Patent Publication Number: US-6662717-B2

Title: Printing control apparatus having printing order information producing function

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printing control apparatus for controlling a stencil printing machine wherein a plurality of stencil sheets, which are made on the basis of printing data, are wound around printing drums with which a print sheet is brought into pressured contact to perform a stencil printing operation. 
     2. Description of the Related Art 
     In the pasts, it has been a usual practice to use a stencil printing machine which enables a single color printing and a multi-color printing to be performed by allocating different ink colors to respective printing drums. Such a stencil printing machine is constructed of, for example, a first printing drum, a second printing drum and a press drum which are rotatably located, with the first and second printing drums being placed in the vicinity of an outer circumferential periphery of the press drum with a central angle of about 90 degrees with respect to the center of the press drum. 
     With such a stencil printing machine, printing data and printing start-up command are input from a PC (personal computer) connected through a communication network. In response to printing data and printing start-up command, the stencil printing machine makes a stencil sheet on the basis of printing data, with the stencil sheet being then wound on the printing drum with an associated ink color for thereby executing the printing operation. In this case, there have been many instances wherein when using different ink colors, the printing drum is replaced with a new one. When this takes place, in a printer driver, it has been a usual practice to provide a display over a display panel of the stencil printing machine or a display monitor with a warning display which calls user&#39;s attention to facilitate the printing operation to be executed with the different ink colors. 
     SUMMARY OF THE INVENTION 
     In order to control the multi-color printing operation with the PC wherein the printer driver is installed, conventionally, there have been many instances wherein printing data is transmitted to the stencil printing machine without any desired treatment. As a result, even in a case where the printing operation is implemented using the same ink color in consecutive pages, it was difficult to continuously execute the printing operation with color numbers used in each page. Further, since the printing operation is performed in a page order, there have been an increased number of times the printing drums are replaced for different ink colors, resulting in a degraded workability. 
     It is therefore an object of the present invention to provide a printing control apparatus which enables a printing operation at an increased operating efficiency to meet user&#39;s purposes in a multi-color printing operation, a recording medium which stores thereon a computer readable program, and a printing system. 
     According to a first aspect of the present invention, there is provided a printing control apparatus for controlling a stencil printing machine wherein a stencil sheet formed on the basis of printing data is wound around a replaceable printing drum with which a print sheet is held in pressured contact to implement a stencil printing operation, which comprises an information producing section configured to produce printing order information on the basis of image ink color information for each page contained in image data representative of an image to be reproduced in the stencil printing operation, in dependence on a page order, in which the stencil printing operation is executed, and the number of times the printing drum is replaced with, and an outputting section configured to output the image data and the printing order information to the stencil printing machine. 
     In accordance with the present invention, even when replacing the printing drum with a new one, printing order information is produced according to an image ink color to control the printing operation of the stencil printing machine. 
     According to a second aspect of the present invention, there is provided a computer-readable record medium having stored thereon a program for controlling a stencil printing machine wherein a stencil sheet is formed on the basis of image data and wound on an replaceable printing drum with which a print sheet is held in pressured contact to perform a stencil printing operation, which comprises an information producing section configured to produce printing order information on the basis of image ink color information for each page contained in image data representative of an image to be reproduced in the stencil printing operation, in dependence on a page order, in which the stencil printing operation is executed, and the number of times the printing drum is replaced with, and an outputting section configured to output the image data and the printing order information to the stencil printing machine. 
     In accordance with the present invention, the presence of a program read out into the computer allows the computer to functions as the aforementioned printing order information producing section and the aforementioned outputting section. 
     According to a third aspect of the present invention, there is provided a printing system which comprise a stencil printing machine wherein a stencil sheet is formed on the basis of image data and wound on a replaceable printing drum with which a print sheet is held in pressured contact to perform a stencil printing process, and a printing control apparatus including an information producing section configured to produce printing order information on the basis of image ink color information for each page contained in image data representative of an image to be reproduced in the stencil printing operation, in dependence on a page order, in which the stencil printing operation is executed, and the number of times the printing drum is replaced with, and an outputting section configured to output the image data and the printing order information to the stencil printing machine. 
     In accordance with the present invention, printing order information is produced on the basis of image ink-color information of each page contained in image data, which is then outputted to the stencil printing machine for controlling the printing operation of the stencil printing machine, thereby enabling the printing operation to be performed in a high operating efficiency to meet user&#39;s purposes in the multi-color printing operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a schematic structural view of a stencil printing machine of a first preferred embodiment according to the present invention; 
     FIG. 2 is a block diagram of a control system for the stencil printing machine of the first preferred embodiment according to the present invention; 
     FIG. 3 is a view for illustrating ink colors for each page to be used in a printing operation using image data; 
     FIG. 4 is a view for illustrating printing order information to be produced by a CPU when executing the printing operation in a page order with the stencil printing machine in the first preferred embodiment; 
     FIG. 5 is a view for illustrating a display screen of a display monitor of a user PC for displaying a page summary display and an ink drum display in accordance with printing order information in the first preferred embodiment; 
     FIG. 6 is a view for illustrating a printing termination display added with a check mark, which represent that the printing step has been terminated during the printing operation carried by the stencil printing machine in the first preferred embodiment, and an order display given with a halftone; 
     FIG. 7 is a general flow diagram for illustrating the basic sequence of a process to be carried out in the CPU when producing printing order information representing that the printing operation is implemented in a page order contained in image data; 
     FIG. 8 is a view for illustrating a printing order table representative of printing order information to be produced in the CPU when executing the printing operation by reducing the number of times the printing drum is replaced in the stencil printing machine; 
     FIG. 9 is a general flow diagram for illustrating the basic sequence of a process to be carried out in the CPU when producing printing order information so as to reduce the number of times the printing drum is replaced; 
     FIG. 10 is a schematic structural view of a stencil printing machine of a second preferred embodiment according to the present invention; 
     FIG. 11 is a block diagram for illustrating a structure of a stencil printing machine of a second preferred embodiment according to the present invention; 
     FIG. 12 is a view for illustrating printing order information to be produced by a CPU when executing the printing operation in a page order with the stencil printing machine in the second preferred embodiment; 
     FIG. 13 is a view for illustrating a printing order table representative of printing order information to be produced in the CPU when executing the printing operation by reducing the number of times the printing drum while keeping the page order is replaced in the stencil printing machine, in the second preferred embodiment; 
     FIG. 14 is a view for illustrating printing order information to be produced in the CPU when executing the printing operation by reducing the number of times the printing drum is replaced in the stencil printing machine, in the second preferred embodiment; 
     FIG. 15 is a view for illustrating a display screen of a display monitor of a user PC for displaying a page summary display and an ink drum display in accordance with printing order information in the second preferred embodiment; 
     FIG. 16 is a view of a display panel of the stencil printing machine for displaying contents on the basis of printing order information; 
     FIG. 17 is a general flow diagram for illustrating the basic sequence of a process to be carried out in the CPU when producing printing order information so as to reduce the number of times the printing drum is replaced, in the second preferred embodiment; and 
     FIG. 18 a view for illustrating printing order information to be produced in the CPU when executing the printing operation so as to reduce the number of times the printing drum is replaced in the stencil printing machine, in the second preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     To describe the present invention more in detail, a preferred embodiment of the present invention will be described below in detail with reference to the drawings. 
