JP2017219758A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suppress a change over time of gradation reproducibility of a multi-gradation image in an image forming apparatus that changes an image forming condition based on a result of detecting the density of a reference density image and changes gradation correction information based on a result of detecting the density of a gradation pattern image.SOLUTION: An image forming apparatus comprises: image forming condition changing means that forms a reference density image having a predetermined density on an image carrier, detects the density of the reference density image, and changes an image forming condition used in forming an image with image forming means on the basis a result of the detection and a target density; and gradation correction information changing means that forms a gradation pattern image on the image carrier, detects the density of the gradation pattern image, and changes gradation correction information used in forming a multi-gradation image with the image forming means on the basis a result of the detection. When forming the gradation pattern image, the image forming apparatus forms the reference density image on the image carrier, detects the density of the reference density image, and sets a result of the detection as the target density.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming apparatus.

  Conventionally, there is known an image forming apparatus that changes an image forming condition based on a density detection result of a reference density image and changes gradation correction information based on a density detection result of a gradation pattern image. In this image forming apparatus, an image forming condition such as a charging potential at the time of image formation is changed based on a detection result of a reference density image having a predetermined density formed on the image carrier and a target density. Further, the gradation correction information used when forming the multi-tone image is changed based on the detection result of the multi-tone image pattern formed on the image carrier.

  Patent Document 1 discloses an image forming apparatus that performs the following potential control (change of image forming conditions) and change of input / output characteristic correction signals (tone correction information). . In this image forming apparatus, the charging potential or the like at which the target toner adhesion amount (target density) is obtained is changed based on the detection result of the solid portion (reference density image) formed on the intermediate transfer belt. The input / output characteristic correction signal (tone correction information) is changed based on the detection result of the area gradation pattern (tone pattern image) having a plurality of gradations formed on the intermediate transfer belt.

  When changing the image forming condition based on the density detection result of the reference density image and changing the gradation correction information based on the density detection result of the gradation pattern image, the gradation reproducibility of the multi-tone image is changed over time. It has been found that there is a risk of significant changes.

  In order to solve the above problems, the present invention provides an image forming means for forming an image on an image carrier, a density detecting means for detecting the density of an image on the image carrier, and a predetermined on the image carrier. Image formation for forming a reference density image of density, detecting the density of the reference density image, and changing an image forming condition used when the image forming unit forms an image based on the detection result and a target density When a gradation pattern image is formed on the image carrier, the density of the gradation pattern image is detected, and a multi-gradation image is formed by the image forming means based on the detection result. A gradation correction information changing means for changing gradation correction information used in the image forming apparatus, wherein the reference density image is formed on the image carrier when the gradation pattern image is formed, and the reference Detects the density of the density image It is characterized in that to set the detection result to the target concentration.

  According to the present invention, the level of a multi-tone image in an image forming apparatus that changes the image forming condition based on the density detection result of the reference density image and changes the tone correction information based on the density detection result of the tone pattern image. It is possible to suppress changes in tone reproducibility over time.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment. 1 is a schematic configuration diagram illustrating an example of a process unit in an image forming apparatus according to an embodiment. 3 is a diagram illustrating a relationship between a charging potential and an exposure portion potential of a photosensitive member and a developing potential (developing bias) of a developing roller in the image forming apparatus according to the embodiment. FIG. 2 is a block diagram illustrating an example of a main configuration of a control system of the image forming apparatus according to the present embodiment. FIG. 3 is a block diagram showing an example of the flow of an image data processing method in the image forming apparatus according to the embodiment. The figure which shows an example of the relationship between a gradation pattern image (test pattern for measurement) and gradation reproducibility. FIG. 4 is a diagram illustrating an example of a gradation pattern image (measurement test pattern) formed on an intermediate transfer belt. The figure which shows an example of the fluctuation | variation of image density with time. 6 is a flowchart illustrating an example of density correction control and gradation correction control in the image forming apparatus according to the embodiment. FIG. 4 is a diagram illustrating an example of a reference density image in density correction control in the image forming apparatus according to the embodiment. FIG. 10 is a diagram illustrating another example of the reference density image in the density correction control in the image forming apparatus according to the embodiment. FIG. 6 is a diagram illustrating an example of a gradation pattern image and a reference density image in gradation correction control of the image forming apparatus according to the embodiment. The figure which shows an example of the determination of the gradation correction information using the detection result of the density | concentration of a gradation pattern image. The figure explaining an example of reflection of the target maximum density image in the timing which reflects gradation correction information. The figure explaining the other example of reflection of the target maximum density image in the timing which reflects gradation correction information. The figure explaining the further another example of reflection of the target maximum density image in the timing which reflects gradation correction information. The graph which shows an example of the setting method of the image creation conditions of a maximum density image. FIG. 10 is a diagram illustrating another example of the gradation pattern image and the reference density image in the gradation correction control of the image forming apparatus according to the embodiment. FIG. 10 is a diagram illustrating another example of the gradation pattern image and the reference density image in the gradation correction control of the image forming apparatus according to the embodiment. FIG. 10 is a diagram illustrating another example of the gradation pattern image and the reference density image in the gradation correction control of the image forming apparatus according to the embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment. The image forming apparatus 1 of this embodiment includes a plurality of process units (image forming units) 10Y, 10C, 10M, and 10K as image forming units, and an intermediate transfer belt (intermediate transfer member) 20 as an image carrier. . Further, the image forming apparatus 1 includes an optical writing device (optical scanning device) 30 as an exposure unit used for forming a latent image in each process unit, and an image as a density detection unit that detects the density of various measurement images. A density sensor 40 and a paper feeding device 50 that supplies paper P as a recording medium are provided. The image forming apparatus 1 also includes a secondary transfer roller 60 as a secondary transfer unit that transfers an image on the intermediate transfer belt 20 to the paper P, and a fixing unit that fixes the image transferred onto the paper P with heat and pressure. And a fixing device 70 composed of a pair of rollers. The image forming apparatus 1 may include an image reading unit (scanner) as an image reading unit, an automatic document feeder (automatic document feeder) as a document supply unit, and the like. In the image forming apparatus according to the embodiment, an image forming unit that forms an image on the intermediate transfer belt 20 includes process units 10Y, 10C, 10M, and 10K and an optical writing device 30.

  The intermediate transfer belt 20 is stretched by a plurality of rollers 21 to 24 and disposed in the transfer unit. The plurality of rollers includes a driving roller 24 that is rotationally driven by a motor or the like, driven rollers 22 and 23, a secondary transfer backup roller 21 and the like. The intermediate transfer belt 20 is made of, for example, a material in which carbon powder for adjusting electric resistance is dispersed in a polyimide resin with little elongation. The intermediate transfer belt 20 is endlessly moved by the rotation of the driving roller 24 while being stretched by the driving roller 24, the secondary transfer backup roller 21, and the driven rollers 22 and 23. A belt cleaning device 25 that cleans the surface of the intermediate transfer belt 20 is provided at a position facing the driven roller 22.

