JP4907195B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus using electrophotography such as a copying machine and a printer, and more particularly to control of execution timing of image density correction.

  In an image forming apparatus using an electrophotographic process, generally, toner is directly transferred onto a toner carrier to form a patch image (reference image), and the toner amount and position are detected to perform density correction and color misregistration correction. Do. For example, in the case of a full-color image forming apparatus, when a mode for appropriately setting the image density of each color (hereinafter referred to as a calibration mode) is set, the cyan, magenta, yellow, and black image forming units are used on the transfer belt. A patch image for correction of each color is formed, and the image is detected by the detection means, and density and color misregistration correction is performed.

  When the amount of toner adhering is large, the reflected light from the belt surface is blocked by the toner, so that the amount of light received by the detecting means is reduced. On the other hand, when the toner adhesion amount is small, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the detection means. Therefore, the density of the patch image of each color is detected based on the output value of the received light signal based on the received reflected light amount, and the charging potential, the developing bias potential, and the exposure amount of the LED head are adjusted in comparison with a predetermined reference density. Thus, density correction is performed for each color.

  Here, in the case of monochrome printing using the black image forming unit, the density of the black toner is mainly related to saturation and lightness, and in the case of color printing using the cyan, magenta, and yellow image forming units, the density of the color toner. Is mainly related to hue. Also, even if the saturation and brightness vary compared with the hue, the image impression does not deteriorate. Therefore, monochrome (black) density correction need not be performed as frequently as color (cyan, magenta, and yellow) density correction.

  Such density correction in the color image forming apparatus has conventionally performed calibration of each color at the same time using the number of printed sheets, printing time, and the like as execution conditions, so that monochrome density correction is performed unnecessarily many times. . In order to solve this problem, for example, Patent Document 1 discloses a case where monochrome and color density correction conditions are individually managed by the number of printed sheets, and color density correction is performed at an interval between printed sheets where monochrome density correction is performed. An image forming apparatus is disclosed in which a larger number is set and monochrome density correction is not performed more than necessary.

  However, even if the monochrome and color correction execution conditions are changed as in Patent Document 1, for example, when a large amount of monochrome printing is performed continuously, the monochrome printing is not performed even though the color printing is not performed. Color density correction is also executed simultaneously at the density correction timing. If this process is repeated many times, the color toner in the developing device is excessively mechanically stressed, and the toner deteriorates more quickly. Further, the toner charge amount may increase and the density may not be obtained during color printing. is there.

Also, since the density correction is normally set so that printing is interrupted and forcibly executed even during continuous printing, the user ends density correction when the correction execution condition is met during continuous printing. Until the image forming efficiency is reduced.
Japanese Patent Laid-Open No. 11-295956

  In view of the above problems, the present invention eliminates unnecessary color density correction by appropriately setting monochrome and color density correction timings to prevent deterioration of color toner and maintain a stable image density. A possible image forming apparatus is provided. Another object of the present invention is to provide an image forming apparatus that improves the image forming efficiency by minimizing the state in which density correction is continuously performed.

  In order to achieve the above object, the present invention provides a first counting means for cumulatively counting the number of printed sheets or printing time for monochrome printing, a second counting means for cumulatively counting the number of printed sheets or printing time for color printing, And a control unit that individually executes monochrome and color density correction based on the count values of the first and second counting units. The control unit includes: When the count value reaches the density correction execution value, only monochrome density correction is executed. When the count value of the second count means reaches the density correction execution value, monochrome and color density correction is executed. It is characterized by doing.

  According to the present invention, in the color image forming apparatus having the above-described configuration, the control unit has the count value of the first count unit reaches a density correction execution value, and the count value of the second count unit is density correction. It is characterized in that monochrome and color density correction is executed when the value is equal to or greater than a predetermined value smaller than the execution value.

  Further, the present invention provides a first counting means for cumulatively counting the number of printed sheets or printing time for monochrome printing, a second counting means for cumulatively counting the number of printed sheets or printing time for color printing, and the first and second And a control unit that individually executes density correction for monochrome and color based on the count value of the counting unit, and the control unit includes the first or second counting unit at the end of printing. When the count value is equal to or greater than a predetermined value smaller than the density correction execution value, density correction is executed in advance.

  Further, according to the present invention, in the color image forming apparatus having the above-described configuration, when the control unit has only the count value of the first count unit equal to or greater than a predetermined value smaller than the density correction execution value at the end of printing, Only correction is executed, and when the count value of the second count means is equal to or greater than a predetermined value smaller than the density correction execution value, monochrome and color density correction is executed.

  According to the present invention, in the color image forming apparatus configured as described above, a storage unit that stores the number of prints per print execution and an integrated value of the number of print executions for each print number, and print execution of the whole or a predetermined number or less. Calculating means for calculating a cumulative occupancy ratio obtained by accumulating the occupancy ratio of the number of times of printing for each number of prints, and the control means is configured to execute density correction execution based on the cumulative occupancy ratio calculated by the arithmetic means. It is characterized by setting the value automatically.

