JP5402856B2 - Image forming apparatus, image forming apparatus control method, and image forming apparatus control program - Google Patents

Description

  The present invention relates to an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program, and more specifically, an image forming apparatus that executes a toner consumption operation for preventing toner from staying in a developing device. The present invention relates to an image forming apparatus control method and an image forming apparatus control program.

  Electrophotographic image forming apparatuses include a scanner function, a facsimile function, a copying function, a function as a printer, a data communication function, and a server function, an MFP (Multi Function Peripheral), a facsimile apparatus, a copying machine, a printer, and the like. is there.

  In general, an image forming apparatus forms an electrostatic latent image on a photosensitive member by exposing the charged photosensitive member, and develops the electrostatic latent image with toner using a developing device to form a toner image. Is transferred from the photosensitive member to the paper, and the toner image after the transfer is fixed on the paper, thereby printing the document on the paper.

  By the way, if the printing of a document with a very low printing rate is continued, the toner consumed by the developing device becomes very small. When the toner consumed in the developing device decreases, the amount of toner staying in the developing device increases, and the quality of the toner deteriorates. As a result, the image quality may be deteriorated.

  In particular, when a color image forming apparatus is used in an office or the like, a document in which black text is mainly used and only a small part of color is used may be printed. Many. If such usage continues, the amount of toner consumed in the color developing device of the color image forming apparatus decreases, the toner staying in the developing device deteriorates, and the image quality deteriorates remarkably.

  Therefore, in order to prevent deterioration in image quality due to a small amount of toner consumed in the developing device, a technique for preventing toner from staying in the developing device when a document with a very low printing rate continues to be printed has been proposed. ing. Such a technique is disclosed in, for example, Patent Documents 1 and 2 below. Patent Document 1 below proposes an image forming apparatus in which developer consumption is detected by a pixel counter to obtain an average developer consumption amount of printed sheets. When the developer consumption is below a predetermined value, this image forming apparatus develops the developer in a non-printing area on the photosensitive drum (consumes the toner outside the document printing range), thereby Perform a refresh.

  However, in the image forming apparatus disclosed in Patent Document 1, the toner consumed by the toner consuming operation (developer refreshing operation) is removed from the photosensitive drum by the cleaning device and collected in the waste toner container. For this reason, if the printing rate decreases and the toner consumption operation increases, the amount collected in the waste toner container increases (pressure on the waste toner container) and the waste toner container must be frequently replaced. It was. Further, for the user, the life of the waste toner container is shortened, so that there is a disadvantage that the cost related to the waste toner container is increased and a disadvantage that the replacement frequency of the waste toner container is increased.

  Also, in Patent Document 2 below, a technique for forcibly consuming a color toner having a low printing rate at the time of image formation by forcibly printing it on a black toner (black toner) printing part in addition to the color toner printing part. Has been proposed. According to this technique, the toner consumed by the toner consuming operation is used for printing on the paper and is not collected in the waste toner container, so that the above-described problem of Patent Document 1 below can be solved.

JP 2001-75438 A JP 2005-49672 A

  However, since the amount of color toner that is forcibly printed on the black toner printing portion is not limited in the technique of Patent Document 2, a fixing failure occurs due to excessively overlapping color toner on the black toner printing portion. There was a problem of causing deterioration of quality.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program capable of suppressing deterioration in image quality.

  An image forming apparatus according to one aspect of the present invention includes a data acquisition unit that acquires print data, a first print rate acquisition unit that acquires a black print rate in print data acquired by the data acquisition unit, and a first print rate acquisition unit. When the black print rate acquired by the print rate acquisition unit is higher than the black reference print rate, the black image density of at least a part of the black image portion that prints black in the print data acquired by the data acquisition unit is set. First processing means for processing the print data so as to decrease, and second processing means for processing the print data so as to add a color image having a color tone other than black to at least a part of the black image portion. .

  Preferably, the image forming apparatus further includes a second printing rate acquisition unit that acquires a printing rate of at least one color having a color tone other than black in the print data acquired by the data acquisition unit, and a second processing unit. When the printing rate for a certain color acquired by the second printing rate acquisition means is smaller than the printing rate serving as the reference for the color, an image of that color is added to the black image portion.

  Preferably, in the image forming apparatus, when the black printing rate acquired by the first printing rate acquisition unit is equal to or less than a printing rate that is a reference for black, the first processing unit does not decrease the black image density.

  Preferably, the image forming apparatus further includes a region determining unit that determines a target image region from the black image portion, and the second processing unit adds a color image to the target image region.

  Preferably, in the image forming apparatus, the area determining unit targets an area formed only of black and having a black image density equal to or higher than a reference density based on the print data acquired by the data acquiring unit. Determined as an image area.

  Preferably, in the image forming apparatus, the area determination unit determines an area that is not a photographic image as a target image area based on the print data acquired by the data acquisition unit.

  Preferably, in the image forming apparatus, the second processing unit is configured such that the total image density including the black and color image densities in the black image portion after the black image density is reduced is equal to or lower than a reference image density. In this way, a color image is added to the black image portion.

  Preferably, the image forming apparatus further includes a black developing unit that performs development using black toner based on the print data processed by the first processing unit, and the black average printing rate of the black developing unit is black. When the average printing rate is lower than the reference, the black developing means forcibly consumes the black toner, and the first processing means is the average printing in which the black printing rate after decreasing the image density becomes the black reference. The black image density is lowered so as to be equal to or greater than the ratio.

  Preferably, the image forming apparatus further includes a color developing unit that performs development using color toner based on the print data processed by the second processing unit, and the color printing unit has an average color printing ratio of color. When the average print rate is lower than the reference, the color developing unit forcibly consumes the color toner, and the second processing unit uses the color print rate in the print data after adding the color image as the color reference. A color image is added so that the average printing rate is below.

