JP2005003152A - Ultrathin wall rolling bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the starting torque of an ultrathin wall rolling bearing in which the value of the ratio of the diameter dB of a ball 3 to a pitch circle diameter PCD is 0.03 or less without shortening a rolling fatigue life. <P>SOLUTION: The curvature of an orbital trench is set 104 to 108% of the diameter dB of the ball at both outer ring 1 and inner ring 2. Even under conventional pre-loading condition, a required starting torque and a rolling fatigue life are satisfied, and a steady, highly rigid and low vibration ultrathin wall rolling bearing is obtained. <P>COPYRIGHT: (C)2005,JPO&amp;NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultra-thin type rolling bearing used in a medical device represented by a CT scanner device. Here, the ultra-thin type rolling bearing means an ultra-thin type large rolling bearing having an inner diameter of 650 mm or more and a ratio of a ball diameter to a pitch circle diameter of 0.03 or less.
[0002]
[Prior art]
FIG. 8 shows an example of a CT scanner device which is a kind of medical equipment. The CT scanner device irradiates the subject 23 with X-rays generated by the X-ray tube device 20 through a wedge filter 21 for uniforming the intensity distribution and a slit 22 for limiting the intensity distribution. X-rays that have passed through the subject 23 are received by the detector 24, converted into electrical signals, and sent to a computer (not shown). Each component such as the X-ray tube device 20, the wedge filter 21, the slit 22, and the detector 24 is mounted on a substantially cylindrical rotary mount 27 that is rotatably supported by a fixed mount 26 via a bearing 25. As the gantry 27 rotates, the periphery of the subject 23 rotates. The X-ray tube device 20 and the detector 24 facing each other rotate around the subject 23 to obtain projection data covering all angles of every point in the inspection section of the subject 23, and pre-programmed from these data A tomographic image is obtained by the reconstructed program.
[0003]
In this CT scanner device, the inner peripheral surface of the fixed gantry 26 is formed to have a large diameter (approximately 1 m in diameter) enough for the subject 23 to enter, so that the bearing 25 between the fixed gantry 26 and the rotary gantry 27 is provided. Uses a so-called ultra-thin type rolling bearing having a remarkably small cross section with respect to its diameter.
[0004]
[Patent Document 1]
JP 2000-329143 A (paragraph number 0002, FIG. 8)
[0005]
[Problems to be solved by the invention]
In medical equipment, care must be taken so as not to give anxiety or fear to the patient undergoing the examination. Especially in the case of a CT scanner device, the patient himself enters a part of the tunnel entrance called a gantry. The drive motors are used as small as possible because they are disliked from mechanical operation sounds and electrical excitation sounds, and are installed in limited spaces in hospital examination rooms. . As a result, the bearings are required to have low noise, low vibration, and low torque. Further, since the CT scanner device is a very expensive medical device, excellent durability is desired, and a long life is required for the bearing.
[0006]
In general, the cross section of the inner and outer raceway grooves of the ball bearing is finished in an arc shape having a slightly larger radius of curvature than the ball used. Since the bearing is a machine part that is mass-produced, this curvature is set to a constant curvature diameter that is most versatile in consideration of mass productivity.
[0007]
In combination angular contact ball bearings (rear array) used in the gantry section of the CT scanner device at a high speed of about 120 rpm or higher, an appropriate preload (minus clearance) is given to the bearing for the purpose of quietness, high rigidity, and low vibration. Alternatively, the clearance is set as small as possible. However, as the drive motor becomes smaller and lighter, it is necessary to reduce the starting torque. There are methods to reduce the starting torque, such as increasing the clearance or decreasing the curvature of the raceway groove (increasing the radius of curvature). There is a problem, and the latter has a problem that the contact surface pressure (Hertz pressure) between the ball and the raceway groove is increased and the rolling fatigue life is shortened.
[0008]
An object of the present invention is to reduce the starting torque of an ultra-thin type rolling bearing while satisfying these conflicting requirements. More specifically, the present invention aims to reduce the starting torque without reducing the rolling fatigue life.
