Abstract:
A roller bearing end hub has a housing that internally houses a plane bearing, pin, and spring. The spring is biased against the plane bearing which is rotatably connected with the pin. The housing includes two half-housings which are configured to be mated together. The bearing is formed of a shape similar to the housing interior. The pin is smaller than an attached axle stub and the spring does not directly interact with the pin such that the amount of friction between the pin and bearing is minimized.

Description:
BACKGROUND 
     Roller conveyors are widely used to efficiently transport items. There are generally two types of conveyor rollers used in industry: roller bearing and plain bearing or “pin bearing”. Of the pin bearing rollers, there are two types: a non-sprung (i.e., no spring) pin bearing type and a sprung (i.e., with spring) pin bearing type. The non-sprung pin bearing has low friction such that the roller can easily rotate, but it cannot be easily inserted into the conveyor because it has to be assembled with the conveyor frame. In contrast, the sprung pin bearing design can be readily inserted and replaced in the conveyor frame because the spring allows the axle stub to retract and provide linear clearance for inserting the roller into the frame. However, the sprung pin has a large diameter that creates higher friction, which in turn causes power losses. Moreover, additional frictional losses are created by the spring engaging the pin. These designs also require the use of a large number of components that increase their expense and make servicing the roller more difficult. Manufacturing these designs can be rather difficult because the bearing housing limits the availability of certain radial features. 
     Thus, there is a need for improvement in this field. 
     SUMMARY 
     The systems and methods described herein address several of the issues mentioned above as well as others. The conveyor roller bearing system allows the roller to be easily installed and at the same time provides low friction. Moreover, it is less expensive because it only has four main components, an axle stub, a bearing, a spring, and a bearing housing. 
     The axle stub includes a hex head that engages the conveyor frame and a small diameter pin that is received in the pin bearing. With the small diameter pin, lower friction losses are created at the smaller diameter. The bearing is biased by a spring to further reduce friction while at the same time allows the axle stub to retract to facilitate installation. The housing utilizes a clamshell design that allows radial features to be easily formed. The pin bearing is keyed in such a manner to only be able to move in a linear direction to facilitate extension or retraction of the axle stub. With the bearing able to move along with the axle stub during extension and retraction, a number of issues associated with previous sprung type designs, such as bearing wear and axle warping, are reduced. 
     In one particular example, a conveyor roller includes a roller tube having end hubs at both opposing ends of the roller tube. Each end hub includes a housing having an internal cavity which is keyed to a bearing. The bearing fits within the cavity and is biased by a spring. The bearing contains a channel which receives a pin. The pin is a small diameter pin and is rotatable with respect to the bearing. The pin is attached to a stub axle which is formed to fit into a support structure. In one example, the bearing has a hexagonal cross-sectional shape that is received in a similarly shaped cavity. The stub axle, pin, and bearing are retractable within the housing as the spring compresses. 
     Further forms, objects, features, aspects, benefits, advantages, and embodiments of the present invention will become apparent from a detailed description and drawings provided herewith. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a roller conveyor system. 
         FIG. 2  is an exploded view of a roller from the  FIG. 1  roller conveyor system. 
         FIG. 3  is a cross-sectional view of the  FIG. 2  roller. 
         FIG. 4  is an exploded view of an end hub used in the  FIG. 2  roller. 
         FIG. 5  is an end view of the  FIG. 4  end hub. 
         FIG. 6  is a cross-sectional view of the end hub as taken along line  6 - 6  in  FIG. 5 . 
         FIG. 7  is an end view of the  FIG. 2  roller. 
         FIG. 8  is a cross-sectional view of the roller as taken along line  8 - 8  in  FIG. 7 . 
         FIG. 9  is a perspective view of a shell used in the  FIG. 4  end hub. 
         FIG. 10  is a back view of the  FIG. 9  shell. 
         FIG. 11  is a front view of the  FIG. 9  shell. 
         FIG. 12  is a side view of the  FIG. 9  shell. 
         FIG. 13  is a cross-sectional view of the shell as taken along line  13 - 13  in  FIG. 11 . 
