Patent Publication Number: US-6988721-B2

Title: Device for stacking of sheets

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for stacking of sheets, wherein a high-speed printer is provided for printing the sheets or at least one continuous web which is cut to sheets and wherein the stacking device is provided to receive sheets in at least one flow of sheets to said stacking device and to transfer thin sheets in the flow thereof to at least one first stacking table in order to form at least one stack of sheets on said table. 
     BACKGROUND OF THE INVENTION 
     The publication U.S. Pat. No. 5,707,058 defines a stacking device wherein a flow of sheets received on a first stacking table, is interrupted by a second stacking table being moved into said flow and dividing or interrupting it such that said flow of shoots is received by this second stacking table. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to improve prior art stacking devices such that they can operate without interrupting the flow of sheets when the stacking of sheets shall be transferred from one stacking table to another. This is arrived at by providing the device with the characterizing features of subsequent claim  1 . 
     Since the device is provided with said characterizing features, stacking of sheets may be carried through at high speeds and without interruptions when one stacking table is full of sheets and one proceeds to fill another stacking table with sheets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further described below with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic side view of a device according to the invention, forming part of a plant for printing sheets in a high-speed printer; 
         FIG. 2  is a schematic perspective view of a device according to the invention and in a part of the plant of  FIG. 1 ; 
         FIG. 3  is a schematic view of a device according to the invention and in a part of the plant of  FIG. 1 ; 
         FIG. 4  is a schematic side view of a device according to the invention and in a part of the plant of  FIG. 1 ; 
         FIG. 5  is a perspective view of a vacuum means forming part of the plant of  FIG. 1 ; 
         FIG. 6  is a plan view of parts of the vacuum means of  FIG. 5 ; 
         FIG. 7  is a side view of the vacuum means of  FIG. 6 ; 
         FIG. 8  is a perspective view of another vacuum means forming part of the plant of  FIG. 1 ; 
         FIG. 9  is a side view, partly in section, of a part of the vacuum means of  FIG. 8 ; 
         FIG. 10  is a plan view of an alternative lateral-movement device forming part of the device according to the invention; and 
         FIGS. 11–14  are schematic side views of parts of a stacking device forming part of the device according to the invention, whereby different parts of the stacking device have different positions. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     In  FIG. 1  there is illustrated a plant  1  for printing sheets  2 , said plant  1  comprising an unrolling stand  3  with a roll  4  of paper or another suitable material which is fed as a continuously running web  5  from said unrolling stand  3  into a high-speed printer  6 , e.g. a laser printer, for printing. With high-speed printer  6  is meant a printer which can print the running web  5  when said web passes the printer at high speed, e.g. 2 m/s or even more. After printing the web  5  in the high-speed printer  6 , it is brought to run to a cutting device  7  in which the web  5  is cut to sheets  2  by means of knives  8  which can be rotatably mounted. From the cutting device  7 , the sheets  2  are fed continuously to a transport device  9  which transports the sheets  2  to a device  10  for lateral movement thereof in opposite lateral directions B, C relative to a main transport direction A (see  FIG. 3 ). The lateral movement of the sheets  2  in lateral directions B, C is carried through for locating the sheets or stacks  2 A,  2 B of sheets  2  in laterally displaced positions relative to each other in a stacking device  11  into which the sheets  2  are transported from the lateral-movement device  10 . Generally, the laterally moved or displaced stacks  2 A,  2 B shall lie on top of each other and there may be more than two such stacks  2 A,  2 B lying on top of each other. 
     The plant  1  may comprise a prior art device (not shown) for locating two webs  5  on top of each other, which are brought to run through the high-speed printer  6  and cut in the cutting device  7  to twin sheets, which are transported by the transport device  9  to the lateral-movement device  10  in which the twin sheets are laterally moved or displaced. Then, the twin sheets are transferred to the stacking device  11 , in which said twin sheets are stacked. Eventually, three or four webs can be located on top of each other and treated in the same way. 