[0009]
[Means for Solving the Problems]
The ultra-thin type rolling bearing of the present invention is an ultra-thin type large-sized rolling bearing having a ratio of the ball diameter to the pitch circle diameter of 0.03 or less, wherein the curvature diameter of the raceway groove is set to the inner ring, The outer ring is characterized by being 104% or more and 108% or less of the ball diameter. According to the present invention, there is provided an ultra-thin type rolling bearing that satisfies the required starting torque and rolling fatigue life even under conventional preload conditions (including small clearance conditions), is quiet, has high rigidity, and has low vibration. it can.
[0010]
As a bearing type, an angular ball bearing is preferable, and a combined angular ball bearing (back surface arrangement) suitable for receiving a moment load, or a double-row angular ball bearing having an outer ring having two rows of raceways is particularly preferable. The present invention can also be applied to a four-point contact ball bearing. In a CT scanner apparatus of about 120 rpm or less, a four-point contact ball bearing that is advantageous in terms of cost is generally used. However, four-point contact ball bearings are usually used with a larger clearance than a combination angular contact ball bearing (rear array) due to the problem of large heat generation when there are two rotating shafts as in this application. The Therefore, although it is disadvantageous in terms of sound, rigidity, and vibration with respect to the combined angular contact ball bearing (rear arrangement), there is no difference in that the torque is low and the required rolling fatigue life is satisfied.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all of the embodiments described below, the ultra-thin type rolling in which the value φ of the ball diameter dB to the pitch circle diameter PCD is 0.03 or less (φ = dB / PCD ≦ 0.03). This is a bearing and corresponds to the detailed structure of the bearing 25 in the above-described CT scanner apparatus shown in FIG.
First, the embodiment shown in FIG. 1 is a case of a so-called combination angular ball bearing in which two angular ball bearings X and Y are combined. This combination angular contact ball bearing is a so-called back surface arrangement in which the back surfaces of the outer rings of the two angular contact ball bearings X and Y are brought into contact with each other. This arrangement can apply a radial load and an axial load in both directions, and is suitable when a moment load is applied. The inner ring 32 of the bearing X, both balls, and the inner ring 32 of the bearing Y are applied to the inner ring 32 through the outer ring 31 so as to act on each other so as to apply an appropriate preload to the inside of the bearing.
[0012]
Here, the outer ring body 33 is screwed to the rotary frame 27 of the CT scanner apparatus shown in FIG. The outer rings 31 of X and Y are fitted into the inner rings 32 of the two bearings X and Y, respectively, on the outer peripheral surface of the inner ring body 34, so that the rotary base 27 is rotatably supported. Now, when the bearings X and Y are unloaded and both the outer rings 31 come into contact with each other on the back surface, the inner rings 32 do not come into contact with each other and a gap remains, so that one end side of the inner ring body 34 and the outer ring body remain. A pressing member 36 is fixed to the other end side of 33 by using a tightening screw 35. The pressing member 36 presses the end face of the outer ring 31 and the end face of the inner ring 32, and the opposite end face is pressed. Preload is applied to the inside of the bearing by receiving the shoulder portions 33a and 34a provided on the outer ring body 33 and the inner ring body 34.
[0013]
A plurality of balls are rollably interposed between the raceway grooves of the inner ring and the raceway of the outer ring, and these balls are held at predetermined intervals by a resin cage. As shown in FIG. 2A, the resin cage 4 is a split type (segment type) in which a plurality of arc-shaped segments 40 are connected in the circumferential direction to form an annular shape. As shown in FIG.2 (b), the concave fitting part 44a and the convex fitting part 44b are provided in the both ends of each segment 40, and the concave fitting part 44a (or one segment) of adjacent segments is provided. By fitting the convex fitting portion 44b) with the convex fitting portion 44b (or the concave fitting portion 44a) of the other segment, the segments 40 adjacent in the circumferential direction are connected to each other. ing.