         FIG. 14  is a cross-sectional view of the  FIG. 2  roller and a conveyor frame in a first installation position. 
         FIG. 15  is a side view of the roller and conveyor frame in the first installation position shown in  FIG. 14 . 
         FIG. 16  is a cross-sectional view of the roller and a conveyor frame in a second installation position. 
         FIG. 17  is a side view of the roller and conveyor frame in the second installation position shown in  FIG. 16 . 
         FIG. 18  is a cross-sectional view of the roller and a conveyor frame in a third installation position. 
         FIG. 19  is a side view of the roller and conveyor frame in the third installation position shown in  FIG. 18 . 
         FIG. 20  is a cross-sectional view of the roller and a conveyor frame in a fourth installation position. 
         FIG. 21  is a side view of the roller and conveyor frame in the fourth installation position shown in  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION 
     For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present invention may not be shown for the sake of clarity. 
     With respect to the specification and claims, it should be noted that the singular forms “a”, “an”, “the”, and the like include plural referents unless expressly discussed otherwise. As an illustration, references to “a device” or “the device” include one or more of such devices and equivalents thereof. It also should be noted that directional terms, such as “up”, “down”, “top”, “bottom”, and the like, are used herein solely for the convenience of the reader in order to aid in the reader&#39;s understanding of the illustrated embodiments, and it is not the intent that the use of these directional terms in any manner limit the described, illustrated, and/or claimed features to a specific direction and/or orientation. 
     The reference numerals in the following description have been organized to aid the reader in quickly identifying the drawings where various components are first shown. In particular, the drawing in which an element first appears is typically indicated by the left-most digit(s) in the corresponding reference number. For example, an element identified by a “100” series reference numeral will first appear in  FIG. 1 , an element identified by a “200” series reference numeral will first appear in  FIG. 2 , and so on. 
       FIG. 1  shows a perspective view of one example of a conveyor system  100 . The conveyor system  100  includes one or more rollers  101  supported by a frame  102 . The frame  102  includes one or more rails  104  between which the rollers  101  extend and one or more cross-beams (or cross-supports)  106  that join the rails together. In the illustrated embodiment, the rails  104  include elongated c-shaped beams that are arranged in a parallel configuration, but it should be recognized that the rails can be configured differently in other embodiments. For example, the rails  104  can be curved in other embodiments. As can be seen, the rollers  101  are rotatably mounted to the rails  104  such that an item placed on conveyor system  100  can travel in a direction generally transverse to the axes of rollers  101 . In the depicted embodiment, the conveyor system  100  is a gravity type conveyor, but in other examples, the conveyor system  100  can be a powered type conveyor. In still yet other variations, the rollers  101  can be incorporated into other types of conveyor systems, such as in belt conveyors. 
       FIG. 2  shows an exploded view of one of the rollers  101 . Each roller  101  includes a roller tube  201  and one or more end hubs  202  that are configured to engage the rails  104 . As shown, the end hubs  202  are located at opposing ends of roller tube  201 . In the illustrated embodiment, the roller tube  201  is the form of a hollow cylindrical tube, but the roller tube  201  can be shaped differently in other embodiments. For instance, the roller tube  201  can be partially or wholly solid and/or include grooves or other features for receiving drive belts and the like. In other examples, the outer surface of the roller tube  201  is bowed or concave in shape for guiding belts or items along the rollers  101 . In one example, the roller tube  201  is made from a metal, such as aluminum and/or steel, but it should be recognized that the roller tube  201  can be made from other materials. Each hub  202  includes a housing  203  and an axle stub  204  that is configured to engage one of the rails  104 . To provide clearance for facilitating insertion of the roller  101  into the frame  102 , the axle stub  204  is able to move in a telescoping fashion relative to the housing  203  of the hub  202 . In the illustrated embodiment, both hubs  202  have axle stubs  204  that are able to move in a telescoping fashion. However, in other examples, only one of the hubs  202  has an axle sub  204  that is able to move in a telescoping fashion, while the other axle stub is fixed such that it is unable to move in a telescoping fashion. The axle stub  204  is also configured to rotate relative to the housing such that the roller  101  is able to rotate about an axis  205 . Each end of the roller tube  201  has an end face  206  that surrounds a hub opening  207  in which a corresponding end hub  202  is received. The roller tube  201  in the depicted embodiment is hollow such that a cavity  208  extends between the hub openings  207 . 