  The process units 10Y, 10C, 10M, and 10K for each color are arranged so as to be arranged at a predetermined interval along the moving direction of the lower tension portion of the intermediate transfer belt 20 in the drawing. A primary transfer charger 15Y as a primary transfer unit is located at a position facing the photoconductors 11Y, 11C, 11M, and 11K as latent image carriers of the process units 10Y, 10C, 10M, and 10K via the intermediate transfer belt 20. , 15C, 15M, and 15K. The primary transfer chargers 15Y, 15C, 15M, and 15K are yellow (Y), cyan (C), magenta (M), and black (K) toner images formed on the photoreceptors 11Y, 11C, 11M, and 11K, respectively. Is used to transfer the toner image to the intermediate transfer belt 20.

  FIG. 2 is a schematic configuration diagram illustrating an example of a process unit in the image forming apparatus 1 according to the embodiment. Since the process units 10Y, 10C, 10M, and 10K for the respective colors have the same configuration, in FIG. 2, subscripts (Y, C, M, and K) for distinguishing the toner colors are added to the reference numerals of the respective members. Do not explain.

  In the process unit 10 of FIG. 2, the photosensitive member 11 is charged by a charging roller 12 as a charging unit, and then the light L from the optical writing device (optical scanning device) 30 is irradiated to the photosensitive member 11 through the mirror 13. (Exposure) and a latent image is formed on the photoreceptor 11. The optical writing device (optical scanning device) 30 drives four semiconductor light sources (LD) as four light sources by, for example, a laser control unit based on image information such as an input image to be output and outputs four writing lights. Exit.

  The optical writing device (optical scanning device) 30 includes, for example, a semiconductor laser (LD) as a light source, an optical deflector (for example, a polygon mirror), a reflection mirror, and an optical lens. In the optical writing device (optical scanning device) 30 having this configuration, the laser beam emitted from the semiconductor laser is deflected by an optical deflector and reflected by a reflection mirror or passed through an optical lens, thereby being applied to the photosensitive member 11. Optical scanning is performed. In addition, as the optical writing device (optical scanning device) 30, an optical scanning device that performs optical scanning with an LED array as a light source may be used instead of the one having such a configuration.

  The latent image formed on the photosensitive member 11 is developed as a toner image on the photosensitive member 11 via a developing roller 14a as a developer carrying member of the developing device 14 having a developer such as toner, and is transferred to the primary transfer portion N. Then, the image is transferred to the intermediate transfer belt 20. The toner remaining on the surface of the photoconductor 11 after the toner image is transferred to the intermediate transfer belt 20 is removed by a cleaning blade 16a of the photoconductor cleaning device 16 or the like. The toner concentration of the developer in the developing device 14 is detected by a toner concentration sensor 14b such as a magnetic permeability sensor as a toner concentration detecting means provided on the wall surface of the housing. For example, when the toner concentration becomes lower than a predetermined threshold value. The toner is supplied from the toner container.

  The toner images formed on the photosensitive units 11Y, 11C, 11M, and 11K of the process units 10Y, 10C, 10M, and 10K for the respective colors are transferred onto the intermediate transfer belt 20 so as to form a full color image. . The full-color image on the intermediate transfer belt 20 is transferred to the paper P supplied from the paper feeding device 50 at the secondary transfer portion opposed to the secondary transfer roller 60 and then fixed by the fixing device 70 (FIG. 1). reference).

  In the image forming apparatus 1 of the present embodiment, when density correction control or gradation characteristic correction control is performed, a reference density image for measurement or a floor is measured on the intermediate transfer belt 20 by the process units 10Y, 10C, 10M, and 10K. A tone pattern image is formed. The density (toner adhesion amount) of the reference density image and gradation pattern image on the intermediate transfer belt 20 is arranged to face the outer peripheral surface of the intermediate transfer belt 20 on the downstream side in the belt movement direction of the black process unit 10K. Detected by the image density sensor 40. The image density sensor 40 can be constituted by a reflection type optical sensor having a light emitting element and a light receiving element, for example. When detecting the image density in the entire width direction of the intermediate transfer belt 20, a line sensor or an area sensor in which imaging elements such as a CCD and a CMOS are arranged one-dimensionally or two-dimensionally may be used.

  Although FIG. 1 shows an example of an image forming apparatus having four color process units, the image forming apparatus according to the present embodiment is an image forming apparatus using a two-color developing device or a white or transparent toner. It may be an image forming apparatus using a five-color developing device to which is added.

  FIG. 3 is a diagram illustrating a relationship between the charging potential and the exposure portion potential of the photoconductor 11 and the developing potential (developing bias) of the developing roller 14a in the image forming apparatus 1 according to the embodiment. The potential when the photoconductor 11 is charged is referred to as “charging potential”, and the potential after exposure on the photoconductor 11 is referred to as “exposure portion potential”. The potential of the developing roller 14a is referred to as “developing potential” or “developing bias”, and the difference between the developing potential (developing bias) and the exposure portion potential is referred to as “developing potential”. The toner has a charge amount according to the state of the agent and the environment, and the toner carried on the developing roller 14a of the developing device 14 moves onto the photoconductor 11 so as to cancel out the potential corresponding to the developing potential. To do. Therefore, the amount of toner adhering to the photoreceptor 11 varies depending on the toner charge amount and the development potential.

FIG. 4 is a block diagram illustrating an example of a main configuration of a control system of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 includes a control unit 90 configured by a computer device such as a microcomputer. The control unit 90 functions as the following units in cooperation with other units in the image forming apparatus 1.
An image forming condition (hereinafter referred to as “image forming conditions”) when a reference density image is formed on the intermediate transfer belt 20, the density of the reference density image is detected, and the image forming unit forms an image based on the detection result and the target density. Image forming condition changing means for determining and changing the image forming condition.
Tone correction used when forming a gradation pattern image on the intermediate transfer belt 20, detecting the density of the gradation pattern image, and forming a multi-gradation image by the image forming means based on the detection result Tone correction information changing means for determining and changing information.
Control means for controlling the image forming means so as to form a multi-tone image based on the image forming conditions and the tone correction information.
Means for forming a reference density image on the intermediate transfer belt 20 when forming a gradation pattern image, detecting the density of the reference density image, and setting the detection result of the density to the target density;

  The control unit 90 includes a CPU (Central Processing Unit) 901. Further, a ROM (Read Only Memory) 903 and a RAM (Random Access Memory) 904 as storage means connected to the CPU 901 via the bus line 902, and an I / O interface unit 905 are provided. The CPU 901 executes various calculations and drive control of each unit by executing a control program which is a computer program incorporated in advance. The ROM 903 stores in advance fixed data such as computer programs and control data. The RAM 904 functions as a work area that stores various data in a rewritable manner.

