Abstract:
A transport conveyor for workpieces, pallets, or workpiece carriers which includes a drive transmission that includes a traction coupling that interrupts the transfer of torque and driving force to the conveyor rollers, belt or the like upon an interruption in the movement of the workpieces, pallets or workpiece carriers on the conveyor. The transmission traction device includes contact-free couplings which can be integrated in the rollers or be mounted outside the drive path of the rollers. Because the couplings operate without physical contact, they are free from wear commonly incurred in the drive transmission as an incident to the interruption of workpiece movement.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to workpiece conveyor or transfer systems, and more particularly, to systems of such type in which the movement of items being conveyed or transferred can be momentarily interrupted or stopped.  
         BACKGROUND OF THE INVENTION  
         [0002]    In order to move workpieces from one processing station to another roller conveyors commonly are used. Roller conveyors, such as shown in GB 788 892, consist of a frame upon which axially parallel rollers are rotatably mounted in side-by-side relation to each other. The workpieces run over the rollers, either directly on the rollers or by being attached to workpiece carriers.  
           [0003]    At the output or downstream end of the roller conveyor, the workpieces should be in a waiting line with as few intervening gaps as possible. For the most part, the workpieces are not taken off at the same rate as they are supplied at the input end of the roller conveyor. Therefore, the workpieces must be moved from the input of the end roller conveyor to the end of the waiting line without being pulled off the conveyor. This inevitably leads to the situation where either the rollers slip under the workpiece carriers or workpieces, as is typical for roller conveyors, or where the rollers, which are in frictional contact with a workpiece or a workpiece carrier, become locked.  
           [0004]    Due to cost reasons, it is not possible for each roller or each workpiece carrier to have its own drive. Rather, all of the rollers are simultaneously set in rotation by means of a transmission element in the form of a chain toothed belt, or a shaft.  
           [0005]    Since slippage of the rollers under the workpieces or workpiece carriers is undesirable, stoppage of the roller is effected with the aid of frictional couplings. The frictional coupling for each roller acts like a gear between the given roller and the transmission element, which couples the roller to the drive motor. Disadvantages of frictional couplings include wear and tear of the components and the necessity of having to set the traction moment or the slippage moment by means of springs.  
           [0006]    The problems with circular conveyors that transport pallets with the aid of endless-belt conveyor are similar. The pallets are led onto the conveyor offset from each other and are hauled by a transmission means in the form of a chain, a toothed belt, or the like. If the pallet stays in place, the pallet must not block the transmission means since other non-blocked pallets must continue to be moved. A given pallet is coupled by means of a gear to the transmission means, which begins to rotate as soon as the course of movement of the pallet is blocked. Frictional couplings also have been used for such circular conveyors.  
           [0007]    The wear and tear on the frictional couplings is relatively high because the ratio between standby time of a roller or a workpiece carrier and the running time is relatively large. This means that the frictional couplings are in a slipping condition of operation most of the time.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a workpiece conveyor or transfer system which has longer service life and less maintenance than conventional systems.  
           [0009]    Another object is to provide a conveyor or transfer system as described above in which movement of workpieces or other items being transferred or conveyed can be interrupted, without causing excessive wear to the components of the drive system for the conveyor or transfer system.  
           [0010]    Still another object is to provide a workpiece conveyor transfer system in which input and output elements of the traction drive cooperate in a non-physical contact manner.  
           [0011]    The invention may be carried out in various forms including workpiece transfer systems, pallet circular conveyors, or roller conveyors. In each device, instead of the frictional couplings between the input element and the output element of the traction device, couplings are provided that are not subject to wear and tear, since they work in a contact-free manner. Such couplings can be configured in the form of hysteresis couplings or viscous couplings.  
           [0012]    For viscous couplings, a highly viscous medium is used so that considerable shear forces can be transferred. By appropriate selection of the viscous medium, a good temperature profile is achieved, which enables the generation of the necessary traction moment in the required temperature range.  
           [0013]    For the viscous coupling, a traction element, which is essentially disk shaped, runs in a closed, pot-shaped space, wherein the gap between the interior of the pot-shaped element and the essentially disk-shaped element is filled with a highly viscous medium. The two parts that move relative to each other are not in direct contact with each other. The advantage of this arrangement is that it is very small. Thus, it is particularly suited for arrangements in which little space is available.  
