Abstract:
A device and method for providing a supply of single sheets wherein each single sheet has a varying thickness. The present invention includes a stack of single sheets that are supported on a lifting platform. The lifting platform includes a compensation device for leveling the stack by compensating for the varying thickness of each single sheet.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device and a method for providing a supply of single sheets, and particularly for its utilization in a printer or copier. 
     FIELD OF THE INVENTION 
     Applications for printers or copiers or the like exist for providing a supply of single sheets, such as single sheets of paper, wherein the thickness of a single sheet varies. For example, when a strip-shaped and preprinted stick-on label is applied to a single sheet, the thickness considerably increases in the area where the stick-on label is applied. Generally, the single sheets are rectangular, wherein the stick-on labels include a strip extending in the direction of the sheet width. As a result, the increased thickness makes it difficult to remove an individual single sheet from the stack during the application of providing the supply of single sheets. 
     An example of this difficulty exists during printing operations that require the single sheets to be removed along the direction of the sheet width for increased throughput of the single sheets. In this case, the longitudinal edge of the uppermost single sheet in the stack has a visible bend due to the varying thickness across the single sheets. As a result of this bend, the throughput of single sheets may decrease because of a paper jam or because single sheets are not individually dispensed from the stack. 
     U.S. Pat. No. 4,942,435 discloses a device for providing a supply of single sheets wherein the single sheets have a greater thickness at one side due to a mylar strip for supporting margin perforations. The uppermost single sheet is removed from the stack in a lengthwise direction during printer operations. This device further includes a compensation device that has two movable plates. These plates are flexibly connected to one another wherein one plate is rigidly supported and the other block is supported by springs. The movable plates are aligned for positioning the uppermost single sheet in a flat or planar position from which it can be easily removed along its lengthwise direction. The device further discloses that the movable plates can be replaced by stationary plates for positioning the uppermost single sheet. 
     German Patent Document DE-A-26 17 334 discloses an insertion device for a pre-folded continuous stock web. The insertion device includes compensation elements for positioning the uppermost single sheet of the paper stack in an optimally planar position. 
     German Patent Document DE-A-27 12 571 discloses a depositing device for a pre-folded continuous stock web in a forms stacker. This device includes a movable plate that upwardly supports the stack of single sheets so that the uppermost sheet is optimally positioned in a planar or flat position. Each of the single sheets has a varying thickness due to a margin region. 
     International Patent Documents WO-A-98/18051 and WO-A-98/18054 have the same applicant as the present invention. These patent documents disclose output devices for single sheets. The output devices include single sheets that form of a stack. The single sheets are removed and fed into a printer or copier device. 
     German Patent Document DE-UI 93 00 292.0 discloses a magazine for storing flat articles made of paper, such as photo sleeves. The magazine has two areas. The first area includes those parts of the photo sleeves that are a single-layer wherein the second area includes parts of the photo sleeves that are in two-layers. The two areas include supporting surfaces that are mechanically decoupled from each other. The stack regions of varying thickness are positioned at different levels as a result thereof. 
     German Patent Document DE LP 532 292 discloses a stack table of a suction pump sheet feeder for printers wherein a plurality of seating boards are adjustable in height. As a result, the positions of the print sheets can be adapted to a suction rod with respect to different suction points in order to achieve improved suction properties. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a device and method for providing a supply of single sheets that is operationally reliable for removing or dispensing single sheets from a stack of single sheets, wherein each of the single sheets has a varying thickness. 
     An object of the present invention is to optimally position all uppermost single sheet of the stack in a planar or flat position. 
     An object of the invention is to increase the throughput results of the single sheets within a printer, a copier or the like wherein the single sheets are dispensed along a direction of a sheet width. 
     A further object of the invention is to provide a device of simple construction that is easily incorporated within presently existing paper supply applications, such as printer and copier applications. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side sectional view of a paper supply device. 
     FIG. 2 shows a side sectional view paper supply device with a lifted compensation element. 
     FIG. 3 shows a side sectional view paper supply device with an extended support element. 
     FIG. 4 shows a top view of a single sheet with a strip-shaped stick-on label. 
     FIG. 5 shows a schematic view of a high performance printer. 
