Image forming apparatus

Abstract

To improve the accuracy of an adjustment operation in image density control in an image forming apparatus that allows a plurality of types of process cartridges to be mounted therein.SOLUTION: An image forming apparatus allows process cartridges to be mounted therein, each having an image carrier on which an electrostatic latent image based on image data is formed, a developer carrier that develops the electrostatic latent image to form a developer image, a storage chamber that stores developer, and a memory. The image forming apparatus comprises: detection means that irradiates patches of the developer image with light, detects reflected light, and outputs information; and a control unit that performs image density control of controlling an image density when the developer image is formed on the basis of the value of the image data and information on the reflected light. The memory stores information corresponding to the amount of developer in the storage chamber. The control unit changes a patch pattern between a case where the information in the memory is information corresponding to a state where the amount of developer is a first amount, and a case where the information in the memory is information corresponding to a state where the amount of developer is a second amount.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] Conventionally, as an image forming apparatus such as a laser beam printer, an in-line color type image forming apparatus having a configuration in which a plurality of photosensitive drums as image carriers are arranged in the rotational direction of an intermediate transfer body is known. In such an image forming apparatus, generally, a process cartridge system is adopted in which the image carrier, the developing means, and the toner storage unit are integrated into a process cartridge and are detachable from the image forming apparatus main body. Further, in such an image forming apparatus, there may be a case where a plurality of process cartridges with different life settings are prepared. The user selects and purchases an arbitrary one from the process cartridges with respective life settings based on price or the like, and mounts it on the image forming apparatus. Further, in some cases, it may be possible to mount process cartridges with different lifetimes depending on the color.

[0003] In such an image forming apparatus, it is possible to perform color adjustment by performing image density control (calibration) according to the degree of use of the process cartridge. Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2003-270901) proposes suppressing changes in image density accompanying an increase in the number of printed sheets by performing image density control based on the density detection results of test images (patches) in a color-printable process cartridge type image forming apparatus.

[0004] Further, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2022-064626) proposes a correction method for correcting image forming conditions such as correction amounts for density gradation and color misregistration according to a combination condition of unit identification information provided in an exchangeable image forming unit including a process cartridge and mounting unit identification information of a unit mounting portion.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2003-270901 Patent Document 2 Japanese Patent Application Laid-Open No. 2022-064626 Summary of the Invention Problems to be Solved by the Invention

[0006] Among the process cartridges with different life settings described above, the types of functional parts such as rollers used in each process of charging and developing and the toner filling amount are different. Therefore, the tendency and degree of change of the image gradation characteristics before image density control are different from each other. However, in the image forming apparatus having the configuration of the conventional example as described above, each image density of the test image (patch) used for image density control and the number of test images (number of patches) are basically determined for each color. Therefore, when the types (such as life) of the process cartridges are different, the above content is not considered.

[0007] The present invention has been made in view of the above problems. An object of the present invention is to improve the accuracy of the adjustment operation of image density control in an image forming apparatus capable of mounting a plurality of types of process cartridges. Means for Solving the Problems

[0008] The present invention employs the following configuration. That is, an image carrier on which an electrostatic latent image is formed by exposing a surface based on image data, a developer carrier that develops the electrostatic latent image with a developer to form a developer image, a storage chamber that stores the developer, and a memory, an image forming apparatus capable of mounting a process cartridge having detection means for irradiating light on a patch of the developer image to detect reflected light and outputting information regarding the reflected light For the process cartridge, an image density control unit performs image density control for controlling the image density when forming the developer image based on the value of the image data and information regarding the reflected light. It includes: In the memory, information corresponding to the amount of developer stored in the storage chamber is saved. When the information in the memory is the first information corresponding to the developer amount being the first amount and when the information in the memory is the second information corresponding to the developer amount being a second amount different from the first amount, the control unit changes the pattern of the patch used for the image density control. An image forming apparatus characterized by the above.

Advantages of the Invention

[0009] According to the present invention, it is possible to improve the accuracy of the adjustment operation of the image density control in an image forming apparatus capable of mounting a plurality of types of process cartridges.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Best Mode for Carrying Out the Invention

[0011] Hereinafter, with reference to the drawings, preferred embodiments of the present invention will be described in detail by way of example. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only to these, unless otherwise specified. Also, the materials, shapes, etc. of the members once described in the following description are the same as the initial description in the subsequent description, unless otherwise described again. In particular, well-known techniques or publicly known techniques in the relevant technical field can be applied to configurations and processes that are not particularly illustrated or described. Also, duplicate descriptions may be omitted.

[0012] [Example 1] First, with reference to the schematic cross-sectional views of FIGS. 1 and 2 and the control block diagram of FIG. 3, the overall configuration of the electrophotographic image forming apparatus 100 will be described. The image forming apparatus 100 of this embodiment is a full-color laser printer that adopts an in-line method and an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a recording material 12 (for example, recording paper) according to image information. The image information is input to the image forming apparatus main body 110 from a host device such as a personal computer (PC 120 in FIG. 3) communicably connected to the image forming apparatus main body 110 or an image reading device connected to the image forming apparatus main body 110. be formed. The image information is input to the image forming apparatus main body 110 from a host device such as a personal computer (PC 120 in FIG. 3) communicably connected to the image forming apparatus main body 110 or an image reading device connected to the image forming apparatus main body 110.

[0013] The image forming apparatus 100 includes, as a plurality of image forming units, first, second, third, and fourth image forming units SY, SM, SC, and SK for forming images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). In the present embodiment, the first to fourth image forming units SY, SM, SC, and SK are arranged in a line along the intermediate transfer belt 31. Note that the image forming unit S includes a primary transfer roller 32 and a process cartridge 7.

[0014] In the present embodiment, the configurations and operations of the first to fourth image forming units are substantially the same except that the colors of the formed images are different. Therefore, hereinafter, when there is no particular need for distinction, the subscripts Y, M, C, and K given to the reference numerals to indicate that they are elements provided for any one of the colors are omitted, and a general description will be given.

[0015] In the present embodiment, the image forming apparatus 100 includes four photosensitive drums 1 arranged along the intermediate transfer belt 31 as a plurality of image carriers. FIG. 2 is a schematic cross-sectional view of the process cartridge 7 in the longitudinal direction (rotation axis direction) of the photosensitive drum 1. The four photosensitive drums 1 have the same configuration. FIG. 3 is a block diagram showing the control block of the image forming apparatus 100.

