Abstract:
A conveyor system comprises a pulley provided with a bearing. The bearing includes an outer bearing race with an outer surface. The conveyor system further comprises a frame with a side plate having a top end defining a first cut-out. At least a portion of the outer surface of the outer bearing race is engaged with the first cut-out. The side plate also defines a second cut-out providing an opening into the first cut-out. The second cut-out facilitates insertion of the bearing into the first cut-out.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a conveyor system, such as a conveyor belt system. The present invention is more particularly directed to a conveyor system with interchangeable bed modules and pulley sleeves. 
     BACKGROUND OF THE INVENTION 
     Conveyor belt systems are widely used to transport objects in various industrial, assembly and automation applications. For transporting relatively small objects, relatively small conveyor belt systems are used with dimensions on the order of several feet in the longitudinal (direction of conveyance) direction and two inches to several feet in the transverse direction. 
     A conventional conveyor belt system, shown in FIG. 1, includes a drive pulley  104 , a tail pulley  108 , a frame  106 , a bed  106 A and a conveyor belt  102 . The belt  102  is looped around the pulleys  104 ,  108  and over the bed  106 A. The drive pulley  104  is driven to rotate in the direction R 1  by a driver (not shown) such as a conventional drive motor. 
     The rotating drive pulley  104  maintains rolling contact with the belt  102 , thereby driving the belt  102  to rotate in the direction R 2  around the frame  106 . The tail pulley  108  also maintains rolling contact with the belt  102 , and freely rotates in the direction R 3  in response to the rotation of belt  102 . In this way, the tail pulley  108  supports rotating belt  102  without significantly impeding its rotation. 
     Frame  106  supports the pulleys  104 ,  108  so that they are appropriately spaced apart from each other. Frame  106  also includes an integral bed  106 A. The integral bed  106 A is generally constructed as a unitary piece with the rest of the, frame  106 , or is permanently fixed thereto. 
     The bed  106 A provides a relatively slick and relatively continuous surface to support the underside of the belt  102 . Because of the fairly continuous surface provided by the bed  106 A, objects placed on the top of the belt  102  will be substantially continuously supported by the underlying bed  106 A, thereby minimizing shear stress and strain on the belt  102  itself. Because the bed  106 A is relatively slick, the belt  102  will slide over the bed  106 A with relatively low friction, even when objects on top of the belt  102  weigh the belt  102  down onto the bed  106 A, thereby minimizing longitudinal forces in the belt  102 . 
     As shown in FIG. 1, the bed surface defines a line, herein called the bed height BH. The belt  102  travels over and along this bed height BH line. The tops of the drive pulley  104  and the tail pulley  108  are both co-linear with the bed height BH line. In other words the pulleys  104 ,  108  have an outer radius of H 1  so that the tops of these pulleys reach the level of the bed. Thus, the height of the pulleys match the height of the bed. 
     This matching of pulley and bed heights is important for several reasons. First, if there is a disparity in heights between the pulley and the bed, then an object being transported on top of the belt  102  may be jolted as it travels over a portion of the system  100  where there is a transition in height between the bed  106 A and a pulley  104  or  108 . This kind of jolting caused by mismatched heights may be especially troublesome in application where two conveyor systems are placed end to end to effect a longer conveyor run. 
     Second, if bed  106 A is significantly lower than the height of the pulleys, then the belt  102  will not be supported by the bed  106 A. When heavy objects are placed on the belt  102 , the belt  102  may be (temporarily or permanently) deformed by objects pushing the unsupported belt  102  down to the level of the bed  106 A. 
     Third, if the bed  106 A is significantly higher than the pulleys  104 ,  108 , then the belt  102  will be pulled tightly around the transverse edges of the bed. This increases wear on the belt  102 . 
     Fourth, if the bed  106 A is significantly higher than the pulleys  104 ,  108 , then the contact area between the belt  102  and the drive pulley  104  will be reduced, thereby decreasing the load which the drive pulley  104  can effectively drive the belt  102  to convey. For at least these reasons, matching pulley and bed height is an important precept in the design of most conveyor belt systems. 
     In the embodiment of FIG. 1, the heights of the pulleys  104 ,  108  and the bed  106 A are exactly the same (all heights are at the BH line). However, depending on factors such as the material of the belt, optimal performance may involve making the height of the bed either slightly higher or slightly lower than the height of the pulleys. In other words, the height of the pulleys may be slightly displaced from the bed line BH. 
     For example, if a conveyor belt is made of a stiff material, then the belt may not follow the outer surface of each pulley for a full 180° (even with an appropriate degree of tightening), and the belt may therefore come off the pulley at an angle relative to the tangent direction taken at the top of the pulley. This phenomenon is known as cupping. In this case, the frame may optimally be designed so that the bed is a bit higher than the top of the pulley, to appropriately account for the angle at which the belt comes off of the pulleys. 
     As used herein, the pulleys and bed are “matched” in height when the height of the pulleys and the height of the bed are close enough to each other to provide good performance and a low degree of belt stress, strain and wear, especially in view of the above-described problems caused by wide height disparities. As used herein, the pulleys and bed may be “matched” in height, even if their heights are not exactly the same, whether the slight disparity in heights is a result of design or random variations (such as manufacturing variations). 
