Abstract:
The sheet transporting device of the invention includes: a transferring device ( 64 ) adapted to transfer a sheet ( 30 ), a conveying device ( 66; 66 A) for conveying a sheet transferred from the transferring device ( 64 ) onto the conveying device, and a controlling means ( 76 ) adapted to control the speed of the conveying device ( 66; 66 A) and defining a transfer cycle (CT). The controlling means ( 76 ) is adapted to slow down the conveying device ( 66 ) when a sheet is conveyed by the related conveying device and to accelerate the conveying device when no sheet is present on said conveying device. The invention can be used for the cutting devices of rotary printing machines.

Description:
[0001]    The present invention relates to a sheet transporting device. 
       BACKGROUND 
       [0002]    Devices for transporting printed products such as sheets of paper are known in the prior art. These transporting devices are used, for example, in offset printing machines in order to transport the printed sheets. 
         [0003]    These transporting devices comprise hollow conveyor rollers which have a transporting surface in contact with the sheet that is to be transported. 
         [0004]    In order to cause the sheet to adhere to the conveyor roller, the transporting surface has cavities connected to a vacuum-creating device. 
       SUMMARY OF THE INVENTION 
       [0005]    However, the printed sheet causes ink to be deposited on the transport surface and this results in poor production quality, particularly when the conveyor roller is a roller that decelerates the sheet. 
         [0006]    An object of the present invention is to improve the quality of the printed products that can be produced by the printing machine, and to do so using simple means. 
         [0007]    The present invention provides a transporting device wherein the control means are designed to slow the first conveying device when a sheet is being conveyed by the first conveying device concerned and accelerate the first conveying device concerned when there is no sheet on this conveying device. 
         [0008]    According to some particular embodiments, the transporting device may include one or more of the following features:
       during a transfer cycle the first conveying device and the transfer device have a transfer phase in which a sheet is transferred onto the first conveying device and an output phase in which a sheet is set down by the first conveying device, and the control means are designed to accelerate the first conveying device between the output phase and the transfer phase and to slow the slowing device between the transfer phase and the output phase;   the control means are designed to drive the first conveying device at a constant speed during the transfer phase and during the output phase;   the control means are designed to drive the transfer device during the transfer phase at a first transfer speed and the conveying device at a second transfer speed which differs from the first transfer speed;   the first transfer speed is higher than the second transfer speed;   the first transfer speed is equal to the second transfer speed;   the control means are designed to drive the transfer device at constant speed throughout an entire transfer cycle;   the first conveying device is a slowing device designed to slow a sheet;   the first conveying device is a conveyor, for example, a belt or chain conveyor;   the control means comprise means for identifying the position of a conveying element of the conveying device and means for generating a conveying device speed setpoint signal dependent on the identified position, for example, electronic cam means;   the transporting device comprises a second conveying device, the transfer device being designed to transfer a sheet onto each of the first and second conveying devices alternately;   the transporting device comprises a cutting device designed to cut a web into sheets and to feed the transfer device with sheets; and   the transfer cylinder is a counterpressure roller of the cutting device.       
 
         [0021]    The present invention also provides a sheet output device comprising:
       a web input;   a sheet stacking device; and   a transporting device of the aforementioned type.       
 
         [0025]    The invention also provides a web offset rotary press comprising an output device of the aforementioned type. 
         [0026]    The present invention also provides a method of transporting sheets comprising the following steps during a transport cycle:
       transferring a sheet from a transfer device to a first conveying device;   slowing the conveying device when there is a sheet placed on the conveying device; and   accelerating the first conveying device when there is no sheet on the conveying device.       