     Referring to  FIG. 3 , which shows a cross-sectional view of the roller  101 , the housing  203  of end hub  202  is slidably insertable into opening  207  of roller tube  201  such that end hub  202  is substantially contained within roller tube  201 . The housing  203  has an annular flange  301  that abuts against face  206  when end hub  202  is fully seated within roller tube  201 . In this way, end hub  202  is prevented from sliding further into roller tube  201 . In one example, the end hubs  202  are secured with a frictionally tight fit to the roller tube  201 , but the end hubs  202  can be secured to the roller tube  201  in other manners, such as with an adhesive, crimping, and/or screws. While the housing  203  of the end hub  202  has a generally cylindrical shape so as to coincide with the shape of the opening  207  of the roller tube  201 , the housing can have different shapes depending on the shape of the opening  207  and/or the roller tube  201  in other examples. For instance, the housing  203  of the end hub  202  can have a hexagonal shape when the opening  207  in the roller tube has a hexagonal shape. With the above-described design, the end hub  202  is able to be easily retrofitted to numerous existing roller conveyor designs. 
       FIG. 4  shows an exploded view of the end hub  202 . As depicted, the end hub  202  includes the housing  203 , the axle stub  204 , a bearing  402 , and a spring  404 . With this four-piece construction, the end hub  202  can be manufactured inexpensively and efficiently as compared to previous sprung-type roller designs. Looking at  FIG. 4 , the housing  203  includes a unique clamshell design in which the housing  203  is formed by clamping two (or more) shells  406 ,  408  together. The shells  406 ,  408  allow the various features of the housing  203  to be formed using a relatively inexpensive injection molding processes with a straight poll die and no “action” in the tool. In the illustrated embodiment, the two shells  406 ,  408  are generally interchangeable and for the purposes of discussion will be sometimes referred to collectively by reference number  406 . With the two shells  406 ,  408  being identical, tooling costs can be reduced. However, the shells  406  can be shaped differently so as to not be interchangeable and/or require more shells  406  than illustrated to form the housing  203 . Moreover, one (or more) of the shells  406 ,  408  can be larger than the other. The shells  406 ,  408  are configured to mate together so as to form a bearing cavity  410  in which the bearing  402  and spring  404  are received. At one end of the housing  203 , the shells  406 ,  408  form a spring support wall  412  against which the spring  404  is biased. In the illustrated example, the spring support wall  412  closes the bearing cavity  410 , but it is envisioned that in other examples the spring support wall  412  can be partially open while still supporting the spring  404 . As should be further appreciated, other structures can be used besides the support wall  412  for supporting the spring  404 , such as adhesives, flanges, and/or protrusions, to name just a few examples. Moreover, while the spring  404  is illustrated as a coil type spring, it should be appreciated that other types of springs and/or biasing mechanisms can be used, such as leaf springs, cantilever springs, tension springs, gas springs, hydraulic type biasing mechanisms, and/or torsion springs, to name just a few examples. Opposite the spring support wall  412 , the shells  406 ,  408  together define an axle stub opening  414  through which the axle stub  204  extends. In other variations, the axle stub opening  414  is formed in only one of the shells  406 ,  408 . For instance, instead of the shells  406 ,  408  being split longitudinally along the axis  205  (as is shown in  FIG. 4 ), the shells  406 ,  408  in other embodiments are divided in a plane that is transverse to the axis  205  such that one of the shells  406 ,  408  defines the end of the bearing cavity  410  having the spring support wall  412 , and the other shell  406 ,  408  defines the axle stub opening  414 . In the bearing cavity  410 , the spring  404  is sandwiched between the bearing  402  and the spring support wall  412 . The spring  404  biases the bearing  402  so that the axle stub  204  is normally in an extended state relative to the housing  203  such that the axle stub  204  extends from the axle stub opening  414 . 