     It is also noted that two pulleys and a bed may be matched in height even if the pulleys have different radii. In order to be matched in height, the top of each pulley should merely be sufficiently close to the height of the bed for optimal performance under the circumstances of the application. 
     Another embodiment of a conventional conveyor belt system  200  is shown in FIG.  2 . Conveyor belt system  200  includes a belt  202 , a drive pulley  204 , a frame  206 , a tail pulley  208  and a bed  210 . The conveyor belt system  200  is similar to conveyor belt system  100 , except that instead of an integral bed such as  106 A, the bed  210  is connected to frame  206 . 
     One advantage of such a detachable bed  210 , is that the bed  210  can easily be made from a different material than the frame  206 . For example the frame  206  may be made from metal, while the bed  210  might be made of ultra high molecular weight polymer (herein UHMW), which provides a smooth, slick supporting surface for the belt  202 . However, conveyor system  200  cannot be used without the detachable bed  210  for two reasons explained below. 
     First, if the system  200  is used without the detachable bed  210 , then the pulley height and the height of the frame  206  (without a bed) will be drastically mismatched. The pulleys  204 ,  208  have an outer radius of H 4  and a resulting height of BH′. Likewise, the bed  210  also has a height of BH′. More specifically, as shown in FIG. 2, when the detachable bed  210  is in place, the aggregate height of the frame  206  (H 2 ) and bed  210  (H 3 ) adds up to H 4 , thereby matching the height of the pulleys  204 ,  208  at the bed height BH′ line. If the bed  210  is removed, ther the height of the frame H 2  would fall short of the BH′ line defined by the tops of the pulleys  204 ,  208 , and the heights would be problematically mismatched. 
     Second, the frame  206  (without the detachable bed  210 ) does not provide a good bed surface for the belt  202 , because it is not continuous. FIG. 3 shows the frame  206  from its underside. The frame  206  is actually a lattice of several elongated, aluminum members  212 ,  214 ,  216 ,  217 ,  218 ,  220 ,  222 . 
     More specifically, the frame  206  is assembled from two extruded side walls  212 ,  214 , three transverse members  216 ,  217 ,  218  and two support members  220 ,  222 . While this frame  206  is considerable lighter and easier to fabricate than a solid aluminum frame would be, the frame does not provide a continuous surface appropriate for supporting a load bearing conveyor belt (as shown in FIGS. 3 arid  4 ). This makes bed  210  a necessary component of conveyor belt system  200 . 
     Because the conveyor belt system  200  requires bed  210 , the pulleys  204 ,  208  must be chosen so that the top of each pulley  204 ,  208  corresponds with the aggregate height of the frame and bed assembly. In both conventional conveyor belt systems  100 ,  200  described above, the effective height of the bed must be determined when the system is designed so that the height of the pulleys will match the height of the bed (integral  106 A or detachable  210 ) which will be used. 
     As will be understood, conventional conveyor belt systems such as  100 ,  200  do not allow for any modifications which would change the effective bed height, because a change in bed height would necessitate a change in the pulleys, which is an extremely difficult change to make in practice. For example, a change to larger pulleys can cause physical interference between the pulleys and the frame. Therefore, any modification in bed height will generally require an entirely new conveyor system, essentially designed from scratch, so that the pulley height appropriately matches the bed height. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of some embodiments of the present invention to provide a conveyor belt system with a modular bed and pulley system, wherein the effective height of the bed and pulleys can easily be changed, without causing a mismatch in height between the bed and pulleys. 
     It is a further object of some embodiments of the present invention, to provide a conveyor system which can be used either with or without a detachable bed module. 
     It is a further object of some embodiments of the present invention to provide a conveyor system which addresses the problems and shortcomings of prior conveyor systems described herein. 
     It is a further object of some embodiments of the present invention to provide a conveyor system design which enables easier interchangeability of conveyor beds, pulleys, belts and frames to simplify the design, manufacture and availability of adaptable systems. 
     According to some embodiments of the present invention, a conveyor belt system includes a first pulley, a second pulley and a frame. The first pulley and second pulleys each have an outer circumferential surface. The frame is rotatably connected to the first pulley and the second pulley, and the frame includes a bed surface which is matched in height to the outer circumferential surface of the first pulley and the outer circumferential surface of the second pulley. The frame also includes bed mounting structures adapted to attach a bed module over the bed surface of the frame. 
     According to some embodiments of the present invention, a conveyor belt system includes a first pulley, a second pulley, a frame, a first pulley sleeve, a second pulley sleeve, and a bed module. The first and second pulley sleeves are attached respectively around the outer circumferential surface of the first and second pulleys. The frame includes a bed surface which is matched in height to the outer circumferential surface of the first pulley and the outer circumferential surface of the second pulley. The bed module is attached to the frame and is matched in height to the outer circumferential surface of the first pulley sleeve and the outer circumferential surface of the second pulley sleeve. 