 
         [0030]    According to some particular implementations, the sheet transporting method may include one or more of the following features:
       during a transfer phase, transferring a sheet from the transfer device to the first conveying device at a transfer speed,   during an output phase, the first conveying device setting down a sheet at an output speed lower than the transfer speed,   between the transfer phase and the output phase, slowing the first conveying device, and   between the output phase and the transfer phase, accelerating the first conveying device;   during the transfer phase and/or during the output phase, the transporting method comprises the step of driving the first conveying device at a constant transfer and/or output speed;   during the transfer phase, the transporting method comprises the step of driving the transfer device at a first transfer speed and the first conveying device at a second transfer speed;   the first transfer speed is higher than the second transfer speed;   the first transfer speed is equal to the second transfer speed; and   before transferring the sheet, the transporting method comprises the step that consists in cutting the sheet from a web.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    The invention will be better understood from reading the description which will follow, given solely by way of example and made with reference to the attached drawings in which: 
           [0041]      FIG. 1  is a schematic side view of a printing machine according to the invention; 
           [0042]      FIG. 2  is a view corresponding to the view of  FIG. 1 , but of an alternative form of a printing machine according to the invention; 
           [0043]      FIG. 3  is a schematic view of the cutting and stacking device according to a first embodiment; 
           [0044]      FIGS. 4 and 5  are diagrams showing the speeds of operation of the transfer device and of the conveying device according to a first and a second mode of operation of the cutting device; 
           [0045]      FIG. 6  is a schematic view corresponding to the view of  FIG. 3  but of a second embodiment of the cutting and stacking device according to the invention; and 
           [0046]      FIG. 7  is a diagram showing the speeds of operation of the transfer device and of the conveying devices during the operation of the cutting device according to the second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]      FIG. 1  depicts a rotary printing machine according to the invention, denoted by the overall reference  2 . 
         [0048]    The printing machine  2  comprises an unwinder  4 , four printing units  6 , a traction device  8  and a cutting and stacking device  10 . The printing machine  2  further comprises a web-gripping device  14  and a powdering device  16 . 
         [0049]    The printing machine  2  could comprise any number of printing units  6 , in theory, from one to n. 
         [0050]    The unwinder  4  is designed to unwind a continuous web  18  that is to be printed. 
         [0051]    The web  18  for printing is a web of coated paper. Coated paper is a paper which has a layer of coating, for example of kaolin or chalk, that improves the mechanical or optical properties of the paper. This paper allows a high-quality printed product to be obtained. As an alternative, it is possible for the web that is to be printed to be a web of uncoated paper. 
         [0052]    The printing machine  2  defines a printing path for the web  18  between the unwinder  4 , through the printing units  6 , the web-gripping device  14 , the powdering device  16  and the traction device  8 , as far as the cutting and stacking device  10 . 
         [0053]    Each printing unit  6  comprises an inking device  20  which is provided with an ink reservoir  22  containing ink  24  which is intended to be printed onto a web of paper  18 . The ink  24  used in the context of the invention will be explained hereinbelow. Each inking device  20  further comprises an ink transfer roller  26  for transferring ink  24  to print rolls  28 . 
         [0054]    The printing units  6  comprise these print rolls  28  which are designed to print on the web of paper  18 . 
         [0055]    The cutting and stacking device  10  is designed to cut the web  18  that is to be printed into individual sheets  30  and to produce a stack of the cut individual sheets. 
         [0056]    The traction device  8  is situated downstream of the most downstream printing unit  6  and upstream of the cutting and stacking device  10 . This traction device  8  is designed to apply a set mechanical tension to the web  18  leaving the most downstream printing unit  6 . 
         [0057]    As shown in  FIG. 1 , the printing machine  2  is designed to transport the printed web  18  suspended freely and exposed to the ambient air throughout the path between the most downstream printing unit  6  and the traction device  8 , with the possible exception of the web-gripping device  14  and the powdering device  16 . Further, the printing machine  2  is also designed to transport the printed web  18  exposed to the ambient air throughout the path between the traction device  8  and the cutting and stacking device  10 . Thus, the printing machine  2  of  FIG. 1  has no drier and occupies only a small amount of space. 
         [0058]    The printing machine  2  according to the alternative form shown in  FIG. 2  differs from the printing machine  2  shown in  FIG. 1  in that between the web-gripping device  14  and the traction device  8  there is an infrared drier  32  through which the printed web  18  is conveyed. The infrared drier  32  may be replaced by some other device that dries the web by heating, such as a hot air drier. The drier  32  is small in size by comparison with the driers of the prior art. 