     FIG. 6 shows a schematic view of a paper input device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The printer shown in FIG.  5  and the input device described in FIG. 6 are described in International Patent Documents WO-A-98/18051 and in WO-A-98/18054. 
     FIG. 5 shows a high performance printer  110  for fast printing of single sheets of paper. The high performance printer  110  contains a first lower printing unit D 1  and a central upper printing unit D 2 . According to the known electro-graphic method, both printing units D 1  and D 2 , work at the same transfer printing speed. Fixing mechanisms, which are schematically indicated in FIG. 1 by two pairs of rollers  112  and  114 , follow the printing units D 1  and D 2 . A paper input  116  is connected to the performance printer The paper input  116  includes a number of paper input compartments A, B, C and D. Each compartment includes a supply of single sheets and an external paper input channel  126  in which single sheets can be supplied from the outside. Single sheets are supplied to an input section  128  via a conveying channel  127 . At the output side, a paper output  130  is connected to the high performance printer  110 . The paper output  130  contains a number of output receptacles  132 ,  134  and  136 . In addition, two output channels  138  and  140  are provided through which single sheets are dispensed to further processing stations. The high performance printer  110  transfers the printed single sheets to the paper output  130  through the output section  142 . 
     Conveying paths for conveying or transferring the single sheets are disposed within the high performance printer  110 . These paths provide for a variety of different operating modes of the high performance printer. The transfer printing conveying paths  144  and  146  connect to the respective printing units D 1  and D 2 . The conveying paths  144  and  146  have drives that adjust the transfer printing speed of each path to correspond with their respective printing units D 1  and D 2 . In addition, the transfer paths  144  and  146  are interconnected by a connection channel  148 . The conveying path of the first printing unit D 1  also includes a ring R 1  located by a supply channel  150 . Single sheets can be supplied from the input section  128  to the second transfer conveying path  146  via the supply channel  150 . Similarly, the conveying path for the second printing unit D 2  includes a ring R 2  located by a discharge channel  152 . Single sheets that are printed by the printer D 1  are supplied to the output section  142  via the ring R 2 . 
     A first shunt W 1  is arranged between the input section  128 , the first transfer printing conveying path  144  and the supply channel  150 . The shunt W 1  provides for single sheets from the input section  128  to be selectively supplied to the first transfer printing conveying path  144  or to the supply channel  150 . Alternatively, single sheets transferred on the supply channel  150  in the direction of the shunt Wl are supplied to the first transfer printing conveying path  144 . 
     Further, a second shunt W 2  and a third shunt W 3  are arranged at the ends of the connection channel  148  and respectively connect to the adjacent conveying paths  144 ,  148 ,  152  and  146 ,  148 ,  150 . A fourth shunt W 4  is situated in close proximity to the output section  142  and connects to the adjacent conveying paths. The paper output  130  includes a fifth shunt W 5  that performs as a turnover device. The high performance printer further includes an ejection mechanism  154  for removing single sheets that are supplied to the ejection mechanism  154  via a shunt W 6 . 
     FIG. 6 shows the paper input  116  of FIG. 5 in greater detail. It has a number of input compartments A through D and an external feeder E. Stacks of single sheets of paper  1   a  through  1   d  are placed in their respective input compartments A through D. The paper stacks  1   a  through  1   d  are pushed upwardly along a direction P. As a result, the paper stacks are pushed against the sheet dispensing devices  4   a  through  4   d  by the lifter devices  2   a  through  2   d . In addition, sensors  5   a  through  5   d  are connected to their respective input compartments A through D. The sensors  5   a  through  5   d  output a signal as soon as the respective compartments A through D are approximately empty of their respective paper stacks. Further, a sensor S is connected to the bottom of each compartments A through D. The sensor S outputs a signal when the respective compartment is also empty. 
     Single sheets are removed from each respective input compartment by a dispensing device  4   a  through  4   d  and then fed to a transfer mechanism  6   a  through  6   d  and  7   a  through  7   d . Due to the transfer mechanism, the single sheets are then transferred on paths a through d and are finally accepted by an additional conveying mechanism  8 . Subsequently, the sheets are transferred to a sheet transfer point  100  from which the sheets are transferred to a print mechanism and copy mechanism (not shown) by the paper output mechanism. 
