JP6745062B2 - Image forming device - Google Patents

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, the image forming conditions such as the charging potential during image formation are changed based on the detection result of the reference density image of a predetermined density formed on the image carrier and the target density. Further, the gradation correction information used when forming the multi-gradation image is changed based on the detection result of the gradation pattern image of a plurality of gradations formed on the image carrier.

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

When the image forming condition is changed based on the density detection result of the reference density image and the gradation correction information is changed based on the density detection result of the gradation pattern image, the gradation reproducibility of the multi-tone image changes with time. It turned out that there is a possibility that it will change drastically.

In order to solve the above problems, the present invention provides an image forming unit that forms an image on an image carrier, a density detecting unit that detects the density of an image on the image carrier, and a predetermined unit on the image carrier. Image formation in which a reference density image of the density is formed, the density of the reference density image is detected, and the image forming condition used when forming an image by the image forming means is changed based on the detection result and the target density. Condition changing means and a gradation pattern image is formed on the image carrier, the density of the gradation pattern image is detected, and the image forming means forms a multi-gradation image based on the detection result. an image forming apparatus comprising: a gradation correction information changing means, the changing the gradation correction information used for a grayscale pattern image when forming the gradation pattern images to be used for changing the gradation correction information The different reference density image is formed on the image carrier, the density of the reference density image is detected, the detection result is set to the target density, and the image formation is performed after the detection timing of the gradation pattern image. At the timing of changing the condition, the reference density image is formed on the image carrier, the density of the reference density image is detected, and the image forming condition is set so that the detection result becomes the set target density. It is characterized by changing .

According to the present invention, it is possible to change the image forming condition based on the density detection result of the reference density image and the gradation correction information based on the density detection result of the gradation pattern image. It is possible to suppress a change in tonality reproducibility with time.

1 is a schematic configuration diagram showing an example of an image forming apparatus according to an embodiment. FIG. 3 is a schematic configuration diagram showing an example of a process unit in the image forming apparatus according to the embodiment. FIG. 4 is a diagram showing a relationship between a charging potential and an exposure portion potential of a photoconductor and a developing potential (developing bias) of a developing roller in the image forming apparatus according to the exemplary embodiment. FIG. 3 is a block diagram showing an example of a main configuration of a control system of the image forming apparatus according to the present embodiment. 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. FIG. FIG. 4 is a diagram showing an example of a relationship between a gradation pattern image (measurement test pattern) and gradation reproducibility. FIG. 4 is a diagram showing an example of a gradation pattern image (measurement test pattern) formed on the intermediate transfer belt. The figure which shows an example of the time-dependent change of image density. 6 is a flowchart showing an example of density correction control and gradation correction control in the image forming apparatus according to the embodiment. FIG. 6 is a diagram showing an example of a reference density image in density correction control in the image forming apparatus according to the embodiment. FIG. 6 is a diagram showing 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 showing 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. FIG. 8 is a diagram showing an example of determination of gradation correction information using the detection result of the density of a gradation pattern image. FIG. 6 is a diagram illustrating an example of reflection of a target maximum density image at a timing of reflecting gradation correction information. FIG. 8 is a diagram illustrating another example of reflecting the target maximum density image at the timing of reflecting the gradation correction information. The figure explaining another example of reflection of a target maximum density image in the timing which reflects gradation amendment information. 6 is a graph showing an example of a method of setting an image forming condition for a maximum density image. FIG. 6 is a diagram showing another example of a gradation pattern image and a reference density image in gradation correction control of the image forming apparatus according to the embodiment. FIG. 6 is a diagram showing another example of a gradation pattern image and a reference density image in gradation correction control of the image forming apparatus according to the embodiment. FIG. 6 is a diagram showing another example of a gradation pattern image and a reference density image in gradation correction control of the image forming apparatus according to the embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to an embodiment. The image forming apparatus 1 of the present embodiment includes process units (image forming units) 10Y, 10C, 10M, 10K as a plurality of 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 exposing unit used for forming a latent image in each process unit, and an image as a density detecting unit for detecting the density of an image for various measurements. A density sensor 40 and a paper feeding device 50 for feeding a 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 the image on the intermediate transfer belt 20 to the sheet P, and a fixing unit that fixes the image transferred to the sheet P with heat and pressure. And a fixing device 70 including 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 (original document feeder) as a document feeding 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 is configured by using the process units 10Y, 10C, 10M, 10K and the optical writing device 30.