         [0059]    The web-gripping device  14  is designed to detect a break in the web of paper  18  and to grip hold of the free end of the web of paper  18  if this occurs. To do that, the web-gripping device  14  comprises appropriate gripper elements  34 . As an alternative, the web-gripping device  14  may be omitted. 
         [0060]    The powdering device  16  is designed to apply anti-offset powder to each of the sides of the printed web  18 . It may apply anti-offset powder to one or both sides of the printed web  18 . To do this, the powdering device  16  comprises a reservoir  36  containing powder  38  and a powdering head  40  connected to the powder reservoir  36  by a pipe  42 , for each of the sides of the web of paper  18 . 
         [0061]    The powdering device  16  is designed to apply the anti-offset powder to the web of paper  18  continuously, preferably continuously and uninterrupted over a length that corresponds to at least twice the print length. 
         [0062]    The powder  38  used for powdering the web is preferably a vegetable powder based on cornstarch, or a mineral powder. 
         [0063]    The traction device  8  associated with the other units of the press allows a web of paper to be printed and received in the cutting and stacking device  10  without drying this web of paper  12  and by evaporating the solvents from the ink. 
         [0064]    The image is printed using the ink  24  contained in the ink reservoir  22 . Advantageously, the ink  24  is a siccative ink, or a “waterless” ink, or a two-part ink. The way in which siccative inks dry is a combination of a first phenomenon known as “penetration into the medium” and of a second phenomenon known as “oxidative polymerization of the oil and resin lacquers”. 
         [0065]    Waterless inks are used with special-purpose impression plates that make it possible to define non-printing zones without resorting to the conventional lithographic method based on a pre-moistened hydrophilic surface repelling an oily ink. The use of these inks may be forseen as well as in addition to conventional siccative inks seen hereinabove, and this means that a drier can be dispensed with, or at least designed less bulky. 
         [0066]    Heat-set inks on the other hand dry through the evaporation of the mineral solvents mixed in with the resin. UV inks are dried by the polymerization of the resin under the effect of ultraviolet irradiation. 
         [0067]      FIG. 3  schematically depicts the cutting and stacking device  10 . 
         [0068]    The cutting and stacking device  10  comprises two input rollers  50 , a cutting cylinder  52  and a counterpressure roller  54 . 
         [0069]    The cutting and stacking device  10  comprises a fixed structure S or stand. 
         [0070]    The input rollers  50  are positioned upstream of the cutting cylinder  52  and of the counterpressure roller  54 . The two input rollers  50  are able to rotate about an axis A and B with respect to the fixed structure S. Each of the input rollers  50  has a shell  60  with through-holes  62 . 
         [0071]    The cutting cylinder  52  comprises a blade  53  and rotates about an axis C. 
         [0072]    The counterpressure roller  54  is able to rotate about an axis D and comprises counterpressure blocks  63  which collaborate with the blade  53  to cut the web of paper into sheets  30 . 
         [0073]    The cutting and stacking device  10  comprises a transfer device  64  and a conveying device  66 . 
         [0074]    The transfer device  64  is designed to pick up a sheet  30  from the counterpressure roller  54  and transfer it to the conveying device  66 . 
         [0075]    The transfer device  64  comprises a transfer cylinder  68  able to rotate about an axis E. The transfer cylinder  68  comprises openings  70 . 
         [0076]    The conveying device  66  comprises a conveying cylinder  72  able to rotate about an axis F. The conveying cylinder  72  comprises openings  74 . 
         [0077]    The cutting device  10  also comprises a suction device  71  designed to create suction in the openings  70 ,  74 . 
         [0078]    The cutting device  10  delimits a path for the web of paper  18  and the sheets  30  running from the input to this device  10  through, in succession, the input rollers  50 , a counterpressure roller  54 , the transfer cylinder  68 , the conveying cylinder  72  as far as a stack  31  of individual sheets  30 . 