[0016] The photosensitive drum 1 is rotationally driven in the direction of arrow A (clockwise in the figure) by a drive source 140 as a driving means. Around the photosensitive drum 1, a charging roller 2 (charging member) as a charging means for uniformly charging the surface of the photosensitive drum 1 while rotating in the direction of arrow J is arranged. The charging roller 2 may rotate following the rotation of the photosensitive drum 1, or may be driven by the drive source 140 to rotate. Also, around the photosensitive drum 1, a developing roller 17 and a cleaning blade 6 are arranged. The developing roller 17 is a developing means for developing an electrostatic latent image into a toner image, and constitutes a developing unit 4 as a developing device. The cleaning blade 6 is a cleaning means for removing toner (transfer remaining toner) remaining on the surface of the photosensitive drum 1 after transfer. The cleaning blade 6 is in contact with the surface of the photosensitive drum 1, and the contacting portion is taken as a contact portion. The process cartridge 7 will be described in more detail later. The recording material 12 is loaded on a recording material holding portion 44, conveyed through a conveyance path R by a pickup roller, and reaches between a secondary transfer roller 33 and a secondary transfer opposing roller 38.

[0017] In this embodiment, the photosensitive drum 1, the charging roller 2 as a process means acting on the photosensitive drum 1, the developing unit 4, and the cleaning blade 6 are integrally formed into a cartridge to form a process cartridge 7. The process cartridge 7 is detachable from the image forming apparatus 100. In this embodiment, the process cartridges 7 for each color have the same shape in main components. The process cartridges 7 for each color are different in that toner for each color of yellow (Y), magenta (M), cyan (C), and black (K) as a developer is accommodated inside each of them.

[0018] [Process Cartridge] Next, the overall configuration of the process cartridge 7 that can be attached to the image forming apparatus 100 of this embodiment will be described. In this embodiment, except for the type (color) of the developer contained, the basic configuration and operation of the process cartridge 7 for each color are the same. The process cartridge 7 has a photoreceptor unit 13 including a photosensitive drum 1 and a developing unit 4 including a developing roller 17 and the like.

[0019] The photoreceptor unit 13 has a cleaning frame body 14 as a frame body that supports various elements within the photoreceptor unit 13. The photosensitive drum 1 is rotatably attached to the cleaning frame body 14 via a bearing (not shown). By transmitting the driving force of a driving motor as a driving source 140 to the photoreceptor unit 13, the photosensitive drum 1 is rotationally driven in the direction of arrow A (clockwise direction) according to the image forming operation. In this embodiment, as the photosensitive drum 1 that is the center of the image forming process, an organic photoreceptor in which an undercoat layer, a carrier generation layer, and a carrier transfer layer, which are functional films, are sequentially coated on the outer peripheral surface of an aluminum cylinder is used.

[0020] Also, a cleaning blade 6 and a charging roller 2 are arranged on the photoreceptor unit 13 so as to contact the circumferential surface of the photosensitive drum 1. The transfer residual toner removed from the surface of the photosensitive drum 1 by the cleaning blade 6 falls by gravity and is accommodated within the cleaning frame body 14.

[0021] The charging roller 2, which is a charging means, is driven to rotate passively by pressing the roller portion of conductive rubber into contact with the photosensitive drum 1. Here, a predetermined DC voltage is applied from a charging power source 142d to the core metal of the charging roller 2 in the charging process, whereby a uniform dark part potential (Vd) is formed on the surface of the photosensitive drum 1. The spot pattern of the laser light emitted corresponding to the image data by the laser light from the scanner unit 30 exposes the photosensitive drum 1, and in the exposed part, the charges on the surface disappear due to the carriers from the carrier generation layer and the potential decreases. As a result, an electrostatic latent image in which the exposed part has a predetermined bright part potential (Vl) and the unexposed part has a predetermined dark part potential (Vd) is formed on the photosensitive drum 1.

[0022] On one hand, the developing unit 4 includes a developing roller 17 (developer carrier), a developing blade 19, a toner supply roller 18 (supply means), and a toner storage chamber 16. The toner storage chamber 16 is a chamber in which the toner 15 is stored. In this embodiment, the toner 15 is a non-magnetic one-component spherical toner that is charged negatively as the normal polarity and has a particle size of 7 μm. Also, silica particles with a particle size of 20 nm are added as an external additive (external additive particles) to the surface of the toner 15.

[0023] The developing blade 19 is in counter-contact with the developing roller 17, and regulates the coating amount and imparts charge to the toner supplied by the toner supply roller 18. The developing blade 19 is made of a thin plate-like member, forms a contact pressure using the spring elasticity of the thin plate, and its surface is brought into contact with the toner 15 and the developing roller 17. The toner 15 is triboelectrically charged and charged with electricity by the rubbing between the developing blade 19 and the developing roller 17, and at the same time, the layer thickness is regulated. Also, in this embodiment, a predetermined voltage is applied from a blade bias power supply to the developing blade 19 to stabilize the toner coating.

[0024] The developing roller 17 and the photosensitive drum 1 rotate so that their surfaces move in the same direction at the opposing portion N1 (contact portion) (the photosensitive drum 1 rotates in the direction of arrow A, and the developing roller 17 rotates in the direction of arrow G). In this embodiment, with respect to the predetermined DC voltage applied from the developing power supply 142f to the developing roller 17, the toner 15 charged negatively by triboelectrification transfers only to the bright part potential portion from the potential difference at the opposing portion N1 where it contacts the photosensitive drum 1, and develops the electrostatic latent image.

[0025] The toner supply roller 18 is disposed to form a predetermined nip portion N2 on the circumferential surface of the developing roller 17. The toner supply roller 18 rotates in the direction of arrow E (counterclockwise in the figure). The toner supply roller 18 of the present embodiment is an elastic sponge roller having a foam formed on the outer periphery of a conductive core metal. The toner supply roller 18 and the developing roller 17 are in contact with each other with a predetermined intrusion amount and rotate so as to move in opposite directions to each other at the nip portion N2. By this rotational operation, toner is supplied from the toner supply roller 18 to the developing roller 17, and the remaining developing toner remaining on the developing roller 1 7 is peeled off.

