JP4260085B2 - Development density adjusting device, image forming device - Google Patents

Description

  The present invention relates to a developing density adjusting device used in an image forming apparatus for transferring a toner image formed on a photosensitive drum onto a sheet via an intermediate transfer belt, and an image forming apparatus including the developing density adjusting device. The present invention relates to a developing density adjusting device having a function of switching whether or not halftone density is adjusted according to the remaining amount, and an image forming apparatus including the developing density adjusting device.

The electrophotographic image forming apparatus will deteriorate the sensitivity characteristics of the photoconductive drum due to long-term use, the output image will become light overall, or the solid image (filled image) part will not be faithfully reproduced, etc. Image quality is degraded. In addition, even if it is not used for a long time, the usage environment fluctuates, the charging condition of the photosensitive drum (formation condition of the electrostatic latent image), the deterioration of the developing roller that supplies the developer (toner) to the photosensitive drum, etc. , Image quality deteriorates due to various causes.
Conventionally, the following first and second density adjustments are performed in order to prevent such a decrease in image quality.
The first density adjustment is to adjust the image density when a so-called solid image is formed. In the first density adjustment, a development bias adjustment patch image (first test pattern) is formed on the intermediate transfer belt, and the density of the development bias adjustment patch image is detected by the density sensor. The developing bias is adjusted so as to obtain a predetermined set density.
The second density adjustment is for adjusting the halftone density, that is, the correspondence between the input image density and the output image density. In this second density adjustment, a plurality of different gradation (halftone density) images (second test patterns) are formed on the intermediate transfer belt, and the respective image densities are detected by a density sensor. Based on the result, adjustment of a gradation table (density conversion table), which is a correspondence relationship between input image density and output image density set in the image processing unit, or formation of an electrostatic latent image on the photosensitive drum The amount of laser light to be adjusted is adjusted.
By appropriately performing the first and second density adjustments as described above, the density and halftone density of the solid image are maintained at appropriate densities, and deterioration of the image quality is prevented.
Japanese Patent Application Laid-Open No. H10-260260 discloses that a remaining amount of toner (developer) is detected based on detection values of a plurality of or movable magnetic sensors in a developing device using a one-component developing system. Further, in Patent Document 2, in an image forming apparatus using a two-component development system, the number of rotations of a replenishment drive motor that replenishes toner to a developing tank is detected from an input pulse, an input voltage, and an input time thereof. A technique for storing, estimating the total amount of toner used from the number of rotations, and detecting the remaining amount of toner (developer) from the total amount of toner used is disclosed.
JP 2001-109248 A JP 2004-109998 A

However, the second density adjustment described above is effective in a state where the remaining amount of the developer in the developing device is sufficient, but in a state where the remaining amount of the developer in the developing device is insufficient. If the second test pattern is not properly output and the second density adjustment is performed based on the image density of such an inappropriate test pattern, the quality of the formed image is deteriorated. There was a problem.
Furthermore, the second density adjustment forms a plurality of the second test patterns corresponding to each gradation of the halftone density as described above, so that the consumption of the developer is large and the remaining amount of the developer is small. In a small state, there is also a problem that a large amount of the developer is wasted.
Further, the above-mentioned Patent Document 1 and Patent Document 2 do not show how to solve the above-mentioned problems.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to prevent improper density adjustment and useless developer consumption therefor when the remaining amount of developer is small. It is an object of the present invention to provide a development density adjusting device capable of achieving the above and an image forming apparatus including the same.

In order to achieve the above object, the present invention transfers a test pattern image for adjusting a developing bias onto an intermediate transfer belt and performs a process for adjusting the developing bias based on its density. A development density adjusting device for transferring a test pattern image for adjusting the halftone density and controlling whether or not to perform the process of adjusting the halftone density based on the density; It is configured as an image forming apparatus including the same.
By adopting such a configuration, it is possible to prevent inappropriate adjustment of the halftone density in a state where the remaining amount of the developer is small, and further, wasteful consumption of the developer is avoided. .
Here, the remaining amount of the developer is detected for each of the plurality of color developers in the color image forming apparatus, and the halftone density is adjusted for each of the plurality of colors according to the detection result. It is conceivable that switching control for determining whether or not to perform is performed.
This prevents the image quality from being deteriorated by adjusting the halftone density for colors with a large amount of developer remaining, and does not adjust the halftone density for colors with a small amount remaining. Appropriate control such as prevention of the consumption of the developer becomes possible.