  According to the first configuration of the present invention, for example, when a large amount of monochrome printing is performed, only the monochrome density correction is executed, so that the color toner developing device can be stopped. Therefore, excessive mechanical stress is not applied to the color toner, so that the deterioration of the toner can be suppressed and the deterioration of the image quality due to the increase in the charge amount of the color toner can be prevented. In addition, when color density correction is required, monochrome density correction is also performed at the same time, so monochrome density correction is not performed immediately after color density correction, improving image formation efficiency. Can be made.

  Further, according to the second configuration of the present invention, in the image forming apparatus having the first configuration, even when the count value of the first count unit reaches the density correction execution value during continuous printing, the second When the count value of the counting means is equal to or greater than a predetermined value smaller than the density correction execution value, color and monochrome density correction are executed at the same time. Therefore, color density correction is performed immediately after monochrome density correction during continuous printing. It is not executed, and the image forming efficiency can be improved.

  Further, according to the third configuration of the present invention, when printing ends just before the count value of the first or second count means reaches the density correction execution value, it precedes after the end of printing. Density correction is executed. Therefore, after the next continuous printing is started, density correction is executed immediately and printing is not interrupted, and the image forming efficiency is improved.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, when the count value of the first count unit satisfies the condition at the end of printing, the monochrome density When correction is performed and both the count values of the first and second counting means satisfy the conditions at the end of printing, both color and monochrome density correction are performed, so continuous color printing starts after monochrome density correction However, the color density correction is not immediately executed, and the image forming efficiency is further improved.

  According to the fifth configuration of the present invention, in the image forming apparatus having any one of the second to fourth configurations, the occupation ratio of the number of print executions for each print number with respect to the total or the number of print executions equal to or less than a predetermined number. Since the predetermined value for density correction execution is automatically set based on the accumulated occupancy ratio, the density correction interrupt execution rate during continuous printing can be reduced below a certain level regardless of the usage status of the user. it can.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side (right side in FIG. 1) of the transfer belt 8. These image forming portions Pa to Pd are provided corresponding to images of four different colors (magenta, cyan, yellow, and black), and magenta, cyan, and yellow are respectively subjected to charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is transferred onto a transfer paper 6 carried and transported by a transfer belt 8 that moves adjacent to each image forming unit, and is further fixed on the transfer paper 6 by a fixing unit 7. It is configured to be discharged from the main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d clockwise in FIG.

  Next, the image forming units Pa to Pd will be described. Around and around the photosensitive drums 1a to 1d rotatably arranged, image information is supplied to the chargers 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d and the photosensitive drums 1a to 1d. LED heads 17a, 17b, 17c and 17d to be exposed, developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and a developer remaining on the photosensitive drums 1a to 1d ( Cleaning portions 5a, 5b, 5c and 5d for removing toner are provided.

  First, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, then irradiated with light by the LED heads 17a to 17d, and electrostatic charges corresponding to the image signals are applied to the photosensitive drums 1a to 1d. A latent image is formed. Each of the developing devices 3a to 3d is filled with a predetermined amount of magenta, cyan, yellow, and black toners by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing units 3a to 3d and electrostatically attached to the toner corresponding to the electrostatic latent images formed by exposure from the LED heads 17a to 17d. An image is formed.

  The transfer paper 6 onto which the toner image is transferred is housed in a paper cassette 16 at the lower part of the apparatus, and is supplied onto the transfer belt 8 via a paper feed roller 13a and a registration roller 13b, and the photosensitive drums 1a to 1d. It is conveyed to the position. As the transfer belt 8, a belt in which both ends thereof are overlapped with each other and joined to form an endless shape, or a belt without a seam (seamless) is used. As a material of the belt, a resin belt is used, and preferably a multilayer rubber belt in which a fluorine resin coating, a silicon coat, a CR rubber, and a PVDF resin sheet are sequentially laminated from the surface layer is used.

  The transfer belt 8 is stretched around the driven rollers 10a, 10b and 10c and the driving roller 11. When the transfer belt 8 starts to rotate counterclockwise, the transfer paper 6 is transferred from the registration roller 13b to the transfer belt 8. It is conveyed onto the transfer belt 8 via the suction roller 14 provided on the most upstream side. A predetermined voltage is applied to the suction roller 14, and the transfer paper 6 is held on the transfer belt 8 by an electrostatic suction force.

  At this time, the image writing signal is turned ON, and an image is formed on the uppermost photosensitive drum 1a at a predetermined timing. A magenta toner image on the photosensitive drum 1 a is transferred onto the transfer paper 6 by applying an electric field to the lower portion of the photosensitive drum 1 a with the transfer roller 4 a to which a predetermined transfer voltage is applied. Thereafter, the transfer paper 6 is conveyed to the next image forming portion Pb, and a cyan toner image is transferred by the photosensitive drum 1b in the same manner as described above.

