Ultrathin-walled rolling bearing

Details Ultrathin-walled rolling bearing Ultrathin-walled rolling bearing

2001-09-05

2003-04-01

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S516000, C384S517000, C384S537000

Reexamination Certificate

active

06540405

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrathin-walled rolling bearing used in industrial robots, machine tools, medical instruments, etc.
2. Prior Art
FIG. 6
shows an example of a CT scanner, which is a kind of medical instrument. As shown, the CT scanner device is so designed that X-rays generated by an X-ray tube assembly
50
are radiated to a subject
53
through a wedge filter
51
for uniformizing intensity distribution and through a slit
52
for restricting intensity distribution. The X-rays passing through the subject
53
is received by a detector
54
, converted into electric signals, which are sent to an unillustrated computer. Such parts as the X-ray tube assembly
50
, wedge filter
51
, slit
52
, and detector
54
are mounted on a substantially cylindrical rotatable block
57
rotatably supported through a rolling bearing
55
, and the rotary driving of said rotatable block
57
causes rotation of the parts around the subject
53
. In the CT scanner device, the rotary movement of the X-ray tube assembly
50
. and detector
54
opposed thereto around the subject
53
provides projection data covering all angles at every point in the inspection cross-section of the subject
53
, and a tomogram is obtained from these data through a reconstructive program prepared in advance.
In this CT scanner device, the inner peripheral surface of a stationary block
56
disposed inside the rotatable block
57
is formed to have a sufficiently large diameter (about 1 m in diameter). to receive the subject
53
, so that a so-called ultrathin-walled roller bearing, which is very small in cross-section for its diameter, is used as the bearing
55
disposed between the stationary block
56
and the rotatable block
57
.
Heretofore, the four-point contact ball bearing, which is capable of supporting a high-moment load acting in opposite directions by using a single bearing and which saves space, has been mainly used as the rolling bearing
55
particularly of the low speed rotation type (about 60-90 rpm) for this CT scanner device. Conventionally, for the sake of assembly, the internal clearances for four-point contact ball bearings are set at 0 or above, of which clearances, the radial internal clearance, for example, is set often in the range of 0.005-0.050 mm in consideration of machining error, etc.
In recent CT scanner devices, further reduction of vibration and improvements in acoustic characteristics are desired from the standpoints of lightening patient's burden, improving radiographic accuracy, etc. With the conventional construction, however, these desires cannot be fully met and further improvements are desired.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to achieve reduction of vibration and improvements in acoustic characteristics of ultrathin-walled rolling bearings, at low cost.
To achieve said object, the invention provides an ultrathin-walled rolling bearing including an outer member having a raceway surface in the inner periphery, an inner member having a raceway surface in the outer periphery, a plurality of rolling elements interposed between the raceway surfaces of the outer and inner members, and a cage for holding the rolling elements in circumferentially equispaced relationship, wherein the ratio of the diameter of the rolling elements to the pitch circle diameter of the bearing is not more than 0.03, the rolling elements are arranged in a single row, being in two-point contact with each of the raceway surfaces of the outer and, inner members, and the internal clearances of the bearing are made negative.
This bearing is a so-called four-point contact rolling bearing, and in this type of bearings, when the internal clearances are made negative, play between the rolling elements disappears. Therefore, the bearing rigidity improves and reduction of noise and vibration due to play between the balls is achieved.
In this case, if one of the inner and outer members is fixed to the rotatable block of a CT scanner device rotating around a subject and the other to the stationary block thereof, then reduction of patient' burden which is brought about by reduction of noise and vibration of said rolling bearing, and improved radiographic accuracy can be achieved.
By constituting one of the inner and outer members by first and second raceway members opposed to each other on the opposite sides of the axial clearance, and adjusting the width of the axial clearance, the internal clearances of the bearing can be made negative by simple means and at low cost. The adjustment of the width of the axial clearance is made by axially relatively moving the first and second raceway members.
Further, by eliminating the difference in the amount of thermal expansion after the rolling element have been installed between the inner and outer members which differ in the amount of thermal expansion, the internal clearances of the bearing can also be made negative by simple means and at low cost.


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