Abstract:
When continuous printing in which color print and monochromatic print are mixedly present is to be effected, the distance between recording sheets is greatly widened to avoid problems when changeover takes place from monochromatic print to color print and therefore, the printing capability (the number of prints per unit time) is reduced.  
     When in an image processing apparatus for forming a color or monochromatic image on a recording sheet conveyed, by yellow, magenta, cyan and black image forming means, a plurality of recording mediums are continuously conveyed and a monochromatic image is to be formed on a preceding recording medium and a color image is to be formed on a succeeding recording medium, a timing signal A corresponding to the succeeding recording medium is outputted earlier than a timing signal B indicative of the start of image formation corresponding to the preceding recording medium.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to an image processing apparatus and a controlling method therefor, and for example, to an image processing apparatus for forming an image by the electrophotographic process and a controlling method therefor.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIGS. 1 and 2 of the accompanying drawings are typical views showing the printing by a color image processing apparatus for successively transferring yellow, magenta, cyan and black colors to a recording material conveyed by a conveying belt.  
           [0005]    When recording sheets long in a conveying direction are to be printed in the order of monochrome and full color, image formation in respective stations for yellow, magenta and cyan is not effected on the preceding recording sheet (shown as the first page in FIG. 1) to be monochromatically printed. At timing whereat the leading end of the recording sheet has arrived at a position corresponding to the exposure starting position of a black photosensitive drum, a vertical synchronization signal (hereinafter expressed as the “TOP signal”) indicative of the output timing of black image data is outputted to a controller, not shown.  
           [0006]    Next, a timing whereat the leading end of the succeeding recording sheet (shown as the second page in FIG. 1) to be color-printed has arrived at a position corresponding to the exposure starting position of a yellow photosensitive drum, a TOP signal indicative of the output timing of yellow image data is outputted to the controller.  
           [0007]    However, in the image processing apparatus shown in FIGS. 1 and 2, in order to decrease the number of signal lines, the TOP signals uses a single signal line (a single signal) irrespective of the monochromatic print and the full color print.  
           [0008]    [0008]FIG. 2 shows a state in which in the image processing apparatus of the same construction as that shown in FIG. 1, recording sheets short in the conveying direction are printed in the order of monochromatic color and full color.  
           [0009]    When as shown in FIG. 2, the distance between the position of the yellow photosensitive drum and the position of the black photosensitive drum is defined as L 1  and the length of the recording sheet in the conveying direction is defined as L 2  and the distance between that recording sheet and the succeeding recording sheet is defined as L 3 , when the relation among them is L 1 &gt;L 2 +L 3 , the image formation of (the first color yellow in) the succeeding full color print precedes the preceding monochromatic print. So, the sheet interval L 3  is widened so that the order of image processing may not be reversed.  
           [0010]    [0010]FIG. 3 of the accompanying drawings is a timing chart in continuous printing wherein full color and monochrome are mixedly present, and shows an example in which printing is effected in the order of monochrome, monochrome, full color, monochrome, full color and full color.  
           [0011]    The TOP signal is used in both of full color print and monochromatic print, and what are designated by the reference numeral  301  in FIG. 3 are the TOP signals for full color print, and what are denoted by the reference numeral  401  are the TOP signals for monochromatic print.  
           [0012]    A controller, in monochromatic print, outputs black image data  403  in synchronism with the TOP signals  401 , and in full color print, outputs first color, i.e., yellow image data  303  in synchronism with the TOP signals  301 , and thereafter outputs magenta, cyan and black image data (designated by the reference numerals  305 ,  307  and  309 , respectively, in FIG. 3). Times denoted by T 1 , T 2  and T 3  in FIG. 3 correspond to the times for which a recording sheet is conveyed over distances from the yellow photosensitive drum to the other color photosensitive drums.  
           [0013]    The number of printed sheets per unit time, i.e., the printing capability, in such a construction can be judged from the output timing of the black image data in both of full color and monochrome, as shown in FIG. 3.  
           [0014]    When continuous print in which full color print and monochromatic print are mixedly present is to be effected, as is apparent from FIG. 3, the sheet interval L 3  is greatly widened to avoid the above-noted problem when changeover takes place from monochromatic print to full color print, whereby the printing capability is reduced.  
         SUMMARY OF THE INVENTION  
         [0015]    It is an object of the present invention to solve the above-noted problem and to prevent any reduction in the image forming capability when continuous image formation in which monochromatic and color images are mixedly present is effected.  