  Thereafter, yellow and black toner images are transferred by the photosensitive drums 1c and 1d by the same method as described above. These four-color images are formed with a predetermined positional relationship that is predetermined with respect to the transfer paper 6 in order to form a predetermined full-color image. Reference numerals 4b, 4c and 4d denote transfer rollers located below the photosensitive drums 1b to 1d. The transfer paper 6 onto which the four color toner images have been transferred is separated from the transfer belt 8 and conveyed to the fixing unit 7. In addition, the photosensitive drums 1a to 1d after the toner images are transferred are prepared by the cleaning units 5a to 5d in preparation for new electrostatic latent images to be subsequently formed.

  The transfer paper 6 conveyed from the transfer belt 8 to the fixing unit 7 is heated and pressed by the fixing roller 18 so that the toner image is fixed on the surface of the transfer paper 6 and a predetermined full color image is formed. The transfer paper 6 on which the full color image is formed is then discharged out of the apparatus main body by the discharge roller 19.

  FIG. 2 is a block diagram showing the configuration of the image forming apparatus according to the first embodiment of the present invention. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes a fixing unit 7, an optical detection unit 9, an image reading unit 30, an AD conversion unit 31, an image forming unit Pa to Pd, a control unit 32, a storage unit 33, an operation panel 34, a monochrome print counter 35, and The color printing counter 36 is configured.

  The optical detection unit 9 irradiates each patch image formed on the transfer belt 8 (see FIG. 1) with the measurement light in the image forming units Pa to Pd, and detects the amount of reflected light from the patch image. A detection result is transmitted to the control part 32 mentioned later as a light reception output signal. As the optical detection means 9, an optical detection means generally comprising a light emitting element made of an LED or the like and a light receiving element made of a photodiode or the like is used. For example, when measuring the toner adhesion amount on the transfer belt, measurement light is emitted from the light emitting element to the toner image. The measurement light is incident on the light receiving element as light reflected by the toner and light reflected by the belt surface.

  The image reading unit 30 includes a scanner lamp that illuminates the document during copying, a scanning optical system equipped with a mirror that changes the optical path of reflected light from the document, and a condensing lens that focuses the reflected light from the document to form an image. , And a CCD that converts the imaged image light into an electrical signal. The image signal read by the image reading unit 30 is converted into a digital signal by the AD conversion unit 31 and then sent to the image memory 40 in the storage unit 33 described later.

  The storage unit 33 includes an image memory 40, a RAM 41, and a ROM 42. The image memory 40 stores an image signal read by the image reading unit 30 and digitally converted by the AD conversion unit 31, and is stored in the control unit 32. Send it out. The RAM 41 and the ROM 42 store a processing program, processing content, and the like of the control unit 32. The RAM 41 (or ROM 42) stores in advance the relationship between the measured output value of the optical detection means 9 and the toner adhesion amount as toner adhesion amount data.

  The operation panel 34 includes an operation unit composed of a plurality of operation keys, and a display unit (none of which is shown) that displays setting conditions, the state of the apparatus, and the like, and the user sets printing conditions and the like. In addition, for example, when the image forming apparatus 100 has a facsimile function, it is also used for various settings such as registering a facsimile transmission destination in the storage unit 33 and reading or rewriting the registered transmission destination.

  The monochrome print counter 35 and the color print counter 36 integrate and count the number of monochrome prints and the number of color prints, respectively. The counted monochrome and color prints are stored in the RAM 41 of the storage unit 33. Instead of the number of printed sheets, the monochrome and color printing times may be integrated and stored in the storage unit 33.

  The control unit 32 generally controls the image reading unit 30, the image forming units Pa to Pd, the fixing unit 7, and the optical detection unit 9 according to the set program and the image signal read by the image reading unit 30. If necessary, the image data is converted into image data by scaling or gradation processing. The LED heads 17a to 17d irradiate laser light based on the processed image data to form latent images on the photosensitive drums 1a to 1d.

  Further, when the calibration mode is executed, the control unit 32 receives the light reception output signal detected by the optical detection unit 9 and calculates the toner adhesion amount based on the toner adhesion amount data stored in the storage unit 33. The density of the patch image is determined based on the calculated toner adhesion amount, and compared with a predetermined reference density, the charging potentials of the chargers 2a to 2d, the developing bias of the developing units 3a to 3d, or By adjusting the exposure amount of the LED heads 17a to 17d, etc., it has a function of correcting the density for each color.

  The calibration mode is automatically executed when a predetermined number of image forming processes have been completed. That is, when the count value of the monochrome print counter 35 reaches a predetermined density correction execution value stored in advance in the RAM 41 (or ROM 42) of the storage unit 33, the control unit 32 performs monochrome density correction (hereinafter referred to as monochrome correction). When the integrated count value of the color print counter 36 reaches the density correction execution value, color density correction (hereinafter referred to as color correction) is executed.

  Therefore, the control unit 32 determines whether or not density correction is necessary for each of monochrome and color, and individually executes monochrome correction and color correction. In addition to the above, the calibration mode may be executed by the key operation of the operation panel 34 by the user, or may be automatically executed when the apparatus is turned on.