     The present invention is applied to a stencil printing machine  50  which is, for example, constructed as shown in FIG.  1 . The stencil printing machine  50  will be described below in detail with respect to a structure including, for example, cartridge type printing drums which are enabled to be exchanged by a user to permit a multi-color printing operation with ink in a large number of colors. Further, the present invention will be described with reference to a first preferred embodiment of a stencil printing machine which includes a single printing drum ad a second preferred embodiment of a stencil printing machine equipped with two printing drums. 
     First Preferred Embodiment 
     The stencil printing machine  50  of the first preferred embodiment is constructed in a manner as shown in FIG.  1 . In FIG. 1, the stencil printing machine  50  is mainly constructed of an original read out section  1 , a stencil making section  2 , a printing section  3 , a paper feed section  4 , a sheet discharge section  5 , and a stencil disposal section  6 . 
     The original read out section  1  includes an automatic paper feed and read out unit  7  for obtaining image data by automatically feeding an original, and an original positioning and read out unit  8  for obtaining image data from the original which is positioned in place. 
     The automatic paper feed and read out unit  7  is constructed of an inclined original resting plate  9  to allow the original to be rested, an original feed roller pair  10  for transferring the original resting on the inclined original resting plate  9 , and a line image sensor  11  for obtaining image data by converting contents of the original, which is transferred, to a train of electric signals. The line image sensor  11  is commonly used as that of the original positioning and read out unit  8 . 
     The original positioning and read out unit  8  includes a horizontal original positioning glass table  12  for allowing the original to be positioned, a pressure plate (not shown) located on the horizontal original positioning glass table  12  for free opening and closing capabilities, a guide belt  15  located in an area below the horizontal original positioning glass plate  12  to be moveable with a drive force of a pulse motor (not shown), and the line image sensor  11  which is guided with the guide belt  15  to move in the area below the original positioning glass plate  12 . 
     Further, the automatic paper feed and read out unit  7  has the line image sensor  11  to be located in a substantially upper right-hand corner of FIG.  1  and reads out the original, which is transferred with the original feed roller pair  10 , with the line image sensor  11 . In the original positioning and read out unit  8 , the line image sensor  11  is guided and moved with the guide belt  15  to scan a lower surface of the original to read out the contents of the original. 
     The stencil making section  2  includes a stencil sheet receiving tray  17  which receives an elongated stencil sheet  16  in the form of a roll, a thermal printing head  18  composed of a writing head which is located at a position downstream of the stencil sheet receiving tray  17  in a transferring direction of the stencil sheet  6 , a platen roller  19  located in opposed relation to the thermal printing head  18  and driven by a pulse motor (not shown), a stencil feed roller pair  20  located downstream of the thermal printing head  18  and the platen roller  19  in the transferring direction of the stencil sheet  16  and rotated with the drive force of the pulse motor (not shown), a stencil feed roller pair  21  located further downstream of the stencil feed roller pair  20  in the transfer direction of the stencil sheet, and a stencil cutter  22  located downstream of the stencil feed roller pair  21 . 
     The thermal printing head  18  includes a plurality of dot-shaped thermal elements located, in a plane perpendicular to the transfer direction of the stencil sheet  16 , to occupy a space in a range equal to a paper size of A3 to meet the maximum size A3 of a print sheet which is intended in the first preferred embodiment. 
     In addition, rotation of the platen roller  19  and the stencil feed roller pairs  20  and  21  allows the stencil sheet  16  to be transferred. During such transfer of the stencil sheet  16 , the dot-shaped thermal elements of the thermal printing head  18  are selectively activated to produce heat on the basis of image data read out with the line image sensor  11  to permit thermal perforation in the stencil sheet  16  to form a desired perforated area, with a trailing edge of the stencil sheet  16 , which has the desired perforated area, being cut with the stencil cutter  22  to form a perforated stencil sheet  16  of a given length. 
     The printing section  3  is constructed of a printing drum  25  including an outer peripheral portion composed of an ink permeable member formed in a perforated structure and rotated in a direction as shown by an arrow A in FIG. 1 with a drive force of a main motor (not shown), and a clamping base  26  mounted to the outer periphery of the printing drum  25  for clamping a leading edge of the stencil sheet  16 . 
     Further, the printing section  3  includes a squeegee roller  30  and a doctor roller  31  located inside the printing drum  25 , an ink supply unit (not shown) for supplying ink  32  to an area between the rollers  30 ,  31 , a press roller  35  for urging a print sheet  34 , which is transferred in synchronism with rotation of the printing drum  25 , against the stencil sheet  16 , and a plunger  36  which selectively moves the press roller  35  into a pressurized engagement position and a waiting position. 
     With such a structure, clamping the leading edge of the stencil sheet  16 , which is transferred from the stencil making section  2 , while permitting rotation of the printing drum  25  in the clamped state of the stencil sheet  16  allows the stencil sheet  16  to be wound around and mounted to the outer periphery of the printing drum  25 . When this occurs, the print sheet  34 , which is transferred in synchronism with the rotation of the printing drum  25 , is brought into pressured contact with the stencil sheet  16  of the printing drum  25  with the action of the press roller  35 , allowing the ink  32  to be transferred through a perforated area of the stencil sheet  16  onto the print sheet  34  to reproduce a desired image thereon. 
     The paper feed section  4  is constructed of a paper feed tray  37  on which a stack of the print sheets  34 , which serve as printing media, is placed, a primary paper feed roller pair  38  for moving only one print sheet  34  from the uppermost position of the stack of the print sheets  34  in the paper feed tray  37 , and a secondary paper feed roller pair  39  for transferring the print sheet  34 , which is transferred with the paper feed roller pair  38 , to an area between the printing drum  25  and the press roller  35  in synchronism with the rotation of the printing drum  25 . The primary and secondary paper feed roller pairs  38 ,  39  are so arranged as to be selectively applied with the drive force of the main motor (not shown) by means of respective paper feed clutches (not shown). 
     The sheet discharge section  5  includes a sheet peeling claw  42 , a belt-conveyer transfer mechanism  43  for transferring the print sheet  34  which is peeled off with the sheet peeling claw  42 , and a paper receiving tray  44  for allowing the print sheet  34 , which has been printed and is transferred with the belt-conveyer transfer mechanism  43 , to be placed in a stacked state. 
     The stencil disposal section  6  includes a stencil separating claw  45  for peeling the stencil sheet  16  off from the printing drum  25 , a stencil separating roller pair  46  for transferring the stencil sheet  16  peeled off with the stencil separating claw  45 , and a stencil disposal box  47  for receiving the stencil sheet  16  which is transferred with the stencil separating roller pair  46 . 
