Abstract:
A dual helical conveyor system, is disclosed having a conveyor belt adapted to move in a first direction along a first helical path and thereafter in a second direction generally opposite the first direction along a second helical path generally concentric with said first helical path. The conveyor belt is further movable through a cross-over section along a cross-over path which connects the first and second helical paths, and a conveyor belt drive mechanism is provided in the cross-over section to frictionally drive the conveyor belt along the cross-over path and between the first and second helical paths. The conveyor belt is driven by friction/slip drive mechanism along the first and second helical paths. The conveyor in the first and second paths may be a single continuous belt or it may be alternatively be comprised of two separate and independent belts. When the conveyor in the first and second paths is comprised of separate and independent conveyor belt systems, communication between the product/discharge end of each system is provided by a third conveyor belt system. Independent friction/slip drive mechanisms are respectively provided for the first and second conveyor paths.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a low tension dual helical conveyor systems capable of conveying articles along concentric helical paths having mutually opposite directions of travel. 
     2. Description of the Related Art 
     Endless conveyors of the type contemplated herein generally include an endless conveyor belt which has sufficient flexibility to allow the belt to travel over concentric helically shaped paths having opposite directions of travel from a product input station to a product discharge station. Since the path is helical, the belt must be capable of flexing at least to a limited extent along at least three mutually orthogonal axes in order to permit the belt to follow such a relatively complex path. With concentric helical paths, the flexibility of the belt along several axes is increasingly significant, particularly when the helical paths are connected by a cross-over section of conveyor belt. 
     In order to permit such multi-directional flexing, such conveyor belts are generally constructed of a plurality of interconnected links which permit at least limited link-to-link articulation along two or more mutually orthogonal axes. In such instances, the links are generally constructed of materials such as steel, plastics, combinations thereof or the like, making the weight of the belt a relatively significant factor in operating the conveyor system. 
     Conveyor belts of the type contemplated herein generally range from about 12 inches to about 60 inches in width, and above about 200 feet in length. Although single helical conveyors generally may be of length up to about 5,000 feet, the possible length of such conveyors is virtually unlimited. When a conveyor belt is constructed of numerous interlocked steel links and is between 12 and 60 inches in width and more than 200 feet in length, the substantial weight of the belt becomes a significant factor to reconcile. For example, the belt must be driven through the work path which begins at the product input station and ends at the product discharge station. Thereafter, the belt enters the return section where it reverses direction and re-enters the product input station to continue operating in its endless path. In helical conveyors, the belt is driven up a helical shaped path in an up-go conveyor, and down a helical shaped path in a down-go conveyor. 
     In certain systems, such as the dual concentric conveyor systems disclosed in U.S. Pat. Nos. 3,664,487 and 4,036,352, the belt is driven by positive drive forces provided by drive members such as rotating drive angles driven on one side of the helical loops. In other systems in which a single helical path is defined, the belt is driven by friction forces imparted to it along the inner edge by a circular shaped rotating cage having friction/slip members attached to it and around which the belt is wrapped in the work zone. When the belt is friction driven, it generally is also provided with additional assistance by a motor driven sprocket which is constructed and arranged to engage the links of the belt directly as it is rotatably driven by the assist motor. Such motor assist is particularly needed in up-go helical conveyors where the relatively heavily weighted belt is made to traverse an up-go helical path against the force of gravity. A motor driven assist sprocket is also utilized in helical shaped down-go conveyors, although the gearing and roller arrangements differ somewhat from the up-go conveyors, and the assist force required is somewhat different. 
     In general, positively driven belts are subjected to greater tensile forces then the belts which are driven by friction forces due in part to the fact that the friction drive surface is generally moving at a faster rate of speed than the rate of speed of the driven edge of the belt. For example, when a friction driven belt of about 36 inches in width travels one revolution, the friction drive mechanism will travel approximately 36 inches further than the corresponding driven edge of the belt. 