           [0014]    The other type of coupling that is free from wear and tear is the hysteresis coupling. For this type of coupling, opposite a part exhibiting hysteresis and/or remanence is a part that is permanently magnetized or magnetized by means of current. If the magnetized part is rotated relative to the part exhibiting hysteresis and/or remanence, the part exhibiting hysteresis and/or remanence is correspondingly remagnetized or driven. Because the part exhibiting hysteresis and/or remanence preferably is highly hysteretic, the remagnetizing process requires work. Hence, the two parts can only be rotated relative to each other with an expenditure of force. The advantage of the hysteresis coupling is that its traction moment is constant over an extremely wide temperature range.  
           [0015]    For both types of couplings, no adjustments are required. In the case of the hysteresis coupling, the traction moment is derived from the material properties of the part exhibiting hysteresis and/or remanence and the permanent magnet, as well as the air gap between the parts, which can be precisely set during manufacture. The same applies for the gap for the viscous coupling. Here, the gap can be precisely preset during manufacture so that later adjustment attempts are unnecessary.  
           [0016]    For the hysteresis coupling, it also is advantageous if the coupling is completely encapsulated. Otherwise, the penetration of magnetic particles could change the behavior of the coupling. Therefore, encapsulation, particularly with magnetically shielded material, also is an advantage so that no ferromagnetic particles collect over time on the outside of the housing of the hysteresis coupling. This is particularly important when the arrangement is operated in an environment with iron particles.  
           [0017]    It will be understood that such contact-free couplings can be mounted between the transmission device and the pallet, or the roller, or within the roller.  
           [0018]    Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a fragmentary perspective of a circular pallet conveyor in accordance with the invention;  
         [0020]    [0020]FIG. 2 is a longitudinal section of one of the hysteresis coupling used in the conveyor shown in FIG. 1;  
         [0021]    [0021]FIG. 3 is a longitudinal section of an alternative embodiment of hysteresis coupling for the circular pallet conveyor shown in FIG. 1;  
         [0022]    [0022]FIG. 4 is a top view of a skid roller conveyor having drive couplings in accordance with the invention;  
         [0023]    [0023]FIG. 5 is a longitudinal section of one of the skid coupling rollers of the skid roller conveyor shown in FIG. 4;  
         [0024]    [0024]FIG. 6 is a schematic of a roller conveyor with hysteresis couplings for the gear drive of the roller shafts in accordance with the invention; and  
         [0025]    [0025]FIG. 7 is a longitudinal section of a viscous conveyor drive coupling in accordance with the invention. 
     
    
       [0026]    While the invention is susceptible of various modifications and alternative constructions, certain illustrated embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0027]    Referring now more particularly to FIG. 1 of the drawings, there is shown a circular pallet conveyor  1  in accordance with the invention. The conveyor includes a frame  2  having guide rails  3 , only one of which is shown in the schematic depiction. It will be understood that a second similar guide rail runs parallel to the visible guide rail  3 . Between the two guide rails  3 , pallets  4  are movable in a longitudinal direction. The guide rails  3  are mere images of each other, and hence, only one need be described in detail.  
         [0028]    As can be seen in FIG. 1, the guide rail  3  is formed with a first track groove  5  for the pallet  4 , a guide groove  6 , and also if necessary, additional attachment grooves  7 . The track groove  5  essentially has a rectangular cross section and opens at a slot  8  in the direction towards the opposite guide rail  3 . The track groove  5  is located in the top part of the guide rail  3 . Conveyor belts  9 ,  11  can be disposed within the track groove  5  in order to prevent running noises with the pallet  4 .  
         [0029]    The lower guide groove  6  is formed such that a triple roller link chain  12 , which contains three series of rollers one next to another, can slide through the groove. Two of the series of rollers lie in the guide groove  6 , while a third series of rollers  13  extends beyond the flat side of the guide rail  3  facing the opposite guide rail  3 . In the region of the guide groove  6 , the guide rail  3  has a greater thickness than in the region of the track groove  5 .  
         [0030]    In addition, in a groove  14  formed in the guide groove  6  there is a chain hold-down device  15 , which ensures that the roller link chain  12  can move through the guide rail  3  in the position shown and ensures that the chain slides on a lower groove edge thereof. The chain  12  cannot slide out of the guide groove  6 . The pallet  4  includes a table or plate-shaped support  16 , on which a workpiece is to be placed. On the two outer sides of the support adjacent to corresponding guide rails  3 , guide rollers  17  are rotatably mounted, which are guided in corresponding track grooves  5 . Due to the perspective, only one of four track rollers  17  can be seen. The track rollers  17  are mounted axially parallel to each other, with two track rollers  17  on each outer side so that the pallet  4  cannot swing about its transverse axis in the track groove  5 .  