     Now, a control system of the stencil printing machine  50  of the first preferred embodiment is described below in detail with reference to FIG.  2 . 
     A body frame  50   a  of the stencil printing machine  50  of the first preferred embodiment is provided with an operation input section  51  and a display panel  52 . The operation input section  51  includes a stencil-making/printing start-up key, ten keys for inputting various input data such as the number of the print sheets, and a single-color print key. The operation input section  51  produces various operation input information in response to user&#39;s various set-up operations and outputs these information to a control section  53 . 
     Input data is outputted from the operation input section  51  to the control section  53 , which responds to the input data and executes general control over an original read-out processor section  54 , a stencil-making processor section (stencil making section)  55 , a stencil-printing processor section (printing section)  56 , a paper-feed processor section  57 , a sheet discharge processor section  58 , and a stencil-disposal processor section (stencil disposal section)  59 . Also, the control section  53  executes control for writing-in or reading-out from a ROM  60 , in which various control programs are stored, and a RAM  61 . 
     Further, the control section  53  is interconnected with a personal computer  71  (which is hereinafter called as a user PC  71 ) via a communication network and is so arranged as to read out image data, which is an object to be printed, scheduled printing order information indicative of a printing order, and printer control commands. 
     The control section  53  responds to the printer control commands, which are produced by a printer driver installed in the user PC  71 , for executing operational control, such as input of image data, start-up and stop control of stencil making operation, and start-up and stop control of printing operation. 
     The user PC  71  is constructed as including a display monitor for providing a display of various contents, an input-output interface for transferring and receiving data, commands and various other information to and from the control section  53  of the stencil printing machine  50  via a communication network, a memory unit which stores image data and printer control programs (i.e., a printer driver) for controlling the operation of the stencil printing machine  50 , and a CPU (Central Processing Unit) which executes the start-up of the printer control programs in response to the user&#39;s operational inputs, transmission of data to the stencil printing machine  50 , and transmission of the printer control commands. 
     Now, a process for producing scheduled printing order information using the CPU will be described below in detail. 
     In this example, the process for producing scheduled printing order information is described with reference to an instance wherein image data, which is the object to be printed, includes a first page involving a black ink color and a blue ink color, a second page involving the black ink color, the blue ink color and a red ink color, a third page involving the black ink color and the red ink color, and a fourth page involving the black ink color and the blue ink color, as shown by a table  62  in FIG. 3, and wherein the printing operation is carried out on the basis of such image data. 
     When printing image data, shown in FIG. 3, in a page order, the CPU produces scheduled order information representing that the printing operation is to be carried out in a sequence indicated in a printing order information table  63  shown in FIG.  4 . Here, in an example shown in FIG. 4, the scheduled printing order is shown with respect to a case wherein the printing operation is performed to complete printing of the first to fourth pages using printing drums with the black, blue and red ink colors, with circled reference numerals representing scheduled printing order displays. 
     More particularly, the CPU produces scheduled printing order information for the first page to be printed with the printing drum in a black ink color followed with the printing drum in a blue ink color, for the second page to be printed with the printing drum in the blue ink color, which has been used in printing the first page, with the printing drum in the black ink color, and with the printing drum in a red ink color, all of which printing drums are sequentially replaced, for the third page to be printed with the printing drum in the red ink color, which has been previously used in printing the second page, and with the printing drum in the black ink color, both of which printing drums are sequentially replaced, and for the fourth page to be printed with the printing drum in the black ink color, which has been previously used in printing the third page, and with the printing drum in the blue ink color, which are sequentially replaced. 
     Based on such scheduled printing order information, the CPU produces display data representing a display screen  65 , as shown in FIG. 5, which will appear over the display monitor of the user PC  71 . The display screen  65  has in an upper part a selection column  65   a  for selecting a suitable item from “kinds of Printer”, a selection column  65   b  for selecting “Kinds of Printing”, a “Print” key button  65   c  and a “Property” button  65   d.  As shown in FIG. 5, the CPU allows a page summary display  81 , which represents a page summary, and an ink drum display  82 , which represents ink drums to be employed for each page, to appear over the display monitor. 
     In accordance with scheduled printing order information, the CPU allows the page summary display  81  to appear on the display screen  65  for providing the user with a summary of the first to fourth pages as viewed in FIG.  5 . The ink drum display  82  involves a plurality of picture pattern displays  82   a  representing respective printing drums  25  allocated with respective ink colors to be used in correlated relationship with the page summary display  81  contained in image data, a scheduled order display  82   b  for displaying a scheduled order in which a particular printing drum is used for printing, and a symbol mark display  82   c  representing the currently interacting printing drum  25  which is in charge for currently printing a particular page, i.e., for, example, a page  3  in FIG.  5 . 
     The CPU responds to a signal, indicative of termination of the printing operation with the respective printing drums, outputted from the stencil printing machine  50 , thereby displaying a printing termination display  83  with check marks being applied to the respective terminated printing drums  25  as viewed in FIG. 6, while giving highlights on the scheduled printing order displays related to the terminated printing drums  25 . When it is needed to replace the printing drum  25  in the blue ink color with another one in the black ink color, the CPU allows the display monitor to provide a display of such requirement for the user. 
     The basic sequence of a process to be executed in the CPU for producing scheduled printing order information to enable printing in the page order contained in image data is described below in detail with reference to FIG.  7 . 
     When the CPU produces image data, which is the object to be printed, and receives a command from the user to execute the printing operation in accordance with the page order, the CPU discriminates from image data whether there is one color to be consecutively printed on successive pages (Step ST 1 ). In this instance, the CPU functions to perform a detecting process to detect the ink color contained in image data which constitutes two successive pages. 
     In the next step ST 2 , the CPU discriminates from image data whether it is possible to consecutively print over more than three pages with the same ink color detected in the step ST 1 . In this instance, the CPU performs a detecting process for detecting the ink color contained in image data which constitutes the next page subsequent to the last page detected in the step ST 1 . When it is found that it is possible to print over three successive pages with the printing drums  25  in the same ink color, the operation goes to step ST 3 , whereas when a difficulty is encountered, the operation goes to step ST 7 . 
     In the next step ST 3 , the CPU assigns upper rank two pages, among the pages whose ink colors are detected in steps ST 1  and ST 2 , as consecutively printable pages, thereby adding consecutively printable information representing a capability of consecutively printing the aforementioned upper rank two pages. 
     In the next step ST 4 , the CPU discriminates whether more than two ink colors are used in a particular page subsequent to the upper rank two pages selected in the step ST 3 . When it is found that more than two ink colors are used in the particular page, the operation goes to step ST 5  to remove those ink colors from candidate ink colors which can be consecutively used in printing, and the operation goes to step ST 6 . 
     On the contrary, if it is found that it is difficult to consecutively print over more than three pages in step ST 2 , the CPU determines a particular ink color to be consecutively used in printing over two pages in step ST 7 , adding consecutively printable information representing the capability of consecutively printing on those two pages, and the operation goes to step ST 6 . 