  In image formation by a tandem color image forming apparatus as shown in FIG. 1, toner images for patch image formation are formed on the photosensitive drums 1a to 1d by the above-described image forming process. The formed toner images are transferred to predetermined positions on the transfer belt 8 by the transfer rollers 4a to 4d, and magenta, cyan, yellow, and black patch images are formed.

  An example of a density correction patch image is shown in FIG. When the calibration mode is set by the user, as shown in FIG. 3A, magenta (M), cyan (C), yellow (Y), and black at the left end in the traveling direction on the transfer belt 8. The rectangular patch images of each color in (B) are formed in a row. The magenta (M) patch image formed by the photoconductive drum 1b is formed in order of the progression of the patch images M1 to M5 in five levels from the white solid image (M1) to the darkest image (M5). Is done.

  FIG. 3B shows an enlarged view of the portions M1 and M2 in FIG. As can be seen from the figure, the adjacent patch images M1 and M2 are each formed in a single color so that the density changes at the boundary. The patch images M3 to M5 are formed in the same manner, and the cyan (C) patch images C1 to C5, the yellow (Y) patch images Y1 to Y5, and the black (B) patch images B1 to B5 are also M1. To M5.

  Since the optical detection means 9 needs to strictly define the distance to the object to be measured, as shown in FIG. 1, the optical detection means 9 counters the driven roller 10c with a small distance fluctuation to the surface of the transfer belt 8. The transfer belt 8 is positioned in the width direction in accordance with the patch image forming position on the transfer belt 8. Based on the detection result of the optical detection means 9, the toner adhesion amount (image density) of each patch image is measured, and density correction is performed in comparison with a predetermined reference density for each color.

  Next, the operation of the image forming apparatus of the present invention will be described. FIG. 4 is a flowchart illustrating an example of density correction control executed in the image forming apparatus according to the first embodiment. With reference to FIG. 2, the density correction control procedure will be described in accordance with the steps of FIG. The color printing referred to in the present invention includes single color printing other than monochrome.

  When printing is started by the user, it is first determined whether or not color printing is performed (step S1). If it is determined that color printing is to be performed, 1 is added to the count value (color printing number) Cc of the color printing counter 36 (step S2). Next, the control unit 32 compares the count value Cc with the density correction execution value A stored in the storage unit 33 to determine whether or not the number of color prints has reached the density correction execution value A (step). S3).

  If it is determined in step S3 that Cc = A, both color and monochrome correction are performed (step S4). Next, the count values Cm and Cc of the monochrome print counter 35 and the color print counter 36 are reset (step S5). If it is determined in step S3 that Cc <A, the process proceeds to the next step without performing density correction. Then, it is determined whether or not printing has been completed (step S6). If printing has been completed, the process is terminated. If printing continues, the process returns to step S1.

  On the other hand, if it is determined in step S1 that monochrome printing is performed, 1 is added to the count value (number of monochrome prints) Cm of the monochrome print counter 35 (step S7). Next, the control unit 32 compares the count value Cm with the density correction execution value A stored in the storage unit 33 to determine whether or not the number of monochrome prints has reached the density correction execution value A (step). S8).

  If it is determined in step S8 that Cm = A, monochrome correction is performed (step S9). Next, the count value Cm of the monochrome printing counter 35 is reset (step S10). If it is determined in step S8 that Cm <A, the process proceeds to the next step without performing density correction. Then, it is determined whether or not printing has been completed (step S11). If printing has been completed, the process is terminated. If printing continues, the process returns to step S1, and thereafter density correction is executed in the same steps (steps S1 to S11).

  In the control procedure shown in FIG. 4, monochrome and color correction can be performed individually. When the count value Cm of the monochrome print counter 35 reaches a predetermined density correction execution value, only monochrome correction is performed, and the color print counter 36 When the count value Cc reaches a predetermined density correction execution value, both monochrome and color correction are performed.

  Accordingly, for example, when a large amount of monochrome printing is performed, only the black image forming unit Pd in FIG. 1 can be driven, and the magenta, cyan, and yellow image forming units Pa to Pc can be stopped. Accordingly, excessive mechanical stress is not applied to the color toner, so that deterioration of the toner can be suppressed, and a state in which the toner charge amount increases during color printing and the density does not occur can be prevented.

  In addition, since density correction is performed by forcibly interrupting image processing even during continuous printing, if color and monochrome correction is performed continuously, image formation efficiency decreases, but color correction is required. In this case, monochrome correction is also executed at the same time, so that monochrome correction is not executed immediately after color correction.

  FIG. 5 is a flowchart illustrating another example of density correction control executed in the image forming apparatus according to the first embodiment. With reference to FIG. 2, the density correction control procedure will be described in accordance with the steps of FIG. When printing is started by the user, it is first determined whether or not color printing is performed (step S1). If it is determined that color printing is being performed, 1 is added to the count value Cc of the color printing counter 36 (step S2). Next, the control unit 32 compares the count value Cc with the density correction execution value A stored in the storage unit 33 to determine whether or not the number of color prints has reached the density correction execution value A (step). S3).