  Preferably, in the image forming apparatus, the first printing rate acquisition unit acquires the printing rate for each print job.

  An image forming apparatus according to another aspect of the present invention provides a data acquisition unit that acquires print data and a color tone other than black on at least a part of a black image portion that prints black in the print data acquired by the data acquisition unit. Color image processing means for processing the print data so as to add a color image having the image density based on the total image density of the black and color image densities in the black image portion A color image is added to the black image portion so as to be as follows.

  An image forming apparatus control method according to still another aspect of the present invention includes a data acquisition step of acquiring print data, and a first print rate acquisition step of acquiring a black print rate in the print data acquired in the data acquisition step. When the black print rate acquired in the first print rate acquisition step is higher than the black reference print rate, at least part of the black image portion that prints black in the print data acquired in the data acquisition step And a second processing for processing the print data so as to add a color image having a color tone other than black to at least a part of the black image portion. Steps.

  An image forming apparatus control program according to still another aspect of the present invention includes a data acquisition step for acquiring print data, and a first print rate acquisition step for acquiring a black print rate in the print data acquired in the data acquisition step. When the black print rate acquired in the first print rate acquisition step is higher than the black reference print rate, at least part of the black image portion that prints black in the print data acquired in the data acquisition step And a second processing for processing the print data so as to add a color image having a color tone other than black to at least a part of the black image portion. Causing the computer to execute the steps.

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing deterioration in image quality, a method for controlling the image forming apparatus, and a control program for the image forming apparatus.

1 is a front view schematically showing a configuration of an image forming apparatus according to an embodiment of the present invention. It is a front view which shows typically the structure of the image formation unit of FIG. 6 is a first part of a flowchart illustrating toner consumption operation processing executed by a print data development unit and an apparatus control unit. 10 is a second part of a flowchart showing toner consumption operation processing executed by the print data development unit and the apparatus control unit. FIG. 10 is a third part of a flowchart illustrating toner consumption operation processing executed by the print data development unit and the apparatus control unit. 10 is a fourth part of a flowchart showing toner consumption operation processing executed by the print data development unit and the apparatus control unit.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a front view schematically showing a configuration of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, a part of the configuration is shown in a block diagram.

  Referring to FIG. 1, an image forming apparatus 1 in the present embodiment is an MFP (Multi Function Peripheral), and includes a print unit 2, a print data development unit 3 (print language → print data development unit), and device control. A unit 4 and an operation panel unit 5 (operation panel) are provided. The print data expansion unit 3 and the device control unit 4 can communicate with each other, and the device control unit 4 and the operation panel unit 5 can communicate with each other.

  The printing unit 2 includes a paper transport unit 10, a toner image forming unit 20, and a fixing unit 30. The paper transport unit 10 includes a paper feed roller 101, a timing roller 102, and a paper discharge roller 103. Each of the paper feed roller 101, the timing roller 102, and the paper discharge roller 103 is downstream in the paper transport direction from the upstream side in the paper transport direction of the paper path R (the lower side in FIG. It arrange | positions in this order toward the side (the upper side in FIG. 1, and may hereafter be called a downstream side). Between the timing roller 102 and the paper discharge roller 103, the secondary transfer roller 240 (secondary transfer unit) of the toner image forming unit 20 and the fixing unit 30 are arranged. In addition, the paper transport unit 10 may include rollers used for transporting paper other than these.

  The sheets loaded in the sheet storage unit 40 arranged at the lower part of the image forming apparatus 1 are fed from the sheet storage unit 40 one by one at the time of printing. Then, the sheet is conveyed to the secondary transfer roller 240 by the sheet feeding roller 101 and the timing roller 102, and a toner image is formed. The toner image is fixed on the sheet on which the toner image is formed, and is discharged from the main body discharge port 430 by the discharge roller 103.

  The toner image forming unit 20 uses a so-called tandem method to synthesize four color images of yellow (Y), magenta (M), cyan (C), and black (B) YMCB as necessary, and color the paper. Form an image. The toner image forming unit 20 includes four image forming units 210Y, 210M, 210C, and 210B (hereinafter, these may be collectively referred to as an image forming unit 210), a primary transfer roller 220, and an intermediate transfer belt. 230 (primary transfer unit), secondary transfer roller 240, exposure unit 250, and four toner bottles 260Y, 260M, 260C, and 260B (hereinafter, these may be collectively referred to as toner bottle 260). Etc.

  Each of the image forming units 210 is juxtaposed directly below the intermediate transfer belt 230. Each of the image forming units 210 is disposed to face the primary transfer roller 220 corresponding to each image forming unit 210 with the intermediate transfer belt 230 interposed therebetween. The intermediate transfer belt 230 has an annular shape and is stretched between the two rollers 231 and 232. The intermediate transfer belt 230 is driven to rotate in the direction indicated by A1 in FIG. 1 by the rotation of the rollers 231 and 232. The secondary transfer roller 240 is disposed so as to face the roller 232 with the intermediate transfer belt 230 interposed therebetween. The interval between the intermediate transfer belt 230 and the secondary transfer roller 240 is adjusted by a pressure contact / separation mechanism (not shown). The exposure unit 250 is arranged to be able to scan the laser beam LB (FIG. 2) with respect to each image forming unit 210. Each of the toner bottles 260 is disposed on the intermediate transfer belt 230.

