JP2023028458A - Image forming apparatus and image density adjustment method - Google Patents

Abstract

To provide an image forming apparatus that executes image density adjustment for intermediate gradation at a more appropriate timing than before and has high convenience for a user.SOLUTION: An image forming apparatus comprises: an image forming unit that forms a toner image to form an image; an image density adjustment unit that executes image density adjustment; a storage unit that stores the ratio of a predetermined type of images that may be affected by a change in the density of images with intermediate gradation to all the types of images formed by the image forming unit in a predetermined period as a contribution ratio of intermediate gradation images; and a control unit that controls the image forming unit, the image density adjustment unit, and the storage unit. The image density adjustment unit executes image density adjustment for maximum density and image density adjustment for intermediate gradation respectively at predetermined execution timings based on the cumulative number of images formed by the image forming unit or the cumulative operating time of the image forming unit. The control unit changes the execution timing of the image density adjustment for intermediate gradation according to the contribution ratio of the intermediate gradation images stored in the storage unit.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image forming apparatus and an image density adjusting method, and more particularly to an image forming apparatus having an image density adjusting function and an image density adjusting method.

Conventionally, in image forming apparatuses such as electrophotographic copiers and printers, test toner patches are formed on the surface of a photosensitive drum or a transfer belt, exposed to light, and detected by a reflective optical sensor. 2. Description of the Related Art A function of adjusting an image density by controlling a developing bias so as to achieve a target image density based on a detected value of reflected light is known.

In addition, with the increasing number of gradations in printed images in recent years, there is also an image density adjustment function for maximum density that adjusts the maximum density image by forming toner patches corresponding to the maximum density on the surface of the photoreceptor drum and the surface of the transfer belt. In addition, there is also known an image forming apparatus having an image density adjustment function for intermediate gradation to adjust an image of intermediate gradation by forming a toner patch for intermediate gradation.

As an invention relating to such image density adjustment for maximum density and image density adjustment for intermediate gradation, conventionally, density control is performed by creating both a reference image pattern for maximum density control and a reference image pattern for halftone control. In addition to the first control mode that performs density control, a second control mode that creates only a reference image pattern for maximum density control and performs density control, and a second control mode that creates only a reference image pattern for halftone control and performs density control. An invention of an image forming apparatus that prepares a third control mode and selects one of these three control modes as needed to perform image density control has been disclosed (see, for example, Japanese Laid-Open Patent Publication No. 2002-100003).

JP-A-2003-35978

Conventionally, the image density adjustment for maximum density and the image density adjustment for intermediate gradation are basically executed at the same timing, or the execution determination is made at the same timing, and when a predetermined condition is satisfied, was running.

The execution timing of the image density adjustment is, for example, when the cumulative number of images formed reaches a predetermined number, when the cumulative time of image formation reaches a predetermined time, or when the temperature changes. Image density adjustment for maximum density and image density adjustment for intermediate gradation are executed when the value of environmental variation such as humidity and humidity reaches a predetermined value.

Although the image quality is stabilized by performing such image density adjustment, since it is necessary to form a toner patch to perform the image density adjustment, the more frequently the image density adjustment is performed, the more toner is consumed. end up

For users who print color images and photographic images infrequently, the need for image density adjustment for intermediate gradation is not so great. There is a risk that image density adjustment for gradation will be performed.

Since the image density adjustment for intermediate gradation requires formation of toner patches of a plurality of gradations, a large amount of toner is consumed each time the image density adjustment for intermediate gradation is performed.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the circumstances as described above, and its object is to perform image density adjustment for intermediate gradation at a more appropriate timing than in the prior art, and to improve the user's convenience in image formation. An object of the present invention is to provide an apparatus and an image density adjustment method.

(1) The present invention provides an image forming section that forms an image by forming a toner image, an image density adjusting section that executes image density adjustment, and all kinds of images formed by the image forming section during a predetermined period. a storage unit that stores, as a contribution rate of a halftone image, a ratio of a predetermined type of image that is likely to be affected by a change in image density of a halftone image in an image; a density adjustment section and a control section for controlling the storage section, wherein the image density adjustment section adjusts the maximum density based on the cumulative number of images formed by the image forming section or the cumulative operating time of the image forming section; and the image density adjustment for intermediate gradation are respectively executed at predetermined execution timings, and the control unit controls the contribution rate of the intermediate gradation image among the images stored in the storage unit. The present invention provides an image forming apparatus characterized by changing execution timing of the image density adjustment for the intermediate gradation.
Further, the present invention provides an image forming process for forming an image by forming a toner image, an image density adjusting process for performing image density adjustment, and all types of images formed by the image forming process during a predetermined period. and a storing step of storing, as a contribution rate of a halftone image, a ratio of a predetermined type of image that may be affected by a change in image density of the halftone image; Based on the cumulative number of images formed or the cumulative operation time of image formation, in the image density adjustment step, the image density adjustment for maximum density and the image density adjustment for intermediate gradation are performed at predetermined execution timings. and changing the execution timing of the image density adjustment for the intermediate gradation according to the contribution rate of the intermediate gradation image stored in the storing step. .

In the present invention, the "image forming apparatus" means a copier or multifunction machine having a copying (copying function) function, such as a printer that uses an electrophotographic method for image formation using toner, or an MFP (Multifunctional Peripheral) that includes functions other than copying. : multi-function peripheral device) that forms and outputs images.
The "contribution rate of intermediate gradation images" is, for example, among the number of all types of images formed in the most recent predetermined period, the intermediate gradation of color photographic images, color character images, etc. is important. This is a value obtained by calculating the ratio of the number of images that becomes .
The "image density adjustment unit" includes, for example, a reflective optical sensor, irradiates light on the toner image formed by the image forming unit at a predetermined stage, and detects the above-described image density detected by the reflective optical sensor. This is the part that adjusts the image density based on the reflected light from the toner image.