     Conveyor belts of the type contemplated herein are generally used for conveying products under various conditions. For example, in some applications, the belts are used to convey dough products through relatively high temperature atmospheres in order to assist the dough in rising prior to formation of a bread product. In other applications, the belts may be made to carry food products through relatively cold atmospheres, sometimes under freezing conditions. In still other applications, the belts may be required to conduct products at room temperature. 
     In each instance, the belt, being made of a plurality of interlocked metal links, will react to the surrounding conditions such as temperatures, cleanliness and the like, with the result that the belt will undergo a natural stretch or compression. Such factors will, in turn, affect the belt tension. For example, some instances, the belt will become longer during operation and, in others, the belt may become shorter. Such variations sometimes make it relatively difficult to drive the belt by friction drive devices, since positively driven systems are relatively less complicated to control. 
     Dual concentric helical conveyor systems of the type disclosed in U.S. Pat. Nos. 3,664,487 and 4,036,352, which are positively driven, generally utilize conveyor belts which are permanently curved to meet the curvature of the helical conveyor paths and to accommodate the positive drive systems. In such instances, the permanent curvature in the belt also accommodates the transitional portion—or cross-over section—which connects both main conveyor systems. Further, the permanent curvature accommodates the positive drive mechanism by providing relative synchronized precision between the positive drive mechanism and the belt in both of the main conveyor sections. 
     Positively driven dual concentric helical conveyor systems have a number of disadvantages. For example, the preset curvature in the belt limits the location and angle of the “product infeed/product discharge” sections. Also, the preset curved nature of the belt prevents reversing the belt to reduce wear and increase belt life. Moreover, the significant tension to which the belt is normally subjected by the positive drive mechanism tends to increase belt wear and limit belt life. We have invented a dual concentric conveyor belt system which incorporates low tension friction drive systems in both of the main conveyor sections which permits the use of a normally straight flexible conveyor belt. In addition, we have invented a low tension friction drive system which can be incorporated into the cross-over section of the main conveyor sections in a manner to communicate the main conveyor sections with a low tension friction drive system, independent of whether the main sections are driven by friction or by positive drive devices, all while reducing the wear on the conveyor belt. 
     SUMMARY OF THE INVENTION 
     The invention relates to a dual helical conveyor system, which comprises a conveyor belt adapted to move in a first direction along a first helical path and thereafter in a second direction generally opposite the first direction along a second helical path inside the first helical path. Preferably the first and second helical paths are generally concentric. The conveyor belt is further movable through a cross-over section along a cross-over path connecting the first and second helical paths. A conveyor belt drive mechanism is provided in the cross-over section to frictionally drive the conveyor belt along the cross-over path and between the first and second helical paths. The conveyor belt is driven by a first friction drive mechanism along the first helical path, and a second friction drive mechanism along the second helical path. The conveyor belt defines a product input/discharge section at at least two locations, and a conveyor belt return device is provided to guide the conveyor belt between the first and second helical paths. The conveyor belt return device comprises a generally circular shaped guide member mounted for rotation at a location between the product input/discharge sections to guide the conveyor belt therebetween. 
     The first friction drive mechanism comprises a first rotatable drive cage positioned adjacent an inner edge of the conveyor belt along the first helical path, the first drive cage having first friction drive devices attached thereto and positioned in engagement with the inner edge of the conveyor belt to frictionally drive the conveyor belt along the first helical path. The second friction drive mechanism comprises a second rotatable drive cage positioned adjacent an inner edge of the conveyor belt along the second helical path, the second drive cage having second friction drive devices attached thereto and positioned in engagement with the inner edge of the conveyor belt to frictionally drive the conveyor belt along the second helical path. The first and second friction drive devices on the first and second rotatable drive cages are preferably made of resinous material, preferably ultra high molecular weight polyethylene. 
     Preferably, the first and second drive cages are independently driven by respective power drive systems, and each power drive system comprises a power drive device having a cage drive member connected thereto to rotatably drive an associated drive cage. The cage drive members each comprise a link chain which is driven by the respective power drive system. Although each power drive device is preferably driven by an electric motor as will be disclosed herein, alternatively other known power drive systems such as hydraulically powered drive systems or the like may be utilized. 
