Abstract:
Rod retention systems are disclosed for modular plastic conveyor belts. In one embodiment the connecting rods, which pass through interdigited link ends of successive modules, each include a circumferential groove at one location, receiving a retaining clip at a position between adjacent interdigited link ends, snapped into position in the groove. The retaining clip provides easy assembly using existing tools, and a rod can easily be removed from the belt by applying sharp force on the end of the rod. In a second embodiment a rod retention system has blocking members at both ends of each module row, forming edges of the belt. A space about two or three link ends wide extends laterally from the blocking member to the first rod-encircling link end inboard of the blocking member; within the space the module is devoid of link end structure which would confine the rod from the bottom of the belt. The rod is forced into a bending configuration for insertion and removal from the bottom of the belt, and assumes a substantially straightened, normal configuration after insertion. In another embodiment the belt has an opening at the location of the blocking structure, aligned with the series of link end openings, but the rod end is preformed in a bent configuration. In a further embodiment the rods each have heads on one end, and the heads reside inboard of the blocking structure in the assembled belt.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention is concerned with modular plastic conveyor belts, and in particular relates to retention of connecting rods in such belts.  
           [0002]    Examples of modular plastic conveyor belts are shown in U.S. Pat. Nos. 4,742,907, 4,901,844, 5,069,330, 5,181,601 and 5,224,583. The conveyor belts are shown formed of plastic modules having sets of link ends or projections extending in fore and aft directions, for interdigiting with similar preceding and succeeding modules. The interdigited projections have transverse openings through which pass connecting rods, typically also of plastic. Each module row includes one or more modules side by side, and the belts can be made up in virtually any length and width, within practical limits.  
           [0003]    The connecting rods of belts such as disclosed in the above referenced patents, and those of other belts of the same general type, must be retained against lateral movement so as to prevent them from extending transversely out of the belt, which would allow the belt to separate between succeeding modules. This need has been addressed in several different ways. U.S. Pat. No. 4,904,844 describes the use of recesses in end members of the integral plastic modules or in separate side plate members at the outside of the belt, to receive connecting rod heads in countersunk relationship. Such rod heads can be formed in the ends of assembled rods by deformation of the rod end, sometimes called “buttoning”.  
           [0004]    U.S. Pat. No. 5,181,601 describes a different approach wherein a connecting rod has an integral, enlarged collar or interference ring on the rod, to be forced into and engaged with the inside of a bore in a plastic module, the bore having a slightly smaller diameter than the interference ring. This creates a positive press fit engagement between the rod and module, so that the rod is tightly retained relative to one module. Rod heading could be eliminated. The same patent also disclosed the use of three separate connecting rod sections serving as a connecting rod for each pair of adjacent modules, with the two outer rod sections retained by the interference fit described above, and a middle rod section floating between the ends of the outer rod sections.  
           [0005]    Other conveyor belts have employed rod heads, on a one-piece connecting rod, to retain the rod in the belt.  
           [0006]    Further approaches to retaining connecting rods without rod heads have been suggested. One approach is a spring clip inserted into a receptacle in an edge link end, as in U.S. Pat. No. 5,123,524. Other approaches have sometimes involved an integrally molded tab or flange at the outside edge of a belt module, positioned to require forcing of the length of the rod past the somewhat flexible tab or flange (or manually holding back the tab), with the tab then springing back to an undeformed position when the rod has been fully inserted. The intention is then for the tab or flange to prevent outward movement of the rod by interfering with its path of movement. See, for example, U.S. Pat. Nos. 4,925,016, 5,058,732, 5,156,262 and 5,156,264. Another approach has not involved a movable tab, but simply a bending path through which the rod must be pushed at the edge of the belt, so that once forced into position past the bend, the rod tends not to migrate out from the belt. The latter type of headless rod retention is shown in U.S. Pat. No. 5,372,248 and a similar arrangement is shown in U.S. Pat. No. 5,598,916, where an off-axis hole is provided in a module edge member. See also U.S. Pat. No. 5,573,106. Examples of other forms of headless rod retention are shown in U.S. Pat. Nos. 4,993,544 and 4,893,710.  
           [0007]    Some types of headless connecting rod retention cause excessive wear against the belt module or against a retaining element or the rod itself, both in radius and linear travel belts.  