The intermediate transfer belt 20 is stretched by a plurality of rollers 21 to 24 and arranged in the transfer unit. The plurality of rollers are composed of a drive roller 24, driven rollers 22, 23, a secondary transfer backup roller 21, etc., which are rotationally driven by a motor or 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 having a small elongation. The intermediate transfer belt 20 is stretched by the drive roller 24, the secondary transfer backup roller 21, and the driven rollers 22 and 23, and is endlessly moved by the rotation of the drive roller 24. 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 of the respective colors are arranged side by side at predetermined intervals along the moving direction of the lower tension portion of the intermediate transfer belt 20 in the figure. A primary transfer charger 15Y as a primary transfer unit is provided 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 are provided. The primary transfer chargers 15Y, 15C, 15M and 15K are yellow (Y), cyan (C), magenta (M) and black (K) toner images formed on the photoconductors 11Y, 11C, 11M and 11K, respectively. Is used to transfer the image onto the intermediate transfer belt 20.

FIG. 2 is a schematic configuration diagram showing 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, the subscripts (Y, C, M, K) for distinguishing the toner colors are added to the reference numerals of the respective members in FIG. Don't explain.

In the process unit 10 of FIG. 2, the photoconductor 11 is charged by the charging roller 12 as a charging unit, and then the light L from the optical writing device (optical scanning device) 30 is applied to the photoconductor 11 via the mirror 13. (Exposure), and a latent image is formed on the photoconductor 11. The optical writing device (optical scanning device) 30 drives semiconductor lasers (LDs) as four light sources by, for example, a laser controller based on image information such as an input image to be output, and outputs four writing lights. Emit.

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, an optical lens, and the like. In the optical writing device (optical scanning device) 30 having this configuration, the laser light emitted from the semiconductor laser is deflected by the optical deflector, and is reflected by the reflection mirror or passed through the optical lens. Optical scanning is performed. Further, as the optical writing device (optical scanning device) 30, a device that performs optical scanning by an LED array as a light source may be used instead of the one having such a configuration.

The latent image formed on the photoconductor 11 is developed as a toner image on the photoconductor 11 via a developing roller 14a as a developer bearing member of a developing device 14 having a developer such as toner, and the primary transfer portion N 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 the cleaning blade 16 a of the photoconductor cleaning device 16. 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, and when the toner concentration becomes lower than a predetermined threshold value, for example. , Toner is replenished from the toner container.

A toner image formed on each of the photoconductors 11Y, 11C, 11M, and 11K of the process units 10Y, 10C, 10M, and 10K of each color can be transferred onto the intermediate transfer belt 20 in an overlapping manner to form a full-color image. .. The full-color image on the intermediate transfer belt 20 is transferred to the sheet P supplied from the sheet feeding device 50 at the secondary transfer portion where the secondary transfer roller 60 faces the sheet, and then fixed by the fixing device 70 (FIG. 1). reference).

Further, in the image forming apparatus 1 of the present embodiment, when performing the density correction control and the gradation characteristic correction control, the reference density image and the floor for measurement are measured on the intermediate transfer belt 20 by the process units 10Y, 10C, 10M, and 10K. A tonal pattern image is formed. The density (toner adhesion amount) of the reference density image and the gradation pattern image on the intermediate transfer belt 20 is arranged so as to face the outer peripheral surface of the intermediate transfer belt 20 on the downstream side in the belt moving direction of the black process unit 10K. It is detected by the image density sensor 40. The image density sensor 40 can be composed of, for example, a reflection type optical sensor having a light emitting element and a light receiving element. When detecting the image density in the entire widthwise direction of the intermediate transfer belt 20, a line sensor or an area sensor in which image pickup devices such as CCD and 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 of the present embodiment uses an image forming apparatus using a two-color developing device and a toner such as white or transparent toner. It may be an image forming apparatus using a developing device for 5 colors to which is added.

FIG. 3 is a diagram showing 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 called “charging potential”, and the potential on the photoconductor 11 after exposure is called “exposure portion potential”. Further, 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 exposed portion potential is referred to as "developing potential". The toner has a charge amount according to the agent state and 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 of the developing potential. To do. Therefore, the amount of toner attached to the photoconductor 11 changes depending on the amount of toner charge and the development potential.

FIG. 4 is a block diagram showing an example of the main configuration of the control system of the image forming apparatus 1 according to this embodiment. The image forming apparatus 1 includes a control unit 90 configured by a computer device such as a microcomputer. The control unit 90 cooperates with other units in the image forming apparatus 1 and functions as the following units.
An image forming condition for forming a reference density image on the intermediate transfer belt 20, detecting the density of the reference density image, and forming an image by the image forming means based on the detection result and the target density (hereinafter, Image forming condition changing means for determining and changing "image forming condition".
Gradation correction used when a gradation pattern image is formed on the intermediate transfer belt 20, the density of the gradation pattern image is detected, and based on the detection result, a multi-gradation image is formed by the image forming means. Gradation 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.
A 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, it is provided with a ROM (Read Only Memory) 903 and a RAM (Random Access Memory) 904 as storage means connected to the CPU 901 via a bus line 902, and an I/O interface section 905. The CPU 901 executes various calculations and drive control of each unit by executing a control program which is a computer program installed in advance. The ROM 903 stores fixed data such as computer programs and control data in advance. The RAM 904 functions as a work area or the like that rewritably stores various data.

