Image formation apparatus

Abstract

To provide an image formation apparatus capable of highly accurately correcting an image formation condition according to the multiple target maximum image densities.SOLUTION: An image formation apparatus 100 can form an image under an image formation condition according to each of a normal mode with different maximum image densities and an image density increase mode. A CPU 301 stores a difference value between the first image formation condition of the normal mode and the second image formation condition of the image density increase mode. The CPU 301, when performing image density adjustment, adjusts the first image formation condition to generate the new first image formation condition of the normal mode and generates the new second image formation condition on the basis of the new first image formation condition and the difference value.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a printer, a copying machine, a multifunction machine, or a facsimile machine, which forms an image on a sheet. [Background technology]

[0002] In addition to home use, image forming apparatuses include office printing machines that are mainly used in offices and production printing machines that are used in the commercial field. The image quality required for office printing machines and production printing machines, such as the maximum image density, differs. In recent years, image forming apparatuses that have the image quality required for both office printing machines and production printing machines have been proposed. Such image forming apparatuses are required to print with image quality according to the user's application. For example, when used as an office printing machine, image quality for office printing applications is required, and when used as a production printing machine, image quality for production printing applications is required.

[0003] In response to such demands, there is an image forming apparatus that can set multiple target maximum image densities and change image forming conditions according to each maximum image density. Patent Document 1 discloses such an image forming apparatus. This image forming apparatus forms a toner pattern image between pages to correct the image forming conditions for the target image density, and corrects the image forming conditions for another target image density by calculating the correction amount without forming a toner pattern image.

[0004] In the image forming apparatus, the image density may not reach a predetermined image density even if the image forming conditions are corrected due to the installation environment or aging of the components. Therefore, the image forming apparatus performs calibration to correct the difference between the target image density and the image density of the actually printed image. In the case of an image forming apparatus that forms a color image, the color balance (so-called color tone) fluctuates due to fluctuations in the image density of each color. Therefore, it is important to suppress the fluctuations in the image density of each color. Patent Document 2 discloses a control that adjusts the image forming conditions so that the maximum image density becomes the target image density by using toner pattern images formed under a plurality of different image forming conditions. The image forming conditions include the amount of exposure, the charging bias voltage, the developing bias voltage, and the like. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-44740 A [Patent Document 2] JP 2018-132544 A Summary of the Invention [Problem to be solved by the invention]

[0006] The technology disclosed in Patent Document 1 has low correction accuracy because it determines image forming conditions for multiple target image densities from a toner pattern image under one image forming condition. In particular, when correcting the correction amount using a preset table or the like, it is not possible to respond to changes in the relationship between the image forming conditions and the image densities due to changes in the state of the image forming device, and the correction accuracy is low.

[0007] The technology disclosed in Patent Document 2 requires adjustment of image formation conditions for each target maximum image density. For example, when there are two target maximum image densities, adjustment control of the image formation conditions needs to be performed twice to obtain each image formation condition. Similarly, when there are three target maximum image densities, adjustment control of the image formation conditions needs to be performed three times. In this way, when the target maximum image densities increase, the number of times of adjustment control of the image formation conditions also increases.

[0008] SUMMARY OF THE PRESENT DISCLOSURE In view of the above problems, it is a primary object of the present invention to provide an image forming apparatus capable of correcting image forming conditions with high accuracy in accordance with a plurality of target maximum image densities. [Means for solving the problem]

[0009] The image forming apparatus of the present invention comprises an image forming means capable of forming an image under image formation conditions corresponding to each of a plurality of image formation modes having different maximum image densities, and a control means for causing the image forming means to form an image in accordance with the image formation conditions, wherein the control means stores a difference value between a first image formation condition of a first image formation mode and a second image formation condition of a second image formation mode, and when adjusting the image density, the control means generates new first image formation conditions for the first image formation mode by adjusting the first image formation conditions, and generates new second image formation conditions based on the new first image formation conditions and the difference value. Effect of the Invention

[0010] According to the present invention, it is possible to highly accurately correct the image forming conditions in accordance with a plurality of target maximum image densities. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 2] FIG. [Diagram 3] FIG. 1 is a diagram showing the configuration of a document scanner. [Figure 4]FIG. [Diagram 5] FIG. 2 is a diagram illustrating the configuration of an image detection sensor. [Figure 6] 4 is a flowchart showing an automatic tone correction control process. [Figure 7] FIG. 13 is a diagram illustrating an example of a development contrast conversion table. [Figure 8] FIG. 11 is a graph showing an example of the relationship between image density value and development contrast. [Figure 9] FIG. 4 is an explanatory diagram of a tone correction table. [Figure 10] FIG. 11 is an explanatory diagram illustrating a target image density. [Figure 11] 11 is a flowchart showing a process for creating a tone correction table. [Figure 12] FIG. [Figure 13] FIG. 4 is an explanatory diagram of a correction LUT. [Figure 14] FIG. 4 is an explanatory diagram of a synthesis correction LUT. [Figure 15] 4 is a flowchart showing an image density adjustment process. [Figure 16] FIG. [Figure 17] FIG. 11 is a graph for explaining the relationship between the difference density and the charging bias change amount. [Figure 18] 11 is a diagram illustrating new image forming conditions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0013] 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus 100 according to the present embodiment forms a color image by an intermediate transfer method. The image forming apparatus 100 is, for example, a laser beam multifunction machine that forms an image by an electrophotographic method that employs a contact charging method and a two-component contact development method.

[0014] The image forming apparatus 100 includes four image forming units Pa, Pb, Pc, and Pd, a scanner unit 31, an intermediate transfer belt 11, a secondary transfer unit 12, and a fixing unit 9. The image forming units Pa, Pb, Pc, and Pd are arranged in series along the rotation direction of the intermediate transfer belt 11. The image forming units Pa, Pb, Pc, and Pd have the same configuration, and only differ in the color of the image they form. The image forming unit Pa of this embodiment forms a yellow (Y) image. The image forming unit Pb of this embodiment forms a magenta (M) image. The image forming unit Pc of this embodiment forms a cyan (C) image. The image forming unit Pd of this embodiment forms a black (K) image. Here, the configuration of the image forming unit Pa will be described, and descriptions of the image forming units Pb, Pc, and Pd will be omitted.

