Abstract:
The invention relates to a stacking device for continuously forming stacks ( 12   a - e ) of bags ( 18   a ), which bags are continuously fed in at least one bag strand ( 16   a,d - e ), which comprises at least one bag row ( 14   a ) and which is endless or cut through after each series of a defined number of bags, the stacking device comprising: at least one stack base ( 24   a - e,    24′   a - b ), which is moved back and forth in a stacking motion ( 22   a - e,    22′   a ) parallel to a stack layer direction ( 20   a ) at least during the formation of a stack ( 12   a - e ); a bag-feeding means (26 a - d ), which lays the at least one bag strand (16 a,d - e ) on the stack base ( 24   a - e,    24′   a - b ) in such a way that the bag strand ( 16   a,d - e ) bends at least substantially because of the stacking motion ( 22   a - e,    22′   a ) after each series of a number of bags that forms a stack layer ( 28   a,c - d ) and forms zig-zag-shaped stack layers ( 28   a,c - d ) or that the bag strand ( 16   a,d - e ) is layered at least substantially because of the stacking motion ( 22   a - e   , 22′   a ) with matching bag orientation into stack layers ( 28   a,c - d ) having the number of bags that forms the stack layer ( 28   a,c - d ); and at least one stack-transporting means ( 30   a - e,    30′   a - b ) for transporting the stacks ( 12   a - e ) out of the region of influence of the stacking motion ( 22   a - e,    22′   a ) after a specified number of stack layers has been reached. According to the invention a first driving unit ( 32   a - e,    32′   a - b ) for driving at least one stacking motion ( 22   a - e ) is provided and a further driving unit ( 32′   a - e,    32   a - b ) for driving at least one transporting motion ( 34   a - e,    34′   a ) of at least one stack-transporting means ( 30   a - e,    30′   a - b ) is provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    A stacking device for continuously forming stacks of bags fed continuously in at least one string of bags that has at least one row of bags and is endless and/or severed after in each case a defined number of bags, having at least one stack base that is moved back and forth in a stacking movement parallel to a stack layer direction at least during the formation of a stack, having a bag feeding means which deposits the at least one string of bags on the stack base such that the string of bags deviates, on account of the stacking movement, in each case after a number of bags that forms a stack layer, and forms zigzag-shaped stack layers, or such that the string of bags is piled up with a consistent bag orientation, on account of the stacking movement, in stack layers with the number of bags that forms the stack layer, and having at least one stack transporting means for transporting the stacks out of the area of influence of the stacking movement once a defined number of stack layers has been reached, has already been proposed. 
       SUMMARY OF THE INVENTION 
       [0002]    The invention proceeds from a stacking device for continuously forming stacks of bags fed continuously in at least one string of bags that has at least one row of bags and is endless and/or severed after in each case a defined number of bags, having at least one stack base that is moved back and forth in a stacking movement parallel to a stack layer direction at least during the formation of a stack, having a bag feeding means which deposits the at least one string of bags on the stack base such that the string of bags deviates, at least substantially on account of the stacking movement, in each case after a number of bags that forms a stack layer, and forms zigzag-shaped stack layers, or such that the string of bags is piled up with a consistent bag orientation, at least substantially on account of the stacking movement, in stack layers with the number of bags that forms the stack layer, and having at least one stack transporting means for transporting the stacks out of the area of influence of the stacking movement once a defined number of stack layers has been reached. 
         [0003]    It is proposed that a first drive unit is provided at least to drive the stacking movement, and a further drive unit is provided to drive at least one transporting movement of at least one stack transporting means. 
         [0004]    In this connection, a “string of bags” should be understood as meaning in particular a string of contiguous bags which are preferably connected together at their ends by way of common sealed seams. Preferably, the sealed seams each have perforations centrally between two bags in order to make it easier for a user to detach the bags. The string of bags can in particular be produced and filled on a flat bag machine and/or a stick pack machine. Such strings of bags and packing machines are known to a person skilled in the art. Preferably, the bags are configured in a flat manner, i.e. their width and length are at least twice the thickness perpendicular to a feeding direction of the string of bags. Strings of bags or even one string of bags can have different types of bag. In this connection, a “row of bags” should be understood as meaning a plurality of bags in a string of bags, which are arranged in succession in the string of bags in the feeding direction of the string of bags. In this connection, a “defined number” should be understood as meaning in particular a number which is defined in a manner corresponding to a desired stack configuration. The number can in particular be part of a parameter set which describes the stack formed by the stacking device. Preferably, the parameter set can be stored on a control unit of the stacking device or of a packing machine having the stacking device. It is likewise possible for the defined number to be defined and/or varied by a user or an upstream process. It may be possible for the defined number to be redefined for each stack and/or each stack layer. In this connection, a “defined number of bags” should be understood as meaning in particular that a number of bags after which the string of bags is severed is defined in a manner corresponding to the desired stack configuration. The defined number of bags after which the at least one string of bags is severed can vary in particular in dependence on the stack layer and/or with each stack. In particular, in the case of a stack which has a plurality of strings of bags, the strings of bags can be severed after in each case different numbers of bags. It may likewise be possible for a stack layer to have a plurality of strings of bags in the stack layer direction. A stack layer can start with one string of bags and end with at least one further string of bags. Advantageously, different bag types can be deposited in one stack layer. It may likewise be possible for the defined number of stack layers in successive stacks to vary and/or for the number of stack layers in the stacks to be redefined in each case before and/or during the stack formation. In this connection, “fed continuously” should be understood as meaning in particular that a feeding movement in which the string of bags is transported is interruption-free, in particular stoppage-free. A feeding speed, in particular caused by an upstream packing process, can preferably vary continually. In