           [0008]    Removal of retaining rods in general has often required the cooperation of at least two technicians, one to pull the rod from one side of the belt and the other to push or strike or otherwise manipulate the rod from the other side of the belt, which can be impractical.  
           [0009]    It is an object of this invention to overcome problems of excessive module or rod wear caused by the rod retention system employed, both in radius and linear travel belts, while also providing a simple and easily used arrangement for engaging the rod retention and further for releasing the rod retention when desired. Another object, in a specific embodiment of the invention, is to facilitate release of the retaining rod by a single person operating from only one side of the conveyor belt.  
         SUMMARY OF THE INVENTION  
         [0010]    A connecting rod retention system in according with the invention, for straight or radius type modular conveyor belts, avoids the need for rod heads or any form of movable flange or tab for locking the rod in place. In addition, the invention in one preferred embodiment allows a connecting rod to be freely and easily pushed into the assembled position through two sets of interdigited projections of successive module rows, without interference or force required for assembly. Wear of the rod, the rod retention device and the modules due to the rod retention arrangement is minimized, in part because the rod is free to rotate and a retention device on the rod preferably is free to rotate relative to the rod and is not squeezed or ground between modules.  
           [0011]    In one embodiment, a rod retention system for a modular plastic conveyor belt of the character described above includes a groove or slot in the surface of a connecting rod, located so as to be between two of the adjacent interdigited projections from the two successive modules which the rod is to connect. At this narrow location, the groove or slot defines a smaller diameter or dimension on the rod than the outside diameter of the rod. A clip, preferably flat in profile, on its side surfaces, is provided for engaging over the slot or groove area of the retaining rod, between the adjacent interdigited projections. The clip is dimensioned so as to allow it to be forced over the rod at the groove, with the clip yielding due to its inherent flexibility, and to be retained on the rod unless a substantial and deliberate force is applied to remove the clip.  
           [0012]    In a preferred embodiment, the groove or slot is a generally circumferential groove around the rod, and the clip comprises a generally C-shaped clip with an open end which is dimensioned to snap over the groove on the rod, and thence to be freely rotatable on the rod.  
           [0013]    In one preferred embodiment the connecting rod is formed of plastic material, and the retaining clip is also formed from a plastic material, which may be acetal (although a steel rod or steel clip may be used). The retention system of the invention avoids wear between the conveyor module itself and the retention means, while also allowing fast and easy assembly using tools already available for brass or steel ring retainers used in other fields. Further, by firmly holding the belt, one can remove any of the rods with a punch and hammer, which provides sufficient force to dislodge and pop the retaining clip off the rod and out of the belt.  
           [0014]    The retention device cannot escape by itself provided the material utilized for the retaining clip is one with a good memory, such as the plastic material acetal; this allows the C-shaped clip to be forced open for assembly, while quickly returning to its original configuration after being positioned in the rod groove.  
           [0015]    In some embodiments of the invention, the modular plastic conveyor belt utilizes discontinuous connection rods such as disclosed in U.S. Pat. No. 5,181,601. Such a discontinuous connection rod may include a free-floating middle section and two opposed edge or side rod sections. With the retention system of the present invention, the two outer rod sections each have the retention device of the invention, with a groove and the clip engaged over the groove; or one end of the belt is closed and the clip is on the rod section at the opposite end.  
           [0016]    In some belts, particularly radius type belts, the faces of adjacent interdigited link ends between which the clip is positioned are reduced in profile. This is to provide ample lateral space for the clip between link ends, to avoid squeezing of the clip and wear of the clip and/or link ends due to relative side forces acting between modules, particularly on curves.  
           [0017]    Another embodiment of a headless rod retention system of the invention employs a retention rod capable of some degree of bending without damage, whereby the rod is bent and inserted through the module row and having been so inserted, reverts to its normal, straight configuration and is laterally retained therein by a solid blocking structure provided at each end of each belt module, in the position of a link end but without a rod hole and not functioning as a link end. The insertion of the rod is made possible by the presence of a space inboard of the blocking structure at least at one side of the module row, free of rod-capturing link ends, which allows the rod to be inserted without the need for bending beyond the bending tolerance of the rod. This system allows removal of the rod by a single person from one side of the belt.  