  Each of the primary transfer rollers 220 to which a high voltage is applied transfers the toner image on the photoconductor 211 (FIG. 2) of each image forming unit 210 to the intermediate transfer belt 230, and on the intermediate transfer belt 230, a sheet of paper is transferred. A mirror image of the toner images for the four colors to be formed is formed (primary transfer). Thereafter, the secondary transfer roller 240 to which a high voltage is applied transfers the toner image formed on the intermediate transfer belt 230 onto the paper, and forms a toner image on the paper (secondary transfer).

  Four toner bottles 260 store toner of each color of YMCB. The toner bottle 260 is rotationally driven by each drive motor, and replenishes the toner stored therein to the developing device 212 (FIG. 2) of each image forming unit 210. The toner replenishing operation is performed when the toner in the developing device 212 is low.

  The fixing unit 30 includes a heating roller 310 and a pressure roller 320. The heating roller 310 is heated by an IH coil or a heater provided inside the heating roller. The fixing unit 30 conveys the sheet on which the toner image is formed between the heating roller 310 and the pressure roller 320, and heats and presses the sheet. As a result, the fixing unit 30 melts the toner adhering to the paper with heat and fixes the toner on the paper.

  FIG. 2 is a front view schematically showing the configuration of the image forming unit in FIG.

  Referring to FIG. 2, each of the image forming units 210 includes a photosensitive member 211 (photosensitive members 211Y, 211M, 211C, and 211B), a developing unit 212 (developing units 212Y, 212M, 212C, and 212B), and a cleaner unit 213. (Cleaner portions 213Y, 213M, 213C, and 213B) and charging chargers 214 (charging chargers 214Y, 214M, 214C, and 214B). Each of the developing device 212, the cleaner unit 213, and the charging charger 214 is disposed around a cylindrical photosensitive member 211.

  In the toner image forming unit 20, the photosensitive member 211 rotates in the direction indicated by the arrow A2 in FIG. The charging charger 214 supplies electric charge onto the photoconductor 211 and charges the photoconductor 211 uniformly. The exposure unit 250 scans the uniformly charged photoconductor 211 with the laser beam LB based on the print data transmitted from the apparatus control unit 4. Thereby, a latent image (electrostatic latent image) is formed on the photoconductor 211. The developing device 212 supplies toner onto the photoreceptor 211 by a developing roller 212a that rotates in the direction indicated by the arrow A3 in FIG. As a result, the latent image on the photoconductor 211 is developed, and a toner image is formed on the photoconductor 211.

  The residual toner on the photoconductor 211 is cleaned by the cleaner unit 213 and is collected in the waste toner container 450 through the waste toner transport unit 460 as indicated by an arrow A4 in FIG. Similarly, the residual toner on the intermediate transfer belt 230 is cleaned by the cleaner unit 233 (primary transfer cleaner unit), and passes through the waste toner conveyance unit 460 to the waste toner storage unit 450 as indicated by an arrow A5 in FIG. To be recovered.

  Referring again to FIG. 1, the print data expansion unit 3 includes a print rate acquisition unit 31, an image area determination unit 32, and an image data processing unit 33. The print rate acquisition unit 31 includes the print amounts D_Black, D_Yellow, D_Magenta, and D_Cyan of the black developer 212B, the yellow developer 212Y, the magenta developer 212M, and the cyan developer 212C, and the developing roller 212a. The rotational speeds R_Black, R_Yellow, R_Magenta, and R_Cyan are acquired from the print data. Then, the printing rate acquisition unit 31 calculates printing rates P_Black, P_Yellow, P_Magenta, and P_Cyan for each color from the printing amount of each color and the rotation speed of the developing roller.

  Here, the print amounts D_Black, D_Yellow, D_Magenta, and D_Cyan correspond to the amount of print pixels of each color (pixels on which toner dots of each color are to be formed) in the print data. For example, in the case of print data that prints black on all pixels of the print data, the black print amount D_Black is the maximum value, and the other print amounts D_Yellow, D_Magenta, and D_Cyan are zero. The rotation speeds R_Black, R_Yellow, R_Magenta, and R_Cyan of the developing roller mean the rotation speeds of the developing rollers for each color necessary for printing the print data. The larger the area of the image to be printed (the more the number of sheets to be printed), the higher the rotation speed of the developing roller. Further, the print ratios P_Black, P_Yellow, P_Magenta, and P_Cyan represent the average print amount per unit rotation number of the developing roller of each color when printing the print data. When all pixels are printed with the maximum printing width during the unit rotation of the developing roller, the printing rate is maximum (100%).

  The image area determination unit 32 acquires attributes such as a character attribute, a graphic attribute, and a photograph attribute for each pixel of the print data when performing the expansion work, and acquires the image density of the print data together with these attributes.

  The image data processing unit 33 processes image data (print data) to be printed based on the results of the print rate acquisition unit 31 and the image area determination unit 32.

The apparatus control unit 4 controls, for example, the entire operation of the image forming apparatus in a lump. The apparatus control unit 4 includes an integrated rotation number detection unit (developing roller integrated rotation number detection unit) 41 and a storage unit 42. The integrated rotational speed detection unit 41 detects the integrated rotational speed of the developing roller 212a in the developing device 212 for each color. The storage unit 42 stores the total number of rotations R _{TTL —} Black, R _{TTL —} Yellow, R _{TTL —} Magenta, and R _{TTL —} Cyan of the developing roller 212a in each color developing device 212, and the cumulative print amount D _TTL of the developing roller 212a in each developing device 212. _Black, D _TTL _Yellow, D _TTL _Magenta, and D _TTL _Cyan are stored. Here, the accumulated print amounts D _TTL _Black, D _TTL _Yellow, D _TTL _Magenta, and D _TTL _Cyan indicate the amount of print pixels of each color required to print the print data since the accumulated print amount was most recently reset. The integrated value. Cumulative rotation speed R _TTL _Black, R _TTL _Yellow, R _TTL _Magenta, and R _TTL _Cyan are the total rotation speed of each color developing roller required to print the print data since the accumulated rotation speed was reset most recently. It is the value.