this connection, a “stack layer direction” should be understood as meaning in particular a direction which is on average parallel to the row of bags or the rows of bags in the at least one string of bags in a stack layer. In this connection, a “bag feeding means” should be understood as meaning in particular a device which feeds the string of bags at the feeding speed in the direction of the stack base. The bag feeding means can have for example a belt edge, pairs of rollers and/or further means which are suitable for feeding a string of bags. The bag feeding means can have a deflection device, in particular at least one pivot plate, which is intended to deflect the string of bags in a direction transversely to the stack layer direction and transversely to the feeding direction and/or a weight force. It may be possible to form a plurality of stacks alongside one another transversely to the stack layer direction and transversely to the feeding direction and/or weight force. The deflection device can deflect the string of bags such that it is deposited in each case on the stack currently being formed. The string of bags can deviate, on account of the stacking movement, in each case after a number of bags that forms a stack layer, and form zigzag-shaped stack layers, or be piled up with a consistent bag orientation, on account of the stacking movement, in stack layers with the number of bags that forms the stack layer. Preferably, a deflection device, in particular at least one pivot plate, can be arranged such that the deviation and/or piling up of the string of bags is supported during the stack layer formation. In particular, the deflection device can be intended to deflect the string of bags in and counter to the stack layer direction. The deflection device can, together with the stacking movement of the stack base, effect the deviation and/or piling up of the stack in stack layers. Preferably, the deviation and/or piling up can take place at least substantially by way of the stacking movement. In this connection, “at least substantially” should be understood as meaning in particular that a relative movement of the string of bags with respect to the stack base results predominantly from the stacking movement. Preferably, the bag feeding means can have separating means, for example crush-cut knives, in order to separate the string of bags after the defined number of bags. Alternatively, the string of bags can be severed in an upstream process, in particular in a sealing process for forming sealed seams of the bags. The individual stack layers of a stack can have the same number of bags. However, it is also possible to form stacks with stack layers which have a different number of bags. In particular, the number of bags can decrease with each stack layer or the stack layers can alternately have a larger and a smaller number of bags. In particular, the stack layers with a different number of bags can have an offset, in particular by half a bag length. The stack layers can be piled up such that bag centers of the bags in one layer come to lie between bag centers in the region of the sealed seams of the bags in a further layer. The bags can be stacked in a particularly compact manner. It may likewise be possible for the stack layers to be piled up transversely to the stack layer direction and feeding direction and/or weight force by in particular half a bag width. In particular long, narrow bags such as “stick packs” can be stacked in a particularly compact manner with an offset transversely to the stack layer direction and feeding direction and/or weight force. In this connection, “zigzag-shaped” stack layers should be understood as meaning in particular stack layers of a stack which is folded from a contiguous zigzag-shaped string of bags. In this connection, a stack having stack layers with a “consistent bag orientation” should be understood as meaning in particular a stack having stack layers in which the string of bags is severed after each stack layer and the stack layers are piled up such that the bags are stacked up in each case with a uniform orientation. In particular, printed front sides of the bags can be oriented in the direction of a stack top side in the opposite direction to the weight force. In this connection, a “front side” of a bag should be understood as meaning in particular a side of the bag which is intended for product presentation and has in particular a product name, a product brand or similar marking and which is intended to be presented first of all to a customer upon opening a pack containing the bags. In this connection, transport “out of the area of influence of the stacking movement” should be understood as meaning in particular that the stacking movement for forming the next stack is no longer transmitted to the stack. This can take place in that the stack is no longer in contact with the stack base or in that a further stack base is used to form the next stack and the stack base carrying the stack remains free from the stacking movement of the next stack while said stack base is in contact with the stack. Through the use of a first drive unit and a second drive unit, continuous stack formation can be possible. One drive unit can drive the stacking movement while a second drive unit drives the transporting movement in order to transport a stack out of the area of influence of the stacking movement. Alternatively, one drive unit can drive the stacking movement for stacking a stack and subsequently drive the transporting movement for transporting the stack of a first stacking unit and a first transporting unit, while the further drive unit drives the stacking movement for forming the next stack and subsequently drives the transporting movement for transporting the further stack of a further stacking unit and a further transporting unit. The string of bags can be fed continuously. It is possible to avoid stopping of the string of bags and/or of an upstream process for producing the string of bags between the formation of two stacks. 
         [0005]    Also proposed is a control unit which is provided to control a stroke and/or a speed of the stacking movement in at least one operating mode in dependence on a number of bags and/or a length of a stack layer in the stack layer direction, a feeding speed of the string of bags and/or an achieved stack height of the stack. The stacking movement can advantageously be adapted to the achieved stack height. In particular, a distance between bag feeding means and the bag feeding means of a facing stack top side can decrease with increasing stack height. An advantageous stroke of the stacking movement for forming the next stack layer can be greater as the distance becomes smaller. The control unit can advantageously set the stacking movement. It is possible for the stack layers to have different bag string lengths and/or numbers of bags. The number of bags, after which the string of bags deviates to form a stack layer, can be influenced by the stroke and/or the speed of the stacking movement. The stacking device can be particularly efficient and/or flexible. Stacks having stack layers with a different number of bags can be formed. Influences of the stack height and/or the distance of the stack top side from the bag feeding means can be compensated. 
