Abstract:
A device for forming stacks of bags, preferably bags of paper, which are individually supplied, includes at least a first transport device with which individual bags are taken up, a collection point to which the bags are fed by the transport device and in which a stack of bags can be produced, and a release device with which the bags are released from the transport device and dropped at the collection point. The device has at least one separation device, which can be inserted into or above the stack at the collection point, to divide the stack into a first and a second stack.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a national stage of PCT/EP10/066648 filed Nov. 2, 2010 and published in German, which claims the priority of German number 10 2009 046 590.1 filed Nov. 10, 2009, hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to a device for forming stacks of bags which are individually supplied. The device has at least a first transport device with which individual bags are taken up, a collection point to which the bags are fed by the transport device and in which a stack of bags can be produced a release device with which the bags are released from the transport device and dropped at the collection point, and at least one separation device which can be inserted into or above the stack at the collection point to divide the stack into a first stack and a second stack. The invention also relates to a method of forming stacks with the inventive device. 
     2. Description of the Prior Art 
     Bags are produced individually in an apparatus for producing bags. Plastic bags are usually provided with welds and usually separated at the same time. For the production of paper bags, first tubes are formed from sheets of paper and then pieces of the tube separated. A bottom is formed at the leading end of each piece of paper tube. 
     The bags so formed are stacked in an apparatus for forming stacks, so that the bags are removed in batches and packaged and/or processed further. 
     Such an apparatus for producing stacks is disclosed in published patent application DE 30 40 021 A1. A transport device is shown which fixes an individual bag from above to the lower run of a suction tape by means of a negative pressure and draws the bag towards a collection point. The bag is detached from the suction belt by means of a separation device while a pressing device presses the bag down at the collection point. The bag is detached from the suction openings of the suction tape. Once, a stack with a desired number of bags has been formed in this way, a conveyor belt on which the stack has been formed moves them on. Then, a new stack is formed at a free collection point of the conveyor belt. 
     The disadvantage of this arrangement is that the feed rate and thus the speed of the bag-making machine is very limited. If the feed rate is increased, the previous stack may not beat a sufficient distanced at the beginning of the forming of the new stack. This disadvantage is acceptable In the manufacture of foil bags because the production speed is limited by other factors. 
     However, in the manufacture of paper bags where speeds of over 1,000 bags per minute may occur, this limitation due to the said stacking limitation is undesirable. 
     DE 20 2007 002 477 U1, therefore, provides two collection facilities, but this arrangement leads to a large space demands and is also likely to be expensive. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is, therefore, to propose a device and a method for forming stacks of bags where the stack forming speed is sufficiently high and the space requirements are minimal. 
     The object is achieved by an inventive device having the characterizing features described herein, including a separation device and a slider. 
     Accordingly, a separation device is provided that can be inserted into or above the stack at the collection point to divide the stack into a first and a second stack. 
     A separation device can be inserted at high speed into the stack or above the already formed stack. Preferably this separation device is inserted above the stack when the stack has reached the desired number of bags. The following bags are then placed above the separation device. Some of the bags lie on the separation device. The first stack formed in this manner, which is located below the separation device, can now be removed without significantly affecting the second stack being started above the separation device. As the insertion of the separation device can be effected within a few milliseconds, this process is usually completed before the first bag of the second stack reaches the collection point. The separation device does not need to cover the entire surface of a bag completely. It is sufficient when only one edge, preferably the leading edge in the direction of the transport of the bag, is covered. 
     It is particularly advantageous if the separation device comprises at least one holding device with which at least the lower bag of the second stack can be held. This holding device enables the newly-begun second stack to be fixed in position. In this way, the effect of the removal of the first stack is minimized. 
     In an advantageous embodiment of the invention, the separation device has at least one wedge-shaped finger. Such a wedge-shaped element can be inserted easily between two bags without any resultant problems. This form is advantageous when the first bag of the second stack has already dropped while the element is still moving. 
     In a preferred embodiment of the invention, the separation device has at least one hole subject to a negative pressure. This suction hole thus serves as a holding facility. This embodiment is useful because devices for bag making have a number of suction openings and there are, therefore, already means available for providing negative pressure, for example in the form of a vacuum pump. 
     Further embodiments of the invention are apparent from the description and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The individual figures show: 
         FIG. 1  Side view of a device according to the invention 
         FIG. 2  Device according to  FIG. 1  during formation of a first stack 
         FIG. 3  Device according to  FIG. 1  after insertion of a separation device 
         FIG. 4  Device according to  FIG. 1  during formation of a second stack 
         FIG. 5  Device according to  FIG. 1  during removal of the first stack 
         FIG. 6  Device according to  FIG. 1  after the removal of the first stack 
         FIG. 7  Device according to  FIG. 1  during the withdrawal of the slide. 
