Abstract:
A device for printing stock such as pieces of mail in postage meters and/or addressing machines. A guide plate, along which the stock slides, is inclined relative to the vertical and has a recessed region for an ink jet printing device with at least one print head. A conveyor advances the stock along the guide plate. The recessed region includes at least one cutout and a downstream region of the guide plate is so far recessed from a bearing surface for the stock that there is no contact with the latter in that location. That ensures sufficient penetration time for ink and prevents smearing of the printed image. The device improves the printing technology and simplifies transport of the piece of mail. The simple construction ensures precise feeding of the stock and a clean printed image.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a division of copending application No. 08/791,629, filed Jan. 31, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The invention relates to a device for printing to stock, in particular a piece of mail in postage meters and/or addressing machines. 
     With such devices, the stock is guided past a printing device and the postage indicia or address is printed in a single pass. 
     The stock is typically guided past the printing device while lying flat as is seen in U.S. Pat. No. 5,467,709, for example, or on edge as is seen in U.S. Pat. No. 5,025,386, for example. 
     In each case, it is important to ensure that the stock and the printing device are brought into a defined position relative to one another so that the mark is printed in the intended location and with sufficient quality. 
     In the case of horizontal transport of the stock, a relatively large bearing surface, corresponding to the largest stock format to be printed, is required, thus the machine has a correspondingly large footprint. 
     In the device disclosed in U.S. Pat. No. 5,467,709, an ink jet print head provides contactless printing. The piece of mail is fed between a driven conveyor and spring-mounted pressure rollers, whereby the piece of mail rests against a longitudinal guide plate. The longitudinal guide plate has a cutout matching the conveyor and a rectangular cutout for the ink jet print head. A row of nozzles in the print head run along the diagonal of the cutout. The conveyor, the longitudinal guide plate and the ink jet print head are located above the piece of mail. Spring-mounted pressure rollers and a spring-mounted pressure roller located in the print area are located below the piece of mail. 
     The spring travel of the pressure rollers and the pressure plate corresponds to the maximum thickness of the piece of mail, which can vary between 2 mm and 20 mm. 
     The spring force must be appropriate for the entire range of weights of pieces of mail, approximately 20 to 1000 g, and must also ensure that the piece of mail is held sufficiently planar in the area of the cutout for the print head. 
     Contactless ink jet printing requires that the smallest possible distance be maintained between the stock and the ink jet print head. That both minimizes the effects of inaccurate ink spray and prevents the stock from contacting the nozzle surface, thus preventing smearing. 
     However, there is still a risk of smearing when the piece of mail leaves the area of the cutout and inevitably glides along the longitudinal guide plate. 
     These conditions are difficult to maintain when rapidly processing pieces of mail of varying dimensions. In other words, the rapid processing does not allow the ink to dry prior to further transport following the imprint. 
     The prior art also discloses a postage meter, as is seen in U.S. Pat. No. 5,025,386, in which the piece of mail is carried on edge and slightly inclined on a rotating conveyor. The pieces of mail rest against a guide block which has a print window. A thermal print head with which the postage indicia is printed on the piece of mail can be moved laterally and vertically within the print window. 
     The size of the print window must be adapted to the maximum length and width of the printed image. 
     The individual piece of mail is transported to the print window, then stopped and pressed through the use of a pressure plate against the guide plate or the print window. The pressure plate is driven by a motor through a toothed gearing and crankshaft. It is a relatively complex mechanism and significant counterpressure must also be provided for thermal printing. 
     After printing, the piece of mail is released and transported away. It is clear that only a low throughput is possible with such an intermittent mode of operation. Positioning of the thermal print head is complex. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a device for printing stock in non-vertical orientation, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which provides simplified transport of a piece of mail and improved printing technology. It is furthermore an object of the present invention to create a device for transporting stock which ensures precise feeding of the stock and a clean printed image through the use of a simple construction. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a device for printing to non-vertical stock, in particular a piece of mail in a postage meter or addressing machine, comprising: 
     a non-vertically aligned guide plate having one side along which stock slides in non-vertical orientation in a transport direction during transport and printing, a downstream end, a recessed region having at least one cutout, and a region following the at least one cutout toward the downstream end at which the stock is substantially free of contact with the guide plate; 
     an advancing device for advancing the stock along the guide plate in the transport direction; and 
     an ink jet print head of an ink jet printing device for printing to the stock disposed in the recessed region, the ink jet print head having a nozzle plane oriented substantially parallel to the guide plate. 