  In order to realize the above-described functions, each of the print data expansion unit 3 and the device control unit 4 includes an HDD, a CPU, a ROM, a RAM, and a network controller.

  The HDD stores data such as print data sent from the outside via the network controller, print data read by the scanner unit, and the like. The CPU reads data from the ROM and RAM and writes data to the ROM and RAM by performing predetermined processing. The ROM is, for example, a flash ROM (Flash Memory). The ROM stores various programs for operating the image forming apparatus including a program for toner consumption operation processing, and various fixed data. The ROM may be non-rewritable. The RAM is a main memory of the CPU. The RAM is used for storing data necessary for the CPU to execute the control program. The network controller communicates with an external device 60 such as another MFP or PC via a LAN or the like by a communication protocol such as TCP / IP according to an instruction from the CPU.

  The operation panel unit 5 includes a liquid crystal display unit and the like. The liquid crystal display unit is a touch panel, and various displays and various settings can be performed from the liquid crystal display unit. In other words, the liquid crystal display unit displays a guidance screen for the user or displays an operation button to accept an instruction by a touch operation from the user. The liquid crystal display unit is controlled by the device control unit 4 to perform display. When the operation button on the operation panel unit 5 is operated by the user, the operation panel unit 5 transmits an operation signal or a predetermined command corresponding to the operation to the device control unit 4. That is, the user can cause the image forming apparatus 1 to execute various operations by performing operations from the operation panel unit 5.

  The image forming apparatus 1 executes a toner consuming operation when the usage state of the developing device 212 satisfies a predetermined condition in order to prevent deterioration in image quality due to toner staying in the developing device 212. As the toner consuming operation, the image forming apparatus 1 executes a toner consuming operation on the paper and a toner consuming operation on a non-printing area (an area outside the document printing range) on the photosensitive member 211 (however, The toner consumption operation is executed only when the user has selected the toner consumption operation reduction mode). During the toner consumption operation on the paper, the image forming apparatus 1 determines an image area having little influence on the image quality. If the black image density in the image area is high, image processing is performed to reduce the black image density. Also, the image density of the color image to be overlaid on this image area is managed. Hereinafter, a toner consumption operation process executed by the print data expansion unit 3 and the device control unit 4 of the image forming apparatus 1 will be described.

  3 to 6 are flowcharts showing toner consumption operation processing executed by the print data development unit and the apparatus control unit.

  Referring to FIG. 3, apparatus control unit 4 resets the integrated rotation speed and integrated print amount of each color developing roller 212a as an initialization operation (S101). This initialization operation is performed when the image forming unit 210 is driven for the first time (for example, when the image forming unit 210 including the developing rollers 212a of the respective colors mounted on the image forming apparatus 1 is replaced with a new one). Is executed).

Specifically, the apparatus control unit 4 stores the accumulated rotation speeds R _{TTL —} Black, R _{TTL —} Yellow, R _{TTL —} Magenta, and R _TTL of the developing rollers 212 a for black, yellow, magenta, and cyan stored in the storage unit 42. _Cyan and integrated print amount D _TTL _Black, D _TTL _Yellow, D _TTL _Magenta, and D _TTL _Cyan are set to 0 for the integrated rotation speed and integrated print amount for the color for which the image forming unit 210 is driven for the first time. .

Subsequently, the apparatus control unit 4 determines whether or not the apparatus control unit 4 has acquired (received) print data (image data) from the external device 60 (FIG. 1) connected to the control of the image forming apparatus ( S103). If print data has been acquired (YES in S103), the process proceeds to step S105. In step S105, the print data expansion unit 3 expands the print data from the print language format to the raster data format. The print data development unit 3 then prints the print amounts D_Black, D_Yellow, D_Magenta, and D_Cyan of each color related to the print of the print data and the developing rollers of the colors related to the print of the print data based on the developed print data of each color The rotational speeds R_Black, R_Yellow, R_Magenta, and R_Cyan of 212a are acquired (S105). The print data development unit 3 then prints the print ratios P_Black, P_Yellow, P_Magenta of each color in the print data according to the following formulas (1) to (4) based on the acquired print amount of each color and the rotation speed of the developing roller 212a. , and calculates the P _{_} Cyan (acquisition) to (S107). This operation is performed by the printing rate acquisition unit 31.

  P_Black = (D_Black / R_Black) (1)

  P_Yellow = (D_Yellow / R_Yellow) (2)

  P_Magenta = (D_Magenta / R_Magenta) (3)

  P_Cyan = (D_Cyan / R_Cyan) (4)

The print data development unit 3 acquires the print amounts D_Black, D_Yellow, D_Magenta, and D_Cyan for each color and the rotation speeds R_Black, R_Yellow, R_Magenta, and R_Cyan for each color for each print job. rate P_Black, P_Yellow, it is preferable to calculate P_Magenta, and P _{_} Cyan the print job unit.

  Next, the print data development unit 3 determines whether or not the toner consumption operation reduction mode is selected by the user (S109). If the toner consumption operation reduction mode is selected (YES in S109), the process proceeds to step S111 in FIG. 4 to operate as the toner consumption operation reduction mode, and if the toner consumption operation reduction mode is not selected. (NO in S109), the process proceeds to step S125 in FIG. 5 to operate as the normal mode. The selection of the toner consumption operation reduction mode by the user is accepted from the operation panel unit 5 (operation panel) provided in the image forming apparatus 1 or when the user issues a print instruction from an external device 60 such as a user PC. It is possible to accept on the screen.