           [0018]    In a preferred form of the above embodiment, link ends or projections extend into the spaces noted above, to overlap the position of the rod, and these link ends are regularly spaced apart, but each comprises essentially a half-ring structure. The half-ring projections cradle the rod on its upper side, such that the rod is unconfined at the bottom of the belt. The half-ring structures, being open at bottom, enable the rod to be slidingly inserted into or removed from the generally aligned link end openings, while providing mechanical interaction and some support between the rod and the half-ring structures of the special link ends of each module.  
           [0019]    In one variation of the above embodiment, the connecting rod is configured into a temporary bend for insertion and removal, but the end of the rod has a head which, when assembled, resides just inboard of a belt edge member having a hole. The head prevents the rod from migrating outwardly.  
           [0020]    In a further embodiment, a headless connecting rod is retained in the belt via a preformed bend in the rod which becomes partially straightened when the bend is forced through a hole in the belt edge structure. Once within the belt, the rod resumes its prebent configuration, placing the end of the rod offset from the hole in the belt edge and retaining the rod in the belt.  
           [0021]    Accordingly, a principal object of the invention is to provide a simple and easily operated and assembled arrangement for retaining and removing connecting rods in a modular plastic conveyor belt, without rod heads and without the need for special moveable elements on the modules. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a plan view showing a portion of a modular plastic conveyor belt with the rod retention system of the invention.  
         [0023]    [0023]FIG. 2 is a plan view similar to FIG. 1 but showing a portion of a radius type conveyor belt, in a curve, again with the retention system of the invention.  
         [0024]    [0024]FIG. 3 is a detail view showing a part of a connecting rod for a modular conveyor belt, illustrated with a retaining clip engaged on the rod in accordance with the retaining system of the invention.  
         [0025]    [0025]FIG. 4 is a profile elevation view of the retaining clip, in one embodiment.  
         [0026]    [0026]FIG. 5 is a plan view of a retaining clip in one embodiment.  
         [0027]    [0027]FIG. 6 is an enlarged detail view showing a groove or slot on the connecting rod.  
         [0028]    [0028]FIG. 7 is a schematic view showing an example of an alternative form of clip which can be used in the rod retention system.  
         [0029]    [0029]FIG. 8 is an exploded perspective view of a pair of solid top belt modules of a second embodiment of the invention in which the connecting rod is forced into a bending configuration for assembly and removed.  
         [0030]    [0030]FIG. 9 is a perspective view of a pair of belt modules as in FIG. 8, here showing the two adjacent modules serially connected by a connecting rod.  
         [0031]    [0031]FIG. 10 is a bottom plan view of a single belt module as shown in FIG. 8.  
         [0032]    [0032]FIG. 11A is a sectional view as seen along the line  11 A- 11 A in FIG. 10, showing the cross-sectional structure of the belt module through a regular link end.  
         [0033]    [0033]FIG. 11B is a sectional view as seen along the line  11 B- 11 B in FIG. 10, showing the cross-sectional structure of the belt module through a special, half-ring link end.  
         [0034]    [0034]FIG. 12 is a fragmentary bottom plan view showing alternative structure to that shown in FIGS.  8 - 10 .  
         [0035]    [0035]FIG. 12A is a side elevation detailed view showing rod assembly.  
         [0036]    [0036]FIG. 13 is a partial perspective view similar to FIG. 8 and showing another alternative structure.  
         [0037]    [0037]FIG. 14 is a perspective view similar to FIG. 8, showing a similar embodiment with a shorter belt pitch.  
         [0038]    [0038]FIG. 15 is a perspective view showing the belt modules of FIG. 14, connected by a retaining rod.  
         [0039]    [0039]FIG. 16 is a bottom plan view of a single belt module of the type shown in FIGS.  14 - 15 .  
         [0040]    [0040]FIG. 17A is a sectional view as seen along the line  17 A- 17 A in FIG. 16, showing cross-sectional structure of the belt module through a regular link end.  
         [0041]    [0041]FIG. 17B is a sectional view as seen along the line  17 B- 17 B in FIG. 16, showing cross-sectional structure of the belt module through a special half-ring link end.  
         [0042]    [0042]FIG. 18 is a perspective view showing the end of one module in accordance with a further embodiment of the invention wherein the connecting rod has a preformed bend.  
