Patent Publication Number: US-6334388-B1

Title: Stencil printer with controlled movement of paper rack and ink drum

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a stencil printer and more particularly to a stencil printer of the type including a multistage paper feeding device capable of feeding papers of different kinds and an ink drum shiftable in the widthwise direction of the papers perpendicular to a direction in which the papers are conveyed. 
     A digital stencil printer is conventional which uses a laminate thermosensitive stencil made up of a thermoplastic resin film and a porous support adhered to each other. The printer includes athermal head for selectively perforating, or cutting, the resin film of the stencil with heat in accordance with image data. After the perforated stencil or master has been wrapped around an ink drum, ink feeding means arranged in the drum feeds an adequate amount of ink to the inner periphery of the drum. A press roller, press drum or similar pressing member presses a paper or similar recording medium against the ink drum so as to transfer the ink from the drum to the paper via the porous portion of the drum and the perforations of the master. As a result, an image represented by the image data is printed on the paper. Usually, a paper feeding device for continuously feeding papers one by one is built in the printer. The paper feeding device generally includes a feed tray to be loaded with a stack of papers and a pair of side fences for guiding the papers in the widthwise direction of the papers. 
     With the above printer, it is possible to shift the position of an image on the paper in the widthwise direction of the paper perpendicular to the direction of paper conveyance by shifting the feed tray of the paper feeding device in the widthwise direction. However, the adjustment of the shift relying on eyesight and the manual shift of the feed tray cannot easily implement delicate adjustment or accurate adjustment. In light of this, Japanese Patent Laid-Open Publication No. 5-306025, for example, discloses an arrangement for automatically shifting the feed tray of the paper feeding device. 
     To meet various kinds of needs, a stencil printer including a multistage paper feeding device has recently been proposed. The multistage paper feeding device has a plurality of paper stocking portions and is capable of feeding papers of particular kind from each paper stocking portion. For such a multistage paper feeding device, Japanese Patent Laid-Open Publication No. 6-345281, for example, teaches an arrangement for automatically shifting a plurality of feed trays in the widthwise direction of the papers at the same time. 
     However, in any one of the conventional arrangements, a discharge tray for receiving papers, or printings, is not shiftable although the feed tray is shiftable. This brings about a problem that when the feed tray is shifted, the resulting printings cannot be accurately positioned on the discharge tray, and a problem that a pair of side fences on the discharge tray must be shifted independently of each other, obstructing easy operation. The arrangement taught in the above Laid-Open Publication No. 6-345281 has a drawback that a complicated construction is necessary for all of the feed trays to be shifted at the same time. Moreover, when the center of any one of the feed trays is deviated, the position of an image on a paper varies and must be adjusted every time the feed tray is selected. 
     Japanese Patent Laid-Open Publication No. 6-293175, for example, proposes an implementation for promoting accurate positioning of papers on the discharge tray, easy operation of the side fences of the discharge tray and simple construction. The implementation taught in this document is such that the feed tray and discharge tray are fixed in place while the ink drum is shiftable in the widthwise direction of papers. At the time of printing, the ink drum is shifted in the above direction for adjusting the position of an image on a paper. 
     A problem with the above Laid-Open Publication No. 6-293175 is that if the center line of any one of the feed trays included in the multistage paper feeding device is deviated, then the ink drum must be readjusted in position by troublesome operation every time the feed tray is selected. Another problem is that adjusting the center tray by tray is not practicable without resorting to highly accurate assembly, increasing the cost and reducing design freedom. 
     Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-40137, 10-1254, and 5-124737. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a stencil printer capable of adjusting, when the center of any feed tray of a multistage paper feeding device is deviated, an image position on a paper easily and automatically without increasing the cost. 
     A stencil printer of the present invention includes a hollow cylindrical, porous ink drum freely rotatable. A multistage paper feeding device includes a plurality of paper stacking portions and capable of feeding papers of particular size from each paper stacking portion. At least one pair of side fences are mounted on each paper stocking portion for positioning the papers in the widthwise direction of the papers. A rack is positioned to stack the papers or printings each carrying a printed image thereon. An ink drum shifting device shifts the ink drum in the width wise direction of the papers perpendicular to the direction of conveyance of the papers. A rack shifting device shifts the rack in the widthwise direction of the papers. A storing device stores the position of a center line of a paper transport path for each of the paper stocking portions. A control section controls the operation of the ink drum shifting device and that of the rack shifting device in accordance with the position of the center line stored in the storing device. 
    
    
     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 fragmentary front view showing a stencil printer embodying the present invention; 
     FIG. 2 is a fragmentary plan view of a paper feeding section included in the embodiment of FIG.  1  and an alternative embodiment of the present invention; 
     FIG. 3 is a partly sectional plan view of an electrically driven rack also included in the embodiment of FIG.  1  and alternative embodiment; 
     FIG. 4 is a partly sectional side elevation of the rack shown in FIG. 3; 
     FIG. 5 is a plan view showing an operation panel further included in the embodiment of FIG.  1  and alternative embodiment; 
     FIG. 6 is a block diagram schematically showing control means particular to the embodiment of FIG. 1; 
     FIG. 7 is a fragmentary front view showing the alternative embodiment; and 
     FIG. 8 is a partly sectional plan view of a modification of the rack shown in FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 of the drawings, a stencil printer embodying the present invention is shown and generally designated by the reference numeral  1 . As shown, the stencil printer includes a casing  9  accommodating an image reading section  2 , a paper feeding section  3  or multistage paper feeding device  3 , a master making section  4 , a paper discharging section  6 , a master discharging section  7 , and a control section  8 . 
     An image reading section  2  is mounted on the top of the casing  9  and includes a glass platen  10  on which a document is to be laid. A document feed tray  11  is used to lay a desired document or documents. A roller pair  12  and a roller  13  convey a document. Guides  14  and  15  respectively adjoin the roller pair  12  and roller  13  for guiding a document being conveyed. A belt  16  conveys a document along the glass platen  10 . A flat direction selector  17  switches a direction in which a document read by the reading section  2  should be discharged. A document discharge tray  18  receives a document driven out via the direction selector  17 . Mirrors  19  and  20  and a fluorescent lamp  21  scan a document. A lens  22  focuses the resulting reflection or image light to a CCD (Charge Coupled Device) image sensor or similar image sensor  23 . 