     The lateral-movement device  10  includes a vacuum generating device V having at least one pair of vacuum means  12 ,  13  or another suitable number of pairs of vacuum means, e.g. three pairs (see  FIG. 3 ). At each vacuum means  12  and  13  there is provided an endless conveyor belt  14  which runs about rolls  15 ,  16  at the opposite end portions of the vacuum means  12  and  13  respectively (see  FIG. 5 ). The conveyor belts  14  are driven or operated in a transport or feed direction by means of a driving device (not shown) and at a speed which is adapted to the speed of the web  5  and the sheets  2 . The vacuum means  12 ,  13  and their conveyor belts  14  are provided diverging somewhat relative to the main transport direction A and the angle α therebetween may lie within a range of 4–8°, which means that the angle between said main transport direction A and each lateral direction B, C is within a range of 2–4°. The angle α however, may lie within a wider range. 
     Each vacuum means  12 ,  13  has three vacuum openings  17 ,  18  and  19  which are located in a row, in line, after each other seen in the respective lateral direction B and C. Another number of vacuum openings than three is also possible. The conveyor belt  14  has a number of vacuum holes  20  which are located in a row after each other in the longitudinal direction of the conveyor belt  14  and these vacuum holes  20  pass over the vacuum openings  17 ,  18 ,  19  of the respective vacuum means  12 ,  13  when the conveyor belt  14  is moved relative to said vacuum means  12 ,  13 . 
     Each vacuum means  12  and  13  respectively, has a channel system  21  which through a compressed-air line  22  is connected to a compressed-air, generating device  23 . The channel system  21  is adapted to guide compressed air to an ejector  24 , i.e. a jet pump, in association with each vacuum opening  17 ,  18 ,  19 . The channel system  21  includes, for each vacuum opening  17 ,  18 ,  19  a horizontal channel  25  to which a vertical channel  26  is connected. The channel  26  transforms into a horizontal ejector channel  27  which is directed beyond the lower end of a vertical hole  28  which at the top communicates with the respective vacuum opening  17 ,  18 ,  19 . The ejector channel  27  runs to a compressed-air outlet  29  through which the compressed air flows out of the ejector  24 . 
     When the ejector  24  is activated, compressed air is brought to pass through the channels or passages  25 ,  26  into its ejector channel  27 . Since the speed of the jet D of compressed air ( FIG. 7 ) in this ejector channel  27  is high, air will be sucked thereinto from each vacuum opening  17 ,  18 ,  19  through the vertical hole  28 , whereby a vacuum is generated, i.e. a negative pressure, in each vacuum opening  17 ,  18 ,  19  and in the vacuum holes  20  communicating therewith, in the conveyor belt  14 . 
     A vacuum control device  30  is provided to see to that there is either a vacuum in the respective vacuum opening  17 ,  18 ,  19  and the vacuum holes  20  in the conveyor belt  14  at said vacuum opening, or to interrupt or withdraw said vacuum. The vacuum control device  30  incorporates a vacuum interrupting or vacuum withdrawing device  31  at each ejector  24  in order to feed compresses air from the compressed-air generating device  23  to the respective vacuum opening  17 ,  18 ,  19  for quick and effective withdrawal of the vacuum therein and in the vacuum holes  20  communicating therewith, in the conveyor belt  14 . Each vacuum interrupting or vacuum withdrawing device  31  includes a valve  32 , preferably an electric valve, through which compressed air can pass from a passage branch  25   a  of the horizontal channel  25  into a horizontal channel  33  having its opening  34  at the top in the vertical hole  28 . When the valve  32  is closed, the connection between the channels or passages  25   a ,  33  is closed too, and the compressed air flows through the vertical channel  26  to the ejector channel  27  with ejector effect in the ejector  24  as a result, and thereby generation of a vacuum in the respective vacuum opening  17 ,  18 ,  19  and consequently in vacuum holes  20 , in the conveyor belt  14 , communicating with the vacuum opening in question. If the valve  32  is opened, compressed air will flow through the channels  25   a ,  33  to the vertical hole  28  and immediately interrupt the vacuum therein and thereby in the respective vacuum opening  17 ,  18 ,  19  as well as in the vacuum holes  20  in the conveyor belt  14 , which communicate with the vacuum opening in question. Preferably, compressed air will in this case generate a certain additional or positive pressure in the vertical hole  28  and in the respective vacuum opening  17 ,  18 ,  19  and thereby in the vacuum holes  20  communicating with the vacuum opening in question, in the conveyor belt  14 . This is marked with an arrow E in  FIG. 7 . 