     The bearing cavity  410  is shaped to generally match the cross-sectional shape of the bearing  402 , but the bearing cavity  410  is longer so as to allow the bearing  402  to slide within the bearing cavity  410 . In previous sprung type designs, the bearing was fixed and unable to move in a linear direction as the pin or axle was extended or retracted. This is turn can create the potential for a whole host of issues. For instance, any dirt or debris on the axle can form transverse grooves, striations, or other wear at the interface between the bearing and axle as the axle slides relative to the bearing, which in turn can create greater friction between the axle and bearing during rotation. Moreover, as the axle extends and retracts, different moment arms or loads are created between the bearing and the axle, and in turn, these differences can lead to problematic bending or warping of the axle and/or damage to the bearing. On the other hand, with the illustrated design, the bearing  402  is able to normally move linearly with the axle stub  204  during extension and retraction, thereby reducing these as well as other issues experienced with the previous designs. Generally speaking, an outer longitudinal surface  416  of the bearing  402  and the bearing cavity  410  are keyed with one another so that the bearing  402  is able to move in a linear direction along the axis  205  but is unable to rotate about the axis  205  (relative to the housing  203 ). In the example shown in  FIG. 4 , the bearing  402  and the bearing cavity  410  each have a substantially hexagonal prism shape, but the bearing  402  and bearing cavity  410  can be shaped in other manners that allow linear movement but not rotational movement of the bearing  402  relative to the housing  203 . For instance, the bearing  402  and bearing cavity  410  can have a triangular, rectangular, pentagonal, and/or star-shaped cross-sectional shape, to name just a few examples, and/or can include keying and/or other structures that facilitate linear movement but prevent rotational movement of the bearing  402 . 
     Looking at  FIG. 4 , the bearing  402  defines an axle pin opening  418  in which a pin  420  from the axle stub  204  is received. As can be seen, the axle stub  204  includes a head portion  422  from which the pin  420  extends. The head portion  422  includes a rail engagement section  424 , a collar section  426 , and a retention flange  428 . The rail engagement section  424  is configured to engage the rail  104 . In the illustrated embodiment, the rail engagement section  424  has a hexagonal shape, but the rail engagement section  424  can be shaped differently in other embodiments. The rail engagement section  424  can be tapered so as to eliminate noise created by rattling of the axle stub  204  in the axle pin opening  418 . The collar section  426  has a cylindrical shape so as to facilitate rotation of the axle stub  204  in the axle stub opening  414  of the housing  203 . The retention flange  428  is designed to retain the axle stub  204  along with the bearing  402  inside the housing  203 . The retention flange  428  in  FIG. 4  has a continuous disc shape, but it can be shaped differently in other embodiments. For instance, the retention flange  428  can be discontinuous and have notches. Around the axle pin opening  418 , the bearing  402  defines a retention flange cavity  430  shaped and configured to receive all or part of the retention flange  428  of the axle stub  204 . The retention flange cavity  430  in the illustrated embodiment has a cylindrical shape to match the shape of the retention flange  428  so as to facilitate rotation of the axle stub  204  relative to the bearing  402 . In other examples, the retention flange cavity  430  is shaped differently than is illustrated in  FIG. 4  or is eliminated. Around the axle stub opening  414 , the housing  203  has an engagement flange  432  that is sized small enough to engage the retention flange  428  of the axle stub  204  but at the same is sized larger than the collar section  426  of the axle stub  204  so as to allow rotation of the axle stub  204  relative to the housing  203 . The engagement flange  432  has a notch portion  434  that is sized and shaped to receive at least part of the retention flange  428  of the axle stub  204 . In the illustrated embodiment, the spring  404  and the pin  420  of the axle stub  204  are made of steel, while the head portion  422  of the axle stub  204  along with the housing  203  and the bearing  402  are made of plastic. With the illustrated embodiment, the plastic-metal interface between the pin  420  of the axle stub  204  and the bearing  402  facilitates smooth rotation. These components can be made from different combinations of materials and/or different materials, however. In order to further reduce friction, the pin  420  of the axle stub  204  and the corresponding axle pin opening  418  in the bearing  402  have a diameter that is smaller than the diameter of the head section  422  of the axle stub. With the pin  420  being smaller than the head section  422 , the end hub  202  experiences less friction as compared to conventional designs in which the axle generally has the same large diameter. In one particular example, the pin  420  of the axle stub  204  in  FIG. 4  has an outer diameter of three-sixteenths of an inch (i.e., 3/16″ OD). 
