Patent Publication Number: US-7712411-B2

Title: Stencil printing apparatus for duplex or simplex printing

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a stencil printing apparatus, and more particularly to a stencil printing apparatus that is capable of switching between simplex printing using a simplex master and single-step duplex printing using a duplex master. 
   2. Description of the Background Art 
   Digital thermal stencil printing is known as a simple conventional printing method. In a stencil printing apparatus used for this stencil printing, a thermal head on which fine heat-generating elements are arranged in series is brought into contact with a master, and the master is conveyed while electrifying the heat-generating elements in a pulsating fashion such that the master is thermally melt-perforated in accordance with image information. The master is then wrapped around the outer peripheral surface of a perforated cylindrical plate cylinder, whereupon the outer peripheral surface of the plate cylinder is pressed via a sheet of paper using pressing means such as a press roller. As a result, ink is transmitted through the perforated portions of the master and transferred onto the sheet, whereby a printed image is obtained. 
   In stencil printing, duplex printing, in which printing is performed on both sides of a sheet, is often performed recently with the aims of reducing paper consumption, reducing the amount of space required to store documents, and so on. When duplex printing is performed using a conventional method, a sheet printed on both sides is obtained by conveying a sheet stacked on a sheet feeding unit to a printing unit, where printing is performed on one side of the sheet, turning the sheet over, and then returning the sheet to the printing unit, where printing is performed on the other side. However, this method is problematic in that it is troublesome to reset the sheet in the sheet feeding unit after it has been discharged and align the sheet after printing has been performed on one side. Furthermore, since the sheet passes through the printing unit twice, another problem arises in that duplex printing requires twice the time of simplex printing even in terms of the net printing time, which is excessive. 
   To solve these problems, a duplex printing apparatus that is capable of obtaining a sheet printed on both sides in a single step has been proposed in Japanese Unexamined Patent Application Publication 2005-246730, for example. In this apparatus, a duplex master on which a first engraved image and a second engraved image are arranged in the rotation direction of a plate cylinder is used. A first sheet is then fed from a sheet feeding unit and one of the engraved images is printed onto the front surface thereof. The sheet is then guided to an auxiliary tray, whereupon a second sheet is fed from the sheet feeding unit and one of the engraved images is printed onto the front surface thereof. The second sheet is then guided to the auxiliary tray, and at the same time, the first sheet is re-fed from the auxiliary tray and the other engraved image is printed onto the rear surface thereof. This sheet is then discharged onto a discharge tray. By performing this operation continuously, a sheet printed on both sides is obtained in a single step. 
   However, if a plurality of plate cylinders are used alternately when employing the technique disclosed in this publication, and the master wrapped around the plate cylinder has been engraved with duplex printing images, only engraving and simplex printing can be performed, and to print the same image on both sides, engraving must be performed again, leading to an increase in master consumption. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a stencil printing apparatus which reduces master consumption by switching between simplex printing using a simplex master and single-step duplex printing using a duplex master automatically in accordance with master information and sheet information. 
   In an aspect of the present invention, a stencil printing apparatus has a plate cylinder that can be attached to and detached from an apparatus main body freely and a pressing device provided so as to be free to contact and separate from the plate cylinder. With duplex printing, a rear surface printing step is performed after a front surface printing step, and simplex printing can be performed alternately by wrapping a duplex master formed with a first engraved image and a second engraved image in a length direction thereof around the plate cylinder during duplex printing, and wrapping a simplex master formed with a third engraved image for simplex printing around the plate cylinder during simplex printing. The stencil printing apparatus comprises a storage unit for storing master identification information, indicating whether the master is engraved with duplex printing images or a simplex printing image during engraving, in association with plate cylinder identification information; and a control device for selecting a duplex printing mode or a simplex printing mode on the basis of at least plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus, and the master identification information stored in the storage unit in association with the plate cylinder identification information. 
   In another aspect of the present invention, a stencil printing apparatus has a plate cylinder that can be attached to and detached from an apparatus main body freely and a pressing device provided so as to be free to contact and separate from the plate cylinder. With duplex printing, a rear surface printing step is performed after a front surface printing step, and simplex printing can be performed alternately by wrapping a duplex master formed with a first engraved image and a second engraved image in a length direction thereof around the plate cylinder during duplex printing, and wrapping a simplex master formed with a third engraved image for simplex printing around the plate cylinder during simplex printing. The stencil printing apparatus comprises a storage unit for storing master identification information, indicating whether the master is engraved with duplex printing images or a simplex printing image during engraving, in association with plate cylinder identification information; and a control device for displaying the master identification information on display means on the basis of at least plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus, and the master identification information stored in the storage unit in association with the plate cylinder identification information. 
   In another aspect of the present invention, a stencil printing apparatus has a plate cylinder that can be attached to and detached from an apparatus main body freely and a pressing device provided so as to be free to contact and separate from the plate cylinder. With duplex printing, a rear surface printing step is performed after a front surface printing step, and simplex printing can be performed alternately by wrapping a duplex master formed with a first engraved image and a second engraved image in a length direction thereof around the plate cylinder during duplex printing, and wrapping a simplex master formed with a third engraved image for simplex printing around the plate cylinder during simplex printing. The stencil printing apparatus comprises a storage unit for storing master identification information, indicating whether the master is engraved with duplex printing images or a simplex printing image during engraving, in association with plate cylinder identification information; and a control device for executing a warning operation when at least plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus differs from the master identification information stored in the storage unit in association with the plate cylinder identification information. 
   In another aspect of the present invention, a stencil printing apparatus has a plate cylinder that can be attached to and detached from an apparatus main body freely and a pressing device provided so as to be free to contact and separate from the plate cylinder. During duplex printing, a rear surface printing step is performed after a front surface printing step, and simplex printing can be performed alternately by wrapping a duplex master formed with a first engraved image and a second engraved image in a length direction thereof around the plate cylinder during duplex printing, and wrapping a simplex master formed with a third engraved image for simplex printing around the plate cylinder during simplex printing. The stencil printing apparatus comprises a storage unit for storing master identification information, indicating whether the master is engraved with duplex printing images or a simplex printing image during engraving, and sheet size information corresponding to the master identification information, in association with plate cylinder identification information; a sheet size detecting device for detecting a sheet; and a control device for executing a warning operation when at least plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus and sheet size detection information from the sheet size detecting device differ from the master identification information and the sheet size detection information stored in the storage unit in association with the plate cylinder identification information. 