  If it is determined in step S3 that Cc = A, color correction is performed (step S4). Next, the count value Cc of the color printing counter 36 is reset (step S5). If it is determined in step S3 that Cc <A, the process proceeds to the next step without performing density correction. Then, it is determined whether or not printing has been completed (step S6). If printing continues, the process returns to step S1, and thereafter density correction is executed in the same steps (steps S1 to S6).

  If printing has ended in step S6, it is determined whether or not the count value Cc of the color print counter 36 is equal to or greater than a value (A−B) that is smaller than the density correction execution value A by a predetermined value B (A−B). Step S7). If A−B ≦ Cc <A, color correction is performed (step S8). Next, the count value Cc of the color printing counter 36 is reset (step S9). If A-B> Cc in step S7, the process is terminated as it is.

  On the other hand, if it is determined in step S1 that monochrome printing is performed, 1 is added to the count value Cm of the monochrome printing counter 35 (step S10). Next, the control unit 32 compares the count value Cm with the density correction execution value A stored in the storage unit 33, and determines whether or not the number of monochrome prints has reached the density correction execution value A (step S11). ).

  If it is determined in step S11 that Cm = A, monochrome correction is performed (step S12). Next, the count value Cm of the monochrome printing counter 35 is reset (step S13). If it is determined in step S11 that Cm <A, the process proceeds to the next step without performing density correction. Then, it is determined whether or not printing is completed (step S14). If printing is continued, the process returns to step S1, and thereafter density correction is executed in the same steps (steps S1 to S13).

  If printing has been completed in step S14, it is determined whether or not the count value Cm of the monochrome print counter 35 is equal to or greater than a value (A−B) that is smaller than the density correction execution value A by a predetermined value B (A−B). Step S15). If A−B ≦ Cm <A, monochrome correction is performed (step S16). Next, the count value Cm of the monochrome printing counter 35 is reset (step S17). If A−B> Cm in step S15, the process is terminated as it is.

  In the control procedure shown in FIG. 5, when the count values Cm and Cc of the monochrome print counter 35 or the color print counter 36 are equal to or larger than a predetermined density correction execution value at the end of printing, density correction is performed in advance. To do. As a result, for example, when printing ends just before the count values Cm and Cc for monochrome or color printing reach the density correction execution value, density correction is executed after printing is completed, and the count value is reset. Therefore, after the next continuous printing is started, the density correction is performed immediately and the printing is not interrupted, and the image forming efficiency is improved.

  In the density correction control shown in FIG. 4, for example, the monochrome and color density correction execution value A is 80 (sheets), and the number of monochrome and color printed sheets is 79 sheets. When two sheets are continuously printed, the count value Cm becomes 80 when monochrome printing is completed, and monochrome correction is executed. Here, the monochrome printing counter 35 is reset, and Cm = 0 and Cc = 79.

  Next, when one color printing is completed, the count value Cc becomes 80, and both monochrome and color corrections are executed. Here, the color printing counter 36 is reset, and Cm = 0 and Cc = 0. Finally, one color printing is performed. That is, there is a possibility that the density correction is executed twice during the printing of three sheets. Further, since the monochrome correction is continuously performed, the black toner is rapidly deteriorated, and the toner charge amount is increased, which adversely affects the image.

  Also in the density correction control shown in FIG. 5, for example, when the number of monochrome and color prints is 79 during continuous printing, when monochrome printing and continuous printing of one color printing are further performed, Similarly, density correction is executed twice. In such a case, the image forming efficiency is lowered and the user feels stress due to the waiting time.

  Therefore, by combining the density correction control shown in FIGS. 4 and 5, excessive color correction is suppressed to prevent color toner deterioration, and density correction is continuously performed during continuous printing, or continuous printing. After the start, it is possible to achieve a control that improves the image forming efficiency by minimizing the state in which density correction is performed with a small number of sheets. Such density correction control is shown in FIG. With reference to FIG. 2, the density correction control procedure will be described in accordance with the steps of FIG.

  In the case of color printing, 1 is added to the count value Cc of the color printing counter 36, and when it is determined that Cc = A as compared with the density correction execution value A, both color and monochrome correction are performed. When the color printing counter 36 is reset and it is determined that Cc <A, the steps (steps S1 to S6) until it is determined whether printing is completed without performing density correction are the same as those in FIG. It is the same.

  If printing has been completed in step S6, it is determined whether or not the count value Cc is equal to or greater than a value (AB) smaller than the density correction execution value A by a predetermined value B (step S7). If A−B ≦ Cc <A, color and monochrome correction is performed (step S8). Next, the monochrome printing counter 35 and the color printing counter 36 are reset (step S9). If A-B> Cc in step S7, the process is terminated as it is.