     The setting of the valves  32  in vacuum generating or vacuum interrupting positions is controlled by means of a vacuum control unit  35  which can be programmed to see to that a vacuum is present in a vacuum opening  17 ,  18 ,  19  or not. 
     The vacuum control device  30  described above can be programmed such that the conveyor belts  14  of the vacuum means  12 ,  13  alternatingly grip or engage and transport or feed one or more sheets  2  in the different lateral directions B or C in order to, in the stacking device  11 , locate the sheets  2  or stacks  2 A,  2 B of sheets in laterally displaced positions relative to each other. If e.g. laterally displaced stacks  2 A,  2 B of sheets containing three sheets each shall be formed in the stacking device  11 , the vacuum control unit  35  is programmed for control of the vacuum generating device V in the following way. Initially, a vacuum is generated in the vacuum openings  17 ,  18 ,  19  of the vacuum means  12  and thereby in the vacuum holes  20  in its conveyor belt  14 , but not in the vacuum openings  17 ,  18 ,  19  of the vacuum means  13  and thereby neither in the vacuum holes  20  in its conveyor belt  14 . When the first sheet  2  is transported or fed to the device  10  for lateral movement, the conveyor belt  14  of the vacuum means  12  will, due to the vacuum in its vacuum holes  20 , grip or engage and transport this sheet  2  in the lateral direction B. The following two sheets  2  will also be moved in the lateral direction B to form a stack  2 A consisting of three sheets  2  in the stacking device  11 . Then, a vacuum is generated in the vacuum openings  17 ,  18 ,  19  of the vacuum means  13  instead, and thereby in the vacuum holes  20  in its conveyor belt  14 , while the vacuum generation in the vacuum openings  17 ,  18 ,  19  of the vacuum means  12  and thereby in the vacuum holes  20  in its conveyor belt  14  is brought to cease or is interrupted. Hereby, the next sheet  2  fed to the device  10  for lateral movement is engaged and transported by the conveyor belt  14  of the vacuum means  13  in the lateral direction C, and so are the following two sheets  2  such that a stack  2 B consisting of three sheets  2  and laterally moved relative to the stack  2 A is formed in the stacking device  11 . This alternating movement laterally is continued until a required number of, relative to each other, laterally moved stacks  2 A,  2 B have been formed in the stacking device  11 . 
     The vacuum control device  30  can be programmed to bring the vacuum generating device V to generate as well as not to generate or interrupt a vacuum in e.g. the following ways: 
     A) A vacuum is generated in the first vacuum opening  17  in the first vacuum means  12  and is generated at the same time or is interrupted at the same time in at least one of the following vacuum openings  18 ,  19  in said first vacuum means  12 . A vacuum is not generated or is interrupted at the same time in at least the first vacuum opening  17  of the vacuum openings  17 ,  18 ,  19  in the second vacuum means  13 . 
     B) A vacuum is generated in the first vacuum opening  17  in the second vacuum means  13  and it not generated at the same time or is interrupted at the same time in at least one of the succeeding vacuum openings  18 ,  19  in said second vacuum means  13 . A vacuum is not generated at the same time or is interrupted at the same time in at least the first vacuum opening  17  of the vacuum openings  17 ,  18 ,  19  of the first vacuum means  12 . 