       FIG. 5  shows an end view of the end hub  202  when assembled, and  FIG. 6  shows a cross-sectional view of the end hub  202  as taken along line  6 - 6  in  FIG. 5 . As can be seen in  FIG. 6 , the end of the spring  404 , which is opposite the spring support wall  412 , is received inside a spring cavity  602  in the bearing  402 . The spring cavity  602  is formed between an outer casing  604  that defines the outer surface  416  of the bearing  402  and an inner casing  606  that defines the pin opening  418  in which the pin  420  of the axle stub  204  is received. Ribs  608  extend radially between the outer casing  604  and the inner casing  606  to connect the casings  604 ,  606  together. The ribs  608  in the illustrated embodiment only extend for a portion of the length of the bearing  204  such that the spring  404  is able to be seated inside the bearing  402 . It should be appreciated that in other variations the spring  404  can be seated or otherwise coupled to the bearing  402  in other manners (or not at all). For instance, the spring  404  in another embodiment simply presses against a flat end of the bearing  402 . 
     As shown in  FIG. 6 , the spring  404  biases the bearing  402  so that the head  422  of the axle stub  204  normally extends from the housing  203 . When the axle stub  204  is extended, the bearing  402  abuts against the engagement flange  432  of the housing  203 . The notch portion  434  in the engagement flange  432  and the retention flange cavity  430  in the bearing  402  form a flange cavity  610 . The space provided by the flange cavity  610  aids in reducing friction between the axle stub  204  and the bearing  402  as well as assists with compensating for tolerance issues between the rails  104  of the frame  102 . As noted before, the spring in conventional sprung pin type roller designs directly contacts the axle stub so as to bias the axle stub into an extended state. This arrangement of the spring contacting the axle stub in turn creates additional friction and wear when the roller is rotated. With the arrangement illustrated in  FIG. 6 , the spring  404  does not directly contact the axle stub  204 , thereby reducing the associated friction and wear. As shown, the spring  404  biases the bearing  402  which in turn biases the axle stub  204 . Again, the bearing  402  is keyed with the bearing cavity  410  so that the bearing  402  is unable to rotate, but the bearing  402  is able to move in a longitudinal direction along the axis  205 . To put it another way, the bearing  402  is sandwiched between the spring  404  and the axle stub  204  such that the axle stub  204  is free to rotate relative to the bearing  402  while at the same time the bearing  402  is able to longitudinally move so as to facilitate extension and retraction of the axle stub  204 . 
       FIG. 7  shows an end view of the roller  101  with the end hub  202  inserted into the roller tube  201 .  FIG. 8  is a cross-sectional view of the roller  101  as taken along line  8 - 8  in  FIG. 7 . During installation, the spring  404  is compressed as the axle stub  204  is pushed longitudinally along the axis  205  into the housing  203 . Once the roller  101  is properly positioned in the frame  102  ( FIG. 1 ), the axle stub  204  is released such that the spring  404  pushes the axle stub  204  to extend and engage the frame  102 . When the axle stub  204  is extended, as is shown in  FIG. 8 , the collar  426  of the axle stub  204  is positioned in the opening  414  of the housing  203 , thereby facilitating smooth rotation of the roller  101 . During operation, the roller  101  is then able to rotate about the about the axle stub  204 . 