     Since printing is contactless, the required pressures are low and friction on the guide plate can be minimized through the use of a correspondingly smooth surface and sliding rails. 
     In accordance with another feature of the invention, the configuration of the region of the guide plate downstream of the print area or the cutout ensures that the stock is not supported at this location. This ensures a sufficiently long penetration time for the ink, preventing smearing of the printed image. 
     In accordance with a further feature of the invention, the fact that the nozzle plane is recessed relative to the region upstream of the cutout and that the downstream region is even farther recessed or open prevents the stock from catching on one of the edges. 
     Specifically, the region of the guide plate downstream of the cutout is either itself cut away or recessed relative to the bearing surface for the stock by an amount which is greater than the greatest expected convexity of the stock in the printed area. This clearance is achieved either by mechanical shaping, such as through the use of the mold in the case of plastic injection molding, or through the use of some metal removing process. 
     In the latter two variants, this amounts to only a few tenths of a millimeter, but can be as much as two millimeters to achieve the desired graduated recess. 
     In accordance with an added feature of the invention, the installation of sliding rails running in the direction of transport on the guide plate greatly reduces the bearing surface for the pieces of mail and thus the friction. The aforementioned unsupported area for the printed area of the stock is easily realized in that the sliding rails are farther apart than the printed image is wide and thicker than the greatest expected convexity of the stock. 
     In accordance with an additional feature of the invention, there is provided an insert of stainless steel as the structured portion of the guide plate, which provides several advantages. This insert can be stamped or cut to size from a piece of sheet metal. Stainless steel can be highly polished, it resists abrasion and it has good sliding properties. The metal effectively dissipates static electricity. 
     In accordance with yet another feature of the invention, if the postage indicia and address are to be printed in a single pass, an ink jet print head can still be used but an appropriate positioning mechanism for the print head is then required. 
     If there is a separate ink jet print head for each cutout or print function, not only is there no need for a positioning mechanism, but different colored inks can also be used, such as red for the postage indicia and black for the address. 
     In accordance with again a further feature of the invention, mounting the incremental transducer and the drive roller on a common axis and the use of a synchronous belt as the conveyor ensures precise monitoring of the conveying distance and no-slip transmission of motion. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a device for printing to stock in non-vertical orientation, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, perspective view of a device according to the present invention which has a planar guide plate and with which a piece of mail is transported on a conveyor with pressure elements; 
     FIGS. 2 a,    2   b  and  2   c  show a guide plate with an insert, in which FIG. 2 a  is a perspective view of a complete device, FIG. 2 b  is a perspective view of the insert, and FIG. 2 c  is a fragmentary, longitudinal-sectional view of a print area; 
     FIG. 3 is a side-elevational view of a device according to the invention which has an L-shaped guide plate and with which the piece of mail is transported on a short leg of the guide plate; 
     FIG. 4 is a fragmentary, perspective view of a conveyor with strip-shaped clamping elements, mounted on edge; 
     FIG. 5 is a view similar to FIG. 4 of a conveyor with strip-shaped clamping elements, mounted flat; 
     FIG. 6 is another view similar to FIG. 4 of a conveyor with ring-shaped clamping elements, mounted on edge; 
     FIG. 7 is a plan view of a conveyor with ring-shaped clamping elements, center mounted on edge; 
     FIG. 8 is a further view similar to FIG. 4 of a conveyor with U-shaped clamping elements; 
     FIG. 9 is an exploded, top and rear perspective view of a pressure element with a spring-mounted pressure plate; 
     FIG. 10 is an exploded, bottom and front perspective view of a pressure element with a spring-mounted pressure plate; 
     FIG. 11 is a partly sectional, plan view of the device of FIG. 1 with three possible positions for the pressure element; 
     FIG. 12 is a fragmentary, perspective view of a conveyor with solid cylinders and clamping jaws; 
     FIG. 13 is a fragmentary, perspective view showing details of a deflection as is shown in FIG. 12 in a reversal zone at the front of the conveyor; and 
     FIG. 14 is a fragmentary, perspective view showing details of the deflection as is shown in FIG. 12 in a reversal zone at the rear of the conveyor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in detail to the figures of the drawings, in which not all parts are shown and which are partly diagrammatic for reasons of simplicity and better comprehension, and first, particularly, to FIG. 1 thereof, there are seen pressure elements  12  which are separably fastened to a rotating conveyor  1 . To this end, the conveyor  1  has holes  100  formed therein through which a mating plate  126  with crowned pins  1261  protrudes. The pins  1261  are inserted into corresponding non-illustrated openings in the pressure elements  12  as is seen in FIGS. 9 and 10. 