           [0016]    It is another object of the present invention to provide an image processing apparatus for forming a visible image on a recording medium conveyed by conveying means, by a plurality of color component image forming means corresponding to a plurality of color components including at least black respectively, having:  
           [0017]    signal outputting means for outputting a timing signal for instructing to start the formation of a first color component image differing depending on image forming modes;  
           [0018]    wherein when a monochromatic image is to be formed on a preceding recording medium and a color image is to be formed on a succeeding recording medium, the signal outputting means outputs the timing signal corresponding to the succeeding recording medium earlier than the timing signal corresponding to the preceding recording medium.  
           [0019]    It is still another object of the present invention to provide a controlling method for an image processing apparatus for forming a visible image on a recording medium conveyed by conveying means, by a plurality of color component image forming means corresponding to a plurality of color components including at least black respectively, having:  
           [0020]    the step of outputting a timing signal for instructing the recording medium conveyed by the conveying means to start the formation of a first color component image differing depending on image forming mode;  
           [0021]    wherein when a monochromatic image is to be formed on a preceding recording medium and a color image is to be formed on a succeeding recording medium, the step outputs the timing signal corresponding to the succeeding recording medium earlier than the timing signal corresponding to the preceding recording medium.  
           [0022]    Other objects, constructions and effects of the present invention will become apparent from the following detailed description and the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a typical view showing the printing by a color image processing apparatus for successively transferring yellow, magenta, cyan and black to a recording sheet conveyed by a conveying belt.  
         [0024]    [0024]FIG. 2 is a typical view showing the printing by a color image processing apparatus for successively transferring yellow, magenta, cyan and black to a recording sheet conveyed by a conveying belt (particularly showing a state in which recording sheets short in a conveying direction are printed in the order of monochrome and full color.  
         [0025]    [0025]FIG. 3 is a timing chart in continuous printing in which full color and monochrome are mixedly present.  
         [0026]    [0026]FIG. 4 shows the general construction of a color image processing apparatus according to a first embodiment.  
         [0027]    [0027]FIG. 5 illustrates the interface signals of the engine and controller of the color image processing apparatus.  
         [0028]    [0028]FIG. 6 is a timing chart showing a TOP signal and horizontal synchronization signals and image data of respective colors when full color print is effected.  
         [0029]    [0029]FIG. 7 is a timing chart showing a TOP signal and a black horizontal synchronization signal and image data when monochromatic print is effected.  
         [0030]    [0030]FIG. 8 is a timing chart in continuous printing in which full color and monochrome are mixedly present.  
         [0031]    [0031]FIG. 9 illustrates the interface signals of the engine and controller of a color image processing apparatus according to a second embodiment.  
         [0032]    [0032]FIG. 10 is a timing chart in continuous printing in which full color and monochrome are mixedly present.  
         [0033]    [0033]FIG. 11 shows the construction of an image processing apparatus of a type transferring toner images directly from photosensitive drums to a recording sheet without using an intermediate transfer belt. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]    Image processing apparatuses according to some embodiments of the present invention will hereinafter be described in detail with reference to the drawings.  
       First Embodiment  
       [0035]    A color image processing apparatus according to a first embodiment is of a construction in which color images formed on an intermediate transfer belt are transferred to a recording sheet, and prevents any reduction in printing capability in continuous printing in which monochromatic print and full color print are mixedly present.  
       Construction  
       [0036]    [0036]FIG. 4 shows the general construction of the color image processing apparatus.  
         [0037]    The color image processing apparatus shown in FIG. 4 forms, for each color, an electrostatic latent image on a photosensitive drum by exposure based on image data in an image forming portion, develops this electrostatic latent image into a visible image, transfers the visible image to a transfer belt  12  and forms a color image, and thereafter transfers the color image to a recording sheet and fix it.  
         [0038]    The color image forming portion is provided with photosensitive drums  5 Y,  5 M,  5 L and  5 K, chargers  7 Y,  7 M,  7 C and  7 K, laser scanners  10 Y,  10 M,  10 C and  10 K, developing devices  8 Y,  8 M,  8 C and  8 K, toner cartridges  11 Y,  11 M,  11 C and  11 K, and primary transfer rollers  6 Y,  6 M,  6 C and  6 K in respective ones of stations juxtaposed by the number of developing colors. The color image forming portion is further provided with an intermediate transfer belt  12 , a secondary transfer roller  9 , a sheet feeding and conveying portion and a fixing device  13 .  