         FIG. 8  Device with an alternate displacement direction of the separation device 
         FIG. 9  illustrates an embodiment of the device in which the separation device includes a gripper. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       FIG. 1  shows a device  1  according to the invention for forming stacks  3  of bags  2 . These bags  2  are made in an apparatus for producing bags and the storage cylinder  4  is shown. The detachment finger  5  detaches individual bags from the storage cylinder and defects them onto the transport belt(s)  7  of the transport device  6 . Each bag is transported with its folded end  13  leading. The folded end  13  thus forms the bottom and faces outwards, so that the bag with its rear side rests completely against the conveyor belt. 
     The transport device  6  comprises a number of adjacent conveyor belts  7  that rotate at the same speed. They run over the pulleys  8 ,  9 , and  10 , although more or fewer pulleys may be provided. The bag  2  can be fixed in various ways during the transport on the conveyor belt  7 . One possible embodiment, using suction means of negative pressure, is already described in DE 30 40 021 A1. In this case, the conveyor belts have suction openings, whose respective distance is greater than the greatest length of the bags that can be produced by the bag machine. The transport belt  7  is guided over suction boxes  11 ,  12 , each of which is connected to a vacuum source, although this is not shown in detail. The pulley  10  is also designed so that the suction openings of the conveyor belt  7  can be subjected to a negative pressure. 
     In order to be able to guide bags of variable length completely around the pulley  10 , the suction box  12  has an extension  14  that is displaceable in the direction of the double arrow  15 . The broken line shows the prolonging recess  16  of the groove of the suction box  12  (not shown). Therefore, as long as the suction opening of the conveyor belt  18  lies above this recess  16 , the bag can be held. The release of the bag  2  is only possible at the end of the recess while the stop  17 , which limits the transport path of the bag  2 , is movable in the direction of the double arrow  18  by means of the extension  14 . The stop  17  may be shaped like a rake or a fork that is able to pass between the individual conveyor belts  7 . The extension  14  and the stop  17  are displaceable by means of a suitable adjusting device (not shown). This adjusting device may be in the form of a spindle/spindle nut combination that can be operated manually and/or by a motor, for example, an electric motor. Other adjustment arrangements are conceivable. The adjusting device can be mounted on a wall or column (not shown) of the machine frame. 
     In order not to damage the bag on release after removal of the negative pressure, the extension  14  comprises a further opening  19  which is pressurized with a positive pressure. Therefore, when the suction openings of the transport belt  7  pass this opening, the bags  2  are released properly. 
     The bags  2  thus conveyed and released at the stop  17  are deposited at the collection point  20  in a stack  3 . The collection point  20  comprises a collection table  21  having a number of parallel ridges that are not shown in the illustration. These ridges pass through the stop  17 . The collection table  21  is movable along the double arrow  22  and can, following each release of a bag, be moved downward by a small distance that is correlated with the thickness of the bag  2 . In this way, a stack  3  of bags  2  is produced until it contains the desired number of bags. Such a situation is shown in  FIG. 2 . 
     In order to be able to start a new stack, the separation fingers  23  of the separation device can now be inserted above this stack in the area of the collection point  20 .  FIG. 3  shows the device after insertion of the separation fingers  23 . For this purpose, the separation fingers  23  can be displaced by means of a holding device  24 , for example a retaining plate. The displacement directions are indicated by the double arrow  25 . A piston-cylinder unit may be provided as a displacement drive  26 . However, any other kind of very fast acting actuator may be used. Linear motors would be also be of advantage here because of their speed and very high positioning accuracy. The displacement actuator  26  is supported on the holding device  24 . The insertion of the separation finger  23  is effected so rapidly that the first succeeding bag  2 ′ can be released onto the separation fingers  23 . In this way, the separation fingers separate the first completed stack from the newly-begun stack  3 ′. 
     With the growth of the stack  3 ′, the separation fingers  23  must also be simultaneously moved downward to the collection table  21 . For this purpose, the holding plate  24  is displaceable in the vertical direction of movement as shown by the double arrow  27 . Here, too, various suitable displacement means are conceivable. The holding plate can be operatively connected with the collection table  21  to enable common displacement. In this case, the holding plate and/or the separation fingers  23  with the sliding drive  26  must be displaceable with respect to the collection table in order to adjust to the desired stack height. However, this adjustment must only be carried out before production. In contrast, the displacement of the collection table and the holding plate takes place during bag production. Therefore, a motor-driven, precisely positioned displacement device is provided to this end. The holding plate  24  must be displaceable along the double arrow  28  synchronously with the stop  17  and/or the extension  14  in order to adapt to the bag length. 
     The first stack  3 , which is now below stack  3 ′ that is being formed, can now be removed. 