   In another aspect of the present invention, a stencil printing apparatus has a plate cylinder that can be attached to and detached from an apparatus main body freely and a pressing device provided so as to be free to contact and separate from the plate cylinder. During duplex printing, a rear surface printing step is performed after a front surface printing step, and simplex printing can be performed alternately by wrapping a duplex master formed with a first engraved image and a second engraved image in a length direction thereof around the plate cylinder during duplex printing, and wrapping a simplex master formed with a third engraved image for simplex printing around the plate cylinder during simplex printing. The stencil printing apparatus comprises a storage unit for storing master identification information, indicating whether the master is engraved with duplex printing images or a simplex printing image during engraving, and sheet size information corresponding to the master identification information, in association with plate cylinder identification information; a plurality of sheet feeding units for feeding sheets; and a plurality of sheet size detecting devices for detecting the size of the sheets in each of the sheet feeding units. When at least plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus and sheet size detection information from each of the sheet size detecting device differ from the master identification information and the sheet size detection information stored in the storage unit, a sheet feeding operation by a sheet feeding unit in which different sheet size information has been detected is prohibited. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings, in which: 
       FIG. 1  is a front view showing the schematic constitution of a stencil printing apparatus to which first through fourth embodiments of the present invention can be applied; 
       FIG. 2  is a view showing a master engraved with duplex printing images, which is used in each embodiment of the present invention; 
       FIG. 3  is a view showing a master engraved with a simplex printing image, which is used in each embodiment of the present invention; 
       FIG. 4  is a view showing the schematic constitution of an operating panel used in each embodiment of the present invention; 
       FIG. 5  is a block diagram showing the constitution of control means used in the first, second, fourth, and fifth embodiments of the present invention; 
       FIG. 6  is a flowchart showing an aspect of master identification information storage processing in the first embodiment; 
       FIG. 7  is a flowchart showing an aspect of master determination processing in the first embodiment; 
       FIGS. 8A and 8B  are enlarged views showing examples of guidance information displayed by display means in the first embodiment; 
       FIG. 9  is a flowchart showing an aspect of master identification information display processing in the second embodiment; 
       FIGS. 10A and 10B  are enlarged views showing examples of display content displayed by display means in the second embodiment; 
       FIG. 11  is a block diagram showing the constitution of control means used in a third embodiment of the present invention; 
       FIG. 12  is a flowchart showing an aspect of master identification information and sheet size information storage processing in the third embodiment; 
       FIG. 13  is a flowchart showing an aspect of warning processing in the third embodiment; 
       FIG. 14  is an enlarged view showing an example of warning content displayed by warning means in the third embodiment; 
       FIG. 15  is a flowchart showing an aspect of master identification information and sheet size information storage processing in the fourth embodiment; 
       FIG. 16  is a flowchart showing an aspect of warning processing in the fourth embodiment; 
       FIG. 17  is an enlarged view showing an example of warning content displayed by warning means in the fourth embodiment; 
       FIG. 18  is a front view showing the schematic constitution of a stencil printing apparatus to which the fifth embodiment of the present invention is applied; 
       FIG. 19  is a flowchart showing an aspect of tray selection prohibition processing in the fifth embodiment; and 
       FIGS. 20A ,  20 B, and  20 C are enlarged views showing examples of display content displayed by display means in the fifth embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A stencil printing apparatus according to each embodiment of the present invention will be described below using the drawings. 
   As shown in  FIG. 1 , a stencil printing apparatus  1  comprises a printing unit  2 , an engraving unit  3 , a sheet feeding unit  4 , a plate discharge unit  5 , a sheet discharge unit  6 , an image reading unit  7 , an auxiliary tray  8 , sheet re-feeding means  9 , a switching member  10 , control means  40 , and so on. 
   The printing unit  2 , which is disposed substantially in the center of an apparatus main body  43 , comprises a printing drum  11  serving as a plate cylinder, and a press roller  12  serving as pressing means. The printing drum  11  is supported on the apparatus main body  43  detachably and rotatably, and is driven to rotate by printing drum driving means, not shown in the drawing. An openable clamper  13  is provided on the outer peripheral surface of the printing drum  11 . During duplex printing, a duplex master  14  engraved by the engraving unit  3  is wrapped around the outer peripheral surface of the printing drum  11 , and during simplex printing, a simplex master  15  engraved by the engraving unit  3  is wrapped around the outer peripheral surface of the printing drum  11 . A rotary encoder, not shown in the drawing, for detecting the position of the printing drum  11  is provided near the outer peripheral surface of the printing drum  11 . In this embodiment, the simplex master  15 , which is capable of printing a sheet P with a maximum size of A3, is wrapped around the printing drum  11 . 
   As shown in  FIG. 2 , a first engraved image  14 A corresponding to a front surface image and a second engraved image  14 B corresponding to a rear surface image are formed on the duplex master  14 , and a non-engraved part S is formed between the engraved images  14 A,  14 B. The duplex master  14  is wrapped around the printing drum  11  such that the first engraved image  14 A corresponds to a front surface region shown in  FIG. 1 , the second engraved image  14 B corresponds to a rear surface region shown in  FIG. 1 , and the non-engraved part S corresponds to an intermediate region shown in  FIG. 1 . In this embodiment, images that can be printed onto a sheet P having a maximum size of A4 lateral (assuming that the short direction of the sheet is the sheet conveyance direction) are created as the first engraved image  14 A and second engraved image  14 B. 
   As shown in  FIG. 3 , a third engraved image  15 A corresponding to a simplex printing image is formed on the simplex master  15 . The simplex master  15  is wrapped around the printing drum  11  such that the third engraved image  15 A corresponds to a range encompassing the front surface region, rear surface region, and intermediate region shown in  FIG. 1 . In this embodiment, an image that can be printed onto a sheet P having a maximum size of A3 is created as the third engraved image  15 A. 