  On the other hand, if it is determined in step S1 that monochrome printing is performed, 1 is added to the count value Cm of the monochrome printing counter 35 (step S10). Next, the control unit 32 compares the count value Cm with the density correction execution value A stored in the storage unit 33 to determine whether or not the number of monochrome prints has reached the density correction execution value A (step). S11).

  If it is determined in step S11 that Cm = A, whether or not the count value Cc of the color printing counter 36 is equal to or greater than a value (AB) that is smaller than the density correction execution value A by a predetermined value B is determined. Is determined (step S12). If A−B ≦ Cc <A, the process proceeds to step S4 to perform color and monochrome correction and reset the monochrome print counter 35 and the color print counter 36 (steps S4 and S5).

  If AB> Cc in step S12, only monochrome correction is performed (step S13). Next, the monochrome printing counter 35 is reset (step S14). If it is determined in step S11 that Cm <A, the process proceeds to the next step without performing density correction. Then, it is determined whether or not printing is completed (step S15). If printing is continued, the process returns to step S1, and thereafter density correction is executed in the same step.

  If printing has ended in step S15, it is determined whether or not the count value Cm of the monochrome print counter 35 is equal to or greater than a value (A−B) that is smaller than the density correction execution value A by a predetermined value B (A−B). Step S16). If A−B ≦ Cm <A, it is next determined whether or not the count value Cc of the color printing counter 36 is equal to or greater than A−B (step S17).

  If A−B ≦ Cc <A, the process proceeds to step S8 to perform color and monochrome correction. Next, the monochrome printing counter 35 and the color printing counter 36 are reset (step S9), and the process is terminated. If AB> Cc in step S17, only monochrome correction is performed (step S18). Next, the monochrome printing counter 35 is reset (step S19). On the other hand, if AB> Cm in step S16, the process is terminated as it is.

  In the control procedure shown in FIG. 6, when printing is completed and both the color and monochrome printing integrated count values satisfy both conditions, both color and monochrome correction are executed. Assuming that A is 80 (sheets) and the predetermined value B is 10 (sheets), monochrome and color correction is executed when printing is completed when both the monochrome and color print sheets are between 70 and 79 sheets. Therefore, the count values before printing are Cm <70 and Cc <70 at the worst, and density correction is not executed for at least 10 sheets in the next continuous printing, and the image forming efficiency is further improved.

  Further, even when the count value Cm reaches the density correction execution value A during continuous printing, color and monochrome correction is executed when the count value Cc is equal to or greater than AB, so that monochrome correction is performed during continuous printing. It is possible to prevent the color correction from being executed continuously as much as possible.

  It should be noted that the density correction execution value A and the predetermined value B can be set as appropriate depending on the specifications of the image forming apparatus, the usage status of the user, and the like. For example, if the monochrome and color density correction execution value A is 80 (sheets) and the predetermined value B is 10 (sheets), from the state where the number of monochrome and color prints is 69, 11 monochrome prints and 12 color prints. When continuous printing of sheets is performed, the count value Cm becomes 80 when 11 monochrome printings are completed, and monochrome correction is executed. Here, the monochrome printing counter 35 is reset, and Cm = 0 and Cc = 69.

  Next, when 11 sheets of color printing are completed, the count value Cc becomes 80, and both monochrome and color corrections are executed. Here, the color printing counter 36 is reset, and Cm = 0 and Cc = 0. Finally, one color printing is performed. That is, there is a possibility that the density correction is executed twice during the printing of 23 sheets.

  Therefore, a user who frequently performs continuous printing of 10 or more sheets can widen the interval of density correction by changing the setting of the predetermined value B when forced interruption by density correction is troublesome. For example, when B is set to 20, density correction is executed twice while 43 sheets are printed, and when B is set to 30, density correction is executed twice while 63 sheets are printed.

  In this example, the density correction execution value A and the predetermined value B in monochrome correction and color correction are the same value, but different density correction execution values may be used for monochrome correction and color correction, or monochrome correction and color correction may be used. The predetermined value B may be changed by the correction.

  FIG. 7 is a block diagram showing a configuration of a color image forming apparatus according to the second embodiment of the present invention. Portions common to FIG. 2 of the first embodiment are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, the number of prints per print execution counted by the monochrome print counter 35 or the color print counter 36 is stored in the storage unit 33 (for example, the RAM 41), and the integrated value of the number of print executions for each print number is further stored. Is stored in the storage unit 33. Then, based on the number of print executions for each number of printed sheets, an operation for calculating a cumulative occupancy ratio in which the occupation ratio of the number of print executions for each print number with respect to the total or less than the predetermined number of print executions is accumulated in order from the smaller number of print sheets A portion 37 is provided.

  Now, a description will be given of the probability of interruption of density correction being executed during continuous printing when the usage conditions of the image forming apparatuses are different among the three users A, B, and C. It should be noted that here, when the number of printed sheets per printing execution is more than 20, it is divisible even if density correction is entered midway, and the usage situation of the number of printed sheets of 20 or less is counted. User A prints from 1 to 20 pages at almost the same rate, User B has a higher rate of printing 10 pages or more than 10 pages, and User C compared to 10 pages. Assuming that the ratio of printing 10 sheets or more is small, the relationship between the number of printed sheets and the cumulative occupation ratio for each user is as shown in FIG.