According to the present invention, among images formed in the past, image density adjustment is performed by changing the execution timing of the image density adjustment for intermediate gradation based on the contribution rate of the intermediate gradation image, whereby the conventional Therefore, it is possible to realize an image forming apparatus and an image density adjustment method that are highly convenient for the user by executing the image density adjustment for intermediate gradation at more appropriate timing.

1 is a perspective view showing the appearance of a digital multi-function peripheral of the present invention; FIG. 2 is a cross-sectional view showing the internal configuration of the digital multi-function peripheral of FIG. 1; FIG. 2 is a block diagram showing a schematic configuration of the digital MFP of FIG. 1; FIG. 2 is a flowchart showing an example of execution processing of image density adjustment of the digital multi-function peripheral of FIG. 1; 2 is a table showing an example of a determination table of image density adjustment frequencies for maximum density and intermediate gradation of the digital multi-function peripheral of FIG. 1; 2 is an explanatory diagram showing an example of execution timing of image density adjustment for maximum density and intermediate gradation of the digital multi-function peripheral shown in FIG. 1; FIG. FIG. 6A shows an example of execution timing in the initial state, FIG. 6B shows an example of a case where the necessity of image density adjustment for intermediate gradation is low, and FIG. An example in which the degree of necessity of image density adjustment for gradation is even lower than that in FIG. 6B is shown. 2 shows an example of a toner patch for image density adjustment of the digital multi-function peripheral shown in FIG. 1. FIG. FIG. 7A shows an example of a toner patch for maximum density, and FIG. 7B shows an example of a toner patch for intermediate gradation. FIG. 11 is a table showing an example of a determination table for determining the number of toner patches to be formed during image density adjustment for intermediate gradation in the digital multi-function peripheral according to Embodiment 2 of the present invention; FIG. FIG. 10 shows an example of toner patches to be formed during image density adjustment for intermediate gradation in the digital multi-function peripheral according to Embodiment 2 of the present invention. FIG. 9A shows a specific example with 3 patches, FIG. 9B shows a specific example with 5 patches, FIG. 9C shows a specific example with 9 patches, and FIG. shows a concrete example with 14 patches. 13 is a flow chart showing an example of image density adjustment execution processing of the digital multi-function peripheral according to Embodiment 3 of the present invention; FIG. 12 is a block diagram showing a schematic configuration of a digital multi-function peripheral according to Embodiment 4 of the present invention; FIG. 14 is a flowchart showing an example of execution processing of image density adjustment after user login of the digital multi-function peripheral according to Embodiment 4 of the present invention; FIG. 14 is a flow chart showing an example of execution processing of image density adjustment after receiving an image forming instruction of the digital multi-function peripheral according to Embodiment 5 of the present invention;

Next, preferred embodiments of the present invention will be described.

(2) In the image forming apparatus according to the present invention, the image forming section has a function of forming a color photographic image, and determines whether or not the image formed by the image forming section is the color photographic image. An image determination unit is further provided, wherein the storage unit stores the number of all types of images and the number of color photographic images formed by the image forming unit during a predetermined period, and the control unit stores the number of the color photographic images. The ratio of the number of color photographic images to the number of all kinds of images may be calculated as the contribution ratio of the halftone image.

In this way, based on the contribution ratio of the halftone image calculated from the ratio of the number of color photographic images among all types of images formed by the image forming unit during a predetermined period, To provide an image forming apparatus which executes image density adjustment for intermediate gradation at a more appropriate timing than in the past by changing execution timing of image density adjustment for intermediate gradation and executing image density adjustment, and which is highly convenient for a user. can be realized.

(3) In the image forming apparatus according to the present invention, the image forming section has a function of forming a color photographic image and a color character image, and the image formed by the image forming section is the color photographic image or the color character image. The storage unit stores the number of all types of images formed by the image forming unit in a predetermined period, the color photographic image and the color photographic image. and the total number of character images, and the control unit calculates the ratio of the total number of the color photographic images and the color character images to the number of the images of all types, and calculates the ratio of the total number of the color photographic images and the color character images to the number of the intermediate gradation images. Contribution rate may be used.

By doing so, the number of halftone images obtained by calculating from the ratio of the total number of color photographic images and color character images among all types of images formed by the image forming section during a predetermined period is obtained. By changing the execution timing of the image density adjustment for the intermediate gradation based on the contribution rate and executing the image density adjustment, the image density adjustment for the intermediate gradation is executed at a more appropriate timing than in the past, improving user convenience. It is possible to realize an image forming apparatus with a high

(4) In the image forming apparatus according to the present invention, the storage unit instructs the image density adjustment unit to shorten the execution timing of the image density adjustment for the intermediate gradation as the contribution rate of the intermediate gradation image increases. A table indicating a relationship between a predetermined contribution rate of the halftone image and the execution timing is stored, and the control unit refers to the table to determine the halftone image from the contribution rate of the halftone image. It may determine the execution timing of image density adjustment for adjustment.

In this way, among the images formed in the past, based on the contribution rate of the intermediate tone image, the execution timing of the image density adjustment for the intermediate tone is determined and the image density adjustment is executed. It is possible to realize an image forming apparatus that performs image density adjustment for intermediate gradation more appropriately and is highly convenient for the user.

(5) In the image forming apparatus according to the present invention, the storage section stores toner image patches to be formed in the image density adjustment section for adjusting the image density for the intermediate gradation as the contribution rate of the intermediate gradation image becomes lower. A table showing the relationship between the contribution rate of the halftone image predetermined to reduce the number and the number of patches is stored, and the control unit refers to the table to determine the number of halftone images. The number of patches may be determined from the contribution rate.

In this manner, the number of toner patches to be formed in the image density adjustment for the intermediate gradation is determined based on the contribution rate of the intermediate gradation image among the images formed in the past, and the image density adjustment is executed. As a result, it is possible to perform image density adjustment for intermediate gradation more appropriately than conventionally, and to realize an image forming apparatus that is highly convenient for the user.