         [0043]    [0043]FIG. 19 is a sectional view showing a portion of two interdigited modules in accordance with another embodiment wherein the connecting rod has a head located inboard of an edge component of the belt, again involving bending of the rod for insertion and removal. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0044]    [0044]FIG. 1 shows in plan view a portion  10  of a modular plastic conveyor belt of the type with which this invention is concerned. In the example shown, plastic integrally molded modules  11 ,  12 ,  13  and  14  are held together with retaining rods  16 . The retaining rods  16 , preferably also of plastic as in previous patents referenced above, including U.S. Pat. No. 5,181,601, pass through transverse openings in sets of projections  18  and  20  of the plastic modules  11 - 14 . The projections or link ends  20  may be called fore or leading projections, and the oppositely-directed projections or link ends  18  may be called aft or trailing link ends for purposes of this discussion, although the belt can be driven in either direction. In the example shown, single modules  11 - 14  extend throughout the width of the belt illustrated; however, this is only one example, and in wider belt assemblies the modules will normally be assembled together widthwise and in staggered relationship. For example, a wider belt might have three modules in one row and only two in the next succeeding row. This avoids continuous module seams through the belt, adding strength to the belt widthwise. Such compounding and staggering of modules is well known in the industry.  
         [0045]    In the embodiment illustrated, retaining clips  22  are secured onto the connecting rods  16 , as illustrated, between interdigited fore and aft projections  20  and  18 . These clips are locked onto the rods so that the rods are permitted very little lateral movement in the belt. As can be seen from FIG. 1, these clips  22  can comprise generally C-shaped retaining clips which are snapped over the rod, in a groove, slot or otherwise reduced-circumference portion of narrow width. The grooves or slots are discussed in more detail below.  
         [0046]    As can be seen from FIG. 1, the rods  16  can be easily assembled to connect the succeeding module rows, by sliding the rods through the openings in the interdigited projections  18  and  20 . Once the rods are in the position desired, a retaining clip  22  is pushed over the rod and snapped into position, the groove or slot having been located in the appropriate position between interdigited projections. Although FIG. 1 shows connecting rods  16  extending from the outermost projections of the modules and of the belt, these rods can be flush or recessed relative to the surfaces of the outermost projections, if desired for a smooth belt edge. Also, different configurations at outermost projections can be employed if desired, for certain types of belt, particularly the type of structure shown in FIG. 2.  
         [0047]    In FIG. 2 a radius type plastic modular conveyor belt portion  25  is shown, of the type disclosed in U.S. Pat. No. 5,181,601, the disclosure of which is incorporated herein by reference. Three module rows  26 ,  27  and  28  are illustrated. The radius conveyor portion  25  is illustrated with integral sideplates  30  (heavier edge projections) as in the referenced patent, and with discontinuous connecting rods  32  as also shown in the referenced patent. Each rod in the illustrated embodiment is made up of two outer or side rod segments  32   a,  and a center rod segment  32   b.  The outer rod segments  32   a  have a slot for groove  34 .  
         [0048]    In a belt designed for radius as well as straight travel, it is important that the connecting rods  32  be of adequate strength to retain the entire tension of the belt in a very narrow region at the outside of the curve, as discussed in the referenced Patent No. 5,181,601. Accordingly, the retaining clips  22  of the invention are inward from either edge of the belt, at a location where the slot or groove  34  in the rod will not fall in this region of very high tension.  
         [0049]    The rod retaining system is best understood with reference to FIGS. 3, 4,  5  and  6  as well as FIG. 2. The radius conveyor belt embodiment shown in FIG. 2 is made up of staggered rows of modules  26 ,  27  and  28  as explained above. Thus, the module row  26  has a pair of modules  26   a  making up that row; the module row  27  has left and right modules  27   a  and a center module  27   b;  and the third module row  28  is similar to the row  26 , having left and right modules  28   a.  Dividing lines between adjacent modules are shown, for example, at  27   c  in the row  27  and at  26   c  in the row  26 . Each module row, and each module, has fore projections or link ends  36  and aft projections  38  (“fore” and “aft” are used for convenience of description; the belt can be driven in either direction). As in radius belts of this type, one set of projections, the aft projections  38  as illustrated, have slotted openings  40  as the transverse openings through the set of projections. When the belt travels around a curve, the outside of the curve, at the right in FIG. 2, experiences a concentration of belt tension stresses near the outside of the belt. As explained in the referenced U.S. Pat. No. 5,181,601, this is the reason for the heavier end projections or integral sideplates  30  shown in FIG. 2. The rod slots  34  in the discontinuous connecting rods  32  illustrated, are remote enough from the outer ends of the belt as to have no adverse effect on the strength capability of the connecting rods. Outer edge stress is the most critical concentration of stress in the rod; in straight belt travel, when the region of the slots or grooves  34  experiences some degree of stress, such stress is far less than what is encountered at the edges and is non-critical.  