Further, the adjustment of the halftone density is performed by adjusting an image gradation table (table corresponding to the input density and the density to be output) set in the control unit or the like of the image forming apparatus. Or by adjusting the light quantity of the writing laser for writing the electrostatic latent image on the photosensitive drum, or by adjusting both of them.
The halftone density depends on the above-described gradation table and the amount of light of the writing laser. By appropriately adjusting these, the halftone density can be effectively adjusted, Quality degradation can be prevented.

  According to the present invention, whether or not to adjust the halftone density is switched according to the remaining amount of the developer, and the image quality is adjusted by adjusting the halftone density when the remaining amount of the developer is large. In the state where the remaining amount of the developer is low, it is possible to prevent inappropriate adjustment of the halftone density performed in this state and to suppress wasteful consumption of the developer. It is.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a schematic configuration diagram of a copying machine A provided with a developing density adjusting device according to an embodiment of the present invention. FIG. 2 is a flowchart showing the procedures of the first density adjustment (solid image density adjustment) and the second density adjustment (halftone density adjustment) in the development density adjustment apparatus according to the embodiment of the present invention. FIG. 4 is a flowchart showing a procedure of development density adjustment processing by the development density adjustment apparatus according to the embodiment of the present invention, and FIG. 4 is a graph showing an example of a gradation table.

FIG. 2 is a schematic configuration diagram of a copying machine A including a developing density adjusting device according to the embodiment of the present invention shown in FIG. 1. The configuration of the copying machine A shown in FIG. 1 is roughly classified into a document reading unit X1, a paper feeding unit X2, a printing unit X3, and a paper discharging unit X4. The document reading unit X1 is disposed above the paper feeding unit X2, and the printing unit X3 is disposed at an intermediate portion between the document reading unit X1 and the paper feeding unit X2.
The copying machine A (an example of an image forming apparatus) is different from the conventional copying machine in the development density adjustment function of the control unit 9 (an example of a part of the development density adjustment apparatus) provided in the document reading unit X1. Are different and will be discussed later.
The document reading unit X1 includes a document setting unit 1, an automatic document feeder (hereinafter referred to as ADF) 2, a document placement table 3, a document discharge unit 4, an exposure device 5, light guide mirrors 6a to 6c, an optical lens 7, a CCD 8, The control unit 9 is configured.
The ADF 2 passes a document S set on the document setting unit 1 through a plurality of conveying rollers R in accordance with a print request made from an operation panel (not shown) disposed on the exterior front surface of the copying machine A or the like. One by one is transported sequentially. The document S transported by the ADF 2 is transported in the sub-scanning direction through a predetermined reading position on the document placing table 3 made of, for example, platen glass, and then discharged to the document discharge unit 4.

Further, the exposure device 5 irradiates light onto the document S moving in a sub-scanning direction (in the direction from the left side to the right side in the drawing) on the document table 3. The reflected light from the document S is guided by the light guide mirrors 6 a, 6 b, 6 c and condensed by the optical lens 7. Further, the CCD 8 converts the image information contained in the reflected light into an electric signal and reads it into the control unit 9.
The control unit 9 includes peripheral devices such as an MPU, a ROM, and a RAM, and executes a control program stored in advance in the ROM, thereby including the overall processing of the copying machine A including image processing of image data. Control. The controller 9 also functions as a developing density adjusting device according to the present invention, and serves as a developing bias adjusting means, an intermediate density adjusting means, and a density adjustment switching control means. .

  The paper feed section X2 is generally composed of a paper feed cassette 10, a paper feed roller 11, a paper remaining amount gauge 12, and the like. Printing paper S ′ is placed in the paper feeding cassette 10 in advance. In response to the print request, the control unit 9 rotates the paper feed roller 11 to convey the print paper S 'placed in the paper feed cassette 10 to the print unit X3. The remaining amount of the printing sheet S ′ placed in the sheet feeding cassette 10 is detected by the sheet remaining amount meter 12, and when the remaining amount is small, a display provided on the exterior of the copying machine A A predetermined display prompting the user to replenish paper is performed from the panel.