     Still other objects of the present invention will become readily apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration, of some of the best modes contemplated for carrying out this invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention as set forth in the detailed description will be more fully understood when viewed in connection with the drawings in which: 
     FIG. 1 is a side view of a conventional conveyor belt system; 
     FIG. 2 is a side view of another conventional conveyor belt system; 
     FIG. 3 is a bottom view of the conventional conveyor system embodiment of FIG. 2; 
     FIG. 4 is a partial sectional view of the conveyor belt system shown in FIG. 2 as viewed from section lines IV in FIG. 2; 
     FIG. 5 is a side view of a first embodiment of a conveyor system according to the present invention with a modular bed module and pulley sleeves in place; 
     FIG. 6 is a bottom view of the conveyor system shown in FIG. 5; 
     FIG. 7 is a partial sectional view of the conveyor system shown in FIG. 5 as viewed from section lines VII in FIG. 5; 
     FIG. 8 is a perspective view of a pulley sleeve used in the conveyor system shown in FIG. 5; 
     FIG. 9 is a side view of the conveyor system shown in FIG. 5 with the modular bed module and the pulley sleeves removed; 
     FIG. 10 is a bottom view of the conveyor system shown in FIG. 9; 
     FIG. 11 is a top view of the conveyor system shown in FIG. 9; 
     FIG. 12 is a side view of a second embodiment of a conveyor belt system according to the present invention; 
     FIG. 13 is a cross-sectional view of the conveyor belt system of FIG. 12, taken along line XIII—XIII thereof; 
     FIG. 14 is a partial, broken-out end view of the drive pulley assembly of the conveyor belt system of FIG. 12; 
     FIG. 15 is a partial side view of the drive pulley assembly of the conveyor belt system of FIG. 12; 
     FIG. 16 is a partial side view of the tail pulley assembly of the conveyor belt system of FIG. 12; 
     FIG. 17 is a partial end view of the tail pulley assembly of the conveyor belt system of FIG. 12; 
     FIG. 18 is a partial side view of the tail pulley shaft and ruler plate of FIG.,  17  illustrating the conveyor belt in an initial state without slack; 
     FIG.  19 . is a partial side view similar to FIG. 18, showing the tail pulley shaft and ruler plate after the belt has been tensioned; 
     FIG. 20 is a partial end view illustrating insertion of the drive pulley bearing into a side plate; 
     FIG. 21 is a partial end view showing the drive pulley bearing of FIG. 20 after insertion and rotation; 
     FIG. 22 is a side view of the second embodiment of a conveyor system with a bed module and pulley sleeves installed; 
     FIG. 23 is a cross-sectional view of the conveyor system of FIG. 22, taken along lines XXIII—XXIII thereof, showing a magnetic bed module; 
     FIG. 24 is a cross-sectional view similar to that of FIG. 23 showing a self-tracking bed module and conveyor belt; 
     FIG. 25 is a cross-sectional view similar to that of FIG. 23 showing a vacuum bed module; 
     FIG. 26 is a partial, broken-out, top view of a vacuum bed and belt assembly in accordance with the present invention; and 
     FIG. 27 is a partial side view of a synchronous conveyor belt embodiment of a conveyor system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings in detail, wherein like numerals indicate the same elements throughout the Figures, FIGS. 5 to  11  set forth an embodiment of a conveyor system  300  according to the present invention which shows the use of a detachable bed module and detachable pulley sleeves that are matched in height. The conveyor system  300  includes a drive pulley  304 , a drive pulley sleeve  305 , a frame  306 , a tail pulley  308 , a tail pulley sleeve  309  and bed module  310 . Before use, a belt appropriate for the desired application would be looped around the outer circumferential surface of the pulley sleeves  305 ,  309  and the bed module  310 , and appropriately tensioned. To simplify the drawings, the belt is not shown in FIGS. 5 to  11 . 
     In FIG. 5, a bed module  310  is detachably attached to frame  306 , and may be one of many types (e.g., vacuum bed, high speed bed, self-tracking bed, magnetic bed) which are discussed in more detail below. As shown in FIGS. 6 and 7, the bed module  310  is detachably attached to the frame  306  by four nuts  330  and four flat-head screws  332 . The quantity and type of fasteners may vary with the specific application and with the length of the conveyor system. Four holes  331  in frame  306  (see FIG. 11) serve as bed mounting structures which allow the bed module  310  to be detachably attached to frame  306 . Of course, other types of bed mounting structures, such as latches, mounting grooves, studs or magnets could be alternatively used to achieve this detachable attachment between the bed module  310  and the frame  306 . Alternatively, the bed module  310  may be permanently attached to the frame  306 , such as by welding these parts together. 
     The bed module  310  is illustrated herein as having a thickness of H 6 . Therefore, when the bed module  310  is attached to the frame, the height in the vicinity of the bed module  310  is increased by thickness H 6  from a height of BH 1  (height of the top of the frame) to a height of BH 2 . This height BH 2  of the bed module  310  needs to be matched at the drive pulley end and the tail pulley end. This matching of heights is preferably accomplished properly sizing pulley sleeves  305  and  309 . 