(6) The image forming apparatus according to the present invention further includes an operation unit for receiving input of various commands from the user, and when the operation unit receives input of an image density adjustment command from the user, the control unit Of all types of images formed by the image forming section during a predetermined period from the time the density adjustment command is received, a predetermined type that may be affected by changes in image density of intermediate gradation. The ratio of the image is stored in the storage unit as a contribution ratio of the halftone image, and the execution timing of the image density adjustment for the halftone image is changed by the image density adjustment unit according to the contribution ratio of the halftone image. After that, the image density adjustment for the highest density and the image density adjustment for the intermediate gradation may be performed at predetermined execution timings.

In this way, image density adjustment for intermediate gradation can be performed based on the contribution rate of the intermediate gradation image among all kinds of images formed during the past predetermined period from the time when the user inputs the image density adjustment command. By executing the image density adjustment by changing the execution timing of , the image density adjustment for intermediate gradation can be executed at a more appropriate timing than in the conventional art, and an image forming apparatus with high user convenience can be realized.

(7) The image forming apparatus according to the present invention further includes a user authentication section that accepts user login authentication, wherein the image density adjustment section adjusts the image formed by the image forming section for each user whose login authentication is accepted. or the cumulative operation time of the image forming unit, the image density adjustment for maximum density and the image density adjustment for intermediate gradation are respectively executed at predetermined execution timings, and the control unit performs login authentication. The execution timing of the image density adjustment for the intermediate gradation may be changed according to the contribution ratio of the intermediate gradation image for each accepted user.

In this way, image density adjustment is executed by changing the execution timing of image density adjustment for intermediate gradation based on the contribution ratio of intermediate gradation image among images formed in the past for the logged-in user. By doing so, it is possible to execute the image density adjustment for intermediate gradation at a more appropriate timing than in the conventional art, and realize an image forming apparatus that is highly convenient for the user.

The present invention will be described in further detail below with reference to the drawings.
It should be noted that the following description is illustrative in all respects and should not be construed as limiting the present invention.

[Embodiment 1]
<Configuration of Digital MFP 1>
A digital multi-function peripheral 1, which is an embodiment of the image forming apparatus of the present invention, will be described with reference to FIGS. 1 and 2. FIG.

FIG. 1 is a perspective view showing the appearance of a digital multi-function peripheral 1 of the present invention.
FIG. 2 is a cross-sectional view showing the internal configuration of the digital multifunction peripheral 1 of FIG.

The digital multifunction peripheral 1 is a device such as an MFP (Multifunction Peripheral) that digitally processes image data and has a copy function, a printer function, a scanner function, a facsimile function, and an e-mail transmission function.

The digital multi-function peripheral 1 has a copy function, a print function, and a FAX function as print modes. A printing function is selected by the control unit 10 (FIG. 3) according to the reception of the print job.

<Internal Configuration of Digital MFP 1>
In FIG. 2, the digital multifunction machine 1 is a color multifunction machine, and includes an optical system unit 50, first to fourth visible image forming units 51 to 54, an intermediate transfer belt 55, a secondary transfer unit 56, a fixing section 2, an internal A paper feed unit 57 , a manual paper feed unit 58 , and a paper discharge tray 75 are provided.

The digital multifunction peripheral 1 forms toner images using these first to fourth visible image forming units 51 to 54, intermediate transfer belt 55 and secondary transfer unit 56. FIG.

The optical system unit 50 is arranged so that beams from four laser light sources 64 reach four sets of photosensitive drums 59 , 65 , 66 and 67 .

The first visible image forming unit 51 has a photosensitive drum 59, a charging roller 60, an optical system unit 50, a developing unit 61a, and a primary transfer unit 62a.

A charging roller 60, a developing unit 61a and a cleaning unit 63 are arranged around a photosensitive drum 59 serving as an image carrier.

These units form a toner image on the photosensitive drum 59 and transfer the toner image to the intermediate transfer belt 55 .

The photoreceptor drum 59 is an image carrier on which a toner image is formed. It includes a substrate and a photosensitive layer formed on the surface of the conductive substrate.

The photoreceptor drum 59 is rotated counterclockwise toward the paper surface of FIG. Rotate with s.

The primary transfer unit 62a is arranged so as to be in pressure contact with the photosensitive drum 59 with the intermediate transfer belt 55 therebetween.

Since the other second to fourth visible image forming units 52 to 54 have the same configuration as the first visible image forming unit 51, description thereof will be omitted.

The developing units 61a, 61b, 61c, and 61d of the units 51 to 54 contain toners of black (K), cyan (C), magenta (M), and yellow (Y), respectively.

Hereinafter, the development units 61a, 61b, 61c, and 61d for each color may be referred to as the development unit 61 as a representative.
Also, the primary transfer units 62a, 62b, 62c, and 62d for each color are sometimes referred to as the primary transfer unit 62 as a representative.

A toner image of each color is transferred to the intermediate transfer belt 55, and the color toner image of each color is superimposed on the surface.
The intermediate transfer belt 55 is driven and rotated by tension rollers 68 and 69 .
A secondary transfer unit 56 is arranged in contact with the tension roller 68 side of the intermediate transfer belt 55 .

The secondary transfer unit 56 transfers the color toner image formed on the intermediate transfer belt 55 to the internal paper feeding unit by applying a high voltage having a polarity opposite to the charged polarity of the toner to the transfer area by the transfer roller 621a or the like. 57 and manual paper feeding unit 58, onto the recording medium 31 fed by feeding rollers 73 and 74, respectively.

After that, the recording medium 31 to which the color toner image has been transferred is conveyed to the position of the fixing section 2 .

Further, the toner remaining on the surface of the intermediate transfer belt 55 after the secondary transfer is collected in the waste toner box 70 arranged on the tension roller 69 side in contact with the intermediate transfer belt 55 .

The fixing section 2 is arranged downstream of the secondary transfer unit 56 .
The fixing section 2 is composed of a fixing belt 71 and a pressure roller 72 .
The pressure roller 72 is pressed against the fixing belt 71 with a predetermined pressure by a pressure mechanism (not shown).
A discharge tray 75 is provided downstream of the fixing section 2 .