[0026] A toner stirring member 20 is provided in the toner storage chamber 16. The toner stirring member 20 includes a sheet-like member that rotates in the direction of arrow H, stirs the toner 15 stored in the toner storage chamber 16, and conveys the toner 15 toward the upper part of the toner supply roller 18. In the present embodiment, the developing roller 17 and the toner supply roller 18 both have an outer diameter of φ20, and the intrusion amount of the toner supply roller 18 into the developing roller 17 is set to 1.5 mm. In the present embodiment, a predetermined DC bias applied to the developing roller 17 is applied from the developing power source 142f, and in the developing portion in contact with the photosensitive drum 1, the electrostatic latent image is visualized by transferring toner only to the bright portion potential portion from the potential difference.

[0027] The process cartridge 7 is provided with a memory m composed of a nonvolatile memory or the like. In the memory m, information related to the toner patch gradation and number when performing image density control, which is used by the controller 72 for the adjustment operation of image density control, is stored as information related to the developer amount. Here, as information related to the toner patch gradation and number when performing image density control, for example, nominal life, toner filling amount, at least one of the roughness and hardness of the charging roller 2, information on the layer structure of the charging roller 2, at least one of the roughness and hardness of the developing roller 17, the material of the surface layer of the photosensitive drum 1, the film thickness, and at least one of the susceptibility to photo-degradation, etc. are included. Also, the gradation and number of the calibration toner patches preset for the cartridge itself may be stored.

[0028] Note that the memory m is configured to be communicable with the controller 72 as the control unit of the image forming apparatus 100 shown in FIG. 1 either in a non-contact manner or through electrical contacts. That is, the controller 72 can read information from the memory m and write information to the memory m. In FIG. 2, the memory m is attached to the photosensitive unit 13, but it may be attached to the developing unit 4. Also, the memory m may be attached to both the photosensitive unit 13 and the developing unit 4. In that case, the memory m on the photosensitive unit 13 side stores information on the photosensitive drum 1 and the charging roller 2, and the memory m on the developing unit 4 side stores information on the developing roller 17 and the toner 15.

[0029] Here, in this embodiment, for each color process cartridge 7, there are a plurality of cartridges with different life settings. Here, the life of the process cartridge 7 is a numerical value representing the usable period of the cartridge, and is typically set according to the toner capacity. When setting the life in terms of the number of printed sheets, the number of sheets that can be printed when printing a typical image using the toner contained in the process cartridge 7 may be used as the life, or a value with a certain margin may be set as the life. Also, the life is typically represented by the number of sheets of printable recording material, but may also be represented in other units based on the time of use of the process cartridge 7, such as the number of days or hours used.

[0030] The process cartridge 7 has a nominal life set by the manufacturer. Here, it is assumed that there are two types: a relatively short-lived process cartridge 7 with a nominal life of 10,000 sheets each, and a relatively long-lived process cartridge 7 with a nominal life of 50,000 sheets.

[0031] Also, as shown in FIG. 1, the image forming apparatus 100 includes a scanner unit 30 as an exposure means (exposure device) that irradiates a laser on the photosensitive drum 1 based on image information to form an electrostatic latent image. Further, the image forming apparatus 100 includes an intermediate transfer belt 31 as an intermediate transfer member for transferring the toner image on the photosensitive drum 1 to the recording material 12, facing the four photosensitive drums 1.

[0032] As shown in FIG. 1, the intermediate transfer belt 31 formed of an endless belt contacts all the photosensitive drums 1 and rotates (moves) in the direction of arrow B (counterclockwise in the figure). The intermediate transfer belt 31 is stretched over a plurality of support members, namely, a tension roller 37, a secondary transfer opposing roller 38 that also serves as a driving roller, and a driven roller (not shown). On the inner peripheral surface side of the intermediate transfer belt 31, four primary transfer rollers 32 as primary transfer means (transfer members) are arranged in parallel so as to face each photosensitive drum 1. A bias having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 32 from the primary transfer bias power source 142a. Thereby, the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt.

[0033] Also, at a position facing the secondary transfer opposing roller 38 on the outer peripheral surface side of the intermediate transfer belt 31, a secondary transfer roller 33 as secondary transfer means is arranged. A bias having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 33 from the secondary transfer bias power source 142b. Thereby, the toner image on the intermediate transfer belt 31 is transferred onto the recording material 12.

[0034] As shown in FIG. 3, the image forming apparatus 100 includes a power source 142. The power source 142 functions as the above-described primary transfer bias power source 142a and secondary transfer bias power source 142b, and a blade bias power source 142c according to the instructions of the controller 72. In the example of FIG. 3, one power source 142 functions so as to also serve as the primary transfer bias power source 142a, the secondary transfer bias power source 142b, the blade bias power source 142c, a charging power source 142d that applies a voltage to the charging roller 2, a supply power source 142e that applies a voltage to the toner supply roller 18, and a developing power source 142f that applies a voltage to the developing roller 17. However, the power supply configuration is not limited to this, and separate power supply devices may be provided for each member. Alternatively, depending on the required functions and performance, etc., a common power supply device may be used for a plurality of power sources. For example, it is conceivable to use a common power supply device for the primary transfer bias power source 142a and the secondary transfer bias power source 142b.

[0035] At the time of image formation, first, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, an electrostatic latent image according to the image information is formed on the photosensitive drum 1 by laser light corresponding to the image information emitted from the scanner unit 30. Next, the electrostatic latent image is supplied with a developer by the developing unit 4 and developed on the photosensitive drum as a toner image (developer image). Next, the developed toner image is transferred (primary transfer) onto the intermediate transfer belt 31 by the action of the primary transfer roller 32.

[0036] For example, at the time of full-color image formation, the above-described process is sequentially performed in the first to fourth image forming units SY, SM, SC, SK, and a four-color toner image is formed by overlapping toner images of each color on the intermediate transfer belt 31. Thereafter, the four-color toner image on the intermediate transfer belt 31 is collectively secondarily transferred onto the recording material 12. Further, the fixing device 34 applies heat and pressure to the recording material 12, and the toner image is fixed on the recording material 12.

[0037] Note that the primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer process is removed and recovered by the cleaning blade 6. Also, the secondary transfer residual toner remaining on the intermediate transfer belt 31 after the secondary transfer process is cleaned by the intermediate transfer belt cleaning device 39.

[0038] As shown in FIG. 3, the image forming apparatus 100 includes a controller 72. The controller 72 is an information processing device having arithmetic resources such as a CPU 73, a ROM 74, and a RAM 75, and functions as a control unit that operates according to a program and instructions via the touch panel of the PC 120 and the image forming apparatus main body 110. The controller 72 controls each of the components in the image forming apparatus, such as a drive source 140 such as a motor, a power supply 142, the scanner unit 30, and the density sensor 41. each of the components.