         [0006]    It is proposed that at least one of the drive units is provided to drive a stacking movement and a transporting movement. Preferably, at least the first drive unit is provided to drive a first stacking movement and a first transporting movement and the second drive unit is provided to drive a second stacking movement and a second transporting movement. Preferably, the first and the second stacking movement and the first and the second transporting movement are intended to alternately form a stack and a further stack. The transporting movement of a stack can advantageously take place independently of the stacking movement of the next stack. 
         [0007]    Advantageously, the stacking device has at least two stack bases and at least two stack transporting means, wherein stack bases and stack transporting means each form stack carriers that are drivable by a common drive unit. The stacks can each be formed on the stack carrier and be transported away by the stack carrier in a next step, while a next stack is formed on a further stack carrier. The stack carriers are driven by at least two independent drive units. The stack carriers can be driven by a revolving linear motor system. A revolving guide can have a secondary part or preferably a primary part of the linear motor system. The stack carriers can have primary parts or preferably secondary parts of the linear motor system and be independently drivable. In particular, the stack carriers can be arranged on two independently driven revolving elements, in particular belts or chains, and be driven in revolution. A revolving element can drive preferably at least one, particularly preferably at least two stack carriers. A revolving element can transport a stack to a stack transfer position by means of a stack carrier, and can transport a further stack carrier, counter to a transporting direction in which the stacks are transported away, into a region adjoining a stack forming region in which a further stack is currently being formed on a stack carrier driven by a further revolving element. Preferably, the stack carriers are formed in the transporting direction by segments connected in an articulated manner and/or elastic segments. Deflection of the stack carriers by a radius at deflection points of the revolving linear motor system and/or the revolving elements can be simplified. Meanwhile, the further revolving element can drive the stack carriers arranged on said revolving element in the stacking movement, wherein the stack is formed on the stack carrier which is located in the stack forming region. The revolving elements can alternately carry out the stacking movement and form stacks on one of their stack carriers, which is located in the stack forming region, and transport stacks to the stack transfer position. Continuous stack formation of stacks can be possible. It is likewise possible for the stack carriers to carry out further movements following the transporting movement by which the stack is transported out of the stack forming region. In particular, the stack carriers can be moved back and forth at a frequency that is increased with respect to the stacking movement, in order to equalize the stack and/or bags in the stack and/or to reduce a stack height. In this connection, “equalize” should be understood as meaning in particular that filling material packed in the bags is distributed evenly by the back-and-forth movement and/or that the stack layers are oriented such that gaps in the stack are reduced. A maximum bag thickness of the bags can be reduced and/or a stack height can decrease. Following the transporting movement, the stack carriers can also move the stack in a synchronized movement with a further process step, in particular with a printing process and/or glue application. 
         [0008]    In a further configuration of the invention, it is proposed that the stack carriers and/or stop means of the stack carriers are mounted on mounting devices so as to be able to be pushed and/or folded away out of a transporting region for the return transport of the stack carriers counter to a transporting direction in which the stacks are transported away. In this connection, a “transporting region” should be understood as meaning in particular a region which is used by further stack carriers and/or stacks during stack formation and/or during the transport of stacks into the stack transfer position. It may be possible for stack carriers to move in the opposite direction to further stack carriers during return transport and to encounter said further stack carriers without collision. It may be possible for the stack carriers to be pushed and/or folded away out of the transporting region for the return transport. It may also be possible for the stack bases of the stack carriers to be arranged in different planes and/or to be transferred into a different plane for return transport, and for stop means of the stack carriers to be folded or pushed away such that the stack carrier which is provided for return transport is located entirely outside the transporting region. The stack carriers can advantageously be moved in the transporting direction for transporting stacks and counter to the transporting direction for return transport. Revolution of the stack carriers can be dispensed with. Preferably, the stack carriers can be driven by a planar linear motor system. The stack carriers can have primary parts or preferably secondary parts of the linear motor system. A guiding unit can support the stack carriers and have a secondary part or preferably a primary part of the linear motor system. The stack carriers can be driven independently by the linear motor system. In a further configuration of the invention, the stack carriers can be formed by two stop means which are intended to delimit the stacks in each case at their ends positioned counter to the transporting direction. The stop means can each be independently drivable. Preferably, the stop means can each have primary parts or preferably secondary parts of the linear motor system. A spacing between stop means which are intended to form a stack can be changed. Preferably, the stop means which are intended to form a stack have stack supporting means, in particular comb-like supporting extensions that mesh with one another. The stack supporting means can form stack bases. A stack layer can be changed by changing a spacing of stop means which are intended to form a stack. The stack device can be adapted to different lengths of stack layers. The stack supporting means can be drivable independently of the stop means. In particular, the stack supporting means can have further primary parts or preferably secondary parts of the linear motor system. Spacings between the stop means and stack supporting means can be set independently. The stacking device can be particularly flexible. It is also proposed that the stop means of the stack carriers are mounted on mounting devices so as to be able to be pushed and/or folded away out of the transporting region, in order to make it easier to push the stacks away, in particular by way of a slider. Pushing and/or folding the stop means away can also facilitate the revolution of the stack carriers at deflection points in the case of stack carriers that are driven in revolution. 