     The conveyor belt drive mechanism adjacent the cross-over path comprises a plurality of friction driven members positioned in moving frictional engagement with an edge portion of the conveyor belt along at least a portion of the cross-over path to frictionally drive the conveyor belt between the first and second helical paths. The friction drive members are preferably made of resinous material, preferably ultra high molecular weight polyethylene. 
     The conveyor belt drive mechanism adjacent the cross-over path comprises a link chain adapted to move along an endless path adjacent the cross-over path, and the ultra high molecular weight polyethylene friction drive members are attached to the movable link chain. 
     In a preferred embodiment, a dual helical conveyor system is disclosed which comprises an endless conveyor belt adapted to move in a first direction along a first helical path portion and thereafter in a second direction generally opposite the first direction along a second helical path portion inside the first helical path. Preferably the first and second path portions are generally concentric. Movable friction/slip drive devices are positioned in engagement with an inner edge portion of the belt in the first helical path portion, and movable friction/slip drive devices are positioned in engagement with an inner edge portion of the conveyor belt in the second helical path portion. The conveyor belt is further movable along a cross-over path which connects the first and second helical paths, and a conveyor belt drive mechanism is positioned adjacent the cross-over path. The conveyor belt drive mechanism includes movable friction/slip members positioned in engagement with an inner edge portion of the conveyor belt in the cross-over section to provide force sufficient to assist movement of the conveyor belt between the first and second helical paths. 
     According to one embodiment, the dual helical conveyor system comprises a first helical conveyor section having a first conveyor belt adapted to move in a first direction along a first helical path, and a second helical conveyor section having a second conveyor belt adapted to move in a second direction opposite the first direction along a second helical path and located inside the first helical path, preferably concentric therewith. Each of the first and second conveyor belts have associated therewith a friction drive mechanism which comprises a rotatable cage having friction drive members attached thereto and positioned in moving frictional/slip engagement with an inner edge portion of the associated conveyor belt to drive the associated conveyor belt along the respective helical path. Each of the first and second helical conveyor sections include a product input/discharge section for receiving and/or discharging products in dependence upon the direction of the respective conveyor belt. The system further comprises a third conveyor section extending between the product input/discharge sections to convey products therebetween. The third conveyor section preferably has an arcuate configuration and is positively driven by positive drive members. Alternatively, the third conveyor section may be driven by a friction drive device having a plurality of friction/slip drive members in movable engagement with an edge portion of the conveyor section. The friction drive device associated with the third conveyor section preferably comprises a link chain having a plurality of friction/slip drive members attached thereto and positioned in movable engagement with the edge portion of the third conveyor section. 
     In another embodiment, the dual helical conveyor system comprises a first helical conveyor section having a first conveyor belt adapted to move in a first direction along a first helical path, and a second helical conveyor section having a second conveyor belt adapted to move in a second direction opposite the first direction of the first belt along a second helical path inside, but preferably concentric with the first helical path. Each of the first and second conveyor sections are independently driven by respective independently controlled friction drive mechanisms and have respective product input/discharge sections. A third conveyor section is positioned and adapted to carry products between the product input/discharge sections of the first and second helical conveyor sections. The third conveyor section preferably has an arcuate configuration and a friction/slip drive mechanism is provided to drive the conveyor section. Alternatively, a positive drive mechanism may be provided to drive the third conveyor section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described hereinbelow with reference to the drawings, wherein: 
     FIG. 1 is a right side perspective view of an endless friction driven low tension dual helical conveyor system constructed according to the present invention, capable of conveying articles along concentric ascending and descending helical paths, and illustrating a friction drive device in the cross-over section between the helical paths; 