         [0031]    For the kinematic connection of the roller link chain  12  to the pallet  16 , a traction device  18  is provided which has an end plate  19  under the pallet  4 . The traction device  18 , which is illustrated separated from the pallet  16 , includes an input means in the form of a chain pinion gear  21 , as well as an output means in the form of a flange plate  19 . The flange plate  19  is connected to the workpiece transport support  16  as a part of the pallet  4 . The pinion gear  21  interlocks with the roller link chain  12  and can rotate relative to the flange plate  19  about an axis that is parallel to the running axes of the track rollers  17 .  
         [0032]    In accordance with the invention, the coupling between the input element  21  and the flange plate  19  is effected through a contact-free coupling  22  that prevents wear to the coupling as a result of the interruption of the flow or transfer of items along the conveyor. To this end, in the embodiment illustrated in FIG. 2, the contact-free coupling is a hysteresis coupling  22 . The hysteresis coupling  22  in this case has a pot-shaped housing part  23 , which is closed by a disk-shaped cover  24 . By means of the cover  24 , the hysteresis coupling  22  may be threaded onto the flange plate  19 , or otherwise connected thereto. The disk-shaped cover  24  is formed with a concentric hole  25 , in which a roller bearing  26  is mounted from the rear side. A shaft  27  is supported with the aid of the roller bearing  26  so that it can rotate. The pinion gear  21  is connected to the shaft so that they rotate together.  
         [0033]    A first coupling part  29  is connected to the shaft  27  so that they rotate together within an interior space  28  enclosed by the pot-shaped housing part  23  and the disk-shaped cover  24 . The first coupling part  29  has the form of a thick disk. On the outer perimeter of this part there is a permanently magnetized ring  31  having an outer circumferential surface concentric to the axis of the shaft  27 . A second coupling part  32  is formed by a ferromagnetic bowl-shaped part, which is connected to the disk-shaped cover  24  so that they rotate together. The coupling part  32  exhibits hysteresis and/or remanence. The outer circumferential surface of the permanent magnet ring  31  is located opposite the inner side of the second bowl-shaped coupling part  32  with a small air gap  33  therebetween.  
         [0034]    The permanently magnetized ring  31  is alternately magnetized so that north and south poles alternate in the circumferential direction on the outer circumferential surface. The magnetic loop is thus closed from one north pole to an adjacent south pole on the outer side of the magnet ring  31  across the air gap  33  and the opposite second coupling part  32 , which acts as a radial magnetic yoke.  
         [0035]    The material for the second coupling part  32  is selected such that it is highly hysteretic. Highly hysteretic means that the position of the magnetic field in the environment must be changed by a considerable degree before the magnetization in the ferromagnetic part follows this change. The magnetization in the second magnetic part is required to maintain its spatial position in the second magnetic coupling part  32 .  
         [0036]    Because the remagnetization in the second coupling part  32  requires work, a torque is produced at the shaft  27 , which is directed against a torque required to turn the shaft  27  in either of the two directions of rotation. The magnitude of the torque is affected by the size of the air gap  33 , the remanence properties of the second coupling part  32 , and the field strengths generated by the magnets in the magnets  31 .  
         [0037]    The arrangement described thus far operates as follows:  
         [0038]    Through an appropriate gear motor  34  of the pallet circular conveyor  1 , the roller link chain  12 , which runs as an endless chain is set in motion. The roller link chain  12  thus runs at a constant track speed through the lower guide groove  6 . The pinion gear  21  engaged with the roller link chain  12  can only rotate relative to the pallet  4  if the holding moment of the hysteresis coupling  22  is overcome. As long as that is not the case, the pinion gear  21  does not turn, and the pallet  4  is hauled along the guide rails  3  through the frame  1 .  
         [0039]    As soon as the illustrated pallet  4  contacts a stop or an already stopped pallet  4  and its further passage is blocked, the pinion gear  21  begins to turn. The connection between the roller link chain  12  and the pallet  4  is simultaneously decoupled, wherein a residual force remains, which pushes the pallet  4  in the transport direction. The force with which the pallet  4  is pressed against the stationary leading pallet  4  or a stop is proportional to the traction moment of the hysteresis coupling  22  and inversely proportional to the radius of the pinion gear  21 .  