[0039] The image forming apparatus 100 of this embodiment includes a density sensor 41 as a detection means. The density sensor 41 is an optical sensor for detecting the toner amount and is used for image density control as calibration. The density sensor 41 is arranged to face the intermediate transfer belt 31 as shown in FIG. 1. The density sensor 41 measures the intensity information of reflected light corresponding to the density of the toner patch formed on the surface of the intermediate transfer belt 31.

[0040] An example of the configuration of the density sensor 41 is shown in FIG. 4. The density sensor 41 includes a light emitting element 51, a light receiving element 52 (the first light receiving element 52a and the second light receiving element 52b), and a processing circuit (not shown) such as an IC that processes the received light data. These are housed in a holder and configured. The density sensor 41 is configured to be able to transmit and receive information with the controller 72. For the light emitting element 51, an infrared light emitting element such as an LED can be used. For the light receiving element 52, for example, a photodiode or a Cds cell can be used.

[0041] The light emitting element 51 irradiates light toward the intermediate transfer belt 31. The first light receiving element 52a detects the intensity of the specularly reflected light from the toner patch 64, and the second light receiving element 52b detects the intensity of the diffusely reflected light from the toner patch 64. By detecting both the intensity of the specularly reflected light and the intensity of the diffusely reflected light, the density of the toner patch 64 from high density to low density can be detected. Note that optical elements such as lenses (not shown) may be used for the coupling of the light emitting element 51 and the light receiving element 52.

[0042] Also, in this embodiment, the intermediate transfer belt 31 is a single-layer resin belt made of polyimide with a circumference of 880 mm. Also, an appropriate amount of carbon fine particles is dispersed in the resin for resistance adjustment of the belt, and the surface color is black. Further, the surface of the intermediate transfer belt 31 has high smoothness and gloss, and the glossiness is about 100% (measured with a gloss meter IG-320 manufactured by Horiba, Ltd.).

[0043] When the surface of the intermediate transfer belt 31 is exposed (toner amount is 0), the concentration sensor 41 mainly detects the reflected light by the first light receiving element 52a. The reason is that, as described above, the surface of the intermediate transfer belt 31 has glossiness. On the other hand, when a toner image is formed on the intermediate transfer belt 31, as the concentration (toner amount) of the toner image increases, the specular reflection output gradually decreases. This is because the toner covers the surface of the intermediate transfer belt 31, reducing the specular reflection light from the belt surface.

[0044] FIG. 5 is a diagram showing the relationship between the detection value of the concentration sensor 41 and the toner amount. Here, the detection value corresponding to the specular reflection output is shown. In the figure, the vertical axis represents the output value voltage of the concentration sensor 41, and the horizontal axis represents the image density (corresponding to the toner amount). Note that the maximum output value voltage of the concentration sensor 41 used in this embodiment is 5V.

[0045] In the image forming apparatus 100 of this embodiment, output correction of the concentration sensor 41 is performed using the output value (base output value) of the intermediate transfer belt 31 in the state without toner. Specifically, the output value of the toner patch is normalized by the base output value of the intermediate transfer body (the output value when the image density is 0 in FIG. 5). (toner patch output / base output). The sensor output characteristics after normalization are shown in FIG. 6. By performing normalization, even when the gloss of the intermediate transfer belt 31 decreases due to causes such as dirt and scratches, the same correction is possible.

[0046] The method of normalizing and correcting the toner patch output with the base output described above is a known method and is used in many commercially available color image forming apparatuses. As the concentration sensor 41, any existing configuration for concentration detection can be used. Also, the wavelength of light is not limited to infrared light. It is not limited.

[0047] <Regarding the image density control operation common to each embodiment> Next, the image density control using the toner patches in each embodiment will be described with reference to the flowchart of FIG. 7. Note that the image density control in the image forming apparatus 100 of the present invention is image gradation control for adjusting the density gradation characteristics of an image. Each step of the flow is executed by the controller 72 referring to the information in the memory m of each process cartridge 7 and the output value of the density sensor 41. and so on.

[0048] [Image Density Control] The image density control can be executed at any timing, and may be performed periodically, or may be performed when fluctuations in the image density are expected. In this embodiment, the formation of the toner patches for this image density control is appropriately controlled even for a plurality of process cartridges 7 of different types.

[0049] First, in step S101, the controller 72 reads the information in the memory m of each process cartridge 7. Next, in step S102, the background measurement of the intermediate transfer belt 31, that is, the density measurement in a state where no toner is loaded, is executed. At this time, the controller 72 rotates and moves the intermediate transfer belt 31 by the drive source 140 so that a predetermined measurement position to be the object of density measurement on the intermediate transfer belt 31 sequentially comes within the measurement range of the density sensor 41. The measurement position and the number of points are the same as those of the toner patches used for the image density control. Next, in step S103, the controller 72 controls the image forming unit to form toner patches. Here, an example of the patch pattern formed on the intermediate transfer belt 31 will be shown with reference to FIG. 8. Along the moving direction (arrow F) of the intermediate transfer belt 31, a plurality of 8 mm square patches 88 are arranged at intervals of 2 mm at a position corresponding to the portion where the density sensor 41 is arranged.

[0050] Note that in this embodiment, based on the information stored in the memory m of each process cartridge read in step S101, the gradation and the number of the toner patches at the time of performing the image control are changed.

[0051] ​ 8 is an example of a patch pattern in which the largest number of toner patches are formed in one image density control in this embodiment. The patches 88 include a yellow patch 88Y, a magenta patch 88M, a cyan patch 88C, and a black patch 88K. Each of the color patches 88Y to 88K includes eight patches with eight different image printing rates (density gradients) (hereinafter, simply referred to as Y1 to Y8, M1 to M8, C1 to C8, and K1 to K8). As a result, a total of 32 patches 88 are formed on the intermediate transfer belt 31.

[0052] The correspondence between each patch 88 and the printing rate (gradation) is set as follows: Y1, M1, C1, K1 = 12.5%; Y2, M2, C2, K2 = 25%, Y3, M3, C3, K3 = 37.5%; Y4, M4, C4, K4 = 50%, Y5, M5, C5, K5 = 62.5%; Y6, M6, C6, K6 = 75%, Y7, M7, C7, K7 = 87.5%, Y8, M8, C8, K8 = 100%.