     Among the above constituents of the image reading section  2 , the document feed tray  11 , roller pair  12 , roller  13 , guides  14  and  15 , belt  16 , direction selector  17  and document discharge tray  18  are mounted on a conventional cover plate, not shown, constituting an ADF (Automatic Document Feeder) unit  24 . The ADF unit  24  may be angularly moved toward and away from the glass platen  10  by hand. 
     The paper feeding section  3  arranged in the lower portion of the casing  9  includes a first tray  28 , a second tray  29 , a third tray  30 , and a fourth tray  25  each constituting a paper stocking portion. 
     The first and second trays  28  and  29  allow papers P 1  and P 2  of the same size to be stacked thereon. The third tray  30  allows papers P 3  of relatively large size to be stacked thereon. The fourth tray  25  allows papers P 4  to be fed by hand. A paper shifter  31  shifts the entire paper stack P 2  from the tray  29  to the tray  28  when the papers P 1  on the tray  28  are used up. Pick-up rollers  32 ,  33  and  26  respectively feed the papers P 1 , P 3  and P 4  one by one. Pressers  34  and  35  press the papers P 1  and P 3  against the pick-up rollers  32  and  33 , respectively. Separation roller pairs  37 ,  38  and  27  are respectively associated with the pick-up rollers  32 ,  33  and  26 , and each separates the top paper from the underlying papers. Additionally included in the paper feeding section  3  are roller pairs  39  and  40  and a group of rollers  41  for conveyance, and a registration roller pair  42 . 
     The second tray  29  may be pulled out of the casing  9  while the printer  1  is in operation. This kind of configuration is taught in, e.g., Japanese Patent Laid-Open Publication No. 5-124737 mentioned earlier. A substantially linear paper transport path extends from the fourth tray  25  into the casing  9  for allowing relatively thick papers, envelopes and other special papers to be fed. 
     FIG. 2 shows major part of the paper feeding section  3  in a plan view, i.e., in the direction in which the papers P 1 -P 4  are fed downward. As shown, the trays  28  and  29  arranged linearly side by side have a common center line C 1  while the tray  30  has a center line C 2 . The tray  25  has a center line C 3 . The center lines C 1 -C 3  each are deviated from the center line C 0  of a paper transport path defined in the casing  9  by a particular amount for design and allowance reasons. Specifically, in FIG. 2, the center line C 1  is deviated to the right by an amount δ1 while the center line C 2  is deviated to the left by an amount δ2. The center line C 3  is deviated to the right by an amount δ3. 
     As also shown in FIG. 2, the trays  28  and  29  respectively include a pair of side fences  28   a  and a pair of side fences  29   a  for guiding the associated papers P 1  and P 2  in the widthwise direction. Likewise, the trays  30  and  25  respectively include a pair of side fences  30   a  and a pair of side fences  25   a  for guiding the associated papers P 3  and P 4  in the widthwise direction. The side fences  28   a ,  29   a ,  30   a  and  25   a  are respectively removably mounted to the trays  28 ,  29 ,  30  and  25  by, e.g., fastening or insertion. Specifically, the paired side fences are engageable with the associated tray at positions equally spaced from the associated center line in the right-and-left direction and corresponding to a desired paper size. The papers P 1 , P 2 , P 3  and P 4  are therefore respectively stacked on the trays  28 ,  29 ,  30  and  25  with their center lines aligning with the center lines C 1 , C 2  and  03 . The centerlines C 1 -C 3  each define the centerline of a transport path for particular one of the papers P 1 -P 4 . 
     Referring again to FIG. 1, a first paper sensor  36  is positioned above the first tray  28  and senses the papers P 1  stacked on the tray  28  and pushed up by the presser  34  when contacting the papers P 1 . A first paper size sensor or paper size sensing means  45  is positioned below the tray  28  and made up of a plurality of shield type sensors. The paper size sensor  45  determines the size of the papers P 1  on the basis of the output of any one of the sensors shielded by the papers P 1 . 
     A second paper sensor  43  and a second paper size sensor or paper size sensing means  46  are arranged below the second tray  29 . The sensors  43  and  46  are respectively responsive to the presence/absence of the papers P 2  on the second tray  29  and the size of the papers P 2 . The sensor  43  is a conventional reflection type sensor and senses the papers P 2  via a hole, not shown, formed in the tray  29 . The sensor  46  is identical in configuration with the sensor  45  assigned to the first tray  28 . 
     A third paper sensor  44  identical with the first paper sensor  36  is positioned above the third tray  30  and responsive to the papers P 3  stacked on the tray  30 . A third paper size sensor or paper size sensing means  47  identical with the first paper size sensor  45  is positioned below the tray  30  and responsive to the papers P 3  stacked on the tray  30 . 
     A fourth paper sensor  55 , like the second paper sensor  43 , is located below the fourth tray  25  and responsive to the papers P 4  stacked on the tray  25 . A fourth paper size sensor or paper size sensing means  56 , like the first paper size sensor  45 , is positioned below the tray  25  for sensing the size of the papers P 4 . 
     The trays  28 - 30 , paper shifter  31 , rollers  32  and  33 , pressers  34  and  35 , roller pairs  37  and  38 , sensors  36  and  43 - 47  and roller pair  39  constitute a multistage paper feeding section  155 . 
     The master making section  4  arranged above the paper feeding section  3  includes a support member  49  supporting a stencil  48  in the form of a roll  48   a . A thermal head  50  perforates, or cuts, the stencil  48  by heating it. A platen roller  51  presses the stencil  48  against the thermal head  50  while conveying the stencil  48 . Cutting means  52  cuts the stencil  48  at a preselected length. Roller pairs  53  and  54  convey the stencil  48 . The master making section  4  is constructed into a unit removable from the casing  9 . 
