Abstract:
In an image forming apparatus having driving conditions for plural image forming modes such as color and monochrome, when an original with a blank sheet (inter-sheet) inserted at an arbitrary position therein is to be printed, the image forming mode for the position where the blank sheet is inserted is properly determined and a transfer belt is caused to contact and separate from an image carrier related to image formation, thereby improving printing productivity.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an image forming apparatus having driving conditions for plural image forming modes such as color and monochrome, and particularly to an image forming apparatus in which, when an original with a blank sheet (inter-sheet) inserted at an arbitrary position therein is to be printed, the image forming mode for the position where the blank sheet is inserted is properly determined and set, thereby improving the productivity of printing. 
         [0003]    2. Description of the Related Art 
         [0004]    In the case of collectively copying and printing an original of plural sheets by an image forming apparatus, a blank sheet (inter-sheet) that is not to be printed, such as a cover, partition or tab sheet, may be inserted at an arbitrary position. 
         [0005]    Therefore, an image forming apparatus such as an electrophotographic digital copying machine or printer has a function of inserting a blank sheet (inter-sheet) that is not to be printed, such as a cover, partition or tab sheet, at an arbitrary position among the recording sheets to be discharged in accordance with an instruction made by a user&#39;s operation of a control panel or an instruction made by an operation of an information terminal via a printer driver. 
         [0006]    For example, the user operates an operating unit of the image forming apparatus to input and set a page where an inter-sheet should be inserted, as “blank sheet insertion”, at each position. (See, for example, JP-A-2006-201696.) 
         [0007]    In the case where the machine type of the image forming apparatus supports a color mode and a monochrome mode as image forming modes, when a blank sheet is to be inserted, an operation of inserting a blank sheet is carried out in accordance with predetermined driving conditions (image forming mode conditions), or if the driving conditions for all the printed matter are the same, in accordance with the driving conditions of the image forming mode. 
         [0008]    Generally, when the driving conditions in the image forming apparatus such as the carrying speed, printing speed and resolution are to be switched, the print sequence is temporarily stopped and then the image forming speed, the sheet carrying speed and the number of rotations of the polygon motor are switch-controlled. After that, the apparatus has to wait for various motors to stabilize. 
         [0009]    In the image forming apparatus that characteristically has plural driving conditions and takes time for switching the driving conditions, switching is frequency required in accordance with the driving conditions for a sheet to be printed and a blank sheet. As a result, there arise problems of lowering of image forming performance and degradation in the mechanical units. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide an image forming apparatus that has plural driving conditions for a color mode and a monochrome mode and selects a proper blank sheet driving condition from the driving conditions before and after the insertion of a blank sheet. 
         [0011]    In an aspect of the present invention, an image forming apparatus includes: 
         [0012]    image reading means for reading an image from an original; 
         [0013]    a developing unit having plural image carriers to form the image of the original read by the image reading means; 
         [0014]    an endless transfer belt that can contact and separate from the image carriers; and 
         [0015]    contact and separation means for causing the transfer belt to contact the image carrier related to image formation and to separate from the image carrier that is not related to the image formation, in accordance with plural image forming modes having different numbers of the image carriers to be used for image formation; 
         [0016]    wherein when a blank sheet is inserted at an intermediate position in the original of plural sheets read by the image reading means, the contact and separation means operates to start printing in accordance with an image forming mode corresponding to an image immediately before the blank sheet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a side sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the invention. 
           [0018]      FIG. 2A  is an enlarged side sectional view showing an exemplary operation corresponding to an image forming mode in an image forming unit of the image forming apparatus. 
           [0019]      FIG. 2B  is an enlarged side sectional view showing an exemplary operation corresponding to an image forming mode in the image forming unit of the image forming apparatus. 
           [0020]      FIG. 3  is an explanatory view of a moving mechanism of the image forming unit of the image forming apparatus. 
           [0021]      FIG. 4  is an explanatory view of the moving mechanism of the image forming unit of the image forming apparatus. 
           [0022]      FIG. 5  is a block diagram showing connection of hardware of the image forming apparatus. 
           [0023]      FIG. 6  is a flowchart showing a basic print process in the image forming apparatus. 
           [0024]      FIG. 7  is a flowchart in the case of inserting a blank sheet in the image forming apparatus. 
           [0025]      FIG. 8  is an explanatory view for explaining a state where plural blank sheets are used. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and methods of the present invention. 