[0015] FIG. 2 is a diagram showing the configuration of the image forming unit Pa. The image forming unit Pa has a photosensitive drum 1a, a charger 2a, an exposure unit 3a, a developing unit 4a, a drum cleaner 5a, and a primary transfer unit 7a. The letter "a" at the end of the reference symbol indicates that the component is a component of the image forming unit Pa. Similarly, the letter "b" at the end of the reference symbol indicates that the component is a component of the image forming unit Pb. The letter "c" at the end of the reference symbol indicates that the component is a component of the image forming unit Pc. The letter "d" at the end of the reference symbol indicates that the component is a component of the image forming unit Pd. An intermediate transfer belt 11, which is an intermediate transfer body, is disposed between the photosensitive drums 1a, 1b, 1c, and 1d of the image forming units Pa, Pb, Pc, and Pd and the primary transfer units 7a, 7b, 7c, and 7d.

[0016] The exposure devices 3a, 3b, 3c, and 3d are integrally configured in a scanner unit 31. The scanner unit 31 is disposed below the image forming sections Pa, Pb, Pc, and Pd, and includes a light source 32, a rotating polygon mirror 33, and an exposure window 34. The light source 32 outputs laser beams the number of which corresponds to each color (four in this example). The laser beams output from the light source 32 are scanned by the rotation of the rotating polygon mirror 33. The luminous flux of the scanning beam is deflected by a plurality of reflecting mirrors, and is focused by an fθ lens on the generatrix of the photosensitive drums 1a, 1b, 1c, and 1d for exposure.

[0017] The light source 32 controls the emission of laser light based on a laser drive signal generated from an image signal representing an image to be formed. Image signals are prepared corresponding to each color. Therefore, the emission of laser light of each color is controlled based on the image signal of the corresponding color. As a result, electrostatic latent images of each color according to the image signals are formed on the photosensitive drums 1a, 1b, 1c, and 1d.

[0018] The developing units 4a, 4b, 4c, and 4d are filled with different color developers. In this embodiment, an example will be described in which a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed at a predetermined mixing ratio is used as the developer. The developing unit 4a is filled with a yellow developer. The developing unit 4b is filled with a magenta developer. The developing unit 4c is filled with a cyan developer. The developing unit 4d is filled with a black developer.

[0019] The developing units 4a, 4b, 4c, and 4d develop the electrostatic latent images formed on the photosensitive drums 1a, 1b, 1c, and 1d with the developer of the corresponding color to form a toner image. The primary transfer units 7a, 7b, 7c, and 7d transfer the toner images formed on the photosensitive drums 1a, 1b, 1c, and 1d to the intermediate transfer belt 11 in a superimposed manner in sequence at a timing according to the arrangement of the photosensitive drums 1a, 1b, 1c, and 1d and the rotation speed of the intermediate transfer belt 11. The intermediate transfer belt 11 functions as an image carrier and conveys the transferred toner images of each color to the secondary transfer unit 12 by rotating. Note that the toner remaining on the photosensitive drums 1a, 1b, 1c, and 1d after the transfer is removed by the drum cleaners 5a, 5b, 5c, and 5d.

[0020] The sheet S on which an image is printed is stored in a paper feed cassette 14, and is fed to the secondary transfer unit 12 in accordance with the timing of image formation in each of the image forming units Pa, Pb, Pc, and Pd. The secondary transfer unit 12 transfers the toner images of each color carried on the intermediate transfer belt 11 to the sheet S all at once. The secondary transfer unit 12 transports the sheet S onto which the toner images have been transferred to a fixing unit 9. The fixing unit 9 fixes the toner image to the sheet S by applying heat and pressure to the sheet S onto which the toner image has been transferred. The sheet S onto which the toner image has been fixed is discharged outside the image forming apparatus 100 as a finished product.

[0021] In addition, a belt cleaner 13 is provided downstream of the transfer position (secondary transfer position) of the toner image by the secondary transfer unit 12 in the rotation direction of the intermediate transfer belt 11 to remove toner remaining on the intermediate transfer belt 11 after transfer and fog toner. The belt cleaner 13 is constantly in contact with the intermediate transfer belt 11 to clean the intermediate transfer belt 11. An image detection sensor 50 is provided upstream of the secondary transfer position in the rotation direction of the intermediate transfer belt 11 to detect the toner image carried by the intermediate transfer belt 11.

[0022] A document scanner 200, which is an image reading device that reads an image of a document, is disposed on the upper part of the thus configured image forming apparatus 100. Further, an operation unit 300, which serves as a user interface, is disposed on the upper part of the image forming apparatus 100.

[0023] The process speed of the image forming apparatus 100 of this embodiment is, for example, 200 [mm / sec]. The image forming apparatus 100 performs image formation processing based on this process speed. When the image forming apparatus 100 starts image formation processing, the image forming units Pa to Pd form toner images on the photosensitive drums 1a to 1d. Here, the operation of the image forming unit Pa will be described with reference to FIG. 2. The other image forming units Pb to Pd form toner images by the same operation as the image forming unit Pa.

[0024] In the image forming section Pa, first, the surface of the photosensitive drum 1a is uniformly charged by the charger 2a. The photosensitive drum 1a is a drum-shaped photosensitive body having a photosensitive layer on its surface, and rotates in the direction of the arrow Y (see FIG. 2) around the drum axis during image forming processing. The charger 2a is, for example, roller-shaped, and both ends of a core metal are rotatably held by bearing members (not shown). The charger 2a is urged toward the photosensitive drum 1a by a pressing member 21a, and is pressed against the surface of the photosensitive drum 1a with a predetermined pressing force. As a result, the charger 2a rotates following the rotation of the photosensitive drum 1a.

