Abstract:
A bearing supports a rotating element. The bearing comprises an inner annular body and an outer annular body about the inner annular body. A bearing surface, which is located between the inner annular body and the outer annular body, supports the outer annular body for rotation about the inner annular body. A cage supports the bearing surface during rotation of the outer annular body about the inner annular body. The cage includes a material that imparts increased flexural modulus that resists deformation during rotation.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/334,340, filed Jun. 16, 1999, abandoned, and entitled “Umbilicus Gimbal with Bearing Retainer,” which is a continuation of U.S. patent application Ser. No. 08/835,928, filed Apr. 11, 1997 (now U.S. Pat. No. 5,989,177). 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to bearings that provide support to a flexible fluid-carrying umbilicus when coupled for use to a rotating fluid processing chamber. The invention also relates generally to centrifugal blood processing systems and apparatus that impart a twisting motion to an umbilicus to rotate a blood processing chamber. 
     BACKGROUND OF THE INVENTION 
     Various blood processing systems now make it possible to collect particular blood constituents, rather than whole blood, from donors. Typically, in such systems, whole blood is drawn from a donor, the particular blood component or constituent is removed and collected, and the remaining blood constituents are returned to the donor. By thus removing only particular constituents, less time is needed for the donor&#39;s body to return to normal, and donations can be made at more frequent intervals than when whole blood is collected. This increases the overall supply of blood constituents, such as plasma and platelets, made available for health care. 
     Whole blood is typically separated into its constituents through centrifugation. This requires that the whole blood be passed through a centrifuge after it is withdrawn from, and before it is returned to, the donor. To avoid contamination and possible infection of the donor, the blood is preferably contained within a sealed, sterile system during the entire centrifugation process. Typical blood processing systems thus include a permanent, reusable centrifuge assembly containing the hardware that spins and pumps the blood, and a disposable, sealed and sterile fluid processing assembly that actually makes contact with the donor&#39;s blood. The centrifuge assembly engages and spins the fluid processing assembly during a collection procedure. The blood, however, makes actual contact only with the fluid processing assembly, which is used only once and then discarded. 
     To avoid the need for rotating seals, and to preserve the sterile and sealed integrity of the fluid processing assembly, blood processing systems often utilize centrifuges that operate on the “one-omega, two-omega” operating principle. This principle, which is disclosed in detail in Brown et al., U.S. Pat. No. 4,120,449, enables centrifuges to spin a closed system without the need for rotating seals and without twisting the components of the system. Blood processing systems that make use of the principle typically include a fluid processing assembly that includes a plastic bag that is spun in the centrifuge and that is connected to the blood donor through an umbilicus. The umbilicus is turned back on itself in the form of an inverted question mark, so that an end portion of the umbilicus is coaxially aligned with the axis of rotation of the bag. The intermediate portion of the umbilicus is twisted as the bag is spun to counteract the twisting that would otherwise take place as the bag is spun. The effect is that the end of the umbilicus, which is opposite the bag and is connected to the donor, does not twist as the bag is spun. The sealed, sterile integrity of the fluid processing assembly is thus maintained without the need for rotating seals. 
     U.S. Pat. No. 5,551,942 to Brown et al., commonly owned by the assignee hereof, discloses one such blood processing apparatus based on the “one-omega, two-omega” operating principle. In this apparatus, a disposable fluid processing assembly having an umbilicus and a processing chamber is mountable within a centrifuge assembly. One end of the umbilicus is held rotationally stationary substantially over the axis of centrifugation. The other end of the umbilicus joins the processing chamber and rotates with the processing chamber around the axis of centrifugation at the two-omega speed. The mid-portion of the umbilicus is supported by a wing plate that rotates around the axis of centrifugation at the one-omega speed. A bearing mounted on the umbilicus permits the umbilicus to rotate relative to the wing plate as the wing plate and the processing chamber turn at different speeds. The bearing slides into a one piece gimbal mounted in a recess provided on the wing plate. The gimbal helps keep the fluid processing assembly properly positioned during the centrifugation procedure. When the procedure is completed, the bearing can be slid out of the gimbal in the wing plate to permit removal of the fluid processing assembly. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention provides a bearing for supporting a rotating element. The bearing possesses enhanced flexural modulus, heat resistance and resistance to deformation during use. 
     In one embodiment, the bearing comprises an inner annular body and an outer annular body about the inner annular body. A bearing surface, which is located between the inner annular body and the outer annular body, supports the outer annular body for rotation about the inner annular body. A cage supports the bearing surface during rotation of the outer annular body about the inner annular body. The cage includes a material that imparts increased flexural modulus that resists deformation during rotation. 
     Another aspect of the invention provides an umbilicus for use in association with a fluid processing system. The umbilicus comprises an umbilicus body, which carries the bearing. 
     Another aspect of the invention provides a fluid processing system, e.g., for blood, which includes a fluid processing chamber that, in use, rotates about an axis. An umbilicus carrying the bearing is coupled to the fluid processing chamber by a bearing support. The bearing support is rotated to impart a twisting motion to the umbilicus, to thereby rotate the fluid processing chamber about an axis. 
     Features and advantages of the invention are set forth in the following Description and Drawings, as well as in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a blood processing apparatus embodying various features of the invention; 
     FIG. 2 is a side elevation view, partially in section, of the blood processing apparatus shown in FIG. 1; 
     FIG. 3 is a side view, partially in section, of a centrifuge included in the blood processing apparatus of FIG. 1 showing the centrifuge in combination with a fluid processing assembly having an umbilicus supported at its midpoint by a wing plate and an umbilicus gimbal embodying various features of the invention; 
     FIG. 4 is an exploded perspective view of an umbilicus bearing and an umbilicus gimbal and bearing retainer included in the blood processing apparatus and embodying various features of the invention; 
     FIG. 5 is a cross-sectional view of the umbilicus gimbal and bearing retainer shown in FIG.  4 . 
     FIG. 6 is front elevation view of an alternate embodiment umbilicus gimbal having alternate bearing retainer configuration intended to facilitate removal of the umbilicus bearing from the bearing retainer; 
     FIG. 7 is a sectional view of the alternate embodiment shown in FIG. 6; 
     FIG. 8 is a perspective view of the alternate embodiment shown in FIGS. 6 and 7 useful in understanding the use thereof; and 
     FIG. 9 is a chart showing the relation between temperature and flexural modulus for Rynite® thermoplastic polyester (DuPont). 
    