   The press roller  12  is disposed below the printing drum  11 . The press roller  12 , which is constituted by a water-repellent elastic body made of fluorine resin or the like, is supported rotatably on an arm member, not shown in the drawing, at either end, while the arm member, not shown in the drawing, is supported so as to be swingable by swinging means, not shown in the drawing. The press roller  12  selectively occupies a removed position shown in  FIG. 1 , in which the peripheral surface thereof is removed from the printing drum  11 , and a pressing position, in which the peripheral surface thereof is pressed against the duplex master  14  on the printing drum  11 . 
   The swinging means, not shown in the drawing, are constituted such that a pressing range of the press roller  12  relative to the printing drum  11  can be switched between a first range covering all of the front surface region, intermediate region, and rear surface region shown in  FIG. 1 , a second range matching the front surface region, and a third range covering a downstream side part of the front surface region, the intermediate region, and the rear surface region. A cleaning roller  16  which performs cleaning by contacting the peripheral surface of the press roller  12  is disposed near the peripheral surface of the press roller  12 . The cleaning roller  16  is driven to rotate by driving means, not shown in the drawing. 
   A sheet re-feeding guidance member  17  for conveying the sheet P, which has been delivered from the sheet re-feeding means  9  and printed on the front surface thereof, along the peripheral surface of the press roller  12  is disposed near the right side of the press roller  12 . A sheet re-feeding resist roller  18  for feeding the sheet P from the auxiliary tray  8  such that the sheet P contacts the peripheral surface of the press roller  12  is disposed below the press roller  12 . A sheet re-feeding conveyance unit  19  having the auxiliary tray  8  on its upper surface is disposed below, and to the left of, the press roller  12 , and is formed integrally with a sheet re-feeding positioning member  20 . A sheet receiving plate  21  is disposed above the sheet re-feeding conveyance unit  19  so as to be free to move along the upper surface of the auxiliary tray  8 . The auxiliary tray  8 , sheet re-feeding guidance member  17 , sheet re-feeding resist roller  18 , sheet re-feeding positioning member  20 , sheet re-feeding conveyance unit  19 , and sheet receiving plate  21  together constitute the sheet re-feeding means  9 . 
   The switching member  10  is disposed to the left of the contact position between the printing drum  11  and the press roller  12 , and above the conveyance path of the sheet P. The switching member  10  is supported rotatably on the apparatus main body  43  by an end portion thereof on the downstream side of the sheet conveyance direction, and is moved by moving means, not shown in the drawing, so as to selectively occupy a first position, shown by the solid line in  FIG. 1 , and a second position, shown by the dot-dot-dash line. When the sheet P passes between the printing drum  11  and press roller  12  and the switching member  10  occupies the first position, the sheet P is guided to the sheet discharge unit  6 . When the switching member  10  occupies the second position, the sheet P is guided to the auxiliary tray  8 . 
   The engraving unit  3  is disposed above, and to the right of, the printing unit  2 . The engraving unit  3  has a well-known constitution comprising a master holding member  23  for holding a master roll on which a master  22  is wound in roll-form, a platen roller  24 , a thermal head  25 , master switching means  26 , a master stock unit  27 , a tension roller pair  28 , a reverse roller pair  29 , and so on. In the engraving unit  3 , the duplex master  14  is created during duplex printing and the simplex master  15  is created during simplex printing. 
   The sheet feeding unit  4  is disposed below the engraving unit  3 . The sheet feeding unit  4  has a well-known constitution comprising a sheet feeding tray  41  carrying the sheet P, a sheet feeding roller, a separating roller, a separating pad, a resist roller pair, and so on. A plurality of sheet size detection sensors  42  serving as sheet size detecting means for detecting the size of the sheet P carried on the upper surface of the sheet feeding tray  41  are disposed on the sheet feeding tray  41 . 
   The plate discharge unit  5  disposed above, and to the left of, the printing unit  2  also has a well-known constitution comprising an upper plate discharge member, a lower plate discharge member, a plate discharge box, a compression plate, and so on. Used duplex masters  14  and simplex masters  15  are peeled away from the outer peripheral surface of the printing drum  11  and disposed of in the interior of the plate discharge box. 
   The sheet discharge unit  6  is disposed below the plate discharge unit  5 . The sheet discharge unit  6  has a well-known constitution comprising a peeling pawl, a sheet discharge conveyance unit, a sheet discharge tray, a peeling fan, and so on. The sheet P is peeled away from the outer peripheral surface of the printing drum  11  and discharged onto the sheet discharge tray. 
   The image reading unit  7  is disposed in the upper portion of the apparatus main body  43 . Although not shown in the drawings, the image reading unit  7  comprises a contact glass on which an original is placed, a pressure plate provided so as to be free to contact and separate from the contact glass, a reflection mirror and a fluorescent lamp for scanning and reading an original image, a lens for condensing the scanned image, an image sensor for processing the condensed image, and so on. 
     FIG. 4  shows an operating panel  30  serving as an operating unit of the stencil printing apparatus  1 . In the drawing, the operating panel  30  has a well-known constitution comprising an engraving start key  31 , a printing start key  32 , a stop key  33 , a numeric keypad  34 , a display apparatus  35  constituted by a seven segment LED, a display apparatus  36  constituted by an LCD, and soon, and is also provided with a duplex printing key  37  that is depressed when performing duplex printing, and a simplex printing key  38  that is depressed when performing simplex printing. 
     FIG. 5  is a block diagram of the control means  40  used in the stencil printing apparatus  1 . In the drawing, the control means  40  are constituted by a well-known computer comprising in its interior a CPU, ROM, RAM, a timer, and so on. The control means  40  control the respective operations of the printing unit  2 , engraving unit  3 , paper feeding unit  4 , plate discharge unit  5 , sheet discharge unit  6 , image reading unit  7 , sheet re-feeding means  9 , and switching member  10  on the basis of operation commands (signals) from a rotary encoder, not shown in the drawing, and the operating panel  30 . 