     The drive pulley  304  is rotatably connected at one end of the frame  306 , and the tail pulley is rotatably connected at the other end of the frame  306 . The drive pulley  304  can be driven to rotate by a driver (not shown), such as a conventional rotary drive motor. As shown in FIG. 5, drive pulley  304  and tail pulley  308  each have a radius of H 5 , such that the tops of these pulleys have a height of BH 1 . In some preferred embodiments, radius H 5  will be about one inch. As further explained below, frame  306  includes a bed surface  306 A, which has a height of BH 1 , which matches the height of the pulleys  304 ,  308 . 
     Drive pulley sleeve  305  is shown in FIG. 8, and is preferably made of urethane, with an inner diameter D 1 , an outer diameter D 2  and an annular thickness H 6 . When the drive pulley sleeve  305  is made of urethane, it can maintain good rolling contact with a belt with sufficient friction to minimize slippage. It is noted that the pulley sleeves can also be made of many other materials, such as butyl rubber, nitryl rubber or neoprene. 
     As shown in FIG. 5, the drive pulley sleeve  305  fits around the drive pulley  304  and is detachably attached thereto. More specifically, in this preferred embodiment, the inner diameter D 1  of the drive pulley sleeve is slightly smaller than the outer diameter of the drive pulley  304 , so that the urethane drive pulley sleeve  305  can be friction fit onto the drive pulley  304 . In order to effect this friction fit, it may be necessary to use an arbor press or a small hydraulic press. 
     When the drive pulley sleeve  305  is placed around the drive pulley  304 , the effective height at the drive pulley end is increased by the annular thickness of the pulley sleeve H 6  from BH 1  to BH 2 . (See FIG. 5.) In other words, the aggregate radius of the drive pulley H 5  and the annular thickness of the pulley sleeve H 6  preferably cause the top of the pulley sleeve to reach a height of BH 2 . It is noted that the pulley sleeve may be stretched to some degree as it is placed around pulley  304 , which can cause a slight decrease in the annular thickness of the sleeve after it is placed around the pulley  304 . In some embodiments, it may be desirable to use a slightly thicker pulley sleeve to compensate for this resulting decrease in thickness. 
     The frame  306  and bed module  310  should be designed so as to avoid physical interference between the pulley sleeve  305  and the frame  306  or bed module  310 . As shown in FIG. 6, there is preferably provided some clearance between the pulley sleeve  305  and the bed module  310 . 
     Similarly, urethane tail pulley sleeve  309  is detachably attached to tail pulley  308 , to increase the height at the tail pulley end by annular thickness H 6  from BH 1  to BH 2 . In this way, the drive pulley end, the vicinity of the bed module  310  and the tail pulley end all have matching effective heights along BH 2 . When a belt is looped around the pulley sleeves  305 ,  309  and over the bed module  310 , all the heights will be matched, thereby avoiding the problems associated with mismatched heights. By using appropriate pulley sleeves  305 ,  309 , various bed modules  310  of various thicknesses can be used with the same basic frame  306 , drive pulley  304  and tail pulley  308 . 
     In addition to the advantage that the conveyor system  300  can be used with various bed modules  310 , the conveyor system  300  can also be used without any bed module  310  or pulley sleeves  305 ,  309 . This is possible because frame  306  includes a substantially continuous bed surface  306 A (see FIGS. 7,  9  and  11 ) and because the bed surface  306 A and the pulleys  304 ,  308  are matched in height (see FIG.  9 ). 
     As shown in FIGS. 7,  9  and  10 , frame  306  is made of a unitary piece of sheet metal, preferably steel, bent into a U-shape. Although FIG. 7 shows relatively sharp corners at the bends in frame  306 , in practice some bend radius will generally be required at the corners. The bend radius will vary depending upon the sheet metal material and the sheet metal thickness which is used. Due to the geometry of frame  306 , the bed surface  306 A of frame  306  is substantially continuous, except for the holes  331 . 
     The term “bed surface” is used herein to mean a surface suitable for supporting a conveyor belt. A lattice of elongated members, as shown in FIG. 3, would not be a bed surface. Because the surface  306 A is relatively continuous and the holes  331  are relatively small, surface  306 A is a suitable bed surface. Therefore, frame  306  includes both a bed surface  306 A and bed mounting structures (e.g. holes  331 ). Although a bed surface, such as bed surface  306 A, does not have to be completely continuous, preferably a bed surface should be effectively continuous in that it is continuous enough to support a conveyor belt for its expected application. 
     As shown in FIG. 5, the bed surface  306 A at the top of the frame  306 , the, top of the drive pulley  304  and the top of the tail pulley  308  all reach a height of BH 11 . Because the bed surface of the frame  306 A, the drive pulley  304  and the tail pulley  308  are all matched in height, a conveyor belt (not shown) can be looped directly around the outer surfaces of these components  304 ,  306 A,  308 . 
     In this way, the conveyor belt system  300  can be used as a basic module (frames and pulleys) without any bed module  310  or pulley sleeves. This allows the basic modules to be stocked in a usable inventory, even if it has not been determined which bed modules  310  (if any) and pulley sleeves  305 ,  309  (if any) will be needed. The basic module without a bed module  310  or pulley sleeves  305 ,  309  is in itself a low profile, general purpose conveyor system. 