[0025] A high-voltage power supply unit 101a is connected to the core of the charger 2a. The high-voltage power supply unit 101a applies a charging bias voltage of a predetermined condition to the core of the charger 2a. As a result, the surface of the rotating photosensitive drum 1a is contact-charged to a predetermined potential with a predetermined polarity. In this embodiment, the charging bias voltage applied to the charger 2a is an oscillating voltage in which a DC voltage and an AC voltage are superimposed. For example, the charging bias voltage is an oscillating voltage in which a sine-wave AC voltage with a frequency of 1.3 [kHz] and a peak-to-peak voltage Vpp of 1.5 [kV] is superimposed on a DC voltage. When a charging bias voltage of -600 [V] is applied, the surface of the photosensitive drum 1a is uniformly charged to -600 [V] (dark potential), which is the same as the DC voltage applied to the charger 2a.

[0026] The image forming apparatus 100 forms an electrostatic latent image on the surface of the charged photosensitive drum 1a by irradiating the surface with laser light by the exposure device 3a as described above. The image forming apparatus 100 supplies toner to the electrostatic latent image on the surface of the photosensitive drum 1a by the development device 4a as described above, thereby forming a toner image (developer image).

[0027] The developing device 4a of this embodiment is a two-component contact developing system in which a magnetic brush made of a two-component developer consisting of a nonmagnetic toner and a magnetic carrier is brought into contact with the photosensitive drum 1a to perform development. The nonmagnetic toner of this embodiment is negative polarity. The developing device 4a is equipped with a nonmagnetic developing sleeve 41a as a developer carrier. The developing sleeve 41a is disposed adjacent to and facing the photosensitive drum 1a, with a part of its outer circumferential surface exposed to the outside of the developing device 4a and maintaining a closest distance (SD gap) to the photosensitive drum 1a of 260 [μm]. The opposing portion of the photosensitive drum 1a and the developing sleeve 41a becomes the developing section.

[0028] The developing sleeve 41a is driven to rotate in the direction of the arrow X. A predetermined developing bias voltage is applied to the developing sleeve 41a from a high-voltage power supply unit 102a. In this embodiment, the developing bias voltage is an oscillating voltage in which a DC voltage and an AC voltage are superimposed. For example, the developing bias voltage is an oscillating voltage in which a square-wave AC voltage with a frequency of 8.0 [kHz] and a peak-to-peak voltage Vpp of 1.8 [kV] is superimposed on a DC voltage of -450 [V]. The toner adheres to the electrostatic latent image due to the potential difference between the developing bias voltage and the electrostatic latent image formed on the surface of the photosensitive drum 1a, and the electrostatic latent image is reversely developed.

[0029] In the image forming apparatus 100, the toner image formed on the photosensitive drum 1a is transferred to the intermediate transfer belt 11 by the primary transfer unit 7a. In this embodiment, the primary transfer unit 7a is configured by a roller. The primary transfer unit 7a is pressed against the photosensitive drum 1a with a predetermined pressing force. A transfer bias voltage of a positive polarity opposite to the negative polarity, which is the charging polarity of the toner, is applied to the primary transfer unit 7a from the high-voltage power supply unit 103a. In this embodiment, for example, a DC voltage of +1k [V] is applied as the transfer bias voltage. The application of the transfer bias voltage causes the toner to be transferred from the photosensitive drum 1a to the intermediate transfer belt 11.

[0030] 3 is a configuration diagram of the document scanner 200. The document scanner 200 includes a first mirror unit 204a, a second mirror unit 204b, an image sensor 205, a lens 215, a motor 216, an original size detection sensor 213, and a home position sensor 206 within a housing. The document scanner 200 includes a document platen glass 202 on which an original D can be placed, on the housing. The document size detection sensor 213 is used to detect the size of the original D placed on the document platen glass 202.

[0031] The first mirror unit 204a includes an illumination lamp 203 and a first mirror 207a. The second mirror unit 204b includes a second mirror 207b and a third mirror 207c. The first mirror unit 204a and the second mirror unit 204b are driven by a motor 216 and are movable in the Z direction.

[0032] When reading an original, the first mirror unit 204a and the second mirror unit 204b are driven by a motor 216 to temporarily move to a home position which is a detection position of a home position sensor 206. One original D is placed on the original glass 202 with its reading surface facing the original glass 202, and is fixed onto the original glass 202 by a pressure plate and an ADF unit (not shown).

[0033] The document scanner 200 turns on the illumination lamp 203 to irradiate the light onto the reading surface of the original 101. While moving in the Z direction, the first mirror unit 204a and the second mirror unit 204b deflect the reflected light (image light) reflected from the original 101 by the first mirror 207a, the second mirror 207b, and the third mirror 207c, and guide it to the lens 215. The lens 215 forms an image of the image light on the light receiving surface of the image sensor 205. The image sensor 205 converts the image light into an electrical signal. In this manner, the image of the original D is read.

[0034] 4 is an explanatory diagram of a control system that controls the operation of image forming apparatus 100 having such a configuration. In the control system, a CPU (Central Processing unit) 301 and a controller 87 mainly cooperate to control the operation of image forming apparatus 100. To the CPU 301, an image data generating section 302, a scanner image processing section 305, a scanner control section 306, a motor control section 91, a paper feed cassette 14, an image detection sensor 50, an image processing section 84, an I / F section 85, a timer 90, and a high voltage control section 92 are connected. Image information 88 is input to the controller 87.

[0035] The image data generating unit 302 is connected to the exposure units 3a to 3d via the laser driving units 303a to 303d. The document scanner 200 is connected to the scanner control unit 306 and the scanner image processing unit 305. The I / F unit 85 is connected to the operation unit 300. The high voltage control unit 92 is connected to the high voltage power supply units 101a to 101d, 102a to 102d, and 103a to 103d.

[0036] The CPU 301 generates various command signals and executes arithmetic processing in order to operate various sensors, motors, and the like provided in the image forming apparatus 100 according to an electrophotographic process. The CPU 301 also includes a built-in memory for storing data.