   The apparatus main body  43  comprises a storage unit  50  storing master identification information for differentiating between the duplex master  14 , which is engraved with duplex printing images during engraving, and the simplex master  15 , which is engraved with a simplex printing image during engraving, in association with information relating to each printing drum that is attached to the apparatus main body  43  during engraving. The apparatus main body  43  is provided with a drum type detection sensor  55  for detecting an ink color and a drum size serving as information relating to the type of the attached printing drum  11 , and a drum attachment detection sensor  56  for detecting the attachment/detachment state of the printing drum  11 . The drum type detection sensor  55  detects the printing drum size and the ink color used by the printing drum  11  from an information recording unit such as a barcode attached to a side plate, not shown in the drawing, of the printing drum  11 , for example. The drum attachment detection sensor  56  may be a limit switch disposed on the back side of the apparatus main body  43 , which switches ON when the printing drum is attached and OFF when the printing drum is detached, for example. The storage unit  50 , drum type detection sensor  55 , drum attachment detection sensor  56 , and sheet size detection sensor  42  are connected to the control means  40  by a signal line such that the respective detection signals thereof are input into the control means  40 . The control means  40  comprise an energy saving mode for halting various operations of the apparatus when no command is issued to the apparatus for a predetermined length of time, and when the control means  40  enter this mode, the apparatus enters a state of rest. When an operation command is input in relation to the apparatus, the energy saving mode is terminated and the control means  40  control the various units to switch the apparatus from a state of rest to an activated state. 
   An operation of the stencil printing apparatus  1  when duplex printing is performed by pressing the duplex printing key  37  will be described below on the basis of the above constitution. 
   When an original is set on the image reading unit  7  and the duplex printing key  37  is pressed by an apparatus operator, the fact that duplex printing has been set is stored by the control means  40 , and a duplex printing operating program is accessed. Then, when the apparatus operator presses the engraving start key  31 , an original image reading operation is performed in the image reading unit  7 , and the plate discharge unit  5  is activated such that the used duplex master  14  or simplex master  15  is peeled away from the outer peripheral surface of the printing drum  11 . Following plate discharge, the first engraved image  14 A and second engraved image  14 B are formed on the master  22  by activating the engraving unit  3 , whereby a new duplex master  14  is engraved, and the new duplex master  14  is wrapped around the printing drum  11 . 
   When the wrapping operation is complete and the stencil printing apparatus  1  has entered a state of duplex printing standby, various printing conditions are set. Then, when the apparatus operator presses the printing start key  32 , the printing drum  11  is driven to rotate at a set speed, and one sheet P is separated from the other sheets P and fed by the sheet feeding unit  4 . The fed sheet P is halted temporarily by the resist roller pair, and then conveyed between the printing drum  11  and press roller  12  at a predetermined timing. Note that the various printing conditions may be set before pressing the engraving start key  31 . 
   When the printing drum  11  has rotated to a predetermined angle such that the front surface region thereof occupies a predetermined position corresponding to the press roller  12 , the press roller  12  occupies the pressing position, and therefore the sheet P is pressed against the first engraved image  14 A of the duplex master  14  on the printing drum  11 . As a result, a front surface image is transferred onto one side of the sheet P. At this time, the swinging means, not shown in the drawing, for swinging the press roller  12  set the pressing range of the press roller  12  relative to the printing drum  11  to the second range. 
   When front surface printing is complete, the sheet P is peeled away from the outer peripheral surface of the printing drum  11  by the tip end of the switching member  10 , which occupies the second position, and is conveyed to the sheet re-feeding conveyance unit  19 . At this time, the tip end of the sheet P is received by the sheet receiving plate  21 , and hence the sheet P is placed on the auxiliary tray  8  from the rear end side. The sheet P on the auxiliary tray  8  is then conveyed in the direction of the arrow in  FIG. 1  by the sheet re-feeding conveyance unit  19  and held temporarily with the tip end thereof abutting against the sheet re-feeding positioning member  20 . 
   While the first sheet P is guided onto the auxiliary tray  8 , the printing drum  11  continues to rotate, and at the same timing as the first sheet P, a second sheet P is fed from the sheet feeding unit  4 . At this time, the swinging means, not shown in the drawing, set the pressing range of the press roller  12  relative to the printing drum  11  to the first range. Similarly to the first sheet P, the front surface image is transferred onto one side of the second fed sheet P by the press roller  12 , whereupon the second sheet P is conveyed to the sheet re-feeding conveyance unit  19  by the switching member  10 , which occupies the second position. 
   After the second sheet P has been fed from the sheet feeding unit  4 , the sheet re-feeding resist roller  18  is activated at a slightly earlier timing than the timing at which the rear surface region of the printing drum  11  reaches the position corresponding to the press roller  12 , whereby the first sheet P stored on the auxiliary tray  8  is pressed against the peripheral surface of the press roller  12 . The first sheet P pressed against the peripheral surface of the press roller  12  is conveyed toward a position of contact with the printing drum  11  by the rotational force of the press roller  12 , which is rotated by being pressed against the printing drum  11 , and when the first sheet P is pressed against the second engraved image  14 B on the duplex master  14 , a rear surface image is transferred onto the other side thereof. 
   When the rear surface image has been transferred onto the first sheet P such that duplex printing thereof is complete, the first sheet P is guided to the sheet discharge unit  6  by the switching member  10  occupying the first position. The tip end portion of the first sheet P is lifted by a blast of air from the peeling fan, whereupon the sheet P is peeled away from the outer peripheral surface of the printing drum  11  by the tip end of the peeling pawl. Having been peeled away, the printed sheet P is conveyed to the sheet discharge conveyance unit and discharged onto the sheet discharge tray. The operation described above is repeated until a set number of sheets to be printed has been exhausted. After the final sheet P has been guided onto the auxiliary tray  8 , the swinging means, not shown in the drawing, set the pressing range of the press roller  12  relative to the printing drum  11  to the third range, and once a duplex printing operation has been performed for the set number of sheets, operations at each site are halted. 
   Next, an operation of the stencil printing apparatus  1  when normal simplex printing is performed by pressing the simplex printing key  38  will be described. 