     Specifically, the stencil roll  48   a  includes a core  48   b  rotatably supported by the support member  49 . A stepping motor, not shown, causes the platen roller  51  to rotate while moving means, not shown, selectively moves the platen roller  51  to a first position indicated by a solid line in FIG. 1 or a second position indicated by a dash-and-dots line. At the first position, the platen roller  51  is pressed against the thermal head  50  by a preselected pressure. At the second position, the platen roller  51  is spaced from the thermal head  50 . The cutting means  52  has a conventional configuration in which an upper edge  52   a  is rotatable or movable up and down relative to a lower edge  52   b.    
     The printing section  5  is arranged at the left of the master making section  4 , as viewed in FIG.  1 . The printing section  5  includes an ink drum  60 , ink feeding means  61 , and a press roller  62  for pressing the paper P 1 , P 2 , P 3  or P 4  (collectively paper P hereinafter) against the outer periphery of the ink drum  60 . 
     The ink drum  60  is made up of a hollow cylindrical, porous support member and a laminate of mesh screens covering the outer periphery of the support member and formed of resin or metal. The ink drum  60  is affixed to flanges, not shown, rotatably mounted on a shaft  63  which plays the role of an ink feed pipe at the same time. Drum drive means, not shown, causes the ink drum  60  to rotate in synchronism with the registration roller pair  42 . The ink drum  60  is removably mounted on the casing  9 . A damper  64  is mounted on the outer periphery of the ink drum  60  for clamping the leading edge of the perforated part of the stencil  48  (master  48  hereinafter). Opening/closing means, not shown, causes the damper  64  to open and then close when the ink drum  60  reaches a preselected angular position. 
     An image position adjusting mechanism (see Japanese Patent Laid-Open Publication No. 6-293175 mentioned earlier), a drum position sensor  69  and a master absence sensor  137  are arranged around the ink drum  60 . The image position adjusting mechanism is driven by a motor or drum shifting means  57  to shift the ink drum  60  in the axial direction of the shaft  63 , thereby shifting an image to be printed on the paper P in the width wise direction of the paper P. The drum position sensor  69  is responsive to the position of the ink drum  60  in the above direction. The master absence sensor  137  is responsive to the absence of the master  48  on the outer periphery of the ink drum  60 . 
     More specifically, the drum position sensor  69  determines the position of the ink drum  60  in terms of a shift of the drum  60  from a preselected home position which is coincident with the centerline C 0 . The master absence sensor  137  is implemented by a reflection type sensor and adjoins the damper  64  when the ink drum  60  is brought to a preselected home position in the circumferential direction, thereby determining whether or not the master  48  is present. When the sensor  137  determines that the master  48  is absent on the ink drum  60 , a step of discharging a used master from the ink drum  60 , which will be described later, is omitted at the time of master making. 
     The ink feeding means  61  disposed in the ink drum  60  includes an ink roller  65  and a doctor roller  66  in addition to the shaft  63 . The ink roller is rotatably supported by side plates, not shown, affixed to the shaft  63 . Drive transmitting means, not shown, including gears and a belt transfers a driving force to the ink roller  65  and causes it to rotate clockwise, as viewed in FIG.  1 . The doctor roller  66  adjoins the ink roller  65  such that the outer periphery of the roller  66  is parallel to the outer periphery of the roller  65 . The ink roller  65  and doctor roller  66  form a generally wedge-shaped ink well  67  therebetween. Ink in the ink well  67  is drawn out while passing through a gap between the two rollers  65  and  66 , forming a thin film on the roller  65 . 
     The press roller  62  is positioned beneath the ink drum  60  and supported by opposite side walls, not shown, of the casing  9  in such a manner as to be rotatable and angularly movable. A cam, for example, causes the press roller  62  to angularly move into and out of contact with the ink drum  60 , although not shown specifically. A spring or similar biasing means, not shown, constantly biases the press roller  62  toward the ink drum  60 . When the press roller  62  is moved away from the ink drum  60 , locking means, not shown, locks the roller  62  in a spaced position shown in FIG.  1 . 
     The paper discharging section  6  arranged at the left of the printing section  5 , as viewed in FIG. 1, includes a peeler  71 , guides  72  and  73 , a conveyor  74 , and an electrically driven rack  75 . The peeler  71  peels off the paper or printing P wrapped around the ink drum  60 . The peeler  71  is pivotally supported by the sidewalls of the casing  9  such that the edge thereof is movable toward and away from the ink drum  60 . The guides  72  and  73  are affixed to the sidewalls of the casing  9  for guiding the printing P separated from the ink drum  60  by the peeler  71 . The conveyor  74  is made up of a drive roller  76 , a driven roller  77 , an endless belt  78  passed over the two rollers  76  and  77 , and a suction fan  79 . While the suction fan  79  sucks the printing P onto the belt  78 , the belt  78  is driven by the drive roller  76  to convey the paper P in the direction indicated by an arrow in FIG.  1 . 
     The paper P conveyed by the conveyor  74  is discharged to the electrically driven rack  75 . The rack  75  includes a tray  80  to be loaded with the papers or printings P, a pair of side fences  81 , an end fence  83 , and a rack body  109 . The rack  75  locates each of the side fences  81  and end fence  83  at a particular position on the basis of a paper size signal output from the paper feeding section  3 . In addition, the rack  75  positions the tray  80  in accordance with the deviations of the trays  28 ,  29 ,  30  stored in storing means which will be described later. The rack body  109  is mounted on the casing  9  such that when the tray  80  is held at a home position, its centerline coincides with the centerline C 0 . 
     As shown in FIG. 3, the above tray  80  has a generally box-like configuration. The side fences  81  each are mounted on a respective slider  59  slidable on and along guide rails  58  which are mounted on the tray  80 . A rack  68  is mounted on the bottom of each slider  59 . A pinion gear  70  is positioned on the centerline C 0  of the tray  80  at the intermediate between the side fences  81 . The surface of each rack  68  opposite to the surface meshing with the pinion gear  70  is slidably supported by a slide guide  82  mounted on the guide rail  58 . A motor or side fence shifting means  85  drives a speed reduction mechanism  84  including an electromagnetic clutch  86 . The pinion gear  70  is operatively connected to the speed reduction mechanism  84  by a timing belt  87 . When the motor  85  is energized and the electromagnetic clutch  86  is coupled, the side fences  81  are shifted toward or away from each other symmetrically with respect to the center line C 0 , i.e., in the widthwise direction of the paper P. 