    
     The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show a blood processing apparatus  10 . The blood processing apparatus  10  is of the type shown and described in U.S. Pat. No. 5,551,942, the specification of which is incorporated by reference herein. The apparatus  10  can be used to collect various blood constituents from a donor while returning uncollected constituents back to the donor. The apparatus  10  can also be used to process other suspensions of biological cellular materials. 
     The blood processing apparatus  10  includes a centrifuge assembly  12  and a fluid processing assembly  14  (FIG. 2) used in association with the centrifuge assembly  12 . The centrifuge assembly  12  is a durable equipment item capable of long term, maintenance free use. The fluid processing assembly  14  is a single use, disposable item loaded on the centrifuge assembly  12  at the time of use. After a processing procedure has been completed, the operator removes the fluid processing assembly  14  from the centrifuge assembly  12  and discards it. 
     The fluid processing assembly  14  includes a processing chamber  16  (FIG.3) In use, the centrifuge assembly  12  rotates the processing chamber  16  to centrifugally separate blood components. Whole blood is conveyed to the processing chamber  16 , and separated blood components are conveyed from the processing chamber  16 , through a plurality of flexible tubes that form part of a fluid circuit  18 . The fluid circuit  18  further includes a plurality of containers  20  that fit on hangers over the centrifuge assembly  12  and that dispense and receive liquids during processing. A plurality of in line cassettes  22  that operate in association with valve and pump stations on the centrifuge assembly  12 , function to direct liquid flow among multiple liquid sources and destinations during a blood processing procedure. A portion of the tubes interconnecting the processing chamber  16 , the containers  20  and the cassettes  22  are bundled together to form a flexible umbilicus  24 . 
     The fluid circuit  18  preconnects the processing chamber  16 , the containers  20  and the cassettes  22 . The fluid processing assembly  14  thereby forms an integral, sterile unit. 
     As illustrated, the centrifuge assembly  12  includes a wheeled cabinet  26  that can be easily rolled from place to place. A user actuable processing controller  30  is provided which enables the operator to control various aspects of the blood processing procedure. A centrifuge  32  is provided behind a fold open door  34  that can be pulled open at the front of the cabinet  26 . A plurality of valve and pump stations  36  are provided on the top face of the cabinet for receiving and controlling the various in line cassettes  22 . A plurality of hooks or hangers  38  are provided on the cabinet  26  for suspending the various containers  20 . 
     In use, the fold open door  34  is opened and the processing chamber  16  of the fluid processing assembly  14  is mounted in the centrifuge  32 . The umbilicus  24  is threaded through the centrifuge  32  and out through an opening  40  in the upper panel of the cabinet  26 . The in line cassettes  22  are snapped into respective ones of the valve and pump stations  36 , and the containers  20  are hung from the appropriate hangers  38 . After appropriate connections are made to the donor using known intravenous techniques, the operator enters appropriate commands on the processing controller to begin the processing procedure. 
     Referring in particular to FIGS. 2 and 3, the centrifuge  32  includes a chamber assembly  42  that is supported for rotation around an axis of centrifugation  44 . The centrifuge further includes a centrifuge yoke assembly  46  that includes a yoke base  48 , a pair of upstanding yoke arms  50 , and a yoke cross member  52  mounted between the arms  50 . The yoke base  48  is rotatably supported on a stationary platform  54  that carries the rotating mass of the centrifuge  32 . The yoke base  48  is also supported for rotation around the axis of centrifugation independently of the chamber assembly  42 . An electric drive  56  rotates the yoke assembly  46  relative to the stationary platform  54  around the axis of centrifugation  44 . The chamber assembly  42  is free to rotate around the axis of centrifugation  44  at a rotational speed that is different from the rotational speed of the yoke assembly  46 . 