         [0009]    In an alternative configuration of the invention, it is proposed that one of the drive units drives only the stacking movement or only the transporting movement. Preferably, one of the drive units is provided only to drive the stacking movement and one of the drive units is provided only to drive the transporting movement. In particular, a stack base can be driven by one drive unit and a stack transporting means can be driven by the further drive unit. The stack base can carry out stacking movements while the stack transporting means transports finished stacks out of the area of influence of the stacking movement to the stack transfer position. Continuous stack formation can advantageously be possible. 
         [0010]    It is proposed that the stack base is formed by a first belt element and the stack transporting means is formed by a further, second belt element adjoining the first belt element. In particular, the belt elements can adjoin one another with mutually opposite belt noses at their belt ends. One belt can carry out the stacking movement while the second belt carries out the transporting movement. Once a stack has been formed, the first belt can interrupt the stacking movement, briefly carry out a further transporting movement in the transporting direction and thus transfer the stack at least partially onto the further belt. The further belt transports the stack out of the area of influence of the stacking movement of the first belt while the first belt is driven with the stacking movement again in order to form the next stack. The stack base is formed by alternating regions of the first belt which are each located in the stack forming region. Preferably, a time span in which the first belt interrupts the stacking movement and carries out the further transporting movement is shorter than the time span which is required to advance the string of bags from the bag feeding means to the stack base by way of the feeding movement. Alternatively, the bag feeding means can have a storage function which makes it possible to briefly stop the continuously fed string of bags. Particularly advantageously, the further transporting movement can already form a start of the stacking movement of the next stack in that the string of bags is deposited on the belt in the direction of the further transporting movement and forms a first stack layer. It is possible to avoid stopping the feeding movement. The stack formation can take place continuously. 
         [0011]    It is furthermore proposed that the stack transporting means is intended to transport stacks out of the stack forming region to an onward transporting unit. In particular, the stack transporting means can have a slider and/or a gripper which collects the stack in the stack forming region on a side counter to the transporting direction and transports it to an onward transporting unit. In this connection, an “onward transporting unit” should be understood as meaning in particular a transporting unit which receives the stack and transports it to a next process step, such as in particular a further packing process. The stack base can carry out the stacking movement continuously. The stack can be transported out of the area of influence of the stacking movement by the stack transporting means. Continuous stack formation can be possible. The stack base can carry out the stacking movement without interruption. 
         [0012]    Alternatively, the stack base can form the stack transporting means for transporting stacks and be mounted under the stacks so as to be able to be folded away for transport in the direction of a weight force and/or beneath the stacks so as to be able to be pulled and/or pivoted away for transport transversely to the direction of the weight force. The stack base can be configured as a trap door, in particular as a two-part trap door. The stack base can carry out the stacking movement for stack formation. Once the stack has been formed, the stack base can fold away downward, such that the stack falls through the open trap door, configured as a stack base, by way of the weight force. Preferably, a chute or a similar suitable transporting device is arranged beneath the stack base, said chute collecting the falling stack and transporting it to an onward transporting unit. Preferably, the stacking movement and the transporting movement, which pulls and/or folds the stack base away under the stack, is driven by the two separate drive units. 
         [0013]    In a further configuration of the invention, it is proposed that the bag feeding means has a brake means which, in at least one operating state, is intended to exert, on at least one portion of the string of bags, a braking force with at least one force component in the opposite direction to a direction of movement of the portion of the string of bags. In this connection, a “portion of the string of bags” should be understood as meaning in particular an end of the string of bags that is delivered to form a stack on the stack base. In particular, the separating means can sever the portion of the string of bags from the string of bags as soon as it comprises the number of bags intended for the stack to be formed. In this connection, a “direction of movement” of the string of bags should be understood as meaning in particular a direction of movement, brought about by the feeding of the string of bags in the feeding direction, of the portion of the string of bags at a contact point of the brake means with the string of bags. Preferably, the brake means can be arranged after the separating means in the feeding direction of the string of bags. The brake means can effectively slow down a movement of the portion of the string of bags in its direction of movement. In particular, it is possible to avoid a situation in which the portion of the string of bags, after it has been detached from the string of bags, falls onto the stack base and/or is deposited on the stack base in an uncontrolled manner and/or at excessive speed under the weight force. Preferably, the brake means is mounted so as to rotate about an axis. In particular, the brake means can be configured as a rotating brush or particularly preferably a roller. Preferably, the brake means can be driven about its axis. Particularly preferably, drive means are provided to drive the brake means synchronously with the feeding speed of the string of bags. Preferably, the separating means can be formed by rotating crush-cut knives. Preferably, the crush-cut knives, at the time of separating, and/or the brake means can have a circumferential speed that is synchronous with the feeding speed. The crush-cut knives and/or the brake means can drive the string of bags and/or the portion of the string of bags at the feeding speed at the time at which the string of bags is separated. Preferably, the brake means can press on the portion of the string of bags with a pressure force against the pivot plate. The pressure force can bring about advantageous static friction between the portion of the string of bags and brake means. The static friction between the brake means and portion of the string of bags can advantageously bring about the braking force. During the stack formation, the pivot plate can advantageously remain in a stack forming position. A spacing between brake means and pivot plate during stack formation can be constant. It is possible to dispense with a mounting of the brake means that is movable back and forth with a movement of the pivot plate. Preferably, the pivot plate can advantageously be pivoted from the stack forming position into an ejection position. The ejection position can be provided to eject defective bags into a waste container. In the ejection position, the pivot plate can advantageously eject the portion of the string of bags out of the stacking device. 