  Various sensors such as an apparatus main body (printer unit) image density sensor 40 and a toner density sensor 14b are connected to the control unit 90 via an I / O interface unit 905. Here, various sensors such as the image density sensor 40 and the toner density sensor 14 b send information detected by each sensor to the control unit 90. Further, a charging bias setting unit (charging bias power source) 920 that applies a predetermined charging bias to the charging roller 12 is connected to the control unit 90 via the I / O interface unit 905. Further, a developing bias setting unit (developing bias power source) 930 for applying a predetermined developing bias (developing potential) to the developing roller 14a of the developing device 14 is connected.

  Further, a primary transfer bias setting unit (primary transfer bias power source) 940 that applies a predetermined primary transfer bias to the primary transfer charger 15 is connected to the control unit 90 via an I / O interface unit 905. Further, an exposure setting unit (light source power source unit) 950 that applies a predetermined voltage or supplies a predetermined current to the light source of the optical writing device 30 is connected.

  In addition, the sheet feeding device 50 is connected to the control unit 90 via an I / O interface unit 905.

  The control unit 90 controls each unit based on control target values of image forming conditions (for example, charging bias, developing bias, exposure amount, primary transfer bias, etc.).

  In the ROM 903 or the RAM 904, for example, a conversion table storing information related to conversion of the output value of the image density sensor 40 into image density (toner adhesion amount per unit area) is stored. In addition, the ROM 903 or the RAM 904 stores control target values of image forming conditions (for example, charging bias, developing bias, exposure amount, primary transfer bias) of each color process unit in the image forming apparatus 1. Further, the ROM 903 or the RAM 904 stores gradation correction information (tone correction data) which is a gradation image forming condition indicating a relationship between a gradation value and an image density in a gradation range used for forming a multi-gradation output image. Is stored.

  Note that the control unit 90 may be configured using, for example, an IC as a semiconductor circuit element manufactured for control in the image forming apparatus 1 instead of a computer device such as a microcomputer.

  The program used in the present embodiment can be stored not only in the nonvolatile memory and / or volatile memory provided in the control unit 90 but also in other storage media. For example, the image forming program is a semiconductor medium (for example, RAM, nonvolatile memory, etc.), an optical medium (for example, DVD, MO, MD, CD-R, etc.), a magnetic medium (for example, hard disk, magnetic tape, flexible disk, etc.). ), And can be stored in other storage media. When such an image forming program is stored, the memory and other storage media constitute a computer-readable recording medium storing the image forming program.

FIG. 5 is a block diagram illustrating an example of a flow of an image data processing method in the image forming apparatus 1 according to the embodiment.
First, image data passed through a printer driver from application software on an external host computer 500 is output to the image forming apparatus 1 shown in FIG. At this time, the image data is converted into PDL (page description language) by the printer driver. When image data described in PDL is input as input data, the rasterization processing unit 101 interprets it and forms a raster image. At this time, for each object, a signal indicating the type and attribute of, for example, a character / line, a photograph, or a graphics image is generated. The signal is sent to the input / output characteristic correction unit 102, the MTF filter processing unit 103, the color correction / gradation correction (abbreviated as “color / gradation correction”) processing unit 104, the pseudo halftone processing unit 105, and the like. Output.

  The input / output characteristic correction unit 102 corrects each gradation value in the raster image so that a desired characteristic is obtained by the input / output characteristic correction signal. In addition, the input / output characteristic correction unit 102 uses the output of the image density sensor 40 from the density sensor output unit 110 and transmits / receives information to / from the storage unit 106 including a nonvolatile memory and a volatile memory. The input / output characteristic correction signal is formed and corrected. The formed input / output characteristic correction signal is stored in the non-volatile memory of the storage unit 106 and used for the next image formation.

  The MTF filter processing unit 103 selects an optimum filter for each attribute according to the attribute signal sent from the rasterization processing unit 101 and performs enhancement processing. Since the MTF filter processing is the same as the conventional technology, detailed description thereof is omitted. The image data after the MTF filter processing is delivered to the color / tone correction processing unit 104 which is the next step.

  The color / gradation correction processing unit 104 performs various correction processes such as the following color correction and gradation correction. In color correction, color conversion from the RGB color space, which is the PDL color space input from the host computer 500, to the CMYK color space, which is a color space composed of toner colors used in the image forming unit 100 such as the process unit 10, is performed. Do. This color correction is performed using a color correction coefficient optimum for each attribute according to the attribute signal sent from the rasterization processing unit. In tone correction, tone correction processing for correcting image data of a multi-tone image to be output is performed based on tone characteristic data created using a tone correction pattern described later. As described above, the color / gradation correction processing unit 104 functions as a gradation correction unit that corrects image data of a multi-gradation image to be output based on the gradation characteristic data. Note that the color / gradation correction processing can be the same as that of the prior art, and thus detailed description thereof is omitted here.

  After the processing in the color / gradation correction processing unit 104, the image data is delivered to the pseudo halftone processing unit 105. The pseudo halftone processing unit 105 performs pseudo halftone processing to generate output image data. For example, pseudo halftone processing is performed on the data subjected to color / gradation correction processing by a dither method. That is, the quantization is performed by comparing and referring to a dither matrix stored in advance.

  The output image data output from the pseudo halftone processing unit 105 is processed by the video signal processing unit 107 and converted into a video signal. Based on this video signal, the PWM signal generation unit 108 generates a PWM signal as a light source control signal. The LD driving unit 109 outputs an LD driving signal for driving a semiconductor laser (LD) as a light source of the optical writing device 30 based on the PWM signal received from the PWM signal generating unit 108.

Next, problems to be solved by the image forming apparatus according to the embodiment will be described.
FIG. 6 is a diagram illustrating an example of a relationship between a gradation pattern image (measurement test pattern) and gradation reproducibility according to a conventional method. In a typical electrophotographic image forming apparatus, the gradation in the gradation range used for forming a multi-gradation output image is set so that the relationship between the document density and the print density (gradation reproducibility) becomes an ideal relationship. Tone correction information indicating the relationship between tone values and image density is set. This is because the relationship between image forming conditions (charging potential, developing bias, exposure amount, etc.) and print density (output image density) is not a simple linear. For example, the relationship between the document density and the potential is set for the density gradation method, and the relationship between the document density and the image processing pattern is set so as to obtain ideal gradation reproducibility for the area gradation method. The

  However, even if gradation correction information is set in advance so that ideal gradation reproducibility can be obtained due to environmental conditions such as temperature and humidity and the degree of developer deterioration, gradation reproducibility changes over time, There is a problem that the print density does not match the target density. In order to solve this problem, a method is known in which a test pattern for measurement determined in advance at a predetermined timing is created, measured by a colorimetric device, and gradation correction information is corrected based on the measurement result. ing. However, this method requires the user to stop printing the print image at every predetermined timing, which causes a waiting time for the user and causes a decrease in productivity.