     Further, when it is discriminated that the ink color to be consecutively printable over the pages consists of one color, the CPU discriminates whether there are a plurality of ink colors to be consecutively printable in step ST 8 . In this instance, when there are not plural ink colors, i.e., when the plural ink colors to be consecutively printed are absent, the operation goes to step ST 9 , which will be discussed later, and when the plural ink colors are present, the operation goes to step ST 10 . 
     In the next step ST 10 , the CPU executes a judgment (step ST 10 ) of whether to enable recognition of the ink color which has been already decided to be consecutively printable in fore and aft pages outside the successive pages which can be consecutively printable. When it is found to be recognized, the operation goes to step ST 11 , and when it is not found to be recognized, the operation goes to step ST 12 . In this instance, the CPU executes a judgment by detecting consecutively printable information added to each page. 
     In consecutive step ST 11 , the CPU removes those consecutively printable ink colors, which have been recognized in the step ST 10 , from the consecutively printable candidate ink colors, thereby executing judgment of whether there are more than two ink colors to be consecutively printable on other successive pages remaining after the particular ink colors have been removed, on the basis of consecutively printable information. 
     When it is judged that there are more than two ink colors which are consecutively printable, the operation goes to step ST 12  to select the ink colors, which remain in the upper rank in a registered order of preset ink colors, as those which can be consecutively printed, and then the operation goes to step ST 6 . In contrast, when it is judged that there are not more than two ink colors to be consecutively printable, the CPU allows the operation to go to step ST 7  to perform the aforementioned operations. 
     Here, the “registered order” refers to a scheduled order which is preliminarily designated by the user in accordance with, for example, the kinds (black, blue and red) of the ink colors. 
     In step ST 6 , the CPU executes judgment of whether the consecutively printable ink colors are selected in the executions of steps ST 3 , ST 7  or ST 12  for the whole pages contained in image data. When it is judged that the consecutively printable ink colors are selected for the whole pages, the operation goes to step ST  13 . When, in contrast, it is judged that the consecutively printable ink colors are not selected for the whole pages, the operation returns to step ST 1  to repeatedly execute the operations of the steps ST 1  to ST 12  again. 
     In step ST 9  in a case wherein it is judged that there are not ink colors to be consecutively printable in step ST 8 , the CPU allows the successive pages to be printed in the page number order, while allowing the discrete page to be printed in the registered order of the ink colors. 
     In step ST 13 , the CPU produces scheduled printing order information on the basis of consecutively printable information indicative of the ink colors, which have been decided to be consecutively printable in the aforementioned operations, and information indicative of the registered order of the ink colors. That is, the CPU recognizes the ink color or the ink colors to be used in an initial printing step and/or a final printing step when printing each page in accordance with information indicative of the consecutively printable ink colors, thereby producing scheduled printing order information to enable printing in accordance with the registered order of the ink colors except the one which is initially used in each page. 
     In particular, in an example of a printing order table  90  shown in FIG. 4, the CPU recognizes an ink color, which is initially used for printing the second page, to be the blue color, and recognizes an ink color, which is finally used in printing the second page, to be the red color, in accordance with information indicative of the ink colors decided to be consecutively printable. With such recognition, the CPU makes it possible to produce scheduled printing order information to allow the same blue ink color to be used for printing the first and second pages and to allow the same red ink color to be used for printing the second and third pages. 
     With such scheduled printing order information, it is possible for the stencil printing machine  50  to execute the printing operation at a high efficiency to meet user&#39;s purpose during multi-color printing in dependence on the page order. 
     When printing the pages in a scheduled order to reduce the number of times the printing drum is replaced, the CPU produces scheduled printing order information to execute the printing operation in a sequence indicated, for example, in a printing order table  90  shown in FIG.  8 . In particular, the CPU produces scheduled printing order information to firstly print first, second, third and fourth pages in order using the printing drum  25  in black ink color, followed to print the first, second and fourth pages in order using the printing drum  25  in blue ink color and finally to print the second and third pages in order using the printing drum in red ink color. With such scheduled printing order information to effectuate the printing operation in a scheduled order, the number of times the printing drum  25  is replaced is reduced to a smaller number of time, i.e., two times, than that required in the example shown in FIG.  4 . 
     Now, an attention is made to the basic sequence of operations to be carried in the CPU for producing scheduled printing order information to reduce the number of times the printing drum is replaced, in conjunction with FIG.  9 . 
     The CPU produces image data to become an object to be printed and responds to user&#39;s command to initiate the printing operation according to the page order to commence the printing operation for each ink color in step ST 21 . That is, the CPU begins to print by designating the ink colors from the uppermost rank page to the lowermost rank page according to the registered order of the preset ink colors. Here, the “registered order of the ink colors” is meant by the fact that, in FIG. 8, the black color remains in the uppermost rank, and the blue and red colors are registered in order. 
     In the next step ST 22 , the CPU detects the ink color to be used for printing with the use of each image data, and allows the printing operation to be executed with the ink color, which is designated in step ST 21 , in accordance with the page order. 
     In the next step ST 23 , the CPU discriminates whether the ink color designated in step ST 21  does not belong to the uppermost rank and whether to designate the subsequent ink color. When it is found that the ink color, which has been used in step ST 22 , does not in the uppermost rank, the operation of the CPU returns to step ST 21  to designate the subsequent ink color to enable the printing operation in step ST 22 . When it is found that the ink color used in step ST 22  belongs to the uppermost rank, then the CPU terminates the printing operation. 
     With such a processing function of the CPU, it is possible to reduce the number of times the printing drum  25  is replaced, thereby enabling the multi-color printing operation at a high efficiency in accordance with the user&#39;s demands. 
     In the aforementioned first preferred embodiment, although the present invention has been described with respect to the example wherein the various contents are arranged to be displayed over the display monitor of the user PC  71 , the display panel  52  of the stencil printing machine  50  may be arranged to display the same contents as those displayed by the display monitor. With such arrangement, it is possible for the stencil printing machine  50  to instruct the user about timings for replacing the printing drums in different ink colors and progressive status of the printing operations, with a resultant highly improved readiness and maneuverability. 
     In the aforementioned first preferred embodiment, although the present invention has been described with respect to the example wherein the stencil printing machine  50  is applied with and is controlled by the printing command, to execute the printing operation according to the paper order, or the printing command, to execute the printing operation in reduced number of replacement times of the printing drums  25  which are transmitted from the user PC  71 , the CPU may produce scheduled printing order information representative of a scheduled order in which the printing operation is started with the printing drum  25  of less density in the strength of the ink color with a priority being given to an image quality on the basis of other factors, i.e., by minimizing the number of re-transfer operations. 
     In the aforementioned example, further, although the present invention has been discussed with respect to the example wherein the CPU produces scheduled printing order information depending on the page order and scheduled printing order information which enables reduction in the number of times the printing drum is replaced, the CPU may produce scheduled printing order information with due regard to plural conditions. That is, the CPU may produce scheduled printing order information on the basis of the page order, while minimizing the number of the re-transfer operations. 