     As mentioned before, the clam-shell design of the housing  203  of the end hub  202  allows the housing to be manufactured inexpensively while also permitting the complex internal shapes within the housing  203 , such as those formed along the bearing cavity  410 .  FIG. 9  shows a perspective view of one of the shells  406 .  FIGS. 10 ,  11 , and  12  respectively show back, front, and side views of the shell  406 .  FIG. 13  shows a cross-sectional view of the shell  406  as taken along line  13 - 13  in  FIG. 11 . Again, the clam-shell design allows complex structures to be inexpensively manufactured using injection molding or similar processes. Looking at  FIGS. 9 ,  11 , and  13 , this manufacturing technique facilitates the formation of complex structures, such as the bearing cavity  410 , the annular flange  301 , and the notched portion  434  on the engagement flange  432 . Located around the bearing cavity  410 , the shells  406 ,  408  have mating surfaces  902  where the shells  406 ,  408  are joined together. 
     To align the shells  406 ,  408  together, the mating surfaces  902  in the illustrated embodiment have one or more alignment pins  904  configured to mate with one or more corresponding alignment openings  906 . In the illustrated embodiment, the alignment pins  904  have a cylindrical shape, but the alignment pins can be shaped differently in other embodiments (e.g., have a box or rectangular shape). It should be appreciated that other alignment and/or securing structures also can be used. For instance, the pins  904  can be reconfigured to mechanically secure the shells together and/or adhesives can be used. With the two shells  406 ,  408  being identical, tooling costs can be reduced. Alternatively or additionally, once assembled, the roller tube  201  can hold the shells  406 ,  408  together. During use, debris can build up inside the bearing cavity  410  which in turn can jam or otherwise damage the end hub  202 . To address this issue, the shells  406 ,  408  have one or more debris openings  908  that facilitate debris removal from the bearing cavity  410 . As shown, the debris openings  908  are located near the end of the bearing cavity  410  by the spring support wall  412 . With this location, as the bearing  402  reciprocates in the bearing cavity  410  as the axle stub  204  is compressed and extended, the bearing  402  pushes the debris towards and/or out the debris openings  908 . To facilitate insertion of the end hub  202  into the roller tube  201 , the shells  406 ,  408  have a chamfer  910  at one end, as is shown in  FIGS. 9 ,  10 ,  11 , and  12 . Alternatively or additionally, the housing  203  can include a slight taper and/or other features to facilitate insertion into the roller tube  201 . Turning to  FIGS. 10 ,  12 , and  13 , in order to reduce the amount of material needed to produce the housing  203 , the shells  406 ,  408  include ribs  1002  with voids  1004  in between that form the exterior of the housing  203 . Using the ribs  1002  ensures the housing  203  is both lightweight and strong. 
     This unique four component, clamshell design for the end hub  202  helps to simplify assembly and reduce manufacturing as well as maintenance costs. A technique for manufacturing the rollers  101  and the end hub  202  will now be initially described with reference to  FIGS. 2 ,  3 , and  4 . During manufacturing, the bearing  402  along with the shells  406 ,  408  are produced via thermoplastic injection molding processes. In a somewhat similar fashion, a thermoplastic is injection molded around one end of the steel pin  420  so as to form the head  422  of the axle stub  204 . In one example, the spring  404  is a standard coil spring that is readily purchased off the shelf. It should be recognized that other techniques and processes, besides injection molding, can be used to form these components. For instance, subtractive techniques, like computer numerical control (CNC) machining, and/or additive techniques, like three-dimensional (3D) printing, can be used to produce these components. Moreover, other materials besides plastics and metals can be used to make these parts. 