     The conveyor  1  preferably includes a synchronous belt  10  and two toothed rollers  11 . The teeth are not shown for reasons of simplicity. It is appropriate that the mating plate  126  be located in a tooth space and therefore the toothed rollers  11  are correspondingly modified or include cutouts as is seen in FIG.  9 . 
     The powered toothed roller  11 , together with an incremental transducer  5 , is mounted so as to be stationary on an axle in the vicinity of a print area. The incremental transducer  5  can be realized as a slotted disk illuminated by a photocell  6 . A photodiode which is mounted behind the slotted disk for evaluation purposes, is not shown. The incremental transducer  5  interacts through an evaluation and control circuit with a sensor  7  for detection of a front edge of a piece of mail to initiate printing at the proper time. 
     Deflecting elements  8  which are seen in FIGS. 4,  5  and  6  are located outside the conveyor  1  but inside the path of the pressure elements  12  where stock such as a piece of mail  3  enters and exits the machine. In this case, these elements  8  are in the form of a connecting link which curves gradually outward. However, they can also be realized as outwardly-bent strips, as is seen in FIGS. 4 through 6. The conveyor  1  may be defined as means for applying an advancing force to the stock  3 . 
     The deflecting elements  8  serve to bend the pressure elements  12  so far backward at the location where the piece of mail  3  enters the machine, that the thickest permissible piece of mail  3  can easily pass onto the conveyor  1 . 
     The deflecting elements  8  serve to bend the pressure elements  12  so far backward at the location where the piece of mail  3  exits the machine, that each conveyed piece of mail  3  is released and can leave the conveyor  1  in the direction of a stacker. 
     In the illustrated embodiment of the invention, the pieces of mail  3  stand on edge during transport on the conveyor  1 . The pressure elements  12  hold a surface  32  to be printed against a guide plate  2 , as is indicated in FIGS. 3 and 11. 
     In order to pre-position the pieces of mail  3  and minimize the transport forces, the guide plate  2  is inclined at an angle of at least α=18° from the vertical. 
     The guide plate  2  is equipped with parallel sliding rails  23 ,  231  extending in the direction of transport as seen in FIG. 1, in order to improve sliding characteristics. 
     In the print area, the guide plate  2  has a first cutout  21  for an ink jet print head  4 . The cutout  21  is disposed at the height at which postage indicia is to be printed. A second, higher cutout  22  is provided in case an address is also to be printed on the piece of mail  3 . 
     As desired, a second ink jet print head  4  can be dedicated to this cutout  22  or a common, adjustable ink jet print head  4  can be used to print both the postage indicia and the address. Regardless of which variant is used, a nozzle plane  40  of the ink jet print head  4  shown in FIG. 2 c  must always be parallel to the guide plate  2  and the piece of mail  3  must be as close as possible, within 2 mm, to the nozzle plane while fed passed the latter. 
     In respective regions  25  downstream of the cutouts  21 ,  22 , the sliding rails  231  are separated by a distance a which is greater than a width b of the printed image. A thickness d of the sliding rails  231  is greater than the greatest expected convexity of the piece of mail  3  in the printed area. 
     As is shown in FIG. 2 a,  the guide plate  2  is equipped in the primary support and print area for the piece of mail  3  with an insert  20  extending in the direction of transport. 
     Cutouts  201 ,  202  for the ink jet print head  4  and an opening  206  for the sensor  7  are punched in the guide plate  2  and all other necessary structures, including sliding rails  203 , are stamped into the insert  20 , as is seen in FIG. 2 b.    
     It is appropriate for the insert  20  to be a piece of stainless steel. 
     The sliding rails  203  are located above and below the cutouts  201 ,  202  for the ink jet print head  4  and extend over the entire length of the insert  20 . 
     In a region  205  downstream of the cutouts  201 ,  202 , the sliding rails  203  are separated by the distance a which is greater than the width b of the printed image. The thickness d of the sliding rails  203  is greater than the greatest expected convexity of the piece of mail  3  in the printed area. A distance a &gt;25 mm and a thickness d=2 mm are sufficient. 