         [0050]    It is generally sufficient that the slot on groove  34  be inboard from the outer belt edge by at least two fore projections  36  and two aft projections  38 . In the form illustrated, the groove is spaced inboard by three projections of each type, i.e., it is located at the sixth inter-projection spacing  39   f.  The first inter-projection spacing  39   a  is generally the location of highest and nearly all stress. The second such spacing  39   b  may also take considerable stress due to rod deformation and slight module deformation under the high tension in a curve. Thus, at the minimum, the slot or groove should be at the third spacing  39   c  or farther inward; more preferably at least the fourth or fifth spacing  39   d  or  39   e.    
         [0051]    [0051]FIG. 2 shows grooves  34  and retaining clips  22  at both left and right of the belt section illustrated, i.e. in both outer belt segments  32   a.    
         [0052]    As shown in FIGS. 3 through 6, the retaining clip or ring  22  has a narrow profile, and the belt groove or slot  34  in the rod is considerably wider. This allows the clip to assume angled positions such as shown in FIG. 3 and also in FIG. 2, to accommodate the angled space relationship existing between interdigited projections when necessary. As one example, if the rod segment  32   a  and the clip  22  are both formed of plastic material, with the clip being, for example, Delrin (acetal) plastic, the clip may have a thickness of about {fraction (1/32)} inch, residing in a groove  34  having a width about twice as great, e.g. about {fraction (1/16)} inch.  
         [0053]    [0053]FIG. 3 shows the ring or clip  22 , which is preferably C-shaped as shown in FIG. 5, being pushed over the slot or groove  34  of the rod or rod segment  32   a . As the C-shaped clip  22  is pushed over the groove, the open end  42  of the clip, which has angled opening surfaces  44 , opens the clip  22  with a camming action, as is known in metal clips used in other arts. The clip  22 , which is preferably plastic, has sufficient flexibility to spread the opening  42  in order to slip over the groove  34  of the rod, and sufficient “memory” to return to its original configuration, thus capturing the clip on the rod. As an example, the open end  42  of the clip may have a minimum dimension of about 0.08 inch, while the diameter of the rod groove may be about 0.116 inch. The depth of the groove or slot  38  may be about 0.02 inch, thus the outer rod diameter being about 0.156 inch in one preferred embodiment which is appropriate for the dimensions outlined. Connecting rods, of course, can be of different outside diameters, depending on the materials used, the specifications and loads on the belt, and the pitch of the belt.  
         [0054]    As seen in FIG. 2, in the module row  28  which is lowermost on the page, the inter-projection spacing  39   f,  i.e., the spacing wherein the reduced-circumference slot or groove  34  is located, may have projections  38   a  and  36   a  of reduced profile. This is especially important in radius-type conveyor belts as illustrated in FIG. 2, because of lateral forces acting between succeeding modules under the stress of travel around curves. In many instances, the retaining clip  22  can be squeezed and rubbed with sufficient force to cause wear on the retaining clip, the projections on either side, and possibly the rod. This can occur, for example, in the interdigited projections  36 ,  38  which connect the module row  26  to the module row  27  in FIG. 2, where no reduced-profile projections are shown. The lowermost line of interdigited projections in FIG. 2 shows the inter-projection spacing  39   f  as enlarged due to reduction of the sides of the adjacent projections  36   a  and  38   a.  These adjacent projections preferably are formed or ground to essentially a planar surface which is perpendicular to the width of the module row. This provides a wider spacing for the clip  22 , a spacing which is free of the typical angled projection ends which are included in radius conveyor modules. The spacing  39   f  thus is essentially rectangular (although a very small angle exists between the adjacent projections  36   a  and  38   a ) and which cannot completely collapse to the point of squeezing, rubbing or grinding on the clip  22 . A minimal spacing is assured because of the interaction of link ends or projections closer to the outermost edge, such as at inter-projection spacings  39   a ,  39   b ,  39   c  and  39   d.    