  FIG. 7 is a diagram showing an example of a gradation pattern image (measurement test pattern) 210 ′ formed on the intermediate transfer belt 20 ′ in another conventional method. In this example, in order to prevent a decrease in productivity, a measurement test pattern 210 ′ as a gradation pattern image is created in addition to the printing area of the intermediate transfer belt 20 ′ during printing of a print image by the user. Then, the density of the measurement test pattern 210 ′ is measured using an image density sensor 40 ′ that is an optical sensor attached to the image forming apparatus, and the gradation correction information is corrected based on the measurement result. There is also known a method for correcting gradation correction information based on the measurement result of density in a region where a user's print image includes a measurable region. (For example, refer to Patent Document 2).

  The method shown in FIG. 7 and the method of Patent Document 2 can maintain gradation reproducibility while preventing a decrease in productivity. However, these conventional methods have the following problems.

  FIG. 8 is a diagram showing an example of a change over time in image density in the conventional method. The gradation reproducibility changes not only due to the influence of gradation correction information, but also depending on conditions such as developer charge amount, toner density, exposure amount during latent image formation, and development potential (development bias). Therefore, for example, if the maximum density of the image forming apparatus changes, the gradation reproducibility also changes. Here, the maximum density refers to the print density (output image density) when the document density is the maximum value. In general, in an image forming apparatus, image forming conditions are set so that a certain reference density image maintains a constant target density so that a constant image density is maintained even when such conditions change.

  As the reference density image, for example, the maximum density image itself or an image having a predetermined image area ratio is used. Other than the maximum density image is used as the reference density image, for example, when a reflective optical sensor is used for detection (measurement) of the density of the reference density image, there are cases where the sensitivity to the density fluctuation is not sufficient in the vicinity of the maximum density image. This is because of such reasons.

  However, even if it is attempted to maintain the image density by setting the image forming conditions, it is difficult to always maintain a constant image density. For example, the density of the actual reference density image always varies around the target density. .

  If the density of the reference density image is deviated from the target density at the measurement timing of the gradation pattern image (test pattern for measurement), the calculated gradation curve is affected by the density deviation. It becomes. Therefore, if the gradation curve is corrected based on the measurement data of the gradation pattern image at this time, it is not optimized for the case where the density of the reference density image is the target density. Therefore, there is a problem that the gradation is not optimized as a whole.

FIG. 9 is a flowchart illustrating an example of density correction control and gradation correction control in the image forming apparatus according to the embodiment.
In FIG. 9, when the image forming apparatus 1 starts printing (S11), it is first determined whether or not it is the timing for reflecting gradation correction information (S12). When it is the gradation correction information reflection timing (Yes in S12), the determined density correction image forming condition is reflected and the determined gradation correction information is reflected (S13, S14).

  On the other hand, if it is not the gradation correction information reflection timing (No in S12), it is determined whether it is the detection timing of the next gradation pattern image pattern (S15). If it is the detection timing of the gradation pattern image pattern (Yes in S15), the gradation pattern image and the reference density image are formed on the intermediate transfer belt 20, and the density of each image is detected (S16). Then, the detection result of the reference density image is set to the target density, and gradation correction information is determined based on the detection result of the gradation pattern image (S17, S18).

  If it is not the detection timing of the gradation pattern image pattern (No in S15), it is determined whether or not it is the density correction timing of the next reference density image (S19). If it is the density correction timing of the reference density image (Yes in S19), the reference density image is formed and the density is detected, and the image forming condition for density correction is determined based on the detection result, and the determination is made. The created image forming conditions are reflected (S20, S21). If it is not the density correction timing of the reference density image (No in S19), it is determined whether or not printing is finished (S22).

  If the printing is not finished (No in S22), the process is repeated from the judgment of the gradation correction information reflection timing (S12 to S22).

  Note that the detection timing of the gradation pattern image pattern and the density correction timing of the reference density image may be arbitrarily set within a range where calculation processing is possible. For example, the density correction timing of the reference density image may be set on the basis of the number of prints, such as every 10 prints and the gradation pattern image pattern detection timing is every 100 prints. It may be set as a reference.

  The gradation correction information reflection timing may be set at a timing at which the gradation correction information is calculated based on the detection result detected at the detection timing of the gradation pattern image pattern. The gradation correction information reflection timing may be set after the time required for calculating the gradation correction information is calculated in advance from the measurement.

FIG. 10 is a diagram illustrating an example of a reference density image in density correction control in the image forming apparatus according to the embodiment.
In the density correction of the reference density image, first, a reference density image 220 as a measurement pattern is created outside the area of the print image 200 that is an output image by the user on the intermediate transfer belt 20. In the following examples, an example in which a maximum density image (for example, a solid image) composed of a solid pattern is used as the reference density image is shown.

  FIG. 10 shows an example of creating a reference density image for one color. In the case of an image forming apparatus having a process unit 10 for each of a plurality of colors, a plurality of reference density images for a plurality of colors are created simultaneously. Also good. Also, the reference density images of a plurality of colors may be created with a timing shift. For example, the reference density image of the first color may be formed at the printing timing of the first sheet, and the reference density image of the second color may be formed at the printing timing of the second sheet. The formation of the reference density image in the case of a plurality of colors is the same for a gradation pattern image in which a measurement pattern described later is formed in gradation correction control and a reference density image formed therewith.

  The reference density image created on the intermediate transfer belt 20 is measured by the image density sensor 40. Then, based on the measured maximum density, which is the detection result of the reference density image detected by the image density sensor 40, at least one of the charging potential, the exposure amount, and the development potential, which are image forming conditions, is adjusted and determined. For example, based on the difference between the measured maximum density and a predetermined target density (target maximum density in this example), it is determined by adjusting at least one of charging potential, exposure amount, and development potential, which are image forming conditions. The initial value of the target density is determined in advance, and then the maximum measured density that is the detection result of the reference density image created during the gradation correction control is set.

  The adjustment (determination) of the image forming condition corresponds to, for example, an image density difference (adhesion amount difference) that is a difference between the measured maximum density and the target maximum density, and a change amount (correction amount) of the image forming condition such as a charging potential. Alternatively, the image forming condition correction data created in advance and stored in the control unit may be used. In this case, it is determined to change the imaging conditions such as the charging potential according to the imaging condition correction data created in advance.

Table 1 is a correction table showing an example of image forming condition correction data.

  As shown in FIG. 3 described above, when the charging potential of the photoconductor 11 is increased, the exposed portion potential is also increased and the developing potential is decreased, so that the image density (toner adhesion amount) is decreased. Conversely, when the charging potential is lowered, the exposed portion potential is also lowered, and the image density (toner adhesion amount) is raised. From this relationship, the difference between the change amount (correction amount) of the charging potential of the photoconductor 11 and the threshold values 1 to 4 of the image density (toner adhesion amount) of the reference density image (hereinafter referred to as “image density difference”). Corresponding image forming condition correction data (correction table) in Table 1 is created and stored in advance. Then, the charging potential is changed and determined according to the image forming condition correction data. The change amount (correction amount) of the charging potential may be determined in advance by confirming the relationship between the charging potential and the change amount of the image density (toner adhesion amount) through experiments.