         [0040]    An alternative embodiment of the hysteresis coupling  22  in accordance with the invention is shown in FIG. 3 in which the magnets are attached as individual discrete magnet plates  35  next to each other on the inner side of the disk-shaped cover  24 . The magnets  35  are individual magnetic disks, which are discrete circular segments, that are magnetized in the axial direction. They are attached on the disk-shaped cover  24  next to each other so that north and south poles alternate in the same axial direction. The first coupling part  29  is formed as a ferromagnetic disk, which runs with a small axial gap  36  in front of the flat front side of the magnets  35 .  
         [0041]    With the arrangement shown in FIG. 2, a slightly smaller axial final depth is possible than with the embodiment from FIG. 3, which, in contrast, can be formed with smaller diameters. It will be understood that the choice between the two variants may be made by the manufacturer depending on the spatial requirements.  
         [0042]    Referring now to FIG. 4, there is shown a skid roller conveyor  38  having contact-free couplings in the traction devices in accordance with the invention. Between two parallel longitudinal beams  39  there are several axially parallel skid rollers  41 . Each skid roller  41  consists of an axle  42  on which two carrier disks  43 ,  44  are attached so that they rotate together at a distance from each other. The carrier disks  43 ,  44  are circular disks and act as rollers with running surfaces for workpiece carriers running on top of these rollers. Every two adjacent skid rollers  41  are coupled together as shown by means of an endless drive element, such as a flat or toothed belt  44 , so that the rollers rotate together.  
         [0043]    In carrying out this embodiment of the invention, an overdrive body  46  is provided in a shaft of the skid roller  41 , which is rotationally coupled by means of a hysteresis coupling  22  to the carrier disk  44 , as depicted in FIG. 5. The overdrive body  46  is tubular or sleeve-shaped and is mounted on the shaft  42  with the aid of two roller bearings  47 . The body in this case has an outer circumferential surface that is cylindrical and smooth, but alternatively, could be provided with toothing. The axial length permits the attachment of two drive belts. On its outer side adjacent the carrier disk  44 , the overdrive body  46  carries a ferromagnetic disk  48 , which is highly hysteretic.  
         [0044]    The carrier disk  44  is on its side adjacent to the overdrive body  46  and has a counter bore  49 , in which a plurality of magnetic disks  35  are attached, e.g., by adhesive, each being adjacent to each other in the circumferential direction. This produces an arrangement that corresponds to the arrangement shown in FIG. 3.  
         [0045]    The illustrated skid roller conveyor  38  operates as follows:  
         [0046]    By means of an appropriate drive device, one of the overdrive bodies  46  is set in rotation. Because this overdrive body  46  is coupled to the adjacent overdrive body by means of the endless drive element  45 , the next overdrive body  46  is also set in rotation, etc. The kinematic coupling of all of the overdrive bodies  46  is effected because each overdrive body  46  is coupled so that they rotate together by means of two endless drive elements  45  with the two adjacent overdrive bodies. The overdrive body  46  can rotate freely due to the roller bearing  47  on the shaft  42 .  
         [0047]    The hysteresis coupling  22  formed by the ferromagnetic disk  48  and the magnets  35  tends to turn with the support disk  44  as long as the support disk  44  is not held with a moment that is greater than the traction moment by the hysteresis coupling  22 . Thus the torque of the hysteresis coupling  22  is transferred to the carrier disk  44  and from there over the shaft  41 , which is coupled so that it rotates with the carrier disk  44 , to the other carrier disk  43  of the same transport  41 .  
         [0048]    Thus, the skids running over the skid roller conveyor  38  are further transported corresponding to the rpm of the skid rollers  41 . If a running skid contacts a stop or a leading skid is stopped, hysteresis coupling is overcome. The overdrive body  46 , which is mounted so that it can rotate on the shaft  41 , can continue to run. As soon as the held skid becomes free, it is set back in motion until it contacts a new stop.  
         [0049]    The coupling connection between the overdrive body  46  and the carrier disk  44  is free from contact, and thus it is also free from wear and tear. The output of energy that occurs during hauling of the hysteresis coupling can be dissipated without any additional means since it is not large enough to cause significant heating.  
         [0050]    Still a further alternative of roller conveyor  50  in accordance with the invention, is shown in FIG. 6, of which only one longitudinal beam  51  and three rollers  52  are depicted. The rollers  52  extend as cylindrical, rotationally symmetric bodies between the longitudinal beam  51  and a second parallel longitudinal beam. They are mounted in the two longitudinal beams  51  by axles or shafts  53 , which extend through the respective longitudinal beam  51 .  