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

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

Further, the paper 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 a control target value of image forming conditions (for example, charging bias, developing bias, exposure amount, primary transfer bias, etc.).

The ROM 903 or the RAM 904 stores, for example, a conversion table that stores information related to conversion of the output value of the image density sensor 40 into image density (toner adhesion amount per unit area). Further, 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 the process units of each color in the image forming apparatus 1. Further, in the ROM 903 or the RAM 904, gradation correction information (gradation 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 an IC or the like 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 non-volatile memory and/or the volatile memory included in the control unit 90, but also in another storage medium. For example, the image forming program is a semiconductor medium (eg, RAM, nonvolatile memory, etc.), optical medium (eg, DVD, MO, MD, CD-R, etc.), magnetic medium (eg, hard disk, magnetic tape, flexible disk, etc.). ), and can be stored in other storage media. When the image forming program is stored, the memory and other storage medium constitute a computer-readable recording medium that stores the image forming program.

FIG. 5 is a block diagram showing an example of the flow of an image data processing method in the image forming apparatus 1 according to the embodiment.
First, the image data that has passed through the printer driver from the application software on the 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, it is interpreted by the rasterization processing unit 101 to form a raster image. At this time, a signal indicating the type or attribute of, for example, a character/line, a photograph, or a graphics image is generated for each object. Then, 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. The input/output characteristic correction unit 102 uses the output of the image density sensor 40 from the density sensor output unit 110 and exchanges information with the storage unit 106 including a non-volatile memory and a volatile memory. The input/output characteristic correction signal is formed and the correction operation is performed. 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 the optimum filter for each attribute in accordance with the attribute signal sent from the rasterization processing unit 101, and performs emphasis processing. Since the MTF filter processing is the same as the conventional technique, detailed description will be omitted. The image data after the MTF filter processing is delivered to the color/gradation 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 the color correction, the 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 the color space formed by the toner colors used in the image forming unit 100 such as the process unit 10, is performed. To do. This color correction is performed by using the optimum color correction coefficient for each attribute in accordance with the attribute signal sent from the rasterization processing unit. In the gradation correction, gradation correction processing is performed to correct the image data of the multi-gradation image to be output, based on the gradation characteristic data created using the gradation correction pattern described below. As described above, the color/gradation correction processing unit 104 functions as a gradation correction unit that corrects the image data of the multi-tone image to be output based on the gradation characteristic data. As the color/gradation correction process, the same process as the conventional technique can be adopted, and therefore 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, the pseudo halftone process is performed on the data that has been subjected to the color/gradation correction process by the dither method. That is, quantization is performed by performing comparison and reference with 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 drive unit 109 outputs an LD drive 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 generation unit 108.

Next, problems to be solved by the image forming apparatus according to the embodiment will be described.
FIG. 6 is a diagram showing an example of a relationship between a gradation pattern image (measurement test pattern) and gradation reproducibility in the conventional method. In a general electrophotographic image forming apparatus, in order to achieve an ideal relationship between the original density and the print density (gradation reproducibility), the steps in the gradation range used for forming the multi-tone output image The gradation correction information indicating the relationship between the tonality value and the image density is set. This is because the relationship between image forming conditions (charge potential, developing bias, exposure amount, etc.) and print density (density of output image) does not have a simple linear shape. For example, in the density gradation method, the relationship between the original density and the potential is set, and in the area gradation method, the relationship between the original density and the image processing pattern is set so that ideal gradation reproducibility is obtained. It

However, due to environmental conditions such as temperature and humidity and the degree of deterioration of the developer, even if the gradation correction information is set in advance so that ideal gradation reproducibility is obtained, the 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 predetermined test pattern for measurement is created at a predetermined timing, this is measured by a color measuring device, and the gradation correction information is corrected based on the measurement result. ing. However, with this method, it is necessary to stop the printing of the print image by the user at every predetermined timing, which causes a waiting time for the user, which 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 a region other than the print area of the intermediate transfer belt 20' during printing of the print image by the user. Then, the density of the measurement test pattern 210' is measured using the image density sensor 40' which is an optical sensor attached to the image forming apparatus, and the gradation correction information is corrected based on the measurement result. Further, when a measurable area exists in the print image of the user, a method of correcting the gradation correction information based on the measurement result of the density of the area is also known. (For example, refer to Patent Document 2).