     The end fence  83 , like the side fences  81 , is mounted on a slider  99  which is, in turn, slidable on a guide rail  107  disposed in the tray  80 . A rack  100  is mounted on the bottom of the slider  99  and held in mesh with a gear  101 . The surface of the rack  100  opposite to the surface meshing with the gear  101  is slidably supported by a slide guide  102  mounted on the guide rail  107 . The gear  100  is operatively connected to a speed reduction mechanism  105  including an electromagnetic clutch  103  and driven by a motor  104 . When the motor  104  is energized and the electromagnetic clutch  103  is coupled, the end fence  83  is shifted in the direction in which the paper is conveyed (direction of paper conveyance hereinafter). 
     A side fence sensor  106  adjoins one of the racks  68  for sensing the position of the side fence associated with the rack  68 . Likewise, an end fence sensor  108  adjoins the rack  100  for sensing the position of the end fence  83 . The sensors  106  and  108 , like the first paper size sensor  45 , each is made up of a plurality of shield type sensors. Tongues  68   a  and  100   a  respectively extend out from the surfaces of the racks  68  and  100  opposite to the meshing surfaces. The position of the fence  81  or  83  is determined on the basis of the sensor shielded by the tongue  68   a  or  100   a , respectively. This kind of sensing configuration is conventional. 
     As shown in FIG. 4, a rail member  110  is disposed in the rack body  109 . A slider  111  is mounted on the bottom of the tray  80  and slidable on and along the rail member  110 . A stepping motor or rack shifting means  112  includes a pinion gear  112   a  and disposed in the rack body  109  upstream of the rail member  110  in the direction of paper conveyance. The pinion gear  112   a  is held in mesh with a rack  113  mounted on the bottom of the tray  80 . Control means  133  (see FIG. 6) controls operation of the stepping motor  112 , as will be described specifically later. 
     As shown in FIG. 1, the master discharging section  7  is located above the paper discharging section  6  and includes an upper discharge member  88 , a lower discharge member  89 , a box  90  for collecting used masters, and a compressor  91 . 
     The upper discharge member  88  is made up of a drive roller  92 , a driven roller  93 , and an endless belt  94  passed over the two rollers  92  and  93 . The drive roller  92  rotates clockwise, as viewed in FIG. 1, causing the belt  94  to move in the direction indicated by an arrow. Likewise, the lower discharge member  89  is made up of a drive roller  95 , a driven roller  96 , and an endless belt  97  passed over the rollers  95  and  96 . The drive roller  95  rotates counterclockwise, as viewed in FIG. 1 to move the belt  97  in the direction indicated by an arrow. Moving means, not shown, selectively moves the lower discharge member  89  to a position shown in FIG. 1 or a position where the circumference of the drive roller  95  contacts a used master  98  wrapped around the ink drum  60 . Lowering means, not shown, selectively lowers the compressor  91  into the box  90  for compressing the used master  98  collected in the box  90 . The two discharge members  88  and  89 , box  90  and compressor  91  are constructed into a unit removable from the casing  9 . 
     FIG. 5 shows a specific arrangement of a control panel  114  mounted on the front part of the top of the stencil printer  1 . As shown, the control panel  114  includes a perforation start key  115  for starting a master making operation, a print start key  116 , a proof print key  117 , a stop key  118 , numeral keys  119 , an enter key  120 , a clear key  121 , a program key  122 , a mode key  123 , a mode clear key  124 , enlarge/reduce keys  125 , print speed keys  126 , image position keys  127 , a tray key  128 , a display  129  implemented by seven-segment LEDs (Light Emitting Diodes), a display  130  implemented by an LCD (Liquid Crystal Display), an error display  131  for displaying, e.g., a jam and implemented by LEDs, and indicators  132  for showing a tray selected on the tray key  128  and implemented by LEDs. Operation commands input on the control panel  114  are sent to the control section  8 , FIG.  1 . 
     The image position keys  127  allow the operator of the printer  1  to shift the position of an image to be printed in the right-and-left direction, i.e., the widthwise direction of the paper P. Usually, the keys  127  each cause the motor  57  to operate for shifting the ink drum  60  inthe widthwise direction of the paper P by any desired amount. In a serviceman program mode, which will be described later, a serviceman is allowed to operate the keys  127  in combination with the mode key  123  for shifting the tray  80  of the rack  75  in the widthwise direction of the paper P by any desired amount via the stepping motor  112 . 
     The tray key  128  allows the operator to select one of the first tray  28 , third tray  30  and fourth tray  25  loaded with desired papers P; every time the operator presses the key  128 , one of the indicators or tray indicating means  132  turns on. In the illustrative embodiment, TRAYS  1 - 3  on the control panel  114  correspond to the first tray  28 , third tray  30  and fourth tray  25 , respectively. In addition, every time the key  128  is pressed, the size of papers P stacked on the desired tray appears on the display  130  on the basis of the output of the paper size sensor  45 ,  47  or  56 . 
     FIG. 6 shows the previously mentioned control means  133  constituting the major part of the control section  8 , FIG. 1, disposed in the casing  9 . As shown, the control means  133  is implemented by a conventional microcomputer including a CPU (Central Processing Unit)  134 , a RAM (Random Access Memory)  135 , a ROM (Read Only Memory)  136 , and an I/O (Input/Output) expander  137 . The control means  133  controls the entire printer  1 . 
     The CPU  134  receives the output signals of the various sensors and control panel  114 . The image reading section  2 , paper feeding section  3 , master making section  4 , printing section  5 , paper discharging section  6  and master discharging section  7  each are connected to the CPU  134  via a respective driver. The CPU  134  performs, based on a program stored in the ROM  136  beforehand, operations with the signals input from the sensors and control panel  114  and sends a particular control signal to the driver of each of the above sections  2 - 7 . At the same time, the CPU  134  sends display signals to the control panel  114 . 