         [0014]    Furthermore, a packing machine having a stacking device is proposed. The packing machine can continuously form product stacks with the mentioned advantages. 
         [0015]    Furthermore, a method for continuously forming stacks is proposed. The method contains in particular the fact that bags are fed continuously in at least one string of bags that has at least one row of bags and is endless or severed after in each case a defined number of bags and are deposited by the bag feeding means on at least one stack base that is moved back and forth in a stacking movement parallel to a stack layer direction at least during the formation of a stack, such that the string of bags deviates, on account of the stacking movement, in each case after a number of bags that forms a stack layer, and forms zigzag-shaped stack layers, or such that the string of bags is piled up with a consistent bag orientation, on account of the stacking movement, in stack layers with the number of bags that forms the stack layer, and the stack is moved out of the area of influence of the stacking movement by way of at least one stack transporting means for transporting the stacks once a defined number of stack layers has been reached, wherein a first drive unit drives the stacking movement and a further drive unit drives a transporting movement of at least one stack transporting means. 
         [0016]    The stacking device according to the invention is not intended to be limited here to the above-described application and embodiment. In particular, the stacking device according to the invention can have a number of individual elements, components and units which differs from the number mentioned herein in order to fulfill a functionality described herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Further advantages can be gathered from the following description of the drawings. Five exemplary embodiments of the invention are illustrated in the drawings. The drawings, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form appropriate further combinations. 
           [0018]    In the drawings: 
           [0019]      FIG. 1  shows a schematic illustration of a first exemplary embodiment of a stacking device for continuously forming stacks, 
           [0020]      FIG. 2  shows a schematic illustration of a second exemplary embodiment of a stacking device for continuously forming stacks, 
           [0021]      FIG. 3  shows a schematic illustration of a third exemplary embodiment of a stacking device for continuously forming stacks, 
           [0022]      FIG. 4  shows a schematic illustration of a fourth exemplary embodiment of a stacking device for continuously forming stacks, 
           [0023]      FIG. 5  shows a schematic illustration of a fifth exemplary embodiment of a stacking device for continuously forming stacks, and 
           [0024]      FIG. 6  shows a schematic illustration of a sixth exemplary embodiment of a stacking device for continuously forming stacks. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows a schematic illustration of a stacking device  10   a  for continuously forming stacks  12   a  of bags  18   a  fed continuously in at least one string of bags  16   a  that has three rows of bags  14   a  and is endless and severed after in each case a defined number of bags, having at least four stack bases  24   a,    24 ′ a  that are moved back and forth in a stacking movement  22   a  parallel to a stack layer direction  20   a  during the formation of a stack  12   a,  having a bag feeding means  26   a  which deposits the string of bags  16   a  on the stack base  24   a  located in each case in a stack forming region  62   a,  such that the string of bags  16   a  deviates, on account of the stacking movement  22   a,  in each case after a number of bags that forms a stack layer  28   a,  and forms zigzag-shaped stack layers  28   a,  and having four stack transporting means  30   a,    30 ′ a  for transporting the stacks  12   a  out of the area of influence of the stacking movement  22   a  once a defined number of stack layers has been reached. A first drive unit  32   a  is provided to drive the stacking movements  22   a  of in each case two stack bases  24   a.  Furthermore, the first drive unit  32   a  is provided to drive transporting movements  34   a  for transporting the stacks  12   a  by way of the two stack transporting means  30   a.  A second drive unit  32 ′ a  is provided to drive transporting movements  34 ′ a  for transporting the stacks  12   a  by way of the two stack transporting means  30 ′ a . Furthermore, the second drive unit  32 ′ a  is provided to drive stacking movements  22 ′ a  of the two stack bases  24 ′ a . The drive units  32   a,    32 ′ a  are thus each provided to drive one of the stacking movements  22   a,    22 ′ a  and one of the transporting movements  34   a,    34 ′ a . The stacking device  10   a  is part of a packing machine  68   a  which is only indicated here. 
         [0026]    The string of bags  16   a  is discharged downward in the direction of a weight force  66   a  by the bag feed means  26   a  in a feeding direction  70   a  in the direction of the stack forming region  62   a.  In the example, the three rows of bags  14   a  of the string of bags  16   a  are separated such that the latter forms three part-strings. It is also possible for the rows of bags  14   a  to be configured in a contiguous manner. The bag feeding means  26   a  has separating means (not illustrated in more detail) for severing the string of bags  16   a  transversely to the feeding direction  70   a  after a defined number of bags. The number of bags can be identical or variable for each stack layer  28   a.  In the case shown, in each case 6 bags  18   a  form a stack layer  28   a,  wherein three bags  18   a  are arranged alongside one another in rows of bags  14   a  transversely to the feeding direction  70   a  and in each case two bags  18   a  are arranged one after another in the feeding direction  70   a.    
         [0027]    Four stack carriers  50   a,    50 ′a form the four stack bases  24   a,    24 ′a and the stack transporting means  30   a,    30 ′ a , which are driven by the two drive units  32   a,    32 ′ a . The drive units  32   a,    32 ′ a  drive two revolving elements configured as belts  72   a,    72 ′ a . The stack carriers  50   a  are arranged on the belt  72   a  and are driven by the drive unit  32   a,  and the stack carriers  50 ′ a  are arranged on the belt  72 ′ a  and are driven by the drive unit  32 ′ a . The two stack carriers  50   a  and the two stack carriers  50 ′ a  are arranged on the respective belts  72   a  and  72 ′ a  in a manner offset in each case by half a belt revolution. 