By the method shown in FIG. 7 and the method of Patent Document 2, it is possible to prevent deterioration of productivity and maintain the gradation reproducibility. However, these conventional methods have the following problems.

FIG. 8 is a diagram showing an example of a temporal change in image density in the conventional method. The gradation reproducibility is changed not only by the influence of the gradation correction information but also by the conditions such as the charge amount of the developer, the toner concentration, the exposure amount at the time of latent image formation, and the developing potential (developing bias). Therefore, if the maximum density of the image forming apparatus changes, the gradation reproducibility also changes. Here, the maximum density refers to the print density (the density of the output image) when the document density is the maximum value. Generally, in an image forming apparatus, image forming conditions are set so that a certain reference density image maintains a constant target density even if 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. When a non-maximum density image is used as the reference density image, for example, when a reflective optical sensor is used to detect (measure) the density of the reference density image, there is a case where the sensitivity to the density variation is not sufficient near the maximum density image. This is because there is a reason such as.

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

At the measurement timing of the gradation pattern image (measurement test pattern), if the density of the reference density image is in a condition deviating from the target density, the calculated gradation curve is affected by the density deviation. Becomes Therefore, if the gradation curve is corrected based on the measurement data of the gradation pattern image at this time, it will not be optimized when 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 showing an example of the density correction control and the gradation correction control in the image forming apparatus according to the embodiment.
In FIG. 9, when the image forming apparatus 1 starts printing (S11), first, it is determined whether it is the gradation correction information reflection timing (S12). (In Yes S12) the gradation correction information reflecting the timing der Ru case, together with the to reflect the image forming condition of the determined density correction to reflect the already determined gradation correction information (S13, S14).

On the other hand, (No in S12) if not the gradation correction information reflecting timing, determines whether the detection timing of the next gradation pattern image picture (S15). When a detection timing of the gradation pattern images image (Yes in S15) forms a gradation pattern image and the reference density image on the intermediate transfer belt 20, to detect the density of each image (S16). Then, the detection result of the reference density image is set to the target density, and the gradation correction information is determined based on the detection result of the gradation pattern image (S17, S18).

If not detected timing of the gradation pattern images image (No in S15), it is determined whether the density correction timing of a 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, the density is detected, 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 the printing is completed (S22).

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

Incidentally, the density correction timing detection timing and the reference density image gradation pattern image picture, to the extent possible calculation process may respectively be set arbitrarily. For example, the reference density correction timing of density images printed every 10 sheets, detection timing is printed 100 sheets each gradation pattern image picture, may be set based on the number of printed sheets as such, the time from start of printing It may be set as a reference.

The gradation correction information reflecting the timing may be set at a timing gradation correction information is calculated based on the detection result detected by the detection timing of the gradation pattern images. Further, the gradation correction information reflection timing may be set in advance after the time required for calculating the gradation correction information is calculated from the measurement, and thereafter.

FIG. 10 is a diagram showing an example of the reference density image in the density correction control in the image forming apparatus according to the embodiment.
In the density correction of the reference density image, first, the reference density image 220 as a measurement pattern is created outside the area of the print image 200 which 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.

Further, although FIG. 10 shows an example in which the reference density image for one color is created, in the case of the image forming apparatus having the process unit 10 for each of a plurality of colors, the reference density images for a plurality of colors are created simultaneously. Good. Further, the reference density images of a plurality of colors may be created at different timings. For example, the first-color reference density image may be formed at the print timing of the first sheet, and the second-color reference density image may be formed at the print timing of the second sheet. The formation of the reference density image in the case of such a plurality of colors is the same for the gradation pattern image in the gradation correction control, which will be described later, and the reference density image formed together with the gradation pattern image.

The reference density image formed on the intermediate transfer belt 20 is measured by the image density sensor 40. Then, based on the measured maximum density that 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 that are image forming conditions is adjusted and determined. For example, based on the difference between the measured maximum density and a predetermined target density (in this example, the target maximum density), at least one of the charging potential, the exposure amount, and the development potential, which are image forming conditions, is adjusted and determined. The initial value of the target density is determined in advance, and then the measured maximum 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 conditions corresponds to, for example, the image density difference (adhesion amount difference), which is the difference between the measured maximum density and the target maximum density, and the change amount (correction amount) of the image forming conditions such as charging potential. It is also possible to use the image forming condition correction data that has been created in advance and stored in the control unit. In this case, it is decided to change the image forming conditions such as the charging potential according to the image forming 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, when the charging potential of the photoconductor 11 is increased, the exposed portion potential is also increased and the development 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 increased. From this relationship, the difference between the change amount (correction amount) of the charging potential of the photoconductor 11 and the thresholds 1 to 4 of the image density (toner adhesion amount) of the reference density image (hereinafter referred to as “image density difference”). The 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) in an experiment.