[0037] Under the control of the CPU 301, the image data generating unit 302 converts the image signal into a laser drive signal for laser control and transmits it to the laser driving units 303a to 303d. The image data generating unit 302 also has a function of generating toner pattern images for various adjustments. The laser driving units 303a to 303d drive the laser elements of the exposure units 3a to 3d based on the laser drive signal obtained from the image data generating unit 302, and control the lighting and light amount of the laser light.

[0038] The scanner control unit 306 controls the illumination lamp 203 of the document scanner 200 and the driving of the motor 216 under the control of the CPU 301. The scanner image processing unit 305 generates an image signal based on an electric signal obtained from the image sensor 205 of the document scanner 200 and transmits it to the CPU 301. The motor control unit 91 is electrically connected to a plurality of driving motors (not shown), and controls the driving timing and driving speed of each driving motor under the control of the CPU 301. The plurality of driving motors are driving sources for carrying the sheet S and rotating the photosensitive drums 1a to 1d, for example. The high voltage control unit 92 controls the output of various bias voltages required for the image forming process, such as a charging bias voltage, a developing bias voltage, and a transfer bias voltage. Under the control of the high voltage control unit 92, the output timing, voltage value, etc. of each bias voltage output from the high voltage power supply units 101a to 101d, 102a to 102d, and 103a to 103d are controlled.

[0039] The timer 90 measures time under the control of the CPU 301. The I / F unit 85 is a communication interface with the operation unit 300. The operation unit 300 has an input interface and an output interface. The input interface is, for example, a key button, a touch panel, etc. The output interface is, for example, a display, a speaker, etc. The CPU 301 accepts inputs such as instructions from the operation unit 300 via the I / F unit 85. The CPU 301 also displays various information on the display of the operation unit 300 via the I / F unit 85. The operation unit 300 may be an external device such as a personal computer connected to the image forming apparatus 100.

[0040] The paper feed cassette 14 is equipped with a sensor that detects the presence or absence of sheets S, for example, and transmits the detection result of the sensor to the CPU 301. The CPU 301 determines the presence or absence of sheets S in the paper feed cassette 14 based on the detection result, and if sheets S are not present, issues an instruction to replenish sheets S via the operation unit 300. The CPU 301 also performs control such as lifting up sheets S in the paper feed cassette 14.

[0041] The image processing unit 84 acquires image information 88 from the controller 87 via the CPU 301, and performs predetermined image processing on the image signal included in the image information 88 under the control of the CPU 301. The laser drive signal generated by the image data generating unit 302 is generated based on the image signal (image information 88) processed by the image processing unit 84. The image detection sensor 50 operates under the control of the CPU 301, and detects the toner image carried on the intermediate transfer belt 11. The image detection sensor 50 transmits the detection result of the toner image to the CPU 301.

[0042] 5 is a diagram illustrating the configuration of the image detection sensor 50. The image detection sensor 50 of this embodiment is of a regular reflection type, and includes a light-emitting unit 51, a light-receiving unit 52, and a control unit 53. The light-emitting unit 51 is composed of a light-emitting element such as an LED (Light Emitting Diode). The light-receiving unit 52 is composed of a light-receiving element such as a photodiode. The control unit 53 is a semiconductor device that controls the operation of the image detection sensor 50 according to an instruction from the CPU 301. For example, the control unit 53 controls the amount of light emitted (amount of light irradiated) by the light-emitting unit 51.

[0043] The light-emitting unit 51 irradiates light onto the surface of the intermediate transfer belt 11 that carries the toner image. The light-emitting unit 51 is arranged so as to irradiate light at an angle of 45 degrees with respect to the normal to the surface. The light-receiving unit 52 is arranged so as to be symmetrical with respect to the light-emitting unit 51 with respect to the normal to the surface. With this arrangement, the light-receiving unit 52 receives specularly reflected light from the base or toner image of the intermediate transfer belt 11 that passes through the area irradiated with light by the light-emitting unit 51, and outputs a value according to the light reception result (reflected light level). The area irradiated with light by the light-emitting unit 51 becomes the measurement area by the image detection sensor 50.

[0044] FIG. 5 shows a state where a toner image carried on the intermediate transfer belt 11 passes through a measurement area of ​​the image detection sensor 50. The toner image is a toner pattern image P1 for detecting image density. A detection value, which is a detection result of the toner pattern image P1 by the image detection sensor 50, varies according to the image density of the toner pattern image P1. The CPU 301 converts the detection value of the toner pattern image P1 by the image detection sensor 50 into an image density value. The CPU 301 acquires the image density value from the detection value of the toner pattern image P1 by the image detection sensor 50, for example, by a conversion table between detection value and image density value that the image processing unit 84 has. The conversion table is created based on the output characteristics of the image detection sensor 50. The detection value may be converted into an image density value by the control unit 53. In this case, the control unit 53 transmits the converted image density value to the CPU 301.

[0045] In this embodiment, the image detection sensor 50 has been described as a specular reflection type, but it may be a diffuse reflection type. Also, the image detection sensor 50 may be configured as a combination of the specular reflection type and the diffuse reflection type. In this case, the image detection sensor 50 includes, for example, a light receiving element that receives specularly reflected light and a light receiving element that receives diffusely reflected light as the light receiving unit 52.

[0046] (Image Formation Mode) The image forming apparatus 100 of this embodiment has a plurality of image forming modes with different maximum image densities. The plurality of image forming modes include a normal mode in which an image is formed based on an image forming condition in which the maximum image density is, for example, 1.50, and an image density increase mode in which an image is formed based on an image forming condition in which the maximum image density is, for example, 1.60. Although the image forming apparatus 100 of this embodiment is described as having two image forming modes, it may be configured to have an image forming mode controlled to image forming conditions in which three or more different maximum image densities are obtained. The image forming apparatus 100 can form an image based on the set image forming mode. The image adjustment method in the normal mode and the image density increase mode will be described below.