  Further, when the development potential (development bias) of the developing roller 14a is increased, the development potential increases, so that the image density (toner adhesion amount) increases, and when the development potential (development bias) is decreased, the image density (toner adhesion amount) increases. descend. From this relationship, image forming condition correction data (correction table) similar to Table 1 in which the change amount (correction amount) of the development potential (development bias) and the image density difference are associated with each other may be created and stored in advance. Good. In this case, the development potential (development bias) is changed and determined according to the image forming condition correction data.

  Similarly, when the exposure amount is increased, the exposed portion potential is decreased and the development potential is increased, so that the image density (toner adhesion amount) is increased. When the exposure amount is decreased, the exposed portion potential is increased and the image density (toner adhesion amount) is increased. descend. From this relationship, image forming condition correction data (correction table) similar to Table 1 in which the exposure amount change amount (correction amount) is associated with the image density difference may be created and stored in advance. In this case, the exposure amount is changed and determined according to the image forming condition correction data.

  Further, a plurality of image forming conditions such as the charging potential, the developing potential (developing bias), and the exposure amount may be corrected in combination. For example, depending on the image forming apparatus, the background potential or the exposure portion potential, which is the difference between the charging potential and the developing potential (developing bias), is set to an arbitrary value for the purpose of dealing with an afterimage or abnormal image of the output image (printed image). You may want to In this case, first, the change amount (correction amount) of the image density difference and the development potential is determined in advance based on experiments as shown in Table 1. Thereafter, the value obtained by adding the developing potential to the exposed portion potential may be set as the developing potential, and the value obtained by adding the background potential to the developing potential may be set as the charging potential, and may be determined by adjusting the image forming conditions.

  Further, when the image forming apparatus using the two-component developer including toner and carrier in the developing device 14 has a toner concentration control method, the detection result of the toner concentration of the developer or the toner concentration target value is changed. Thus, the image forming conditions may be changed. For example, the image forming condition correction data (correction table) as shown in Table 1 in which the image density difference and the change amount of the toner density target value are associated in advance is provided, and the toner is set according to the image forming condition correction data (correction table). The density target value may be changed and determined.

  FIG. 11 is a diagram illustrating another example of the reference density image in the density correction control in the image forming apparatus according to the embodiment. If the density information of the reference density image is obtained, the line sensor 41 may be used as the image density sensor as shown in FIG. Further, the reference density image 220 may be created outside the area in the main scanning direction as shown in FIG. 10 as long as it is outside the area of the output image (printed image) 200 by the user, or sub-scanning as shown in FIG. It may be created outside the direction area. Note that the measurement pattern creation position is the same even when a measurement pattern described later is a gradation correction pattern image. Hereinafter, an example in which a measurement pattern is created outside an area in the main scanning direction will be described.

FIG. 12 is a diagram illustrating an example of the gradation pattern image and the reference density image in the gradation correction control of the image forming apparatus according to the embodiment.
At the detection timing of the gradation pattern image in the gradation correction control, for example, a measurement pattern including a gradation pattern image 210 and a reference density image (maximum density image) 215 as shown in FIG. 12 is created. The gradation pattern image 210 is formed so as to have a plurality of different gradation (density) image portions so that the relationship between the document density and the print density shown in the graph on the right side in FIG. It is desirable to do. Although FIG. 12 shows an example of the gradation pattern image 210 having three gradation (density) image portions, the number of a plurality of gradation (density) image portions included in the gradation pattern image 210 is increased. Thus, calculation of gradation correction information, which is a gradation image forming condition, can be performed with higher accuracy. On the other hand, when the number of a plurality of gradation (density) image parts included in the gradation pattern image 210 is increased, the amount of toner consumed for forming the gradation pattern image 210 increases, or the time required for measuring the density of the gradation pattern image 210 is increased. Is necessary. Therefore, the number of gradation (density) image parts included in the gradation pattern image 210 may be determined in consideration of the balance between the document density and the accuracy of the relationship between the print density.

  The reference density image (maximum density image) 215 formed together with the gradation pattern image 210 in the gradation correction control is created with the same maximum density as the reference density image (maximum density image) 220 used in the above-described density correction control. It is a pattern.

  The densities of the gradation pattern image 210 and the reference density image (maximum density image) 215 are detected by the image density sensor 40, respectively.

  The gradation pattern image 210 may have only one gradation (density) image portion and one reference density image (maximum density image) 215. However, in consideration of variations in the main scanning direction and measurement errors, more In order to obtain an accurate value, a plurality of values may be created and the average value may be used. Further, as shown in FIG. 20 described later, an area that can be used for density measurement of gradation correction control is extracted from the area of the output image (printed image) by the user, and the density detection result (measured value) of the area is extracted. ) May be used.

  FIG. 13 is a diagram illustrating an example of determination of gradation correction information using the density detection result of the gradation pattern image. When the detection of the density of the gradation pattern image 210 is completed, the gradation (area ratio) and the image as shown in FIG. 13 based on the detection result (in the example shown, the detection result of the density at four measurement points). Get the relationship with concentration.

  When measurement is performed using a user output image (print image) as shown in FIG. 20 described later, the area ratio of the measurement region in the output image (print image) depends on the output image (print image). For this reason, an image with an arbitrary area ratio cannot be measured. However, also in this case, as shown in FIG. 13, based on the detection result of the density in the measurement region in the output image (printed image), the density value at each area ratio is calculated as the predicted value, and the predicted value is Gradation correction may be performed based on this. As a calculation method of the predicted value, for example, it may be calculated by using a quadratic approximation based on the density value at the measurement point. Of course, other approximations such as a first-order approximation or a third-order approximation may be used in consideration of the characteristics of the apparatus and calculation load.

  After reflecting the determined gradation correction information, the output gradation corresponding to the original density (in order to obtain the image density specified in each part of the original density (input image) using the relationship of the gradation correction information ( If the area ratio is determined, a desired concentration can be obtained.

  FIG. 14 is a diagram for explaining an example of the reflection of the target maximum density image at the timing of reflecting the gradation correction information. After detecting the densities of the gradation pattern image and the maximum density image at the detection timing (measurement timing) of the measurement pattern for gradation correction control, the gradation correction information is calculated and determined. The calculation of the gradation correction information requires a calculation time compared to the case of the density correction in which the image forming condition is determined based on the detection result of the maximum density image described above. Therefore, in general, there is a certain time difference between the detection timing (measurement timing) of the measurement pattern for gradation correction control and the reflection timing of the gradation correction information determined by the above calculation.