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

Similarly, when the exposure amount is increased, the potential of the exposed portion is decreased and the development potential is increased, so that the image density (toner adhesion amount) is increased, and when the exposure amount is decreased, the exposed portion potential is increased and the image density (toner adhesion amount) is increased. descend. Based on this relationship, image forming condition correction data (correction table) similar to Table 1 in which the amount of change in exposure amount (correction amount) and the difference in image density are associated 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 combined and corrected. For example, depending on the image forming apparatus, the background potential or the exposed 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 taking measures against afterimages of the output image (printed image) and abnormal images. 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 as shown in Table 1 based on experiments and the like. After that, the value obtained by adding the development potential to the exposed portion potential may be set as the development potential, and the value obtained by adding the background potential to the development potential may be set as the charging potential, and the image forming conditions may be adjusted and determined.

Further, when the image forming apparatus using the two-component developer containing the toner and the carrier in the developing device 14 has the toner concentration control method, the detection result of the toner concentration of the developer or the toner concentration target value is changed. Therefore, the image forming condition 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 with each other is stored in advance, and the toner is corrected according to the image forming condition correction data (correction table). The density target value may be changed and determined.

FIG. 11 is a diagram showing 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 except for the area of the output image (print image) 200 by the user, or as shown in FIG. It may be created outside the area of the direction. Note that the creation position of such a measurement pattern is the same even when the measurement pattern described later is a gradation correction pattern image. Hereinafter, an example in which the measurement pattern is created outside the area in the main scanning direction will be described.

FIG. 12 is a diagram showing an example of a gradation pattern image and a 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 the gradation pattern image 210 and the reference density image (maximum density image) 215 as shown in FIG. 12 is created. The gradation pattern image 210 is formed to have image portions of a plurality of gradations (density) different from each other so that the relationship between the document density and the print density shown in the graph on the right side of FIG. It is desirable to do. Although FIG. 12 shows an example of the gradation pattern image 210 having an image portion with three gradations (density), increasing the number of a plurality of gradation (density) image portions included in the gradation pattern image 210. Thus, it is possible to more accurately calculate the gradation correction information that is the gradation image formation condition. On the other hand, when the number of a plurality of gradation (density) image portions included in the gradation pattern image 210 is increased, the toner consumption amount used for forming the gradation pattern image 210 increases, and it takes time to measure the density of the gradation pattern image 210. Will be required. Therefore, the number of gradation (density) image portions included in the gradation pattern image 210 may be determined in consideration of the balance between the accuracy of the relationship between the document density and the print density.

The reference density image (maximum density image) 215 formed 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 density correction control described above. It is a pattern.

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

Note that each of the plurality of gradation (density) image portions and the reference density image (maximum density image) 215 of the gradation pattern image 210 may be one, but in consideration of variations in the main scanning direction and measurement errors, In order to obtain an accurate value, a plurality of them may be created and the average value thereof 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 (print image) by the user, and the density detection result (measurement value) of the area is extracted. ) May be used.

FIG. 13 is a diagram showing an example of determination of gradation correction information using the detection result of the density 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 are displayed 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 the measurement is performed using the output image (print image) of the user 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). Therefore, it is not possible to measure an image with an arbitrary area ratio. However, also in this case, as shown in FIG. 13, the value of the density at each area ratio is calculated as the predicted value based on the detection result of the density in the measurement region in the output image (printed image), and the predicted value is set as the predicted value. The gradation correction may be performed based on this. As a method of calculating the predicted value, for example, it may be calculated using a quadratic approximation based on the value of the concentration at the measurement point. Further, other approximations such as the first-order approximation and the third-order approximation may be used in consideration of the characteristics of the device and the calculation load.

After the gradation correction information determined above is reflected, the relationship between the gradation correction information is used to obtain the output gradation () corresponding to the original density so that the image density specified in each part of the original density (input image) can be obtained. By determining the area ratio, a desired concentration can be obtained.

FIG. 14 is a diagram illustrating an example of reflecting 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 of the gradation correction control, the gradation correction information is calculated and determined. The calculation of the gradation correction information requires more calculation time than 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 some time difference between the detection timing (measurement timing) of the measurement pattern of the 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 timing of reflecting the 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. As a result, after the reflection timing of the gradation correction information, the target maximum density matches the maximum density of the detection timing (measurement timing) of the measurement pattern for gradation correction control. Therefore, it is possible to maintain the optimum state of the gradation correction information calculated and determined, and it is possible to stabilize the overall image quality of a multi-gradation output image.

