Abstract:
In a motorized conveyor pulley of the type comprising a cylindrical pulley drum with axially opposite end plates enclosing an electric motor and drive transmission, the pair of end plates of the pulley are constructed with an increased axial thickness compared to prior art end plates and are supported on a pair of shaft ends by pairs of bearings and are sealed by a pair of lubricant seals between each pair of bearings. The enlarged end plates and the pairs of bearings resist bending loads exerted on the conveyor pulley by the conveyor belt and thereby reduce loading stresses on the motor and drive transmission contained in the pulley permitting more economical manufacture of the motor and drive transmission.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention pertains to a motorized conveyor pulley of the type comprising a cylindrical pulley drum with axially opposite end plates enclosing an electric motor and drive transmission. The end plates of the pulley are mounted on a pair of shaft ends that pass through the end plates at the axially opposite ends of the pulley and support the motor and drive transmission in the pulley. In particular, the present invention pertains to the pair of end plates of the pulley that are constructed with an increased axial thickness compared to prior art end plates and are supported on the pair of shaft ends by pairs of bearings and are sealed by a pair of lubricant seals between each pair of bearings. The enlarged end plates and the pairs of bearings resist bending loads exerted on the conveyor pulley by the conveyor belt and thereby reduce loading stresses on the motor and drive transmission contained in the pulley permitting more economical manufacture of the motor and drive transmission. 
     (2) Description of the Related Art 
     A motorized conveyor pulley is employed at one end of a flat, continuous belt conveyor where the belt of the conveyor is looped or wrapped over the motorized conveyor pulley at one end of the conveyor and wrapped over an idler pulley at an opposite end of the conveyor. In order to provide sufficient friction engagement between the pair of pulleys and the belt to avoid slipping of the belt on the pulleys when the belt is conveying a substantial load, the belt is usually stretched very tight between the pair of pulleys resulting in a substantial load exerted on the pulleys by the belt. 
     The load exerted by the belt on the motorized conveyor pulley is transferred to the component parts contained inside the pulley. A typical motorized conveyor pulley includes a cylindrical pulley drum having a hollow interior. A pair of circular end plates close off the axially opposite ends of the drum. The end plates have coaxial center bores and stationary stub shafts extend through the center bores. Each stub shaft has a bearing mounted on its exterior that is received in the center bore of one of the end plates, thereby mounting the pulley drum for rotation on the stationary stub shafts. 
     Contained inside the pulley drum is an electric motor and a gear carrier that are mounted stationary to the ends of the two stub shafts projecting into the interior of the pulley drum. The electric motor drives a gear transmission mounted on the gear carrier that in turn drives a ring gear mounted on the interior of one of the pulley end plates imparting rotation to the pulley drum. The pulley drum contains a bath of lubricant, at times filling half the interior volume of the drum, that both cools and lubricates the motor and the transmission gearing. 
     The substantial load exerted on the motorized conveyor pulley by the conveyor belt causes the pulley to bend between the ends of the stub shafts projecting from the axially opposite ends of the pulley drum. The bending of the pulley drum is transferred through the end plates to the internal components of the motorized conveyor pulley. This at times would result in the bending of the gear carrier in the interior of the pulley drum which would result in gears of the transmission coming out of mesh, excessive gear chatter or gear noise and at times the breaking of gear teeth. The bending of the drum would also result in the leakage of lubricant past lip seals mounted on the stub shafts in the center bores of the pulley end plates. 
     The prior art solution to the bending transferred to the internal components of the pulley was to beef up the construction of the internal components. For example, the end shield of the motor to which the gear carrier of the transmission was attached would be constructed of cast iron or other cast metal with an increased thickness to resist the bending of the end shield. In addition, the gear carrier of the transmission connected to the motor end shield would be cast with an increased thickness or with reinforcing gussets or webs to resist the bending of the gear carrier. Unfortunately, beefing up the construction of the component parts of the motorized conveyor pulley significantly increases the cost of manufacturing the motorized conveyor pulley. 
     What is needed to overcome the problem of bending of motorized conveyor pulleys is an improved construction of the pulley that isolates the internal components of the motorized conveyor pulley from the bending loads without appreciably increasing the cost of manufacture of the internal components and the motorized conveyor pulley. 