  In step S111, the print data expansion unit 3 determines (determines) the target image area from the acquired print data. The target image area is an image area to be controlled in the toner consumption operation reduction mode, and is an image area to which a color image is added. The target image area is determined from a black image portion where black is printed. The target image area includes, in particular, a black image portion (A) an image area in which an image to be printed is only black (area formed using only black), and (B) a density based on the black image density. An image area that is above (for example, 80% or more with respect to the maximum image density (80% or more when only black is concealed)), and (C) an image area whose image attribute is other than a photo attribute (not a photo image (Region) may be determined from an image region that satisfies at least one of the conditions, or may be determined from an image region that satisfies all the conditions. By setting the above conditions (A) to (C), even if toners of yellow, magenta, and cyan (hereinafter, these colors may be referred to as “color”) having a color tone other than black are overlapped, the apparent color It is possible to determine (select) a high-density black image portion that hardly appears as a change in color (a small change in color) as a target image region. The operation of determining the target image area is performed by the image area determination unit 32.

Next, the print data expansion unit 3 compares the black print rate P_Black obtained in step S107 with the black print rate P _TH _Black (S113). The black print rate P _TH —Black can be arbitrarily set, but is preferably the same as the average black print rate P _TH —Black used in step S131 described later. Is higher than the printing rate P _TH _BLACK the black printing rate P _{_} Black is the reference of black (YES in S113), the print data developing unit 3, so as to lower the image density of a black target image area (black The print data is processed so that the number of pixels to be printed is reduced (S115). This operation is performed by the image data processing unit 33.

When the image density of black is reduced in step S115, the printing ratio P _{_} Black black after lowering the image density is the average printing ratio P _TH _BLACK or as a reference for black (average printing ratio P _TH _BLACK It is preferable that the black image density of the target image area is equal to or higher than a reference density (for example, a range not lower than 80% with respect to the maximum image density). In this way, by reducing the black image density of the target image area as much as possible, the amount of consumed black toner can be saved, and a color image can be superimposed on the black image portion without causing fixing failure. As much color toner as possible can be stacked.

  After the processing of the print data is completed by the image data processing unit 33, the print data development unit 3 re-acquires the black print amount D_Black in the processed print data (or corrects the acquired black print amount D_Black). (S117), the process proceeds to step S119.

In step S113, when the black printing rate P_Black is equal to or lower than the black printing rate P _TH _Black (NO in S113), the processing in steps S115 and S117 is omitted, and the print data developing unit 3 performs the black printing rate. Does not degrade. Thereby, it can suppress that the black printing rate becomes lower than necessary. In this case, the process proceeds to step S119.

Print data developing unit 3 in step S119, the color of each color deficiency of the printing rate P1 _UP _Yellow of calculating the P1 _UP _Magenta, and P1 _UP _Cyan. Printing rate of these shortfall, the printing ratio P _TH _Yellow as a reference for the color of each color, P _TH _Magenta, and P _TH for _Cyan, the obtained color each color printing rate P _{_} Yellow in step S107, P _{_} Magenta, and a shortage of P _{_} Cyan. The printing ratios P _TH —Yellow, P _TH —Magenta, and P _TH —Cyan are average printing ratios P _TH —Yellow, P _TH —Magenta, and It may be the same as P _TH _Cyan. Color each color deficiency of the printing rate P1 _UP _Yellow of, P1 _UP _Magenta, and P1 _UP _Cyan, for example, it is calculated according to the following formula (5) to (7). However, the result of the calculation is when a negative value is, shortage of printing rate P1 _UP _Yellow for that color, are P1 _UP _Magenta, and P1 _UP _Cyan 0.

P1 _up _Yellow = P _TH _Yellow−P_Yellow (5)

_{P1 up _Magenta = P TH _Magenta-} P_Magenta ··· (6)

P1 _up _Cyan = P _TH _Cyan−P_Cyan (7)

Subsequently, the print data expansion unit 3 processes the print data so as to form print data of each color (add a color image) in the target image area of the print data (S121). This operation is performed by the image data processing unit 33. An additional amount of color the color of the print data, the color of each color deficiency of the printing rate P1 _UP _Yellow of, are P1 _UP _Magenta, and P1 additional amount as an amount corresponding printing rate corresponding to the _UP _Cyan increases. As a result, the color toner corresponding to the shortage printing rate of each color is consumed, and the printing rate of each color is supplemented (increased). Also, the printing of the color in the print data after adding color each color print data _{(P_Yellow + P1 UP _Yellow, P_Magenta} + P1 UP _Magenta, and P_Cyan + P1 _UP _Cyan), the color of each color of the average print rate _{P TH _Yellow, P TH _Magenta,} P TH It is below _Cyan. Thereby, it is possible to prevent the color toner from being consumed more than necessary.

  Here, the total image density (maximum number of pixels per unit area) of all colors (black, yellow, magenta, cyan) printed in the target image area is equal to or less than the reference image density (number of reference pixels). Is done. The reference image density is, for example, the maximum image density (the maximum number of pixels and the maximum amount of toner) of all the colors per unit area during normal color printing. Therefore, an upper limit value for satisfying the above condition is set for the additional amount of print data for each color. By providing the upper limit in this way, it is possible to prevent a fixing failure due to an excessive amount of toner per unit area.

  By determining the amount of print data for each color in the target image area as described above, the amount of color toner developed per unit area applied to the target image area is increased when the color print rate is low. Therefore, the toner consumption can be increased, and the retention of toner in the developing device 212 can be reduced.