The printing unit X3 includes a conveying roller 13, a photosensitive drum 14, an LSU unit 15, various mirrors 16a and 16b, a polygon mirror 17, a charging unit 18, a developing device 19, a fixing device 20, a densitometer 21, an intermediate transfer belt 22, The magnetic sensor 23 is generally configured.
The printing paper S ′ is transported by the transport roller 13. The surface of the photosensitive drum 14 is uniformly charged by a charging unit 18. Laser light based on the image information from the LSU unit 15 is irradiated to the photosensitive drum 14 through various mirrors 16a and 16b, a polygon mirror 17, and various lenses (not shown), and thereby on the photosensitive drum 14. An electrostatic latent image is formed on. The toner on the developing roller provided in the developing device 19 is attracted to the surface of the photosensitive drum 14, and the electrostatic latent image is caused by the toner to generate a potential gap (developing bias) between the photosensitive drum 14 and the developing roller. ) To be visualized as a toner image. The adjustment of the developing bias is performed by adjusting the potential applied to the developing roller provided in the developing device 19 and opposed to the photosensitive drum 14 by the control unit 9.

The toner image formed on the photosensitive drum 14 is transferred to the intermediate transfer belt 22 and transferred to the printing paper S ′ conveyed by the conveyance roller 13 by driving the intermediate transfer belt 22. . Then, the printing paper S ′ to which the toner image has been transferred is conveyed to the fixing device 20 and fixed to the printing paper S ′ by, for example, a heat roller. Here, the density of the toner image on the intermediate transfer belt 22 is detected by the densitometer 21 (an example of image density detecting means) that detects the brightness of the toner image by a CCD element or the like and obtains the density from the brightness. When each density adjustment described later is performed, a detection value of the patch image (a specific example of a test pattern image) generated on the intermediate transfer belt 22 by the densitometer 21 is used for each density adjustment. The toner remaining amount in the developing device 19 is detected by a magnetic sensor 23 as described later.
The printing paper S ′ on which the toner image is fixed is conveyed to the paper discharge unit X4 and discharged.

The solid image density and halftone density of the toner image formed on the photosensitive drum 14 deteriorate with time due to various factors. For example, the controller 9 of the copier A is turned on. It is necessary to execute it at an appropriate timing, such as every time when a predetermined number of images are formed.
The density of the toner image formed on the photosensitive drum 14 is such that the density of the so-called solid image depends on the developing bias, and the halftone density depends on the amount of laser light from the LSU unit 15 or the control unit 9 in advance. It depends on the stored gradation table.
In this example, the density of the solid image is adjusted by the control unit 9 (an example of development bias adjusting means) that adjusts the development bias, and the adjustment of the halftone density is performed by the control unit 9 (halftone density adjustment). An example of the means is performed by adjusting the amount of the laser light. Hereinafter, the density adjustment of the solid image by adjusting the developing bias is referred to as a first density adjustment, and the halftone density adjustment by adjusting the light amount of the laser light is referred to as a second density adjustment.

FIGS. 2A and 2B are flowcharts showing examples of procedures of the first density adjustment (solid image density adjustment) and the second density adjustment (halftone density adjustment). It is. Hereinafter, an example of the first concentration adjustment procedure will be described with reference to FIG. S1, S2,... Represent step (processing procedure) identification symbols.
The control unit 9 generates patch image data that is predetermined solid image data for developing bias adjustment (S1).
Further, the control unit 9 controls the charging unit 18 to minimize the development bias (set to a predetermined minimum level) (S2).
In this state, the control unit 9 controls the LSU unit 15 and the developing device 19 to control a toner image (development bias adjustment) based on the development bias adjustment patch image data (solid image data) generated in step S1. The patch image) is transferred to the intermediate transfer belt 22 (S3). The density of the toner image (development bias adjustment patch image) transferred onto the intermediate transfer belt 22 in this way is detected by the densitometer 21 and input to the controller 9 (S4).