     FIG. 2 is a plan view of the friction drive device of the cross-over section of the conveyor of FIG. 1; 
     FIG. 3 is a plan view, greatly enlarged, of a portion of the friction drive device of FIG. 2, illustrating the link chain drive having friction drive plates attached thereto; 
     FIG. 4 is a partially schematic plan view of the dual helical conveyor system of FIG. 1, illustrating the upper frame structure, the dual independent helical drive system, and the friction drive device of the cross-over section; 
     FIG. 5 is a partially schematic plan view of the dual helical conveyor system of FIG. 1, illustrating the conveyor belt return system in the lowermost portion of the conveyor, and the locations of the product input, product discharge sections; 
     FIG. 5A is a cross-sectional view taken along lines  5 A— 5 A of FIG. 5, illustrating the conveyor belt return channel guide; 
     FIG. 6 is a partial schematic plan view of the dual helical conveyor of FIG. 1, illustrating various alternative directions and angular orientations available for the product input and product discharge sections, utilizing the flexible conveyor belt of the invention; and 
     FIG. 7 is a partial schematic plan view of an alternative embodiment of the invention, wherein two concentric conveyor sections are separate and independently driven by friction or other type drive devices and product communication is provided by an arcuate conveyor communicating the product input/discharge section of one conveyor section with the product input/discharge section of the other concentric conveyor section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1, there is shown a perspective view of a low tension dual helical conveyor  10  constructed according to the invention. Conveyor  10  includes external helical conveyor section  12  which surrounds internal helical conveyor section  14  as shown. Although it is preferred that the external helical conveyor section  12  is concentric with the internal helical conveyor  14  as shown (i.e. having a common center), it is also contemplated that the invention can be practiced wherein conveyor sections  12  and  14  have different centers of rotation. 
     As indicated by the direction of arrows  16 ,  17 ,  18 ,  19 , depending upon the selected direction of movement of each conveyor section  12 ,  14 , the outer section  10  can function as an ascending or “up-go” conveyor, while the inner conveyor section  14  can function as a descending or “down-go” conveyor. Further, by reversing the direction of movement of the conveyor belt, outer conveyor section  12  will function as a descending, or “down-go” conveyor, and inner conveyor section  14  will function as an ascending, or “up-go” conveyor. The conveyor belt  20  is flexible and is generally made of metal, plastic, combinations thereof, or the like. Such belt is generally constructed of collapsibly interconnected multi-directionally articulated links which make it capable of flexing or bending along at least two, but preferably three mutually orthogonal directions so as to be directed along a continuously changing arcuate path to assume a helical shape as shown in FIG.  1 . The belt  20  includes a plurality of links connected together by cross rods to permit selective, sometimes limited, bending along three orthogonal directions as noted. 
     In general, the belt is most flexible about an axis perpendicular to the direction of movement, while limited flexible articulation is permitted about the remaining two orthogonal axes. The belt can generally be folded over upon itself about the axis perpendicular to the direction of travel, while the limited flexibility permitted about the remaining two axes generally requires limited flexible bending of the links, particularly at the link-to-link connections. The links are generally of steel construction, making the weight of the belt a relatively significant factor in the operation of the conveyor. 
     Conveyor belt  20  and the helical drive system of the present conveyor are of the type disclosed in commonly assigned co-pending application Ser. No. 09/631,337, filed Aug. 3, 2000, the disclosure of which is incorporated herein by reference and made part of this disclosure. As noted, another example of a dual concentric endless conveyor belt construction is described in U.S. Pat. No. 3,664,487 to Ballenger, the disclosure of which is incorporated herein by reference and made a part of this disclosure. Still another example of such belt construction is disclosed in U.S. Pat. No. 4,846,339 to Roinestad, the disclosure of which is incorporated herein by reference and made part of this disclosure. Conveyor belts of flexible construction of the types disclosed herein are contemplated. 
     U.S. Pat. No. 3,682,295 to Roinestad relates to an edge driven conveyor system in which a frictional edge drive is provided to support the belt, and which includes a friction edge drive in combination with any of several means to maintain the belt in the requisite driving engagement with the edge drive. The disclosure of U.S. Pat. No. 3,682,295 is incorporated herein by reference and made a part of this disclosure. 