         [0027]    Hereinafter, an embodiment of the invention will be described with reference to the drawings. 
         [0028]      FIG. 1  is a side sectional view showing a schematic configuration of an image forming apparatus. As shown in  FIG. 1 , as a basic layout of each unit that forms an image forming apparatus  1 , an image forming unit  2  is arranged substantially at a central part of the apparatus body. An internal paper discharge unit  6  is arranged to the lateral side of this image forming unit  2 . Also, toner cartridges  3 Y,  3 M,  3 C and  3 k for respective colors are housed and arranged above the image forming unit  2 . An original reading unit  4  is arranged above these toner cartridges  3 Y,  3 M,  3 C and  3 K. Also, an automatic document feeder (ADF)  5  is arranged to the lateral side of the original reading unit  4 . An operating unit and a display unit (not shown) are formed above the original reading unit  4 . Also, a paper feeder unit  7  is provided below the image forming unit  2 . 
         [0029]      FIG. 2A  and  FIG. 2B  are enlarged side sectional views of the image forming unit.  FIG. 2A  shows a case where image formation of all the four colors is carried out (a color mode, which is a multiple-color image forming mode).  FIG. 2B  shows a case where image formation of only black is carried out (a monochrome mode, which is a single-color image forming mode). In  FIG. 2A  and  FIG. 2B , the subscript letters (Y, M, C, K) to the respective numerals show that they are parts for yellow, magenta, cyan, and black. These parts differ only in the color of toner housed in the developing unit, and have the same configuration. The image forming unit  2  is of a tandem system and is configured with developing units  14 Y,  14 M,  14 C and  14 K having photoconductive drums  12 Y,  12 M,  12 C and  12 K as four image carriers, linearly arrayed facing a belt carrying surface (outer circumferential surface) of an endless transfer belt  11  made of, for example, semiconducting polyimide. 
         [0030]    The developing units  14 Y,  14 M,  14 C and  14 K have the photoconductive drums  12 Y,  12 M,  12 C and  12 K, chargers  13 Y,  13 M,  13 C and  13 K, developing devices  15 Y,  15 M,  15 C and  15 K, and cleaners  16 Y,  16 M,  16 C and  16 K corresponding to the respective toner colors C (cyan), Y (yellow), M (magenta) and K (black). A predetermined gap is provided between the chargers  13 Y,  13 M,  13 C,  13 K and the developing devices  15 Y,  15 M,  15 C,  15 K in the casings of these developing units  14 Y,  14 M,  14 C and  14 K. Via this gap, the circumferential surfaces of the photoconductive drums  12 Y,  12 M,  12 C and  12 K 1  are exposed to and irradiated with light by exposure means  17  (shown in  FIG. 1 ) formed by a laser scanner or LED. The chargers  13 Y,  13 M,  13 C and  13 K evenly charge the circumferential surfaces of the corresponding photoconductive drums  12 Y,  12 M,  12 C and  12 K with predetermined electric charges. The exposure means  17  exposes to light the charged circumferential surfaces of the photoconductive drums  12 Y,  12 M,  12 C and  12 K in accordance with image information and thus forms electrostatic latent images thereon. Then, the developing devices  15 Y,  15 M,  15 C and  15 K transfer toner corresponding to the formed electrostatic latent images and thus form (develop) toner images. 
         [0031]    Also, transfer members  18 Y,  18 M,  18 C and  18 K are arranged to the other side of the carrying surface of the transfer belt  11 . The toner images formed (developed) on the circumferential surfaces of the photoconductive drums  12 Y,  12 M,  12 C and  12 K are transferred onto the surface of the transfer belt  11  carried thereto, by transfer fields formed by the corresponding transfer members (primary transfer rollers)  18 Y,  18 M,  18 C and  18 K. The transfer members  18 Y,  18 M,  18 C and  18 K are respectively movable in the direction of an arrow A by a moving mechanism, which will be described later, and they contact and separate from the transfer belt  11  in accordance with the image forming mode (color mode or monochrome mode). Also, interlocked with this contact and separation, the transfer belt  11  contacts and separates from the photoconductive drums  12 Y,  12 M,  12 C and  12 K. 
         [0032]    That is, in the case of the color image forming mode, all the transfer members  18 Y,  18 M,  18 C and  18 K contact the transfer belt  11 . On the other hand, in the case of the monochrome image forming mode, only the black transfer member  18 K contacts the transfer belt  11 . 