         [0028]    In order to support the stack formation and to orient the stacks  12   a,  the stack bases  24   a,    24 ′ a  each have stop means  36   a,    36 ′ a  which delimit and orient the stacks  12   a  on both sides in a transporting direction  52   a  at a spacing corresponding to a length  44   a  of a stack layer  28   a  in the stack layer direction  20   a.    
         [0029]    In  FIG. 1 , a stack carrier  50   a  is currently in the stack forming region  62   a.  The stack carrier  50   a  is driven with the stacking movement  22   a  by the drive unit  32   a.  A stack  12   a  is formed on the stack base  24   a  of the stacking carrier  50   a.  Optionally, the stack formation, as illustrated in  FIG. 1 , can be supported by a pivot plate  82   a  which is moved back and forth in a pivoting movement  84   a  and deflects the string of bags  16   a  in the stack layer direction  20   a.  The deflection additionally increases a relative movement, caused by the stacking movement  22   a,  of the string of bags  16   a  with respect to the stack base  24   a.  The further stack carrier  50   a  is located on an opposite side, in the direction of the weight force  66   a,  of the revolving belt  72   a.  At the same time, one of the stack carriers  50 ′ a  transports a stack  12   a  already formed on the stack base  24 ′ a  of the stack carrier  50 ′ a  to a stack transfer position  74   a  with the transporting movement  34   a.  The stack carriers  50   a,    50 ′ a  having the stack bases  24   a,    24 ′ a  and the stop means  36   a,    36 ′ a  are formed by a plurality of segments (not illustrated in more detail here) that are connected in an articulated manner and are mounted on the belts  72   a,    72 ′ a . In the region of the stack transfer position  74   a,  the stack carrier  50 ′ a  is deflected. The rear stop means  36 ′ a  in the transporting direction  52   a  dip first downward under the stack  12   a  in the direction of the weight force  66   a.  A slider  76   a  pushes the stack  12   a  from the stack transfer position  74   a  in the direction of an onward transporting unit  64   a  and/or to a downstream process step. The front stop means  36 ′ a  in the transporting direction  52   a  can likewise dip under the stack  12   a  in order for the stack  12   a  to be pushed off by the slider  76   a,  in order to facilitate the pushing off operation. In the example shown, the geometry of the front stop means  36 ′ a  in the transporting direction  52   a  and of the slider  76   a  is designed such that the slider  76   a  can pass through the stop means  36 ′ a  such that it is not necessary for the front stop means  36 ′ a  in the transporting direction  52   a  to dip for the pushing off operation. Subsequently, the remaining parts of the stack carrier  50 ′ a  are deflected. These process steps subsequently repeat with the stack carrier  50   a  carrying the next stack  12   a.    
         [0030]    The further stack carrier  50 ′ a  is located in a manner offset by half a length of the belt  72 ′ a  and adjoins the stack forming region  62   a  counter to the transporting direction  52   a.  Once the stack  12   a  formed on the stack carrier  50   a  has been completed, the stack carrier  50   a  is driven with the transporting movement  34   a  and the stack carrier  50 ′ a  is moved into the stack forming region  62   a,  where it is driven with the stacking movement  22   a  and the next stack  12   a  is formed. 
         [0031]    As an alternative to the shown zigzag folding of the stacks  12   a,  the stacking movement  22   a  can also be controlled and the string of bags  16   a  can also be separated such that the string of bags  16   a,  on account of the stacking movement  22   a,  is piled up in stack layers  28   a  with the number of bags forming the stack layer  28   a  with a consistent bag orientation. 
         [0032]    In order to control the stacking movements  22   a,    22 ′ a  and the transporting movements  34   a,    34 ′ a , provision is made of a control unit  38   a  which controls the drive units  32   a  and  32 ′ a . The control unit  38   a  controls a stroke  40   a  and a speed  42   a  of the stacking movement  22   a  in dependence on the number of bags and the length  44   a  of a stack layer  28   a  in the stack layer direction  20   a,  a feeding speed  46   a  of the string of bags  16   a  and an achieved stack height  48   a  of the stack  12   a.  In particular, the stroke  40   a  of the stacking movement  22   a  is all the greater, the greater the stack height  48   a  is and the smaller the remaining spacing between the stack  12   a  and bag feeding means  26   a  is. 
         [0033]    The following description and the drawings of four further exemplary embodiments are limited substantially to the differences between the exemplary embodiments, wherein, with regard to identically designated components, in particular with regard to components with the same reference signs, reference can be made in principle also to the drawings and/or the description of the other exemplary embodiments. In order to distinguish between the exemplary embodiments, the letters b, c, d and e are placed after the reference signs of the further exemplary embodiments rather than the letter a. 
         [0034]      FIG. 2  shows a second exemplary embodiment of a stacking device  10   b.  The stacking device  10   b  of the second exemplary embodiment differs from the stacking device  10   a  in particular in that two stack carriers  50   b,    50 ′ b  are arranged on in each case one linear motor  80   b ,  80 ′ b  of a linear motor system  78   b.  The linear motors  80   b,    80 ′ b  form drive units  32   b,    32 ′ b  and can be driven independently. 