     In the aforementioned example, furthermore, although the present invention has been discussed with respect to the example of an automatic order mode wherein scheduled printing order information is automatically produced, in response to the printing commands, with the user PC  71  in accordance with the ink colors of image data, the user PC  71  may produce scheduled printing order information responsive to the user&#39;s operation for controlling the stencil printing machine  50  and may also automatically produce scheduled printing order information which can be altered by user&#39;s manual operation input in a manual order mode. 
     Second Preferred Embodiment 
     Now, a stencil printing machine of a second preferred embodiment will be described below in detail. As shown in FIG. 10, the stencil printing machine  100  of the second preferred embodiment is mainly constructed of an original read out section  102 , a stencil making section  103 , a printing section  104 , a paper feed section  105 , a sheet discharge section  106 , and stencil disposal sections  107 ,  107  mounted at two locations. 
     The original read out section  102  is located above a body frame  108  and reads out an image pattern as input image data of an original to produce a train of electric signals. The read out information is processed to produce image data for ink of a first printing drum and for ink of a second printing drum. 
     The stencil making section  103  includes a stencil making unit  109  mounted in the body frame  108  for free horizontal movement. The stencil making-unit  109  is moveable with a stencil making unit transfer device  110  between a first stencil sheet feeder position to allow a first perforated stencil sheet  111  to a first printing drum  125  and a second stencil sheet feeder position to allow the stencil sheet  111  to a second printing drum  126 . The stencil making-unit transfer device  110  is constructed having a stencil making-unit transfer motor  112 , a worm gear  113  fixed to a rotary shaft of the stencil sheet making-unit transfer motor  112 , a worm wheel (not shown) meshing with the worm gear  113 , a pinion gear  114  connected to the worm wheel at an central axis thereof, and a rack  115  fixedly mounted to the body frame  108 . 
     The stencil making unit  109  includes a stencil sheet roll container  116  which receives an elongated stencil sheet  111  formed in a rolled shape, a plurality of feed rollers  117  adapted to guide a leading edge of the stencil sheet  111  received in the stencil sheet roll container  116  toward a downstream side, a thermal printing head  118  located at a downstream side of the feed rollers  117 , a platen roller  119  which is located in an opposed position of the thermal printing head  118  and which rotates with drive force exerted by a pulse motor (not shown), a stencil sheet feed roller  120  located at a downstream side relative to the platen roller  119  and the thermal printing head  118  and adapted to be driven with the drive force of the pulse motor, a guide plate  121  to which the stencil sheet feed roller  120  is held in pressured contact, and a stencil sheet cutter  122  located between a first area of the stencil sheet feed roller  120  and the guide plate  121  and a second area of the platen roller  119  and the thermal printing head  118 . 
     The printing section  104  includes the first printing drum  125 , the second printing drum  126 , and a press drum  127 , which serves as a rotary printing press member to impart printing pressure to the first and second printing drums  125  and  126 , with the first and second printing drums  125  and  126  being located in right and left positions which are obliquely oriented relative to the center of the press drum  127 . In particular, the first and second printing drums  125  and  126  are placed in close proximity to an outer circumferential periphery of the press drum  127  in the left and right positions angled at 90 degrees relative to a central axis of the press drum  127 . The first and second printing drums  125  and  126  and the press drum  127  are rotatably mounted in the body frame  108 , and are rotated with a printing drum rotating mechanism (not shown) at the same peripheral speeds in the vicinities of a first contact zone between the first printing drum  125  and the press drum  127  and a second contact zone between the second printing drum  126  and the press drum  127 . The printing drum rotating mechanism is driven with a main motor (not shown) which serves as a drive source. 
     The first and second printing drums  125  and  126  have respective annular frame pairs (bearing no reference numerals) which are interconnected with stencil clamping bases  128 , forming respective parts of outer circumferential peripheries of the first and second printing drums  125  and  126 , respectively. The stencil clamping bases  128  have respective stencil clamping segments  129 , by which leading edges of the stencil sheets  111  are clamped, respectively. Also, a leading edge of a screen  130  is fixed to each of the stencil clamping bases  128 , with each screen  130  being wound on each of outer circumferential peripheries of the first and second printing drums  125  and  126 . 
     A trailing edge portion of each screen  130  is stretched over each of the stencil clamping bases  128  by a spring  131 , with each screen  130  being arranged to be expandable outward against the force of the spring  131 . Each screen  130  is constructed of, for example, a mesh-shaped porous structure which, when it is pressed with an inner press roller  133 , which will be discussed below, permits printing ink  138  to permeate from inward to outward. Thus, each screen  130  forms each outer circumferential periphery, which is supplied with printing ink  138 , of each of the first and second printing drums  125  and  126 . 
     Inside each of the screens  130  of the first and printing drums  125  and  126 , an inner press mechanism  132  is accommodated. Each inner press mechanism  132  includes the inner press roller  133  which has a first function to exert a printing pressure to the screen  130  and a second function to supply the printing ink  138  to the screen  130 . 
     Each of the inner press rollers  133  is rotatably supported by a pair of roller support members  134  located at both sides of each press roller and is rotated with a drive means, which is not shown, in synchronism with rotations of the first and second printing drums  125  and  126 . The roller support members  134  are supported on a pivot shaft  135  for rotational movement thereabout such that, with rotation of the roller support members  134  in a direction as shown by an arrow a in FIG. 10, the roller support members  134  are moveable between an operative, press engagement position to cause the inner press roller  133  to press an inner periphery of the screen  130 , and an inoperative, wait position when the roller support members  134  are rotated in a direction as shown by an arrow b. Each of the inner press rollers  33  assumes either the press engagement position during printing operation or the wait position during non-printing operation. 
     Further, each of the roller support members  134  carries first and second doctor rollers  136  and  137 . The first and second doctor rollers  136  and  137  include cylindrical columns, respectively, and both are located in the vicinity of the inner press roller  133 . Printing ink  138  is supplied from an ink supply unit (not shown) to a specified area in the vicinities of an outer circumferential space of the inner press roller  133  and an upper space surrounded between the first and second doctor rollers  136  and  137 , with an ink pool  139  being formed in the specified area. The first printing drum  125  is supplied with printing ink  138  with a first color, and the second printing drum  126  is supplied with printing ink  138  with a second color. 
     A gap (an opposing distance) between the first doctor roller  136  and the inner press roller  133  is preset to a value sufficient for printing ink to be applied to the inner press roller  133  to form an ink film with a given thickness, and a gap between the second doctor roller  137  and the inner press roller  133  is preset to have a value suitable for printing ink to be prevented from being leaked. That is, as the inner press roller  133  rotates, printing ink with the given film thickness is continuously adhered to an outer circumferential surface of the inner press roller  133  owing to the gap between the first doctor roller  136  and the press roller  133 , allowing the inner press roller  133  to supply printing ink onto the screen  130 . 
     In addition, a print sheet clamp segment  140  is located at a given position of an outer circumferential periphery of the press drum  127 , which serves as the rotary printing press member to impart a printing pressure to the printing drum, thereby clamping an edge of the print sheet  141  which is a print medium. 