     Referring further to FIG. 3, the chamber assembly  42  defines an annular chamber  58 , centered around the axis of centrifugation  44 , for receiving the processing chamber  16  of the fluid processing apparatus  14 . The umbilicus  24 , through which fluids are introduced into and withdrawn from the processing chamber  16 , extends through the lower center of the chamber assembly  42  in alignment with the axis of centrifugation  44 . A lower support block  60  integrally molded or otherwise mounted onto the umbilicus  24 , is received in a lowermost umbilicus mount  62  located at the lower center of the chamber assembly  42 . The lower support block  60  and umbilicus mount  62  function to transfer torque between the umbilicus  24  and chamber assembly  42  so that the chamber assembly  42  rotates around the axis of centrifugation in response to twisting of the umbilicus  24  around its axis. 
     The other end of the umbilicus  24  is supported by means of an upper support block  64  that is removably received in an upper umbilicus mount  66  positioned over the centrifuge chamber assembly  42  substantially in alignment with the axis of centrifugation  44 . An over center clamp  68  at the end of the upper umbilicus mount  66  clamps onto the upper support block  64  to hold the adjacent segment of the umbilicus  24  rotationally stationary and in collinear alignment with the axis of centrifugation  44 . The upper support block  64  is preferably integrally molded or otherwise securely joined with the umbilicus  24 . 
     As further illustrated in FIG. 3, the portion of the umbilicus  24  between the upper support block  64  and the lower support block  60  is supported by a middle umbilicus mount  70  that is carried at the lower end of a wing plate  72  extending outwardly and downwardly from the yoke cross member  52 . As the electric drive  56  rotates the centrifuge yoke assembly  46  around the axis of centrifugation  44 , the wing plate  72  and middle umbilicus mount  70  pull the middle portion of the umbilicus  24  around the axis of centrifugation  44  as well. As the umbilicus is so moved, a twisting action is imparted to the umbilicus  24  around its own axis. The middle portion of the umbilicus  24  is free to rotate around its axis relative to the wing plate  72  as the yoke assembly  46  is turned. The umbilicus is thus free to “untwist” against the twisting motion imparted by the rotating yoke assembly  46 . As it untwists in this manner, the umbilicus  24  spins the centrifuge chamber assembly  42  around the axis of centrifugation  44 . 
     To maintain balance as the yoke assembly  46  turns, an additional wing plate  74  extends from the yoke cross member  52  diametrically opposite the wing plate  72 . A counterweight  76  sufficient to balance the mass of the middle umbilicus mount  70  and umbilicus  24  is carried on the lower end of the additional wing plate  74 . 
     In accordance with one aspect of the invention, the middle portion of the umbilicus  24  is supported on the wing plate  72  by means of an umbilicus gimbal assembly  78  having a bearing retainer. Referring to FIGS. 3,  4  and  5 , the manner in which the middle portion of the umbilicus  24  is supported and carried by the wing plate  72  is shown in detail. 
     As illustrated (See FIG.  3 ), a bearing assembly  80  is located on the umbilicus between the upper and lower support blocks  64  and  60 . As FIG. 4 shows, the bearing assembly  80  includes an inner race  82  in the form of a collar that slips over the umbilicus  24  and is held in place by a retaining clip  84 . The inner race includes a slotted forward flange portion  86  that is squeezed against the umbilicus under the clamping force of the clip  84 , and further includes a rear race portion  88  that encircles the umbilicus  24  and defines a raceway for a plurality of balls  90 . 