     The CPU  134  temporarily writes the program read out of the ROM  136  in the RAM  135 . The program written to the RAM  135  may be rewritten via the control panel  114 , as desired. Further, when the center lines C 1 -C 3  of the first tray  28 , third tray  30  and fourth tray  25  should be brought into alignment with the center line C of the casing  9 , the deviations δ1, δ2 and δ3 stated earlier are written to the RAM  135  by a procedure to be described later; in this sense, the RAM  135  plays the role of storing means. 
     More specifically, the ROM  136  stores a plurality of different programs for operating various actuators included in the printer  1 . Among them, a program for causing the center lines C 1 , C 2  and C 3  to coincide with the center line C 0  is implemented as a program for operating the motor  57  and stepping motor  112 . 
     The printer  1  having the above construction will be operated as follows. First, a procedure for causing the centerlines C 1 -C 3  to align with the center line C 0  will be described. This procedure is effected only at the manufacturer&#39;s station before shipment, but cannot be done by the user after shipment. 
     Specifically, a worker at the manufacturer&#39;s station calls the previously mentioned serviceman program mode by operating the program key  122 , mode key  123  and so forth arranged on the control panel  114 . 
     The serviceman program mode can be called only if the keys are manipulated in a preselected manner or if a password, for example, is input. This inhibits the user from calling the serviceman program mode. 
     Assume that the worker called the serviceman program mode presses the tray key  128  to select TRAY  1 . In response, the control means  133  sends a particular drive signal to each of the motors  85 ,  104  and stepping motor  112 . As a result, the tray  80  of the electrically driven rack  75  is brought to its home position. At the same time, the side fences  81  and end fence  83  each are moved to a particular home position outside of a position corresponding to a maximum paper size available with the printer  1 , then moved to a preselected position corresponding to the size of the papers P 1  sensed by the paper size sensor  45 , and then stopped on the basis of the output of the fence sensor  106  or  108 . At this instant, the control means  133  locates the ink drum  60  at its axial home position and clears the area of the RAM  135  expected to store the deviations δ1, δ2 and δ3 which will be described specifically later. 
     After the selection of TRAY  1 , the worker lays a single document on the document feed tray  11  and then presses the perforation start key  115 . In response, the document reading section  2  reads the document and sends an image data signal representative of the document to the control means  133 . 
     The master discharging section  7  performs a master discharging operation in parallel with the image reading operation of the document reading section  2 . Initially, however, the used master  98  is absent on the ink drum  60 . Therefore, in response to the master absence sensor  137 , the master discharging operation is omitted. After the ink drum  60  has been rotated to a preselected master feed position, the control means  133  causes the opening/closing means to open the damper  64 . The ink drum  60  is held in a stand-by position for waiting for the master  48 . 
     The document reading operation is followed by a master making operation. Specifically, when the ink drum  60  reaches the stand-by position, the control means  133  energizes the stepping motor, not shown, for causing it to rotate the platen roller  51  and rollers  53  and  54 . As a result, the stencil  48  is paid out from the roll  48   a l and perforated by the thermal head  50 , as stated previously.    
     The perforated part of the stencil, i.e., the master  48  is conveyed toward the damper  64 . When the control means  133  determines, in terms of the number of steps of the stepping motor, that the leading edge of the master  48  has reached a position where it is ready to be clamped by the damper  64 , the control means causes the opening/closing means to close the damper  64 . The damper  64  therefore retains the leading edge of the master  48  on the ink drum  60 . 
     Subsequently, the ink drum  60  is rotated clockwise, as viewed in FIG. 1, at a peripheral speed equal to the conveyance speed of the master  48 , so that the master  48  is sequentially wrapped around the ink drum  60 . When the control means  133  determines, in terms of the number of steps of the stepping motor, that a single master  48  has been completed, the control means  133  causes the platen roller  51  and roller pairs  53  and  54  to stop rotating. At the same time, the control means  133  causes the upper edge  52   a  to move relative to the lower edge  52   b  for thereby cutting off the master  48 . The ink drum  60  in rotation pulls the cut master  48 . When the ink drum  60  again reaches its circumferential home position, it is brought to a stop to end the master wrapping operation. 
     After the master  48  has been wrapped around the ink drum  60 , a trial printing is produced, as follows. Before the end of the master wrapping operation, the control means  133  causes the presser  34  to press the first tray  28  upward until the top of the stack of papers P 1  contacts the pick-up roller  32 . Then, the control means  133  stops elevating the presser  34  and thereby locates the first tray  28  at a preselected paper feed position. 
     After the ink drum  60  has been stopped at the circumferential home position, the control means  133  causes the drum  60  to start rotating at a low speed and causes the pick-up roller  32 , separation roller pair  37 , roller pair  40  and roller group  41  to start rotating. The pick-up roller  32  and separation roller pair  37  cooperate to pull out the top paper P from the first tray  28 . The registration roller pair  42  nips the leading edge of the paper P 1  fed from the tray  28 . 
     When the leading edge of the image area of the master  48  wrapped around the ink drum  60  reaches a position corresponding to the press roller  62 , the control means  133  causes the registration roller pair  42  to start rotating and driving the paper P 1  toward the gap between the ink drum  60  and the press roller  62 . The control means  133  actuated the registration roller pair  42 , as stated above, causes the locking means to unlock the press roller  62 . As a result, the press roller  62  is angularly moved toward the ink drum  60 . 
     The press roller  62  presses the paper P 1  fed from the registration roller pair  42  against the master  48  existing on the ink drum  60 . Consequently, the paper P 1  and master  48  are pressed between the press roller  62  and the ink drum  60 . Ink fed to the inner periphery of the ink drum  60  by the ink roller  65  penetrates through the porous support and mesh screens of the ink drum  60  and then fill is the interstice between the ink drum  60  and the master  48 . Finally, the ink is transferred from the ink drum  60  to the paper P 1  via the perforations of the master  48 . 
     The peeler  71  peels off the paper P 1  carrying the ink thereon from the ink drum  60  while introducing it into the gap between the guides  72  and  73 . The paper P 1  is conveyed to the left, as viewed in FIG. 1, by the belt  78  while being held on the belt  78  by the suction of the suction fan  79 . As a result, the paper or trial printing P 1  is driven out to the tray  80 . 