     SUMMARY OF THE INVENTION 
     The motorized conveyor pulley of the invention eliminates or significantly reduces the bending of the cylindrical pulley drum due to the conveyor belt load and thereby isolates the internal component parts of the pulley from stresses due to bending. The motorized conveyor pulley of the invention is similar to prior art conveyor pulleys in that it is comprised of a cylindrical pulley drum having a hollow interior with end plates at the axially opposite ends of the drum. However, the axial thickness of the end plates is substantially increased. By increasing the thickness of the end plates, the axial length of the center bores passing through the end plates is also increased. The increase in the axial length of the center bores allows the positioning of pairs of bearings inside the center bores and on the stub shaft ends that pass through the center bores. In the preferred embodiment of the invention, the increased axial thickness of the end plates and the increased length of the end plate center bores allows the positioning of two axially spaced bearings in each of the center bores and on each of the stub shaft ends. The axial spacing of the pairs of bearings also allows the positioning of a shaft seal in each center bore between the pairs of bearings. In the preferred embodiment, the axial spacing allows the positioning of two shaft seals on each stub shaft providing a redundant system for preventing leakage of lubricant from the interior of the pulley drum. The use of two bearings mounting each end plate of the pulley drum on each of the stub shaft ends effectively unloads all of the internal components of the pulley from excessive loading due to belt tension bending. In an extreme comparison, the pair of stub shaft ends, their associated pairs of bearings and the end plates of the pulley drum they support may exist without any internal support required to satisfactorily take up the belt tension loading. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and features of the invention are revealed in the following detailed description of the preferred embodiment of the invention and in the drawing figures, wherein: 
     FIG. 1 is a side view in section of the motorized conveyor pulley of the present invention; 
     FIG. 2 is a perspective view of the conveyor pulley of FIG. 1 removed from the cylindrical pulley drum; 
     FIG. 3 is a side view of the conveyor pulley of FIG. 2 with one of the conveyor end plates removed and with the ring gear of the pulley transmission removed; 
     FIG. 4 is a side perspective view of the transmission mechanism of the conveyor pulley. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the motorized conveyor pulley  10  of the present invention. The motorized conveyor pulley  10  is similar to prior art motorized conveyor pulley constructions in that it is basically comprised of a cylindrical pulley drum  12  having a center axis of rotation A, a first end plate  14  and a second end plate  16  at axially opposite ends of the pulley drum  12 , a first stub shaft end  18  and a second stub shaft end  22  at axially opposite ends of the conveyor pulley  10 , and a drive assembly  24  contained in the interior of the pulley drum  12 . 
     The first and second shaft ends  18 ,  22  are similar to the shaft ends employed in prior art motorized conveyor pulleys. The first shaft end  18  has a cylindrical exterior surface and axially opposite exterior  26  and interior  28  ends. A hollow bore  32  passes through the center of the first shaft end. The hollow bore  32  is employed in routing electrical wiring (not shown) from the motor of the drive assembly  24  from the interior of the motorized conveyor pulley  10  through the bore  32  to the exterior of the pulley. A pin  34  passes through the first shaft end  26  securing the shaft adjacent its interior end  28  to a gear carrier of the drive assembly to be described. The second shaft end  22  also has a cylindrical exterior surface and axially opposite interior  36  and exterior  38  ends. Unlike the first shaft end, the second shaft end is solid but it does also include a pin  42  securing the second shaft end  22  to the motor of the drive assembly  24  yet to be described. In the operative environment of the motorized conveyor pulley  10  both the first shaft end  18  and second shaft end  22  are fixed stationary to a support structure of the conveyor system (not shown) in which the motorized conveyor pulley  10  is employed. 
     As stated above, a pin  42  secures the interior end  36  of the second shaft end  22  to a motor  44  of the conveyor pulley drive assembly  24 . The motor  44  shown in FIGS. 1 through 3 is only one example of an electric motor which may be employed with the conveyor pulley of the invention. Unlike prior art motors employed in motorized conveyor pulleys however, the motor  44  can be an off the shelf motor and it is not necessary that its construction, in particular the construction of its opposite end shields  46 ,  48 , be beefed up to resist bending forces exerted on the internal components of typical prior art motorized conveyor pulleys. As shown in FIG. 1, a second end shield  48  of the motor is secured to the second shaft end  22  by the pin  42 . The pin  42  secures the motor  44  stationary to the second shaft end  22 . 