         [0055]    It should be understood that other configurations of rod slots and Clips can be employed. For example, the slot in the rod could be non-continuous around the rod, merely sufficient to enable some form of clip to be securely and positively located on the rod at the desired position and captively held thereon. Some form of indentation in the rod is required for this purpose. Clips can take different forms, although the C-shaped clip or ring  22  illustrated is preferable and advantageous. As another example, a clip formed of stiff metal wire, in the configuration  46  generally as shown in FIG. 7, could be employed. In the preferred embodiment, the generally C-shaped clip such as shown in FIGS. 3, 4 and  5  can have the advantage of being freely rotatable and capable of angular displacement within the groove as discussed above. For this purpose, the diameter of the C-shaped interior bore of the preferred clip  22  may be about 0.118 to 0.120 inch, as compared to the rod diameter of about 0.116 inch in the groove. This gives sufficient clearance for angling of the clip within the groove as shown in FIG. 3 and in FIG. 2.  
         [0056]    [0056]FIGS. 8 and 9 show in perspective, from the bottom side, an embodiment of the invention wherein a retaining rod  55  is threaded through transverse openings  56  in spaced apart fore and aft projections  59 ,  59   a  (sometimes called link ends herein) and is prevented from moving laterally by solid blocking structures  60  positioned at opposed ends of each belt module  61 . In the modules illustrated the link ends  59  on a first side are longer than link ends  59   a  on a second side, with a transverse member  65  which is offset from the fore/aft center of the module. The modules may be driven by sprocket teeth entering spaces  64  formed between the link ends  59  and by the transverse members  65 , and opposite the member  65 , by the opposing link end  59   a  of a connected adjacent module (FIG. 9).  
         [0057]    In this embodiment a space  62  inboard of each blocking structure  60  allows insertion into the module row of a rod, by forcing the rod through a bend. Having been so inserted, the rod reverts to its unbent essentially straight shape. The length of the space at the end of each module row is such that it allows the rod to be inserted without the need for bending the rod beyond its mechanical tolerance and without the need for the application of more force than can be reasonably supplied by a single technician.  
         [0058]    Open half-ring structures  63  project into the spaces  62 , cradling the inserted rod  55 , such that the rod is unconfined at the bottom of the belt, but is cradled on its upper surface, preferably throughout about half its circumference. These half-ring structures, being open at bottom, enable the rod to be easily inserted or removed from the generally aligned transverse openings  56 , while also providing mechanical interaction and some degree of enhanced support due to the contact between the rod and the half-ring projections close to the ends of the module. FIG. 9 shows the arrangement of two such belt modules serially joined by a retaining rod  55 . This embodiment of the invention allows a single technician to remove or insert a retaining rod from one side of the belt, using pliers or a special tool, without the need for assistance at the other side of the belt to manipulate the module or rod or apply force to the rod. Preferably the rod is not required to bend more than about 45°, for example, for a rod made of acetal or nylon and about ⅛ to {fraction (3/16)} inch diameter. More preferably, the rod should be required to bend not more than about 20°. The rod&#39;s configuration on insertion or removal is shown in FIG. 10A, with the angle a shown between the pivot axis and the rod  55 , due to the bend in the rod. FIG. 12 shows in section one end of two assembled modules, with half-ring link ends  63  from the two modules shown interdigited. The modules are inverted, bottom side up, for consistency with the other drawing figures.  
         [0059]    [0059]FIG. 10 shows in bottom plan view a single belt module  61  of the configuration shown in FIGS. 8 and 9. The projections  59 , which may be regularly spaced apart, are shown with transverse openings  56  through which the rod  55  is to be threaded. The half-ring structures  63  are at outer ends of the module, located at the spaces  62  at the end of each module  61 .  
         [0060]    Although the drawings show single modules having the blocking structures or closed link ends  60  at each end of each module, this only illustrates modules for use on a narrow belt, e.g. about 6 inches. In most cases the belt will be wider, comprised of module rows each including several modules withwise. In that case, edge modules will have blocking members  60  at one end, but the other end of such a module will be adapted to be abutted with another module widthwise, to form a wide belt whose other end has an edge module with a blocking structure. Interior module edges can be generally as shown in U.S. Pat. No. 5.181,601 of KVP Systems, Inc. For this reason, FIG. 10 is shown with break lines indicating the module can be virtually as wide as desired, with the blocking structures  60  at each end of FIG. 10 representing the ends of edge modules in most cases, although the structures shown in FIG. 10 can represent ends of a single module.  