     For this purpose, a slider  29  is provided, comprising a number of bars (only the front is visible). Positioning elements  31  are provided at right angles to the slider that take the form of a fork between the ridges of the collection table  21 . The positioning elements  31  are still superposed by a wedge  30  or several wedges that can be inserted through the free space created by the separation fingers  23  between the stack  3  and the stack  3 ′. The slider  29  is supported on a support means  32  that is, in turn, connected to a carriage  33 . This carriage  33  is shown along a rail assembly  34 ; in this case, the example here is of a single rail, sliding in the direction of the double arrow  35 . The rail assembly is also displaceable in the direction of the double arrow  36  so that the vertical position of the slider  29  is adaptable to the position of the said free space. Following the adjustment to this position, which is shown in  FIG. 4 , the slider can be moved along the displacement direction  35 . This is shown in  FIG. 5 . During the displacement process, the new stack  3 ′ is formed on the facing surface of the stack  3 ′. The slider can thus take over the function of the collection table  21  during this period. 
     It is essential that at least the lower bag of the stack  3 ′ can be held stable in its position with respect to the collection table  20  by means of a holding device so that the newly-begun stack  3 ′ is not displaced. Any displacement of the bags can result in a poor stack quality, which should be avoided. For this reason, in the illustrated embodiment, the separation finger  23  has openings  37  on the upper side which are subject to a negative pressure. This negative pressure can already be present when the first bag  2  of the new stack  3  rests on the separation finger  23 . This can lead to an improvement in the quality of the stack  3 ′ during its formation. The opening  37  as well as the channels  38  and the suction line  39  are shown in  FIG. 1 . Instead, the holding means may, for example, be mechanical. One or more grips  41  (see  FIG. 9 ) could seize at least the lower bag. Holding devices based on other physical operating principles are also conceivable. 
     Thus, an electrostatic attractive force can be used for such purposes. This is particularly applicable when the bag has, for example, a window made of a plastic material. 
     The stack  3  is moved by the slider against the transport direction x of the bag  2  shortly before its release. This direction points away from the separation fingers  23  so that the lower bag  2 ′ of the new stack  3 ′ is displaced and any damage avoided. The stack  3  is moved to a storage device  40  from which it can be further transported or removed. After the stack  3  has completely left the collection table  21 , the latter is raised again and positioned under the lower bag of the new stack  3 ′. This situation is shown in  FIG. 6 . The stack  3 ′ now lies on the collection table  21 , so that the separation fingers  23  can be brought back into the starting position, which is shown in  FIG. 7 . In addition, the slider  29  can be withdrawn to its starting position, so that now the situation is again produced according to  FIG. 1 . 
     The individually necessary components for the described method and described device can be arranged in various ways and can be optionally bonded to one another without departing from the inventive concept. In addition, the displacement devices mentioned as well as all of the necessary drives can be implemented in a variety of ways. Of particular note, however, is the use of linear motors, which allow quick displacements and very accurate positioning. Linear motors can be used for all the above-described displacement devices. 
       FIG. 8  shows a device in which the separation finger  23  is not horizontally but vertically displaceable. This is advantageous because during insertion of the separation finger, there is no risk of displacing the bag. In addition, the separation finger  23  can be moved on the release of the upper bag  2  of the stack  3  so that is not necessary to wait until the released bag lies completely on the stack. So this offers a time saving. In the upper position, the separation finger lies between or above the suction channels  12  and/or the extension  14  so that the formation of the stack  3  is not disturbed. 
     With the illustrated and described apparatus, therefore, stacks of bags with a desired number of bags can be produced and transported away, without the collection process in the apparatus being interrupted or having to be continued at a reduced speed. 
     The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims. 
     REFERENCE NUMERAL LIST 
     
         
           1  Device for forming stacks of bags 
           2  Bags 
           3  Stacks 
           4  Storage cylinder 
           5  Separation finger 
           6  Conveyor device 
           7  Conveyor belts 
           8  Pulley 
           9  Pulley 
           10  Pulley 
           11  Suction box 
           12  Suction box 
           13  Folded end of the bag  3   
           14  Extension of the suction box  12   
           15  Displacement device of the extension  14   
           16  Prolonged recess 
           17  Stop 
           18  Direction of movement of the stop  17   
           19  Opening 
           20  Collection table 
           21  Collection table 
           22  Movement direction of the collection table  21   
           23  Separation finger 
           24  Holding device 
           25  Double arrow 
           26  Displacement drive 
           27  Movement direction of the holding plate  24   
           28  Double arrow 
           29  Slider 
           30  Wedge 
           31  Positioning element 
           32  Support facility 
           33  Carriage 
           34  Rail arrangement 
           35  Displacement direction of the slider 
           36  Double arrow 
           37  Openings 
           38  Channel 
           39  Suction line 
           40  Storage facility 
         x Transport direction of the bag just before its release