[0053] The base measurement of the intermediate transfer belt 31 is performed by patching the area where the above-mentioned 32 patches 88 are formed. The base measurement is performed before the patch 88 is formed. For example, the base measurement may be performed one revolution before the patch 88 is formed. Also, as will be described later, each patch 88 may be printed in only one color, and monochrome image density control may be performed.

[0054] Furthermore, another example of the patch pattern is shown in Fig. 9. In this example, four toner patches 88 are formed for each color. As shown in Fig. 9, the intervals between toner patches of the same color may be continuous. For example, among the toner patches arranged continuously, changing the number of image densities of the toner patches in Fig. 9 from four to three is included in the change in the number of toner patches of the present invention.

[0055] The controller 72 rotates the intermediate transfer belt 31 by the drive source 140 of the image forming apparatus 100, and sequentially moves each patch formation position to a position facing the image forming unit. Then, the controller controls the image forming unit to form a toner patch 88 as described with reference to FIG. 8 on the intermediate transfer belt 31.

[0056] Then, in step S104, the controller 72 uses the density sensor 41 to detect the amount of reflected light from the toner patch 88 such that the positions where patches are formed on the intermediate transfer belt 31 sequentially come within the measurement range of the density sensor 41. Then, in step S105, the controller 72 calculates the density of the toner patch 88. At this time, first, the output value of the density of the toner patch 88 is normalized by the output value of the base of the intermediate transfer belt 31 (toner output / base output). Such normalization of the patch output is performed for all the patches 88 using the output value of the base obtained at the position corresponding to the patch. Next, the controller 72 converts the normalized value into a density value using a density conversion table. The density conversion table is stored in advance in the ROM 74.

[0057] Subsequently, in step S106, the controller 72 performs image gradation control (gradation correction). The image gradation control will be described with reference to FIG. 10. Here, only the gradation correction for cyan color will be described, but the same method is used for magenta, yellow, and black.

[0058] In FIG. 10, the horizontal axis represents image data (e.g., pixel value %), and the vertical axis represents the density detection value of density sensor 41 (the value after normalization correction of the output value voltage). Also, the "○" (open circles) in the figure represent the detected density values of density sensor 41 for each of the patches C1, C2, C3, C4, C5, C6, C7, and C8. The curve γ passing through each point of C1 to C8 represents the density gradation characteristic in a state where density control (tone correction control) is not performed. Note that the controller 72 calculates the value of the image data by performing spline interpolation so as to pass through the origin and each point of C1 to C8 for the image density at the tone where no patch is formed.

[0059] Next, the straight line T represents the target density gradation characteristic of the image density control. In the present embodiment, the target gradation characteristic T is determined such that the relationship between the image data and the density is a proportional relationship. Note that the gradation characteristic is not limited to a straight line. As can be seen by comparing the curve γ and the straight line T, in the illustrated example, when tone correction is not performed, in the range where the image data value is low, printing is performed such that the image density becomes low with respect to the image data value, and in the range where the image data value is high, printing is performed such that the image density becomes high with respect to the image data value. That is, printing different from the desired color tone by the user is performed.

[0060] And the curve D represents the tone correction table calculated by the control of the present embodiment. The controller 72 calculates the tone correction table D by obtaining the symmetric point of the gradation characteristic γ before correction with respect to the target gradation characteristic T. The calculated tone correction table D is stored in the RAM 75. Stored.

[0061] When forming a printed image, the controller 72 can obtain the target gradation characteristic by correcting the value of the image data with reference to the tone correction table D. For example, in the range where the image data value is low, correction is performed using the tone correction table D so that the image data value becomes high. By determining the control value of the image forming apparatus 100 using the corrected image data value, the density of the printed image can be increased and the gradation characteristic can be lifted up to the straight line T.

[0062] In addition, the method of image density control implemented here may be a known method for controlling image formation conditions. Examples of image formation conditions include, for example, the spot pattern conditions of the laser beam emitted corresponding to the image data by the laser beam from the scanner unit, the development conditions such as the development bias, and the charging conditions such as the charging bias. The controller 72 forms a plurality of predetermined patterns (such as halftone patterns) patches in which these image formation conditions are changed in multiple stages on the intermediate transfer belt 31, detects the density of the patch pattern, and calculates the image formation conditions under which a desired density can be obtained.

[0063] Next, the transition in which the curve γ changes when printed will be described with reference to FIG. 11. Immediately after performing image density control according to the above flow, by correcting with the above-described gradation correction table D, the relationship between the image data value and the image density becomes a line of the straight line T. However, as the number of printed sheets increases from there, the deviation of the density gradation becomes larger. Here, when the case between the curve Li_u and the curve Li_b is set as the allowable range as the image density, image density control is performed at the timing when any gradation of the curve γ goes out of the allowable range, and the color reproducibility can be maintained by returning the curve γ to T. The above is the description of the image density control (image gradation correction) in this embodiment.

[0064] [Example of adjustment operation of image density control] In this embodiment, as the process cartridges 7 with different lifetimes, there are a process cartridge with a nominal lifetime of 10,000 sheets (hereinafter referred to as Type1 and also referred to as the first process cartridge 7a. The first process cartridge 7a is set with a first lifetime), and a process cartridge with a nominal lifetime of 50,000 sheets (hereinafter referred to as Type2 and also referred to as the second process cartridge 7b. The second process cartridge 7b is set with a second lifetime longer than the first lifetime). Each of Type1 and Type2 in this embodiment has a different filling amount of toner 15. Specifically, the Type2 cartridge has a larger filling amount of toner 15 than Type1.

[0065] Note that the image forming apparatus of this embodiment executes image density control every 1000 sheets and maintains color reproducibility in a temperature and humidity environment within a predetermined range. FIGS. 12 and Table 1 show toner patches C1 to C8 for image density control at the timing just exceeding the above-mentioned predetermined number of sheets, which is 1000 sheets, for process cartridges of Type1 and Type2 with different lifetimes, and show what densities they were with respect to the curves Li_u and Li_b that are the allowable ranges. Fig. 12(a) shows the results for the process cartridge of Type1, and Fig. 12(b) shows the results for the process cartridge of Type2. Toner patches outside the allowable range are indicated by "●" (filled black circles).

Table 1

[0066] As can be seen from FIGS. 12 and Table 1, for the process cartridge of Type1 with a short lifetime, it went out of the allowable range over a wide range, while for the process cartridge of Type2 with a long lifetime, only C2, C3, and C4 in the middle tone where the density gradation is likely to change were out of the allowable range. The above results are considered to be because the mixing ratio of the old toner to the new toner in the developing unit is high in the short-life process cartridge, while it is limited in the long-life process cartridge where toner is supplied abundantly from the developing container.