     On the other hand, if the need for a special purpose conveyor system, such as a vacuum conveyor system or a magnetic conveyor system, does arise, the basic module can be quickly and easily converted to any number of special purpose conveyor system with the selective addition of an appropriate bed module and matched height pulley sleeves. Several types of special purpose bed modules will be discussed below in connection with another preferred embodiment of the invention (conveyor system  400 ). 
     FIGS. 12 to  26  show a second modular conveyor system  400  according to the present invention. FIGS. 12 to  17  show the basic module without any detachable bed or pulley sleeves. As shown in FIG. 12, the belt  402  is looped around drive pulley assembly  404  and tail pulley assembly  408 . The frame holding the pulley assemblies  404 ,  408  includes frame main body  406 , drive pulley side plate  434 , tail pulley side plate  468  and threaded rod  464 . This frame holds the pulley assemblies  404 ,  408  in a spaced apart relationship, thus defining the longitudinal length of conveyor system. As further explained below, threaded rod  464  allows longitudinal adjustment of tail pulley assembly  408  so that the tension of the belt  402  can be adjusted. 
     As shown in FIG. 13, frame main body  406  is made of a single piece of bent sheet metal. Steel is a preferred material because it is 250% stiffer than aluminum and it is less expensive than aluminum. The (load carrying) top portion of belt  402  is supported by bed surface  406 A of frame main body  406 . The (non-load carrying) return portion of belt  402  shown in FIG. 13 is supported because it is stretched between the pulley assemblies  404 ,  408 . The bed mounting holes  431  through bed surface  406 A are small enough that bed surface  406 A remains a suitable load bearing bed surface. 
     As shown in FIG. 13, two aluminum extrusions  438 , each having two longitudinal T-slots  439 , are mounted to the main frame body  406  by extrusion mounting screws  440  and extrusion mounting nuts  442 . The complex cross-sectional profile of the extrusions  438  is easy to form because these parts are made of extruded aluminum. 
     The T-slots  439  allow attachment of other equipment such as proximity switches (not shown) or guard rails. For example, in some applications, a cleated conveyor belt is used. For these applications, guard rails can be mounted by screws to the T-slots  439 , so that the rails extend along the transverse sides of the cleated belt and past the pulley assemblies  404 ,  408 . The guard rails can help prevent objects from getting into pinch points caused by the moving cleats or from otherwise interfering with the cleats. 
     The extrusions  438 , which are highly visible from the sides of the conveyor system  400  (see FIG.  12 ), are aesthetically advantageous in certain applications (such as most automation applications) in that they will tend to match extruded aluminum parts of adjacent machinery. However, the conveyor system  400  is stronger than an aluminum frame conveyor system because of the steel main frame member  406  which lies behind the extrusions  438 . 
     As shown in FIG. 12, the main frame body  406  is mounted on drive side bottom mounts  448  and tail side bottom mounts  449 . The bottom mounts  448 ,  449  are precisely adjustable so that the conveyor system  400  can be precisely leveled. However, it is noted that drive pulley side plate  434  extends sufficiently below the moving belt so that the bottom surface of drive pulley side plate  434  can be used as a (non-adjustable) mount in lieu of the drive side bottom mounts  448 . In this preferred variation, only the tail side bottom mounts  449  are required, and the conveyor belt system can still be precisely leveled by the adjustable tail side bottom mounts  449 . 
     The drive pulley side plate  434  and the tail pulley side plate  468  are fixed to the main frame body  406  by means of screws or the like. The side plate  434  is reversible so that the same plate  434  can be used at either transverse side of the drive pulley assembly  404 . A driver (such as a rotary motor, not shown) can be flush mounted at the drive mounting holes  436  in drive pulley side plate  434 . The driver is aligned to turn keyed drive pulley shaft  472  and to thereby drive the drive pulley assembly  404  and the belt  402 . The tail pulley assembly  408  freely rotates in response to its rolling contact with the belt  402 . 
     One transverse end of the drive pulley assembly  404  is shown in more detail in FIGS. 14 and 15. As shown in FIG. 14, the drive pulley assembly  404  includes a drive pulley  470 , a drive pulley shaft  472 , an inner bearing race  474 , and an outer bearing race  476 . The outer bearing race  476  is securely supported by the frame within spherical profile cut-out  480  in side plate  434 . The inner bearing race  474  and shaft  472  freely rotate within the outer bearing race  476  by means of ball bearings (not shown) therebetween. The driver (not shown) is connected to the end of keyed shaft  472  and its keyway  473  so that it can drive the shaft  472  as explained above. 
     As shown in FIG. 14, the outer circumferential edge  478  of outer race  476  has a spherical (rounded) profile. First cut out or spherical profile cut-out  480  in side plate  434  securely holds the outer race  476  so that it is self-aligning. In other words, the outer race  476  can pivot within first cut-out or spherical cut-out  480  in side plate  434  to compensate for misalignment of the central axis of drive pulley  470 . For example, this self-aligning, pivoting action can compensate for mechanical misalignment between the drive pulley assembly side plates  434 , or deflection in the central axis of the drive pulley caused by the belt  402 . In this way, conveyor system  400  can withstand much greater loads than conventional conveyor systems having needle bearings. 