         [0035]    The stack carriers  50   b,    50 ′ b  are mounted so as to be displaceable in the direction of a weight force  66   b  and stop means  36   b,    36 ′ b  are arranged in a foldable manner on mounting devices  54   b  on stack bases  24   b,    24 ′ b , such that the stack carriers  50   b,    50 ′ b  can be pushed away, with the stop means  36   b,    36 ′ b  folded away parallel to a transporting direction  52   b,  out of a transporting region  56   b  in which stacks  12   b  are transported. In  FIG. 2 , a stack  12   b  is formed on the stack carrier  50   b,  while the stack carrier  50 ′ b  delivers a further stack  21   b  to an onward transporting unit  64   b  in a stack transfer position  74   b  supported by a slider  76   b.  Subsequently, the stack carrier  50 ′ b  is moved counter to the transporting direction  52   b  into a position in which it adjoins a stack forming region  62   b  on the side counter to the transporting direction  52   b.  In order, during this movement, to avoid a collision with the stack  12   b  which is currently being formed on the stack carrier  50   b  and with the stack carrier  50   b,  the stop means  36 ′ b  are folded away into a position parallel to the transporting direction  52   b  and the stack carrier  50 ′ b  is pushed away out of the transporting region  56   b  in the direction of the weight force  66   b.  Subsequently, the stop means  36 ′ b  are folded up again and the stack carrier  50 ′ b  is pushed back counter to the weight force  66   b,  and the stack carrier  50 ′ b  is moved into the stack forming region  62   b  for the formation of the next stack  21   b,  as soon as the stack carrier  50   b  has left the stack forming region  62   b  with the completed stack  12   b  formed on the stack carrier  50   b.  During stack formation, the stack carrier  50   b,    50 ′ b  which is located in the stack forming region  62   b  is driven, as in the first exemplary embodiment, with a stacking movement  22   b.    
         [0036]      FIG. 3  shows a third exemplary embodiment of a stacking device  10   c.  The stacking device  10   c  of the third exemplary embodiment differs from the stacking device  10   a  in particular in that a stacking movement  22   c  and a transporting movement  34   c  are driven by independent drive units  32   c,    32 ′ c . A stack base  24   c  and a stack transporting means  30   c  are formed by two mutually adjoining belt elements  58   c,    60   c.  The belt element  58   c  forms in this case a stacking belt and the belt element  60   c  forms a transporting belt. The belt element  58   c  is driven with the stacking movement  22   c.  Once a defined number of stack layers  28   c  has been achieved, the belt element  58   c  is briefly moved in the direction of the belt element  60   c  until a stack  12   c  currently being formed rests to a sufficient extent on the belt element  60   c  such that the belt element  60   c  receives the stack  12   c  and transports it to an onward transporting unit  64   c  with the transporting movement  34   c.  The belt element  58   c  is driven with the stacking movement  22   c  again. The next stack  12   c  is formed in the region of the belt element  58   c  that has just come to lie in a stationary stack forming region  62   c.  This region of the belt element  58   c  forms in each case the stack base  24   c,  wherein the region can be formed in each case on alternate portions of the belt element  58   c . A return movement of the belt element  58   c  is therefore not necessary. The movement with which the belt element  58   c  moves the preceding stack  12   c  in the direction of the belt element  60   c  already forms the start of the stacking movement  22   c  with which the next stack  12   c  is formed. The interruption of the stacking movement  22   c  for moving the stack  12   c  to the belt element  60   c  is therefore short enough that a bag feeding means  26   c  can continuously deliver a string of bags  16   c  for stack formation. 
         [0037]      FIG. 4  shows a fourth exemplary embodiment of a stacking device  10   d.  The stacking device  10   d  of the fourth exemplary embodiment differs from the stacking device  10   c  of the third exemplary embodiment in particular in that a stack transporting means  30   d  formed by a slider  76   d  is intended to transport stacks  12   d  out of a stack forming region  62   d  to an onward transporting unit  64   d.  A stack base  24   d  is formed by a plate that is driven in a manner oscillating back and forth with a stacking movement  22   d.  Once a stack  12   d  with a defined number of stack layers has been piled up, the separately driven slider  76   d  pushes the stack  12   d  with a transporting movement  34   d  onto the onward transporting means  64   d  configured as a belt. At the same time, the formation of the next stack  12   d  starts on the stack base  24   d.  In a development of the stacking device  10   d,  the stack base  24   d  is mounted so as to be displaceable in the direction of a weight force  66   d.  During stack formation, the stack base  24   d  is displaced in the direction of the weight force  66   d  by a height of the formed stack layer  28   d  with every newly formed stack layer  28   d.  A spacing between a stack top side of the stack  12   d  and a bag feeding means  26   d  can remain constant, such that conditions under which a string of bags  16   d  deviates in a zigzag-shaped manner remain unchanged. 