[0067] Based on these results, in the image forming apparatus of this embodiment, as shown in Table 2, in the memory m of each of the process cartridges of Type1 and Type2, the gradation and number of toner patches for controlling the image density preset for the cartridge itself were stored in the memory m. In this case, it can be said that information corresponding to the amount of developer stored in the storage chamber is stored in the memory m. For example, if the amount of developer stored in the Type1 cartridge is the first amount and the amount of developer stored in the Type2 cartridge is the second amount, then in the memory of the Type1 cartridge, the first information corresponding to the fact that the amount of developer is the first amount is stored. Similarly, in the memory of the Type2 cartridge, the second information corresponding to the fact that the amount of developer is the second amount is stored. Here, for simplicity of explanation, two types of information are used, but various information can be considered according to the amount of developer that can be accommodated.

Table 2

[0068] In the example of Table 2, for simplicity of explanation, all toner patches were formed in the Type1 process cartridge, but C5 and C8 may be excluded from the formation targets. Also, in the above example, the gradation and number of toner patches themselves were stored in the memory m, but it is not limited to this. For example, variables for each type of process cartridge may be stored in the memory m, and calculations may be performed by referring to the mathematical formulas and coefficients of the controller 72, so that information as shown in Table 2 may be finally obtained. Also, referring to the filling amount or the life stored in the memory m, the controller 72 may perform control to simply reduce the number of toner patches when the filling amount is large (the life is long).

[0069] As described above, in this embodiment, by utilizing the characteristic of gradation change caused by a predetermined specification of a process cartridge having different lifetimes due to different toner filling amounts, the adjustment operation of image density control is optimized. That is, by using the nominal lifetime (in other words, the toner filling amount) as information related to the gradation and number of toner patches, in the process cartridge of Type 2 with a longer lifetime, the adjustment of image density control can be performed with a smaller number of toner patches than in the case of Type 1.

[0070] Note that in the present invention, it is only necessary to be able to change the amount of toner used during image density control and optimize the operation by controlling the calibration pattern according to the toner filling amount and lifetime. As long as such control of the calibration pattern is possible, methods other than controlling the number of toner patches may be used. For example, when the filling amount is large, the amount of toner may be adjusted by reducing the area of each toner patch. For example, if the toner patch is rectangular, there are methods such as shortening the width or shortening the length (widening the gap between toner patches) to reduce the area of the toner patch. If the toner patch is other than rectangular, it may be reduced according to its shape.

[0071] Also, when it is determined to be a high-capacity cartridge, instead of reducing the number of toner patches, it is also possible to improve the accuracy of image density control while maintaining the number. For example, when using 8 toner patches as shown in Table 2, for a high-capacity (Type 2) process cartridge, the intervals of C2, C3, and C4 may be divided into 8 parts, and the corresponding 8 toner patches may be formed to perform image density control. Also, in this example, instead of dividing C2 to C4 into 8 parts, a smaller number (for example, 5) of toner patches may be formed. Thereby, the accuracy is improved in the section where image density control is required, and the number of toner patches itself can be reduced.

[0072] Also, for both Type 1 and Type 2, although the gradation of the toner patch is ALL, the number of divisions may be changed while keeping the gradation common, such as 8 divisions for Type 1 and 7 divisions for Type 2.

[0073] However, the image forming apparatus of this embodiment is not limited to the above content. For example, during manufacturing, the tip position of each developing blade of each process cartridge and the drum sensitivity incorporated in each process cartridge are written into the memory m, and the gradation characteristics may be changed according to the changes. Also, the toner patch conditions may be changed based on information on parameters related to the toner. As an example, generally, the higher the degree of intrusion of the blade tip position into the developing roller, the larger the toner uptake amount of the developing roller, and the lower the toner charge amount. Therefore, in consideration of the fact that even a small electrostatic latent image is easily developed and the gradation becomes generally darker, it is advisable to adjust the image density control. As another example, even when the amount of light during exposure is the same, the higher the drum sensitivity, the greater the change in surface potential, so the gradation becomes generally darker. In addition, the gradation and number of toner patches may be determined in consideration of various factors that affect the gradation change characteristics other than the life.

[0074] As described above, in this embodiment, a method for optimizing the adjustment operation of image density control based on the information in the memory that stores information related to the developer amount used in the adjustment operation of image density control possessed by each process cartridge has been described. As a result, it becomes possible to suppress the amount of toner consumed per density control while maintaining the quality. As a result, even if the toner filling amount in the process cartridge is the same, the number of printable sheets can be increased, or a lightweight and easy-to-handle process cartridge can be provided.

[0075] [Embodiment 2] Next, Embodiment 2 will be described. Note that descriptions of parts overlapping with those of Embodiment 1 will be omitted. In this embodiment, even when the image forming apparatus is used in a wider range than in Embodiment 1, it is possible to suppress the amount of toner consumed per image density control while maintaining the quality.

[0076] In Example 1, by utilizing the gradation change characteristics of process cartridges with different toner filling amounts resulting in different lifetimes, that is, based on predetermined specifications or information determined during manufacturing, the adjustment operation of image density control was optimized. In contrast, in Example 2 , it is different in that the information on the usage history of the image forming apparatus is also used to optimize the adjustment operation of image density control. In Example 2 as well, similar to Example 1, Type1 and Type2 process cartridges with different lifetimes will be used for explanation.

[0077] FIG. 13 shows, for a Type2 process cartridge, at the timing just exceeding a predetermined number of sheets, which is 1000 sheets as in Example 1, what densities the toner patches C1 to C8 for image density control were with respect to the curves Li_u and Li_b within the allowable range. Here, the paper feeding condition in Example 2 is different from that in Example 1 in that the toner consumption amount at the time of feeding 1000 sheets is larger. That is, in Example 2, it is assumed that the printing rate during paper feeding is higher than that in Example 1. Here, the printing rate refers to the ratio of the area where the developer image is formed to the area where an image can be formed on the recording material 12. For example, a solid black image can be defined as having a printing rate of 100%, and a white image as having a printing rate of 0%.