     The paper feed section  105  is constructed as having a paper feed tray  142  on which print sheets  141 , each serving as a print medium, are stacked, primary paper feed rollers  143 , which is kept in press engagement with an uppermost print sheet  141  stacked on the paper feed tray  142 , a secondary paper feed roller pair  144  located downstream of the primary paper feed rollers  143  and a guide plate pair  145  serving as a transfer guide for the print sheet between the secondary paper feed roller pair  144  and the press drum  127 . Rotation of the paper feed rollers  143  causes only the uppermost print sheet  141  on the stack thereof to be transferred to the secondary paper feed roller pair  144 , with the transferred print sheet  141  being fed to the printing section  104  in synchronism with the press drum  127  due to rotation of the paper feed roller pair  144 . 
     The sheet discharge section  106  includes an upper limit guide segment  146  for guiding the leading edge of the print sheet  141  after it&#39;s printing step has been completed, a sheet separator claw  147  for separating the print sheet  141  from the press drum  127 , a sheet discharge roller pair  148 , which transfers the print sheet  141  guided by the upper limit guide  146  or the print sheet  141  separated with the sheet separator claw  147 , and a paper receiving tray  149  which stacks the print sheets  141 , discharged from the sheet discharge roller pair  148 , in a stacked state. 
     The stencil disposal sections  107  are located in the body frame  108  in the vicinities of the first and second printing drums  125  and  126 , respectively. Each of the stencil disposal sections  107  includes a pair of stencil discharge rollers  150  and  151 , which are located in the vicinity of each of the first and second printing drums  125  and  126  in a slightly spaced relationship relative to each outer periphery, a stencil guide belt  152  which guides a leading edge of the stencil sheet  11  released from the stencil clamp segment  129 , a stencil discharge roller  153  which transfers the stencil sheet  111 , guided with the stencil guide belt  152 , while separating it from each of the first printing drum  125  and the second printing drum  126  in conjunction with the stencil discharge roller  151 , a stencil disposal box  154  for receiving the stencil sheet  111  transferred from the stencil discharge rollers  151  and  153 , and a stencil compressing plate  155  for compressing the stencil sheets  111  toward a rearmost side of the stencil disposal box  154 . 
     Now, a control system for controlling the operation of the stencil printing machine  100  is described below in detail with reference to FIG.  11 . As shown in FIG. 11, the body frame of the stencil printing machine  100  of the second preferred embodiment of the present invention is provided with an operation input section  161  and a display panel  162 . The operation input section  161  includes a stencil-making/printing start-up key, ten keys for inputting various input data such as the number of print sheets and a single-color printing key, which allow the user&#39;s operation to produce operation input information to be transmitted to a control section  163 . The display panel  162  provides a display of various data transmitted from the control section  163 . 
     Input data is outputted from the operation input section  161  to the control section  163 , which responds to the input data and executes general control over an original read-out processor section  164 , a stencil-making processor section (stencil making section)  165 , first and second stencil-printing processor sections (printing sections)  166  and  167 , a paper-feed processor section  168 , a sheet discharge processor section  169 , and stencil-disposal processor sections  170  and  171 , which are located at two different positions. Also, the control section  163  executes control for writing-in or reading-out from a ROM  172 , in which various control programs are stored, and a RAM  173 . 
     Further, the control section  163  is interconnected with a personal computer  181  (which is hereinafter called as a user PC  181 ) via a communication network such that it is enabled to read in image data and printer control commands from the user PC  181 . 
     The control section  163  responds to printer control commands, which are produced by a printer driver installed in the user PC  181 , for executing operational control, such as input of image data, start-up and stop control of stencil making operation, and start-up and stop control of printing operation. 
     As executed by the CPU in the first preferred embodiment, the CPU in the second preferred embodiment responds to a user&#39;s command to perform the printing operation 
     When implementing the printing operation with the stencil printing machine  100  responsive to the user&#39;s command, like the CPU of the first preferred embodiment discussed above, the CPU of the second preferred embodiment transmits scheduled printing order information representative of a scheduled order of the printing process, as well as image data, to the stencil printing machine  100 . 
     When executing a printing operation to reproduce image data, shown in FIG. 3, in the order of particular pages, the CPU produces scheduled printing order information to execute the printing operation in a programmed order as indicated by a printing order table  190  shown in FIG.  12 . In an example of the printing order table  190  shown in FIG. 12, there is shown a scheduled printing order for the printing process to be implemented, with the use of the printing drums with ink in black, blue and red colors, over a first page to a fourth page, with the scheduled printing order bearing numerals (hereinafter referred to as “enclosed numerals”) enclosed with circles and the first and second printing drums bearing non-enclosed numerals added to the enclosed numerals. That is, in FIG. 12, a symbol “{circle around ( 1 )}-1” represents that a first printing step is performed using the first printing drum  125 . 
     Now, a technology for producing printing sequence information without using ink color information is described below in detail with reference to FIG.  12 . According to the printing order table  190  shown in FIG. 12, the first printing operation is executed over the first page using the first printing drum  125  with ink in a black color, followed with the second printing drum  126  with ink in blue color. In a second printing operation, similarly, the printing of the second page is carried out using the first printing drum  125  with ink in black color and the second printing drum  126  with ink in blue color. Subsequently, in a third printing operation, the printing of a third page is performed using the first printing drum with ink in black color and the second printing drum  126  whose printing ink is replaced with ink in red color from the ink in blue color. In a fourth printing operation, the printing of a fourth page is performed using the first printing drum with ink in black color and the second printing drum  126  whose printing ink is replaced with ink in blue color from the ink in red color. In a fifth printing operation, the printing of the third page is implemented using only the second printing drum whose printing ink is replaced with ink in red color from the ink in blue color. In this case, the order of the pages to be printed is not fixed requiring the replacement of the printing drums in three times. 
     Now, the basic sequence for the CPU to process for producing scheduled printing order information representative of the order of the pages, contained in image data, for which the printing process is to be implemented is described below in detail in conjunction with FIG.  13 . 
     First, the CPU produces image data representative of an image object to be printed, and upon receiving the user&#39;s command for printing according to the order of the pages, in step ST 31 , the CPU begins to count the number of times each ink color is used throughout whole pages contained in image data. 
     In step ST 32 , the CPU determines most frequently used two ink colors and, in the next step ST 33 , the CPU discriminates whether the number of printing times associated with each ink color, counted in step ST 31 , is equal to one another or is different from one another. When discriminating that the number of printing times associated with each ink color is equal to one another, the operation goes to step ST 35  whereas if not, the operation goes to step ST 34 . 
     In step ST 34 , the CPU discriminates whether there are a plurality of most frequently used ink colors among the respective ink colors counted in step ST 31 . When discriminating that there are most frequently used ink colors, the operation goes to step ST 35  and, if not, the operation goes to step ST 36 . 
     In step ST 35 , the CPU processes to allocate the higher rank ink colors, which remain in the registered order, to the first and second printing drums  125  and  126 , and the operation goes to step ST 40 . 