     As can be seen in FIG. 2 c,  a region area  204  upstream of the cutouts  201 ,  202 , the nozzle plane  40  of the ink jet print head  4  and a region  205  thereafter are progressively recessed. This prevents the pieces of mail from catching, thus preventing jams and increasing the reliability of transport of the piece of mail. 
     Production is unproblematic if the insert is manufactured from an appropriate sheet steel. 
     As is shown in FIG. 3, the guide plate  2  is L-shaped, whereby the piece of mail  3  stands on one edge  31  and stands on or slides along a short leg  27  of the L-shaped portion of the guide plate  2  while resting against a long leg  26  or the sliding rails  23  thereon. The two legs  26  and  27  are, of course, orthogonal to one another. The short leg  27  is highly-polished in the direction of transport. This would also be true for the entire guide plate  2  if there were no sliding rails  23 . 
     Otherwise, this embodiment is configured analogous to that described above. 
     There are a variety of possible configurations for the pressure elements  12 . They can be fastened in roughly the center of the conveyor  1  or at the greatest possible distance from the guide plate  2 . 
     In the embodiment shown in FIG. 4, the pressure elements  12  are strip-shaped clamping elements standing on one longitudinal edge, perpendicular to the direction of travel and fastened to the conveyor at an end  1201  facing away from the guide plate  2 . 
     Unlike FIG. 1, a permanent connection is preferred and can be realized through the use of gluing or bonding. 
     In a reversing zone at the front of the conveyor, the clamping element  12  is bent opposite the direction of transport by the deflecting element  8  and slides smoothly along the deflecting element  8 , moving laterally until coming in contact with the piece of mail  3 . 
     In the embodiment shown in FIG. 5, the strip-shaped clamping elements lie flat on the conveyor  1  and perpendicular to the direction of transport while being connected to the conveyor  1  at the end  1201  facing away from the guide plate  2 . The clamping element slides along the deflecting element  8 , moving downward until coming in contact with the piece of mail  3 . 
     In the embodiment shown in FIG. 6, the clamping element  12  is realized as a ring-shaped clamping element standing on edge and being fastened to the conveyor  1  at the part  1201  farthest away from the guide plate  2 . 
     FIG. 7 shows an embodiment in which the ring-shaped clamping element  12  is connected to the conveyor  1  in the center of a frontmost section  1202  of the element relative to the direction of transport indicated by an arrow. 
     In an analogous embodiment shown in FIG. 8, the pressure elements  12  are realized as U-shaped clamping elements. The U-shaped clamping elements  12  stand on edge, are perpendicular to the direction of transport and are connected to the conveyor  1  at legs  1203 , which face away from the guide plate  2 . The semi-circular region of the clamping element  12  stands on edge on the conveyor  1  and deflects opposite to the direction of transport. 
     All of the clamping elements  12  described above are made of an elastic material, preferably a polyurethane material. 
     In the embodiment shown in FIGS. 9 and 10, the pressure element  12  is realized as a spring-mounted bracket  121 , having an axle  123  which is mounted perpendicular to the direction of transport in a friction bearing  1251 . The friction bearing  1251  is rigidly connected to a bearing bracket  125 , which is in turn fastened to the conveyor  1 . 
     Mounted on one end of the axle  123  is a pressure plate  1211  having a friction lining  122  facing the guide plate  2 , so that the pressure plate  1211  can form a force-locking connection to only one piece of mail  3 . A force-locking connection is one which connects two elements together by force external to the elements, as opposed to a form-locking connection which is provided by the shapes of the elements themselves. 
     If no piece of mail  3  is present, the pressure plate  1211  slides along the sliding rail  23  or  203 , i.e. the friction lining  122  is thinner than the thickness d of the sliding rail  23 ,  203  or the amount by which it protrudes, and is thus free, as is seen in FIG.  11 . 
     A cover or top plate  1212 , which rests against a rear wall  1252  of the bearing bracket  125  and is terminated by a rear all  1213 , is connected to the rear of the pressure plate  1211  to prevent the pressure plate from tipping. 
     The pressure plate  1211  has a bore  12111  and the rear wall  1213  has a bore  12131 . Both bores  12111 ,  12131  are used to seat the axle  123 . 
     A U-shaped spring  124  is located between the pressure plate  1211  and the bearing bracket  125  in such a manner that a curved portion thereof rests against the pressure plate  1211  and free legs  1241  are held in the bearing bracket  125 . 
     A center section  1240  of the spring  124  has a bore  12401  through which the spring  124  is slid onto the axle  123 , where it is snugly seated. 