[0078] Here, when comparing FIG. 13 with FIGS. 12(a) and 12(b) respectively, it can be seen that it is similar to FIG. 12(a) corresponding to Type1 with a short lifetime. This is presumably because even for a long-life process cartridge, when the toner consumption amount during printing is large, the mixing ratio of the old toner to the new toner in the developing unit becomes as high as that of a short-life process cartridge, and the density gradation changes over a wider gradation range.

[0079] Therefore, in this example, the gradation change characteristics taking into account the toner consumption amount are grasped and stored in the memory m in advance. Then, using the information regarding the usage amount of the developer written in the memory m each time printing is performed (for example, the printing rate and its history), the adjustment operation of image density control is optimized.

[0080] The controller 72 in this embodiment calculates the printing rate based on the image data for each sheet of paper passed, and changes the tone and number of toner patches according to the average printing rate at the timing of image density control (for example, when 1000 sheets of paper have passed). For example, when the average printing rate is equal to or higher than a predetermined threshold value, even when using a long-life Type 2 process cartridge, the number of toner patches is set to 8, the same as in the case of Fig. 12(a) (Type 1). Note that the patch patterns are not limited to two types, and the number of toner patches may be changed stepwise according to the printing rate.

[0081] Also, in this embodiment, control may be performed using the integrated value of the toner consumption amount instead of the printing rate. In that case, the controller 72 calculates the toner consumption amount based on the image data and accumulates it each time a sheet of paper is passed. Then, at the timing of image density control (for example, when 1000 sheets of paper have passed), the patch pattern is selected such that the larger the integrated value of the toner consumption amount, the larger the number of toner patches.

[0082] Also, the image forming apparatus of this embodiment is not limited to the above example, and for example, parameters related to toner deterioration such as the rotation time, rotation speed, and surface movement distance of the developing roller 17 may be used. The controller 72 may determine the number and tone of the toner patches used for image density control based on a predetermined program according to these parameters. The patch pattern is selected such that the longer the rotation time of the developing roller 17, the higher the rotation speed, or the longer the surface movement distance, the larger the number of toner patches.

[0083] Also, as the life of the process cartridge approaches, parameters may be appropriately set to change the tone and number of toner patches to be used. Specifically, for example, even in the case of the Type2 process cartridge with a long life, as shown in Table 3, immediately after starting use (until the remaining life reaches a predetermined value), all toner patches from C1 to C8 are formed, and after the remaining life becomes a predetermined percentage or less (20% or less in this embodiment), image density control is performed using only the toner patches from C2 to C4. The reason for this is that for some time from when it is new (until the remaining life reaches a predetermined percentage), the toner circulation in the developing container is not in a sufficient state, and it is considered that the tone characteristics are unstable because it tends to be selectively developed and transferred from toner with a small particle size and high charge. Particle size and high charge toner is selectively developed and transferred, so the tone characteristics are considered unstable.

Table 3

[0084] Alternatively, it may be a form in which image density control is performed using all toner patches from C1 to C8 once for a predetermined number of times of image density control performed at predetermined page intervals.

[0085] [Example 3] Next, Example 3 in the present invention will be described. Note that descriptions of parts overlapping with the above examples are omitted. In this example, the image density control method is different from that in the above examples.

[0086] In the above example, a toner patch is formed on the intermediate transfer belt 31, and the image density and tone are adjusted using the result measured by the density sensor 41. On the other hand, the controller 72 in this example acquires the arithmetic parameters for image density control stored in advance in the ROM 74 of the image forming apparatus 100 and the parameters in the memory m of each process cartridge, and uses these arithmetic parameters to perform arithmetic operations to adjust the image density and tone as predictive control without using the detection result of the toner patch.

[0087] Specifically, the controller 72 refers to information stored in advance in the memory m of each process cartridge, which is used to determine whether image density control (predictive control) can be performed by calculation. When the controller 72 detects that image density control by calculation is effective, subsequent image density control switches to image density control by calculation. The controller 72 uses the member information (types of charging roller and developing roller, drum sensitivity) and parameters related to the process cartridge regarding the cartridge life recorded in the memory m, and the temperature and humidity information, number of printed sheets, toner amount in the cartridge, etc. obtained by the controller 72 from the image forming apparatus to calculate the image density at each time.

[0088] The density calculation program is stored in the ROM 74 and is obtained in advance by performing machine learning using the above parameters. By executing image density control using this calculation parameter, it is possible to complete image density control only by the calculation processing time without a series of operation times such as patch formation on the intermediate transfer belt and measurement by the density sensor. Therefore, by increasing the control frequency, it is possible to improve the color reproducibility equal to or higher than that of image density control based on toner patch detection.

[0089] As described above, conventionally, since image density control has been performed in the same way regardless of the type of process cartridge, there have been cases where toner patches more than necessary were formed depending on the situation. However, according to the present invention, based on the information in the memory that stores the information related to the developer amount used for the adjustment operation of image density control possessed by each process cartridge, the adjustment operation of image density control can be optimized. Therefore, it is possible to suppress the amount of toner consumed per density control while maintaining the quality without updating the device control software of the image forming apparatus. As a result, even if the toner filling amount in the process cartridge is the same, the number of printable sheets can be increased, or a lightweight and easy-to-handle process cartridge can be provided. Also, in each embodiment, four process cartridges were used, but the number is not limited to this and may be one or more.