     Looking again at  FIG. 4 , to assemble the end hub  202 , the spring  404  is positioned inside the bearing cavity  410  of one of the shells  406 . The pin  420  of the axle stub  204  is inserted into the pin opening  418  of the bearing  402 . The combined axle stub  204  and bearing  402  subassembly is then positioned inside the bearing cavity  410  of the shell  406  along with the spring  404 . One end of the spring  404  is received inside the spring cavity  602  of the bearing  402  ( FIG. 6 ). The retention flange  428  of the axle stub  204  is positioned inside the bearing cavity  410  so that the engagement flange  432  of the shell  406  is able to retain the axle stub  204  with the head  422  of the axle stub extending through the axle stub opening  414 . In this state, the bearing  402  is then sandwiched between the spring  404  and the axle stub  204 . In another variation of this assembly technique, the axle stub  204 , bearing  402 , and spring  404  are loaded into the bearing cavity  410  of one of the shells  406  individually. This individual loading can occur in any order such that the axle stub  204  or the bearing  402  is first loaded before the spring  404  is loaded into the bearing cavity  410 . In still yet another variation, the axle stub  204 , bearing  402 , and spring  404  can be pre-assembled together before the combined assembly is loaded into the bearing cavity  410  of the shell  406 . It is envisioned that other subassembly combinations can be created before insertion into the bearing cavity  410 . Alternatively or additionally, various components can be integrated together to form a single unit. For example, the spring  404  can be integrated into the bearing  402  and/or the shells  406 ,  408 . For instance, the spring  404  can be an integral plastic spring formed at one end of the bearing  402  during injection molding. Once the axle stub  204 , the bearing  402 , and the spring  404  are loaded into the bearing cavity  410 , the shells  406 ,  408  are brought together so as to form the housing  203 . As noted before with respect to  FIG. 9 , the alignment pins  904  are received in the alignment holes  906  when the shell  406 ,  408  are brought together so as to ensure proper alignment. Together the shells  406 ,  408  form the completed bearing cavity  410  where the axle stub  204 , the bearing  402 , and the spring  404  are disposed in the housing  203  of the end hub  202 . In one example, the shells  406 ,  408  are joined together, such as via an adhesive and/or welding, but the shells  406 ,  408  can be joined together in other manners or not at all. In another example, the shells  406 ,  408  are held together with the roller tube  201 . Referring to  FIGS. 2 and 3 , once assembled, the end hub  202  is inserted into the hub opening  207  of the roller tube  201 . The end hub  202  can be held in place via friction between the end hub  202  and the roller tube  201 . Alternatively or additionally, the end hub  202  can be held in place inside the roller tube  201  in other ways, such as with an adhesive. In one variation, both ends of the roller  101  have end hubs  202  with retractable axle stubs  204 . However, in other variations, only one end of the roller  101  has an axle stub  204  that is retractable while the other end has an axle stub that is fixed or non-retractable (but is able to rotate, if needed). 
     A technique for replacing a roller  101  in the frame with a new roller  101  will now be described with reference to  FIGS. 14-21 .  FIGS. 14 ,  16 ,  18 , and  20  illustrate cross-sectional views of the roller  101  as the roller  101  is inserted into the frame  102 .  FIGS. 15 ,  17 ,  19 , and  21  show the corresponding side views of the insertion stages illustrated in  FIGS. 14 ,  16 ,  18 , and  20 , respectively. Looking at  FIG. 15 , each rail  104  of the frame  102  has a series of one or more axle receptacles  1501  in which a portion of the rail engagement section  424  of the axle stub  204  ( FIG. 4 ) is received. In the illustrated embodiment, the axle receptacle  1501  has a hexagonal shape, but the axle receptacle  1501  can be shaped differently in other embodiments. Moreover, the axle receptacle  1501  in the illustrated embodiment is located near the top of the rail  104  so as to permit items wider than the frame  102  to roll on the rollers  101 , but it is envisioned that the rollers  101  can be positioned elsewhere on the rails  102 , such as in the middle or near the bottom of the rails  102 . Moreover, the spacing between the axle receptacles  1501  can be different than is illustrated. 