     The free legs  1241  of the spring  124  are form-lockingly connected in slot-shaped cutouts  12521  in the rear wall  1252  of the bearing bracket  125 . Ends  12411  of the legs  1241  protrude somewhat beyond the rear wall  1252 , thus serving as a buffered stop for the rear wall  1213  of the bracket  121 . 
     The spring  124  is preferably made of rubber to achieve good service life, elasticity and damping characteristics. Last but not least, this material is economical. 
     The rear wall  1213  of the bracket  121  includes an extension  12132  which can engage the deflection elements  8 . At the front of the conveyor  1 , the extension  12132  engages a part  81  of the connecting link  8  curving toward the guide plate  2 . At the rear of the conveyor, the extension  12132  engages a part  82  of the connecting link  8  curving away from the guide plate  2 , as is seen in FIGS. 1 and 11. 
     FIG. 11 shows three characteristic positions which the pressure element  12  can assume. For the sake of clarity, the section below the top plate  1212  of the bracket  121  is shown. In the lower position, the pressure element  12  has just been released by the part  81  of the connecting link  8  curving towards the guide plate  2 . The piece of mail  3  is clamped between the friction lining  122  and the sliding rails  23 . 
     In the center position, there is no piece of mail present. The pressure plate  1211  rests against the sliding rail  23  and the friction lining  122  is at some distance from the guide plate  2  and is thus exposed. The rear wall  1213  of the bracket  121  rests against the ends  12411  of the U-shaped spring  124 . 
     In the upper position, the pressure element  12  is pulled away from the guide plate  2  by the part  82  of the connecting link curving away from the guide plate  2 . The spring  124  is compressed and the rear wall  1213  rests with the extension  2132  seen in FIG. 10 against the deflecting element  82 . 
     In FIG. 12, the pressure elements  12  are realized as elastic, solid cylinders  120  that are held perpendicular to the direction of transport between clamping jaws  1205 . The clamping jaws  1205  are fastened to and extend across the width of the conveyor  1 . The piece of mail  3  is clamped between an end surface  1204  of the solid cylinder  120  and the guide plate  2 . The clamping jaws  1205  are spread apart where the conveyor  1  reverses due to the curvature of the conveyor  1 , so that the solid cylinders  120  lie loosely between the clamping jaws  1205  and can be easily displaced. 
     As is shown in FIG. 13, the reversing zone at the front of the conveyor  1  is enclosed in a cage  83  which prevents the solid cylinders  120  from falling out of the clamping jaws  1205  while also serving as the deflecting element  8 . 
     To this end, the cage  83  encloses the conveyor  1  so closely from the turning point on that the solid cylinders  120  are held by friction between the conveyor  1  and an inner top wall  830  of the cage  83 . Furthermore, a portion of the inner top wall  830  has a tooth profile  8301  inclined in the direction of the guide plate  2  and running diagonally to the direction of transport. Due to the force-locking connection between the solid cylinder  120  and the inner top wall  830  or the tooth profile  8301 , an elastic counter-profile is impressed into a jacket surface  1206  of the solid cylinder  120 , and the latter is rotated so as to move perpendicular to the direction of transport and toward the guide plate  2 . The force-locking connection and tooth profile  8301  are provided in such a way that the solid cylinder  120  only moves so far outward that there is a slight distance between the end surface  1204  of the solid cylinder  120  and the guide plate  2  and a thin piece of mail  3  can be lightly held. With thick pieces of mail  3 , the cylinders slide back in adjustment. 
     FIG. 14 represents the prevailing conditions at the rear reversing zone of the conveyor  1 . In this case, a cage  84  encloses the conveyor  1  and the cage likewise prevents the solid cylinders  120  from falling out of the clamping jaws  1205  while also serving as a deflecting element. To this end, an inner side wall  841  adjacent the guide plate  2  is angled outward. 
     The loose solid cylinders  120  slide with their end surface  1204  along the inner side wall  841  and are thus pushed so far outward that the thickest permissible piece of mail  3  easily fits between the end surface  1204  and the guide plate  2 , and is thus released. 
     An inner top wall  840  of the cage  84  is at such a distance from the conveyor  1  as to ensure that the solid cylinders  120  are loosely held. The cage  84  encloses a sufficient length of the conveyor  1  to ensure that the solid cylinders  120  are again clamped between the clamping jaws  1205  as they leave the reversing zone.