Abstract:
It is intended to suppress rattling in the fitted state of segments to improve operating efficiency in bonding the segments together. 
     A cage composed of a plurality of arcuate segments, wherein a 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 to thereby annularly bond the segments. In this cage, said joining projection and joining recess have tapered fitting surfaces as seen in a radial section, and the two fitting surfaces are closely contacted and joined together.

Description:
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 raceway surfaces of said outer and inner members, and in this ultrathin-walled rolling bearing, the cage having the rolling elements circumferentially equispaced therein is capable of reliably preventing the generation of abnormal sounds due to contact between the segments and the raceway surfaces of the inner and outer members. 
     If one of the outer and inner members in this ultrathin-walled rolling bearing is fixed in the rotary frame of a CT scanner device rotating around a subject and the other is fixed in the fixed frame of the CT scanner device, then it is possible to provide a CT scanner device which has low noise and is superior in radiographic accuracy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first embodiment of the invention, wherein (a) is a plan view of one segment formed with a joining recess, and (b) is a view taken in the direction of arrow A in (a); 
     FIG. 2 shows the first embodiment of the invention, wherein (a) is a view taken in the direction of arrow B in (b), and (b) is a plan view showing the other segment formed with a joining projection; 
     FIG. 3 showing the first embodiment of the invention is a partial enlarged perspective view showing the state after adjacent segments have been joined; 
     FIG. 4 showing the first embodiment of the invention is a partial enlarged perspective view showing the state before the adjacent segments are joined; 
     FIG. 5 is an axial sectional view, partly omitted, showing an ultrathin-walled rolling bearing to which the invention is applied; 
     FIG. 6 shows a second embodiment of the invention, wherein (a) is a plan view showing one segment having an annular recessed engaging section formed in a joining recess, and (b) is a view taken in the direction of arrow A in (a); 
     FIG. 7 shows the second embodiment of the invention, wherein (a) is a view taken in the direction of arrow B in (b), and (b) is a plan view showing the other segment having an annular projecting engaging section formed in a joining projection; 
     FIG. 8 showing the second embodiment of the invention is a partial enlarged perspective view showing the state after adjacent segments have been joined; 
     FIG. 9 showing the second embodiment of the invention is a partial enlarged perspective view showing the state before the adjacent segments are joined; 
     FIG. 10 shows a third embodiment of the invention, wherein (a) is a plan view of one segment formed with a shallow joining recess, and (b) is a view taken in the direction of arrow A in (a); 
     FIG. 11 shows the third embodiment of the invention, wherein (a) is a view taken in the direction of arrow B in (b), and (b) is a plan view of the other segment formed with a shallow joining projection; 
     FIG. 12 showing the third embodiment of the invention is a partial enlarged perspective view showing the state after adjacent segments have been joined; 
     FIG. 13 showing the third embodiment of the invention is a partial enlarged perspective view showing the state before adjacent segments are joined; 
     FIG. 14 is a sectional view showing a schematic arrangement of a CT scan device; 
     FIG. 15 is a front view showing a schematic arrangement of a cage used in an ultrathin-walled rolling bearing incorporated into the CT scan device; 
     FIG. 16 is a developed plan view showing the bonding sections of segments constituting the cage; 
     FIG. 17 shows a conventional example of the cage of an ultrathin-walled rolling bearing, wherein (a) is a plan view of one segment formed with a recessed fitting section and (b) is a view taken in the direction of arrow A in (a); 
     FIG. 18 shows the conventional example of the cage of an ultrathin-walled rolling bearing, wherein (a) is a view taken in the direction of arrow B in (b) and (b) is a plan view of the other segment formed with a projecting fitting section; 
     FIG. 19 showing the conventional example of the cage of an ultrathin-walled rolling bearing is a partial enlarged perspective view showing the state after adjacent segments have been joined; and 
     FIG. 20 showing the conventional example of the cage of an ultrathin-walled rolling bearing is a partial enlarged perspective view showing the state before adjacent segments are joined. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 shows a concrete constructional example of an ultrathin-walled rolling bearing  6  assembled to a CT scanner device shown in FIG.  14 . This bearing  6 , as shown in the same figure, comprises an annular outer ring  21 , which is an outer member, an annular inner ring  22 , which is an inner member, disposed concentrically on the inner peripheral side of the outer ring  21 , a plurality of balls  23 , which are rolling elements, interposed between the raceway surface  22   a  of the inner ring  22  and the raceway surface  21   a  of the outer ring  21 , a cage  24  for holding the balls  23  at circumferentially equispaced intervals, and seals  25  and  26  for sealing the openings at the opposite ends of the bearing  6 . 