     To further secure the bearing assembly  80  to the umbilicus  24 , various adhesives can be used. In the illustrated embodiment, the umbilicus  24  is formed from extruded polyester elastomer such as HYTREL®4 or HYTREL®6 plastic (DuPont). In this arrangement, polyurethane adhesives can be used, possibly including polyurethane in cyclohexane, as they bond well to material of the umbilicus  24  through beta-bonding. Five percent (5%) polyurethane in cyclohexane has shown to work well, but other adhesives suitable for bonding to HYTREL® could be used. The inner surface of the collar and/or the outer surface of the umbilicus  24  can be roughened to heighten adhesiveness. The adhesive  83  can be used by itself or in combination with the retainer clip  84 . 
     The balls  90 , which are preferably formed of a durable metal such as stainless steel, are confined between the inner race  82  and an outer race  92  having a generally annular form as indicated. A cage  94  between the rear race portion  88  of the inner race  82  and the outer race  92  keeps the balls separated and regularly spaced around the inner and outer races  82 ,  92 . The bearing assembly  80  permits the umbilicus to rotate with very little friction relative to the outer race  92 , while the adhesive  83 , the clip  84  (if used), and the forward portion  86  of the inner race  82  resist axial movement of the bearing assembly relative to the umbilicus  24 . 
     The inner race  82 , and the outer race  92  and the cage  94  can be constructed with a wide range of materials. Several material characteristics are desired, including high formability with minimal shrinkage, greater dimensional accuracy and endurance, high rigidity and mechanical strength, high heat stability, and very low electrical conductivity to minimize the potential for static energy build up. 
     In order to maintain the necessary very close tolerances between the bearing and the gimbal, a bearing that resists dimensional changes with changing temperature, pressure and humidity conditions is desirable. It is also desirable to minimize any cage deflection and cage wear against the outer race of the bearing assembly. In addition, it is desirable to reduce any noise that the bearing may cause at high operating speeds. 
     The inner race  82 , and the outer race  92  and the cage  94  can be constructed with reinforced polyesters. Several reinforced polyesters have the desired mechanical characteristics, and would perform suitably. Within the family of reinforced polyesters, thermoplastic crystalline polymers may perform particularly well due to their high formability with minimal shrinkage, greater dimensional accuracy and endurance, high rigidity and mechanical strength, high heat stability, and very low electrical conductivity to minimize the potential for static energy build up during rotation. 
     FIG. 9 shows for Rynite® thermoplastic polyester (DuPont) how flexural modulus decreases with increasing temperature. Increased temperature would be expected at high rotational speeds because of friction. 
     Preferably, the inner race  82 , and the outer race  92  and the cage  94  are machined from high molecular weight thermoplastic/thermoset materials rather than injection molded from thermoplastic materials. By machining rather than molding these parts, the parts can be held to tighter dimensional tolerances (e.g., 0.001″) than is practically and economically achievable using injection molding techniques. Thermoplastic polyester resins are noted for their excellent flow characteristics in thin wall applications, close molding tolerances, and high productivity from multicavity molds 
     In the illustrated embodiment, the cage  94  is constructed of the thermoplastic crystalline polymer polybutylene Terephthalate (PBT). Preferably, the cage  94  material includes an additive to raise the flexural modulus and heat resistance, and provide increased lubricity. 
     To demonstrate the effects of additive inclusion, the following Table 1 and Table 2 show that a 10% increase in additive content can lead to greater than a 20% increase in flexural modulus. For Rynite® thermoplastic polyester (DuPont) the following relation between flexural modulus was shown for 20% and 30% fiber additive content: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Flexural Modulus 
                 Flexural Modulus 
               