     To insert roller  101  into the frame  102 , the axle stub  204  at one end of the roller  101  is inserted into the axle receptacle  1501 , as is shown in  FIGS. 14 and 15 . Looking at  FIGS. 16 and 17 , the axle stub  204  at the other end of the roller  101  is pushed in such that axle stub  204  is mostly situated inside the end hub  202 . The axle stub  204  is retracted to an extent so as to provide clearance for inserting the roller  101  into the frame  102 . If needed, the other axle stub  204  that is already inserted in the axle receptacle  1501  can be pressed in so as to provide additional clearance for the roller  101 . Turning to  FIGS. 18 and 19 , with the axle stub  204  now depressed, the end of the roller  101  is lowered until the axle stub  204  is aligned with the coinciding receptacle  1501 . As noted before, the spring  404  is biased so as to extend the axle stub  204 . While the end of the roller  101  is lowered, the axle stub  204  can be released once the axle stub  204  reaches the frame  102  such that the axle stub  204  is able to ride along the inner surface of the rail  104 . Once axle stub  204  reaches the axle receptacle  1501 , the spring  404  causes the axle stub  204  to pop into the axle receptacle  1501 , as is shown in  FIGS. 20 and 21 . In another variation, the axle stub  204  is held in a retracted state until the axle stub  204  is aligned with axle receptacle  1501  and the axle stub  204  is released such that the spring  404  extends the axle stub  204  into the axle receptacle  1501 . In still yet another variation, the axle stubs  204  at both ends of the roller  101  are simultaneously compressed and released during insertion of the roller  101  into the frame  102 . 
     As alluded to before, having the spring  404  biasing the bearing  402  rather than contacting the axle stub  204  allows the axle stub  204  to rotate more freely due to reduced friction. This in turn allows the axle stub  204  to be easily rotated into position for insertion into the axle receptacle  1501 . In the previous designs where the spring directly contacts the axle stub, it was found that the axle stubs were harder to rotate into position during insertion because of the greater friction created by the axle stub being compressed against the spring. On the other hand, the roller  101  shown in the drawings does not experience these issues because the bearing  402  acts as a buffer between the linear compression movement of the spring  404  and the rotary movement of the axle stub  204 . This ability to easily rotate can be especially helpful when the rail engagement section  424  of the axle stub  204  and/or the axle receptacle  1501  have a non-circular or keyed shape requiring a specific rotational orientation, such as the hexagonal shape of the rail engagement section  424  and axle receptacle  1501  shown in the drawings. 
     With the roller  101  now installed in the frame, as is depicted in  FIGS. 20 and 21 , the roller conveyor system  100  ( FIG. 1 ) can be used. The axle stubs  204  in the illustrated embodiment are shaped to fit within receptacles  1501  such that any rotational motion is restricted, but in other embodiments, the rotational movement need not be restricted. In the illustrated configuration, the roller tube  201  is free to rotate about the axis  205  as axle stubs  204  are held stationary. When a force is imparted on roller  101  tending to cause that roller to rotate about the axis  205 , the axle stubs  204  on both ends of the roller  101  are held stationary and bearing  402  rotates about pin  420 . The small size of the pin  420  relative to the head  422  of the axle stub  204  results in reduced friction between the pin  420  and the bearing  402 . This limited surface friction results in correspondingly limited frictional losses during operation of the rollers  101 . Furthermore, with the spring  404  abutting against the bearing  402 , rather than the axle stub  204 , frictional losses between the pin  420  of the axle stub  204  and the spring  404  are eliminated. 
     The illustrated design also helps to simplify servicing. The rollers  101  can be readily removed from the frame  102  by simply compressing one or both of the axle stubs  204  and pulling the roller  101  from the frame. During operation of the conveyor system  100 , dirt and contaminants can enter into the end hub  202  and/or the roller tube  201 . The relative ease of removal of the rollers  101  allow the rollers  101  to be easily removed, replaced, and/or serviced. When contaminants enter the end hub  202 , the contaminants may be expelled through debris openings  908  via air pressure, through the use of gravity, and/or in other manners. As noted above, the compression of the axle stub  204  can also cause the bearing  402  to push the contaminants out the debris openings  908 . Faulty end hubs  202  can be readily swapped out for new ones by simply pulling the old ones from the roller tube  201  and inserting new ones. With the four component design, components within the end hub  202 , such as the bearing  402  and/spring  404 , can be easily replaced. Once the roller  101  has been serviced (or a replacement roller  101  is acquired), the roller  101  can be reinserted into the frame in the manner as described above with reference to  FIGS. 14-21 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the inventions defined by following claims are desired to be protected. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.