Patent Publication Number: US-2003234162-A1

Title: Boost drive for a modular plastic conveyor belt

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims the benefit of U.S. Provisional Application Serial No. 60/319,328, filed Jun. 19, 2002. 
    
    
     
       BACKGROUND OF INVENTION  
       [0002] This invention relates to power-driven conveyors and, more particularly, to conveyors using modular plastic conveyor belts.  
       [0003] Modular plastic conveyor belts are widely used to convey food and other products. These belts are constructed of a series of rows of one or more belt modules interconnected at hinge joints by hinge pins installed through passageways formed in interleaved hinge eyes extending from the modules at each row. The hinge joint allows the belt to articulate about primary drive or idler sprockets and drums. The belts usually include drive structure drivingly engaged by the teeth of drive sprockets or drums.  
       [0004] In some applications, such as long belt runs, multiple belt turns, or spiral conveyors, belt tension can be high. A belt running at high tension is susceptible to stretching, disengaging with the drive, and early failure. One solution is to use a stronger, heavier belt with greater tension-handling capability. But that solution is unsatisfactory in many instances owing to the greater cost or weight of a heavier duty belt. And, in other applications, it is important that the belt tension at certain sections of the conveying path be low. This is the case, for example, at the entrance to a spiral drive drum.  
       [0005] Thus, there is a need for apparatus to reduce the tension of a modular plastic conveyor belt along its conveying path.  
       SUMMARY OF INVENTION  
       [0006] This need and other needs are satisfied by a boost drive embodying features of the invention. In a conveyor system using a modular plastic conveyor belt driven by a primary drive along a belt path, the boost drive includes a first drive wheel and a second drive wheel. The first drive wheel rotates about a first axis of rotation transverse to the direction of belt travel. The second drive wheel rotates about a second axis of rotation transverse to the direction of belt travel. The first wheel engages a top side of the belt, and the second wheel engages the bottom side of the belt. A drive mechanism drives at least one of the first and second drive wheels directly. In this way, the tension in the belt as it exits the boost drive is greatly reduced.  
       [0007] In another aspect of the invention, a conveyor system comprises a modular plastic conveyor belt having a top side and an opposite bottom side and arranged to follow a conveying path. A first wheel engages the top side of the belt. A second wheel engages the bottom side of the belt at a point along the conveying path proximate the first wheel. A drive mechanism directly driving at least one of the first and second wheels lowers the tension in the belt as it leaves the wheels. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0008] These and other features, aspects, and advantages of the invention are better understood by reference to the following description, appended claims, and accompanying drawings in which:  
     [0009]FIG. 1 is a top perspective view of one version of a boost drive for a modular plastic conveyor belt embodying features of the invention;  
     [0010]FIG. 2 is a bottom perspective view of a portion of the boost drive of FIG. 1;  
     [0011]FIG. 3 is a side elevation schematic of another version of a boost drive for a modular plastic conveyor belt embodying features of the invention;  
     [0012]FIG. 4 is a front elevation cross section of the boost drive of FIG. 3;  
     [0013]FIG. 5 is a partial side elevation view as in FIG. 3 showing boost drive sprocket details;  
     [0014]FIG. 6 is a front elevation view of yet another version of a boost drive for a modular plastic conveyor belt embodying features of the invention;  
     [0015]FIG. 7 is a side elevation view of the boost drive of FIG. 6; and  
     [0016]FIG. 8 is a schematic view of a spiral conveyor system using a boost drive as in FIG. 1, FIG. 3, or FIG. 6. 
    