  In the gradation correction control of the present embodiment, at the reflection timing of gradation correction information, the target maximum density in the image forming apparatus is changed to the measured maximum density that is the detection result of the maximum density image formed together with the gradation pattern image. Thereby, after the reflection timing of the gradation correction information, the target maximum density coincides with the maximum density of the measurement pattern detection timing (measurement timing) of the gradation correction control. Therefore, the gradation correction information determined by calculation can be maintained in an optimum state, and the overall image quality in the multi-tone output image can be stabilized.

  A correction table in which the amount of change in the density of the maximum density image is associated with the amount of change in the imaging condition of the maximum density image is stored in advance, and the maximum density image according to the correction table at the reflection timing of the gradation correction information. The image forming conditions may be changed. In this case, since the imaging condition of the maximum density image changes without waiting for the timing of density correction control using the detection result of the next maximum density image, the effect of stabilizing the image quality by changing the target maximum density is further improved. It can be reflected quickly.

  FIG. 15 is a diagram illustrating another example of reflecting the target maximum density image at the timing of reflecting the gradation correction information. In this example, the target maximum density is changed using an average value obtained by averaging a plurality of detection results (measured values) of the maximum density. When a certain time is required at the measurement timing for detecting the gradation pattern image 210 or calculating the gradation correction information, the maximum density of the maximum density image 215 may be detected and measured a plurality of times during the measurement timing. . Then, the target maximum density may be changed to an average value obtained by averaging the measurement values of the plurality of maximum densities.

  When it is necessary to reduce the calculation load in the control unit, the maximum measurement image density of the maximum density image 215 at the start of the measurement timing or at the end of the measurement, or the maximum density image at any point between the measurement timings. The target maximum density may be changed to the measured maximum density of 215.

  FIG. 16 is a diagram illustrating still another example of reflection of the target maximum density image at the timing of reflecting the gradation correction information. In this example, the target maximum density is changed using an average value obtained by averaging a plurality of maximum density detection results (measured values) including detection results in the latest past gradation correction control. When the gradation correction control for changing the gradation correction information based on the measurement pattern detection result is performed a plurality of times, the average value of the maximum measured density of the maximum density image 215 at the time of the previous and current measurement pattern detection is calculated. The average value may be set to the target maximum density of this time. In this case, the influence of measurement error can be reduced.

  Although FIG. 16 shows an example in which the average value of the maximum measured density of the maximum density image 215 at the time of detection of the previous and current measurement patterns is used, the present invention is not limited to this example. For example, an average value of the measured maximum density of the maximum density image 215 at each of the past detection times of arbitrary number of times (two or more times) may be used. In addition, the average value of the maximum measured density of the maximum density image 215 at the time of detection of the measurement pattern at an arbitrary number of times (two times or more) and at the time of detection of the current measurement pattern may be used.

Furthermore, it is also possible to weight the measured value of the density of the maximum density image 215 in any past number of times, calculate an average value after the weighting, and set the average value as the target maximum density. For example, when weighting is performed as shown in Table 2, the average value of the following equation (1) may be calculated, and the average value may be set as the target maximum density.
(A + 2 × b + 3 × c + 4 × d + 5 × e) / 15 (1)

  FIG. 17 is a graph illustrating an example of a method for setting the image forming condition of the maximum density image. In this example, instead of the above-described correction table, the image density (toner adhesion amount) is different from each other on the intermediate transfer belt 20 at a predetermined timing different from the gradation correction control and the maximum density control. A plurality of density detection patterns are created under a potential condition. Then, the image density (toner adhesion amount) of the plurality of density detection patterns is detected, and the relationship between the detection result (measured value) of the plurality of image densities (toner adhesion amount) and the potential condition is calculated. Using this relationship, an image forming condition (development potential in the example of FIG. 17) for obtaining a target adhesion amount (target density) as shown in FIG. 17 is calculated, and a predetermined value is used using the calculated image forming condition. The image forming conditions at the reflection timing may be changed.

  FIG. 18 is a diagram illustrating another example of the gradation pattern image and the reference density image in the gradation correction control of the image forming apparatus according to the embodiment. In this example, since the actual maximum density always fluctuates during the formation of the output image (during printing), in order to obtain a more accurate value, the maximum density image 215 as a reference density image is obtained as shown in FIG. Are created before and after the gradation pattern image 210 in the moving direction of the intermediate transfer belt. Then, an average value of density detection results (measured values) of a total of four maximum density images 215 before and after the gradation pattern image 210 is calculated, and the average value is set as a target maximum density.

  FIG. 19 is a diagram illustrating another example of the gradation pattern image and the reference density image in the gradation correction control of the image forming apparatus according to the embodiment. In this example, a pattern whose density continuously changes is used as the gradation pattern image 210. By using such a pattern, a more detailed gradation state can be measured, so that the accuracy of gradation correction information can be increased. However, since the amount of memory and the calculation time are required as the number of concentration measurement points increases, the measurement points are determined in consideration of balance with accuracy.

  FIG. 20 is a diagram illustrating another example of the gradation pattern image and the reference density image in the gradation correction control of the image forming apparatus according to the embodiment. In this example, the user output image (printed image) 200 includes a gradation measurement image area 201 corresponding to the gradation pattern image and a maximum density measurement image area 202 corresponding to the maximum density image. . Then, instead of the gradation pattern image and the maximum density image, the density of the gradation measurement image area 201 and the maximum density measurement image area 202 are measured by the image density sensor (line sensor) 41 in the print image of the user. ing.

  In the case of the example in FIG. 20, the control unit 90 of the image forming apparatus 1 according to the embodiment uses an image information acquisition unit that acquires image information of an output image, and uses it as a reference density image or a gradation pattern image in the output image. It also functions as a region search means for searching for a region that can be used. The area search means searches for all areas of the image indicated by the image information obtained from the image information acquisition means to be set as the colorimetric adaptation area to be a colorimetric target.

  The search for the colorimetric adaptation region is performed as follows, for example. That is, a pixel at a predetermined position in the pixel matrix represented by the image information of the output image is set as a target pixel, and a region having a predetermined size centered on the target pixel is extracted as a partial region. For example, in the first extraction, for example, the pixel in the 21st column and the 21st row from the upper left in the pixel matrix having a resolution of 200 dpi is the pixel of interest, and a pixel of about 41 mm × 41 pixels having a size of about 5 mm square. Extract the region as a partial region. And the flatness which shows the flatness of the light and dark as the whole partial area is calculated, referring the pixel value (C, M, Y, K) of each pixel in the extracted partial area. As the flatness, those obtained by various calculation methods can be used.

  As a first example of flatness, one obtained by the following calculation method can be cited. That is, first, the variance of each pixel is obtained for C, M, Y, and K, respectively. Next, a value obtained by adding a negative sign to the sum of the variances is obtained as the flatness in the partial region.