[0047] The normal mode is an image forming mode used for a product printed with documents, graphs, etc., such as those output by an office printer. The image density increase mode is an image forming mode used for a product printed with an image, such as a photographic image, such as those output by a production printer. The normal mode has an advantage of being able to reduce toner consumption compared to the image density increase mode. On the other hand, the image density increase mode has an advantage of being able to improve the image quality in the high density range to that of a production printer compared to the normal mode. The user can select and set such an image forming mode for each job, for example, by the printer driver or the operation unit 300. Note that, for example, the image forming mode is not limited to the above-mentioned configuration of being set for each job, and may be configured to be switched regardless of the job based on a user's instruction from the operation unit 300.

[0048] (Image density control) In this embodiment, image density control is performed when a user or a serviceman inputs an instruction to execute image density control from the operation unit 300, or when certain conditions are met, such as the cumulative number of image forming operations reaching a predetermined number or more.

[0049] In order to perform image density control, it is necessary to obtain an image density target that is a target for the image density. The image density target for image density control is obtained by automatic tone correction that is instructed to be executed by the user through the operation unit 300. Fig. 6 is a flowchart showing automatic tone correction control processing including maximum image density control processing. This processing is performed by the CPU 301 executing a computer program stored in the memory of the image processing unit 84.

[0050] The CPU 301 forms a toner pattern image P1 for maximum image density control on the intermediate transfer belt 11 by the image forming units Pa to Pd (S101). The toner pattern image P1 is configured by combining a plurality of pattern images with different image densities. The image forming conditions for each pattern image of the toner pattern image P1 are set as follows. Here, the development contrast Vc, the charging bias voltage Vd, the development bias voltage Vdc, and the exposure amount LPW by the scanner unit 31 are set as the image forming conditions, but other items may be included in the image forming conditions. Note that five pattern images are formed for each of the colors of yellow (Y), magenta (M), cyan (C), and black (K) in the toner pattern image P1. DmaxY1, DmaxM1, DmaxC1, DmaxK1:Vc1, Vd1, Vdc1, LPW1 DmaxY2, DmaxM2, DmaxC2, DmaxK2: Vc2, Vd1, Vdc1, LPW2 DmaxY3, DmaxM3, DmaxC3, DmaxK3: Vc3, Vd2, Vdc2, LPW2 DmaxY4, DmaxM4, DmaxC4, DmaxK4:Vc4, Vd3, Vdc3, LPW2 DmaxY5, DmaxM5, DmaxC5, DmaxK5:Vc5, Vd3, Vdc3, LPW3

[0051] The charging bias voltages Vd are Vd1 -500 [V], Vd2 -600 [V], and Vd3 -700 [V]. The developing bias voltages Vdc are -350 [V], Vdc2 -450 [V], and Vdc3 -550 [V], taking into account the fog removal potential of 150 [V]. The exposure amount LPW of the laser light is such that the surface light amount on the photosensitive drum 1 is LPW1 = 0.16 [μJ / cm 2 ], LPW2 is 0.24 [μJ / cm 2 ], LPW3 is 0.32 [μJ / cm 2 In this embodiment, the correction control is performed using the pattern images output under the above five conditions, but the number of pattern images and the image forming conditions are not limited to these.

[0052] The development contrast Vc is determined by the charging bias voltage Vd and the exposure amount LPW. Fig. 7 is an example of a development contrast conversion table showing the relationship between the development contrast Vc, the charging bias voltage Vd, and the exposure amount LPW. The development contrast conversion table is created in advance in accordance with the characteristics of the photosensitive drum and stored in the image processing unit 84. In this embodiment, the development contrast Vc is as follows: Vc1 is 90 [V], Vc2 is 160 [V], Vc3 is 231 [V], Vc4 is 301 [V], and Vc5 is 370 [V].

[0053] The CPU 301 detects the image density of each pattern image of the toner pattern image P1 by converting the detection result (detection value) of the toner pattern image P1 by the image detection sensor 50 using a conversion table between detection value and image density value (S102). The CPU 301 acquires a development contrast VcA that is an image density target Target A in the normal mode and a development contrast VcB that is an image density target Target B in the image density up mode based on the detected image density (S103). Target A is, for example, "1.50", and Target B is, for example, "1.60".

[0054] Fig. 8 is an exemplary diagram showing the relationship between the image density value detected from the toner pattern image P1 and the development contrast Vc. Based on the relationship shown in Fig. 8, the CPU 301 calculates the development contrast VcA representing the image density target Target A and the development contrast VcB representing the image density target Target B by linear interpolation between two points on either side of the target. In this embodiment, the development contrast VcA is set to 129 [V] and the development contrast VcB is set to 171 [V].

[0055] The CPU 301 calculates a difference value ΔVcd between the development contrast VcA and the development contrast VcB (S104). In this embodiment, the difference value ΔVcd is 171-129=42 [V]. The CPU 301 determines an image creation condition A (image forming condition A) for the development contrast VcA and an image creation condition B (image forming condition B) for the development contrast VcB (S105). In this embodiment, as an example, the exposure amount LPW for the development contrast Vc is set to 0.21 [μJ / cm 2 ] and change the charging bias voltage Vd, the imaging conditions (image forming conditions) are determined using the development contrast conversion table shown in FIG.

[0056] In this embodiment, the image forming condition A of the development contrast VcA is set to a charging bias voltage VdA of −500 [V] and an exposure amount PLWA of 0.21 [μJ / cm 2 The image forming condition B for the development contrast VcB is that the charging bias voltage VdA is −575 [V] and the exposure amount PLWA is 0.21 [μJ / cm 2 ]

[0057] Here, the imaging conditions are obtained by linear interpolation using the development contrast conversion table of Fig. 7, but the method of obtaining the imaging conditions is not limited to this. Also, the method of determining the imaging conditions in which the exposure amount is kept constant and the development contrast is changed is described as a preferred example because it causes less change in the gamma characteristic compared to the case in which the exposure amount is changed with the potential setting kept the same. However, the method of determining the imaging conditions is not limited to this.

[0058] The processes of S101 to S105 are maximum image density control processes based on the detection results of the toner pattern image P1. As a result, image creation conditions (image formation conditions) such as development contrast, charging bias voltage, and exposure amount during image formation in each image formation mode are determined. After the maximum image density control process, a gradation correction control process is performed.