     On completing the above sequence of steps, the printer  1  waits for an actual printing operation. The worker checks the trial printing P 1  driven out to the tray  80  by eye so as to determine to which side and how much the position of the printed image is deviated from the center line of the printing P 1 . In the illustrative embodiment, the image is assumed to be deviated to the front side of the printer  1  by the amount δ1, as shown in FIG.  2 . Subsequently, the worker causes the motor  57  and stepping motor  112  to operate via the mode key  123  and image position key  127  such that the ink drum  60  and tray  80  are shifted to the front side by the above amount δ1. Such a shift of theinkdrum  60  and tray  80  is digitally displayed on the display  129 . 
     After the positioning of the ink drum  60  and tray  80 , the worker presses the proof print key  117 . In response, another paper P 1  is fed from the first tray  28  and nipped by the registration roller pair  42  in the same manner as the first paper P 1 . At the same time, the ink drum  60  is caused to rotate at a high speed at the same timing as in the trial printing procedure. The registration roller pair  42  drives the paper P 1  toward the gap between the ink drum  60  and the press roller  62 . The paper P 1  is pressed against the master  48  present on the ink drum  60  by the press roller  62  with the result that the ink is transferred to the paper P 1  for forming an image. Again, the peeler  71  removes the paper P 1  from the ink drum  60 , and the conveyor  74  conveys the paper P 1  to the tray  80 . As soon as the ink drum  60  is returned to the circumferential home position, the proof printing procedure ends. 
     Assume that the worker watching the above paper or proof printing P 1  determines that the position of the image is coincident with the center line of the paper P 1 . Then, the worker operates the program key  122 , mode key  123  and so forth to call a program for writing the deviation in the RAM  135  of the control means  133 . At this stage of procedure, the worker has already selected TRAY  1  on the tray key  128  (TRAY  1  included in the tray indicating means  132  turning on) and has shifted the ink drum  60  and tray  80  to the front side by δ1. In this condition, the worker presses, e.g., the enter key  120  with the result that the deviation of the center line C 1  of the first tray  28  from the center line C 0  of the paper transport path (δ1 to the front side) is written to the RAM  135 . 
     Next, the worker selects TRAY  2  on the tray key  128 . Zero is stored in the area of the RAM  135  assigned to the deviation of TRAY  2 , as stated earlier. Therefore, the ink drum  60  is brought to its axial home position. Subsequently, the worker presses the perforation start key  115 . In response, the printer  1  executes the master making step, master feeding step and trial printing step to thereby output a paper or trial printing P 3  to the tray  80 . The worker measures the deviation of an image printed on the paper P 3 , causes the ink drum  60  and tray  80  to move to the rear side of the printer  1  by δ2, and then presses the proof print key  117 . When another paper or proof printing P 3  is driven out to the tray  80 , the worker determines whether or not an image printed on the paper P 3  is coincident with the center line of the paper P 3 . If the answer of this decision is positive, the worker again calls the program for writing a deviation in the RAM  135  and then presses the enter key  120 . 
     As a result, the deviation of the center line C 2  of the third tray  3  from the center line C 0  (δ2 to the rear side) is written to the RAM  135 . 
     The worker repeats the above procedure described in relation to TRAY  2  with TRAY  3  so as to determine the deviation of a paper P 4  driven out to the tray  80 . The steps to follow are the same as in the above procedure except that the ink drum  60  and tray  80  are shifted to the front side by δ3, and that the deviation δ3 between the center lines C 3  and C 0  is written to the RAM  135 . 
     On confirming that the deviations of the trays  28 ,  30  and  25  have been written to the RAM  135 , the worker escapes from the serviceman program mode by operating the program key  122 , mode key  123  and so forth. The centerlines C 1 , C 2  and C 3  of the trays  28 ,  30  and  25  are now coincident with the centerline C 0  of the casing  9 . 
     The printer  1  is operated at the user&#39;s station, as follows. First, the operator at the user&#39;s station lays a desired document on the document feed tray  11  and selects a desired tray on the tray key  128 . The tray indicator  132  displays the tray selected. The operator may operate either one of the enlarge/reduce keys  125  for selecting a desired magnification. In the following description, assume that the operator selects TRAY  3  (fourth tray  25 ) on the tray key  128 . 
     When the operator presses the perforation start key  115 , the image reading section  2  reads the document while sending an image data signal representative of the document to the control means  133 . In the paper feeding section, the elevating means raises the fourth tray  25  until the top of the paper stack P 4  contacts the pick-up roller  26 . 
     When the operator presses the perforation start key  115 , the deviation of the centerline C 3  of the fourth tray  25  is read out of the ROM  136 . The control means  133  causes the motor  57  and stepping motor  112  to automatically shift the ink drum  60  and tray  80  to the front side of the printer  1  by δ3. Further, the control means  133  drives the motors  85  and  104  such that the si de fences  81  and end fence  83  each are located at the respective home position and then moved to a particular position matching with the size of the papers P 4  as determined by the fourth paper size sensor  56 . After the fences  81  and  83  have been positioned on the basis of the outputs of the fence sensors  106  and  108 , respectively, the suction fan  79  is driven. 
     The master discharging section  7  removes the used master  98  from the ink drum  60  in parallel with the operation of the image reading section  2 , as stated earlier. Of course, when the printer  1  is operated for the first time at the user&#39;s station, such a master discharging operation is omitted because a used master is absent on the ink drum  60 . 
     The drum drive means, not shown, causes the ink drum  60  with the used master  98  wrapped therearound to rotate counterclockwise, as viewed in FIG.  1 . When the control means  133  determines that the trailing edge of the used master  98  has reached a preselected discharge position corresponding to the drive roller  95 , the control means  133  causes the drive means and moving means to rotate the drive rollers  92  and  95  and move the lower discharge member  89  toward the ink drum  60 . At the time when the drive roller  95  contacts the used master  98 , the ink drum  60  is rotating counterclockwise. Therefore, the used master  98  picked up by the drive roller  95  is nipped by the upper discharge roller  89  and lower discharge roller  88  and peeled off from the drum  60  thereby. Thereafter, the used master  98  is conveyed to the box  90  by the discharge members  89  and  88  and compressed in the box  90  by the compressor  91 . 