[0014]
FIG. 3 is a plan view in which the segment 40 is developed. The segment 40 in the illustrated example is provided between a base portion 41 having an arc shape obtained by dividing an annular body at a plurality of locations in the circumferential direction, a column portion 42 extending from the base portion 41 in the axial direction, and an adjacent column portion 42. A plurality of pockets 43a, 43b. The column part 42 extends to one side in the axial direction beyond the pitch circle P of the balls. The pockets 43a and 43b in the illustrated example have two shapes, one of which is a first pocket 43a in which the wall surface on the pocket opening side from the pocket center is a concave arc surface in plan view, and the other is the wall surface in the axial direction. The second pocket 43b has a straight surface. The first pockets 43a and the second pockets 43b are alternately provided in the circumferential direction. The wall surfaces of both pockets 43a and 43b are concave curved surfaces having a curvature center at the pocket center. The balls are accommodated in the pockets 43a and 43b by pushing the balls from the axial openings of the pockets 43a and 43b toward the back of the pocket. At this time, in the first pocket 43a, it is necessary to push the ball while expanding the column part 42 on the inlet side, but in the second pocket 43b, such trouble is not required, so that the ball is incorporated into the cage 4. The process can be simplified. Note that the shapes and structures of the pockets 43a and 43b described above are merely examples, and pockets having various shapes and structures can be used according to the use conditions of the bearing, such as a single pocket.
[0015]
Next, the ultra-thin type rolling bearing of the embodiment shown in FIG. 4 is a case of a double-row angular ball bearing, and the ring-shaped outer ring 1 and the ring-shaped outer ring 1 are arranged concentrically on the inner peripheral side of the outer ring 1. The inner ring 2, the plurality of balls 3 interposed between the outer ring 1 and the inner ring 2, and the cage 4 that holds the balls 3 at a predetermined interval in the circumferential direction are main components, and further, both ends of the bearing are opened. Seals 5a and 5b for sealing the portion, and preload applying means S for applying a preload to the inside of the bearing. This bearing 25 is the same as the embodiment of FIG. 1 in that the balls 3 are arranged in two rows, but differs in that the outer ring 1 is an integral type, that is, a double row outer ring in which two rows of raceways are formed. The combination of both bearing parts is the same as the rear arrangement in the embodiment of FIG. 1, and the intersection of the rolling element load action lines Q is outside the pitch circle P. The contact angle (the angle formed by the rolling element load direction and the plane perpendicular to the center axis of the bearing) of both bearing portions is, for example, 30 °.
[0016]
The outer ring 1 has a structure in which the outer ring 31 and the outer ring body 33 in the embodiment of FIG. 1 are integrated, and the raceway groove 1c on which the ball 3 rolls corresponds to the number of rows of the balls 3 on the inner peripheral surface thereof. And formed in a double row. The inner ring 2 includes an annular member 2a having a structure in which one inner ring 32 and an inner ring body 34 in the embodiment of FIG. 1 are integrated, and a ring-shaped fitting member 2b fitted to the outer periphery of the annular member 2a. Composed. On the outer peripheral surface of one end of the annular member 2a, there is a step portion 2a1 having a smaller diameter than the other portion, and a fitting member 2b is fitted to the step portion 2a1. A raceway groove 2c is formed on each of the outer peripheral surfaces of the annular member 2a and the fitting member 2b, and the balls 3 can freely roll between the two raceway grooves 2c and the double row raceway grooves 1c of the outer ring 1. Is intervening.
[0017]
The preload applying means S applies an appropriate preload to the inside of the bearing by pressurizing the fitting member 2b toward the inside of the bearing, and is configured as follows, for example. The fitting member 2b is fitted to the annular member 2a with a loose eye that can be moved by tightening a pressing member 6 described later. Before the presser member 6 is tightened, there is an axial clearance t between the shoulder 2a2 of the annular member 2a and the end face 2b1 on the other end side (left side in the figure) of the fitting member 2b, and the fitting member An end surface 2b2 on one end side (right side in the drawing) of 2b protrudes slightly in the axial direction from the one end side end surface 2a3 of the annular member 2a. This protrusion amount is the same as or slightly larger than the width of the axial clearance t.