     C) A vacuum is generated in the first vacuum opening  17  in the second vacuum means  13  and in at least one of the succeeding vacuum openings  18 ,  19  in said second vacuum means  13 . A vacuum is not generated at the same time or is interrupted at the same time in the vacuum openings  17 – 19  in the first vacuum means  12 . 
     D and E) A vacuum is generated in the first vacuum opening  17  in the first vacuum means  12  and is not generated or is interrupted at the same time in the first vacuum opening  17  in the second vacuum means  13  while it at the same time is generated in any or both of the other vacuum openings  18 ,  19  in the second vacuum means  13  or vice versa. 
     F and G) A vacuum is generated in all vacuum openings  17 ,  18 ,  19  in the first vacuum means  12  but is not generated at the same time or is interrupted at the same time in all vacuum openings  17 ,  18 ,  19  in the second vacuum means  13  or vice versa. 
     The vacuum control device  30  can be programmed to bring the vacuum generating device V to generate respectively to not generate or interrupt a vacuum in another order depending on the size of the sheets  2  relative to the length of the conveyor belts  14  and/or the feed speed or in dependence of other circumstances. 
     The vacuum control device  30  can also control the vacuum generating device V such that a vacuum is generated in a vacuum opening  17 ,  18  or  19  when front portions of a sheet  2  during transport by the conveyor belt  14  reach over this vacuum opening  17 ,  18  or  19  and such that the generation of vacuum is interrupted when said front portions of the sheet  2  leave their positions over said vacuum opening  17 ,  18  or  19 . Furthermore, the vacuum control device  30  can control the vacuum generating device V such that a vacuum is interrupted or withdrawn in such a vacuum opening  19  within the extension of which rear portions of a sheet  2  are situated when front portions of the sheet  2  are brought to leave the conveyor belt  14  transporting said sheet  2 , e.g. when said sheet is turned over by the conveyor belt to the stacking device  11 . These functions may alternatively be obtained by a particular shape and/or location of the vacuum openings  17 – 19 . 
     Two conveyor belts  14  may lie so close to each other that the sheets  2  can have such a size that they during transport on one of the conveyor belts  14 , at least during a part of their transport along said conveyor belt  14 , move above the other conveyor belt  14 . At such a relative location of the conveyor belts  14 , it is important that the vacuum control device  30  controls the vacuum to be present only in that conveyor belt  14  which transports the sheets, and that a vacuum is not present in the other conveyor belt  14 . Hereby, it is ensured that the transport of the sheets  2  with one conveyor belt  14  is not disturbed by a vacuum in the other conveyor belt  14 . 
     The transport device  9  of the plant  1  includes several, e.g. six conveyor belts  9   a  located beside each other. These conveyor belts  9   a  extend around vacuum means  9   b  illustrated in  FIG. 8 . Each vacuum means  9   b  has a first vacuum opening  9   c  and a second vacuum opening  9   d  which are elongated and located in a row after each other in the main transport direction A of the sheets  2 . The first vacuum opening  9   c  has closed end portions  9   ca  and  9   cb , while the second vacuum opening  9   d  has a front end portion  9   da , seen in the main transport direction A, which is closed, but an open rear end portion  9   db.    
     The vacuum means  9   b  form part of a vacuum generating device VA which is adapted to generate a vacuum in the vacuum openings  9   c ,  9   d  and thereby in vacuum holes  9   e  provided in the conveyor belts  9   a  such that sheets  2  transported to the transport device  9 , are engaged by the conveyor belts  9   a  and maintained in contact therewith for transport through said transport device  9 . 