     A supply of single sheets that is fed into the external feeder E are transferred via the conveying mechanism  7   e  along a conveying path e until they are accepted by the conveying mechanism  7   d  that is located at the end of the conveying path d. Light sensors  9  are provided at different locations along the conveying paths a through e for monitoring this transfer. 
     During an automatic sheet output, a single sheet, which was removed by the sheet dispensing device  4   a  from a sheet stack  1   a  of compartment A, is transferred along the conveying path by the conveying mechanism  6   a ,  7   a  and  8  to the sheet transfer point  100 . Similarly, single sheets that were removed from the input compartments B, C and D are conveyed along the conveying path b through d via the conveying mechanism  6   b ,  7   b ,  8  and  6   c ,  7   c ,  7   b ,  8  and  6   d ,  7   d ,  7   c ,  7   b  and  8  to the sheet transfer point  100 . 
     In relation to FIGS. 5 and 6, FIG. 1 shows the construction of a paper supply device that is utilized in a variety of different printer, copier or other like applications, such as the high performance printer application as illustrated in FIGS. 5 and 6. In this application, the paper supply device is located in one or a number of the input compartment of the high performance printer of FIGS. 5 and 6. 
     The paper supply device includes a stack  10  of rectangular single sheets. Each of the single sheets has longitudinal side that extends in the direction L 1  and a latitudinal side that extends in direction L 2 . In relation to the high performance printer of FIGS. 5 and 6, the stack  10  corresponds to the stacks  1   a ,  1   b ,  1   c ,  1   d  in the compartments A, B, C, D of FIG.  6 . 
     In addition, the single sheets of the stack  10  have a strip-shaped stick-on label that is located in a section or strip region  12 . The stick-on label almost completely covers the single sheet in a latitudinal direction L 2 . The stick-on label has a constant thickness. As well as the strip region  12 , each of the single sheets of the stack  10  has a section or non-strip region  14  in which the single sheet does not have a stick-on label. Therefore, the stack  10  is considerably thicker in the area or strip region  12  than in the area or non-strip region  14 . 
     The stack  10  is supported by a lifting platform  16  that has a bottom plate  18 . The stack  10  is further held in place by a paper width adjuster  15 . The lifting platform  16  moves along a direction P in both an upward and downward direction. During printing, the height of the lifting platform  16  is adjusted such that the uppermost single sheet is pushed against the dispensing device, such as the dispensing device  4   a ,  4   b ,  4   c , and  4   d  of the high performance printer  110  which removes the uppermost single sheet of the stack  10  in the latitudinal direction L 2 . On the other hand, the lifting platform  16  moves in the downward direction away from the dispensing device when the stack of single sheets is first placed or loaded on the lifting platform. 
     The lifting platform  16  further includes a compensation device  20  that is disposed between the bottom  18  and the stack  10  of single sheets. The compensation device  20  supports the lowermost single sheet of the stack  10  for positioning the height of the strip region  12  below the height of the non-strip region  14  that has a lesser height or thickness than the strip region  12 . Thus, the uppermost single sheet is held approximately in a planar or flat position so that each single sheet of the stack is individually removed from the stack by the dispensing device. 
     The compensation device  20  further includes a stationary plate  22  that is rigidly connected to four supports  24  (FIG. 1 only shows two supports  24 ). The stationary plate  22  supports the non-strip region  14  of the single sheets. In section  12 , the stack  10  is supported by a great number of lamellae  26  that extend in the direction L 2 . The lamellae are movably interconnected to form a movable plate. On both sides and at both ends, the lamellae  26  are supported by bearing legs  28  (only one can be seen in FIG.  1 ). The upper edge of the bearing legs  28  has a concavely arced surface that the lamellac  26  conform thereto. The bearing legs  28  are rigidly interconnected by a dog element  30  and are swivelled around a rotational axis  32 . The compensation devices also includes a lever  34  that is rotatably mounted around a rotational axis  36 . The rotational axis  36  includes a pintail that has a pillow block or bearing block  38 . The pillow block  38  rests in a stationary position on the bottom plate  18  of the lifting platform  16 . 
     The lever  34  further includes a first lever arm  40 , whose end abuts against the end of a stationary detent  42  relative to the printer housing during an upward movement of the lifting platform  16 . This detent  42  is adjustably mounted and is incorporated in a fastening block  44 . The other end of the lever  34  includes an eccentric  46  and has a control surface at its upper side. The control surface engages the dog element  30  during an upward movement of the eccentric  46 . 