    
     DETAILED DESCRIPTION  
     [0017] One version of a boost drive embodying features of the invention is shown in FIGS. 1 and 2. A conveyor  10  is constructed of a modular plastic conveyor belt  12 , such as an Intralox Series 2200 belt manufactured by Intralox, Inc. of Harahan, La., USA. The belt is supported in a framework  14 . The framework also supports a motor-driven primary drive  16  at one end. The primary drive in this example includes a set of sprockets mounted on a drive shaft, which is supported between bearings attached to the framework. The shaft and the sprockets are rotated by a motor to drive the belt in a direction of belt travel  18 . The other end of the belt is looped about an idler sprocket set  20 , which is generally identical to the primary sprocket drive, but without the motor. The modular plastic belt shown is typical of modular plastic belts in that it includes a series of rows  22 , each composed of one or more belt modules transversely across its width. Hinge eyes  24  of adjacent rows are interleaved and interconnected at a hinge joint by hinge pins  26 . The hinge joint allows the belt to articulate about the drive and idler sprockets at the ends of the conveying path. As the belt is pulled along the conveying path by the primary drive, there is tension in the belt. In the example of FIG. 1, the tension is typically the greatest at the belt&#39;s entry into engagement with the primary drive. A boost drive  28  is used to decrease the maximum tension in the belt.  
     [0018] The boost drive includes a first drive wheel  30  mounted on a first shaft  32  defining a first axis of rotation  34 . The first shaft is supported at a side edge of the conveyor by a support structure  36  including a shaft bearing  38 . The first drive wheel frictionally engages the top side  40  of the belt. A second drive wheel  31  frictionally engages the bottom side  41  of the belt. The second drive wheel is similarly mounted to a second drive shaft  33  defining a second axis of rotation  35 . Both axes of rotation  34 ,  35  are parallel to each other and transverse to the direction of belt travel  18 . The second drive shaft is attached to the framework in a similar way as the first drive shaft. First and second gear wheels  42 ,  43  are mounted on the first and second shafts opposite the drive wheels. The teeth of the gear wheels mesh to link the drive wheels. A chain drive sprocket  44  is also mounted, in this example, on the second drive shaft  33 . A chain  46  is wrapped between the drive sprocket  44  and a sprocket  48  extending from a gearbox  50  driven by an electric motor  52 . The drive mechanism directly drives the second drive wheel in the version of FIGS. 1 and 2, but could just as well have been connected directly to the first drive shaft  32 . In any event, because of the gearing between the drive shafts, the motor drives both wheels in tandem.  
     [0019] As shown in FIGS. 1 and 2, the drive shafts  32 ,  33  are vertically arranged on opposite sides of the belt. Consequently, in this version, the first and second drive wheels are vertically aligned on opposite sides of the belt. In effect, the drive wheels pinch the belt between themselves as they feed it through. The wheels are constructed of a metal hub with an outer contact surface made of a high-friction material such as a polyurethane material forming rollers. The polyurethane grips the surface of the belt, which is typically made of relatively slick polyethylene, polypropylene, acetal, or composite plastic materials.  
     [0020] Another version of boost drive is shown in FIGS.  3 - 5 . In this version, the first and second drive wheels are realized as toothed sprockets  54 ,  55  rotating about first and second drive shafts  32 ,  33 . Teeth  56  along the outer periphery of the sprockets positively engage drive structure, in this example, surfaces  58  formed on the hinge eyes  24  of the modules. Thus, engagement with the belt in this version is positive rather than frictional.  
     [0021] Other features shown in this version, which could likewise be used in the version of FIGS. 1 and 2, include back-up shoes  60  arranged on the top and bottom sides of the belt just upstream and downstream of the first and second drive wheels and an edge shoe  62  at the side edge of the belt. The shoes help guide the belt and aid in disengagement of the belt from the drive wheels. In this version, the sprocket wheels are offset from each other in the direction of belt travel to avoid interference between the teeth of each sprocket wheel.  
     [0022] Like the boost drive shown in FIGS. 1 and 2, this version of boost drive has bearings  64  to rotatably support the drive shafts  32 ,  33 . Meshed gear wheels  42 ,  43  mounted in the drive shafts similarly link the two drive wheels, which are driven in tandem in a way similar to that for the frictional wheel version.  
     [0023] In yet another version of the boost drive, the first and second drive wheels are not geared together. Instead, one of the drive wheels is biased against the belt by spring pressure, for instance. As shown in FIGS. 6 and 7, the belt  12  is pinched between drive wheels  80 ,  81  on the top  40  and bottom  41  sides at its side edges. The drive wheels  81  engaging the bottom side of the belt are shown connected directly to a drive mechanism through a common drive shaft  82 . The shaft terminates in a sprocket  44  or a pulley driven by a chain  46  or a drive belt by a gearbox  50  and motor  52 . The drive wheels  80  on the top side of the belt are rotatably mounted in wheel housings  84  via an axle  86 . A spring  88  or other biasing means pushes the wheels toward the top side of the belt in the direction of arrow  90 . In this way, the top wheels apply pressure to the top side of the belt to keep it in contact with the drive wheels on the opposite side. As the top and bottom sides of the belt and the surfaces of the wheels wear, the spring maintains the pressure of the top wheels against the belt. In this sense, the boost assembly shown in FIGS. 6 and 7 is self-adjusting.  
     [0024] Thus, all these versions decrease the tension in the belt at its exit from the boost drive.  
     [0025] One application in which either version of the boost drive can be used is shown schematically in FIG. 8. In this spiral system application, a modular plastic conveyor belt is wrapped helically around a vertical drive cage or drum  66  that rotates about its axis. As the cage rotates, it drives the belt in the direction of the arrows by its engagement with the inside edges of the belt. Various take-up and feed sprockets or drums  67 - 72  define the conveying path. The primary spiral drive  72  decreases the tension in the belt between the drive cage and itself. If, however, the primary drive cannot be located close to the infeed of the spiral, the primary drive may not be able to provide the low tension needed at the infeed tangent. A boost drive  74 , such as exemplified by the versions described, positioned just before the infeed tangent provides a supplemental driving force to the belt. The boost drive can engage the belt at one side edge or both side edges of the belt. By reducing the belt tension at a position on the conveying path that otherwise would be extremely high, the boost drive can be used to adapt modular plastic conveyor belts to otherwise high-tension metal belt applications.  
     [0026] Although the invention has been described in detail with respect to a few preferred versions, other versions are possible. For example, the shoes shown with the sprocket version could be used with the roller version. As another example, the offset sprocket arrangement shown with the sprocket version applies to the roller version as well. Drive mechanisms other than the chain drive mechanism, such as line drives, as only one example, can be used on the boost drive with equivalent effect. A boost drive can be positioned other than just upstream of the infeed tangent of a spiral drum drive. It can be positioned along the conveying or return path wherever low tension or supplemental driving is needed. As these few examples suggest, the scope of the claims is not meant to be limited to the details of the versions described in detail.