         [0061]    [0061]FIG. 11A shows in cross section the structure of the module shown in FIG. 10. FIG. 11 shows the module structure as taken through a regular link end  59   a  at the second side of the module having the shorter link ends, and through a spacing between the regular link ends  59  at the first side of the module with the longer link ends. FIG. 11B, on the other hand, is taken along the line  11 B- 11 B in FIG. 10 and shows the half-ring link end  63   a  from the second side of the module (not in section) and a half-ring link end  63  at the first side of the module (in section). FIG. 11B also reveals, beyond the half-ring link end  63 , a portion of the blocking structure  60  at the end of the module. FIG. 11B additionally shows the transverse member or cross member  65  of the module, which is displaced toward the second side of the module in this particular embodiment of solid top module, as discussed above.  
         [0062]    It should be understood that the half-ring link ends  63  and  63   a  at the ends of the first and second sides of the modules or module rows can be configured differently. FIG. 12 is a partial bottom plan view showing an alternative construction in which a solid structure  66  replaces the two half-ring link ends  63  shown at the right side of FIG. 10. The single structure  66  extends through the same width, i.e. through the space  62  shown in FIG. 10. (The half-ring structure  66  may be formed as a half-cylinder (or less than a half-cylinder), extending widthwise to and adjoining the blocking structure  60  at the edge of the module. Thus, a connecting rod is partially cradled by the wide half-ring structure  66 .  
         [0063]    To the left of the structure  66  in FIG. 12 is a gap  68  to accommodate a link end  59   a  from an adjacent module, similar to the link end  59   a  at the other side of the belt shown in FIG. 12. In this arrangement, no half-ring link ends are included at the second side of the module, between the illustrated regular link end  59   a  and the edge of the module. In this area the module simply has an angled edge  64  which is similar to the edges  64  shown in FIGS. 11A and 11B, shaped to engage against the exterior barrel shape of a succeeding link end, but in this case against the barrel shape of the wide half-ring structure  66 .  
         [0064]    A further modification (not shown) is that the half-ring structure  66  of FIG. 12 need not have the full half-cylindrical shape but need only have a downward curve at the leading edge (which could be the trailing edge of the module), providing a partial barrel shaped surface adjacent to which an angled edge  64  of an adjacent module is positioned in the assembled belt, so that the closed-top belt remains essentially closed as the belt bends at connecting rods traveling around a sprocket.  
         [0065]    [0065]FIG. 13 shows a further variation of the structures shown in FIGS.  8 - 12 . This embodiment has a thicker end link providing a blocking structure  70  defining a ramp  72  which is included to aid in insertion and removal of a connecting rod, by helping to guide the rod.  
         [0066]    FIGS.  14 - 17 B show a smaller-pitch embodiment of the modules and belt section shown in FIGS.  8 - 12 . In this form of the module and belt, which still may be a solid top embodiment, the pitch is so short as to provide only a very slender flat portion at the top of each module, best seen at  74  on the underside of the belt in FIG. 16. As in the earlier embodiment, at each end of the belt (and shown on a single module  76  in FIGS. 14 and 15) is a solid blocking structure  78  adjacent to a space  79  wherein a connecting rod is unconfined from the bottom side. Although both left and right sides of the module  76  are shown blocked, the belt usually is formed in much wider widths, and a typical module would have only the blocking structure at one end, to mate widthwise with an additional module for staggered assembly of module rows so that seams between adjacent modules are staggered from row to row, as shown in the earlier KVP patent referenced above. Thus, FIGS.  14 - 17 A show blocking structures  78  on both ends of a single module only for purposes of illustration, although a narrow, single-module width belt can be formed in this way if desired. FIG. 16 shows the module broken, so that the structure in FIG. 16 can comprise a belt width with several modules between the module ends at left and right in the figure. The modules shown in FIGS.  14 - 17 A can have a pitch of about one half inch, which has an advantage of allowing the belt to form a tight return over a roller or series of sprockets, providing for transfer of relatively small articles from belt to belt.  