     In addition, in this embodiment, the balls  23  are illustrated as the rolling elements, but rollers may be used. Further, the invention is not limited to a single row rolling bearing having a single row of rolling elements, and is applicable to a double row rolling bearing having two rows of rolling elements. 
     This bearing  6  is an ultrathin-walled rolling bearing in which the ratio φ of the diameter DB of the balls  23  to the pitch circle diameter PCD is not more than 0.03 (φ=(DB/PCD) ≦0.03); for example, these factors are set such that the ball diameter is ½ inch (12.7 mm), the PCD is 1041.4 mm, and their ratio φ is 0.012. The bearing  6  is a large diameter bearing whose PCD is mainly 500 mm-1500 mm or so. 
     Attaching holes  27  are formed in an end surface on one end side (right-hand side in the figure) of the outer ring  21 , and unillustrated fastening means, such as bolts, are screwed into the attaching holes  27 , whereby the outer ring  21  is fixed to the rotary frame  8  of the CT scanner device shown in FIG.  14 . Attaching holes  28  are likewise formed in an end surface on the other end side of the inner ring  22 , and unillustrated fastening means, such as bolts, are screwed into the attaching holes  28 , whereby the inner ring  22  is fixed to the fixed frame  7 . 
     Thus, it is seen from the above that the outer ring  21  constitutes a rotary member which rotates with the rotary frame  8  and that the inner ring  22  constitutes a nonrotatable fixed member. Depending upon the construction of the CT scanner device, in a manner reverse to the above, the outer ring  21  may be made to be the nonrotatable fixed side and the inner ring  2  to be the rotary side rotating with the rotary frame  8 . 
     The cage  24  is formed by injection-molding a resin material into a predetermined shape, which resin material is suitably PPS (polyphenylene sulfide) for example. This cage  24 , as in the prior art, is a split type in which a plurality of arcuate segments  25  of resin are circumferentially connected together in annular form (see the segment  12  of a conventional cage  11  shown in FIG.  15 ). 
     Each segment  25  has a plurality of pockets formed at circumferentially equispaced intervals for receiving the balls  23  (see the pockets  15  of the conventional segment  12  shown in FIG.  16 ). While open type pockets with one axial side opened are illustrated as the pockets, a window type pocket with the periphery closed, not shown, may be used. 
     Each segment  25 , as shown in FIGS.  1 ( a ) and ( b ) and FIGS.  2 ( a ) and ( b ), is formed at its opposite ends with bonding sections  26  and  27  for bonding with adjacent segments  25 . In addition, FIG. 3 shows the assembly-completed state after the bonding sections  26  and  27  of adjacent segments  25  have been fitted together, and FIG. 4 shows the state before the bonding sections  26  and  27  of adjacent segments  25  are fitted together. 
     One bonding section  26  is formed with a joining projection  28  circumferentially extending from the end surface of the segment  25 . This joining projection  28  is constricted in the proximal end and is composed of a neck on the proximal end side and a head axially extending therefrom on the front end side. It is only necessary for the head to have an axial width in a portion thereof greater than the axial width of the neck; for example, it is formed as a circle as seen in a plan view, as shown. In addition, it may be other than a circle or it may be a polygon. 
     The other bonding section  27  is formed with a joining recess  29  disposed backwardly of the end surface of the segment  25 . This joining recess  29  is shaped to be suited to the joining projection  28  and is composed of a constricted section corresponding to the neck and an enlarged section corresponding to the head. 
