Abstract:
A roller conveyor in an as such known manner includes a plurality of driven rollers disposed in two parallel tracks. With each driven roller a drive motor is associated. From a first voltage source a first set of the driven rollers is supplied, wherein a second voltage source is provided, from which a further set of the driven rollers is supplied. This arrangement offers a high degree of redundancy in the event of the failure of individual components of the roller drive, thereby guaranteeing an emergency operation in such a situation.

Description:
RELATED APPLICATIONS 
   The present invention claims the benefit of the filing date of German Patent Application, Serial No. 10 2006 005 978.6, filed Feb. 8, 2006; the content of which is incorporated by reference herein. 
   This application also relates to concurrently filed U.S. patent application Ser. No. 11/701,169, entitled ROLLER CONVEYOR; and, 11/701,176, entitled SET OF ROLLER CONVEYORS 
   TECHNICAL FIELD 
   The invention relates to a roller conveyor comprising a plurality of driven rollers disposed in two parallel tracks; a plurality of drive motors for driving the rollers; and, at least one voltage source, from which the drive motors are supplied. 
   BACKGROUND OF THE INVENTION 
   Roller conveyors are used to transport goods carriers such as e.g. pallets. In the automobile industry they are often used to transfer vehicle bodies or parts of vehicle bodies between individual processing stations. The vehicle bodies are in said case fastened on so-called skids. This term is used for transport racks that have two mutually parallel skid runners. During the conveying operation the skid runners rest on rollers of the roller conveyor, which are disposed successively in conveying direction along two tracks. When the rollers are set in rotation, the skid with the vehicle body fastened thereon is fed in conveying direction, wherein it is sufficient to provide only some of the rollers with a rotary drive. 
   The roller conveyors of the initially described type, such as are currently known from the market, have only a single common voltage source for all of the driven rollers. If this voltage source fails or some other fault arises in the drive train, the article being conveyed comes to a standstill and has to be removed possibly laboriously by hand. In the event of failure of a single driven roller, transport is no longer possible over a considerable section corresponding to a roller conveyor module, this generally leading likewise to an interruption of conveying on the roller conveyor. 
   The present invention is provided to solve these and other problems. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to develop a roller conveyor of the initially described type in such a way that greater operational reliability is achieved. This object is achieved according to the invention in that: with each driven roller a drive motor is associated; a first voltage source is provided, from which a first set of the driven rollers is supplied; and, at least one second voltage source is provided, from which at least one further set of the driven rollers is supplied. 
   Thus, in accordance with the present invention, two measures are taken that ensure a redundancy in the drive system of the driven rollers and hence provides fail safety. That is, the number of driven rollers is considerably increased compared to the background art so that in the event of failure of a single driven roller, instead of a larger section of the roller conveyor being left without a drive, adjacent rollers are substantially able additionally to perform the function of the failed driven roller. And also, the voltage source is provided at least in duplicate so that, in the event of an electrical fault in the one drive train that leads to the failure of one set of driven rollers the other drive train remains operational and the driven rollers situated in this drive train may maintain at least one emergency conveying function. Admittedly, in such an emergency operating situation, because the number of rollers is reduced it is not possible to achieve the same accelerations and speeds as during trouble-free operation. The performance of the remaining, operational driven rollers is however sufficient to allow at least problem-free clearing of the roller conveyor or to keep the roller conveyor in operation for a specific time, albeit at a reduced conveying capacity. 
   Generally, it is sufficient to provide two voltage sources. It is only in extremely rare situations that both voltage sources develop faults simultaneously. 
   Given the use of two voltage sources, the arrangement may be such that one voltage source supplies all the driven rollers of the one track and the other voltage source supplies all the driven rollers of the other track. In terms of cabling, this arrangement is particularly simple to realize. It does however have the drawback that the transport racks (skids) moving along the roller conveyor are driven at one side only. 
   It is therefore in principle also possible for rollers, which are supplied from different voltage sources, to be disposed on the same track. In the event of failure of one set of driven rollers, there are nevertheless still driven rollers on both tracks, albeit at a greater distance apart from one one another. This variant of the roller conveyor according to the invention does however entail a slightly greater outlay for cable installation. 
   The drive motors are advantageously low-voltage motors in particular d.c. low-voltage motors, because then the safety requirements are lower and the semiconductor components less expensive. 
   For spatial and assembly reasons, it is preferable that the drive, motors are hub motors, which with the driven rollers form a sub-assembly. 
   These and other objects and advantages will be made apparent from the following brief description of the drawings and the detailed description of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a roller rail forming part of a roller conveyor of the present invention; 
       FIG. 2  is a plan view—with partial electric cabling—showing a first embodiment of the roller conveyor of the present invention; and, 
       FIG. 3  is a plan view—with partial electric cabling—showing a second embodiment of a roller conveyor of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. 
   Reference is made first to  FIG. 1 , which shows a perspective view of a roller rail that is denoted as a whole by the reference character  10 . The roller rail  10  comprises a longitudinal beam  12 , which takes the form of a hollow section with a rectangular cross section. In the longitudinal beam  12  two driven rollers  14  and two non-driven rollers  16  are arranged alternately in longitudinal direction. The driven rollers  14  are unprofiled and carry a high-friction coating. The non-driven rollers  16  have a profile with wheel flanges on both sides. The wheel flanges effect lateral guidance of the runners of the skids to be transported. 
   Associated with each of the driven rollers  14  is a separate electric hub drive motor, which with the rollers  14 , forms in each case a compact drive module and is not itself visible in the drawing. 