         [0067]    As in the earlier embodiment, the modules shown in FIG. 14- 15  have first and second sets of normal projections  80  and  80   a,  and first and second sets of half-ring edge projections  82  and  82   a . Variations of this structure can follow the variations shown in FIGS. 12 and 13 and as discussed in the description of those embodiments. A connecting rod  84  is inserted into and removed from the belt in the same manner as discussed above, by bending the rod as it is inserted or removed (FIG. 10A), to clear the blocking structure  78 . Once inserted, the belt resumes essentially its straight and undeflected configuration.  
         [0068]    [0068]FIGS. 17A and 17B are similar to FIGS. 11A and 11B, showing cross sections of the smaller-pitch modules  76  at different locations  17 A and  17 B- 17 B of FIG. 16. Again, a beveled or sloped edge  64  is shown where the module engages closely adjacent to the barrel of an adjacent link end to establish the closed-top structure of this embodiment.  
         [0069]    [0069]FIG. 18 shows another form of rod retention according to the invention. A module  88  (shown inverted), an end portion of which is shown in FIG. 18, is generally similar to the modules shown in FIGS.  8 - 11 B, but preferably with a smaller space  90 , adjacent to an edge member  92 , which space  90  has no rod restriction from the bottom. The module portion  88  shown in FIG. 18 is indicated with a connecting rod  94 , but without showing the adjoining module which is to be interdigited with the module  88 , i.e. with the illustrated module&#39;s rear link ends  96  assembled side-by-side with front link ends  98  of the adjoining, not-shown similar module. The space  90  includes a half diameter rear link end  100 , and on one side of this link end  100  will be received a regular front link end  98 , while on the other side will be inserted a half width front link end  102  which is shown at the front of the module  88 . The space  90  can be wider if desired, and the half width link ends  100 ,  102  can be replaced with somewhat similar structure which does not envelop the connecting rod at all.  
         [0070]    The module embodiment  88  of FIG. 18 has a connecting rod hole  104  in the edge member  92 , preferably aligned with all other openings in the link ends  96  which receive the connecting rod  94 . At an opposite side of the module  88 , or of a row of modules, is an edge member which may be similar but without a rod opening, thus serving as a blocking member at the opposite edge of the belt. The rod  94  is retained within the belt by virtue of a preformed bend  106  in the rod. The plastic rod  94  is sufficiently flexible that the preformed bend  106  straightens to an almost linear configuration when the rod is inserted through the hole  104  and through the link ends  96 ,  98  of adjacent interconnected modules until the bend  106  reaches the edge member  92 , at which point the rod is pushed with light to moderate force through the opening  104 . The rod then springs back to its preformed configuration with the bend  106 , putting that end of the rod offset from the rod opening  104  and preventing the rod from moving out of the belt.  
         [0071]    [0071]FIG. 19 shows a further embodiment of the invention wherein a rod  110  is retained within a pair of assembled, interdigited belt modules  112 . In the embodiment of FIG. 19 the belt portion is again shown inverted. In this embodiment, the rod  110  has a head  114 , which prevents the rod from lateral movement out through a hole  116  in an edge member  118  of the belt. The belt may have similar end openings  116  at both ends, with the rod having the head  114  only at one end. In this way, tooling is similar for modules which are to be interconnected by rods having heads formed at the exterior of the edge members  118 , or connected by rods as shown in FIG. 19. The rod  110  is inserted and removed from the bottom, by flexing the rod a sufficient distance to clear the blocking end structure  118 , including passing the rod head  114  under this structure. As shown in the drawing, a recess  126  is provided to receive or cradle the rod head  114  after the rod has been fully assembled in the belt. This recess both allows the belt to resume a linear configuration after insertion, and helps prevent lateral movement of the rod in the assembled belt.  
         [0072]    The sectional view of FIG. 19, taken at the center of the connecting rod  110 , shows a module  112  which is in many respects similar to those of FIG. 8, interconnected with a trailing module, a regular link end  120  of which is seen at the left of the fragmentary belt portion shown in the figure. Additional link end structures of the trailing module, shown at  122 , may be half-ring link ends such as shown at  100  in FIG. 18 or at  63  in FIG. 8, for example. Alternatively, they can simply provide a relatively flat bed on which the rod  110  lies. FIG. 19 also shows interdigited special link ends  124  of the module  112  which has the blocking edge structure  118 , and these interdigited link end structures will follow the same form as the link end structures  122 .  
         [0073]    The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.