Abstract:
An apparatus and method for destacking a stack of flat sheet-like articles, comprising a bearing surface for supporting the stack at a fixed elevation, and a separating arrangement for repeatedly separating the uppermost article from the stack and transferring it laterally onto a removal conveyor. The separating arrangement is mounted for vertical movement so as to float downwardly as the height of the stack decreases, and the separating arrangement can be lifted upwardly at the conclusion of the destacking operation so that a further stack can be fed onto the bearing surface along a lateral feed plane which includes the bearing surface.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This is a continuation of international application PCT/CH01/00719 filed Dec. 17, 2001 and designating the U.S. The disclosure of the referenced application is expressly incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to an apparatus for, and a method of, destacking a stack of flat articles, of the general type disclosed in WO 00/46135 and corresponding U.S. Pub. No. 2001/0054788. As there disclosed, a stack of flat articles, in particular printed products, rests on a bearing surface and is destacked from above by a separating arrangement. The separating arrangement is supported on the stack from above by means of a load bearing structure, with the result that its vertical distance from the stack is always constant during destacking.  
           [0003]    The separating arrangement as disclosed in the above documents is used to separate out individual articles from the stack and to transfer them to a removal arrangement in the form of a belt conveyor. The separating arrangement comprises a sucker by means of which the article which is located at the top of the stack in each case is attached by suction at one end. A pusher then grips beneath the article and pushes it out of the stack in the direction of the removal arrangement. By virtue of articles being periodically separated out, an imbricated stream of partially overlapping articles is produced on the belt conveyor. The removal arrangement can be pivoted in the manner of a rocker, with the result that it is possible for the height of the region in which articles can be received to be adapted to the current stack height and for the articles to be pushed onto the belt conveyor essentially in their own plane. The removal arrangement is connected to the separating arrangement via the load-bearing structure, with the result that the height adaptation likewise takes place passively by sensing of the current stack height.  
           [0004]    The above referenced documents propose that, during destacking or once destacking has taken place, a further stack of flat articles is fed to the region of the bearing means from beneath, i.e. in the normal direction to the bearing surface. The further stack here is located on a further bearing means, which is oriented parallel to the first-mentioned bearing means and is moved in the normal direction thereto. In order to ensure a continuous changeover from one stack to the next and thus a gap-free imbricated stream, it is necessary for the bearing means located between the two stacks to be removed in a suitable manner. As an alternative, the above documents propose using individual products in an imbricated stream in a plane which runs parallel to the bearing surface of the stack, but is located therebeneath. It is also the case with this variant that the bearing surface between the two sub-stacks has to be removed at a given time. This can only be realized with high design related outlay.  
           [0005]    DE 1947095 B2 and U.S. Pat. No. 3,776,544 disclose an apparatus which is intended for discharging flat articles and in the case of which individual stacks are supplied on a conveying belt and removed from beneath. For this purpose, the stack, in the destacking position, is tilted by a barrier which is inclined in the vertical, and the respectively lowermost article of the stack is drawn out of the stack by a belt conveyor, while the articles located thereabove are retained by the barrier. The problem here is that the weight of the entire stack always bears on the article which is to be removed, the latter thus being subjected to mechanical stressing during removal.  
           [0006]    The object of the invention is thus to provide an apparatus for, and a method of, destacking a stack of flat articles in the case of which the destacking follows from above in a manner which does not adversely affect the articles, and the operation of feeding the stack is simplified in relation to the known apparatuses.  
         SUMMARY OF THE INVENTION  
         [0007]    The above and other objects and advantages of the invention are achieved by the provision of a destacking apparatus which has a bearing surface for supporting a vertical stack of the articles, and a separating arrangement mounted for vertical movement so that its vertical distance from the uppermost article on the stack is essentially constant during destacking. The separating arrangement is configured for repeatedly separating out at least the uppermost article from the stack and transferring it to a removal arrangement.  
           [0008]    A lifting mechanism is provided for lifting the separating arrangement to a predetermined height, once destacking has taken place. A further stack which is to be destacked can be introduced into the resulting gap between the bearing surface and the separating arrangement by being fed along a feed plane which is defined by the bearing surface. There is thus no need for any complicating lifting mechanism for the stack itself. The operation of feeding a new stack can be realized by straightforward means, for example a belt conveyor. Thus in accordance with the invention, the changeover from one stack to the next is possible in an extremely straightforward manner.  
           [0009]    The invention dispenses with the gap-free discharge of articles to a removal arrangement during the changeover between two stacks, with the result that it is possible for gaps to be produced in the product stream which is to be removed. The invention is thus used particularly advantageously in conjunction with a removal arrangement in the case of which the articles are moved by individually moveable conveying means, with the result that it is possible to change the distances between two articles during removal and to compensate again for gaps in the product stream, if required.  