   When an original is set on the image reading unit  7  and the apparatus operator presses the simplex printing key  38 , the fact that simplex printing has been set is stored by the control means  40 , and a simplex printing operating program is accessed. Then, when the apparatus operator presses the engraving start key  31 , an original image reading operation is performed in the image reading unit  7 , and the plate discharge unit  5  is activated such that the used duplex master  14  or simplex master  15  is peeled away from the outer peripheral surface of the printing drum  11 . Following plate discharge, the third engraved image  15 A is formed on the master  22  by activating the engraving unit  3 , whereby a new simplex master  15  is engraved, and the new simplex master  15  is wrapped around the printing drum  11 . 
   When the wrapping operation is complete and the stencil printing apparatus  1  has entered a state of simplex printing standby, various printing conditions are set. Then, when the apparatus operator presses the printing start key  32 , the printing drum  11  is driven to rotate at a set speed, and one sheet P is separated from the other sheets P and fed by the sheet feeding unit  4 . The fed sheet P is halted temporarily by the resist roller pair, and then conveyed between the printing drum  11  and press roller  12  at a predetermined timing. 
   When the printing drum  11  has rotated to a predetermined angle such that the front surface region thereof occupies a position corresponding to the press roller  12 , the press roller  12  occupies the pressing position, and therefore the sheet P is pressed against the third engraved image  15 A of the simplex master  15  on the printing drum  11 . As a result, an image is transferred onto the sheet P. At this time, the swinging means, not shown in the drawing, for swinging the press roller  12  set the pressing range of the press roller  12  relative to the printing drum  11  to the first range. 
   When the image has been transferred onto the sheet P such that printing thereof is complete, the sheet P is guided to the sheet discharge unit  6  by the switching member  10  occupying the first position. The tip end portion of the sheet P is lifted by a blast of air from the peeling fan, whereupon the sheet P is peeled away from the outer peripheral surface of the printing drum  11  by the tip end of the peeling pawl. Having been peeled away, the printed sheet P is conveyed to the sheet discharge conveyance unit and discharged onto the sheet discharge tray. The operation described above is repeated until a set number of sheets to be printed has been exhausted. Once a simplex printing operation has been performed for the set number of sheets, operations at each site are halted. 
   Next, embodiments of the control performed by the control means  40  will be described in sequence. The hardware constitution of the control means  40  is identical in each embodiment, and therefore, in the following description, identical reference numerals are allocated thereto. Further, when using flowcharts to describe the embodiments, the description of steps having an identical content will be limited to the first embodiment, and duplicate detailed description of these identical steps will be omitted. 
   First Embodiment 
   In this embodiment, a duplex printing mode or a simplex printing mode is selected on the basis of printing drum identification information detected (obtained) anew by the drum type detection sensor  55  when various apparatus operation commands are input into the control means  40  from the operating panel  30  or a printing drum attachment/detachment command is input from the drum attachment detection sensor  56 , and master identification information stored in the storage unit  50 . 
   Master identification information indicating whether the master is the duplex master  14  or the simplex master  15  is stored in the storage unit  50  by means of master identification information storage processing, an example of which is shown in  FIG. 6 . When engraving processing is executed in a step A 1  of  FIG. 6 , a determination is made in a step A 2  as to whether or not engraving has been completed correctly according to a signal from a well-known master jam detection sensor, not shown in the drawing, provided in the engraving unit  3 , for example. When engraving has not been completed correctly, the storage processing ends, and when engraving has been completed correctly, the routine advances to a step A 3 . In the step A 3 , a determination as to whether or not duplex printing images have been engraved is made using an image signal of the engraving. When duplex printing images have been engraved, the routine advances to a step A 4 , and when duplex printing images have not been engraved, it is assumed that a simplex printing image has been engraved, and the routine advances to a step A 5 . 
   In the step A 4 , a signal from the drum identification detecting means  55  is stored in a storage area  50 A of the storage unit  50  corresponding thereto in association with information indicating that the master has been engraved with duplex printing images (i.e. that the master is the duplex master  14 ). In the step A 5 , a signal from the printing drum identification detecting means  55  is stored in a storage area  50 B of the storage unit  50  corresponding thereto in association with information indicating that the master has been engraved with a simplex printing image (i.e. that the master is the simplex master  15 ). The processing is then terminated. 
   The control means  40  execute master determination processing shown in  FIG. 7 . In a step B 1  of  FIG. 7 , signals generated when the various switches of the operating panel  30  are operated and a signal from the drum attachment detecting means  56  are taken in, and in a step B 2 , a printing drum identification signal is read from the printing drum  11  attached to the apparatus main body  43  by the drum identification detecting means  55 . In a step B 3 , a determination as to whether or not the master is wrapped around the printing drum  11  is made according to the output of a well-known optical sensor, not shown in the drawing, provided on the peripheral portion of the printing drum. When the master is wrapped around the printing drum  11 , the routine advances to a step B 4 , and when the master is not wrapped around the printing drum  11 , the routine advances to a step B 8 , where an engraving mode is set. Since the printing drum  11  can be attached to and detached from the apparatus main body  43  freely, the printing drum  11  may be detached from the apparatus main body  43  and replaced with a different printing drum  11  during multi-color printing, and new printing may also be performed. Here, in consideration of a case in which new printing is executed, the engraving mode is set so that engraving can be executed in preparation for the new image printing operation. In this case, the control means  40  control an operation of the engraving unit  3  in accordance with image signals to engrave either the duplex master  14  or simplex master  15  in the manner described above. 
   In the step B 3 , when the master is wrapped around the printing drum  11 , the routine advances to the step B 4 , where master identification information corresponding to the drum identification information is read from the storage unit  50 . The routine then advances to a step B 5 . In the step B 5 , a determination is made as to whether or not the read master identification information indicates a master (the duplex master  14 ) engraved with duplex printing images. When the master is engraved with duplex printing images (i.e. when the master is the duplex master  14 ), the routine advances to a step B 6 , where the duplex printing mode is set. When the master is not engraved with duplex printing images (i.e. when the master is not the duplex master  14 ), it is determined that the master is engraved with a simplex printing image (i.e. that the master is the simplex master  15 ), and therefore the routine advances to a step B 7 , where the simplex printing mode is set. The control is then terminated. When the duplex printing mode or simplex printing mode is set, the control means  40  execute the corresponding printing by controlling the various units. More specifically, when the power is switched on, low energy mode or the like is switched to normal mode, or the drum is replaced, the control means  40  refer to the drum identification information relating to the printing drum  11  currently attached to the apparatus main body  43 , access the information recorded in association with the drum identification information during engraving from the storage area  50 A or the storage area  50 B of the storage unit  50 , and switch between the duplex printing mode and simplex printing mode automatically in accordance with the content of the information (whether the master is engraved with duplex printing images or a simplex printing image). 