         [0039]    Each photosensitive drum is of a construction in which an organic photoconductive layer is formed on the outer periphery of an aluminum cylinder, and is counter-clockwisely rotated by a driving motor, not shown. The photosensitive drum is primary-charged by the charger provided with a charging sleeve  7 YS,  7 MS,  7 CS or  7 KS. The surface of the photosensitive drum is exposed to a laser beam on the basis of inputted image data, whereby an electrostatic latent image is formed thereon. The electrostatic latent image is developed into a visible image by the developing device provided with a developing sleeve  8 YS,  8 MS,  8 CS or  8 CK.  
         [0040]    The intermediate transfer belt  12  is an endless belt passed over a drive roller  18   a  and driven rollers  18   b  and  18   c,  and is in contact with the respective photosensitive drums and is clockwisely rotated. The toner images on the photosensitive drums are transferred to the surface of the belt by the primary transfer rollers.  
         [0041]    Recording sheets  1  contained in the sheet feed cassette  2  of a sheet feeding portion or recording sheets  1  placed on a sheet feed tray  3  are conveyed one by one on a conveying path  25  by a feed roller  4  and conveying rollers  24 , and arrive at the position of an ante-registration sensor  19 . The recording sheet  1  is further conveyed by a predetermined distance and arrives at registration rollers  23 , and is made to wait while forming a loop.  
         [0042]    The recording sheet  1  liberated from waiting is conveyed to the portion of contact between the intermediate transfer belt  12  and the secondary transfer roller  9  and is nipped and conveyed between the intermediate transfer belt  12  and the secondary transfer roller  9 , whereby visible color images superimposed and transferred onto the intermediate transfer belt  12  are collectively secondary-transferred to the recording sheet  1 . During transfer, the secondary transfer roller  9  is in contact with the intermediate transfer belt  12  as indicated by solid line, but during the other time, it is spaced apart to a position indicated by dotted line. Any residual toners remaining on the intermediate transfer belt  12  are removed by a cleaning blade contained in a cleaner container  21 , and are stored as waste toners in the cleaner container  21 .  
         [0043]    The fixing device  13  fixed the toner images on the recording sheet  1  while conveying the recording sheet  1 . The fixing device  13  is provided with a fixing roller  14  for heating the toners, and a pressure roller  15  for bringing the recording sheet  1  into pressure contact with the fixing roller  14 . The fixing roller  14  and the pressure roller  15  are formed into a hollow shape and contain a heater  16  or  17  therein.  
         [0044]    The recording sheet  1  having the toners fixed thereon has its normal discharge from the fixing device  13  detected by a fixing discharge sensor  20 , and is discharged to a sheet discharge portion, not shown, by discharge rollers, not shown, thus completing the image forming operation.  
         [0045]    [0045]FIG. 5 illustrates the interface signals of the engine and controller of the color image processing apparatus.  
         [0046]    A TOP signal (vertical synchronization signal)  203  and horizontal synchronization signals  204  to  207  of respective colors are sent from the engine  201  to the controller  202 . Image data  208  to  211  of respective colors synchronized with the horizontal synchronization signals  204  to  207  of respective colors are sent from the controller  202  to the engine  201 .  
       Print Timing  
       [0047]    [0047]FIG. 6 is a timing chart showing the TOP signal and the horizontal synchronization signals and image data of respective colors when full color print is effected.  
         [0048]    The controller  202  causes the engine  201  to start the printing operation when it is instructed to start full color print by a host computer or the like, not shown. When it starts the printing operation, the engine  201  drives the photosensitive drums  5 Y,  5 M,  5 C and  5 K, the intermediate transfer belt  12  and the laser scanners  10 Y,  10 M,  10 C and  10 K and makes preparations for forming images of respective colors. At a point of time whereat the preparations have been made, the engine  201  outputs to the controller  202  the TOP signal  301  for taking vertical synchronization for the first color.  
         [0049]    The controller  202  outputs yellow image data  303  synchronized with the TOP signal  301  and the yellow horizontal synchronization signal  302  inputted from the engine  201 . The engine  201  primary-transfers a yellow toner image onto the intermediate transfer belt  12  by the above-described procedure on the basis of the yellow image data  303  inputted thereto. The controller  202  outputs magenta image data  305  after the lapse of a time T 1  shown in FIG. 6 in order to fit to the timing at which the yellow toner image on the intermediate transfer belt  12  arrives at the primary transfer position of a magenta toner image. The controller  202 , likewise for cyan and black, outputs cyan image data  307  and black image data  309  after the lapse of a time T 2  and after the lapse of a time T 3 , respectively.  