         [0033]    The photoconductive drums  12 Y,  12 M,  12 C and  12 K are driven separately and individually. Indexes (not shown) are installed in the photoconductive drums  12 Y,  12 M,  12 C and  12 K, and they generate one pulse per rotation of the photoconductive drums  12 Y,  12 M,  12 C and  12 K. At which position in one rotation the photoconductive drums  12 Y,  12 M,  12 C and  12 K are situated, is detected by a home position detector (not shown) that detects a predetermined home position, and the rotation is controlled with the result of the detection. 
         [0034]    Also, a registration detection sensor  19  provided facing the belt carrying surface (outer circumferential surface) of the transfer belt  11  is a sensor that detects the state of alignment (registration deviation) in superimposing the respective colors. Also, a transfer belt cleaner  28  is arranged facing the belt carrying surface (outer circumferential surface) of the transfer belt  11 . 
         [0035]    Next, a contact and separation mechanism will be described that causes the above transfer members  18 Y,  18 M,  18 C and  18 K to contact and separate from the transfer belt  11  and thus causes the transfer belt  11  to contact and separate from the photoconductive drums  12 Y,  12 M,  12 C and  12 K. 
         [0036]      FIG. 3  is an explanatory view for schematically explaining the layout of the transfer members  18 Y,  18 M,  18 C,  18 K facing the transfer belt  11 , and the contact and separation mechanism. The transfer belt  11  is driven by a driving roller  21  and travels in the direction of an arrow S. A bias voltage is applied to the transfer members  18 Y,  18 M,  18 C and  18 K, which are the primary transfer rollers arranged at the positions facing the photoconductive drums  12 Y,  12 M,  12 C and  12 K, and the toner images developed on the surface of the photoconductive drums  12 Y,  12 M,  12 C and  12 K are transferred onto the surface of the transfer belt  11 . In this case, with their own weights and the pressurization by compression springs  22 , the transfer members  18 Y,  18 M,  18 C and  18 K press the transfer belt  11  to the photoconductive drums  12 Y,  12 M,  12 C and  12 K while forming predetermined nipping parts. 
         [0037]      FIG. 4  is a perspective view of the separation mechanism, as viewed from the bottom, for explaining the separation of the transfer belt  11  from the photoconductive drums  12 Y,  12 M,  12 C and  12 K due to the movement of the transfer members  18 Y,  18 M,  18 C and  18 K facing the transfer belt. 
         [0038]    That is, a separation mechanism  30  includes a cam  32 , a driving system  33  for operating the cam  32 , links  34  and  35 , lifters  36 Y,  36 M,  36 C and  36 K, a belt stretching roller  37 , a roller cam  38 , and a roller holder  39 . 
         [0039]    The link  34  is to drive the black (K) primary transfer roller (transfer member)  18 K, and the link  35  is to drive the color primary transfer rollers  18 Y,  18 M,  18 C and  18 K. The link  34  moves the lifter  36 K, and the link  35  moves the lifters  36 Y,  36 M,  36 C and  36 K. The roller holder  39  is energized upward by a tension spring. 
         [0040]    The cam  32  is rotated by the driving system  33 , and the lifters  36 Y,  36 M,  36 C and  36 K rotate via the links  34  and  35 . The hooks at the ends of the lifters  36 Y,  36 M,  36 C and  36 K lift the primary transfer rollers  18 Y,  18 M,  18 C and  18 K. At the same time, the roller cam  38  rotates and the roller holder  39  is lifted by tension springs  40 , thus causing the transfer belt  11  to separate from the photoconductive drums  12 Y,  12 M,  12 C and  12 K. 
         [0041]    With these configurations, in the color mode, that is, the multi-color image forming mode to which the plural photoconductive drums  12 Y,  12 M,  12 C and  12 K are related, all the photoconductive drums  12 Y,  12 M,  12 C and  12 K related to color image formation are in contact with the transfer belt  11 , as shown in  FIG. 2A . On the other hand, in the monochrome mode, that is, the single-color image forming mode to which the single photoconductive drum  12 K is related, only the photoconductive drum  13 K is in contact with the transfer belt  11  and the photoconductive drums  13 Y,  13 M and  13 C that are not related to the image formation are separated from the transfer belt  11 , as shown in  FIG. 2B . 
         [0042]    The toner cartridges  3 Y,  3 M,  3 C and  3 K are attachable and toners of the respective colors of yellow (Y), magenta (M), cyan (C) and black (K) are housed therein. 