   The control means  40  display guidance on the LCD display apparatus  36  of the operating panel  30  as means for informing the apparatus operator of whether the duplex printing mode or simplex printing mode has been set. In the duplex printing mode, this guidance is displayed as “printing is possible (duplex)”, as shown in  FIG. 8A , and when the simplex printing mode is set, the guidance is displayed as “printing is possible (simplex)”, as shown in  FIG. 8B . 
   Hence, the duplex printing mode or simplex printing mode is selected by the control means  40  on the basis of the drum identification information, which is obtained anew during input of an operation command to the apparatus or an attachment/detachment command relating to the printing drum  11 , and the master identification information stored in the storage unit  50 . Therefore, situations in which the master breaks or ink adheres to the press roller  12  when simplex printing is performed mistakenly using the duplex master  14  or duplex printing is performed mistakenly using the simplex master  15  can be prevented, and master consumption due to re-engraving during duplex printing can be suppressed. 
   Second Embodiment 
   In this embodiment, the master identification information is displayed on the LCD display apparatus  36  serving as display means on the basis of printing drum identification information detected (obtained) anew by the drum type detection sensor  55  when various apparatus operation commands are input into the control means  40  from the operating panel  30  or a printing drum attachment/detachment command is input from the drum attachment detection sensor  56 , and the master identification information stored in the storage unit  50 . 
   This master identification information display processing will be described using the flowchart in  FIG. 9 . Note that steps C 1  to C 5  in  FIG. 9  are identical in content to the steps B 1  to B 5  in  FIG. 7 , and hence description thereof has been omitted. 
   In the step C 3 , when the master is wrapped around the printing drum  11 , the routine advances to the step C 4 , where the master identification information corresponding to the drum identification information is read from the storage unit  50 . The routine then advances to the step C 5 . In the step C 5 , a determination is made from the read master identification information and the drum identification information detected in the step C 2  as to whether or not the master on the drum is the duplex master  14  or the simplex master  15 . When the master is the duplex master  14 , the routine advances to a step C 6 , where information indicating duplex printing is displayed on the LCD display apparatus  36  of the operating panel  30 , and when the master is not the duplex master  14 , it is determined that the master is the simplex master  15 , and the routine advances to a step C 7 *, where information indicating simplex printing is displayed on the LCD display apparatus  36 . The control is then terminated. 
   During duplex printing, display such as “the duplex printing master is wrapped around the drum” is displayed, as shown in  FIG. 10A , and during simplex printing, display such as “the simplex printing master is wrapped around the drum” is displayed, as shown in  FIG. 10B , for example. 
   By displaying the master identification information indicating whether the master is the duplex printing master or simplex printing master on the LCD display apparatus  36  using the control means  40  on the basis of the drum identification information, which is obtained anew during input of an operation command to the apparatus or an attachment/detachment command relating to the printing drum  11 , and the master identification information stored in the storage unit  50 , unnecessary engraving can be suppressed, leading to a decrease in master consumption, and the apparatus operator can prepare paper corresponding to the master more easily. 
   Third Embodiment 
   In this embodiment, a warning operation is executed when the printing drum identification information, which is detected (obtained) anew by the drum type detection sensor  55  when various apparatus operation commands are input into the control means  40  from the operating panel  30  or a printing drum attachment/detachment command is input from the drum attachment detection sensor  56 , and the master identification information stored in the storage unit  50  are different. To realize this constitution, a separate storage unit  60  to the storage unit  50  is added to the control system of the embodiment, as shown in  FIG. 11 . In this embodiment, the master identification information, indicating whether the master is the duplex master  14  or simplex master  15 , is stored in the storage unit  50  during engraving, while the storage unit  60  stores master identification information indicating the duplex master  14  or the simplex master  15  from a single engraving operation. Storage processing to the storage units  50 ,  60  is performed by means of master identification information storage processing, an example of which is shown in  FIG. 12 . 
   When engraving processing is executed in a step D 1  of  FIG. 12 , a determination is made in a step D 2  as to whether or not engraving has been completed correctly. When engraving has not been completed correctly, the storage processing ends, and when engraving has been completed correctly, the routine advances to a step D 3 . In the step D 3 , a determination as to whether or not duplex printing images have been engraved is made using an image signal of the engraving. When duplex printing images have been engraved, the routine advances to a step D 4 , and when duplex printing images have not been engraved, it is assumed that a simplex printing image has been engraved, and the routine advances to a step D 6 . 
   In the step D 4 , a signal from the drum identification detecting means  55  is stored in the storage unit  50  in association with information indicating that the master has been engraved with duplex printing images (i.e. that the master is the duplex master  14 ). The routine then advances to a step D 5 , where information indicating that the master has been engraved with duplex printing images, i.e. that the master is the duplex master  14 , is stored in the storage unit  60 . The control is then terminated. In the step D 6 , a signal from the printing drum identification detecting means  55  is stored in the storage unit  50  in association with information indicating that the master has been engraved with a simplex printing image (i.e. that the master is the simplex master  15 ). The routine then advances to a step D 7 , where information indicating that the master has been engraved with a simplex printing image, i.e. that the master is the simplex master  15 , is stored in the storage unit  60 . The control is then terminated. 
   Next, warning processing will be described using the flowchart shown in  FIG. 13 . Steps E 1  to E 3  in  FIG. 13  are identical in content to the steps B 1  to B 3 . 