         [0050]    [0050]FIG. 7 is a timing chart showing the TOP signal and the black horizontal synchronization signal and image data when monochromatic print is effected.  
         [0051]    The controller  202  causes the engine  201  to start the printing operation when it is instructed to start monochromatic print by the host computer or the like, not shown. When it starts the printing operation, the engine  201  drives at least the photosensitive drum  5 K, the intermediate transfer belt  12  and the laser scanner  10 K to thereby make preparations for monochromatic image formation. At a point of time whereat the preparations have been made, the engine  201  outputs to the controller  202  a TOP signal  401  for taking black vertical synchronization.  
         [0052]    The controller  202  outputs black image data  403  synchronized with the TOP signal  401  and a horizontal synchronization signal  402  inputted from the engine  201 . The engine  201  primary-transfers the black toner image onto the intermediate transfer belt  12  by the above-described procedure on the basis of the black image data  403 .  
       Print Timing When Full Color and Monochrome are Mixedly Present  
       [0053]    [0053]FIG. 8 is a timing chart in continuous printing in which full color and monochrome are mixedly present, and like FIG. 3, it shows an example in which printing is effected in the order of monochrome, monochrome, full color, monochrome, full color and full color.  
         [0054]    The engine  201  outputs the TOP signals  301  and  401  so that the controller  202  which can know the order of print modes in advance can output black image data common to full color print and monochromatic print at predetermined intervals.  
         [0055]    In the timing chart shown in FIG. 8, as compared with the timing chart shown in FIG. 3, the order of the TOP signal of the second page (monochromatic print) and the TOP signal of the third page (full color print) changes places. Likewise, the order of the TOP signal of the fourth page (monochromatic print) and the TOP signal of the fifth page (full color print) change places.  
         [0056]    The controller  202  knows not only the order of the print modes, but also the length of the recording sheet in the conveying direction thereof. It can also known the distance between recording sheets which is a constant value set by the engine by the use of the serial communication line, not shown, between the engine  201  and the controller  202 . Therefore, when the distance between the position of the yellow photosensitive drum and the position of the black photosensitive drum is defined as L 1  and the length of the preceding recording sheet to be full-color-printed in the conveying direction is defined as L 2  and the distance between the preceding recording sheet and the succeeding recording sheet to be monochromatically printed is defined as L 3 , the controller  202  can judge whether L 1 &gt;L 2 +L 3 . Consequently, on the basis of the result of this judgment, the controller  202  can know whether the inputted TOP signal is a TOP signal corresponding to which recording sheet.  
         [0057]    Also, when printing is to be effected in the order of full color, monochrome and monochrome, when the length of the recording sheet to be monochromatically printed (the second sheet) in the conveying direction is L 4 , even if the recording sheets are ones small in L 2  and L 4 , L 2 +L 3 +L 4 +L 3 &gt;L 1  without fail and therefore, next to the TOP signal for monochromatic print (the second sheet), the TOP signal for full color print (the first sheet) comes.  
         [0058]    That is, in continuous printing in which full color print and monochromatic print are mixedly present, the engine  201  outputs the TOP signal so that the controller  202  can output black image data at substantially constant intervals. Finally, printing is rightly effected in the designated order of print modes.  
         [0059]    As described above, when in the image processing apparatus wherein the TOP signal is outputted only at the first color image formation starting timing in the print modes of full color print and monochromatic print, monochromatic print is to be effected on the preceding recording sheet and full color print is to be effected on the succeeding recording sheet, if the sum of the length of the preceding recording sheet in the conveying direction and the distance between the recording sheets is shorter than the distance from the station for the first color to the station for monochrome (black) in full color print, the TOP signal (A in FIG. 8) for the succeeding recording sheet is outputted earlier than the TOP signal (B in FIG. 8) for the preceding sheet and therefore, when continuous printing in which monochromatic print and full color print are mixedly present is to be effected, the distance between the recording sheets need not be widened and any reduction in the printing capability (the number of prints per unit time) during continuous printing can be prevented.  
       Second Embodiment  
       [0060]    An image processing apparatus according to a second embodiment of the present invention will be described hereinafter. In the second embodiment, members similar to those in the first embodiment are given the same reference numerals and need not be described in detail.  