         [0043]    In the original reading unit  4 , an original fed by an automatic document feeder device  74  shown in  FIG. 5  is sequentially read by a scanner device  73  and sent to an image processing unit  75 . In the image processing unit  75 , the original is stored as image data into an image data file provided as storage means, and predetermined image processing is performed on this image data. 
         [0044]    Also, the original reading unit  4  has an automatic document feeder (ADF) not shown, reads each sheet of an original including plural sheets set on the ADF, and generates image data. One side or both sides of an original can be read in accordance with the user&#39;s instruction. 
         [0045]    An automatic duplex unit (ADU)  6 A provided in the internal paper discharge unit  6  is a mechanism to reverse the side of one sheet at the time of printing. That is, there is a double-side copying function to print on both sides of a sheet as a copying function. In double-side copying, after printing is done on one side of a sheet fed from the cassette that houses sheets, the sheet is carried to the ADU  6 A to reverse the side of the sheet and printing is done on the other side, thus making print on both sides of the sheet. The double-side copying to print on both sides of a sheet includes “one side to double side” copying, in which one side of the original is read and copied to both sides of the sheet, and “double side to double side” copying, in which both sides of the original are read and copied to both sides of the sheet. 
         [0046]    Even though the ADU  6 A is loaded, in one-side copying, the sheet after printing on its one side is discharged through a route in the internal paper discharge unit, without being carried to the ADU  6 A. The one-side copying to print on one side of a sheet includes “one side to one side” copying, in which one side of the original is read and copied to one side of the sheet, and “double side to one side” copying, in which both sides of the original are read and copied to one side of the sheet. 
         [0047]    A fixing unit  6 B is formed in the internal paper discharge unit  6 , and it is formed by a heat roller  6   b  and a press-contact roller  6   c  facing the heat roller. 
         [0048]    Also, the paper feeder unit  7  is provided below the image forming unit  2 . Plural paper feed cassettes  7   a  and  7   b  housing sheets of various sizes are provided in the paper feeder unit  7 . Moreover, a manual insertion paper feeder unit  7   c  that feeds a sheet paper by manual insertion is provided therein. 
         [0049]      FIG. 5  is a block diagram showing the connection of hardware related to the image forming apparatus. The control system of the image forming apparatus  1  of the above configuration will be described with reference to  FIG. 5 . 
         [0050]    Roughly, the control system has a system unit  50 , an engine unit  60 , and a scanner unit  70 . 
         [0051]    A system CPU  50 A of the system unit  50  is connected to a ROM  51 , a RAM  52 , and a NVRAM (non-volatile memory)  53 , and is also connected to a control panel device  54 , an external I/F device  55  for network connection, a page memory control device  56  that controls a page memory  56   a,  and I/F circuits  57 A and  57 B that are connected to the engine unit  60  and the scanner unit  70 , respectively. 
         [0052]    In the system unit  50 , the system CPU  50 A drives the units  51  to  57  forming the system unit  50 , in accordance with control programs stored in the ROM  51  and an HDD (not shown). The system CPU also receives status information sent from an engine CPU  60 A of the engine unit  60  and a scanner CPU  70 A of the scanner unit  70 , and input information inputted from the control panel device  54 , and controls the entire image forming apparatus  1 . 
         [0053]    The engine CPU  60 A of the engine unit  60  is connected to a ROM  61 , a RAM  62 , a NVRAM  63 , an image editing device  64 , a laser driving device  65  that drives a polygon motor  65   a,  a paper feeder device  66  having a resist motor  66   a,  a paper feeding motor  66   b,  a carrying motor  66   c  and an ADU motor  66   d,  a developing process device  67  having a transfer motor  67   a,  a drum motor  67   b  and a developing motor  67   c,  and the fixing device  6 B having a fixing motor  6   bm,  and controls these units. 
         [0054]    The scanner CPU  70 A of the scanner unit  70  is connected to a ROM  71 , a RAM  72 , the scanner device  73 , the automatic document feeder device  74 , and the image processing device  75 . In the scanner unit  70 , the scanner CPU  70 A drives each part of the scanner (not shown) and performs control related to image reading, by using the memories  71  and  72 . 
         [0055]    Next, a basic printing operation for image formation in the full-color image forming apparatus  11  of the above configuration will be described. 
         [0056]      FIG. 6  is a basic flowchart of the image forming operation. 