     Referring again to FIG. 1, flexible conveyor belt  20  is endless and forms a helical path which begins adjacent the infeed/discharge section  22 ,  24  where products are introduced or discharged in dependence upon the direction of movement of the belt  20 . When the direction of the belt  20  is as indicated by arrow  18 , products (i.e. food products such as bread, etc.) are introduced at product input  24  in the direction of arrow  18 , they are made to travel over an ascending helical path on outer conveyor section  12 . Thereafter the product path enters a cross-over section  26  which directs the belt to the inner descending helical conveyor  14  which ultimately leads to product discharge section  22  as indicated by product direction arrow  17 . 
     When the direction of conveyor belt  20  is reversed as indicated by arrow  16 , products are introduced at product input  22  in the direction of arrow  16 , and are made to follow an ascending path on inner ascending helical inner conveyor  14 . When the products reach the uppermost level of inner conveyor  14 , they enter the cross-over section  26  which directs them to outer helical conveyor  12  which is now in a descending mode, and thereafter to product discharge section  24  while moving in the direction of arrow  19 . 
     As noted, the conveyor belt  20  is flexible at least to a limited extent, and endless in that when it exits product discharge section  22 ,  24  (depending upon the belt direction at any given time) it wraps around respective rollers  28 ,  30  and reverses direction. Upon reversing direction, the belt is guided about the freely rotatable guide  32 , which is located at or near the lowermost level of the conveyor. Freely rotatable belt guide  32  is best shown schematically in FIG.  5 . Preferably, guide  32  is a freely rotating bearing mounted circular shaped guide having a channel-like cross-section which receives and guides the inner edge of the conveyor belt  20  between input/discharge section  22  and input/discharge section  24 , in dependence upon the direction of movement of the belt  20 , as shown schematically in FIGS. 1 and 5. FIG. 5A is a cross-sectional view taken along lines  5 A— 5 A of FIG. 5, illustrating guide channel  32  with flexible belt  20  shown schematically and positioned between upper and lower flanges  32 A,  32 B. The belt  20  is guided along the circular path defined by guide channel  32  as shown in FIG. 5 between product input/discharge sections  22 ,  24 . As can be seen from FIG. 5, although outer helical conveyor section  12  is concentric with inner helical conveyor section  14 , the freely rotating belt return guide  32  is not concentric with either of helical sections  12  or  14  and its axis of rotation  34  is offset by dimension “Y” from the axis of rotation  36  of helical conveyor sections  12 ,  14 . 
     Referring now to FIG. 4 in conjunction with FIG. 1, when belt  20  of helical conveyor sections  12 ,  14  is of metal construction, each section  12 ,  14  is respectively driven by rotating cages  40 ,  42  which are constructed of a metal framework having attached thereto and facing radially outwardly therefrom, members  44 ,  46  fabricated of a suitable low friction/slip material such as ultra high molecular weight polyethylene, and generally referred to as “UHMW”. Other suitable low friction resinous materials are also contemplated, including polyamides such as nylon, or other polyolefins, for example. When the belt  20  is constructed of plastic, or combinations of plastic and metal, the friction/slip members of the drive cage may be constructed of a metal such as stainless steel, or a combination of plastic and steel, depending upon the precise material and construction of the inner edge of the driven belt. The individual members  44 , 46  of cages  40 ,  42  are attached to the cage framework to form a circular array of low friction members. Each of cages  40 ,  42  is respectively rotated by an endless motor driven chain  48 ,  50 . 