         [0079]    The cutting device  10  comprises control means, for example, a controller  76  designed to control the speed V 66  of the conveying device  66  and the speed V 64  of the transfer device  64 . The controller  76  defines a transfer cycle for the transferring of a sheet  30 . A transfer cycle is, for example, one full revolution of the transfer cylinder. 
         [0080]    When a sheet  30  is being conveyed by the conveying device  66 , the control means  76  are designed to slow this conveying device  66 . When there is no sheet  30  on the conveying device, the controller  76  is designed to accelerate the conveying device  66 . 
         [0081]      FIG. 4  depicts a transfer cycle CT of the cutting device  10 . 
         [0082]    The abscissa axis shows the time T in a transfer cycle, therefore one rotation of the transfer cylinder  68  through 360°. The ordinate axis shows the speed V 64  of the transfer device  64  and the speed V 66  of the conveying device  66 . 
         [0083]    Thus, in a transfer cycle CT, the transfer device  64  and the conveying device  66  have a transfer phase PT in which a sheet  30  that is on the transfer cylinder  68  is transferred from the transfer device  64  onto the conveying device  66 , and an output phase PS in which the sheet  30  is set down on the stack  31  by the conveying device  66 . Furthermore, after the transfer phase PT and before the output phase PS of the same cycle, there is a deceleration phase PD during which the conveying device  66  is decelerated. Also, after the output phase PS and before the transfer phase PT of the same cycle, there is an acceleration phase PA during which the conveying device  66  is accelerated. 
         [0084]    In other words, the controller  76  is designed to accelerate the conveying device  66  between the output phase PS and the transfer phase PT and to slow the conveying device  66  between the transfer phase PT and the output phase PS of the same cycle. 
         [0085]    The controller  76  is designed to drive the conveying device  66  at a constant speed V 66  during the transfer phase PT and during the output phase PS. During the output phase PS, the conveying device  66  is driven at an output speed VS. 
         [0086]    Likewise, the controller  76  is designed to drive the transfer device  64  at a constant speed V 64  throughout an entire transfer cycle. In particular, during the transfer phase PT, the speed V 64  and the speed V 66  are identical to a transfer speed VT. 
         [0087]      FIG. 5  depicts an alternative form of the transfer cycle. In this alternative form, the controller  76  is designed so that, during the transfer phase PT, the transfer device  64  is driven at a first transfer speed VT 1  and the conveying device  66  is driven at a second transfer speed VT 2 . 
         [0088]    The speed V 64  of the transfer device  64  is, throughout one and the same cycle, higher than the speed V 66  of the conveying device  66 . Thus, the first transfer speed is higher than the second transfer speed. 
         [0089]    In particular, the conveying device  66  is a slowing device designed to slow a sheet. Thus, the conveying cylinder is a slowing cylinder. 
         [0090]    The controller  76  is preferably means employing ECAM (that is to say electronic cam) technology. The controller is therefore designed to control the speed of each of the transfer  64  or conveying  66  devices according to the position of the conveying element of this device. The conveying element is either a cylinder, for example the cylinder  68 , or a belt or band. 
         [0091]    When the conveying element is a cylinder, the controller  76  is designed to identify the angular position of the cylinder and to control the speed according to this position. The controller advantageously comprises a processor connected to a sensor that senses the angular position of the cylinder and a memory connected to the processor. The memory contains information that allows the angular position information to be converted into information representing a speed setpoint for the corresponding cylinder. The processor has means of transmitting the speed setpoint to a speed regulator. 
         [0092]      FIG. 6  depicts a schematic view of a second embodiment of the cutting and stacking device  10  according to the invention. 
         [0093]    In what follows, only differences by comparison with the first embodiment will be explained. Elements that are analogous bear the same references. 
         [0094]    This cutting and stacking device  10  comprises a cutting cylinder  52  and a counterpressure roller  54 . The transfer device  64  comprises the counterpressure roller  54  such that the transfer cylinder  68  consists of the counterpressure roller. 
         [0095]    Moreover, the transporting device comprises a first  66 A and a second  66 B conveying device, each of which is a slowing device. The counterpressure roller  54  is therefore designed to feed each of the first  66 A and second  66 B conveying devices directly. 