         [0057]    First, an original set on an original table (not shown) by the document feeder device  5  and the like is optically read by the original reading unit  4  and its image data is transmitted to the exposure means  17  of the image forming unit  2  (the image data is inputted to the image forming apparatus  1 ) (step S 1 ). 
         [0058]    It is determined whether the image data is a monochrome image or color image (step S 2 ). 
         [0059]    In the case of a color image (color mode), driving of the transfer belt  11 , the photoconductive drums  12 Y,  12 M,  12 C and  12 K, and the polygon motor (not shown) of the exposure means  17  is started (step S 3 ). 
         [0060]    In this case, since it is the color mode and a color deviation is generated by a misalignment, alignment correction of the transfer carrier belt  11  is carried out (whether it is in contact with the rib or not) (step S 4 ) In the case of a monochrome image (monochrome mode) the transfer belt  11  is separated, in addition to starting driving of the transfer belt  11 , the photoconductive drums  12 Y,  12 M,  12 C and  12 K, and the polygon motor (not shown). 
         [0061]    In this case, since it is the monochrome mode and no color deviation occurs even if there is a misalignment, alignment correction of the transfer belt  11  is not carried out (step S 2 - 1 ). 
         [0062]    It is determined whether the number of rotations of the polygon motor has reached a predetermined number of rotations or not, after the transfer carrier belt  11  contacts the rib (not shown) in the case of the color mode, or after the transfer belt  11  is separated in the case of the monochrome mode (step S 5 ). 
         [0063]    When the predetermined number of rotations has reached, the exposure means  17  scans a laser beam from a laser oscillating unit (not shown) with a polygon mirror in accordance with the image signal, then causes the laser beam to pass through several optical lenses (not shown), guides the optical path with a folding mirror, and casts the laser beam to the photoconductive drums  12 Y,  12 M,  12 C and  12 K. As the photoconductive drums  12 Y,  12 M,  12 C and  12 K rotate synchronously with the image signal read by the original reading unit  4 , latent images are formed on the photoconductive drums  12 Y,  12 M,  12 C and  12 K by the scanning laser beam from the exposure means  17  (step S 6 ). 
         [0064]    The latent images formed on the photoconductive drums  12 Y,  12 M,  12 C and  12 K are made visible (developed) with toner by the developing units  14 Y,  14 M,  14 C and  14 K 3  as developing means. The images, thus made visible, are transferred onto the transfer belt  11 , which is an endless belt, by the transfer members (primary transfer rollers)  18 Y,  18 M,  18 C and  18 K (step S 7 ). 
         [0065]    In the case of the monochrome mode, the above operation is carried only for black. In the case of the color mode, the above process is continuously carried out for each color of yellow, cyan, magenta, and black, and as the transfer belt  11  moves in the direction of the arrow S at a constant process speed, the toner images of the respective colors are sequentially superimposed and transferred to the transfer belt  11 . 
         [0066]    Meanwhile, recording sheets (not shown), which are transfer materials, are stacked in the feed cassettes  7   a  and  7   b.  A recording sheet is picked up by a feed roller and carried along a recording sheet carrying path by plural carrier rollers (not shown). Then, the toner images of the respective colors transferred on the transfer belt are transferred to the transfer sheet (recording sheet) (step S 8 ). 
         [0067]    After that, as heat and pressure are applied by the fixing unit  6 B, the toner images of the respective colors are fixed on the transfer sheet, which is then discharged. 
         [0068]    If it is determined that the transfer to the recording sheet ends (step S 9 ), cleaning of the photoconductive drum  12 Y,  12 M,  12 C and  12 K 1 , and the transfer belt  11  is started. Then, the transfer belt  11  is constantly shifted to the color mode side within this cleaning time (step S 10 ). 
         [0069]    That is, in the case where image formation has been carried out in the monochrome mode, the transfer belt  11  is moved to contact the photoconductive drums  12 Y,  12 M,  12 C and  12 K. On the other hand, in the case where image formation has been carried out in the color mode, the transfer belt  11  is maintained in contact with the photoconductive drums  12 Y,  12 M,  12 C and  12 K. 
         [0070]    The toner remaining on the surfaces of the photoconductive drums  12 Y,  12 M,  12 C and  12 K is collected by the cleaning units  16 Y,  16 M,  16 C and  16 A, and the photoconductive drums  12 Y,  12 M,  12 C and  12 K are cleaned. 