[0090] [Configuration 1] An image forming apparatus capable of mounting a process cartridge having an image carrier on which an electrostatic latent image is formed on a surface by exposing the surface based on image data, a developer carrier that develops the electrostatic latent image with a developer to form a developer image, a storage chamber that stores the developer, and a memory, detection means for irradiating light on a patch of the developer image to detect reflected light and output information regarding the reflected light, a control unit that performs image density control for controlling an image density when forming the developer image based on a value of the image data and information regarding the reflected light with respect to the process cartridge, and includes, information corresponding to the amount of developer stored in the storage chamber is stored in the memory, when the information in the memory is first information corresponding to the developer amount being a first amount and second information corresponding to the developer amount being a second amount different from the first amount, the control unit changes a pattern of the patch used for the image density control The image forming apparatus is characterized by this. [Configuration 2] The control unit refers to the memory and changes the pattern of the patch such that the amount of developer used when forming the patch in the image density control decreases as the amount of developer stored in the storage chamber increases. The image forming apparatus according to Configuration 1, characterized by this. [Configuration 3] The control unit changes the pattern of the patch such that the number of patches decreases as the amount of developer stored in the storage chamber increases. The image forming apparatus according to Configuration 2, characterized by this. [Configuration 4] The control unit changes the pattern of the patch such that the size of the patch decreases as the amount of developer stored in the storage chamber increases. The image forming apparatus according to Configuration 2 or 3, characterized in that... [Configuration 5] In the memory, as the information corresponding to the amount of developer, the amount of the developer stored in the storage chamber, which is determined as the specification of the process cartridge or determined during the manufacture of the process cartridge, is stored. The image forming apparatus according to any one of Configurations 1 to 4, characterized in that... [Configuration 6] In the memory, as the information corresponding to the amount of developer, the life of the process cartridge is stored. The image forming apparatus according to any one of Configurations 1 to 4, characterized in that... [Configuration 7] The life of the process cartridge is the number of sheets of recording material on which an image can be formed using the process cartridge. The image forming apparatus according to Configuration 6, characterized in that... [Configuration 8] The control unit changes the pattern of the patch in the image density control based on information regarding the history when an image is formed on a recording material by the image forming apparatus. The image forming apparatus according to any one of Configurations 1 to 7, characterized in that... [Configuration 9] The control unit changes the pattern of the patch so that the amount of the developer used when forming the patch in the image density control increases as the average printing rate when an image is formed on a predetermined number of sheets of the recording material by the image forming apparatus is higher. The image forming apparatus according to Configuration 8, characterized in that... [Configuration 10] The control unit changes the pattern of the patch so that the amount of the developer used when forming the patch in the image density control increases as the amount of the developer consumed while an image is formed on a predetermined number of sheets of the recording material by the image forming apparatus is larger. The image forming apparatus according to Configuration 8, characterized in that... [Configuration 11] The memory includes information on whether to change the adjustment operation of the image density control to predictive control as information related to the amount of developer used in the adjustment operation of the image density control. The image forming apparatus according to any one of Configurations 1 to 10, characterized by the above. [Configuration 12] The control unit acquires gradation characteristics when forming the developer image based on the value of the image data and the image density obtained by the adjustment operation of the image density control, and performs the image density control so that the gradation characteristics become target gradation characteristics. The image forming apparatus according to any one of Configurations 1 to 11, characterized by the above. [Configuration 13] The image forming apparatus can simultaneously mount a plurality of the process cartridges, and the control unit can change the content of the adjustment operation of the image density control for each of the plurality of process cartridges. The image forming apparatus according to any one of Configurations 1 to 12, characterized by the above. [Configuration 14] The image forming apparatus further includes an intermediate transfer body onto which the developer image formed by the process cartridge is transferred, and the pattern of the patch is formed on the intermediate transfer body. The image forming apparatus according to any one of Configurations 1 to 13, characterized by the above.

Description of Reference Numerals

[0091] 1: Photosensitive drum, 4: Developing roller, 7: Process cartridge, 10: Toner, 41: Density sensor, 72: Controller, 100: Image forming apparatus

Claims

1. An image forming apparatus capable of mounting a process cartridge having an image carrier on which an electrostatic latent image is formed on a surface by exposing the surface based on image data, a developer carrier that develops the electrostatic latent image with a developer to form a developer image, a storage chamber that stores the developer, and a memory, detection means for irradiating light on a patch of the developer image to detect reflected light and outputting information regarding the reflected light, a control unit that performs image density control for controlling an image density when forming the developer image based on a value of the image data and information regarding the reflected light for the process cartridge, comprising: information corresponding to the amount of developer stored in the storage chamber is stored in the memory, when the information in the memory is first information corresponding to the developer amount being a first amount and when the information in the memory is second information corresponding to the developer amount being a second amount different from the first amount, the control unit changes a pattern of the patch used for the image density control An image forming apparatus characterized by the above.

2. The control unit refers to the memory and changes the pattern of the patch such that the amount of developer used when forming the patch in the image density control decreases as the amount of developer stored in the storage chamber increases. The image forming apparatus according to claim 1, characterized by the above.

3. The control unit changes the pattern of the patch such that the number of patches decreases as the amount of developer stored in the storage chamber increases. The image forming apparatus according to claim 2, characterized by the above.

4. The control unit changes the pattern of the patch such that the size of the patch decreases as the amount of developer stored in the storage chamber increases. The image forming apparatus according to claim 2, characterized by the above.

5. Stored in the memory as the information corresponding to the amount of developer is the amount of developer stored in the storage chamber, which is determined as a specification of the process cartridge or determined during manufacture of the process cartridge. The image forming apparatus according to claim 1, characterized by the above.

6. Stored in the memory as the information corresponding to the amount of developer is the life of the process cartridge. The image forming apparatus according to claim 1, characterized by the above.

7. The service life of the process cartridge is the number of sheets of recording material on which an image can be formed using the process cartridge. The image forming apparatus according to claim 6, characterized in that.

8. The control unit changes the pattern of the patch in the image density control based on information regarding the history when an image is formed on a recording material by the image forming apparatus. The image forming apparatus according to any one of claims 1 to 7, characterized in that.

9. When the control unit determines that an image has been formed on a predetermined number of sheets of the recording material by the image forming apparatus the higher the average printing rate, the more the amount of the developer used when forming the patch in the image density control, and the pattern of the patch is changed. The image forming apparatus according to claim 8, characterized in that.

10. The control unit changes the pattern of the patch such that the more the amount of the developer consumed while an image is formed on a predetermined number of sheets of the recording material by the image forming apparatus, the more the amount of the developer used when forming the patch in the image density control. The image forming apparatus according to claim 8, characterized in that.

11. The memory includes information on whether to change the adjustment operation of the image density control to predictive control as information related to the amount of the developer used for the adjustment operation of the image density control. The image forming apparatus according to any one of claims 1 to 7, characterized in that.

12. The control unit acquires gradation characteristics when forming the developer image based on the value of the image data and the image density obtained by the adjustment operation of the image density control, and performs the image density control so that the gradation characteristics become target gradation characteristics. The image forming apparatus according to any one of claims 1 to 7, characterized in that.

13. The image forming apparatus can simultaneously mount a plurality of the process cartridges, and the control unit can change the content of the adjustment operation of the image density control for each of the plurality of process cartridges. The image forming apparatus according to any one of claims 1 to 7, characterized in that.

14. The image forming apparatus further includes an intermediate transfer body onto which the developer image formed by the process cartridge is transferred, and the pattern of the patch is formed on the intermediate transfer body. The image forming apparatus according to any one of claims 1 to 7, characterized in that.

Images