     A gear carrier  52  that makes up a part of the motorized conveyor pulley of the invention is connected between the first end shield  46  of the motor  44  and the first shaft end  18 . The gear carrier  52  is secured to the first shaft end  18  by a pin  34 . The opposite end of the gear carrier or the left hand end of the carrier as seen in FIG. 1 is secured to the first end shield  46  of the motor by threaded fasteners  54 . The gear carrier  52  is shown removed from the motorized conveyor pulley  10  and attached between the first end shield  46  and the first shaft end  26  in FIG.  4 . 
     The gear carrier  52  is an improvement over prior art gear carriers in that it supports both ends of gear shafts of a reduction transmission of the drive assembly  24  where prior art transmissions often employed cantilevered shafts, or shafts supported at only one end. The particular transmission shown in the drawing figures is an example of only one type of gearing transmission that may be employed with the motorized drive pulley  10  of the invention. The particular transmission shown employs two pairs of gears, with each pair of gears mounted on a common shaft. As seen in FIG. 1, the motor  44  has a drive shaft  56  with an output gear  58  mounted on the drive shaft. The motor output gear  58  is not shown in FIG.  4 . The motor output gear  58  meshes with a larger gear  62  of a first pair of gears mounted on a first shaft  64 . As seen in FIG. 4, one end of the first shaft  64  is mounted to the first end shield  46  of the motor and the opposite end is mounted in a first journal  66  of the gear carrier  52 . Thus, the opposite ends of the first shaft  64  are both supported for rotation. A smaller gear  68  of the first pair of gears is also mounted on the first shaft for rotation with the large gear  62 . The smaller gear  68  meshes with a larger gear  72  of the second pair of gears mounted on a second transmission shaft  74 . The second gear shaft  74  is also mounted for rotation at its opposite ends in the first end shield  46  of the motor at one end and a second journal  76  of the gear carrier at its opposite end. A smaller second gear  78  is also mounted on the second gear shaft  74  for rotation with the larger second gear  72 . The smaller second gear  78  meshes with an internally threaded ring gear  82  that is secured by threaded fasteners  84  to the first end plate  14  of the motorized conveyor pulley. Thus, the construction of the gear carrier  52  of the invention supports both the first gear shaft  64  and the second gear shaft  74  in respective first  66  and second  76  gear journals at one end of the shafts with the opposite ends of the gear shafts being supported in journals provided in the first end shield  46  of the motor  44 . With the particular drive transmission shown in the drawing figures, rotation of the motor output gear  58  drives the large gear  62  of the first pair of gears. Rotation of the large gear  62  is also transmitted to rotation of the smaller gear  68  of the first pair of gears. The smaller gear  68  of the first pair meshes with the larger gear  72  of the second pair transmitting its rotation to the larger second gear. Rotation of the larger gear  72  of the second pair also causes rotation of its associated smaller gear  78 . The smaller gear  78  of the second pair meshes with the ring gear  82  fastened to the first end plate  14  and thereby transmits rotation to the first end plate and the pulley drum  12 . 
     The constructions of the first and second end plates  14 ,  16  and the manner in which they are mounted to the respective first and second shaft ends  18 ,  22  are the primary improvements provided by the motorized conveyor pulley  10  of the invention. 
     The first end plate  14  has an increased axial thickness over that of prior art end plates. The end plate  14  is circular and has axially opposite interior  86  and exterior  88  surfaces. The end plate has a cylindrical peripheral surface  92  that is dimensioned to fit in tight friction engagement in a first opening of the cylindrical pulley drum  12  on the right-hand end of the drum as seen in FIG.  1 . An annular groove  94  is formed in the peripheral surface and an o-ring  96  is received in the groove providing a seal between the peripheral surface and the interior surface of the pulley drum  12 . A plurality of internally threaded fastener holes  98  are also formed into the peripheral surface at circumferentially spaced positions. The fastener holes  98  receive threaded fasteners that attach the first end plate  14  to the first end of the pulley drum  12 . An annular collar  102  having an exterior diameter dimension that is slightly smaller than that of the peripheral surface  92  projects inwardly from the interior surface  86  of the first end plate  14 . The ring gear  82  of the drive assembly transmission is secured to the annular collar by threaded fasteners  84 . A cylindrical center bore  104  passes through the center of the first end plate. As seen in FIG. 1, the center bore  104  is formed in the center of the first end plate  14  with portions of the center bore having different interior diameter dimensions. The portions of the center bore adjacent the interior surface  86  and exterior surface  88  of the end plate have the largest interior diameter dimensions and are dimensioned to receive a first pair of bearings  106 . The first pair of bearings  106  can be any type of commercially available bearing assemblies and will be chosen depending on the overall size of the motorized conveyor pulley  10  and the belt loads to which it will be subjected. As seen in FIG. 1, each bearing of the first pair of bearings  106  has an axial dimension and the combined axial dimensions of the bearings  106  is less than the minimum axial thickness of the first end plate  14  measured between its interior surface  86  and its exterior surface  88 . This provides an axial spacing in the center bore  104  between the first pair of bearings  106 . In the preferred embodiment of the invention the axial spacing is occupied by a seal assembly. Also in the preferred embodiment of the invention the seal assembly is comprised of a pair of annular seals  108  mounted on the exterior surface of the first shaft end  18  and in the center bore  104  of the first end plate. The pair of annular seals  108  are mounted on the first shaft end  18  with a small axial spacing  110  between the seals. The small axial spacing  110  is provided to contain a small amount of lubricant between the two seals  108 . Keeping the seals lubricated in this manner extends their working life, preventing the seals from leaking. A zert fitting (not shown) could also be added to the first end plate  14  with a conduit communicating between the zert fitting and the axial spacing  110  between the seals  108  to resupply lubricant to the axial spacing between the seals when needed. 