         [0051]    On the outer side of the longitudinal beam  51  the shaft  53  of the roller  52   a  carries a bevel gear  54 , which intermeshes with a bevel gear  55 , which is supported by means of a roller bearing  56  on a common drive shaft  57 . The drive shaft  57  runs parallel to the longitudinal beam  51  and is set in rotation by a common drive motor. On its larger outer surface pointing in the axial direction, the bevel gear  55  carries a ferromagnetic disk  58 , which stands opposite a carrier disk  59 . The carrier disk  59  is coupled to the shaft  57  so that they rotate together. On its side opposite the bevel gear  55 , the carrier disk  59  is provided in turn with several magnets  35  positioned at distances from each other, which are separated by an air gap from a ferromagnetic ring disk  58 . Together with the ferromagnetic disk  58 , the discrete magnets  35  form a hysteresis coupling, which corresponds in design to the hysteresis coupling from FIG. 3.  
         [0052]    The roller  52   b  is likewise driven by a hysteresis coupling  22 , which, however, is built like the hysteresis coupling shown in FIG. 2, thus with a radial gap. The bevel gear  55  here carries a bowl-shaped magnetic yoke  61 , while the carrier  59  is provided with the magnetic ring  31 . The operation is the same as for the hysteresis coupling  22  for the roller  52   a.    
         [0053]    Instead of providing the hysteresis coupling  22  on the input side relative to the bevel gears  44  and  55 , alternatively the hysteresis coupling may be on the output side, as can be seen in connection with the roller  52   c . The bevel gear  54  for the roller  52   c  is supported by means of a roller bearing  62  so that it can rotate on the axle  53 . The bevel gear carries, in turn, on its rear side the ferromagnetic ring  58 . The ferromagnetic ring  58  stands opposite individual magnets  35 , which are polarized in an alternating and opposite way, and which are attached to a carrier  63 , which sits on the axle  53  so that they rotate together. In contrast, the driven bevel gear  55  is connected to the input shaft  57  so that they rotate together. In each of the foregoing embodiments, it will be understood that instead of permanent magnets, electromagnets can also be used.  
         [0054]    For the embodiments explained above, a hysteresis coupling is used as a frictionless coupling for coupling the rollers of the workpiece carrier or the pallet. Instead of the hysteresis coupling, a viscous coupling also can be used, as shown by the coupling  65  shown in FIG. 7. The viscous coupling has a closed, pot-shaped housing  66 , which consists of a bowl-shaped base part  67  and a cover part  68 . The bowl-shaped base part  67  is assembled in one piece and includes a base  69  and a cylindrical edge  72  projecting from this base. Concentric to the edge  71 , there are several annular ribs or walls  72  in the interior of the bowl-shaped base part concentric to the edge  71 .  
         [0055]    The cover  68  is likewise bowl-shaped and grips at its edge  73  the edge  71  of the base part  67 . In its middle section, the cover includes a tubular projection  74  that is concentric to the edge  71  and has a hole  75 . An annular groove which surrounds the hole  75  holds an O-ring seal  76 . The already described axle  27  is guided through the hole  75 . The axle  27  is coupled to a rotor  77  in the housing  66  so that they rotate together. The rotor  77  consists of a disk  78  with the annular ribs  79  that are coaxial to the axle  27  and coaxial to the edge  71 . Each rib  79  runs in a gap between adjacent ribs  72  or a rib  72  and the edge  71  of the base part  67  as shown.  
         [0056]    In this way, a comb structure is produced, as can be seen from the figure, with intermeshing teeth. The meandering gap remaining between the ribs  72  and  79  or the edge  71  is filled with a viscous material which can transfer a shear force so that a torque can be transferred from the axle  27  to the housing  66 , or vice versa.  
         [0057]    It will be seen that the illustrated viscous coupling  65  can be used instead of the hysteresis couplings shown in FIGS. 2 and 3. The viscous coupling  56  similarly works without contact because the rotor  67  with its ribs  79  does not contact the ribs  72  or the edge  71 .  
         [0058]    The illustration in FIG. 7 is very simplified and it will be understood that it may be desirable in certain instances to provide ball bearings or the like for support of the shaft  27 . Also, it is possible to form the ribs with a filigree pattern and to increase their number.  
         [0059]    From the foregoing, it can be seen that a transport device for workpieces, pallets, or workpiece carriers is provided which has contact-free couplings in the form of a hysteresis coupling or a viscous coupling for the transfer of the required torque or the traction force. These couplings can either be integrated in the rollers or lie outside the rollers in the drive path to the rollers. Because these types of couplings operate without contact, they are free from wear and tear and thus require no maintenance.