     In particular, motor  52  rotatably drives a sprocket (not shown) which in turn rotates sprockets  54 ,  56 , which drive endless chain  48  along an endless path about the UHMW outer drive cage  40 . Similarly, motor  58  rotatably drives a sprocket (not shown) which in turn rotates sprockets  60 ,  62  which drive endless chain  50  along an endless path about UHMW inner drive cage  42 . The driving mechanism between the chains  48 ,  50  and the cages  40 ,  42 , include a plurality of sprocket teeth extending radially outward from cages  40 ,  42  and spaced circumferentially from each other so as to be progressively engaged by drive chains  48 ,  50  so as to continuously rotate cages  40 ,  42  positively in either of two alternative rotational directions as indicated by arrows  64 ,  65 . Alternatively, other power drive systems can be used in place of electric motors  52 ,  58 , such as hydraulic power drive systems or the like. 
     Referring again to FIG. 4 in conjunction with FIG. 1, outer cage  40  and inner cage  42  rotate continuously in the same rotational direction while UHMW members  44 ,  46  frictionally engage the inner edge of the respective section of conveyor belt to cause the outer conveyor belt section  12  to move in one direction (i.e. either up or down) while causing the inner concentric conveyor belt section  14  to move in the opposite direction. As will be appreciated, the direction of movement of outer conveyor section  12  and concentric inner conveyor section  14  can readily be reversed by reversing the direction of rotation of drive motors  52 ,  58  and respective drive chains  48 ,  50 . The individual drive mechanism for each of conveyor sections  12 ,  14  is similar to the drive mechanism for the single helical conveyor as disclosed in commonly assigned co-pending application Ser. No. 09/631,337, filed Aug. 3, 2000, the disclosure of which is incorporated herein by reference and made a part of this disclosure. 
     Referring now to FIGS. 2 and 3 in conjunction with FIGS. 1 and 4, the drive mechanism in the conveyor belt cross-over section  26  will now be described. Since the configuration of the articulating flexible belt  20  in the cross-over section  26  necessarily causes the belt to assume a continuously changing radius and configuration, at different locations, it has been generally difficult to provide the precise moving force required to maintain continuous movement of the conveyor belt in both the inner and the outer sections as well as in the cross-over section  26 , while minimizing the tension in the belt. In prior art conveyors, positive drive devices increased belt tension. To accomplish the precisely controlled belt movement while generating minimum tension in the belt  20  in the cross-over section, cross-over drive mechanism  38  is configured as shown in FIGS. 2 and 3. Cross-over drive mechanism  38  is comprised of frame  66  having an outer arcuate section  68  and a straight section  70 . Frame  66  supports a sprocket driven endless link chain  72  which is driven along a continuous endless path including arcuate path section  69  and straight path section  71  as shown. Electric drive motor  74  is arranged to rotatably drive toothed sprocket  76  via drive belt or chain  78  such that the teeth of sprocket  76  engage link chain  72  to drive it around idler sprocket  77  and along its endless path as shown. 
     As can be seen in FIG. 3, link chain  72  is formed of links  80  having flanges  82  extending outwardly therefrom. Flanges  82  each have a member  84  formed of ultra high molecular weight polyethylene (UHMW) and having a generally rectangular cross-section as shown. Members  84  are made to frictionally engage and drive the inner edge of the conveyor belt  20  in the cross-over section  26  between the outer conveyor section  12  and the inner conveyor section  14 . Although link chain  72  is positively driven by electric drive motor  74  and toothed sprocket  76 , the driving force of the conveyor belt  20  in the cross-over section  26  is actually provided by friction/slip engagement between the UHMW members  84  in a manner similar to the friction/slip engagement used to drive the conveyor belt  20  in the main outer section  12  and the main inner concentric section  14 . It will be appreciated that by providing such unique friction/slip driving force, the tension of the belt in the cross-over section  26  and throughout the system can be controlled and minimized in contrast to the positively driven dual conveyor systems which are presently known. Furthermore, by utilizing such friction/slip drive system in the cross-over section  26  and in the main concentric sections  12 ,  14 , it is now possible to utilize a conveyor belt of the type which is flexible and capable of articulation along three mutually orthogonal axes thus making it possible to reverse the belt to periodically equalize and reduce wear on the belt. Thus by reversing the top and bottom surfaces of the belt the friction/slip drive force will be applied to the previously unused edge, thereby reducing excessive wear on the driven edge. Additionally, the upper product surface wear will be reduced and the life of the belt extended. 