  Further, examples of the flatness include those utilizing color frequency characteristics. Specifically, the Fourier transform is performed using each pixel value in the partial region, and the sum of the squares of the absolute values of the Fourier coefficients of the specific frequency is obtained. A flatness is obtained by adding a negative sign to this sum. A plurality of frequencies can be used for the specific frequency.

  In the flatness of the first example, there is a case in which a flat region cannot be identified for an image subjected to halftone processing due to the influence of the pattern of halftone processing. On the other hand, in flatness using Fourier transform, flatness excluding the influence of halftone processing can be calculated by using the sum of the squares of the absolute values of the Fourier coefficients of a specific frequency. The calculation of the flatness is not limited to these, and a known flatness calculation technique can be used.

  When the flatness of the extracted partial areas is obtained, it is next determined whether or not all partial areas have been extracted (whether or not extraction of partial areas has been completed for all areas of the image). If it is determined that there is a partial area that has not yet been extracted, the position of the target pixel is shifted by one pixel in the right direction, and an area of about 5 mm square of 41 pixels × 41 pixels centered on it is obtained. Extract as a partial area. Similarly, the flatness of the color of the extracted partial area is calculated. Thereafter, when extracting the third, fourth, fifth,..., Nth partial area, the position of the target pixel is shifted by one pixel to the right. After shifting the position of the pixel of interest in the column direction from the right end of the matrix to the 21st position, the position of the pixel of interest in the column direction is returned from the left end of the matrix to the right to the 21st position. At the same time, the position in the row direction is shifted downward by one pixel. Thereafter, the process of shifting the position of the target pixel to the right by one pixel is repeated. As described above, the position of the target pixel is sequentially shifted like raster scanning to cover the entire area of the image.

  Instead of shifting the target pixel by one pixel, each partial area may be extracted so that the edges of the extracted partial areas do not overlap each other. For example, after extracting a partial region having a size of 41 pixels × 41 pixels centered on the pixel of interest in the 21st column and the 21st row, 41 pixels × centering on the pixel of interest in the 62nd column and the 62nd row A partial region having a size of 41 pixels is extracted.

  When partial areas are extracted from the entire area of the image and the flatness is calculated, it is determined whether or not the flatness of all the partial areas is better than a predetermined reference flatness. If it is excellent, the partial area is set as a colorimetric adaptation area suitable for colorimetry.

  Next, the average density of each partial area that has become the colorimetric adaptation area is calculated from the image information. Then, it is determined whether or not there is a colorimetric region where the density is within a certain range with respect to the density of each of the plurality of gradation image portions in the predetermined gradation pattern image. Only the gradation image portion in which the color measurement area does not exist is created as a gradation pattern image in the non-image area.

  By utilizing the user output image (printed image) in this way, the frequency of creating the measurement pattern (tone pattern image and reference density image) is reduced, so that the amount of toner used for measurement can be reduced.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
Image forming means such as a process unit 10 for forming an image on an image carrier such as the intermediate transfer belt 20, density detecting means such as an image density sensor 40 for detecting the density of the image on the image carrier, and image carrier A reference density image 220 having a predetermined density is formed thereon, the density of the reference density image is detected, and based on the detection result and the target density, image formation such as a charging potential used when an image is formed by the image forming unit The image forming condition changing means such as the control unit 90 for changing the conditions, and the gradation pattern image 210 is formed on the image carrier, the density of the gradation pattern image is detected, and the image formation is performed based on the detection result. When the gradation pattern image 210 is formed in the image forming apparatus 1 including gradation correction information changing means such as the control unit 90 that changes the gradation correction information used when the multi-tone image is formed by the means. Base Forming a density image 215 on an image bearing member, and detects the density of the reference density image and sets the detection result to the target concentration.
Specifically, it has been found that the above problem occurs in the following cases. That is, after changing the image forming conditions based on the detection result of the density of the reference density image and the target density, the state of the image forming apparatus fluctuates due to environmental fluctuations, and the image density at the time of image formation deviates from the target density. May vary. In some cases, a gradation pattern image is formed at a timing when the image density at the time of image formation deviates from the target density, and the gradation correction information is changed based on the detection result of the gradation pattern image. The gradation correction information after the change is changed so that a predetermined gradation is reproduced with the image density of the gradation pattern image deviated from the target density. Therefore, when the image density at the time of image formation changes due to environmental changes or the like thereafter, the tone reproducibility of the multi-tone image formed based on the changed tone correction information may change greatly with time. is there.
In this aspect, when forming a gradation pattern image used for changing gradation correction information, a reference density image is formed, and the detection result of the density of the reference density image is used as a target used for changing the image forming condition. Set to concentration. Thereafter, the image forming condition is changed based on the target density set when the gradation correction information is changed and the detection result of the reference density image. Due to this change in the image forming conditions, the variation in image density during subsequent image formation is centered on the image density during image formation when the gradation correction information is changed so that the predetermined gradation is reproduced. The fluctuation is relatively small. Accordingly, the gradation reproducibility of the multi-tone image formed based on the gradation correction information is changed with a smaller change width than when the target density is not set when changing the gradation correction information. Become. Therefore, it is possible to suppress the change with time of the gradation reproducibility of the multi-tone image.
(Aspect B)
In the above aspect A, the image forming means exposes the charging surface such as the charging roller 12 that charges the surface of the latent image carrier such as the photoreceptor 11 to a predetermined charging potential, and the charged surface of the latent image carrier. The latent image formed on the latent image carrier by the exposure means such as the optical writing device 30 and the like is developed by the developer carried on the developer carrier such as the developing roller 14a to which a predetermined developing bias is applied. The image forming conditions include at least one of a charging potential by the charging unit, an exposure amount by the exposure unit, and a developing bias applied to the developer carrying member.
According to this, as described in the above embodiment, by determining at least one of a charging potential, an exposure amount, and a developing bias having a large influence on the image density as an image forming condition, the image density can be more reliably increased. The target concentration can be accurately controlled.
(Aspect C)
In the above aspect A or B, the image forming means includes a charging means for charging the surface of the image carrier to a predetermined charging potential, an exposure means for exposing the charged surface of the image carrier, and an image carrier by exposure. A developing means for developing a latent image formed on the body with a developer including a toner and a carrier carried on a developer carrying body to which a predetermined developing bias is applied, and controlling a toner density of the developer in the developing means Toner density control means such as a control unit 90, and the image forming conditions include a target value of toner density in the toner density control means.
According to this, as described in the above embodiment, the image density is controlled to the target density more reliably and accurately by determining the target value of the toner density having a large influence on the image density as the image forming condition. it can.
(Aspect D)
In any one of the above aspects A to C, the reference density image is a maximum density image.
According to this, as described in the above embodiment, the image density at the time of image formation is determined by determining the image formation condition based on the density detection result of the maximum density image having a large density change with respect to the change in the image formation condition. Can be controlled to a target concentration with higher accuracy.
(Aspect E)
In any one of the above aspects A to D, the density correction control unit controls the image forming unit to form a plurality of reference density images, and calculates an average value of the density detection results of each of the plurality of reference density images. The image forming conditions are changed based on the average value and the target density.
According to this, as described in the above embodiment, the influence on the detection result of the density of the reference density image due to the variation in the detection of the reference density image by the density detection means and the variation in the position of the reference density image on the image carrier. Can be reduced.
(Aspect F)
In any one of the aspects A to D, the target density setting unit calculates an average value of a plurality of detected densities of the density of the reference density image detected within the time when the density of the gradation pattern image is detected. The average value is set as the target density.
According to this, as described in the above embodiment, the influence on the detection result of the density of the reference density image due to the variation in the detection of the reference density image by the density detection means and the variation in the position of the reference density image on the image carrier. Can be reduced.
(Aspect G)
In any one of the aspects A to D, the target density setting unit calculates an average value of the density detection result of the reference density image and the density detection result of one or more reference density images in the past, and Set the average value to the target density.
According to this, as described in the above embodiment, the influence on the detection result of the density of the reference density image due to the variation in the detection of the reference density image by the density detection means and the variation in the position of the reference density image on the image carrier. Can be reduced.
(Aspect H)
In any one of the above aspects A to G, the density correction control means includes image formation condition correction data created in advance in association with a density change amount of a reference density image and a correction amount of an image formation condition, and a reference The image forming condition is changed based on the density detection result of the density image.
According to this, as described in the above embodiment, by using the image forming condition correction data, the image forming condition changing process based on the detection result of the density of the reference density image is simplified. Can be quickly controlled to the desired concentration.
(Aspect I)
In any of the above aspects A to H, the maximum information that can be used as the reference density image or the gradation pattern image in the image information acquisition means such as the control unit 90 that acquires the image information of the output image and the output image 200. An area search means such as a control unit 90 for searching for an area such as a density measurement image area 202 or a gradation measurement image area 201, and an area that can be used as a reference density image or a gradation pattern image in an output image Is present, the density of the region is detected as the density of the reference density image or the gradation pattern image and used for control.
According to this, as described in the above embodiment, the image forming conditions or the gradation correction information can be determined and changed without separately forming the reference density image or the gradation pattern image on the image carrier.
(Aspect J)
In any of the above aspects A to I, the tone correction control unit includes a calculation unit such as a control unit 90 that calculates a density predicted value corresponding to each tone based on the density detection result of the tone pattern image. The tone characteristic obtained from the density predicted value corresponding to each tone calculated by the calculating means determines the tone correction information based on the target tone characteristic.
According to this, as described in the above embodiment, the number of gradations in the gradation pattern image can be reduced.