  At this time, the relationship between the predetermined value B and the density correction interruption execution probability for each user is shown in FIG. As is apparent from FIG. 9, the probability of density correction during printing is greatly changed depending on the usage status of the user. For example, if the predetermined value B is 10 sheets, it is 3.3% for user A, 5.5% for user B, and 1% for user C. In this way, when the usage situation varies depending on the user, the setting of the predetermined value B is not necessarily the default value appropriate for all users, and the user himself / herself sets the optimal predetermined value B. It is also difficult.

  Next, the relationship with the density correction interruption execution probability when the number of printed sheets for a certain cumulative occupation ratio in FIG. For example, if the number of printed sheets when the cumulative occupancy is 80% is set to a predetermined value B, the predetermined value B is 16 for user A, 18 for user B, and 11 for user C from FIG. Become. Further, the density correction interruption execution probability with respect to the cumulative occupation ratio is shown in FIG.

  As is apparent from FIG. 10, the density correction interruption execution probability when the number of printed sheets at which the cumulative occupancy is 80% is set to the predetermined value B is 0.2% for user A, 0.16% for user B, It becomes 0.8% for the user C, and almost no density correction is executed in the middle of printing a small number of sheets. Therefore, in the image forming apparatus according to the present embodiment, the predetermined value B is automatically set for each apparatus by the above-described series of controls using the cumulative occupancy calculated by the calculation unit 37, and updated as needed. It is possible to execute density correction in accordance with the usage status of the. The predetermined value B is updated by calculating the cumulative occupancy every time the total number of printed sheets from the most recent update reaches a certain number.

  FIG. 11 is a flowchart illustrating control for automatically setting the predetermined value B in the image forming apparatus according to the second embodiment. With reference to FIG. 7, the procedure for setting the predetermined value B will be described according to the steps in FIG. Here, it is assumed that the predetermined value B is updated when the total number n of printed sheets from the most recent setting of the predetermined value B becomes 500 or more. First, when printing is executed by the user (step S1), the monochrome printing counter 35 or the color printing counter 36 counts the number of prints per printing execution (step S2). The counted number of printed sheets is stored in the storage unit 33 (step S3), and the number of printing executions for each number of printed sheets is also accumulated and stored (step S4).

  Next, it is determined whether or not the number n of printed sheets from the most recent setting of the predetermined value B is 500 or more (step S5). If n does not exceed 500 sheets, the process returns to step S1, and the printing, the counting of the number of printed sheets, and the storage of the cumulative printing execution number for each number of printed sheets are continuously performed (steps S1 to S4). When n is 500 or more in step S5, the calculation unit 37 calculates the occupancy ratio of the number of print executions for each print number with respect to the total number of print executions, and further accumulates the occupancy ratio in order from the smallest print number. The cumulative occupation ratio is calculated (step S6).

  Then, an optimal predetermined value B is set based on the calculated cumulative occupancy (step S7), and the storage unit 33 is overwritten. Finally, the number n of prints is reset to 0 (step S8), and the same processing is repeated from step 1 again.

  The above routine is continued until the image forming apparatus is powered off. When the power of the image forming apparatus is turned off, the predetermined value B at that time, the number of times of printing for each number of printed sheets, and the number of printed sheets n from the most recent setting are stored in the storage unit 33. Next, when the power is turned on, density correction is performed using the stored predetermined value B, and automatic setting of the predetermined value B may be continued using the stored number of printing executions and the number of printed sheets n.

  Here, the monochrome printing counter 35 and the color printing counter 36 are used to count the number of printed sheets per printing execution. However, a continuous printing counter for counting the number of printing sheets per printing execution is separately provided. Also good. Further, instead of providing the calculation unit 37, the control unit 32 can also serve as the calculation unit 37, and calculation processing in the calculation unit 37 can be performed in the control unit 32. In the above control example, the occupancy ratio of the number of print executions for each print number with respect to the total or the number of print executions equal to or less than the predetermined number is accumulated in order from the smaller number of print sheets to calculate the cumulative occupancy ratio. For example, a predetermined value for density correction execution can be set in exactly the same way based on the cumulative occupation ratio calculated by accumulating the occupation ratio of the number of times of printing for each number of printed sheets in order from the larger number of printed sheets.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the monochrome print counter 35 and the color print counter 36 are used to count the total number of monochrome and color prints, and the density correction control is performed based on the total count. It is also possible to integrate printing time and perform density correction control based on the accumulated printing time.

  In the above embodiment, a tandem color image forming apparatus including a plurality of image forming units has been described as an example. However, the present invention is not limited to this, and a plurality of developing cartridges are disposed at positions facing the photosensitive drum. Needless to say, the present invention can also be applied to a rotary color image forming apparatus or a color printer that sequentially develops and moves the electrostatic latent image on the photosensitive drum.