  Subsequently, proceeding to FIG. 5, the print data expansion unit 3 determines whether or not a color image has been added to the target image area in step S121 (S122). When a color image is added to the target image area (YES in S122), the print data expansion unit 3 reacquires the print amounts D_Yellow, D_Magenta, and D_Cyan of each color in the processed print data (or the acquired color of each color). The printing amounts D_Yellow, D_Magenta, and D_Cyan are corrected) (S123), and the process proceeds to step S125.

  If a color image is not added to the target image area in step S122 (NO in S122), it is determined in step S115 whether or not the black image density in the target image area has been reduced (S151). If the black image density in the target image area is not reduced (NO in S151), the process proceeds to step S125. When the black image density in the target image area is reduced (YES in S151), the black image density in the target image area reduced in step S115 is the original image density (when the print data was acquired in step S103). The black image density of the target image area is restored (S153). Then, after the black print amount D_Black is returned to the original black print amount (black print amount when the print data is acquired in step S105) (S155), the process proceeds to step S125.

  In step S125, the apparatus control unit 4 uses the printing unit 2 to perform a printing operation (printing) according to the printing data (if the printing data is processed, the processed printing data or the prepared image data), and prints the sheet. An image is formed (S125). During the printing operation, the developing device 212 for each color develops the processed print data using the color toner, so that the toner consumption operation for the paper is executed together with the printing operation.

Then the device control unit 4, the color of the print quantity D_Black required for printing operation, D_Yellow, D_Magenta, and each of D_Cyan, the following equation (8) to the respective colors in accordance with (11) accumulated printing amount D _TTL _BLACK, D _TTL _Yellow, integrating for each of the D _TTL _Magenta, and D _TTL _Cyan.

D _TTL _Black (after integration) = D _TTL _Black (before integration) + D_Black (8)

D _TTL _Yellow (after integration) = D _TTL _Yellow (before integration) + D_Yellow (9)

D _TTL _Magenta (after integration) = D _TTL _Magenta (before integration) + D_Magenta (10)

D _TTL _Cyan (after integration) = D _TTL _Cyan (before integration) + D_Cyan (11)

Further, the apparatus control unit 4 determines the rotation speeds R_Black, R_Yellow, R_Magenta, and R_Cyan of each color developing roller 212a required for the printing operation according to the following formulas (12) to (15). Integration is performed for each of R _{TTL —} Black, R _{TTL —} Yellow, R _{TTL —} Magenta, and R _{TTL —} Cyan (S127).

R _TTL _Black (after integration) = R _TTL _Black (before integration) + R_Black (12)

R _TTL _Yellow (after integration) = R _TTL _Yellow (before integration) + R_Yellow (13)

R _TTL _Magenta (after integration) = R _TTL _Magenta (before integration) + R_Magenta (14)

R _TTL _Cyan (after integration) = R _TTL _Cyan (before integration) + R_Cyan (15)

  The accumulated print amount and accumulated rotation number after accumulation are stored in the storage unit 42.

Subsequently, the apparatus control unit 4 determines a reference rotation speed R _CHK that is a rotation speed that determines a predetermined execution period of the toner consumption operation, and integrated rotation speeds R _TTL —Black, R _TTL —Yellow after integration of the developing rollers 212a of the respective colors. , and compares the R _TTL _Magenta, and R _TTL _Cyan (S129). As the reference rotation speed R _CHK , it is preferable to set the integrated rotation speed of the developing roller that is normally required to print about 100 sheets of A4 size.

Cumulative revolution speed R _TTL _BLACK of each color of the developing roller _{212a, R TTL _Yellow, R TTL} _Magenta, and if at least one cumulative revolution number of the R _TTL _Cyan exceeds the reference rotation speed R _CHK YES at (S129 The apparatus control unit 4 determines a developing device that requires a forced toner consumption operation, and proceeds to step S131 in FIG. 6 to execute the forced toner consumption operation related to the developing device. On the other hand, if any of the integrated rotation speeds R _{TTL —} Black, R _{TTL —} Yellow, R _{TTL —} Magenta, and R _{TTL —} Cyan of each color developing roller 212a is equal to or less than the reference rotation speed R _CHK (NO in S129) 3) The apparatus control unit 4 proceeds to step S103 in FIG. 3 to wait for the next print data from the external device 60 without performing the forced toner consumption operation.

Device control unit 4 at step S131, the colors of the accumulated printing amount _{D TTL _Black, D TTL _Yellow,} D TTL _Magenta, and D _TTL _Cyan and the accumulated number of revolutions R _TTL _BLACK of each color of the developing roller 212a, R _TTL _Yellow, R based on the _TTL _Magenta, and R _TTL _Cyan, colors accumulated printing ratio in the execution cycle of the toner consumption operation _{(D TTL _Black / R TTL _Black} ), (D TTL _Yellow / R TTL _Yellow), (D TTL _Magenta / R _TTL _Magenta), and obtains the _{(D TTL _Cyan / R TTL _Cyan} ).

Here accumulated printing ratio _{(D TTL _Black / R TTL _Black} ), (D TTL _Yellow / R TTL _Yellow), and _{(D TTL _Magenta / R TTL _Magenta} ), and _{(D TTL _Cyan / R TTL _Cyan} ), accumulated printing This represents the average printing amount per unit rotation number of the developing roller of each color in printing of print data from the time when each of the amount and the integrated rotation number was reset most recently.