           [0010]    The apparatus preferably comprises a removal arrangement which is coupled mechanically to the separating arrangement and can be height adjusted together with the latter.  
           [0011]    Various possibilities are known for the purpose of separating out the uppermost article from the stack. The separating arrangement can attach the uppermost article by suction, using negative pressure, and, finally, separate it out using a pusher, as described, for example, in WO 00/46135 and U.S. Publ. No. 2001/0054788, the disclosures of which are incorporated herein by reference. Furthermore, it is possible to use, for example, a suitably configured separating element to rotate the uppermost article out of the stack, in its own plane, with a force or friction fit, as described, for example, in CH 436349. In a further development of the principle known from CH 436349, the separating element can be used to push a corner of the uppermost article against a stop, the uppermost article sliding laterally past the latter as a result of bending, while articles located beneath it are stopped. A corresponding separating mechanism is described by the same applicant in pending U.S. application Ser. No. 10/076,200, filed Feb. 14, 2002.  
           [0012]    As a removal arrangement, it is possible to use a belt conveyor which is configured so that the height at which it is capable of receiving articles is variable. For example, use is made of the design described in WO 00/46135. In this case, the separating arrangement is coupled mechanically to the belt conveyor, which is designed as a rocker, by means of a load-bearing structure, with the result that the height of the separating arrangement and of the removal conveyor are adapted passively to the height of the stack which is to be destacked. A further possible removal arrangement is a gripper conveyor as described, for example, in WO 99/33731 or WO 99/33734. The removal arrangement preferably has a plurality of grippers which can be moved individually along a rail by conveying means. The position in which the grippers close is preferably adapted to the current height of the stack which is to be destacked. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    Exemplary embodiments of the invention are described hereinbelow and illustrated in the drawing, in which, purely schematically:  
         [0014]    FIGS.  1 A-D show a side view of an apparatus according to the invention at a number of different points in time as the method according to the invention is implemented;  
         [0015]    [0015]FIG. 2 shows a side view of an apparatus according to the invention with a pivotably mounted removal conveyor designed as a belt conveyor; and  
         [0016]    [0016]FIGS. 3A, B show a side view of an apparatus according to the invention with the removal conveyor designed as a gripper conveyor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    FIGS.  1 A-D show a destacking apparatus  1  in a number of stages as the destacking method is implemented. A first stack  2  is located in the destacking position on a bearing surface  4 . The individual sheet-like articles  16  here are oriented with their surface parallel to the bearing surface  4 . The bearing surface  4  is formed by the conveying belt of a belt conveyor  10 . Further stacks  2 ′,  2 ″ are located on a further belt conveyor  9 , which is located in a common plane, the feed plane E, with the first-mentioned belt conveyor  10 . The two belt conveyors  9 ,  10  convey in the same direction and form a feed arrangement  5 , by means of which stacks  2 ,  2 ′,  2 ″ which are to be destacked are fed to the destacking apparatus  1 . Prior to destacking, the stacks  2 ,  2 ′,  2 ″ have a maximum height H. It is also possible for the heights of the individual stacks  2 ,  2 ′,  2 ″ to be different.  
         [0018]    The stack  2  located on the bearing surface  4  is destacked by means of a separating arrangement  11 , a separating element  12  pushing the respectively uppermost article beyond the outline of the stack and thus transferring it to a removal arrangement  6 . The separating element  12  is, for example, a roller with a surface which has a good grip. This rests on the stack  2  and thus removes the uppermost article in each case from the stack  2 . The separating element  12  is connected rigidly, at least in the vertical direction, to the removal arrangement  6  via a load-bearing structure  13 . The removal arrangement  6  is thus also always retained at a height which is adapted to the current stack height.  
         [0019]    The removal arrangement  6  comprises a belt conveyor  7  which can be pivoted in the manner of a rocker about an axis  8  running transversely to the removal direction. The belt conveyor  7  is always moved, via the load-bearing structure  13  and the separating element  12 , also serving for height-sensing purposes, such that its edge  7   a , which is directed toward the stack  2  which is to be destacked, is located approximately at the height of the uppermost article. The separating mechanism  11  further comprises a transporting roller  14 , which is likewise arranged on the load-bearing structure  13  and conveys the articles further on the removal conveyor with a force or friction fit or by gripping behind the trailing edges thereof.  
         [0020]    According to the invention, the destacking apparatus  1  includes a lifting arrangement  3 , by means of which the height of the separating arrangement  11  above the bearing surface  4  can be changed actively, i.e. irrespective of the stack which is to be destacked.  