Next, based on FIG. 3, a schematic configuration of the digital multifunction peripheral 1 will be described.
FIG. 3 is a block diagram showing a schematic configuration of the digital multi-function peripheral 1 of FIG. 1. As shown in FIG.

As shown in FIG. 3, the digital multifunction peripheral 1 includes a control unit 10, an image data acquisition unit 11, an image forming unit 12, a storage unit 13, an image processing unit 14, a communication unit 15, a timer 16, an operation panel 17, a paper feeder A section 18 and an image density adjustment section 19 are provided.

Each component of the digital multifunction peripheral 1 will be described below.

The control unit 10 integrally controls the digital multifunction peripheral 1, and includes a CPU, a RAM, a ROM, various interface circuits, and the like.

In order to control the overall operation of the digital multifunction machine 1, the control unit 10 monitors and controls all loads such as detection of each sensor, motor, clutch, operation panel 17, and the like.

The image data acquisition unit 11 is a part that detects and reads a document placed on a document platen or a document conveyed from a document tray, and generates image data.
Alternatively, image data may be acquired from an external PC, information processing device, or the like via a wired/wireless network (not shown), and image data may be recorded on a USB or the like from a USB terminal (not shown). Image data may be obtained, or a combination thereof may be used.

The image forming section 12 is a section that prints out on paper the image data acquired by the image data acquiring section 11 and processed by the image processing section 14 , and includes an LSU 121 .

The LSU 121 is a device that forms an electrostatic latent image by irradiating the surfaces of the photosensitive drums 59, 65, 66, and 67 in a charged state with laser light corresponding to information of image data composed of digital signals.

The storage unit 13 is an element or a storage medium that stores information necessary for realizing various functions of the digital multifunction peripheral 1, control programs, and the like. For example, semiconductor devices such as RAM and ROM, and storage media such as hard disks, flash storage units, and SSDs are used.

The storage unit 13 stores information related to jobs such as printing and data necessary for executing jobs such as image data.

In addition, the storage unit 13 stores the relationship for calculating the output number of color photographs, color characters, black-and-white photographs, and black-and-white character images in the most recent predetermined period, and the image density adjustment necessity Xht for intermediate gradation (described later). Stores data such as formulas.

Note that programs and data may be held in different devices, such as a hard disk drive as a data holding area and a flash memory as a program holding area.

The image processing unit 14 converts the image data input from the image data acquisition unit 11 into appropriate electric signals based on a job command such as printing input from the operation unit 172, and is suitable for output such as enlargement/reduction. This is the part that processes

The communication unit 15 is a part that communicates with an external device such as an external personal computer (PC), a mobile information terminal, or an information processing device via a wired/wireless network.

The timer 16 is a part that measures and counts time, and obtains the time through, for example, a built-in clock or a wired/wireless network.

The operation panel 17 includes a display panel made up of a liquid crystal panel or the like, and a touch panel of a capacitive type or the like which is arranged over the display panel and detects a position touched by a finger. A portion 172 is provided.

The display unit 171 is a part that displays various kinds of information.
The display unit 171 is composed of, for example, a CRT display, a liquid crystal display, an EL display, or the like, and is a display device such as a monitor or line display for displaying electronic data such as the processing state of the operating system or application software.

The control unit 10 displays the operation and status of the digital multifunction peripheral 1 through the display unit 171 .

The operation unit 172 is an interface for operating the digital multifunction peripheral 1, and is a part that receives commands from the user.

The paper feed unit 18 is a part that conveys paper stored in a paper feed cassette or a manual feed tray to the image forming unit 12 .

The image density adjusting section 19 is a part that adjusts the image density.
The image density adjustment unit 19 includes an image density sensor 191, illuminates test patch toner images formed on the photosensitive drums 59, 65, 66, and 67, and detects the patch toner images with a reflective optical sensor. The image density is adjusted based on the reflection value from the .

<Execution Processing of Image Density Adjustment of Digital MFP 1 of Embodiment 1 of the Present Invention>
Next, image density adjustment execution processing of the digital multifunction peripheral 1 according to the first embodiment of the present invention will be described with reference to FIGS. 4 to 7. FIG.

FIG. 4 is a flowchart showing an example of image density adjustment execution processing of the digital multi-function peripheral 1 of FIG.

At step S1 in FIG. 4, the control unit 10 counts the cumulative number of printed sheets (step S1).

Specifically, the cumulative number of printed sheets after adjusting the image density for the highest density and the cumulative number of printed sheets after adjusting the image density for intermediate gradation are separately counted. Execute image density adjustment.

Next, in step S2, the control unit 10 determines whether or not the timing for adjusting the image density for maximum density has come (step S2).
Specifically, the control unit 10 determines whether or not the cumulative number of printed sheets since the previous image density adjustment for maximum density has reached a predetermined number.

When it is time to adjust the image density for the highest density (when the determination in step S2 is Yes), in step S3, the control unit 10 determines that the image has been formed by the image forming unit 12 during a predetermined period. Among the images, the image density adjustment frequency for intermediate gradation is determined based on the contribution rate of the intermediate gradation image (step S3).
After that, the control unit 10 makes a determination (described later) in step S4.

On the other hand, if the timing for adjusting the image density for the highest density has not come (if the determination in step S2 is No), the control unit 10 returns the process to step S1.

FIG. 5 is a table showing an example of a determination table of image density adjustment frequencies for maximum density and intermediate gradation of the digital multi-function peripheral 1 of FIG.

As shown in FIG. 5, the maximum density image density adjustment frequency and the intermediate tone image density adjustment frequency are determined according to the value of the contribution rate Xht/N of the halftone image.

The halftone image density adjustment necessity Xht is a predetermined index for determining the necessity of halftone image density adjustment, and is determined based on the following equation, for example.