   As may be seen from  FIG. 2 , a roller conveyor  1  is composed of a plurality of roller rails  10  of the type illustrated in  FIG. 1  by arranging these roller rails  10  into two parallel rows or “tracks”. The distance between the two tracks of roller rails  10  corresponds to the distance between the runners of the skids that are to be conveyed along the roller conveyor  1 . 
   The driven rollers  14  of the various roller rails  10  are supplied with electrical energy in the following manner: 
   A line carrying the system voltage available at the site of installation of the roller conveyor is provided in  FIG. 2  with the reference character  18 . Two direct voltage supply devices  20   a ,  20   b  are connected to the supply line  18  and generate at in each case two outputs a low direct voltage of for example 24 V. One of these direct voltage supply devices  20   a  supplies all of the driven rollers  14   a  in one of the two tracks of the roller conveyor  1 , while the other of the two direct voltage supply devices  20   b  supplies the driven rollers  14   b  of the second track. 
   The one output of the direct voltage supply device  20   a  is connected by a line  22   aa  to all of the driven rollers  14   a  that are situated, viewed from the direction of the direct voltage supply devices  20   a ,  20   b , on one side thereof, while the second output of the direct voltage supply device  20   a  is connected by a line  22   ab  to all of the driven rollers  14   a  that are situated at the opposite side of the direct voltage supply devices  20   a ,  20   b.    
   In a corresponding manner, one of the two outputs of the direct voltage supply device  20   b  is connected by a line  22   ba  to all of the driven rollers  14   b  of the second track of the roller conveyor  1  that are situated, viewed from the direction of the direct voltage supply devices  20   a ,  20   b , on one side thereof, while the second output of the direct voltage supply device  20   b  via a line  22   bb  supplies all of the driven rollers  14   b  of the, in  FIG. 2 , right track that are situated on the opposite side of the direct voltage supply devices  20   a ,  20   b.    
   The use of hub drive motors operated with a low voltage offers a whole range of advantages: 
   The foremost of these is the fact that the safety requirements are then considerably lower than would be the case with drive technology operating with full system voltage. This leads to savings in terms of installation technology. Furthermore, the semiconductor components that are used in the direct voltage supply devices  20   a ,  20   b  and in the control components of the driven rollers  14  are considerably less expensive. The printed conductors on the printed-circuit boards, for the prevention of voltage flashovers, do not have to maintain such large safety distances from one another, with the result that the printed-circuit boards themselves are reduced in size and may be integrated without difficulty e.g. into a compact drive module with driven roller  14  and corresponding control components. The driven rollers  14  may be used in a braking operation as generators, with the result that electrical energy may be saved. Finally, lower losses occur in low voltage circuit components, with the result that once more an energy-saving effect arises and only small cooling surfaces are required. 
   As the direct voltage supply devices  20   a ,  20   b  are provided in duplicate, the roller conveyor  1  has an “emergency operation property” for the eventuality of a fault occurring in one of the two drive trains that are supplied by the direct voltage supply devices  20   a ,  20   b . The respective intact “drive train” may then perform the entire drive function for a specific time, albeit at the cost of specific cutbacks in acceleration and speed. 
   The embodiment of a roller conveyor  101  illustrated in  FIG. 3  is very similar to the embodiment described above with reference to  FIG. 2 . Corresponding parts are therefore denoted by the same reference characters plus  100 . The roller conveyor  101  of  FIG. 3  is also composed of a plurality of roller rails  110 , of the type illustrated in  FIG. 1 . To this extent, the mechanical construction of the embodiment of  FIG. 3  is no different from that of  FIG. 2 . However, the various driven rollers  114   a ,  114   b  in the two tracks of the roller conveyor  101  are supplied in a different manner. 
   As may be seen from  FIG. 3 , along both tracks of the roller conveyor  101  of  FIG. 3  there extend two lines  122   aa ,  122   ba  and  122   ab ,  122   bb  respectively, which carry a low direct voltage. The supply lines  122   aa  and  122   ab  are both connected to one of the two direct voltage supply devices  120   a , while the two supply lines  122   ba  and  122   bb  are connected to the second direct voltage supply device  120   b.    
   As  FIG. 3  reveals, all of the driven rollers  114   a  of the left track of the roller conveyor  101  are connected alternately, on the one hand, to the supply line  122   aa  and, on the other hand, to the supply line  122   ba . The result of this is that in each of the roller rails  110  there is in each case one driven roller  114  that is supplied from the one direct voltage supply device  120   a  and one driven roller  114  that is supplied from the other direct voltage supply device  120   b.    
   The conditions in the, in  FIG. 3 , right track of the roller conveyor  101  are similar. Here too, the driven rollers  114  are connected alternately to the line  122   ab  and the line  122   bb , ultimately therefore alternately to the direct voltage supply device  120   a  and the direct voltage supply device  120   b.    
   In the embodiment of the roller conveyor  101  in  FIG. 3 , in the event of failure of one of the electric “drive trains”, for example one of the two direct voltage supply devices  120   a ,  120   b , then as in the embodiment of  FIG. 2  an emergency operation of the roller conveyor  101  is possible. However, whereas in the embodiment of  FIG. 2  there are driving forces exclusively in one track of the roller conveyor  1 , in the embodiment of  FIG. 3  even in the event of failure of one “drive train” there are still driven rollers  114  in both tracks. This promotes the directional stability of the skids during emergency operation. 
   Control of the various driven rollers  14 ,  114  is effected via an industry-standard bus system. 
   It should be emphasized that the above-described embodiments of the present invention, particularly, any “preferred” embodiments, are possible examples of implementations merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without substantially departing from the spirit and principles of the invention. All such modifications are intended to be included herein within the scope of this disclosure and the present invention, and protected by the following claims.