     After the used master  98  has been fully removed from the ink drum  60 , the ink drum  60  is further rotated to the previously mentioned master feed position. Subsequently, the control means  133  causes the opening/closing means to open the camper  64 . In this condition, the ink drum  60  waits for a new master. This is the end of the master discharging operation. 
     The above master discharging operation is followed by the master making operation described previously. The master making operation will not be described specifically in order to avoid redundancy. The difference is that in this case the paper P 4  is fed from the fourth tray  25 . 
     After a new master  48  has been wrapped around the ink drum  60  by the previously stated manner, the trial printing step is executed. After the ink drum  60  has been stopped at the circumferential home position, the control means  133  causes the drum  60  to start rotating at the low speed and causes the pick-up roller  26 , separation roller pair  27 , roller pair  40  and roller group  41  to start rotating. The pick-up roller  26  and separation roller pair  27  cooperate to pull out the top paper P 4  from the fourth tray  25 . The registration roller pair  42  nips the leading edge of the paper P 4  fed from the tray  25 . 
     When the leading edge of the image area of the master  48  wrapped around the ink drum  60  reaches a position corresponding to the press roller  62 , the control means  133  causes the registration roller pair  42  to start rotating and driving the paper P 4  toward the gap between the ink drum  60  and the press roller  62 . The control means  133  actuated the registration roller pair  42 , as stated above, causes the locking means to unlock the press roller  62 . As a result, the press roller  62  is angularly moved toward the ink drum  60 . 
     The press roller  62  presses the paper P 4  fed from the registration roller pair  42  against the master  48  existing on the ink drum  60 . Consequently, the paper P 4  and master  48  are pressed between the press roller  62  and the ink drum  60 . Ink fed to the inner periphery of the ink drum  60  by the ink roller  65  penetrates through the porous support and mesh screens of the ink drum  60  and then fills the interstice between the ink drum  60  and the master  48 . Finally, the ink is transferred from the ink drum  60  to the paper P 4  via the perforations of the master  48 . At this instant, because the center line of the paper P 4  and the center line of the ink drum  60  are in alignment, an image is printed at the center of the paper P 4  in the widthwise direction of the paper P 4 . 
     The peeler  71  peels off the paper P 4  carrying the ink thereon from the ink drum  60  while introducing it into the gap between the guides  72  and  73 . The paper P 4  is conveyed to the left, as viewed in FIG. 1, by the belt  78  while being held on the belt  78  by the suction of the suction fan  79 . As a result, the paper or trial printing P 4  is driven out to the tray  80 . At this instant, because the center line of the paper P 4  and that of the tray  80  are coincident, the paper P 4  hits against the end fence  83  and is then accurately positioned between the side fences  81 . On completing this operation, the printer  1  waits for an actual printing operation. 
     In the above condition, the operator presses the proof print key  117 . In response, another paper P 4  is fed from the first tray  25  and nipped by the registration roller pair  42  in the same manner as the first paper P 4 . At the same time, the ink drum  60  is caused to rotate at a high speed at the same timing as in the trial printing procedure. The registration roller pair  42  drives the paper P 4  toward the gap between the ink drum  60  and the press roller  62 . The paper P 4  is pressed against the master  48  present on the ink drum  60  by the press roller  62  with the result that the ink is transferred to the paper P 4  for forming an image. Again, the peeler  71  removes the paper P 4  from the ink drum  60 , and the conveyor  74  conveys the paper P 4  to the tray  80 . As soon as the ink drum  60  is returned to the circumferential home position, the proof printing procedure ends. Again, the center of this paper P 4  and the centers of the ink drum  60  and tray  80  are coincident, so that an image is printed at the center of the paper P 4  inthe widthwise direction of the paper P 4 . The paper P 4  with such an image is accurately positioned on the tray  80  by being guided by the side fences  81 . 
     The operator may press the image position keys  127  in order to shift an image on the paper P 4  for, e.g., providing the paper P 4  with a binding margin. In this case, the axial home position of the ink drum  60 , of course, includes the deviation of the fourth tray  25 , i.e., it is coincident with a position deviated from the center line C 0  to the front side by δ3. 
     If desired, exclusive keys for setting up an image position including abiding margin may be provided on the operation panel  114 . The exclusive keys will be used to write, as offset positions, tray-by-tray image positions each including a particular binding margin (deviations from the center line C 0 ) in the RAM  135  of the control means  133  in the same manner as the tray-by-tray deviations δ1-δ3. By combining the exclusive keys with the tray key  128 , it is possible to easily and automatically shift any one of the trays  28 ,  30  and  25  to an image position including a binding margin. In this case, the operator may press the image position keys  127  only when the image position needs fine adjustment. 
     With the above construction, the illustrative embodiment achieves the following unprecedented advantages. Even when any one of the centers C 1 , C 2  and C 3  of the trays  28 ,  30  and  25 , respectively, is deviated from the center C 0  of the paper transport path of the casing  9 , it is possible to easily and automatically adjust an image position without increasing the cost and to write the adjusted image position in the RAM  135 . This allows a plurality of paper stocking portions to be assembled without resorting to high accuracy which would increase the cost. Further, the illustrative embodiment enhances design freedom because it allows the center of the individual paper stocking portion to be shifted for design reasons or similar reasons. 
     Referring to FIG. 7, an alternative embodiment of the present invention is shown. As shown, a stencil printer, generally  138 , is essentially similar to the previous stencil printer  1  except for the following. A paper feeding section or multistage paper feeding device  139  with a multistage paper feeding section  140  is substituted for the paper feeding section  3 . A control section  141  is substituted for the control section  8 . 