Xht=α×Ncp+β×Nct+γ×Nbp+ω×Nbt

Here, Ncp, Nct, Nbp, and Nbt are respectively the number of color photographs, color characters, black-and-white photographs, and black-and-white character images output in the most recent predetermined period. There is a relationship like

N=Ncp+Nct+Nbp+Nbt

In the example of FIG. 5, N=200 sheets.

Also, α, β, γ, and ω are coefficients indicating the degree of weighting (degree of importance) of intermediate gradations of various images, and are set to the following values in the example of FIG.

”
Ncp=1.0, Nct=0.3, Nbp=0.3, Nbt=0.1

Here, when images are roughly classified into photographic images and character images, intermediate gradation is important in photographic images, such as the shading of skin and clouds in the sky.
However, in most cases, a character image can be tolerated even if its intermediate gradation is somewhat low, so the weighting of the intermediate gradation is smaller in a character image than in a photographic image.

A monochrome image, especially a black-and-white image, is often tolerant even if the intermediate gradation is slightly lower than that of a multi-color image.

In the above formula, the output numbers of black-and-white photographs and black-and-white character images are also taken into consideration. However, if only the ratio of color photographic images is taken into consideration, Ncp=1.0 and Nct=Nbp=Nbt=0. good.
Usually only color photographic images need be considered.

If only the ratio of color photographs and color character images is taken into consideration, then Ncp=Nct=1.0 and Nbp=Nbt=0.

Based on the value of the contribution rate Xht/N of the halftone image calculated as described above, the control unit 10 refers to the table shown in FIG. decide.

The type of output image is determined from the density distribution of the output image and the features of pixels or the entire image (process such as area separation in image processing) by analyzing the read image data.
Alternatively, the type of output image may be determined based on the user's print settings.

In the example of FIG. 5, when Xht/N<25%, the image density adjustment frequency for maximum density is every 200 sheets, while the image density adjustment frequency for intermediate gradation is every 800 sheets.

In the case of 25%≦Xht/N<50%, the image density adjustment frequency for maximum density is every 200 sheets, while the image density adjustment frequency for intermediate gradation is every 600 sheets.

Further, when 50%≦Xht/N<75%, the image density adjustment frequency for the highest density is every 200 sheets, while the image density adjustment frequency for the intermediate gradation is every 400 sheets.

Further, when Xht/N≧75%, the image density adjustment frequency for the highest density is every 200 sheets, whereas the image density adjustment frequency for the intermediate gradation is every 200 sheets.

As described above, the image density adjustment frequency for intermediate gradation is changed according to the output ratio of color photographs, color characters, black-and-white photographs, and black-and-white character images output in the most recent predetermined period.

Basically, the higher the output ratio of character images and the higher the output ratio of black-and-white images than color images, the lower the frequency of image density adjustment for intermediate gradation than the frequency of image density adjustment for maximum density. Let

In addition, based on the ratio of the number of color photographic images or the total number of color photographic and color character images to the number of all kinds of images processed in the most recent predetermined period, the image density for intermediate gradation An adjustment frequency may be determined.

In this case, if the ratio of the number of color photographic images or the total number of color photographic images and color character images to the number of all types of images processed in the most recent predetermined period is, for example, 75% or more, 200 Image density adjustment for intermediate gradation is performed for each sheet, every 400 sheets for 50% to less than 75%, every 600 sheets for 25% to less than 50%, and every 800 sheets for less than 25%.

In this embodiment, even if the degree of necessity of image density adjustment for intermediate gradation is extremely low, a limit is set for the frequency of image density adjustment for intermediate gradation.
In the example of FIG. 5, halftone image density adjustment is performed every 800 sheets at most.
The reason why such a limit is set is that even if the intermediate gradation is not important from the past history, it is not necessarily the case that there will be no output of an image that requires the intermediate gradation. This is for guaranteeing image quality.

Thus, the maximum density image density adjustment frequency and the intermediate tone image density adjustment frequency are determined.

Next, in step S4, the control section 10 determines whether or not the timing for adjusting the image density for intermediate gradation has come (step S4).

When it is time to adjust the image density for the intermediate gradation (if the determination in step S4 is Yes), in step S5, the control unit 10 causes the image density adjusting unit 19 to adjust not only the maximum density but also the intermediate gradation. is also executed (step S5), and the image density adjustment process is terminated.

On the other hand, in step S4, if it is not the timing that also requires image density adjustment for intermediate gradation (if the determination in step S4 is No), in step S6, the control unit 10 causes the image density adjustment unit 19 to adjust the image density for the maximum density. Only density adjustment is executed (step S6), and the image density adjustment process is terminated.

FIG. 6 is an explanatory diagram showing an example of execution timing of image density adjustment for maximum density and intermediate gradation of the digital multi-function peripheral 1 shown in FIG.

FIG. 6A shows an example of execution timing in the initial state.
In the example of FIG. 6A, the image density adjustment for both the maximum density and the intermediate gradation is performed every 200 cumulative printed sheets.

FIG. 6B shows an example in which the degree of necessity of image density adjustment for intermediate gradation is low.
In the example of FIG. 6B, image density adjustment for maximum density is performed every 200 cumulative printed sheets, whereas image density adjustment for intermediate gradation is performed every 400 cumulative printed sheets.

FIG. 6C shows an example in which the degree of necessity of image density adjustment for intermediate gradation is even lower than that in FIG. 6B.
In the example of FIG. 6C, image density adjustment for maximum density is performed every 200 cumulative printed sheets, whereas image density adjustment for intermediate gradation is performed every 600 cumulative printed sheets.

In the example of FIG. 6, in order to shorten the user's waiting time, the execution timing of the image density adjustment for intermediate gradation is matched with the execution timing of the image density adjustment for maximum density, but they are executed at different timings. You may do so.

FIG. 7 shows an example of a toner patch for image density adjustment of the digital multi-function peripheral shown in FIG.
FIG. 7A shows an example of a toner patch for maximum density, and FIG. 7B shows an example of a toner patch for intermediate gradation.

When executing image density adjustment for maximum density, as shown in the example on the left side of FIG. Density toner patches are formed on the surface of photoreceptor drums 59 , 65 , 66 , 67 or on the surface of intermediate transfer belt 55 .