     As shown in FIGS. 14 and 15, the side plate  434  also has second cut-out  482  to facilitate insertion of the drive pulley bearing  474 ,  476 . FIGS. 20 and 21 show how the drive pulley bearing  474 ,  476  can be inserted into the side plate  434  through second cut-out  482 . First, as shown in FIG. 20, the bearing  474 ,  476  is dropped into the bearing through second cut-out  482  so that the bearing  474 ,  476  is perpendicular to the side plate  434 . Next, as shown in FIG. 21, the bearing is rotated  900  in the direction R 4  so that the bearing  474 ,  476  is parallel to side plate  434 . As the bearing  474 ,  476  rotates, spherical outer circumferential surface  478  of the outer bearing race  476  is rotated into pivoting engagement with first cut-out or spherical cut-out  480  in bearing plate  434 . 
     In this way, second cut-out  482  provides for easy insertion of the bearing still allowing an extensive spherical surface of engagement between outer race  476  and side plate  434 . The first cut-out or spherical cut-out  480  extends all the way around spherical surface  478  (except in the vicinity of second cut-out  482 ) so that bearing  476 ,  474  is more secure in its self-aligning engagement with side plate  434 , than it would be if a conventional cylindrical bearing were used. 
     The second cut-out  482  has been located at top end of the side plate  434 . This placement of second cut-out  482  provides a couple of advantages. 
     First, this top-end placement of second cut-out  482  prevents side plate  434  from extending up over the height of the conveyor belt  402 , despite the fact that the bearing outer race  476  has a diameter almost as large as the diameter of the pulley. This arrangement allows the use of a relatively large drive pulley bearing (i.e., a bearing as large or almost as large as the drive pulley itself), without having the drive pulley bearing, or the side plate holding the drive pulley bearing, extending up over the level of the top of the conveyor belt, where there could be interference with loads being conveyed which overhang the belt in a transverse direction. 
     Second, the second cut-out  482  is not located on a surface of the side plate  434  which bears the load caused by the pull of the belt  402 . More particularly, the belt  402  pulls the drive pulley  470  and the bearing outer race  476  in a direction towards the tail pulley assembly  408 , which causes the bearing outer race  476  to exert force on the portion of spherical cut-out surface  480  oriented toward the tail pulley. The second cut-out  482  is located away from this load bearing portion of first cut-out or spherical cut-out  480 , which helps prevent damage to the bearing outer race  476 . 
     FIGS. 16 and 17 show one transverse end of the tail pulley assembly  408 . The tail pulley assembly includes tail pulley  450 , tail pulley bearing outer race  454 , ball bearings  456 , tail pulley bearing  458  and tail pulley shaft  460 . As further explained below, the tail pulley  450  and the outer bearing race  454  freely rotate in direction R 5  in response to the rolling contact between belt  402  and tail pulley  450 . 
     Tail pulley shaft  460  is inserted into groove  469  in side plate  468 . Groove  469  prevents the tail pulley shaft from rotating about its central axis (in direction R 5 ). More specifically, groove  469  engages flat  462  at the end of tail pulley shaft to prevent the tail pulley shaft  460  from rotation. Inner bearing race  458  is fixed to tail pulley shaft  460  and is therefore also prevented from rotating. However, ball bearings  456  between inner race  458  and outer race  454  do allow the outer race  454  and tail pulley  450  to rotate in direction R 5 . 
     As shown in FIG. 16, flat  462  of shaft  460  is adjacent to the upper side of groove  469 . However, if the tail pulley assembly  408  needs to be slightly lowered for better belt height alignment, this can be achieved by flipping the tail pulley assembly  408  so that flat  462  lies along the bottom side of groove  469 , rather than the top side. 
     Similarly to the drive pulley assembly  404  explained above, outer race  454  has a spherical circumferential outer edge  455  which engages with spherical cut-out  452  to allow for a pivoting, self-aligning action, which can compensate for misalignment in the central axis of tail pulley  450 . However, unlike the drive pulley assembly  404 , the outer race  454  is disposed within the body of the pulley  450 , rather than being within the side plate  468  of the frame. 
     In some preferred embodiments of the present invention, a non-self-aligning bearing, such as a cylindrical bearing, may be used at the tail pulley end because the deflection and alignment problems at the tail pulley end are generally not as great as they are at the drive pulley end. 
     The longitudinal position of the tail pulley assembly  408  relative to the frame can be precisely controlled, thereby allowing belt  402  to be precisely tensioned. More specifically, the tail pulley assembly  408  can be precisely adjusted away from the drive pulley assembly  404  to increase the tension in belt  402 . 
     This longitudinal adjustment of the tail pulley assembly  408  will now be explained with reference to FIGS. 16,  17 ,  18  and  19 . As shown in FIGS. 16 and 17, threaded rod  464  passes through a threaded hole in tail pulley shaft  460 . When the rod  464  is rotated (by hand in this embodiment), tail pulley shaft  460 , along with the entire tail pulley assembly  408 ), will move along groove  469  in the longitudinal direction as a result of its threaded engagement with rotating rod  464 . 