         [0071]    Also, the toner remaining on the transfer belt  11  is collected by a transfer carrier belt cleaner (not shown) and the transfer belt  11  is cleaned. At the time when the cleaning of the transfer carrier belt  11  is completed, the print job ends (step S 11 ). 
         [0072]    Next, a process in the case of inserting a blank sheet after automatic reading of an original in the full-color image forming apparatus  1  of the above configuration will be described. In a “print processing” step in the process where a blank sheet is inserted, the print operation described above with reference to  FIG. 6  (step S 3  and the subsequent steps) is carried out. 
         [0073]    The basic ideas to efficiently carry out the process of inserting a blank sheet include the following. 
         [0074]    (1) In the case where a blank sheet is inserted on the first sheet of the original, the image forming mode (color or monochrome mode) for the sheet after the blank sheet is determined and printing is carried out in the determined image forming mode. 
         [0075]    (2) In the case where a blank sheet is inserted on the second or subsequent sheet of the original, the image forming mode (color or monochrome mode) for the sheet before the inserted blank sheet is determined and printing is carried out in the determined image forming mode. 
         [0076]      FIG. 7  is a flowchart of the process in the case of inserting a blank sheet after automatic reading of an original in the full-color image forming apparatus  1 . In the section of “print processing” in the flowchart of  FIG. 7 , the image forming processing in the image forming process shown in  FIG. 6  is carried out as described above (step S 3  and the subsequent steps). 
         [0077]    First, an original set on the original table (not shown) by the document feeder device  5  and the like is optically read by the original reading unit  4  and the result of reading is stored into a storage unit (step S 21 ) As the original is read, the information of the original is received by the system unit  50  (step S 22 ). 
         [0078]    From the received information, it is determined whether the first sheet of the original is blank or not (step S 23 ). 
       [Flow in the Case Where the First Sheet is Blank] 
       [0079]    When it is determined that the first sheet of the original is blank, information about how many blank sheets are included is received, and the image forming mode after the blank sheet is acquired (step S 24 ). 
         [0080]    As shown in the schematic diagram of  FIG. 8 , the number of blank sheets is specified (step S 25 ). 
         [0081]    It is determined whether the number of blank sheets is equal to or less than a prescribed number of sheets that is predefined in accordance with the memory capacity in order to prevent memory errors (step S 26 ). 
         [0082]    If the number of blank sheets is equal to or less than the prescribed number, the system unit  50  sets insertion of blank sheets in the image forming mode acquired in step S 24  (step S 27 ). 
         [0083]    In the image forming mode set in step S 27 , print processing is carried out in accordance with an instruction from the system unit  50  (step S 28 A). 
         [0084]    On the other hand, if it is determined in step S 26  that the number of blank sheets is not equal to or less than the prescribed number, the system unit  50  sets insertion of blank sheets in a predetermined image forming mode (step S 29 ). 
         [0085]    In the image forming mode set in step S 29 , print processing is carried out in accordance with an instruction from the system unit  50  (step S 28 B). 
         [0000]    [Flow in the Case where the First Sheet is Not Blank] 
         [0086]    If it is determined in step S 23  that the first sheet of the original is not blank, information about the image forming mode before the blank sheet inserted in the plural sheets of the original, is acquired, or information that there is no insertion of a blank sheet is acquired (step S 30 ) 
         [0087]    On the basis of the acquired information about the image forming mode before the blank sheet or the information that there is no insertion of a blank sheet, print processing is carried out in accordance with an instruction from the system unit  50  (step S 28 C). 
       [Flow of Continuation of Printing] 
       [0088]    It is determined whether continuation of printing is possible or not (step S 31 ). 
         [0089]    If printing is to be continued, the system unit  50  sets insertion of a blank sheet in accordance with the information about the image forming mode acquired and set in the above processes (step S 32 ). 
         [0090]    Print processing is carried out in accordance with an instruction from the system unit  50  (step S 28 D). 
         [0091]    After the printing ends, the processing returns to step S 31  again and it is determined whether continuation of printing is possible or not. This is repeated, and when continuation of printing is impossible, the printing ends. 
         [0092]    If continuation of printing is impossible in step S 31 , the printing ends. 
         [0093]    According to the above processes, since the image forming mode need not be changed every time a blank sheet is inserted, the image processing process can be carried out efficiently without lowering the productivity of the image forming apparatus even in the process where a blank sheet is inserted. 
         [0094]    Although exemplary embodiments of the present invention have been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications, or alterations to the invention as described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications, and alterations should therefore be seen as within the scope of the present invention.