   In the step E 3 , when the master is not wrapped around the printing drum  11 , the control is terminated, and when the master is wrapped around the printing drum  11 , the routine advances to the step E 4 , where the master identification information corresponding to the drum identification information is read from the storage unit  50  as a current value. The routine then advances to a step E 5 . In the step E 5 , the previously stored master identification information is read from the storage unit  60  as a previous value, whereupon the routine advances to a step E 6 . In the step E 6 , a determination is made as to whether or not the current value and the previous value are identical. When the current value and previous value are identical, the processing ends, and when the current value and previous value are different, the routine advances to a step E 7 , where warning content is displayed on the LCD display apparatus  36 . The control is then terminated. As an example of the warning content, “a master having different images (duplex/simplex) to the previous operation is wrapped around the drum” may be displayed, as shown in  FIG. 14 . 
   Hence, a warning operation, in which warning content is displayed on the LCD display apparatus  36 , is executed when the drum identification information, which is obtained anew during input of an operation command to the apparatus or an attachment/detachment command relating to the printing drum  11 , and the master identification information stored in the storage unit  50  differ from the master identification information serving as the previous value stored in the storage unit  60 , and therefore the apparatus operator can be warned that the printing drum  11  attached to the apparatus main body  43  or the master is different to that of the previous operation. In so doing, unnecessary engraving can be suppressed, leading to a decrease in master consumption. 
   When color printing using two or more colors is performed while exchanging the printing drum  11  and the warning display described above is not executed, erroneous printing in which the printed image is not positioned correctly or the like may occur. Such erroneous printing occurs when engraving is performed in advance for each color, and both duplex printing and simplex printing are performed while exchanging the printing drum such that the duplex master  14  engraved with duplex printing images is used first and the simplex master  15  engraved with a simplex printing image is used next. However, if the warning display described above is executed, the warning display is displayed on the LCD display apparatus  36  of the operating panel when the drum is exchanged, and therefore the apparatus operator can be warned. 
   Fourth Embodiment 
   In this embodiment, the master identification information and sheet size information corresponding to the master identification information are stored in the storage unit  50  in association with plate cylinder identification information during engraving, and if sheet size information corresponding to printing drum identification information that is detected (obtained) anew by the drum type detection sensor  55  when various apparatus operation commands are input into the control means  40  from the operating panel  30  or a printing drum attachment/detachment command is input from the drum attachment detection sensor  56  differs from the sheet size information stored in the storage unit  50 , a warning operation is executed. 
   The control means  40  execute processing for storing the master identification information and sheet size, as shown in  FIG. 15 . When engraving processing is executed in a step F 1  of  FIG. 15 , a determination is made in a step F 2  as to whether or not engraving has been completed correctly. When engraving has not been completed correctly, the storage processing is terminated, and when engraving has been completed correctly, the routine advances to a step F 3 . In the step F 3 , a determination is made as to whether or not duplex printing images have been engraved. When duplex printing images have been engraved, the routine advances to a step F 4 , and when duplex printing images have not been engraved, it is assumed that a simplex printing image has been engraved, and the routine advances to a step F 5 . 
   In the step F 4 , drum identification information from the drum identification detecting means  55 , information indicating that the master is engraved with duplex printing images (i.e. that the master is the duplex master  14 ), and information indicating the sheet size that can be printed by this master, are stored in association in the storage unit  50 , whereupon the control is terminated. In the step F 5 , drum identification information from the drum identification detecting means  55 , information indicating that the master is engraved with a simplex printing image (i.e. that the master is the simplex master  15 ), and information indicating the sheet size that can be printed by this master, are stored in association in the storage unit  50 , whereupon the control is terminated. 
   The warning processing of this embodiment will now be described using the flowchart shown in  FIG. 16 . Steps G 1  to G 3  of  FIG. 16  are identical in content to the steps B 1  to B 3 . 
   In the step G 3 , when the master is not wrapped around the printing drum  11 , the control is terminated, and when the master is wrapped around the printing drum  11 , the routine advances to a step G 4 , where the master identification information and sheet size information corresponding to the drum identification information are read from the storage unit  50 . The routine then advances to a step G 5 . 
   In the step G 5 , sheet size information from the sheet size detecting means  42  and the read sheet size information are compared, and a determination is made as to whether or not a sheet P that can actually be used for printing is set on the sheet feeding tray  41 . Here, when the sheet size information from the sheet size detecting means  42  indicates a sheet size that can be used for printing, the control is terminated. When the sheet size information indicates a sheet size that cannot be used for printing, the routine advances to a step G 6 . In the step G 6 , warning content indicating that no sheets of a printable size are present on the sheet feeding tray  41  is displayed on the LCD display apparatus  36 . The control is then terminated. As an example of the warning content, “the sheet in the sheet feeding tray cannot be printed. Please insert a size { } sheet in the sheet feeding tray” may be displayed, as shown in  FIG. 17 . The size of the sheet that should be set (for example, A4 vertical, B5 vertical) is displayed within { } in the drawing. 
   When two engraved images are formed on a single master and the auxiliary tray  8  is provided, as in the stencil printing apparatus shown in  FIG. 1 , the sheet sizes that can be printed by the master are limited by the images formed on the master. Hence, by executing a warning operation, in which warning content is displayed on the LCD display apparatus  36 , when the drum identification information and sheet size information, which are obtained anew during input of an operation command to the apparatus or an attachment/detachment command relating to the printing drum  11 , differ from the sheet size information stored in the storage unit  50  in association with the drum identification information, the apparatus operator can be warned thereof. As a result, situations in which the master breaks or ink adheres to the press roller  12  when simplex printing is performed mistakenly using the duplex master  14  or duplex printing is performed mistakenly using the simplex master  15  can be prevented, and master consumption due to re-engraving during duplex printing can be suppressed. 
   Fifth Embodiment 
   In this embodiment, as shown in  FIG. 18 , the stencil printing apparatus comprises a plurality of sheet feeding units  4 A and  4 B for feeding the sheets P. The sheet feeding units  4 A,  4 B are constituted identically to the sheet feeding unit  4 , and sheet feeding trays  41 A,  41 B thereof are provided respectively with sheet size detection sensors  41 A,  42 B for detecting the size of the sheets set on each tray. In this embodiment, the master identification information, indicating whether the master is engraved with duplex printing images or a simplex printing image during engraving, and sheet size information corresponding to the master identification information, are stored in the storage unit  50  in association with the drum identification information, and if sheet size information corresponding to printing drum identification information that is detected (obtained) anew by the drum type detection sensor  55  when various apparatus operation commands are input into the control means  40  from the operating panel  30  or a printing drum attachment/detachment command is input from the drum attachment detection sensor  56  differs from the sheet size information stored in the storage unit  50 , a sheet feeding operation by the sheet feeding unit  4 A or  4 B in relation to which the different sheet size information was detected is prohibited. 