The apparatus control unit 4 then calculates the average printing rates P _TH —Black, P _TH —Yellow, P _TH —Magenta, and P _TH —Cyan for each color from the calculated cumulative printing rates for each color according to the following equations (16) to (19). each color deficiency of the printing rate P2 _UP _BLACK of, P2 _UP _Yellow, calculates the P2 _UP _Magenta, and P2 _UP _Cyan. However, if the result of the calculation is a negative value, deficiency of the printing rate P2 _UP _BLACK for that _{color, P2 UP _Yellow, P2 UP _Magenta} , are P2 _UP _Cyan 0.

_{P2 UP _Black = P TH _Black- (} D TTL _Black / R TTL _Black) ··· (16)

_{P2 UP _Yellow = P TH _Yellow- (} D TTL _Yellow / R TTL _Yellow) ··· (17)

_{P2 UP _Magenta = P TH _Magenta- (} D TTL _Magenta / R TTL _Magenta) ··· (18)

_{P2 UP _Cyan = P TH _Cyan- (} D TTL _Cyan / R TTL _Cyan) ··· (19)

Then the device control unit 4, the calculated deficiency of the printing rate _{P2 UP _Black, P2 UP _Yellow,} P2 UP _Magenta, and P2 is not an 0 in the _UP _Cyan discriminates whether or (S132). In step S132, the calculated deficiency of the printing rate _{P2 UP _Black, P2 UP _Yellow,} P2 UP _Magenta, and P2 _UP (YES at S132) if there is non-zero in _Cyan, forced toner consumption in step S133 The action is executed. Calculated deficiency of the printing rate _{P2 UP _Black, P2 UP _Yellow,} P2 UP _Magenta, and if P2 _UP _Cyan is 0 none (NO at S132), since the forced toner consumption operation is unnecessary, the step S135 Proceed to

Device control unit 4 at step S133, the calculated deficiency of the printing rate _{P2 UP _Black, P2 UP _Yellow,} P2 UP _Magenta, and of an amount corresponding to P2 _UP _Cyan force the toner consumption operation for consuming toner Then, the developer 212 is executed (S133). In this toner consumption operation, corresponding toner is supplied from the developing device 212 to a non-printing region (region outside the document printing range) on the photosensitive member 211, and the toner supplied to the developing device 212 is used as a waste toner container 450. It is executed by storing it. Note that when the printing rate for the shortage is 0, the toner consumption operation for that color is not executed. That is, the toner consumption operation corresponding to the value for the color whose deficiency print rate is greater than 0 is performed.

Here, when the toner consumption operation on the paper is executed in step S125, the toner development amount increases due to the toner consumption operation on the paper, and the increase in the toner development amount is the integrated print rate (D of each color). _TTL _Black / R _TTL _Black), are reflected in _{(D TTL _Yellow / R TTL _Yellow} ), (D TTL _Magenta / R TTL _Magenta), and _{(D TTL _Cyan / R TTL _Cyan} ). Therefore, by performing the toner consumption operation on the paper, the frequency of the toner consumption operation (contained toner consumption operation) to the non-printing area on the photosensitive member 211 can be reduced and stored in the waste toner storage unit. The toner amount can be reduced.

Subsequently, the apparatus control unit 4 resets the integrated rotation speed and the integrated print amount of the developing roller 212a in each color developing device 212 (S135). Specifically, the apparatus control unit 4 sets each value of the accumulated rotation speeds R _{TTL —} Black, R _{TTL —} Yellow, R _{TTL —} Magenta, and R _{TTL —} Cyan stored in the storage unit 42 to 0, The integrated print amounts D _{TTL —} Black, D _{TTL —} Yellow, D _{TTL —} Magenta, and D _{TTL —} Cyan for each color developer 212 are set to zero. Thereafter, in order to wait for the next print data from the external device 60, the process proceeds to step S103 in FIG.

  [Effect of the embodiment]

  The image forming apparatus according to the present embodiment includes a black developing device and at least one color developing device, and the printing rates for the development for black and the color based on the information of the document to be printed. And a color image forming apparatus having means for performing a toner consumption operation on the paper according to the printing rate when it is determined that the printing rate is lower than a predetermined reference printing rate. Is. In this image forming apparatus, when the printing rate relating to the color development acquired by the means for acquiring the printing rate is lower than a predetermined reference printing rate, the color toner is superimposed on the black image portion and printed. Is done. In addition, when the printing rate for black development acquired by the means for acquiring the printing rate is higher than a predetermined reference printing rate, the printing rate for black development is reduced. It is a feature.

  In addition, the image forming apparatus according to the present embodiment analyzes the black image portion to be printed in order to increase the printing rate when the printing rate of the color image is low, and the appearance color changes even when the color toner is superimposed. The color toner is superimposed on a small high density portion for printing. In this image forming apparatus, the maximum amount of toner to be overlaid is limited to the same amount as in normal printing control, and the amount of black image printed is reduced as much as possible so that as much color toner as possible can be overlaid. To do.

  According to the image forming apparatus of the present embodiment, even when the color image of a document to be printed has a low printing rate, the change in the apparent color of the black image portion formed with black toner is not noticeable (comparison) By printing a color image over a high density area), the color image printing rate can be increased without greatly degrading the image quality. The frequency of the toner consumption operation can be suppressed. As a result, waste toner (frequency of deteriorated toner consumption operation) due to the toner consumption operation to the non-printing area on the photoconductor can be reduced, and the life reduction of the waste toner container can be suppressed more than ever.

  In addition, image areas that have little effect on image quality are judged as image areas to be overlaid with color images, and if the printing rate applied to the black developer is high, image processing is performed to reduce the printing rate, and the amount of color image to be overlaid is reduced. By managing, it is possible to prevent the image quality from being greatly deteriorated. Since the color toner superimposed on the black image portion has been conventionally consumed in the waste toner storage portion, the number of printable sheets does not decrease due to the above processing.