     The outer peripheral surface of the head of the joining projection  28  is formed with a fitting surface  30  which is tapered as seen in a radial section, that is, it is a conical surface. The inner peripheral surface of the enlarged section of the joining recess  29  is formed with a fitting surface  31  which is tapered as seen in a radial section, that is, it is a conical surface. The smallest outer diameter of the joining projection  28  and the smallest inner diameter of the joining recess  29 , and the largest outer diameter of the joining projection  28  and the largest inner diameter of the joining recess  29  are set at the same dimension, respectively. 
     In the above arrangement, the bonding between adjacent segments  25  is effected in the following procedure. First, the segments  25  are disposed in radially separated parallel relation as shown in FIG. 4, and from this state the joining projection  28  is radially pushed into the joining recess  29  (see FIG.  3 ). This results in close fitting between the conical fitting surface  30  of the joining projection  28  and the conical fitting surface  31  of the joining recess  29 . 
     Fitting the conical fitting surfaces  30  and  31  together in this manner makes it possible for a change in interference between the joining projection  28  and the joining recess  29  due to molding errors or the like to radially escape at the fitting surfaces  30  and  31 , so that rattling in the fitted state can be suppressed to realize a stabilized fitted state. In addition, in the embodiment described above, the joining projection  28  formed in one of the adjacent segments  25  has substantially the same radial dimension (thickness) as the radial dimension (thickness) of the segment  25 . Further, the joining recess  29  formed in the other has substantially the same radial dimension (depth) as the radial dimension (thickness) of the segment  25 . 
     Further, projecting engaging sections  33  are formed on the butt surface  32  of the bonding section  26  in one of the adjacent segments  25 , while recessed engaging sections  35  are formed in the butt surface  34  of the bonding section  27  of the other, and the two butt surfaces  32  and  34  butt against each other. The provision of the bonding sections  26  and  27  of the segments  25  with the engaging sections  33  and  35  adapted to have a mutual recess-projection engagement at the butt surfaces  32  and  34  of the mating segments  25  serves as a slip-off prevention means for preventing radially inward or outward deviation between the adjacent segments  25 . 
     In the first embodiment described so far, the butt surfaces of the bonding sections are formed with recessed and projecting engaging sections, respectively; however, as in the second embodiment shown in FIGS. 6 through 9, the fitting surface  31  of the bonding section  26  of one of the adjacent segments  25  may be formed with a projecting engaging section  33 ′, while forming the fitting surface  30  of the bonding section  27  of the other with a recessed engaging section  35 ′. 
     Thereby, in fitting the bonding sections  26  and  27  of the segments  25  together at the fitting surfaces  31  and  30 , the engaging sections  33  and  35  formed in the fitting surfaces  31  and  30  are brought into a recess-projection engagement, thereby serving as a slip-off prevention means for preventing radially inward or outward deviation between the adjacent segments  25 . 
     In addition, besides forming annular engaging sections  33 ′ and  35 ′ continuous peripherally of the fitting surfaces  31  and  30  as in the second embodiment, they may be engaging sections of noncontinuous shape formed peripherally of the fitting surfaces. 
     In the first and second embodiments, a description has been given of a case where the joining projection  28  and joining recess  29  have the same thickness as that of the segments  25 ; however, the invention is not limited thereto; the invention may be in the form of a third embodiment having a construction shown in FIGS.  10 ( a ) and ( b ), FIGS.  11 ( a ) and ( b ), and FIGS. 12 and 13. 
     The third embodiment differs from the first and second embodiments described above only in the thickness of the joining projection  28 ′ and joining recess  29 ′ formed in the bonding sections  26  and  27  of the segments  25 . Therefore, since other arrangement, function and effect are the same as in the first and second embodiments, a description thereof is omitted. In a cage according to the third embodiment, the thickness of the joining projection  28 ′ and the depth of the joining recess  29 ′ of the segments  25  are reduced to about ½ of the thickness of the segments  25 .