[0018]
A mounting hole 8 is formed on one end face of the outer ring 1, and a bolt or the like (not shown) is screwed into the mounting hole 8 to fix the outer ring 1 to the rotary mount 27 of the CT scanner device (FIG. 8). Similarly, a mounting hole 9 is provided in the end face on the other end side of the inner member 2 (in this embodiment, the end face on the other end side of the annular member 2a), and a bolt or the like (not shown) is screwed into the mounting hole 9. Thus, the inner ring 2 is fixed to the fixed mount 26. In this way, the outer ring 1 becomes a rotating member that rotates together with the rotary mount 27, and the annular member 2a and the fitting member 2b that constitute the inner ring 2 become non-rotating fixed members. Depending on the structure of the CT scanner device, contrary to the above, the outer ring 1 may be a non-rotating fixed side and the inner ring 2 may be a rotating side rotating together with the rotary base 27.
[0019]
A ring-shaped pressing member 6 is fixed to the end surface on the one end side of the annular member 2a by using fastening means 7 such as a bolt. The outer diameter end of the pressing member 6 is substantially at the same level as the outer peripheral surface of the fitting member 2b. A seal 5 a on one end side of the pair of seals is located at a position opposite to the outer diameter end of the pressing member 6.
[0020]
In the above configuration, when the fastening means 7 is fastened, the presser member 6 pressurizes the fitting member 2b and pushes it into the bearing inside. As a result, the preload applying means S functions, the axial clearance t is reduced, and the applied pressure is transmitted to the outer ring 1 via the balls 3 to push the outer ring 1 toward the other end in the axial direction. Therefore, the bearing clearance is killed at both bearing portions, and a preload is applied. By setting the width of the initial axial clearance t in advance so that a predetermined amount of preload is obtained when the fitting member 2b is pushed in until the axial clearance t becomes zero, the preload adjustment can be performed with high accuracy. And it can be done by simple work. In addition, a constant pressure preload can be applied to the bearing portion by a method such as managing the tightening torque of the fastening means 7 (in this case, the axial clearance t after the preload is not always zero).
[0021]
With the above structure, the number of parts can be reduced by the amount corresponding to the outer ring 31 and the one pressing member 36 as compared with the embodiment of FIG. 1, so that part costs and assembly costs can be reduced. In addition, since the number of parts is small, high accuracy can be easily obtained, and finishing processing for obtaining such accuracy can be simplified to further reduce costs.
[0022]
In the embodiment shown in FIG. 5, a pair of fitting members 2b are fitted to a step portion 2a1 provided on the outer circumferential surface of the annular member 2a, and the raceway grooves 2c are formed on the outer circumferential surfaces of the respective fitting members 2b. It is provided. The fitting member 2b on the other end side is locked by a shoulder portion 2a2 provided on the outer peripheral portion of the other end of the annular member 2a. There is an axial clearance t between the two fitting members 2b. By tightening the presser member 6 so that the clearance t is reduced, the preload applying means S functions and a predetermined preload is applied to the inside of the bearing. The
[0023]
In the embodiment of FIG. 5, the seals 5 a and 5 b that seal the opening at both ends of the bearing are extended to the outer diameter side of the annular member 2 a and the pressing member 6, and are brought close to the inner peripheral surface of the outer ring 1. Although a case where a non-contact seal is configured is shown, non-contact type seal members such as seal washers 5a and 5b may be employed for the outer ring 1 as in the embodiment of FIG. Of course, a contact-type seal can also be adopted. An annular oil groove 10 is provided between the seals 5a, 5b and both raceway grooves 1c on the inner peripheral surface of the outer ring 1, and the outer peripheral surfaces of the annular member 2a and the pressing member 6 facing the oil groove 10 are provided. An oil sump 11 is formed by meat removal. The above description has focused on the differences from the embodiment of FIG. 4, but other configurations, operational effects, modifications, etc. are generally the same as those of the embodiment of FIG. Numbers are assigned and duplicate explanations are omitted.
[0024]
As a typical angular contact ball bearing unit used in a general CT scanner apparatus, taking the configuration shown in FIG. 4 as an example, the bearing specifications and loads are as follows.