         [0021]    The situation at the beginning of the operation of destacking a stack  2  is illustrated in FIG. 1A. The end  7   a  of the removal arrangement  6 , said end being directed toward the stack  2 , is located at the height H of the stack  2  which is to be destacked. Dashed lines illustrate the position of the removal conveyor  6  when the stack has been fully destacked. FIG. 1B shows the situation with the stack fully destacked and the bearing surface  4  empty. The separating element  12 , which also serves for height-monitoring purposes, in this case rests on the bearing surface  4 . Via the load-bearing structure  13 , the removal arrangement  6  is also positioned such that its front end  7   a  is located approximately at the height of the bearing surface  4 .  
         [0022]    Once destacking has taken place, the separating arrangement  11  and removal arrangement  6  is displaced upward by means of the lifting arrangement  3 , with the result that a gap equal to the height H for receiving a further stack  2 ′ is produced between the separating element  12  and the bearing surface  4 . The feed arrangement  5  is moved in order to displace a further stack  2 ′ into the destacking position on the bearing surface  4 . The separating arrangement  11  can then be lowered again onto the stack. A new destacking cycle can begin. The lifting arrangement  3  is deactivated, with the result that the position of the separating arrangement  11  and of the removal arrangement  6  is adapted automatically to the height of the stack  2 ′ which is now to be destacked.  
         [0023]    The operations of feeding stack  2 ,  2 ′,  2 ″ and removing individual articles  16  in the form of an imbricated stream  15  take place here essentially in the same direction in the drawing plane. It is also possible, however, for the feed and removal operation to take place in different directions. It is also possible for pushing means to push the stacks  2 ,  2 ′,  2 ″ into the destacking position.  
         [0024]    [0024]FIG. 2 shows a further view of an apparatus according to the invention for destacking stacks  2 ,  2 ′. As has already been described, stacks  2 ,  2 ′ are brought into the destacking position on the bearing surface  4  by a feed arrangement  5 , comprising two belt conveyors  9 ,  10  arranged one behind the other. The separating mechanism  11  is connected rigidly to the front end  7   a  of the removal arrangement  6  via a load-bearing structure  13 , comprising individual structural elements  13   a ,  13   b ,  13   c ,  13   d . All the elements of the load-bearing structure  13  are arranged to the sides of, or above, the feed arrangement  5 , with the result that they do not obstruct the stacks fed. The separating arrangement  11  and the removal arrangement  6  are described in specific terms in WO 00/46135 and U.S. Publ. No. 2001/0054788. To supplement this, the apparatus according to FIG. 2 has a lifting arrangement  3 , by means of which the separating element  12  can be displaced to a predetermined height H irrespective of the height of the stack  2  which is to be destacked.  
         [0025]    [0025]FIGS. 3A and 3B show a further apparatus according to the invention, this time with a gripper conveyor as removal arrangement  6 . A feed arrangement  5  brings a stack  2  into the destacking position on a bearing surface  4 , which in this case is formed by an end region of the belt conveyor. By means of a separating arrangement  11 , the uppermost articles  16  in each case are pushed laterally out of the stack  2 . They are gripped by grippers  17  at their ends  16 a projecting out of the stack. The grippers are fastened on conveying means  18  which are moved along a rail  19 . The conveying means  18  can be moved individually. In the present case, in each case a certain number of conveying means  18  is guided past the stack  2  which is to be destacked. These each receive an article until the stack  2  has been destacked. In the situation according to FIG. 3B, in which there are still three articles present in the stack  2 , a further three empty grippers  17  approach the transfer region, while further grippers  17 ′ are stopped by means of a blocking element  22 .  
         [0026]    These further grippers  17 ′ are only released when the further stack  2 ′ has advanced into the destacking position and destacking of articles is continued. Since the conveying means  18  can be moved individually along the rails  19 , it is possible to compensate again for the resulting gap into the product stream. There is no need, however, for stacks to be destacked without interruption.  
         [0027]    The separating arrangement  11  is connected to a closing guide  20  via a load-bearing structure  13 . The closing guide  20  serves for closing the grippers  17 . It is arranged such that closure takes place a little way above the plane defined by the uppermost article in the stack. The height conditions described are realized by the separating element  12  or a pressure-exerting element  23 , which serves for sensing the height of the stack  2 . A lifting mechanism  3  can be used to bring the separating arrangement  11  and the closing guide  20  to a predetermined height again once destacking has taken place.  
         [0028]    The grippers  17 ,  17 ′ are transported in a closed state and are only opened in the vicinity of the transfer region, by means of an opening guide  21 . The conveying means  18  are moved along the rail  19  by means of a drive  24 .  
         [0029]    Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.