Then, light is applied to the toner patch, and based on the detected value of the reflected light detected by the image density sensor 191, the development bias is controlled so as to achieve the target image density, and image density adjustment for maximum density is executed.

Further, as shown in the example on the right side of FIG. 7(A), by repeating the highest density toner patch a plurality of times (three times in the example on the right side of FIG. 7(A)), the Variation on the surface or surface of the intermediate transfer belt 55 can be reduced.

When executing image density adjustment for intermediate gradation, as shown in the example of FIG. Toner patches of a plurality of gradations up to the density (the number of patches is 14 in the example of FIG. 7B) are formed on the surface of the drums 59 , 65 , 66 and 67 or the surface of the intermediate transfer belt 55 .

Then, light is applied to the toner patch, and the development bias is controlled so as to achieve a target image density based on the detected value of the reflected light detected by the image density sensor 191, thereby executing image density adjustment for intermediate gradation.

Since the density of the intermediate gradation depends on the maximum density, the toner patch with the maximum density is important for both character images and photographic images.
Therefore, after determining the maximum density, the ratio of each intermediate gradation to the maximum density is usually determined.

In this way, among the images formed by the image forming unit 12 during a predetermined period, the image density adjustment frequency for the intermediate gradation is determined and executed based on the contribution rate of the intermediate gradation image. , the image density adjustment for intermediate gradation can be executed at a more appropriate timing than before, and the digital multi-function peripheral 1 with high user convenience can be realized.

[Embodiment 2]
Next, image density adjustment execution processing of the digital multi-function peripheral 1 according to the second embodiment of the present invention will be described with reference to FIGS. 8 and 9. FIG.

A schematic configuration of a digital multi-function peripheral 1 according to Embodiment 2 of the present invention is the same as that of Embodiment 1 (FIG. 3), so description thereof will be omitted.

In the first embodiment, the number of toner patches to be formed when adjusting the image density for the halftone image is uniformly 14. However, in the second embodiment, the number varies depending on the value of the halftone image contribution ratio Xht/N. Image density adjustment for intermediate gradation is performed with the number of toner patches.

FIG. 8 is a table showing an example of a determination table for determining the number of toner patches to be formed during image density adjustment for intermediate gradation in the digital multi-function peripheral 1 according to Embodiment 2 of the present invention.
FIG. 9 shows an example of toner patches to be formed during image density adjustment for intermediate gradation in the digital multi-function peripheral 1 according to Embodiment 2 of the present invention.

As shown in FIG. 8, the number of toner patches to be formed when adjusting the image density for the halftone image is determined according to the value of the contribution ratio Xht/N of the halftone image.

In general, image density adjustment for intermediate gradation is performed by causing the image forming section 12 to form patch toner images having a plurality of gradations when an execution request is received, and using the image density sensor 191 to measure the image density of each patch toner image. Then, a correction value (amount of gamma correction) is set so as to obtain a reference sensor value set in advance for each gradation.

In the second embodiment, by reducing the number of toner patches according to the degree of necessity of intermediate gradation, in addition to reducing the consumption amount of toner associated with the formation of the reduced patch toner image, patch toner To shorten the time required to form an image.

In the example of FIG. 8, when Xht/N<25%, the number of toner patches to be formed during image density adjustment for intermediate gradation is three.
FIG. 9A shows a specific example with three patches.

Further, when 25%≦Xht/N<50%, the number of toner patches to be formed when adjusting the image density for intermediate gradation is five.
FIG. 9B shows a specific example of five patches.

Further, when 50%≦Xht/N<75%, the number of toner patches to be formed when adjusting the image density for intermediate gradation is nine.
FIG. 9C shows a specific example of nine patches.

Further, when Xht/N≧75%, the number of toner patches to be formed when adjusting the image density for intermediate gradation is 14.
FIG. 9D shows a specific example of 14 patches.

In this manner, the number of toner patches to be formed during image density adjustment for the halftone image is determined according to the value of the contribution rate Xht/N of the halftone image.

Note that the reduced number of toner patches is appropriately interpolated using an approximation formula.

When the value of the contribution rate Xht/N of the halftone image is low, the amount of toner associated with the formation of the toner patches can be reduced by reducing the number of toner patches to be formed when adjusting the image density for the halftone image. , the time required to form a toner patch can be shortened.

In this manner, the number of toner patches to be formed during image density adjustment for the intermediate gradation is determined based on the contribution rate of the intermediate gradation image among the images formed by the image forming unit 12 during the predetermined period. As a result, the image density adjustment for intermediate gradation can be performed more appropriately than before, and the digital multi-function peripheral 1 that is highly convenient for the user can be realized.

[Embodiment 3]
Next, with reference to FIG. 10, the image density adjustment execution process of the digital multi-function peripheral 1 according to Embodiment 3 of the present invention will be described.

A schematic configuration of a digital multi-function peripheral 1 according to Embodiment 3 of the present invention is the same as that of Embodiment 1 (FIG. 3), so description thereof will be omitted.

In the first embodiment, image density adjustment is performed at predetermined timings, but in the third embodiment, image density adjustment is also performed when an image density adjustment command is received from the user.

FIG. 10 is a flowchart showing an example of image density adjustment execution processing of the digital multi-function peripheral 1 according to Embodiment 3 of the present invention.

The processes of steps S11, S12 and S15 to S18 in FIG. 10 respectively correspond to the processes of steps S1 to S6 in FIG. 4 (embodiment 1), so description thereof will be omitted.

Here, processing of steps S13 and S14 in FIG. 10, which are not described in the first embodiment, will be described.

In step S12 of FIG. 10, if the timing at which the image density adjustment for the highest density is required has not come (when the determination in step S12 is No), in step S13, the control unit 10 causes the operation unit 172 to input the image from the user. It is determined whether or not the input of the density adjustment command has been received (step S13).