     The illustrated embodiment of the vacuum generating device VA includes a compressed-air generating device  9   f  which cooperates with an ejector  9   g  at each vacuum opening  9   c ,  9   d . The ejector  9   g  can be located in the vacuum means  12  and/or  13  which preferably is elongated and about which the conveyor belt  9   a  runs. Hereby, the ejector  9   g  is situated close to the conveyor belt  9   a , which, inter alia, provides for a simple construction, since there is no need for long channels or passages between the ejector  9   g  and the conveyor belt  9   a . At the illustrated embodiment, the ejector  9   g  is provided in a vacuum means  12  and/or  13  in the form of an elongated rule including said rolls  15 ,  16  around which the conveyor belt  9   a  runs. Thus, the compressed-air generating device  9   f  is at each vacuum opening  9   c ,  9   d , through a channel  9   h , connected with an ejector  9   g  such that a jet D of compressed air with high speed is formed in an ejector passage  9   k . This jet D of compressed air generates a vacuum in a vertical hole  9   m  which at the top communicates with each vacuum opening  9   c ,  9   d , whereby a vacuum, i.e. a negative pressure, is generated also in each vacuum opening  9   c ,  9   d  as well as in vacuum holes  9   e  communicating therewith, in the conveyor belt  9   a . The compressed air leaves the ejector  9   g  through a compressed-air outlet  9   n.    
     There may be a device generating a vacuum at the beginning of a vacuum means  9   b , seen in the main transport direction A, while it generates less or no vacuum at the end of the vacuum means  9   b , such that a vacuum is generated in vacuum holes  20  in a conveyor belt  14  running around the vacuum means  9   b  when said vacuum holes  20  pass the beginning of the vacuum means  9   b , but less vacuum or no vacuum is generated when said vacuum holes  20  pass the end, of the vacuum means  9   b.    
     Since the first vacuum opening  9   c  has closed end portions  9   ca ,  9   cb  while the second vacuum opening  9   d  has one open end portion  9   db , the vacuum effect can be brought to be larger in the first vacuum opening  9   c  than in the second vacuum opening  9   d . Since the open end portion  9   db  of the second vacuum opening  9   d  is situated at a rear end  9   ba  of the vacuum means  9   b , i.e. that end which—seen in the main transport direction A—is situated where the sheets  2  leave the conveyor belt  9   a , the vacuum effect will be less at the rear end portion  9   db  of the vacuum opening  9   d  than at its front end portion  9   da . Hereby, it is achieved that the vacuum effect is at its largest at the beginning of the vacuum opening  9   d , but diminish or decrease towards its end portion  9   db , and hereby, the sheets  2  transported over the vacuum openings  9   c ,  9   d  by the conveyor belts  9   a  are affected by an ever decreasing vacuum until the leave the conveyor belts  9   a . This effect can be further improved while the vertical hole  9   m  of the vacuum generating device VA at the second vacuum opening  9   d  is located closer to the first end portion  9   da  of said second vacuum opening  9   d  than to its second end portion  9   db . The vacuum means  9   b  may of course have another number of vacuum openings than two. 
     At the embodiment illustrated in  FIG. 2 , the stacking device  11  includes a sheet conveyor  11   a  for receiving laterally moved sheets  2  from the device  10  for lateral movement, and for transferring said sheets to a first or second stacking table  11   b ,  11   c  such that stacks  2 A,  2 B of sheets according to  FIG. 3  are formed thereon. The stacking device  11  further includes a first elevator device  11   d  which can receive one stacking table  11   b  or  11   c  at a time and lower it successively while said stacks  2 A,  2 B of sheets are formed. The first elevator device  11   d  can lower the stacking table  11   b  or  11   c  to a stack conveyor  11   e  which is adapted to transport the stacks  2 A,  2 B away from the respective stacking table  11   b ,  11   c . The stack conveyor  11   e  includes a number of conveyor belts  11   f  and each stacking table  11   b ,  11   c  has elongated holes  11   g  for said conveyors  11   f . The first elevator device  11   d  can lower each stacking table  11   b ,  11   c  so far relative to the stack conveyor  11   e  that its conveyor belts  11   f  from below will project upwards through the holes  11   g  in the respective stacking table  11   b ,  11   c . Hereby, stacks  2 A,  2 B lying on the respective stacking table  11   b ,  11   c  will instead locate themselves on the conveyor belts  11   f  (see  FIG. 14 ), which will feed them away from the stacking table  11   b ,  11   c.    
