing as has a pitch circle diameter (PCD) greater than 500 mm has its cage
4
′ formed in a ring-like shape by joining together, for example, brass-based metal plates (segments) each having a circular section by welding. Each segment has a pocket for accommodating the rolling element
3
′. This allows the rolling elements
3
′ to be held circumferentially equidistantly. Between the pocket of the cage
4
′ and the surface of the rolling element
3
′ is formed a cage pocket clearance so as to provide flexibility in the mutual movement between them.
In a small-sized bearing, neither the inner peripheral surface nor the outer peripheral surface of the cage makes contact with the inner or outer member. That is, the cage is guided in rotation by the rolling element alone. On the other hand, in a large-diameter ultrathin walled rolling bearing as described above, the cage
4
′ is guided in rotation by bringing the inner peripheral surface of the cage
4
′ into contact with the outer peripheral surface of the inner member
2
′, or bringing the outer peripheral surface of the cage
4
′ into contact with the inner peripheral surface of the outer member
1
′. In this case, the core deviation between the center of rotation of the bearing and that of the cage becomes unduly great. This increases the whirling movement of the cage, which may result in noise.
Moreover, depending upon the state of the inner or outer member and the cage in contact, an undesirable increase in the noise level may possibly occur.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce the noise level of an ultrathin walled rolling bearing and improve the sound characteristics thereof.
To achieve the above object, according to the present invention, an ultrathin walled rolling bearing is provided with an outer member having in its inner periphery a raceway surface, an inner member having in its outer periphery a raceway surface, a plurality of rolling elements interposed between the raceway surfaces of the outer and inner members, and a cage for circumferentially equi-spacing the rolling elements. In this construction, the ratio of the diameter of the rolling element to the pitch circle diameter of the bearing is equal to or less than 0.03, and a ratio L/M falls within a range from 0.8 to 0.95 in which L is a radial thickness of the cage, and M is a radius difference between an inner peripheral surface of the outer member and an outer peripheral surface of the inner member.
Here, the range of the L/M value is wider than in conventional constructions. Accordingly, as compared with the conventional constructions, the radial movement of the cage
4
is restricted properly. This allows the center of rotation of the cage to come close to that of the bearing, and thereby the amount of radial whirling movement of the cage
4
is reduced. Consequently, occurrence of noise due to the whirling movement of the cage can be successfully prevented.
It is preferable that the ratio L/DB of the radial thickness L of the cage to the diameter DB of the rolling element be set to a range of 0.4 to 0.5.
Either or both of the inner and outer peripheral surfaces of the cage may have a lubricant storage portion formed thereon. The lubricant collected on this storage portion allows a sufficient supply of oil to the contact-making portions between the cage and the inner or outer member. Consequently, occurrence of noise due to the friction between the cage and the component making contact therewith can be successfully prevented.
The cage may be made of resin and is thus lighter in weight as compared to a metal-made construction. This makes further reduction in the noise level possible.
Of the outer and inner members, one may be fixed to a rotary platform of a CT scanner rotating about a subject, and the other may be fixed to a stationary platform of the CT scanner. This allows the rotary platform of the CT scanner to be rotatably supported with respect to the stationary platform.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.


REFERENCES:
patent: 3647268 (1972-03-01), Haines
patent: 5540575 (1996-07-01), Takano et al.
patent: 5860749 (1999-01-01), Hirakawa et al.

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