If the operation unit 172 has not received the input of the image density adjustment command from the user (if the determination in step S13 is No), the control unit 10 returns the process to step S11.

On the other hand, when the operation unit 172 receives an input of the image density adjustment command from the user (when the determination in step S13 is Yes), in step S14, the control unit 10 sets the time point when the input of the image density adjustment command is received. As a reference, determination and judgment regarding image density adjustment are performed (step S14).

In this manner, image density adjustment is executed by changing the execution timing of image density adjustment for intermediate gradation based on the contribution rate of intermediate gradation image for a predetermined period in the past from the time when the user inputs the image density adjustment command. As a result, the image density adjustment for intermediate gradation can be performed at a more appropriate timing than before, and the digital multifunction peripheral 1 that is highly convenient for the user can be realized.

[Embodiment 4]
Next, image density adjustment execution processing of the digital multi-function peripheral 1 according to the fourth embodiment of the present invention will be described with reference to FIGS. 11 and 12. FIG.

FIG. 11 is a block diagram showing a schematic configuration of a digital multifunction peripheral 1 according to Embodiment 4 of the present invention.

A schematic configuration of a digital multi-function peripheral 1 according to Embodiment 4 of the present invention is the same as that of Embodiment 1 (FIG. 3) except that a user authentication section 20 is provided.
Here, the configuration of the user authentication unit 20, which is not described in the first embodiment, will be described.

The user authentication unit 20 compares information such as a login name and a password input from the operation unit 172 with corresponding information recorded in advance in the storage unit 13 to determine whether the user is a legitimate user. This is the part that performs authentication.

The user authentication unit 20 may authenticate whether or not the user is an authorized user based on information such as the user ID read from the user's IC card through a card interface unit (not shown). .

FIG. 12 is a flow chart showing an example of execution processing of image density adjustment after user login of the digital multi-function peripheral 1 according to Embodiment 4 of the present invention.

In the fourth embodiment, it is assumed that the user executes image density adjustment after login.
Note that when image density adjustment is performed without the user logging in, the same processing as in FIG. 4 (embodiment 1) is performed.

The processes of steps S22 and S24 to S26 in FIG. 12 correspond to the processes of steps S2 and S4 to S6 in FIG. 4 (embodiment 1), respectively, so description thereof will be omitted.

Here, the processes of steps S21 and S23 of FIG. 12, which are not described in the first embodiment, will be described.

In step S21 of FIG. 12, the control unit 10 counts the cumulative number of printed sheets for each logged-in user (step S21).

Next, in step S22, when it is time to adjust the image density for the maximum density (when the determination in step S22 is YES), in step S23, the control unit 10 adjusts a predetermined value for each logged-in user. Among the images formed by the image forming unit 12 during the period, the image density adjustment frequency for intermediate gradation is determined based on the contribution rate of the intermediate gradation image (step S23).

In this manner, among images formed by the image forming unit 12 during a predetermined period for each logged-in user, the image density adjustment frequency for intermediate gradation is determined based on the contribution rate of the intermediate gradation image. By executing this, it is possible to execute the image density adjustment for intermediate gradation at a more appropriate timing than before, and realize the digital multifunction peripheral 1 that is highly convenient for the user.

[Embodiment 5]
Next, with reference to FIG. 13, the image density adjustment execution process of the digital multi-function peripheral 1 according to the fifth embodiment of the present invention will be described.

A schematic configuration of a digital multi-function peripheral 1 according to Embodiment 5 of the present invention is the same as that of Embodiment 1 (FIG. 3), so description thereof will be omitted.

FIG. 13 is a flow chart showing an example of image density adjustment execution processing after the digital multi-function peripheral 1 according to the fifth embodiment of the present invention receives an image forming instruction.

In the fifth embodiment, it is assumed that the digital multi-function peripheral 1 executes image density adjustment after receiving an image forming instruction.

In step S31 of FIG. 13, when the operation unit 172 receives an input of an image formation instruction from the user (step S31), in step S32, the control unit 10 confirms that the image formation instruction is to form a color image or a photographic image. It is determined whether or not this is the case (step S32).

If the image formation instruction does not relate to the formation of a color image or a photographic image (the determination in step S32 is No), in step S37, the control section 10 causes the image forming section 12 to form an image (step S37). .

On the other hand, if the image formation instruction is for forming a color image or a photographic image (if the determination in step S32 is YES), in step S33, the control unit 10 sets the image density adjustment frequency for intermediate gradation to the initial value. It is determined whether or not it is lower than the state (step S33).

When the image density adjustment frequency for intermediate gradation is the same as the initial state (when the determination in step S33 is No), in step S37, the control section 10 causes the image forming section 12 to form an image (step S37).

On the other hand, if the frequency of image density adjustment for intermediate gradation is lower than the initial state (if the determination in step S33 is Yes), in step S34, the control unit 10 adjusts A deterioration risk of a color image or a photographic image is estimated (step S34).

Note that the deterioration risk of a color image or a photographic image is estimated based on the past image forming data stored in the storage unit 13 from the elapsed time after the previous image density adjustment for intermediate gradation. may be estimated according to

Next, in step S35, the control section 10 determines whether or not the deterioration risk of the color image or the photographic image is equal to or greater than a predetermined value (step S35).

When the deterioration risk of the color image or the photographic image is not equal to or greater than the predetermined value (when the determination in step S35 is No), in step S37, the control section 10 causes the image forming section 12 to form an image (step S37). .

On the other hand, if the deterioration risk of the color image or the photographic image is greater than or equal to the predetermined value (if the determination in step S35 is Yes), in step S36, the control section 10 causes the image density adjustment section 19 to adjust the image density. Execute (step S36).

After that, in step S37, the control section 10 causes the image forming section 12 to form an image (step S37).

In this way, when an image formation instruction from the user is received, if there is a high risk of deterioration of a color image or a photographic image, image density adjustment for intermediate gradation is executed, thereby enabling intermediate gradation to be performed at a more appropriate timing than in the past. It is possible to realize a digital multi-function peripheral 1 that is highly convenient for the user by executing image density adjustment for adjustment.