               
                 Temperature 
                 (Mpa) 
                 (Mpa) 
               
               
                 (° C.) 
                 20% Fiber Additive 
                 30% Fiber Additive 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 −40 
                 7950 
                 10300  
               
               
                 23 
                 6480 
                 8960 
               
               
                 90 
                 2690 
                 3580 
               
               
                 150 
                 1870 
                 2690 
               
               
                   
               
             
          
         
       
     
     For RTP Company polybutylene terephthalate, the following results demonstrated the effects of carbon filler: 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Carbon Filler Content 
                 Unfilled 
                 10% 
                 20% 
                 30 
                 40% 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Flexural Strength (Mpa) 
                  83 
                 172 
                 220 
                 193 
                 262 
               
               
                 Flexural Modulus 
                 400 
                 950 
                 1,700 
                 2,500 
                 3,000 
               
               
                 (psi E-9) 
                   
                   
                   
                   
                   
               
               
                 Tensile Strength 
                  55 
                 103 
                 138 
                 138 
                 172 
               
               
                 (MPa) 
                   
                   
                   
                   
                   
               
               
                 Tensile Elongation 
                 275 
                 3.5 
                 3 
                 1.5 
                 1.5 
               
               
                 (%) 
               
               
                   
               
             
          
         
       
     
     Many suitable PBT fillers are available, including for example: aramid fiber, glass beads, TEFLON®, molybdenum disulfide, silicon, PTFE, minerals such as mica, stainless steel, or nickel-coated carbon fiber. These fillers could work well in varying concentrations to produce the desired results, including ease in injection moldability, high stiffness, high flexural modulus, and low tensile elongation. However, with high flexural modulus and low tensile elongation, brittleness often complicates use, and could lead to cage cracking during use. Therefore, the preferred embodiments retain high stiffness and high flexural modulus, low tensile elongation percentages, while retaining a minimal level of ductility to avoid too brittle of a cage. 
     Preferably, the cage  94  is constructed of PBT with a carbon fiber additive, because carbon fiber shows similar strength characteristics to glass or other filler materials as shown in Tables 1 and 2, but carbon fiber adds greater lubricity than does the glass or other mineral fiber. Even more preferably, the PBT is filled with 5%-50% carbon fibers. Even more preferably, the PBT is filled with 10%-30% carbon fibers. Most preferably, the PBT is filled with 15% carbon fibers, based on weighing the above criteria of high flexural modulus, high formability with minimal shrinkage, greater dimensional accuracy and endurance, high rigidity and mechanical strength, high heat stability, and very low electrical conductivity to minimize the potential for static energy build up. 
     Alternatively, the cage material could be constructed with fillers comprising aramid fiber, TEFLON®, glass beads, molybdenum disulfide, silicon, PTFE, minerals such as mica, stainless steel, or nickel-coated carbon fiber, glass fiber filler, or mineral fiber filler, or a combination of glass and mineral fillings. The addition of glass fibers and other reinforcing materials can raise the heat resistance to over 200 degrees C. Although the glass fiber filler provides sufficient stiffness, it does not provide as much lubricity as the preferred carbon fiber additive. 
     The cage  94  is molded, preferably to within tolerances of 0.005″ 