     A lower transfer device  11   h  is provided for moving the stacking tables  11   b ,  11   c  from the first elevator device  11   d  to a second elevator device  11   k , which is adapted to receive said stacking tables. This may occur when the respective stacking table  11   b ,  11   c  has been released from the stack conveyor  11   e , and may be carried through by said first elevator device  11   d  raising the stacking table  11   b ,  11   c  somewhat until it goes free from the stack conveyor  11   e . The second elevator device  11   k  is provided to raise the respective stacking table  11   b ,  11   c  from its cooperation with the lower transfer device  11   h  in upwards direction to a ready position BL, in which it is located just beneath the sheet conveyor  11   a  (see  FIG. 11 ). During this movement, the stacking table  11   b  and  11   c  respectively, has also been brought to cooperate with an upper transfer device  11   m . This is done by providing the upper transfer device  11   m  with at least one downwardly directed driver  11   n , which will be inserted into a hole  11   p  in the respective stacking table  11   b ,  11   c  by raising said stacking table to its ready position. 
     The upper transfer device  11   m  is provided to move the respective stacking table  11   b ,  11   c  with high speed in a direction in parallel or substantially in parallel with the direction in which the sheet conveyor  11   a  transports the sheets  2  (arrow R;  FIG. 12 ) from the ready position BL to a receiving position ML ( FIG. 13 ). During this movement, the respective stacking table  11   b ,  11   c  divides or cuts the flow AS 1  and/or AS 2  of sheets between two sheets  2  such that the stacking on a stacking table is interrupted and stacking commences on the stacking table which has been moved into said flow AS 1  and/or AS 2  of sheets. 
     During said movement of the respective stacking table  11   b ,  11   c  into the flow AS 1  and/or AS 2  of sheets, the stacking table  11   b ,  11   c  in question will be brought to cooperate with the first elevator device  11   d . When stacking commences on the stacking table which has been moved into the flow AS 1  and/or AS 2  of sheets, this stacking table is lowered by the first elevator device  11   d , and is thereby moved out of cooperation with the driver  11   n  of the upper transfer device  11   m . The upper transfer device  11   m  may then be reset to receive a stacking table  11   b  which is raised to ready position BL by the second elevator device  11   k.    
     In  FIGS. 11–14 , the operation of the stacking device  11  is illustrated in more detail. Thus,  FIG. 11  illustrates stacking of sheets  2  on the first stacking table  11   b , which is located in a receiving position ML and which is gradually lowered. The second stacking table  11   c  is set in its ready position BL and cooperates with the upper transfer device  11   m.    
     In  FIG. 12  it is shown how the other, second, stacking table  11   c  is moved in the direction of arrow R by the upper transfer device  11   m , whereby said second stacking table  11   c  is moved or transferred in between two sheets  2  in the flow AS 1  and/or AS 2  thereof, which flow is then divided such that stacking of sheets  2  on the first stacking table  11   b  is interrupted and stacking of sheets commences on the second stacking table  11   c  without having to interrupt the flow AS 1  and/of AS 2  of sheets. 
     In  FIG. 13  it is shown how the first stacking table  11   b  is lowered with finished stacks  2 A,  2 B and how stacking is carried through on the second stacking table  11   c . The second stacking table  11   c  has been lowered out of engagement with the upper transfer device  11   m , i.e. it is situated beneath the driver  11   n.    
     In  FIG. 14  it is shown how the first stacking table  11   b  has been lowered relative to the stack conveyor  11   e  such that the stacks  2 A,  2 B have been placed from above on the conveyor belt  11   f  of the stack conveyor  11   e  for transport thereby of the stacks  2 A,  2 B away from the first stacking table  11   b . Additionally, the upper transfer device  11   m  has been reset such that it can be brought to cooperate with the first stacking table  11   b  when said stacking table is raised to the ready position BL. 