     In step ST 36 , the CPU allocates the most frequently used ink color to the first printing drum  125  and, in the next step ST 37 , the CPU discriminates whether there are plural more frequently used ink colors. When it is discriminated that there are plural more frequently used ink colors, the operation goes to step ST 38  and, if not, the operation goes to step ST 39 . 
     In step ST 38 , the CPU allocates a particular ink color, which is selected from the higher rank ink colors which remain in the registered order, to the second printing drum  126 , and the operation goes to step ST 40 . 
     In step ST 39 , the CPU allocates the second most frequently used ink color to the second printing drum  126 , and the operation goes to step ST 40 . 
     In step ST 40 , the CPU leads the operation to determine for allocating the other ink color, which remains non-allocated to the printing drum in the aforementioned processing steps, to the printing drum to be used within the page to be printed. 
     In the next step ST 41 , the CPU discriminates whether there are more frequently used ink colors within the page. When the absence of the more frequently used ink colors within the page is discriminated, the operation goes to step ST 42 , and if the CPU finds it to be YES, the operation then goes to step ST 43 . 
     In step ST 42 , the CPU allocates the ink colors to the respective printing drums in the registered order, and in step ST 46 , the CPU produces scheduled printing order information to enable printing on the interrelated pages according to the page order. 
     In step ST 43 , the CPU discriminates whether there is one color present in the more frequently used ink colors. When it is discriminated that there is the one color present in the more frequently used ink colors, the operation then goes to step ST 44 , and if not, the operation goes to step ST 45 . 
     In step ST 44 , the CPU combines the higher rank ink color remaining in the registered order with the more frequently used ink color and allocates such an ink color combination to either one of non-allocated printing drums. Subsequently, the remaining ink colors are allocated to respective printing drums according to the registered order. In the next step ST 46 , the CPU produces scheduled printing order information to enable printing for the associated pages according to the page order. 
     In step ST 45 , the CPU allocates the more frequently used, two ink colors to the particular printing drums in accordance with determination, with the remaining more frequently used ink colors being assigned to respective printing drums according to the registered order. In the next step ST 46 , the CPU produces scheduled printing order information to enable printing for the associated pages according to the page order. 
     When printing image data onto a print sheet according to the page order as seen in FIG. 3, the CPU produces scheduled printing order information to enable printing in a sequence as represented by a printing sequence table  192  shown in FIG.  14 . 
     According to the printing order table  192  shown in FIG. 14, in a first printing step, a first page is printed using the first printing drum  125  with black ink color and the second printing drum  126  with blue ink color. In the next, second printing step, the second page is similarly printed using the first printing drum  125  with the black ink color and the second printing drum  126  with the blue ink color. In a third printing step, the third page is printed using only the second printing drum  126  under a condition wherein the blue ink color is replaced with the red ink color. In a fourth printing step, the third page is printed using the first printing drum  125  with the black ink color and the printing drum  126  with the red ink color. In a fifth printing step, a fourth page is printed using the first printing drum  125  with black ink color and with the second printing drum  126  wherein the red ink color is replaced with the blue ink color. It will thus be seen that even when executing the printing operation on the basis of image data shown in FIG. 3, the CPU enables the printing operation in the page order while limiting the number of times the printing drum is replaced to two times. 
     During execution of the process discussed above, the CPU allows a display screen  194  as shown in FIG. 15 to appear on the display monitor of the user PC  181 . According to the display screen  194  shown in FIG. 15, the display screen  194  has in an upper part a selection column  194   a  for selecting kinds of printer, a selection column  194   b  for selecting kinds of printing, a print key button  194   c  and a property button  194   d.  As shown in FIG. 15, the CPU allows a page summary display  191 , which represents a page summary, and an ink drum display  192 , which represents ink drums to be used for associated pages, to appear over the display monitor. 
     The ink drum display  192  involves a plurality of picture pattern displays  192   a  representing the first printing drum  125  and the second printing drum  126  added with respective ink colors to be used in correlated relationship with the page summary display  191  contained in image data, sequence order displays  192   b  each for displaying a sequence order in which the printing operation is executed with the first printing drum  125  or the second printing drum  126 , and using printing drum displays  192   c  each representing the using printing drum. 
     Like in the first preferred embodiment, the CPU responds to a signal, indicative of termination of the printing operation with the first and second printing drums  125 ,  126 , outputted from the stencil printing machine  100 , thereby allowing a printing termination display given with check marks to appear in the display screen  194 , while allowing the presence of need for either the first printing drum  125  or the second printing drum  126  to be replaced to appear on the display screen  194  to instruct the user. 
     Further, the CPU produces display data, to display the contents of the printing sequence over the display screen  194 , on the basis of printing sequence information, with resultant display data being transmitted to the stencil printing machine  100 . Responding to such display data, the control section  163  of the stencil printing machine  100  allows the display panel  162  to display the contents of a printing schedule table  196  as viewed in FIG.  16 . 
     As seen in FIG. 16, the display monitor  162  displays the printing schedule table  196 , which involves a file&#39;s title display  201  for displaying the title assigned to image data, an owner&#39;s name display  202  for displaying the user&#39;s name who operates the user PC  181 , a printing order display  203  representative of a printing order for each page, a page summary display  204  for displaying a page summary associated with the printing order display  203 , a page display  205  for displaying a page number and the contents of each page, a first drum display  206  displaying whether to execute the printing operation with the first printing drum  125  in dependence on the printing order display  203  while displaying the ink color to be used for the first printing drum  125 , and a second drum display  207  displaying whether to execute the printing operation with the second printing drum  126  in dependence on the printing order display  203  while displaying the ink color to be used for the second printing drum  126 . 
     With such a printing schedule table  196 , it is possible for the stencil printing machine  100  to instruct the user, who is in charge of exchanging the ink colors for the first printing drum  125  and the second printing drum  126 , about various information such as the printing execution order, and the timings at which the first and second printing drums  125 ,  126  are to be replaced. 
     Now, the basic sequence of a process to be carried out in the CPU for producing printing sequence information in order to reduce the number of times the printing drums is replaced is described below in detail with respect to FIG.  17 . 
     First, the CPU produces image data which becomes an object to be reproduced and upon receiving the print command initiated by the user&#39;s operation so as to reduce the number of times the printing drums are to be replaced, discriminates, in step ST 51 , whether more than two ink colors are used for each page contained in image data or not. When it is discriminated that more than two ink colors are used in each page, the operation goes to step ST 52  and if not, the operation goes to step ST 63  which will be described later. 
     In the next step ST 52 , the CPU counts the sum N of the number of times each of the ink colors is used, and the sum n of the number of times the printing is performed with combined two ink colors for each ink color, throughout the whole pages. That is, the CPU counts the sum n and the sum N in order to know about what is the maximum number of times the printing operation can be consecutively executed without causing replacement of the first and second printing drums  125 ,  126 . 