     Ruler plate  466 , which is marked with markings at 1 mm intervals, can be used to precisely control the position of the tail pulley assembly to precisely adjust the tension in the belt  402 . First, a new belt  402  is looped around the drive pulley  470  and the tail pulley  450  so that there is just enough tension to remove all the slack from the belt. This initial state is easy to achieve because it is visually apparent when all of the slack is taken up. 
     Now, the belt  402  needs to be appropriately tensioned. Conventionally this tensioning process has been subject to guesswork because there is generally not a visual indication of how far the belt  402  should be pulled beyond the initial state. This can result in over-tensioning or under-tensioning of the belt  402 . According to the present invention, ruler plate  466  provides a clear visual indication of the appropriate amount of tensioning. 
     FIG. 18 shows the tail pulley shaft  460  and the ruler plate  466  when the initial (no slack) state is achieved. The register point  463  of flat  462  of tail pulley shaft  460  is lined up with the ‘4’ mark on the ruler plate  466 . In this example, it will be assumed that the belt  402  is 4 feet in length, and that the belt  402  is made of a material such that it should be tightened 1 mm for every foot of belt length. Therefore, the belt  402  needs to be tightened 4 mm from the initial state shown in FIG.  18 . 
     After the initial state is achieved, threaded rod  464  is rotated so that the register point  463  on the tail pulley shaft  460  is observed to move an appropriate distance (e.g., 4 mm) along the ruler plate  466 . In this example, the register point  463  should move from the ‘4’ mark on ruler plate (initial state shown in FIG. 18) 4 millimeters in distance to the ‘0’ mark (as shown in FIG.  19 ). When the register point  463  is observed to be at the ‘0’ mark, as shown in FIG. 19, the belt  402  is appropriately tensioned. 
     By using the simple ruler plate  466  to accomplish belt tensioning, expensive, conventional belt tensioning gauges, such as those which directly measure the tension or strain of the belt are not needed. Although the ruler plate  466  may riot allow the ultra-high precision of some expensive, conventional belt tensioning gauges, it will provide more than enough precision for most applications. 
     It is noted that a similar threaded rod  464  and ruler plate  466  may be provided at the other transverse end of the tail pulley assembly  408 , so that both ends of the tail pulley can be precisely brought into longitudinal alignment at an appropriate belt tension. Proper longitudinal alignment can help prevent mistracking of the belt, wherein the belt gradually displaces relative to the pulley in the transverse direction. 
     FIG. 22 is a side view of the conveyor system  400  with bed module  410  and pulley sleeves  405 ,  409  installed. Conveyor belt  402  is looped around the pulley sleeves  405 ,  409  and over the bed module  410 . It is noted that the conveyor belt  402  must be a little longer to accommodate the larger diameter pulleys. The drive pulley assembly  404 , the bed module  410  and the tail pulley assembly  408  are all matched in height because the thickness of bed module  410  is equal to the annular thickness of pulley sleeves  405 ,  409 . While reference number  410  denotes a bed module generally, several different kinds of specific bed modules will be discussed below with reference to FIGS. 23 to  27 . 
     FIG. 23 shows a magnetic bed module  510  which is mounted on bed surface  406 A by bed mounting screws  512 . There is a permanent magnet  511  embedded in bed module  510 . By using magnetic bed module  510 , the conveyor belt can securely transport magnetic objects such as small pieces of metal hardware, without the risk that the objects will fall off the conveyor belt because the objects are held in place by magnetic forces of the magnet  511  in the bed module  510 . 
     FIG. 24 shows the use of a self-tracking bed module  610  and a special self-tracking conveyor belt  602 . This self-tracking belt is designed to keep the conveyor belt from mistracking (i.e., shifting in the transverse direction). More specifically, the conveyor belt  602  has a raised portion  602 A on its underside. This raised portion  602 A fits into a groove  614  in bed module  610 . The pulley sleeves  405 ,  409  may also be formed with a similar groove to accommodate the raised portion  602 A. Also, bed module  610  has low retaining walls  611  on either transverse side of the conveyor belt  602 . 
     Because of the engagement of the conveyor belt  602  (including raised portion  602 A) and the groove  614  and retaining walls  611 , this self-tracking embodiment can withstand side loads, such as those generated when the conveyor belt is loaded from the transverse direction. Bed module  610  is mounted to bed surface  4063 A by bed mounting screws  612 . Although bed module  610  has both retaining walls and a groove, other preferred self-tracking bed modules may not include both of these features. 
     FIG. 25 shows a vacuum conveyor embodiment which has vacuum bed module  710  mounted to the main frame body  406  by vacuum bed module mounting screws  712 . In a vacuum conveyor belt system, suction forces through apertures  703  in the vacuum conveyor belt  702  will pull objects down onto the conveyor belt  702 , and thereby secure the objects to the belt  702  through this vacuum force. 