     Referring further to FIGS. 3,  4  and  5 , the outer race  92  of the bearing assembly  80  is mounted onto the middle umbilicus mount  70  of the wing plate  72  by means of the umbilicus gimbal assembly  78 . The umbilicus gimbal assembly  78  comprises a gimbal  96  that is received in the middle umbilicus mount  70  and a bearing retainer  98  that is received in the gimbal  96 . The middle umbilicus mount  70  comprises a circular opening  100  formed in the lowermost end of the wing plate  72 . Preferably, the sidewall of the circular opening is inwardly or concavely shaped as shown, thereby giving the opening a generally spherical shape. A gap  102  is formed in the end of the wing plate  72  and opens into the circular opening to enable the umbilicus  24  and bearing assembly  80  to be inserted into the middle umbilicus mount  70  from the side. A pair of orthogonally oriented pivot pins  104  extend from the side walls of the wing plate  72  into the interior of the circular opening  100 . 
     The gimbal  96  comprises a generally annularly-shaped member having a ring-like form. The outer sidewalls  106  of the gimbal  96  are outwardly rounded or convex as shown, thereby giving the gimbal  96  a generally spherical shape that matches the shape of the opening  100 . A pair of elongate transverse slots  108  are formed through the sidewalls  106  and are positioned and dimensioned to receive the pivot pins  104  when the gimbal is received in the circular opening  100 . The rounded sidewalls  106  of the gimbal  96 , together with the elongate slots  108  and pivot pins  104  received therein, enable the gimbal  96  to pivot within the circular opening  100  around two orthogonal axes. A “gimbal” action is thus provided. A gap  110  is formed through the side of the gimbal  96  to permit entry of the umbilicus  24 . The gimbal  96  is preferably formed of a durable, rigid, low-friction plastic such as Delrin. 
     The bearing retainer  98  comprises a generally cylindrical ring-like structure and is preferably formed of a resilient, durable, springy material such as stainless steel. The bearing retainer includes a substantially constant diameter middle segment  112 , a flared outer end  114  at one end of the middle segment  112 , and a reduced diameter inner end  116  at the other end of the middle segment  112 . A gap  118  opening through the side of the bearing retainer permits entry of the umbilicus  24 . 
     In accordance with one aspect of the invention, the bearing retainer  98  and the gimbal  96  are configured so that the bearing retainer is loosely received in the gimbal  96 , and yet positively retained in the gimbal  96 . To this end, the inner end  116  of the bearing retainer  98  includes a pair of retaining wings or lugs  120 , each extending partially around the periphery of the rear end of the middle segment  112 . Referring to FIG. 5, each wing  120  defines a substantially square sectioned channel having a bottom wall  122 , an outer side wall  124  and an inner side wall  126 . The bottom side walls  122  of the wings  120  effectively define a region of reduced diameter as compared with the diameter of the middle section  112  of the bearing retainer  98 . As further illustrated in FIG. 5, one end of the gimbal  96  is provided with an integrally formed rim or ledge  128  that is positioned and dimensioned to be received in the channels formed by the wings  120 . A pair of clearance slots  130  are formed in the outer end wall of the gimbal  96  to provide clearance for the outer side walls  124  of the wings. The ends  132  of the clearance slots provide abutment surfaces that engage the ends of the side walls  124  to limit rotational movement of the bearing retainer  98  relative to the gimbal  96  when the bearing retainer  98  is received in the gimbal  96 . 
     In further accordance with the invention, the bearing retainer is configured to receive and accommodate umbilicus bearings having outer races  92  of differing diameters. At the same time, gimbal  96  is configured to remain movable within the opening  100  of the wing plate  72  without binding. This is accomplished by providing lateral clearance between the outer side walls of the bearing retainer  98  and the inner side walls of the gimbal  96 . Referring to FIG. 5., it will be seen that a gap or space exists between the inner end wall of the gimbal rim  128  and the bottom wall  122  of the bearing retainer wing  120 . Similar clearance is provided between the outer side wall  124  of the wing  122  and the radially outlying adjacent portion