     The second end plate  16  is a mirror image of the first end plate  14  except that it does not include the annular collar  102  of the first end plate. Like the first end plate, the second end plate  16  has opposite interior  112  and exterior  114  surfaces with a cylindrical peripheral surface  116  extending therebetween. The peripheral surface  116  is dimensioned to fit tight inside a second opening of the pulley drum  12  to the left of the drum as viewed in FIG.  1 . The peripheral surface  116  has an annular groove  118  that receives an o-ring  122  that provides a seal between the peripheral surface of a second end plate and the interior surface of the cylindrical pulley drum  12  at the second end of the drum. The second end plate peripheral surface  116  is also provided with a plurality of internally threaded holes  124  that receive threaded fasteners that attach the second end plate to the second end of the pulley drum  12 . A cylindrical center bore  126  passes through the center of the second end plate  16 . As with the first end plate, the center bore  126  of the second end plate is formed with portions having different interior diameter dimensions. The portions of the center bore adjacent the end plate interior surface  112  and exterior surface  114  have the larger diameter dimensions and are dimensioned for receiving a second pair of bearings  128  therein. Each bearing of the second pair of bearings  128  has an axial dimension and the combined axial dimensions of the second pair of bearings is less than the minimum axial thickness of the second end plate  16  between its interior surface  112  and exterior surface  114 . This provides an axial spacing between the second pair of bearings  128  in the second end plate center bore  126 . The axial spacing is occupied by a seal assembly comprised of a pair of annular seals  132 . The pair of annular seals seal between the exterior surface of the second shaft end  22  and the interior surface of the second end plate center bore  126 . As with the first pair of annular seals  108 , an axial spacing  134  is also provided between the pair of annular seals  132  mounted on the second shaft end  22 . The axial spacing  134  is provided to contain an amount of lubricant to extend the working life of the seals  132 . A zert fitting (not shown) could also be provided on the second end plate  16  to supply lubricant to the axial spacing between the annular seals when needed. 
     The increased axial thickness of the first and second end plates  14 ,  16  and their associated pairs of bearings  106 ,  128  mounted in the center bores of the end plates adjacent their interior and exterior surfaces effectively unloads all of the internal components of the motorized conveyor pulley from excessive loading due to belt tension. In an extreme comparison, the first and second shaft ends  18 ,  22  and the pairs of bearings  106 ,  128  could exist without any internal support from the internal components of the conveyor pulley  10  and satisfactorily take up the belt tension loading. The arrangements of the pairs of annular seals  108 ,  132  between the pairs of bearings isolates the seals from the belt tension loads and thereby provides an improved seal of the conveyor pulley over that of the prior art. By eliminating the bending and deflection, stresses on the bearings, the gears and other internal component parts of the conveyor pulley are reduced, allowing use of less expensive materials to construct the motor and the drive transmission assembly. Instead of cast iron end shields employed in prior art motorized conveyor pulleys, cast aluminum may be used for the end shields as well as for the transmission gear carrier and transmission gears. The ability of the axially spaced bearings in each of the end plates to isolate the internal components from bending loads could also lead to the use of plastics in the motor and transmission constructions. 
     While the present invention has been described by reference to specific embodiments, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the invention defined in the following claims.