  The present invention provides a first counting means for counting the number of printed sheets or printing time for monochrome printing, a second counting means for counting the number of printed sheets or printing time for color printing, and the counting of the first and second counting means. In the color image forming apparatus including a control unit that individually executes monochrome and color density correction based on the value, the control unit, when the count value of the first count unit reaches the density correction execution value, Only monochrome density correction is executed, and when the count value of the second count means reaches the density correction execution value, monochrome and color density correction is executed.

  As a result, the color toner developing device can be stopped and only monochrome correction can be executed, so that excessive mechanical stress is not applied to the color toner, so that the deterioration of the toner can be suppressed and the charge amount of the color toner is increased. Deterioration of image quality can be prevented. In addition, when color correction is necessary, monochrome correction is also performed at the same time, so monochrome correction is not performed immediately after color correction, and a high-quality image can be obtained without reducing image formation efficiency. An image forming apparatus capable of forming images is provided.

  Even when the count value of the first count unit reaches the density correction execution value during continuous printing, if the count value of the second count unit is equal to or greater than a predetermined value smaller than the density correction execution value, color and color Since the monochrome correction is performed simultaneously, it is extremely rare that the monochrome correction and the color correction are continuously performed during continuous printing, thereby preventing a decrease in image formation efficiency due to the interruption of printing.

  Further, when the count value of the first or second counting means is equal to or larger than a predetermined value smaller than the density correction execution value at the end of printing, the density correction is executed in advance, so that continuous printing starts next. Then, the density correction is performed immediately and printing is not interrupted, and the image forming efficiency is improved.

  Further, when only the count value of the first count means is equal to or greater than a predetermined value smaller than the density correction execution value at the end of printing, only monochrome density correction is executed, and the count value of the second count means is density correction execution. Since the monochrome and color density correction is executed when the value is equal to or larger than the predetermined value smaller than the value, the density correction is executed and printing is interrupted when the next continuous print number is less than the predetermined value. And the image forming efficiency is further improved.

  Further, if a predetermined value for density correction execution is automatically set based on the cumulative occupancy ratio of the number of print executions for each print number with respect to the total or less than the predetermined number of print executions, it can be determined according to the usage situation of the user. By setting the optimum predetermined value, the interrupt execution rate for density correction during continuous printing can be reduced below a certain level, and the image forming apparatus can be further improved in image forming efficiency.

FIG. 1 is a schematic diagram showing an overall configuration of a color image forming apparatus of the present invention. FIG. 1 is a block diagram showing a configuration of a color image forming apparatus according to a first embodiment of the present invention. FIG. 4 is a schematic diagram of a patch image for density correction. These are flowcharts showing an example of density correction control executed in the image forming apparatus of the present invention. These are flowcharts showing another example of density correction control. These are flowcharts showing another example of density correction control. These are block diagrams which show the structure of the color image forming apparatus which concerns on 2nd Embodiment of this invention. These are graphs showing the relationship between the number of printed sheets and the cumulative occupancy due to the difference in usage status. These are graphs showing the relationship between the density correction execution number and the density correction interruption execution probability due to the difference in usage status. These are graphs showing the relationship between the cumulative occupation ratio and the density correction interruption execution probability. These are the flowcharts which show the control which automatically sets the predetermined value B in the image forming apparatus of 2nd Embodiment.

Explanation of symbols

Pa to Pd Image forming unit 1a to 1d Photosensitive drum 2a to 2d Charger 3a to 3d Developer 4a to 4d Transfer roller 7 Fixing unit 8 Transfer belt 9 Optical detection means 17a to 17d LED head 30 Image reading unit 32 Control unit (Control means)
33 Storage section (storage means)
34 Operation panel 35 Monochrome printing counter (first counting means)
36 color printing counter (second counting means)
37 Calculation unit (calculation means)
100 Image forming apparatus

Claims (2)

Among the plurality of image forming units, a first counting unit that integrally counts the number of prints or print time of monochrome printing that performs monochrome printing using a black image formation unit, and the number of prints of color printing other than the monochrome printing or Excluding the second counting means for cumulatively counting the printing time and the monochrome density correction that is the density correction of the black image forming section and the black image forming section based on the count values of the first and second counting means. A color image forming apparatus including a control unit that performs color density correction, which is density correction of all image forming units,
The control means executes only monochrome density correction when the count value of the first count means reaches the density correction execution value, and the count value of the second count means reaches the density correction execution value. given when performs monochrome and color density correction, the count value of said first counting means reaches the density correction execution value, than and count density correction execution value of the second counting means A color image forming apparatus, wherein monochrome correction and color density correction are executed when the value is not less than a small value . The control means executes only monochrome density correction when only the count value of the first count means is smaller than a density correction execution value by a predetermined value at the end of printing, and the second count means 2. The color image forming apparatus according to claim 1, wherein monochrome and color density correction is executed when the count value is equal to or larger than a density correction execution value by a predetermined value .