[0059] The CPU 301 prints a test image of 64 gradations for each color used for tone correction control on the sheet S by the image forming apparatus 100 (S106). The image forming conditions at this time are image forming conditions A in the normal mode. In this embodiment, the image forming conditions A are a charging bias voltage VdA of −500 [V], an exposure amount LPWA of 0.21 [μJ / cm 2 ]. Note that the number of gradations of the test image is not limited to this. Sheet S on which the test image is printed is placed on platen glass 202 of document scanner 200. CPU 301 reads the test image printed on sheet S by document scanner 200, and detects the image density of the test image based on the reading result of the test image (S107).

[0060] CPU 301 performs an interpolation process and a smoothing process on the image density of the detected test image to generate engine gamma characteristics (also called gradation characteristics) for the entire image density region. CPU 301 creates a gradation correction table (hereinafter referred to as an "initial correction LUT (Look Up Table)") for converting an image signal so that the generated engine gamma characteristics become ideal gradation characteristics (gradation target) (S108). FIG. 9 is an explanatory diagram of the gradation correction table. In this embodiment, the gradation correction table is created by performing an inverse conversion process on the engine gamma characteristics so that they match the gradation target. The gradation correction table makes the image density of the image on sheet S match the gradation target in the entire image density region.

[0061] CPU 301 forms a toner pattern image for target acquisition by image forming units Pa to Pd (S109). In step S109, CPU 301 first causes image processing unit 84 to convert the image signal for target acquisition based on the gradation correction table. Next, CPU 301 uses the converted image signal for target acquisition to form a toner pattern image including a plurality of pattern images on intermediate transfer belt 11 based on image creation condition A (image formation condition A). CPU 301 then detects image density based on the detection result of the toner pattern image by image detection sensor 50 (S110). The detected image density value becomes the target image density for the image signal on intermediate transfer belt 11 during correction control.

[0062] In this embodiment, after the gradation correction table is created, a toner pattern image including pattern images of five gradations (30H, 60H, 90H, C0H, FFH) for each color is formed on the intermediate transfer belt 11. The CPU 301 acquires an image density value of the toner pattern image from the image detection sensor 50 (S111). The CPU 301 stores the acquired image density value in memory as a target image density (S112). FIG. 10 is an explanatory example diagram of the target image density. In this way, the target image density acquisition process is completed, and the automatic gradation correction ends.

[0063] The gradation patterns and number of gradations to be created are not limited to those described above, and may be set as appropriate as necessary. For example, the number of pattern images in the mid-tone portion may be increased in order to focus on correcting the mid-tone region where the image density changes greatly due to the engine γ characteristics. Also, the number of pattern images in the high image density region may be increased in order to stably output the high image density side. Furthermore, the number of pattern images in the low image density region may be increased in order to place importance on the gradation on the highlight side.

[0064] (Image density adjustment) The image forming apparatus 100 periodically performs an image density adjustment process to stabilize the image density of the delivered image. In the image density adjustment process, a toner pattern image for adjusting the image density is periodically formed on the intermediate transfer belt 11, and this toner pattern image is detected by the image detection sensor 50. A correction table for correcting the gradation correction table is created by comparing the detection result of the toner pattern image by the image detection sensor 50 with the above-mentioned target image density and performing an inverse conversion process on the detection result. The image forming apparatus 100 updates the gradation correction table by combining the correction table with the gradation correction table, thereby stabilizing the density of the image formed by the image forming apparatus 100.

[0065] FIG. 11 is a flowchart showing the process of creating a gradation correction table. The CPU 301 of this embodiment starts the process of creating a gradation correction table when, for example, the cumulative number of image forming operations reaches a predetermined number or more. This process is performed by the CPU 301 executing a computer program stored in the memory of the image processing unit 84. The process of creating a gradation correction table may also be performed when the time elapsed since the previous process of creating a gradation correction table was completed or when the installation environment (temperature and humidity) of the image forming apparatus 100 changes significantly. The time elapsed since the previous process of creating a gradation correction table was completed is measured by, for example, a timer 90. The change in the installation environment of the image forming apparatus 100 can be detected by, for example, providing an environmental sensor such as a temperature sensor or a humidity sensor in the image forming apparatus 100.

[0066] After starting the process of creating the gradation correction table, CPU 301 causes image forming units Pa to Pd to form a toner pattern image for gradation correction on intermediate transfer belt 11 based on image creation condition A (image forming condition A) (S201). At this time, image processing unit 84 generates an image signal for forming a toner pattern image used in step S201 by converting an image signal for gradation correction based on the initial correction LUT. CPU 301 acquires the image density of the toner pattern image based on the detection result of image detection sensor 50 for the toner pattern image (S202). Since the toner pattern image is configured by combining multiple pattern images with different image densities, CPU 301 acquires multiple image densities corresponding to each pattern image.

[0067] CPU301 creates a density curve based on the acquired multiple image densities (S203). FIG. 12 is an explanatory diagram of a density curve. CPU301 plots the acquired image densities for each gradation and creates a density curve (dashed line) for the acquired image densities indicated by white circles. The density curve is created by a general approximation method such as using an approximation formula. CPU301 creates a correction table (correction LUT) based on the created density curve (S204). FIG. 13 is an explanatory diagram of the correction LUT. CPU301 creates a correction LUT (long dashed line) by performing an inverse conversion to correct the created density curve (dashed line) to a density curve (dotted line) of a target image density.

[0068] The CPU 301 creates a composite correction LUT from the created correction LUT and the initial correction LUT (S205). Fig. 14 is an explanatory diagram of the composite correction LUT. The CPU 301 multiplies the created correction LUT and the initial correction LUT to create a composite correction LUT (long two-dot chain line), which is reflected in the image of the deliverable and output.

[0069] (Image formation processing of the product) In the image forming apparatus 100 of this embodiment, the image creation conditions (image formation conditions) may change due to image density adjustment during image formation processing. That is, when the image adjustment conditions are satisfied during image formation processing on the sheet S, image density adjustment is performed and the image creation conditions (image formation conditions) change. Therefore, new image creation conditions are determined after the image density adjustment. The next image formation on the sheet S is performed under the new image creation conditions. FIG. 15 is a flowchart showing the image density adjustment processing during image formation processing. This processing is performed by the CPU 301 executing a computer program stored in the memory of the image processing unit 84.