         [0061]    The engine  201  of the image processing apparatus according to the second embodiment has the function of informing of the print mode for the outputted TOP signal at real time.  
         [0062]    [0062]FIG. 9 illustrates the interface signals of the engine and controller of the color image processing apparatus, and a signal line  501  is added to the interface in the first embodiment shown in FIG. 5 to thereby make the informing of the print mode possible. The signal line  501  is for a full color informing signal, and if it is a high level at the falling edge of a TOP signal, it indicates that the TOP signal requires color image data (specifically, yellow image data), and if it is a low level, it indicates that the TOP signal requires black image data.  
         [0063]    [0063]FIG. 10 is a timing chart in continuous printing in which full color and monochrome are mixedly present, and like FIG. 3, it shows an example in which printing is effected in the order of monochrome, monochrome, full color, monochrome, full color and full color.  
         [0064]    By the use of a serial communication line, not shown, between the engine  201  and the controller  202 , the controller  202  designates in advance to the engine  201  the print mode (the distinction between full color and monochrome) for each print page and the type (the length in the conveying direction) of the recording sheet, prior to the continuous printing operation. On the basis of this information, the engine  201  judges whether full color print or monochromatic print should be effected on individual recording sheets.  
         [0065]    The engine  201  outputs a TOP signal  203  and informs of a print mode corresponding to the TOP signal by a full color informing signal  501  so that the controller  202  can output black image data common to full color print and monochromatic print at substantially constant intervals.  
         [0066]    Instead of informing of the print mode by the full color informing signal  501 , use can be made of the serial communication line, not shown, between the engine  201  and the controller  202 , or the like. If this is done, the engine  201  can inform the controller  202  of the print mode before it outputs the TOP signal.  
         [0067]    As described above, in continuous printing in which full color print and monochromatic print are mixedly present, the engine  201  outputs the TOP signal and also informs the controller  202  of the print mode corresponding to the TOP signal, whereby the controller  202  can make the output intervals of black image data substantially constant.  
         [0068]    As described above, according to the present embodiment, any reduction in the image forming capability when effecting continuous image formation in which monochromatic and color images are mixedly present can be prevented.  
       Modification  
       [0069]    While in each of the above-described embodiments, an image processing apparatus in which toner images of full color formed on an intermediate transfer belt are transferred to a recording sheet has been taken as an example, there is also an image processing apparatus of a type as shown in FIG. 11 wherein without the use of an intermediate transfer belt, toner images are directly transferred from photosensitive drums to a recording sheet.  
         [0070]    If the output timing of the TOP signal and the full color informing signal described in the above-described embodiments are applied to the image processing apparatus shown in FIG. 11, as in the above-described embodiments, any reduction in the printing capability (the number of prints per unit time) can be prevented when effecting continuous printing in which monochromatic print and full color print are mixedly present.  
       Other Embodiments  
       [0071]    The present invention may be applied to a system comprised of a plurality of apparatuses (for example, a host computer, an interface apparatus, a reader, a printer, etc.) or an apparatus comprising an instrument (such as a copier or a facsimile apparatus).  
         [0072]    Also, the objects of the present invention is of course achieved by supplying a storing medium (or a recording medium) having recorded therein the program code of software for realizing the function of the aforedescribed embodiments to a system or an apparatus, and the computer (or the CPU or the MPU) of the system or the apparatus reading out and executing the program code stored in the storing medium. In this case, the program code itself read out of the storing medium realizes the function of the aforedescribed embodiments, and the storing medium storing the program code therein constitutes the present invention. Also, there is of course covered a case where by the program code read out by the computer being executed, not only the function of the aforedescribed embodiments is realized, but on the basis of the instructions of the program code, an operating system (OS) or the like working on the computer carries out some or all of actual processing, and the function of the aforedescribed embodiments is realized by the processing.  
         [0073]    Further, there is of course covered a case where the program code read out of the storing medium is written into a memory provided in a function expanding card inserted into the computer or a function expanding unit connected to the computer, whereafter on the basis of the instructions of the program code, a CPU or the like provided in the function expanding card or the function expanding unit carries out some or all of actual processing, and the function of the aforedescribed embodiments is realized by the processing.  
         [0074]    While the present invention has been described above with respect to some preferred embodiments, it is apparent that the present invention is not restricted to these embodiments, but various modifications and applications are possible within the scope of the invention as defined in the appended claims.