         [0096]    Each conveying device  66 A,  66 B comprises a conveying cylinder  72 . Each cylinder  72  has openings  74 . 
         [0097]    Each of the first conveying device  66 A and second conveying device  66 B comprises a reduced-pressure chamber extending over a first angular field α and a raised-pressure chamber extending over a second angular field β. 
         [0098]    Each of the conveying devices  66 A,  66 B comprises an ambient chamber extending over a third angular field γ. 
         [0099]    Each of the chambers is connected to the openings  74  in the corresponding angular field. 
         [0100]    The controller  76  is designed to control the speed of each of the conveying devices  66 A and  66 B and that of the transfer device  64 . 
         [0101]    The transfer device  64  is designed to transfer a sheet  30  onto one  66 A and the other  66 B of the conveying devices alternately. 
         [0102]    The transporting device defines a transfer cycle which consists of the transfer of two successive sheets  30 . 
         [0103]      FIG. 7  is a diagram showing the operating speeds of the transfer device  64  and of the conveying devices  66 A,  66 B during operation of the cutting device according to the second embodiment. 
         [0104]    The abscissa axis shows the time T in a transfer cycle CT. The ordinate axis shows the speed V 64  of the transfer device  64 , the speed V 66 A of the first conveying device  66 A and the speed V 66 B of the second conveying device  66 B. 
         [0105]    Over a transfer cycle CT, the first conveying device  66 A and the transfer device  64  have a transfer phase PT 1  in which a sheet  30  is transferred from the transfer device  64  onto the first conveying device  66 A, and an output phase PS 1  in which a sheet  30  is set down by the first conveying device  66 A onto the first stack  31  of sheets. 
         [0106]    Further, after the transfer phase PT 1  and before the output phase PS 1  of the same cycle, there is a deceleration phase PD 1 . Also, after the output phase PS 1  and before the transfer phase PT 1  of the same cycle, there is an acceleration phase PA 1  of the first conveying device. Unlike in the first embodiment, the acceleration phase PA 1  is shorter than the deceleration phase PD 1 . Thus, the sheet  30  is slowed with a relatively low deceleration, limiting the marking on the paper. 
         [0107]    Also, over a transfer cycle CT, the second conveying device  66 B and the transfer device  64  have a transfer phase PT 2  in which a sheet  30  is transferred from the transfer device  64  onto the second conveying device  66 B and an output phase PS 2  in which a sheet  30  is set down by the second conveying device  66 B onto the second stack  31  of sheets. 
         [0108]    Further, after the transfer phase PT 2  and before the output phase PS 2  of the same cycle there is a deceleration phase PD 2  of the second conveying device  66 B. Also, after the output phase PS 2  and before the transfer phase PT 2  of the same cycle, there is an acceleration phase PA 2  of the second conveying device  66 B. Unlike in the first embodiment, the acceleration phase PA 2  is shorter than the deceleration phase PD 2 . Thus, the sheet  30  is slowed with a relatively low deceleration, limiting the marking on the paper. 
         [0109]    Feeding the two conveying devices  66 A,  66 B alternately also allows the sheets to be slowed with a low deceleration for a given sheet production rate. 
         [0110]    During the transfer phases PT 1  and PT 2  and during the output phases PS 1  and PS 2 , the controller  76  is designed to drive the conveying devices  66 A,  66 B at a constant transfer speed VT and a constant output speed VS. 
         [0111]    By way of an alternative that has not been depicted, the conveying device  66 ,  66 A,  66 B is a conveyor, notably a belt or chain conveyor. In this case, the conveying device has no cylinder. 
         [0112]    The term “speed” means the speed of the element in contact with the sheet  30 . In the case of the transfer cylinder  68 , the speed is the circumferential speed of this transfer cylinder. In the case of the conveying cylinder  72 , the speed is the circumferential speed of this conveying cylinder. When the transfer and/or conveying devices comprise conveyor belts, the corresponding speed is the speed of the belt. 
         [0113]    In general, a transfer cycle is the time that elapses between a given configuration of the transfer device and of the conveying device.