Preferred aspects of the invention also include combinations of any of the aspects described above.
In addition to the embodiments described above, various modifications of the present invention are possible. Those modifications should not be construed as not belonging to the scope of the present invention. The present invention should include all modifications within the scope of the claims, the meaning of equivalents, and the scope.

1: Digital MFP 2: Fixing Unit 10: Control Unit 11: Image Data Acquisition Unit 12: Image Forming Unit 13: Storage Unit 14: Image Processing Unit 15: Communication Unit 16: Timer 17 : operation panel 18: paper feed section 19: image density adjustment section 20: user authentication section 31: recording medium 50: optical system unit 51: first visible image forming unit 52: second visible image forming unit 53: third visible image forming unit 54: fourth visible image forming unit 55: intermediate transfer belt 56: secondary transfer unit 57: internal paper feeding unit 58: manual paper feeding feeding unit 59, 65, 66, 67: photosensitive drum 60: charging roller 61, 61a, 61b, 61c, 61d: developing unit 62, 62a, 62b, 62c, 62d: primary transfer unit 63, 63a: cleaning blade, 64: laser light source, 68, 69: tension roller, 70: waste toner box, 71: fixing belt, 72: pressure roller, 73, 74: feeding roller, 75: discharge tray, 76: Static elimination unit 77: Cleaning roller 121: LSU 171: Display unit 172: Operation unit 191: Image density sensor 621a: Transfer roller N: Total number of output sheets RT1, RT2, RT3, RT4: Conveyance path Xht: Necessity of image density adjustment for intermediate gradation

Claims (8)

an image forming unit that forms an image by forming a toner image;
an image density adjustment unit that performs image density adjustment;
A halftone image is defined as a ratio of a predetermined type of image that may be affected by a change in image density of a halftone among all types of images formed by the image forming unit during a predetermined period. a storage unit that stores the contribution rate of
a control unit that controls the image forming unit, the image density adjustment unit, and the storage unit;
The image density adjusting section predetermines image density adjustment for maximum density and image density adjustment for intermediate gradation based on the cumulative number of images formed by the image forming section or the cumulative operating time of the image forming section. Execute each at the specified execution timing,
The image forming apparatus, wherein the control section changes execution timing of the image density adjustment for the intermediate gradation according to the contribution rate of the intermediate gradation image stored in the storage section. The image forming unit has a function of forming a color photographic image,
further comprising an image determination unit that determines whether the image formed by the image forming unit is the color photographic image;
wherein the storage unit stores the number of images of all types and the number of color photographic images formed by the image forming unit during a predetermined period;
2. The image forming apparatus according to claim 1, wherein the control unit calculates a ratio of the number of the color photographic images to the number of the images of all types, and uses the ratio as the contribution rate of the halftone image. The image forming unit has a function of forming a color photographic image and a color character image,
further comprising an image determination unit that determines whether the image formed by the image forming unit is the color photographic image or the color character image;
The storage unit stores the number of all kinds of images formed by the image forming unit in a predetermined period and the total number of the color photographic images and the color character images,
2. The image according to claim 1, wherein said control unit calculates a ratio of the total number of said color photographic images and said color character images to the number of said images of all types, and sets it as a contribution rate of said halftone image. forming device. The storage unit stores the contribution of the halftone image determined in advance so that the higher the contribution rate of the halftone image, the shorter the execution timing of the image density adjustment for the halftone image in the image density adjusting unit. storing a table showing the relationship between the rate and the execution timing;
4. The image forming method according to claim 1, wherein the control unit refers to the table and determines the execution timing of the image density adjustment for the halftone image from the contribution rate of the halftone image. Device. The storage unit is configured in advance such that the number of toner image patches to be formed in the image density adjustment unit during adjustment of the image density for the intermediate gradation decreases as the contribution rate of the intermediate gradation image decreases. storing a table showing the relationship between the contribution rate of the halftone image and the number of patches;
5. The image forming apparatus according to claim 1, wherein the control unit refers to the table and determines the number of patches from the contribution rate of the halftone image. It also has an operation unit that accepts input of various commands from the user.
When the operation unit receives an input of an image density adjustment command from the user, the control unit controls all types of images formed by the image forming unit during a predetermined period from the time when the image density adjustment command is received. storing in the storage unit a ratio of a predetermined type of image among them, which may be affected by a change in image density of a halftone image, as a contribution ratio of the halftone image;
In accordance with the contribution rate of the intermediate tone image, the image density adjusting unit changes the execution timing of the image density adjustment for the intermediate tone, and then adjusts the image density for the highest density and the image density for the intermediate tone. 6. The image forming apparatus according to any one of claims 1 to 5, wherein each adjustment is executed at a predetermined execution timing. further comprising a user authentication unit that accepts user login authentication,
The image density adjustment unit performs image density adjustment for maximum density and intermediate density adjustment based on the cumulative number of images formed by the image forming unit or the cumulative operation time of the image forming unit for each user whose login authentication has been accepted. each executing image density adjustment for gradation at a predetermined execution timing;
7. The controller according to any one of claims 1 to 6, wherein the control unit changes the execution timing of the image density adjustment for the intermediate gradation according to the contribution ratio of the intermediate gradation image for each user whose login authentication is accepted. The image forming apparatus according to . an image forming step of forming an image by forming a toner image;
an image density adjustment step of performing image density adjustment;
A halftone image is defined as a ratio of a predetermined type of image that may be affected by a change in image density of a halftone among all types of images formed by the image forming process during a predetermined period. and a storing step of storing as a contribution rate of
In the image density adjustment step, image density adjustment for maximum density and image density adjustment for intermediate gradation are determined in advance based on the cumulative number of images formed in the image formation step or the cumulative operation time of image formation. Execute each at the execution timing,
2. An image density adjustment method, comprising: changing execution timing of the image density adjustment for the intermediate gradation according to the contribution rate of the intermediate gradation image stored in the storing step.

Images