It should be noted that a correction table that associates the amount of change in the density of the maximum density image with the amount of change in the image forming condition of the maximum density image is stored in advance, and the maximum density image is displayed according to the correction table at the timing of reflecting the gradation correction information. The image forming conditions of may be changed. In this case, since the image forming condition of the maximum density image changes without waiting for the timing of the 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 and 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 measured values of the plurality of maximum densities.

Further, when it is necessary to reduce the calculation load in the control unit, the measured maximum density of the maximum density image 215 at the start or the end of the measurement timing 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 the 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 by using an average value obtained by averaging a plurality of detection results (measurement values) of maximum density including the detection result in the latest past gradation correction control. When the gradation correction control for changing the gradation correction information based on the detection result of the measurement pattern is performed a plurality of times, the average value of the measured maximum densities of the maximum density image 215 at the time of the previous and present measurement pattern detection is calculated. However, the average value may be set as the current target maximum density. In this case, the influence of measurement error can be reduced.

Note that FIG. 16 shows an example of using the average value of the measured maximum densities of the maximum density image 215 at the time of detecting the measurement patterns of the previous time and this time, but the present invention is not limited to this example. For example, the average value of the measured maximum densities of the maximum density image 215 at each of the past arbitrary times (two or more times) of detection of the measurement pattern may be used. Further, the average value of the measured maximum densities of the maximum density image 215 at the time of detecting the measurement pattern for an arbitrary number of times (twice or more) in the past and at the time of detecting the measurement pattern of this time may be used.

Further, the measured values of the densities of the past maximum density image 215 may be weighted, an average value of the weighted values may be calculated, and the average value may be set 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 showing an example of a method of setting the image forming condition of the maximum density image. In this example, instead of the above-described correction table, the image densities (toner adhesion amounts) on the intermediate transfer belt 20 are different from each other at predetermined timings different from the gradation correction control and the maximum density control. A plurality of density detection patterns are created under the potential condition. Then, the image densities (toner adhesion amount) of the plurality of density detection patterns are 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 the target adhesion amount (target density) is calculated as shown in FIG. 17, and the calculated image forming condition is used to determine a predetermined value. The image forming condition may be changed at the reflection timing.

FIG. 18 is a diagram showing 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 actual maximum density is constantly changing even during formation of the output image (during printing). Therefore, in order to obtain a more accurate value, the maximum density image 215 as the 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 the density detection results (measurement values) of the four maximum density images 215 before and after the gradation pattern image 210 is calculated, and the average value is set as the target maximum density.

FIG. 19 is a diagram showing 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 in which the 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 improved. However, as the number of density measurement points increases, the amount of memory and the calculation time will increase. Therefore, the measurement points are determined in consideration of the balance with accuracy.

FIG. 20 is a diagram showing 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, in the output image (print image) 200 of the user, there is 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, in the print image of the user, instead of the gradation pattern image and the maximum density image, the density of each of the gradation measurement image area 201 and the maximum density measurement image area 202 is measured by the image density sensor (line sensor) 41. ing.

In the case of the example in FIG. 20, the control unit 90 of the image forming apparatus 1 of the embodiment uses the image information acquisition unit that acquires the image information of the output image, and the reference density image or the gradation pattern image in the output image. It also functions as a region search means for searching a possible region. The area searching means searches which area, out of the entire area of the image indicated by the image information obtained by the image information obtaining means, is to be the colorimetric adaptive area to be the colorimetric target.

The search for the colorimetric adaptation area 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 of 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 from the upper left and the 21st row in the pixel matrix having a resolution of 200 dpi is set as the pixel of interest, and the pixel of interest is 41 pixels×41 pixels of about 5 mm square. The area is extracted as a partial area. Then, referring to the pixel value (C, M, Y, K) of each pixel in the extracted partial area, the flatness indicating the flatness of the light and shade of the entire partial area is calculated. As the flatness, it is possible to use those obtained by various calculation methods.

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

Further, as the flatness, one utilizing a frequency characteristic of color can be cited. 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 negative sign is added to this sum to obtain flatness. A plurality of frequencies can be used as the specific frequency.

With the flatness of the first example, there are cases in which a flat region cannot be identified due to the effect of the pattern of halftone processing on an image that has been halftone processed. On the other hand, in the flatness using the Fourier transform, the flatness without the influence of the halftone processing can be calculated by using the sum of the squares of the absolute values of the Fourier coefficients of the specific frequencies. The calculation of the flatness is not limited to these, and a known flatness calculation technique can be used.