     The paper feeding section  139  includes, in addition to the multistage paper feeding section  140  which will be described later, the pair of side fences  25   a , pick-up roller  26 , separation roller pair  27 , roller pair  40 , fourth paper sensor  55  and fourth paper size sensor  56  as well as an additional roller pair  142 . The paper feeding section  139  has a paper transport path including the above roller pair  142  in addition to the paper transport path extending from the fourth tray  25  and including the roller pair  40 . The paper transport path including the roller pair  142  extends downward in the casing  9  and terminates at an opening  143  formed in the bottom of the casing  9 . A connector  144   a  is mounted on the bottom of the casing  9 . 
     The control section or control means  141  is positioned in the lower portion of the casing  9 . The control means  141  is implemented by a microcomputer including a CPU, a ROM and a RAM although not shown specifically. The control means  141  controls the image reading section  2 , paper feeding section  139 , master making section  4 , printing section  5 , paper discharging section  6  and master discharging section  7  in accordance with a program stored in the ROM. When the center line C 3  of the tray  25  should be aligned with the center line C 0  of the casing  9 , the deviation δ3 is written to the RAM of the control means  141 . 
     The multistage paper feeding section  140  is bodily removable from the casing  9  and includes the first to third trays  28 - 30 , side fences  28   a ,  29   a  and  30   a , paper shifter  31 , pick-up rollers  32  and  33 , pressers  34  and  35 , first paper sensor  36 , separation roller pairs  37  and  38 , roller pair  39 , second paper sensor  43 , third paper sensor  44  and first to third paper size sensors  45 - 47  as well as a roller pair  145 . A paper transport path downstream of the roller pair  145  in the direction of paper conveyance extends upward in the multistage paper feeding section  140  and is communicable to the opening  143 . A connector  144   b  connectable to the connector  144   a  is mounted on the top of the multistage paper feeding section  140 , so that power can be supplied from the printer  138  to the multistage paper feeding section  140 . 
     A control section or storing means  146  is located in the lower portion of the multistage paper feeding section  140 . The control section  146  is also implemented by a microcomputer including a CPU, a ROM and a RAM although not shown specifically. When the center lines C 1  and C 2  of the first and third trays  28  and  30 , respectively, should be aligned with the center line of the casing  9 , the deviations δ1 and δ2 are written to the RAM. When the printer  138  and multistage paper feeding section  140 , i.e., the connectors  144   a  and  144   b  are electrically connected together, the control section  146  interchanges signals with the control section  141  for writing the deviations δ1 and δ2 in the RAM and sending the data written in the RAM. A back-up battery is associated with the RAM of the control section  146  so as to hold data stored in the RAM even when the connector  144   b  is disconnected from the connector  144 . 
     In the illustrative embodiment, the multistage paper feeding section  140  includes the storing means  146  for storing the centers C 1  and C 2  and deviations δ1 and δ2 of the trays  28  and  30 , respectively. Therefore, once the deviations are set, the center of the individual paper stocking portion successfully aligns with the center of the paper transport path without the deviations being set all over again later at the time of mounting. The printer  138  is therefore easy to operate. Moreover, by replacing the multistage paper feeding section  140 , it is possible to use a number of different paper stocking portions and therefore to realize various kinds of printing. 
     FIG. 8 shows an electrically driven rack  147  representative of a modification of the embodiments described above. As shown, the rack  147  differs from the rack  75  of the previous embodiments in that it does not include the rack body  109 , has the tray  80  affixed to the casing  9 , and corrects the deviation of any one of the trays  25 ,  28  and  30  from the casing  9  only by moving the side fences  81 . As for the rest of the construction, the rack  147  is identical with the rack  75 . 
     As shown in FIG. 8, the side fences  81  each are mounted on a respective slider  149  slidable on guide rails  148  disposed in the tray  80 . A rack  150  is mounted on the bottom of the each slider  149  and held in mesh with a gear  151 . The surface of each rack  150  opposite to the surface meshing with the gear  151  is slidably supported by a slide guide  152  mounted on the rail  148 . A stepping motor  153 , bifunctioning as rack shifting means and side fence shifting means, is drivably connected to the gears  151  via worms  154 . In this configuration, the stepping motor  153  causes the side fences  81  to move toward and away from each other in the widthwise direction of the paper. 
     The control means  133  or the control section  141  operates in relation to the above modification, as follows. The control means  133  or the control section  141  performs calculation with any one of the deviations δ1, δ2 and δ3 of the trays  28 ,  30  and  25  and the paper size sensed by the associated sensor  45 ,  47  or  56 . The control means  133  or the control section  141  locates, based on the result of the above calculation, one of the side fences  81  at a reference position taking account of the deviation and then positions the other side fence  81  on the basis of the number of steps counted from the reference position. 
     In the illustrative embodiments, the side fences  28   a ,  29   a ,  30   a  and  25   a  each are mounted to the associated tray  28 ,  29 ,  30  or  25  by fastening or insertion. Alternatively, the above side fences, like the side fences  81 , may be so arranged as to be movable in the widthwise direction of the paper symmetrically to each other with respect to the associated center lines C 1 -C 3  via a rack and pinion mechanism. In such a case, a construction for automatic movement including drive means and a construction for manual movement not including drive means will be provided together. 
     The illustrative embodiments each include the first to fourth trays  28 ,  29 ,  30  and  25  and essentially use the trays  28 ,  30  and  25  at the time of printing in a three-stage configuration. Alternatively, four or more trays may be arranged in a multistage configuration. 
     Further, the pairs of side fences  28   a ,  29   a ,  30   a  and  25   a  respectively provided on the first to fourth trays  28 ,  29 ,  30  and  25  each may be replaced with two or more pairs of side fences. In such a case, an arrangement should preferably be made, for a simple construction, such that when one pair of side fences are moved, the other pairs of side fences associated therewith are moved in interlocked relation. 
     In summary, it will be seen that the present invention provides a stencil printer having various unprecedented advantages, as follows. Even when any one of the centers of paper stocking portions is deviated, it is possible to easily and automatically adjust an image position without increasing the cost and to write the adjusted image position in storing means. This allows a plurality of paper stocking portions to be assembled without resorting to high accuracy which would increase the cost. Further, the stencil printer of the present invention enhances design freedom because it a lows the center of the individual paper stocking portion to be shifted for design reasons or similar reasons. 
     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.