     As shown in FIGS. 25 and 26, in the vacuum bed module  710 , a plurality of channels run from a transverse surface of the vacuum bed module  710  to a groove  713  formed along the top surface of the vacuum bed module  710 . A vacuum (i.e., relatively low pressure) is maintained in the groove  713  by drawing air out of the groove  713  through the channels  711 . This causes suction forces, in the direction of arrow S, through the apertures  703  of the vacuum conveyor belt  702 . 
     The vacuum is maintained in the groove  713  and channels by means of a vacuum pump  716 . Connector  715  forms a substantially air tight connection at the transverse surface of the bed module  710  in the vicinity of the channels  711 . Air is drawn out of the channels  711 , through connector  715  and hose  714  to maintain the vacuum. 
     This embodiment with vacuum bed module  710 , provides an important advantage over many conventional vacuum conveyor belt systems. In many conventional vacuum conveyor belt systems, a vacuum is maintained in an open volume within the frame (see the open area  407  within frame  406 ). However, the frame is generally not air tight, so air will leak into the frame, especially through the space between the frame and the pulley at the transverse ends of the frame. Maintaining a vacuum in the face of this air leakage requires the vacuum pump to have a large capacity. On the other hand, according to the present invention, the vacuum is confined to relatively small channels  711  and groove  713 . Maintaining a vacuum in this relatively small volume, confined within bed module  710 , does not require as much vacuum capacity of the vacuum pump  716 . 
     FIG. 27 shows a side view of the drive pulley end of a synchronous conveyor belt embodiment according to the present invention. In this synchronous embodiment, special synchronous conveyor belt  802  is looped around synchronous drive pulley sleeve  805 . Teeth  802 A on synchronous conveyor belt  802  mesh with teeth  805 A on synchronous pulley sleeve  805 . The engagement of these teeth prevents conveyor belt  802  from slipping in the longitudinal direction. 
     Synchronous pulley sleeve  805  and synchronous belt  802  are used with a flat bed module  410 . (In some preferred embodiments, a bed module for use in a synchronous system will have either retaining walls or a groove for self-tracking purposes.) Furthermore, the pulley sleeve at the tail pulley end does not need teeth because the mesh engagement of teeth at the drive pulley end only is sufficient to prevent longitudinal slippage for most applications. It is noted that the synchronous drive pulley sleeve  805 , bed module  410  and the tail pulley sleeve (not shown) are matched in height. Pulley sleeve  805  is preferably formed of aluminum in order to facilitate the formation of teeth  805 A. 
     In the preferred conveyor system  400  with optional bed modules,  410 ,  510 ,  610 ,  710 , the drive pulley  470 , the tail pulley  450  and main body  406  are dimensioned so that 0.5 inch thickness bed plates  410 ,  510 ,  610 ,  710  can be used. This allows the majority of bed plates to be manufactured from standard 0.5 inch thick sheet stock (e.g., 0.5 inch thick UHMW stock). Designing the conveyor system so that the bed plates have a thickness which is a standard sheet stock thickness, like 0.5 inches) can reduce the cost of manufacturing the bed plates. However, it is noted that the pulley sleeves may have an annular thickness which is slightly greater than the thickness of the bed plate, because pulley sleeves tend to be made of more elastic materials, such as rubber or urethane which may decrease in thickness when they are friction fit over the pulleys. 
     The magnetic bed module  510 , the self-tracking bed module  610 , the vacuum bed module  710 , and the synchronous conveyor belt embodiment with synchronous pulley sleeve  805 , demonstrate the versatility of a conveyor belt system according to the present invention. A single basic module can be utilized in several different special applications as the need arises with the installation of an appropriate bed module and pulley sleeves. This is especially advantageous in a setting where many different conveyor belts are used because inventories of the basic module can be maintained, even when its eventual application (e.g., magnetic, vacuum) is not yet known. 
     Through the use of a basic module (with a bed surface) that can be used alone or with various special purpose bed modules, a single conveyor system can be used for a variety of applications which would otherwise require resorting to several different conveyor systems. In this way, the present invention can reduce maintenance costs. This can also reduce the number of spare parts which need to be stocked, by virtue of the fact that spare parts need only be stored for a single system). Furthermore, this can also reduce the number of basic conveyor belt systems that need to be kept in inventory, because the same basic module can be used regardless of whether desired applications which arise require a basic conveyor belt or a special purpose conveyor belt (such as a magnetic or high speed system). 
     Other types of special application bed modules and pulley sleeves are also possible. For example, a bed module and pulley sleeves might be used to assemble a high speed conveyor system embodiment. Because the pulley sleeves increase the affective outer diameter of the drive pulley, the conveyor belt will travel faster, for a given rotational velocity, when a pulley sleeve is installed. Also, the conveyor belt can be operated without any bed module or pulley sleeves, as shown in FIG.  12 . By using the basic module, without bed module or pulley sleeves, the vertical profile of the conveyor belt is minimized. 
     Of course, many modifications to the above-described conveyor belt system embodiments are possible. For example, the present invention is applicable to center drive conveyor belts. The foregoing examples and various preferred embodiments of the present invention set forth herein are provided for illustrative purposes only and are not intended to limit the scope of the invention defined by the claims. Additional embodiments of the present invention and advantages there,of will be apparent to one of ordinary skill in the art and within the scope of the invention defined by the following claims.