After obtaining the flatness of the extracted partial areas, it is next determined whether or not all the partial areas have been extracted (whether or not the extraction of the partial areas has been completed for all the areas of the image). When it is determined that there is a partial area that has not been extracted yet, the position of the pixel of interest is shifted to the right by one pixel, and a 41 mm×41 pixel area of about 5 mm square centering on that is shifted. Extract as a partial area. Then, similarly, the flatness of the color of the extracted partial region is calculated. Thereafter, when extracting the third, fourth, fifth,... Nth partial regions, the position of the target pixel is shifted rightward by one pixel. Then, after shifting the position of the pixel of interest in the column direction from the right end of the matrix to the 21st position to the left, the position of the pixel of interest in the column direction is returned to the 21st position from the left end of the matrix to the right. At the same time, the position in the row direction is shifted downward by one pixel. After that, the process of shifting the position of the pixel of interest to the right by one pixel is repeated. As described above, the position of the pixel of interest 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 centered on the target pixel on the 21st column and the 21st row×41 pixels, 41 pixels centered on the target pixel on the 62nd column and the 62nd row× A partial area having a size of 41 pixels is extracted.

When the partial areas are extracted from all the areas 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 adaptive area suitable for colorimetry.

Next, the average density of each partial area that has become the colorimetric adaptive area is calculated from the image information. Then, it is determined whether or not there is a colorimetric region in which the density is within a certain range for 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 colorimetric area does not exist is created as a gradation pattern image in the non-image area.