  [Others]

  The toner consumption operation shown in step S133 of FIG. 6 may be performed in any form. Further, the toner consumption operation shown in step S133 may not be performed, and excess toner may be consumed only by forming a color image on the target image area of the paper in step S125 of FIG.

  Further, even if a color image is added so that the total image density of the black and color image densities in the black image portion is equal to or lower than the reference image density without reducing the image density of the black image portion. Good.

  The processing in the present embodiment may be performed by software or may be performed using a hardware circuit. In addition, a program for executing the processing in this embodiment can be provided, and the program is recorded on a recording medium such as a CD-ROM, a flexible disk, a hard disk, a ROM, a RAM, or a memory card and provided to the user. You may decide. The program is executed by a computer such as a CPU. The program may be downloaded to the apparatus via a communication line such as the Internet.

  This embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Printing part 3 Print data expansion | deployment part 4 Apparatus control part 5 Operation panel part 10 Paper conveyance part 20 Toner image formation part 30 Fixing part 31 Print rate acquisition part 32 Image area judgment part 33 Image data processing part 40 Paper accommodation Unit 41 Accumulated rotational speed detection unit 42 Storage unit 60 External device 101 Paper feed roller 102 Timing roller 103 Paper discharge roller 210, 210Y, 210M, 210C, 210B Image forming unit 211, 211Y, 211M, 211C, 211B Photoconductor 212, 212Y , 212M, 212C, 212B Developer 212a Developing roller 213, 213Y, 213M, 213C, 213B, 233 Cleaner 214, 214Y, 214M, 214C, 214B Charging charger 220 Primary transfer roller 230 Intermediate transfer belt 231 232 Over La 240 secondary transfer roller 250 exposure unit 260,260Y, 260M, 260C, 260B toner bottle 310 heating roller 320 pressure roller 430 body outlet 450 the waste toner storing portion 460 waste toner conveying portion LB laser light R sheet path

Claims (13)

Data acquisition means for acquiring print data;
First printing rate acquisition means for acquiring a black printing rate in the print data acquired by the data acquisition unit;
When the black print rate acquired by the first print rate acquisition unit is higher than the black reference print rate, in the print data acquired by the data acquisition unit, at least part of the black image portion that prints black First processing means for processing the print data so as to reduce the image density of black;
An image forming apparatus comprising: a second processing unit that processes print data so as to add a color image having a color tone other than black to at least a part of the black image portion. A second print rate acquisition unit that acquires a print rate of at least any color having a color tone other than black in the print data acquired by the data acquisition unit;
The second processing means includes
The image of the color is added to the black image portion when a printing rate for a certain color acquired by the second printing rate acquisition unit is smaller than a printing rate serving as a reference for the color. The image forming apparatus described.   3. The first processing unit does not decrease the black image density when the black printing rate acquired by the first printing rate acquisition unit is equal to or lower than the black reference printing rate. 4. Image forming apparatus. A region determining means for determining a target image region from within the black image portion;
The image forming apparatus according to claim 1, wherein the second processing unit adds a color image to the target image area.   The area determination unit determines, as the target image area, an area formed only of black and having a black image density equal to or higher than a reference density based on the print data acquired by the data acquisition unit. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 4, wherein the area determination unit determines an area that is not a photographic image as the target image area based on the print data acquired by the data acquisition unit.   The second processing means is configured to reduce the black image density so that a total image density of the black and color image densities in the black image portion after the black image density is reduced is equal to or lower than a reference image density. The image forming apparatus according to claim 1, wherein a color image is added to the image portion. Further comprising black developing means for developing using black toner based on the print data processed by the first processing means;
When the black average printing rate of the black developing unit is lower than the black average printing rate, the black developing unit forcibly consumes black toner,
8. The method according to claim 1, wherein the first processing unit reduces the black image density so that the black printing rate after reducing the image density is equal to or higher than an average printing rate serving as the black reference. The image forming apparatus described in 1. A color developing unit that performs development using color toner based on the print data processed by the second processing unit;
When the average color printing rate of the color developing unit is lower than the average printing rate serving as a color reference, the color developing unit forcibly consumes color toner,
The said 2nd process means adds a color image so that the printing rate of the color in the printing data after adding a color image may become below the average printing rate used as the reference | standard of the said color. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the first print rate acquisition unit acquires a print rate in units of print jobs. Data acquisition means for acquiring print data;
In the print data acquired by the data acquisition means, color image processing means for processing the print data so as to add a color image having a color tone other than black to at least a part of the black image portion for printing black,
The color image processing means adds a color image to the black image portion so that a total image density of the black and color image densities in the black image portion is equal to or lower than a reference image density. apparatus. A data acquisition step for acquiring print data;
A first print rate acquisition step of acquiring a black print rate in the print data acquired in the data acquisition step;
When the black print rate acquired in the first print rate acquisition step is higher than the black reference print rate, in the print data acquired in the data acquisition step, at least part of the black image portion that prints black A first processing step for processing the print data so as to reduce the black image density;
And a second processing step of processing the print data so as to add a color image having a color tone other than black to at least a part of the black image portion. A data acquisition step for acquiring print data;
A first print rate acquisition step of acquiring a black print rate in the print data acquired in the data acquisition step;
When the black print rate acquired in the first print rate acquisition step is higher than the black reference print rate, in the print data acquired in the data acquisition step, at least part of the black image portion that prints black A first processing step for processing the print data so as to reduce the black image density;
A control program for an image forming apparatus, causing a computer to execute a second processing step for processing print data so as to add a color image having a color tone other than black to at least a part of the black image portion.

Images