         [0038]      FIG. 5  shows a fifth exemplary embodiment of a stacking device  10   e.  The stacking device  10   e  of the fifth exemplary embodiment differs from the stacking device  10   d  of the fourth exemplary embodiment in particular in that a stack base  24   e  forms a stack transporting means  30   e  for transporting stacks  12   e  and is mounted so as to be able to be folded away under the stacks  12   e  for transport in the direction of a weight force  66   e.  To form the stacks  12   e,  the stack base  23   e  is moved with a stacking movement  22   e.  Once the defined number of stack layers  28   e  has been achieved, the stack base  24   e,  which is divided along a centerline parallel to the stacking movement  22   e,  is folded away downward on both sides with a transporting movement  34   e  and thus forms the stack transporting means  30   e  for transporting the stack  12   e  in the direction of the weight force  66   e.  On account of the weight force  66   e,  the stack  12   e  falls onto an onward transporting means  64   e  and is transported by the latter to a next process step. Optionally, the stack  12   e  can fall into a container arranged beneath the stack base  24   e  and/or the onward transporting means  64   e  can transport containers into which the stack  12   e  falls. Subsequently, the stack base  24   e  is folded back again, such that a next stack  12   e  can be formed. The transporting movement  34   e  is sufficiently quick for a bag feeding means  26   e  to be able to deliver a string of bags  16   e  continuously for stack formation. The stacking movement  22   e  is driven by a drive unit  32   e  and the transporting movement  34   e  is driven independently by a drive unit  32 ′e. As in the fourth exemplary embodiment, in a development of the stacking device  10   e,  the stack base  24   e  can be mounted so as to be displaceable in the direction of the weight force  66   e.    
         [0039]      FIG. 6  shows a schematic illustration of a bag feeding means  26   f  of a sixth exemplary embodiment of a stacking device  10   f  for continuously forming stacks  12   f.  The bag feeding means  26   f  differs from the bag feeding means  26   a - e  of the previous exemplary embodiments in particular in that it has a brake means  86   f  which, in at least one operating state, is intended to exert, on at least one portion  88   f  of a string of bags  16   f,  a braking force  90   f  with at least one force component in the opposite direction to a direction of movement  92   f  of the portion  88   f  of the string of bags. As a result of the brake means  86   f,  it is possible to effectively avoid a situation in which the portion  88   f  of the string of bags that is severed by the separating means  96   f  falls onto the stack  12   f  or a stack base  24   f  in an uncontrolled manner. The bag feeding means  26   f  can advantageously be used in the stacking devices  10   a - e  instead of the bag feeding means  26   a - e  described in the exemplary embodiments. 
         [0040]    The string of bags  16   f  is transported in the direction of a stack forming region  62   f  at a feeding speed  46   f  in a feeding direction  70   f  between two driven transporting rollers  94   f  The string of bags  16   f  is subsequently guided between two rotating separating means  96   f  which each have a crush-cut knife  98   f  in their circumference. The separating means  96   f  separate the portion  88   f  of the string of bags from the string of bags  16   f  as soon as it has reached the number of bags desired for the stack  12   f.    
         [0041]    The brake means  86   f  has a rubberized brake roller  100   f  which is driven via a belt drive  102   f  at the same circumferential speed as the transporting rollers  94   f.  In the shown operating state in which stacks  12   f  are formed, a pivot plate  82   f  is located in a stack forming position  104   f  In contrast to the pivot plate  82   a - e  of the preceding exemplary embodiments, the pivot plate  82   f  remains in this position. If for example defective bags  18   f  are intended to be removed from the stacking device  10   f,  the pivot plate  82   f  can be pivoted into an ejection position (not illustrated here), in which the portion  88   f  of the string of bags is guided in the direction of a waste container. 
         [0042]    The brake roller  100   f  is arranged on a side of the portion  88   f  of the string of bags that is opposite the pivot plate  82   f  in the stack forming position  104   f  at a spacing  106   f  that is somewhat smaller than an average bag thickness of the bags  18   f.  Therefore, the brake roller  100   f  presses the bags  18   f  of the portion  88   f  of the string of bags against the pivot plate  82   f  with a pressure force at a contact point  108   f  of the brake roller  100   f.  The rubberizing of the brake roller  100   f  has the effect that fluctuations in the bag thickness are equalized. In addition, the brake roller  100   f  can be mounted in a spring-loaded manner in the direction of the spacing  106   f.  On account of the static friction that exists as a result of the pressure force between the brake roller  100   f  and the portion  88   f  of the string of bags, the brake roller  100   f  can exert the braking force  90   f  on the portion  88   f  of the string of bags. If, after being severed from the string of bags  16   f  by the separating means  96   f,  the portion  88   f  of the string of bags is accelerated by a weight force  66   f,  the brake roller  100   f  brakes the portion  88   f  of the string of bags by way of the braking force  90   f  such that it is moved at the feeding speed  46   f  synchronously with the transporting rollers  94   f  in the direction of movement  92   f.  The braking force  90   f  can also reverse its direction and accelerate the portion  88   f  of the string of bags, should it become slower than the feeding speed  46   f.  In the configuration shown with the weight force  66   f  which acts in the feeding direction  70   f , this case generally does not occur. If the bag feeding means  26   f  is used in different configurations, this case is conceivable, however. If the portion  88   f  of the string of bags is intended to be able to be delivered onto the stack  12   f  at speeds other than the feeding speed  46   f  of the string of bags  16   f,  the braking roller  100   f  can, in a variant of the invention, be driven by a drive independent of the drive of the transporting rollers  94   f.  It may likewise be possible for the pivot plate  82   f,  as in the previous shown exemplary embodiments, to be pivoted back and forth with a pivoting movement during stack formation. In this case, the brake means  86   f  has bearing means which make it possible to move the braking roller  100   f  along with the pivoting movement of the pivot plate  82   f  such that, at least when the portion  88   f  of the string of bags has been severed from the string of bags  16   f,  the spacing  106   f  is small enough for the braking roller  100   f  to be able to exert the braking force  90   f  on the portion  88   f  of the string of bags.