     In the next step ST 53 , the CPU responds to the counted results achieved in step ST 52  to obtain a particular ink color having the maximum value in the aforementioned sum n and another particular ink color having the maximum value in the aforementioned sum N, thereby determining the ink color to be used with first priority. 
     In the next step ST 54 , the CPU discriminates whether there are plural ink colors having the maximum values in the sum n and the sum N or not. When it is discriminated that there are no plural ink colors having the maximum values in the sum n and the sum N with the same number of usage times, the operation goes to step ST 55 . When the presence of the associated plural ink colors is discriminated, the operation goes to step ST 56 . 
     In step ST 55 , the CPU determines the ink color, which has the maximum values in the sum n and the sum N, as a first priority ink color and counts the number of times the ink color is used for printing in combination with the first priority ink color which has been determined to obtain the ink color having the maximum value, rendering the operation to go to step ST 58 . 
     In step ST 56 , the CPU counts the number of times the printing operation is performed with the other ink color for each ink color. In step ST 57 , the CPU determines the particular ink color and the other ink color, having the maximum value in the number of times the printing operation is executed, as the first priority ink colors. 
     In the next step ST 58 , the CPU determines the ink color, to be used as two ink color pair, which is used for printing together with the first priority ink color determined in step ST 55  or in step ST 57 . After such determination, the CPU register two-color printing information representative of a combination of the ink colors to be used for a two-color printing operation with concurrent use of the first printing drum  125  and the second printing drum  126 . 
     In the next step ST 59 , the CPU processes to delete the combinations of the ink colors determined in step ST 56  for each page contained in image data. That is, the CPU determines to execute the printing operation over the page associated with the ink colors incorporated in the particular combination determined in step ST 58 . 
     In the next step ST 60 , the CPU discriminates whether determination of the two-ink color pair, for executing the printing operation concurrently using the first printing drum  125  and the second printing drum  126 , has been terminated or not. Upon terminating the determination process for the two-ink color pair to be used for the printing operation, the operation goes to step ST 61  and when determination process is not completed, the operation returns to step ST 51  to step ST 59  for repeated processing purposes. 
     In step ST 63  wherein the absence of usage of more than two ink colors for each page in step ST 51  is discriminated, the CPU discriminates whether the single ink color is used for plural pages. When discriminating that the single ink colors are used for the plural pages, the operation goes to step ST 64  and if not, the operation goes to step ST 65 . 
     In step ST 64 , the CPU detects particular plural pages for which the printing operation is consecutively performed according to the printing order, then going to step ST 61 . 
     In step ST 65 , the CPU discriminates whether to use the ink colors, which have been registered in the two-color printing information determined in step ST 58 , in the single color printing operation. When the CPU discriminates that the ink colors, which have been registered in the two-color printing operation, are used for executing the single color printing operation, the operation goes to step ST 66  and when the discrimination is made not to use the registered ink colors for the single color printing, the operation goes to step ST 67 . 
     In step ST 66 , the CPU determines whether the single color operation is performed subsequent to or prior to the two-color printing operation on the basis of the page order which is intended for executing the single color printing operation, thereby going to step ST 61 . 
     In step ST 67 , the CPU assigns the page, which uses the ink color unused in the two-color printing operation in step ST 65 , as that is to be printed with the least priority, thereby going to step ST 61 . 
     In step ST 61 , the CPU discriminates whether the process steps have been completed in the aforementioned step ST 63  to step ST 67  throughout the whole pages to be printed in the single color printing operation. When it is discriminated that the process in steps ST 63  to step ST 67  for the whole pages to be printed in the single color printing operation, the operation goes to step ST 62 , and if not, the operation returns to step ST 63  to prosecute the processes subsequent to step ST 63 . 
     In step ST 62 , the CPU determines printing order information according to the degree of priority with respect to the two-color printing operation obtained in step ST 58  and the single color printing operation obtained in step ST 64 , step ST 66  and step ST 67 . That is, taking into account the degree of the first priority given to the two-color printing operation to be maximum, the CPU produces information representative of the single color printing operation having the same ink color as that used in the two-color printing operation, information representative of the single color printing operation having the ink color used in the plural pages, and printing order information on the basis of information representative of the single color printing operation having the ink color to be singularly used. 
     As such, according to the printing order table  198  shown in FIG. 18, first to third printing processes are implemented to print on the first page, the second page and the fourth page using the first printing drum  125  with black color and the second printing drum  126  with the blue ink color. Subsequently, in the fourth printing process, the third page is printed, using the first printing drum  125  and the second printing drum  126  wherein the blue color is replaced with the red ink color. Next, in a fifth printing process, the second page is printed using only the second printing drum  126  with the red ink color. Thus, even when executing the printing operation on the basis of image data shown in FIG. 3, the CPU makes it possible for the stencil printing machine to perform the printing operation with only one time the printing drum is replaced. 
     Having explained the example wherein the stencil printing machine is supplied with image data and printing order information, representative of the printing order to be employed in the printing operation with the use of image data, which are transmitted from the user PC  71 , it may be possible for the user to produce printing order information with the control section  53  by referring to the display panel. In this instance, also, the control section  63  implements control so as to display the display screen, as shown in FIG. 15, over the display panel of the stencil printing machine  50 . With such stencil printing machine  50 , it is possible to obtain the same results as those obtained in the aforementioned example. 
     While, in the second preferred embodiment, description is made in conjunction with the case wherein the stencil printing machine  100  operates to control the printing order in response to print command, to execute the printing operation according to the page order, or print command, to enable the printing operation so as to reduce the number of times the first printing drum  125  and the second printing drum  126  are replaced with, transmitted from the user PC  181 , based on other conditions, namely, in order to give the first priority to the image quality by minimizing the number of re-transfer of image, it may be possible to produce print order information representative of the order in which the printing operation is commenced by suing the first printing drum  125  and the second printing drum  126  with the ink colors in lower ink color concentration. 
     While, in the aforementioned example, a description is made with respect to the case wherein, when executing the printing operation, the CPU produces scheduled printing order information based on the page order and print order information to reduce the number of times the first printing drum  125  and the second printing drum  126  are replaced with, the CPU may produce scheduled printing order information taking into account the plural conditions. That is, for example, the CPU may produce printing order information on the basis of the page order while minimizing the number of re-transfer of image. 
     While, in the aforementioned example, a description is made with respect to the case wherein the user PC  181  is responsive to print command to automatically produce scheduled printing order information, in accordance with the ink color contained in image data, in the automatic sequence mode, the user PC  181  may produce scheduled printing order information in dependence on the user&#39;s operation input for controlling the stencil printing machine  100 , or may take the manual mode responsive to user&#39;s operation input to update scheduled printing order information which has been automatically produced. Also, it may be possible for the user to operate the user PC  181  to select either one of the automatic mode or the manual mode with the user&#39;s operation input. 
     While, in the second preferred embodiment discussed above, the stencil printing machine  100  has been shown and described as having two printing drums, the present invention is not limited thereto and may be modified so as to have other number of the printing drums to obtain the same results and advantages as those explained above.