of the gimbal  96 . Finally, similar clearance is provided between the interior side wall  134  of the gimbal  96  and the exterior sidewall of the bearing retainer  98 . The clearances thus provided between the bearing retainer  98  and the gimbal  96  enable the bearing retainer  98  to expand to accommodate larger bearing races  92  without interfering with or expanding the size of the gimbal  96 . Similarly, the bearing retainer  98  can close down to accommodate outer races  92  of smaller size without compromising the retaining function provided through the interaction of the gimbal ridge  128  with the retaining wings  120 . In this manner, the bearing retainer  98  can accommodate bearings of different sizes without affecting the ability of the gimbal  96  to pivot within the opening  100  of the wing plate  72 . 
     To further avoid possible binding of the gimbal  96  and bearing retainer  98  within the opening  100 , clearance slots  136  can be formed in the outer side wall of the middle portion  112  of the bearing retainer  98  under the slots  108  of the gimbal  96  to provide clearance for the ends of the pivot pins  104 . 
     As further illustrated in FIG. 5, the middle portion  112  of the bearing retainer  98  is elongated to project well past the sides of the wing plate  72 . In addition, the middle portion  112  terminates in the flared outer section  114 . These attributes enable the gimbal  96  and bearing retainer  98  carried therewith to pivot around the pivot pins  104  over a wide range before the bearing retainer  98  hits the wing plate  72  and thereby limits further travel. 
     In use, the bearing retainer  98  is snapped into the gimbal  96  with the retaining wings  120  received in the retaining slots  130 . The gimbal  96  and bearing retainer  98  are then inserted into the opening  100  of the wing plate  72  with the pivot pins entering the respective slots  108 . The gimbal  96  should, at this point, be freely pivotable relative to the wing plate  72  and the slots  102 ,  110  and  118  in the wing plate  72 , the gimbal  96  and the bearing retainer  98  should all line up. The umbilicus  24  can then be inserted sideways through the slots  102 ,  110  and  118 , and the outer race  92  of the umbilicus bearing assembly  80  is pressed axially into the bearing retainer  98  from the flared end  114 . The bearing retainer  98  should expand as necessary to receive the outer race  92  and should firmly grip the outer race  92  with a tight frictional fit to resist withdrawing movement of the bearing assembly  80 . At the same time, such expansion of the bearing retainer  98  should be accommodated by the radial clearance between the bearing retainer  98  and the gimbal  96 , and the outer dimension of the gimbal  96  should not change. Accordingly, the gimbal  96 , and the bearing retainer  98  and bearing assembly  80  mounted therein, should remain freely pivotable relative to the wing plate  72 . In this manner, the umbilicus gimbal assembly  78  provides for positive and reliable retention of umbilicus bearings of differing outer dimension without compromising the effectiveness of the gimballing action provided by the assembly  78 . 
     An alternate embodiment bearing retainer  98 ′ is shown in FIGS. 6,  7  and  8 . In this embodiment, a pair of outwardly projecting thumb tabs  138  are integrally formed in the flared outer end  114  of the bearing retainer  98 ′ adjacent the gap  118 . In addition, an inwardly projecting lip or ridge  140  (FIG. 7) is formed at the juncture of the flared outer end  114  and the middle segment  112 . 
     The ridge  140  provides an audible or tactile “click” when the bearing assembly  80  is fully and properly seated in the bearing retainer  98 ′. In addition, the ridge  140  resists withdrawing movement of the bearing assembly  80  once seated and helps retain the bearing assembly  80  within the bearing retainer  98 ′. 
     It will be appreciated that the thumb tabs  138  and the ridge  140  can be included each separately or in combination with each other as desired. 
     The thumb tabs  138  facilitate removal of the bearing assembly  80  from the bearing retainer  98 ′ following a processing procedure. By wrapping four fingers of the hand around the downstream portion of the umbilicus and thereafter pressing down on one of the tabs  138  with the thumb as shown in FIG. 8, the bearing assembly  80  is forced upwardly out of and away from the bearing retainer  98 ′.