     In this way, both stacking tables  11   b ,  11   c  can be brought to interrupt the flows AS 1  and AS 2  of sheets alternatingly, such that one of the stacking tables  11   b ,  11   c  always is in receiving position ML for receiving sheets  2 , while the other stacking table  11   b ,  11   c  is in a ready position BL for quick transfer or movement into a flow of sheets. 
     The elevator devices  11   d ,  11   k  and the transfer devices  11   h ,  11   m  may include endless belts for movement of the stacking tables  11   b ,  11   c , but said devices may of course be designed in other ways. If the upper transfer device  11   m  has a driver  11   n , said driver may be located on the endless belt of the transfer device  11   m.    
     There may of course be more than two stacking tables in the stacking device  11  if necessary. 
     In  FIG. 10  it is illustrated that the transport device  9  can transport or feed sheets  2  in at least two flows AS 1  and AS 2  of sheets. The sheets  2  in the flow AS 1  thereof are transported to a first pair TB 1  of conveyor belts and the sheets  2  in the flow AS 2  thereof to a second pair TB 2  of conveyor belts for lateral movement of the sheets in each flow AS 1 , AS 2  of sheets relative to each other, and thereby form two different groups of stacks beside each other. 
     The conveyor belts  14  in each pair TB 1 , TB 2  thereof are mounted such that an angle between each conveyor belt  14  and a centre line CL between said conveyor belts are the same or substantially the same. The pairs TB 1 , TB 2  of conveyor belts are located relative to each other such that their centre lines CL—seen in the main transport direction A—diverge. The angle δ between said centre line CL and the main transport direction A is preferably larger than 2° and less than 30°. 
     Since the pairs TB 1 , TB 2  of conveyor belts are mounted with their centre lines CL making an angle δ relative to each other, it is possible to form two groups of stacks beside each other and if there are more than two pairs of conveyor belts, more than two groups of stacks can be formed beside each other. 
     By operating both conveyor belts  14  in each pair TB 1 , TB 2  thereof, it is possible to form more such groups of stacks beside each other, where each group of stacks contains several, relative each other laterally displaced stacks  2 A,  2 B. By operating only one conveyor belt  14  in at least one pair TB 1  and/or TB 2  of conveyor belts, several groups of stacks can be formed beside each other, where the sheets  2  are not laterally displaced relative each other within the group of stacks. 
     The device described above may vary within the scope of the appended claims with regard to its operation and construction. As examples of not further described alternatives, it should be mentioned that the vacuum generating device V and/or VA can generate a vacuum in other ways than with compressed air and with other devices than ejectors  24  and  9   g  respectively, and that the vacuum interrupting or vacuum withdrawing device  31  can interrupt the presence of vacuum in other ways than with compressed air and when interrupting or withdrawing a vacuum, this can be carried through in other ways than with compressed air. Also, each vacuum means  12 ,  13  and  9   b  respectively, may be provided with another number of vacuum openings  17 ,  18 ,  19  and  9   c ,  9   d  respectively, than the number shown in the drawings, and said vacuum openings may preferably be elongated and situated in a row, in line with each other. Furthermore, it should be mentioned that the device  10  for lateral movement can be located in another position in the plant  1  than the one shown, it may include another suitable number of conveyor belts  14  than shown and it may include conveyor belts  14  which instead are mounted above a friction plate and which transport and move laterally the sheets on said friction plate. It should finally be mentioned that the compressed-air generating devices  23  and  9   f  respectively, may be one and the same device. 
     Also, in the plant  1  there may be more than one transport device  9  and/or may said transport device or transport devices  9  be located in other places in the plant  1 . Each transport device  9  may include six or another suitable number of conveyor belts  9   a  with associated vacuum means  9   b.