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

What has been described above is an example, and the following unique effects can be obtained.
(Aspect A)
An image forming unit such as a process unit 10 that forms an image on an image carrier such as the intermediate transfer belt 20, a density detecting unit such as an image density sensor 40 that detects the density of an image on the image carrier, and an image carrier. A reference density image 220 having a predetermined density is formed on the upper side, the density of the reference density image is detected, and based on the detection result and the target density, image formation such as charging potential used when forming an image by the image forming means. An image forming condition changing unit such as a control unit 90 that changes the condition, a gradation pattern image 210 is formed on the image carrier, the density of the gradation pattern image is detected, and image formation is performed based on the detection result. When a gradation pattern image 210 is formed in the image forming apparatus 1 including a gradation correction information changing unit such as a control unit 90 that changes the gradation correction information used when forming a multi-tone image. The reference density image 215 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.
It has been found that the above-mentioned problems specifically occur 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 changes due to environmental changes, etc., and the image density during image formation deviates from the target density. It may fluctuate like this. Then, a gradation pattern image may be formed at a timing when the image density at the time of image formation deviates from the target density, and the gradation correction information may be changed based on the detection result of the gradation pattern image. The changed gradation correction information 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 gradation reproducibility of the multi-tone image formed based on the changed gradation correction information may change significantly over time. is there.
In this aspect, when forming the gradation pattern image used for changing the gradation correction information, the reference density image is formed, and the detection result of the density of the reference density image is used as the target used for changing the image forming condition. Set to concentration. Subsequent changes in the image forming conditions are performed based on the target density and the detection result of the reference density image set when the gradation correction information is changed. Due to the change of the image forming condition, the fluctuation of the image density during the subsequent image formation is centered on the image density during the image forming when the gradation correction information is changed so that the predetermined gradation is reproduced. The fluctuation is relatively small. Therefore, the gradation reproducibility of the multi-gradation image formed based on the gradation correction information changes with a smaller change width than that when the target density is not set when the gradation correction information is changed. Become. Therefore, it is possible to suppress changes in gradation reproducibility of a multi-tone image with time.
(Aspect B)
In the above aspect A, the image forming means exposes the charging means such as the charging roller 12 that charges the surface of the latent image carrier such as the photoconductor 11 to a predetermined charging potential and the charged surface of the latent image carrier. The exposure means such as the optical writing device 30 and the latent image formed on the latent image carrier by the exposure are developed by the developer carried on the developer carrying body such as the developing roller 14a to which a predetermined developing bias is applied. The image forming condition includes at least one of a charging potential by the charging unit, an exposure amount by the exposing 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 the charging potential, the exposure amount, and the developing bias that have a large influence on the image density as the image forming condition, the image density can be more reliably and The target concentration can be controlled accurately.
(Aspect C)
In the above aspect A or aspect B, the image forming means includes a charging means for charging the surface of the image carrier to a predetermined charging potential, an exposing means for exposing the charged surface of the image carrier, and an image bearing by exposure. Developing means for developing a latent image formed on the body with a developer containing toner and a carrier carried by a developer carrying body to which a predetermined developing bias is applied, and controlling the toner concentration of the developer in the developing means And a toner density control unit such as a control unit 90, and the image forming condition includes a target value of the toner density in the toner concentration control unit.
According to this, as described in the above embodiment, by determining the target value of the toner density that greatly affects the image density as the image forming condition, the image density is controlled to the target density more reliably and accurately. it can.
(Aspect D)
In any 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, by determining the image forming condition based on the detection result of the density of the maximum density image in which the density change is large with respect to the change of the image forming condition, Can be controlled to the target concentration more accurately.
(Aspect E)
In any one of the above modes 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 detection results of the density of each of the plurality of reference density images. The image forming condition is 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 dispersion of the detection of the reference density image by the density detection means and the dispersion of the position of the reference density image on the image carrier. Can be reduced.
(Aspect F)
In any of the above modes 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. , 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 dispersion of the detection of the reference density image by the density detection means and the dispersion of the position of the reference density image on the image carrier. Can be reduced.
(Aspect G)
In any one of the above aspects A to D, 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 past density images, 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 dispersion of the detection of the reference density image by the density detection means and the dispersion of the position of the reference density image on the image carrier. Can be reduced.
(Aspect H)
In any of the above aspects A to G, the density correction control means associates the amount of change in the density of the reference density image with the correction amount of the image forming condition, which is created in advance, The image forming condition is changed based on the detection result of the density of the density image.
According to this, as described in the above embodiment, by using the image forming condition correction data, the process of changing the image forming condition based on the detection result of the density of the reference density image is simplified, so that the density of the output image is reduced. Can be quickly controlled to the target concentration.
(Aspect I)
In any one of the above aspects A to H, the maximum image information acquisition unit such as the control unit 90 that acquires the image information of the output image and the maximum that can be used as the reference density image or the gradation pattern image in the output image 200. An area that can be used as a reference density image or a gradation pattern image in the output image, and an area searching unit such as a control unit 90 that searches for an area such as the density measurement image area 202 or the gradation measurement image area 201. When there is, the density of the area 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 condition 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 one of the above aspects A to I, a calculation unit such as a control unit 90 that calculates a predicted density value corresponding to each gradation based on the detection result of the density of the gradation pattern image is provided, and the gradation correction control unit is provided. Determines the gradation correction information based on the target gradation characteristic, which is the gradation characteristic obtained from the density prediction value corresponding to each gradation calculated by the calculating means.
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
14 developing device 14a developing roller 14b toner concentration 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's 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,
A density detecting means for detecting the density of the image on the image carrier,
An image used when forming a reference density image of a predetermined density on the image carrier, detecting the density of the reference density image, and forming an image by the image forming means based on the detection result and the target density. Image forming condition changing means for changing the forming condition,
Gradation correction used when a gradation pattern image is formed on the image carrier, the density of the gradation pattern image is detected, and based on the detection result, the image forming unit forms a multi-gradation image. An image forming apparatus comprising: gradation correction information changing means for changing information,
When forming the gradation pattern image used for changing the gradation correction information, the reference density image different from the gradation pattern image is formed on the image carrier, and the density of the reference density image is detected. , Set the detection result to the target concentration ,
At the timing of changing the image forming condition after the detection timing of 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 An image forming apparatus , wherein the image forming condition is changed so that the set target density is obtained . The image forming apparatus according to claim 1,
The image forming unit includes a charging unit that charges the surface of the latent image carrier to a predetermined charging potential, an exposure unit that exposes the charged surface of the latent image carrier, and the latent image carrier by the exposure. And a developing means for developing the formed latent image with a developer carried on a developer carrying body to which a predetermined developing bias is applied,
The image forming apparatus is characterized in that the image forming condition includes at least one of a charging potential by the charging unit, an exposure amount by the exposing unit, and a developing bias applied to the developer carrying member. The image forming apparatus according to claim 1,
The image forming unit includes a charging unit that charges the surface of the image carrier to a predetermined charging potential, an exposure unit that exposes the charged surface of the image carrier, and an image forming unit that is formed on the image carrier by the exposure. Developing means for developing the latent image with a developer containing a toner and a carrier carried by a developer carrying body to which a predetermined developing bias is applied,
Toner concentration control means for controlling the toner concentration of the developer in the developing means,
The image forming apparatus is characterized in that the image forming condition includes a target value of the toner density in the toner density control means. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein the reference density image is a maximum density image. The image forming apparatus according to any one of claims 1 to 4,
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 detection results of the densities 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 any one of claims 1 to 4,
An average value of a plurality of detection results of the densities of the reference density image detected within the time when the density of the gradation pattern image is detected is calculated, and the average value is set as the target density. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 4,
An average value of the density detection result of the reference density image and the past density detection result of one or more of the reference density images is calculated, and the average value is set as the target density. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 7,
The image forming condition changing means detects the density of the reference density image and image forming condition correction data created in advance by associating the amount of change in 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 the result. The image forming apparatus according to any one of claims 1 to 8,
Image information acquisition means for acquiring image information of the output image,
A region searching 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 characterized by being used for control. The image forming apparatus according to any one of claims 1 to 9,
A calculation unit that calculates a density prediction value corresponding to each gradation based on the detection result of the density of the gradation pattern image,
The image forming apparatus, 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 calculating unit.