1 Image forming apparatus 10 (10Y, 10C, 10M, 10K) Process unit (image forming unit)
11 (11Y, 11C, 11M, 11K) Photoconductor 12 Charging roller 13
DESCRIPTION OF SYMBOLS 14 Developing device 14a Developing roller 14b Toner density sensor 15 (15Y, 15C, 15M, 15K) Primary transfer charger 16 Photoconductor cleaning device 20 Intermediate transfer belt 30 Optical writing device (optical scanning device)
40 Image density sensor 41 Image density sensor (line sensor)
90 Control unit 100 Image forming unit 200 Output image (user print image)
201 gradation measurement image area 202 maximum density measurement image area 210 gradation pattern image 215 reference density image (maximum density image)
220 Reference density image (maximum density image)

JP 2011-164240 A JP 2012-165296 A

Claims (10)

An image forming means for forming an image on the image carrier;
Density detecting means for detecting the density of the image on the image carrier;
An image used when a reference density image having a predetermined density is formed on the image carrier, the density of the reference density image is detected, and the image forming unit forms an image based on the detection result and the target density. Image forming condition changing means for changing the forming conditions;
Gradation correction used when a gradation pattern image is formed on the image carrier, the density of the gradation pattern image is detected, and a multi-gradation image is formed by the image forming unit based on the detection result. In an image forming apparatus comprising gradation correction information changing means for changing information,
An image characterized in that when forming the gradation pattern image, the reference density image is formed on the image carrier, the density of the reference density image is detected, and the detection result is set to the target density. Forming equipment. The image forming apparatus according to claim 1.
The image forming means includes a charging means for charging the surface of the latent image carrier to a predetermined charging potential, an exposure means for exposing the charged surface of the latent image carrier, and the latent image carrier by the exposure. And developing means for developing the latent image formed on the developer carrier carried on the developer carrier to which a predetermined development bias is applied,
The image forming apparatus includes at least one of a charging potential by the charging unit, an exposure amount by the exposure unit, and a developing bias applied to the developer carrying member. The image forming apparatus according to claim 1 or 2,
The image forming unit is formed on the image carrier by charging, a charging unit that charges the surface of the image carrier to a predetermined charging potential, an exposure unit that exposes a charged surface of the image carrier, and the exposure. Developing means for developing the latent image with a developer including a toner and a carrier carried on a developer carrying body to which a predetermined developing bias is applied;
Toner density control means for controlling the toner density of the developer in the developing means,
The image forming apparatus, wherein the image forming condition includes a target value of toner density in the toner density control means. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the reference density image is a maximum density image. The image forming apparatus according to claim 1,
The image forming condition changing unit controls the image forming unit to form a plurality of the reference density images, calculates an average value of the density detection results of each of the plurality of reference density images, and calculates the average value and the An image forming apparatus, wherein the image forming condition is determined based on a target density. The image forming apparatus according to claim 1,
The target density setting means calculates an average value of a plurality of detection results of the density of the reference density image detected within a time when the density of the gradation pattern image is detected, and the average value is calculated as the target value. An image forming apparatus characterized in that the density is set. The image forming apparatus according to claim 1,
The target density setting means calculates an average value of the density detection result of the reference density image and the density detection result of one or more of the reference density images in the past, and uses the average value as the target density. An image forming apparatus comprising: setting. The image forming apparatus according to claim 1,
The image forming condition changing unit detects the density of the reference density image and the image forming condition correction data created in advance by associating the change amount of the density of the reference density image with the correction amount of the image forming condition. An image forming apparatus, wherein the image forming condition is determined based on a result. The image forming apparatus according to claim 1,
Image information acquisition means for acquiring image information of the output image;
A region search means for searching a region that can be used as the reference density image or the gradation pattern image in the output image;
When there is a region that can be used as the reference density image or the gradation pattern image in the output image, the density of the region is detected as the density of the reference density image or the gradation pattern image. An image forming apparatus used for control. The image forming apparatus according to claim 1,
A calculation means for calculating a predicted density value corresponding to each gradation based on the detection result of the density of the gradation pattern image;
The image forming apparatus according to claim 1, wherein the gradation correction information changing unit determines the gradation correction information based on a gradation characteristic obtained from a density prediction value corresponding to each gradation calculated by the calculation unit.