[0070] The CPU 301 forms and outputs an image on the sheet S under image forming conditions in the normal mode or the image density increase mode by the image forming apparatus 100 according to the print job (S301). The image forming conditions at this time (charging bias voltage Vd, developing bias voltage Vdc, exposure amount LPW) are determined by the above-mentioned automatic tone correction control process. FIG. 16 is an example diagram of the image forming conditions. This image forming condition is an initial state after the automatic tone correction control and before the image density adjustment, and the correction LUT is the initial correction LUT. In addition, in this embodiment, the same correction LUT is used in the normal mode and the image density increase mode. In this embodiment, the charging bias voltage Vd is changed with the exposure amount LPW kept constant in the normal mode and the image density increase mode. Therefore, the change in gradation when the maximum image density changes is smaller than when the exposure amount LPW is changed, and the gradation is less likely to be broken even if the same correction LUT is used.

[0071] During the image forming process or after output of the result, CPU 301 judges whether or not a predetermined start condition for executing image density adjustment is satisfied (S302). The start condition for image density adjustment is judged based on values ​​related to fluctuations in image density, such as the cumulative number of image forming operations, the time elapsed since the previous image density adjustment, the amount of toner used for printing, the amount of fluctuation in toner used, the amount of toner replenishment, and environmental changes of image forming apparatus 100. For example, in the case of the cumulative number of image forming operations, whether or not the start condition for image density adjustment is satisfied is judged based on whether or not the cumulative number is equal to or greater than a predetermined number.

[0072] If the start conditions for image density adjustment are not satisfied (S302: N), the CPU 301 continues image formation (S301). Alternatively, if the print job is completed, the CPU 301 ends the process. If the start conditions for image density adjustment are satisfied (S302: Y), the CPU 301 starts image density adjustment and causes the image forming units Pa to Pd to form toner pattern images for maximum image density adjustment on the intermediate transfer belt 11 (S303). The CPU 301 acquires the image density of the toner pattern image based on the detection result of the toner pattern image by the image detection sensor 50 (S304).

[0073] In this embodiment, the image density adjustment is performed under the image forming conditions in the normal mode, regardless of the image forming mode before the start of the image density adjustment. Therefore, the toner pattern image is formed under the image forming conditions in the normal mode (hereinafter referred to as image forming conditions A1) shown in Fig. 16. The maximum image density adjustment in this embodiment uses a method of calculating the amount of change from the difference between the image density detected from a pattern image with an image density of 100% (FFH), which is the maximum image density, and the target image density of the maximum image density.

[0074] The CPU 301 calculates a difference density ΔD between the image density detected from the toner pattern image for adjusting the maximum image density formed under the image forming conditions of the image forming conditions A1 and the target image density (1.50) of the maximum image density (S305). The CPU 301 determines the amount of change in the image forming conditions based on the relationship between the difference density ΔD and the amount of change in the charging bias (S306). The CPU 301 changes the image forming conditions based on the amount of change in the image forming conditions determined (S307).

[0075] 17 is an explanatory diagram of the relationship between the difference density ΔD and the charging bias change amount. The CPU 301 holds information (table) that represents the relationship between the difference density ΔD and the charging bias change amount in advance, and determines the change amount of the image forming conditions based on the table. In this case, the change amount of the image forming conditions is the change amount of the charging bias voltage Vd.

[0076] For example, if the target image density for the maximum image density is "1.50" and the detected image density is "1.42", the difference density ΔD is "-0.08". Therefore, the change amount ΔVd of the charging bias voltage Vd is +60 [V]. As a result, the charging bias voltage Vd, which is an image formation condition (imaging condition), is changed from 500 [V] to 560 [V].

[0077] The image forming conditions after the image density adjustment are changed from the imaging condition A1 in which the charging bias voltage VdA1 is -500 [V] to the imaging condition A2 in which the charging bias voltage VdA2 is -560 [V]. Also, the image forming conditions after the image density adjustment are changed from the imaging condition A1 in which the development contrast VcA1 is 129 [V] to the imaging condition A) in which the development contrast VcA2 is 163 [V]. There is no change in the exposure amount. The exposure amount A1 is, for example, 0.21 [μJ / cm 2 ].

[0078] This completes the maximum image density adjustment. Next, CPU 301 causes image forming units Pa to Pd to form a toner pattern image for gradation control on intermediate transfer belt 11 under the image forming condition A2 (S308). CPU 301 acquires the image density of the toner pattern image based on the detection result of the toner pattern image by image detection sensor 50 (S309). CPU 301 compares the acquired image density with the target image density acquired by automatic gradation correction (S310).

[0079] The CPU 301 performs the above-mentioned inverse conversion process based on the comparison result to create a new composite correction LUT (S311). In this way, the correction LUT (LUT_A1) used before the image density adjustment is changed to the new correction LUT (LUT_A2). The CPU 301 determines the image formation conditions for each image formation mode (S312).

[0080] Fig. 18 is a diagram illustrating the new image forming conditions determined by the process of Fig. 15. As described above, the image forming conditions A1 in the normal mode are: the charging bias voltage VdA2 is -560 [V], the exposure amount LPWA2 is 0.21 [μJ / cm 2 The image forming condition A2 is changed to the image forming condition A1 in which the development contrast VcA2 is 163 [V] and the image forming condition B in the image density increasing mode is also determined without forming a pattern image.

[0081] In this embodiment, during automatic gradation correction, a difference value ΔVcd in the development contrast between the normal mode and the image density increase mode is calculated (the process of S104 in FIG. 6). The development contrast in the image density increase mode is calculated by adding this difference value ΔVcd in the development contrast to the development contrast in the normal mode.