     Turning to FIG. 1, a support element is connected to the bearing legs in section  48  and engages or supports a bottom side of the lamellae  26 . The support element  50  includes a pressure spring  52  that acts to move the support element  50  upward. 
     Turning to FIGS. 2 through 6, the device shown in FIG. 1 operates to provide a supply of single sheets. As previously discussed, the paper supply device is utilized in a variety of different printer, copier or like applications. An exemplary example of the device is within the high performance printer  110 . In this application, the supply device is provided in at least one of the input compartments A, B, C, D of the printer (FIGS.  5  and  6 ). The supply stacks  1   a ,  1   b ,  1   c ,  1   d  (FIG. 6) are thereby referred to as supply stack  10  in FIG.  1 . The supply stacks  1   a ,  1   b ,  1   c ,  1   d , move along P in an upward direction due to the lifting devices  2   a ,  2   b ,  2   c  and  2   d  that include the lifting platform as shown in FIG.  1 . The lifting platform continually moves the supply stack  10  upward until it pushes against the dispensing device  4   a ,  4   b ,  4   c , or  4   d  as the height of the stack decreases. 
     Returning to the FIGS. 2 and 3, the lever arm  40  of the lever  34  is impeded by the detent  42  during its upward movement in the direction P and rotates around a rotational axis  36 . The detent  42  is thereby fixed to the device at the printer and at the respective input compartment A, B, C, D, and therefore does not move during the upward movement. As a result, during the upward movement in the direction P of the lever  40 , the eccentric  46  moves upwardly. As a result, its upper, arced control surface pushes against the dog element  30  and pivots the bearing legs  28  around the rotational axis  32 . Therefore, the lamellae  26 , which at least partially rest on the upper edges of the bearing legs  28 , move upward, so that the thickness in the area  12  of the stack  10  is compensated and so that the uppermost single sheet are positioned approximately in a planar or flat position. In addition, the support element  50 , which is moved upward together with the bearing legs  28 , lifts a part of the lamellae  26  upward as a result of the spring force of the spring  52 . This movement results because the weight of the stack  10  in the section  12  is reduced when the stack height is decreased. When the stack weight is reduced, the support element  50  acts upon section  12  or the strip region due to the force exerted by the spring  52 . The spring force  52  is transmitted to the strip region through the lamellae  26 . The determined sag of the connected lamellae  26 , that is determined by the arch of the upper edge of the bearing legs  28 , is reduced as a result thereof. Due to the support element  50  action, the uppermost single sheet remains in a planar or flat position even as the stack height decreases. 
     As further illustrated in FIG. 3, the stack  10  includes only a few single sheets. The lifting platform  16  is moved upwardly. The lever  34  is correspondingly swivelled in a large angle and pushes the bearing legs  28  upward. Due to the reduced weight of the stack  10  in the area  12 , the support element  50  acts against the area  12  as a result of the spring force of the spring  52  and pushes the connected lamellae  26  upward, so that they almost lie in a plane. As a result, the single sheets also lie approximately in a plane and therefore are easily removed by the dispensing device. The lifting platform  16  moves downward again into a position shown in FIG. 1 when the last single sheet is removed and a new stack  10  of single sheets is placed again on the lifting platform of the paper supply device. 
     FIG. 4 shows a single sheet E that is rectangular in shape, such as a DIN A 4  shape. The single sheet also has a width L 2  and a length L 1 . A stick-on label AK is attached to the single sheet in the strip region  12 . The stick-on label has a width ranging from about 5 cm to about 7 cm. The thickness of the stick-on label AK approximately equals the thickness of the single sheet E. The single sheet E and the stick-on label AK are preferably preprinted and also preferably include fields in which data are printed during a subsequent printing. 
     The present invention is not limited to the exemplary embodiment shown in the FIGS. 1-6. For example, a rigid plate is provided instead of the interconnected lamellae  26  that are supported by the support element  50 . In addition, the strip region  12  is not located in the margin of the single sheet but rather is located in the middle of the single sheets. In this case, the movable plate  22  or the lamellae  26  are also positioned at this location. Further, single sheets are removed by the dispense device in the longitudinal direction instead of the latitudinal direction. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.