   The master identification information and sheet size are stored in the storage unit  50  using processing having the same steps as the processing shown in  FIG. 15 . Tray selection prohibition processing will now be described using the flowchart shown in  FIG. 19 . Steps H 1  to H 4  of  FIG. 19  are identical in content to the steps G 1  to G 4 . In the step H 4 , similarly to the step G 4 , the master identification information and sheet size information corresponding to the drum identification information are read from the storage unit  50 , whereupon the routine advances to a step H 5 . In the step H 5 , sheet size information from the respective sheet size detecting means  42 A,  42 B and the sheet size information read from the storage unit  50  are compared, and the sheet feeding tray  41  set with a sheet P that can actually be used for printing is determined. When one of the sheet feeding trays is set with a sheet size that can be used for printing, measures are taken in a step H 6  to ensure that this sheet feeding tray is used, whereupon the control is terminated. When one of the sheet feeding trays is set with a sheet size that can be used for printing, the routine advances to a step H 7 , where use of the sheet feeding tray set with the unprintable sheet is prohibited. The control is then terminated. 
   Here, making the sheet feeding tray set with a sheet size that can be used for printing usable involves displaying the sheet sizes set on the sheet feeding trays attached to the apparatus main body  43  on the LCD display apparatus  36  so that a usable sheet size can be selected therefrom, as shown in  FIGS. 20A and 20B , or displaying the usable sheet feeding trays so that a usable tray can be selected, as shown in  FIG. 20C , for example. 
   Prohibiting use of a sheet feeding tray set with a sheet size that cannot be used for printing may involve displaying the sheet size set on the sheet feeding tray  41 A or the sheet feeding tray  41 B attached to the apparatus main body  43  on the LCD display apparatus  36 , and preventing selection of the sheet sizes that cannot be used by displaying these sheet sizes in the form of a matrix, as shown in  FIG. 20A , not displaying the sheet sizes that cannot be used, as shown in  FIG. 20B , or not displaying the sheet feeding tray set with an unusable sheet, as shown in  FIG. 20C . In these cases, the LCD display apparatus  36  is preferably a so-called touch panel switch having a switch function, rather than simply a display apparatus. When use of a switch displayed on the LCD display apparatus  36  of the operating panel  30  is disabled or a switch is not displayed, the corresponding sheet feeding tray cannot be selected, and thus a sheet feeding operation by the sheet feeding unit comprising the corresponding sheet feeding tray can be prohibited. 
   When two engraved images are formed on a single master and the auxiliary tray  8  is provided, as in the stencil printing apparatus shown in  FIG. 1 , the sheet sizes that can be printed by the master are limited by the images formed on the master. Hence, when the sheet size information corresponding to the printing drum identification information that is detected (obtained) anew by the drum type detection sensor  55  differs from the sheet size information stored in the storage unit  50 , a sheet feeding operation by the sheet feeding unit  4 A or the sheet feeding unit  4 B in which the different sheet size information is detected can be prohibited, and as a result, erroneous selection of an unprintable sheet size by the apparatus operator can be forestalled. 
   In each embodiment, the various control functions of the control means  40  were described individually. However, these embodiments may be combined appropriately and executed in a series of control operations having a plurality of control functions. For example, the first embodiment may be combined with the second and third embodiments, the first embodiment may be combined with the fourth embodiment, and the first embodiment may be combined with the fifth embodiment. 
   According to the present invention described above, the following effects are obtained.
     (1) The duplex printing mode or the simplex printing mode is selected on the basis of at least plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus and master identification information stored in the storage unit in association with the plate cylinder identification information. Therefore, situations in which the master breaks or ink adheres to the pressing means when simplex printing is performed mistakenly using a master engraved with duplex printing images or duplex printing is performed mistakenly using a master engraved with a simplex printing image can be prevented, and master consumption due to re-engraving during duplex printing can be suppressed.   (2) The master identification information is displayed on the display means on the basis of at least plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus and master identification information stored in the storage unit in association with the plate cylinder identification information. Therefore, unnecessary engraving can be suppressed, leading to a decrease in master consumption, and the apparatus operator can prepare paper corresponding to the master more easily.   (3) A warning operation is executed when at least the plate cylinder identification information, which is obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus, and the master identification information stored in the storage unit in association with the plate cylinder identification information differ from each other. Hence, the apparatus operator can be warned, and unnecessary engraving can be suppressed, leading to a decrease in master consumption.   (4) A warning operation is executed when at least the plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus and sheet size detection information from the sheet size detecting means differ from the master identification information and sheet size detection information stored in the storage unit in association with the plate cylinder identification information. Hence, the apparatus operator can be warned, situations in which the master breaks or ink adheres to the pressing means when simplex printing is performed mistakenly using a master engraved with duplex printing images or duplex printing is performed mistakenly using a master engraved with a simplex printing image can be prevented, and master consumption due to re-engraving during duplex printing can be suppressed.   (5) When at least the plate cylinder identification information obtained anew when an operation command or a plate cylinder attachment/detachment command is input into the apparatus and sheet size detection information from respective sheet size detecting means differ from the master identification information and sheet size detection information stored in the storage unit in association with the plate cylinder identification information, a sheet feeding operation by the sheet feeding unit in which the different sheet size information was detected is prohibited. Therefore, situations in which the master breaks or ink adheres to the pressing means when simplex printing is performed mistakenly using a master engraved with duplex printing images or duplex printing is performed mistakenly using a master engraved with a simplex printing image can be prevented, master consumption due to re-engraving during duplex printing can be suppressed, and erroneous selection by the apparatus operator of a sheet size that cannot be printed can be forestalled.   

   Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure, without departing from the scope thereof.