     Furthermore, as indicated in connection with external conveyor section  12  and internal conveyor section  14 , UHMW is the preferred friction/slip material used to drive the belt  20  in cross-over section  26  when the belt  20  is of metal construction. However, when the belt is made of alternative materials such as plastic, metal, or combinations thereof, or other materials, friction/slip drive members  84  in the cross-over section  26  may be made of alternative materials compatible with the material or materials from which the belt is constructed. For example, when the belt  20  is constructed of plastic along the inner edge, friction/slip drive members  84  will preferably be made of a material such as metal. 
     Referring now to FIG. 6, there is illustrated a significant advantage to the low tension endless dual helical conveyor constructed according to the present invention. By incorporating a flexible conveyor belt which articulates generally along three mutually orthogonal axes, the flexibility permits selective spacing of the two product input/discharge sections from each other by any desired or predetermined relative angular orientations by simply predetermining the length of the belt and structure of the corresponding framework. For example, whereas prior art positively driven dual concentric conveyor systems utilized conveyor belts having predetermined fixed curvatures along several directions (i.e. along the driven edge and on the top surface), the structure of the present system utilizes a flexible belt which has a straight and uncurved configuration in its normal state. Thus, the belt of the present dual concentric conveyor system can be designed to include product input/discharge sections at any predetermined locations along the periphery of the conveyor. For example, referring to FIG. 6, product input/discharge sections can be provided as shown at  22 ,  24  as is also illustrated in FIGS. 1 and 5. Alternatively as shown in FIG. 6, product input/discharge sections can also be provided at any selective pair of locations, such as the exemplary locations shown for example at  86 ,  88 ,  90 ,  92 ,  94  and  96 . Although the examples of such locations is shown in FIG. 6 as illustrated, the locations for such product input/discharge locations is substantially unlimited and may be provided in any configuration desired by the end user. In particular, since the flexible articulating belt is initially straight and reversible as noted, locating the pair of product input/discharge sections for such dual conveyor is not limited due to the substantial flexibility of the belt which can be curved along either edge as well as about either the top or the bottom surfaces. 
     Referring now to FIG. 7, there is disclosed an alternative embodiment of the invention wherein external helical conveyor section  100  surrounds internal helical conveyor section  102 , preferably in generally concentric relation. Both external section  100  and internal section  102  are of the type disclosed in the aforementioned commonly assigned application Ser. No. 09/631,333 wherein a take-up section and a counterbalance weight is provided. 
     In the system shown in FIG. 7, external conveyor section  100  includes take-up section  104  and internal conveyor section  102  includes take-up section  106 . At the top of the respective take-up sections  104 ,  106  is the respective product input/discharge sections as disclosed in application Ser. No. 09/631,337. 
     Referring again to FIG. 7, a third arcuately shaped conveyor section  108  is positioned and arranged to transport products between the product input/discharge sections  104 ,  106 . Conveyor section  108  may be positively driven, or alternatively conveyor section  108  may be friction driven as described in connection with the previous embodiment. In either embodiment, the outer and inner helical conveyor sections  100 ,  102  are separately and independently driven by rotating friction-type drive cages as described in connection with the previous embodiment. As noted, since helical conveyor sections  100 ,  102  are separate and independently controlled, they also include a belt take-up section which permits excess conveyor belt to accumulate, with an appropriate counter-balance system whereby operational fluctuations in the length of the belt may be accommodated. The counter balance system may be of the fixed weight type as generally known in the art, or alternatively it may be of the type disclosed and claimed in application Ser. No. 09/631,337. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the type described above. Further, while the invention has been illustrated and described as embodied in a low tension dual helical conveyor system, it is not intended to be limited to the details shown, since it will be understood that various omissions, modifications, substitutions and changes in the forms and details of the device illustrated, and in its operation, can be made by those skilled in the art without departing in any way from the spirit of the present invention as described and defined by the following claims.