[0082] Here, the development contrast in the normal mode after adjustment is 163 [V], and the difference value ΔVcd calculated during automatic tone correction is 42 [V], so the development contrast in the newly set image density up mode is 205 [V]. Furthermore, by the above processing, the charging bias voltage VdB2 in the image density up mode is −635 [V], and the exposure amount PLWB2 is 0.21 [μJ / cm 2 ]

[0083] As described above, when the image adjustment conditions are satisfied during image formation, the image forming apparatus 100 performs image adjustment to determine new image formation conditions, and performs the next image formation under the determined image formation conditions. Whether the image formation mode is the normal mode or the image density increase mode, the image forming apparatus 100 performs image adjustment under the image formation conditions for the normal mode, and determines new image formation conditions for each image formation mode.

[0084] The effects of this embodiment will be described below. As a comparative example, a method of calculating image forming conditions in each image forming mode, that is, the normal mode and the image density increasing mode, during image adjustment will be described.

[0085] The image forming apparatus 100 updates the image forming conditions for the normal mode and the image density increasing mode based on the detection result of the pattern image for the normal mode without forming a pattern image for the image density increasing mode. Therefore, the image forming apparatus significantly reduces the adjustment time required for image adjustment during image formation.

[0086] In the image forming apparatus 100 that can set a plurality of image forming modes such as a normal mode and an image density increase mode, it is necessary to determine the image forming conditions for each image forming mode by image adjustment. In this embodiment, the image forming conditions for each image forming mode are determined by the process shown in FIG. 15. That is, a difference value between the image forming conditions for each image forming mode is calculated in advance during automatic tone correction. When image adjustment is performed, image adjustment is performed in the image forming mode in which the target image density was obtained during automatic tone correction, which is the normal mode in this embodiment, and the image forming conditions for the image density increase mode are determined using the image forming conditions for the normal mode and the difference value.

[0087] Therefore, the image forming conditions in the normal mode and the image density increase mode can be corrected without separately executing image adjustment for the image density increase mode. Note that, if the image forming conditions for the image density increase mode are determined during automatic gradation correction and the target image density for the image density increase mode is obtained, image adjustment is performed by returning to the image forming conditions for the image density increase mode even during normal mode operation. This reduces the adjustment time.

[0088] On the other hand, when the image forming conditions for the normal mode and the image density increase mode are calculated for each image forming mode during image adjustment, the process is as follows. In this case, the process shown in FIG. 15 is performed multiple times. In this embodiment, as described above, the charging bias voltage is changed in the normal mode and the image density increase mode, rather than the exposure amount. Therefore, the change in gradation when the maximum image density changes is smaller than when the exposure amount is changed. Therefore, the same LUT is used in the normal mode and the image density increase mode.

[0089] For this reason, it is not necessary to create a correction LUT for the image density up mode, but it is necessary to determine at least the development contrast for the image density up mode, and it is necessary to perform correction calculation processing by forming and detecting a pattern image for adjusting the maximum image density. For the above reasons, the adjustment of the image formation conditions for each image formation mode takes longer than in this embodiment.

[0090] As described above, the image forming apparatus 100 of this embodiment has a plurality of target maximum image densities and can change the image forming conditions according to each target maximum image density. This image forming apparatus 100 can perform correction control to a plurality of image forming conditions corresponding to a plurality of maximum image densities without increasing the control time, regardless of the image forming conditions during image formation.

Claims

1. an image forming means capable of forming an image under image forming conditions corresponding to each of a plurality of image forming modes having different maximum image densities; A control means for controlling the image forming means to form an image according to an image forming condition, the control means stores a difference value between a first image forming condition in a first image forming mode and a second image forming condition in a second image forming mode; the control unit generates new first image forming conditions for the first image forming mode by adjusting the first image forming conditions when adjusting the image density, and generates new second image forming conditions based on the new first image forming conditions and the difference value. Image forming device.

2. an image carrier on which an image is formed by the image forming means; an image detection unit that detects the image formed on the image carrier, the control means forms a pattern image for correcting a maximum image density on the image carrier by the image forming means under the first image forming condition, and generates the new first image forming condition by changing the first image forming condition according to a change amount of the first image forming condition determined based on a detection result of the pattern image by the image detection means.

2. The image forming apparatus according to claim 1.

3. the control means forms a plurality of pattern images having different image densities for correcting a maximum image density on the image carrier by the image forming means, obtains a target image density for the first image forming mode and a target image density for the second image forming mode based on a detection result of each of the plurality of pattern images by the image detection means, and generates the difference value from each target image density.

3. The image forming apparatus according to claim 2.

4. The control unit starts a process for determining an amount of change in the first image forming condition based on a value related to a fluctuation in image density.

3. The image forming apparatus according to claim 2.

5. The control unit starts a process for determining an amount of change in the first image forming condition based on an accumulated number of times of the image forming operation by the image forming unit.

3. The image forming apparatus according to claim 2.

6. the control means forms a plurality of pattern images having different image densities for correcting a maximum image density on the image carrier by the image forming means, and generates the difference value based on the detection results of each of the plurality of pattern images by the image detection means.

3. The image forming apparatus according to claim 2.

7. the image forming means includes a photoconductor, a charging means for uniformly charging the photoconductor, an exposure means for exposing the charged photoconductor to light to form an electrostatic latent image, and a developing means for developing the electrostatic latent image; the image forming conditions include at least one of a charging bias voltage for the charging means to charge the photoconductor, an exposure amount by the exposure means, a developing bias voltage for development by the developing means, and a development contrast determined by the charging bias voltage and the exposure amount; 2. The image forming apparatus according to claim 1.

8. the control means calculates a difference value between the development contrasts of the first image forming condition and the second image forming condition as the difference value, generates a development contrast of the new first image forming condition, and generates a development contrast of the new second image forming condition based on the development contrast of the new image forming condition and the difference value.

8. The image forming apparatus according to claim 7.

9. an exposure amount in the first image forming mode and an exposure amount in the second image forming mode are equal to each other, 9. The image forming apparatus according to claim 8.

10. a maximum image density in the second image forming mode is higher than a maximum image density in the first image forming mode, 2. The image forming apparatus according to claim 1.

Images