Inner diameter: 820mm
Outer diameter: 960 mm (excluding flange)
Width: 60mm
Ball diameter: 1/2 inch Number of balls: 110 / row pitch circle diameter: 914 mm
Moment load: 750kgf x 100mm
Rotation speed: 120rpm
[0025]
In all the embodiments described above, the curvature (diameter) of the raceway groove is 104% or more and 108% or less of the ball diameter for both the inner and outer rings. When the starting torque of this bearing was measured under actual clearance conditions, it was about a half of the upper limit of the starting torque. FIG. 6 shows the calculated values. The required level for the starting torque is the upper limit value, and “1” in FIG. 6 indicates this level. The □ mark is the actual measurement value. In Comparative Example 1 where the curvature diameter of the starting groove is 102% of the ball diameter for both the inner and outer rings, the upper limit value of the starting torque is exceeded on the upper side of the recommended preload level. In all cases, the upper limit value of the starting torque is satisfied. It should be noted that the starting torque is expected to reach about 80% of the upper limit value at the lower limit value of the clearance (the upper limit value of the recommended preload level). In the future, the demands for reducing the starting torque will become more severe due to the increase in the size of CT scanner devices (there are more than 40-inch size) and the reduction in the size and weight of the drive motor. Become important.
[0026]
The disadvantage of reducing the curvature of the raceway groove is that the rolling fatigue life is shortened. Therefore, the influence is verified, and FIG. 7 shows the life obtained from the Lundberg-Palmgren theoretical formula. The level equivalent to 10 years of actual machine use is the required level, and “1” in FIG. 7 indicates this level. From FIG. 7, it can be seen that within the range of the recommended preload level, Example 1, Example 2, and Example 3 all satisfy the lower limit value of the rolling fatigue life. In both the inner and outer rings, Comparative Example 2 in which the curvature diameter of the raceway groove is 110% of the ball diameter is lower than the lower limit value of the rolling fatigue life on the upper limit side of the recommended preload level.
[0027]
6 and 7, in order to satisfy the upper limit of the starting torque, the curvature diameter of the raceway groove needs to be 104% or more of the ball diameter for both the inner ring and the outer ring. On the other hand, in terms of rolling fatigue life, the inner ring It can be seen that both outer rings require 108% or less of the ball diameter. Therefore, in order to satisfy both the starting torque and the rolling fatigue life, it is necessary to set the curvature diameter of the raceway groove within the range of 104% or more and 108% or less of the ball diameter for both the inner ring and the outer ring.
[0028]
【The invention's effect】
According to the present invention, it is possible to satisfy both of the conflicting demands of reduction of the starting torque and long life that are important in an ultra-thin type rolling bearing for medical equipment such as a CT scanner device.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an ultra-thin type rolling bearing showing an embodiment of the present invention.
FIG. 2 a is a side view of the cage, and b is a view as seen from the arrow b.
FIG. 3 is a developed plan view of segments constituting the cage.
FIG. 4 is a cross-sectional view of an ultra-thin type rolling bearing showing another embodiment.
FIG. 5 is a cross-sectional view of an ultra-thin type rolling bearing showing another embodiment.
FIG. 6 is a diagram showing the relationship between preload and starting torque.
FIG. 7 is a diagram showing the relationship between preload and rolling fatigue life.
FIG. 8 is a cross-sectional view of a CT scanner device.
[Explanation of symbols]
1 outer ring 1c raceway groove 2 inner ring 2c raceway groove 3 ball 4 cage dB ball diameter PCD pitch circle diameter

Claims (3)

An ultra-thin type large-sized rolling bearing having a ratio of the ball diameter to the pitch circle diameter of 0.03 or less, and the curvature diameter of the raceway groove is 104% or more of the ball diameter for both the inner ring and the outer ring, and 108 An ultra-thin type rolling bearing characterized by being less than%. 2. The ultra-thin type rolling bearing according to claim 1, which is an angular ball bearing. The ultra-thin type rolling bearing according to claim 2, wherein the bearing is a double-row angular ball bearing.

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