Next, the control unit 9 controls the charging unit 18 to maximize the development bias (set to a predetermined maximum level) (S5). In this state, the control unit 9 controls the LSU unit 15 and the developing device 19 to control a toner image (development bias adjustment) based on the development bias adjustment patch image data (solid image data) generated in step S1. The patch image) is transferred to the intermediate transfer belt 22 (S6). The density of the toner image transferred onto the intermediate transfer belt 22 is detected by the densitometer 21 and input to the controller 9 (S7).
As described above, the density of the patch image for adjusting the developing bias when the developing bias is at the maximum level and the minimum level is input to the control unit 9. From these input values, the control unit 9 determines (calculates) the development bias necessary to generate a solid image having a predetermined solid image density (S8). The set value is recorded in a storage unit included in the control unit 9.
As described above, the control unit 9 (an example of the developing bias adjusting means) transfers the developing bias adjusting patch image (an example of the developing bias adjusting test pattern image) to the intermediate transfer belt 22, and the density meter 21 ( The developing bias is adjusted based on the detected density by an example of density detecting means.

The second density adjustment is performed, for example, according to the procedure shown in FIG.
In the copying machine A according to the present embodiment, as described above, the second density adjustment (halftone density adjustment) is performed by adjusting the amount of laser light in the LSU unit 15.
In addition, the adjustment of the amount of light of the laser light is performed in a predetermined number n of different gradations (for example, n = about 5 to 6) (halftone density) within the range from the minimum density gradation to the maximum density gradation. ) Patch image (hereinafter referred to as a halftone density adjustment patch image), and adjusting (setting) the laser light quantity table used for setting the light quantity (output) of the laser light based on the detected density value of the patch image Is done. S101, S102,... Represent step (processing procedure) identification symbols, and variable i represents the number (i = 1 to n) of each of the above-mentioned n gradations.
First, the control unit 9 sequentially generates predetermined halftone density adjustment patch image data for each gradation of i = 1 to n (S101).
Further, the control unit 9 controls the LSU unit 15 and the developing device 19, and a toner image (patch) based on the halftone density adjustment patch image data of each gradation i = 1 to n generated in step S101. Each image) is sequentially transferred to the intermediate transfer belt 22 (S102).
The density of the toner image of each gradation i = 1 to n transferred onto the intermediate transfer belt 22 in this way is sequentially detected by the densitometer 21 and input to the controller 9. (S103).
Finally, the control unit 9 determines an appropriate laser light amount value for each gradation from the minimum density gradation to the maximum density gradation based on the density detection value of each of the n gradation toner images. The laser light quantity table is adjusted (updated) based on the determined values (S104).
For example, a reference density and a reference laser light quantity corresponding to each toner image (patch image) for i = 1 to n are stored in the control unit 9 in advance, and according to the difference between the reference density and the actual detected density. Then, each of the reference laser light amounts is corrected, and the correspondence relationship between the reference density and the corrected laser light amount is stored in the control unit 9 as the laser light amount table.
In this way, the control unit 9 (an example of halftone density adjustment means) transfers the halftone density adjustment patch image (an example of a halftone density adjustment test pattern image) to the intermediate transfer belt 22, and The halftone density is adjusted based on the density detected by the densitometer 21 (an example of density detecting means).

In the prior art, when the first concentration adjustment is performed, the second concentration adjustment is always performed.
On the other hand, in the copying machine A, the remaining amount of the toner remaining in the developing device 19 is detected, and whether to perform the second density adjustment is switched according to the detection result.
The method for detecting the remaining amount of toner is different between the one-component development method and the two-component development method, but here, the description will be made assuming that the one-component development method is used. In the one-component development system, magnetic toner is often used, and the magnetic force of a toner tank (not shown) in the developing device 19 changes according to the remaining amount of toner. In this case, for example, as shown in Patent Document 1, the magnetic sensor 23 (an example of a part of the developer remaining amount detecting means) that detects the magnetic force is provided outside the developing device 19, and the control unit 9 assumes that the remaining amount of toner (an example of developer) is estimated (an example of detection) based on the detection value of the magnetic sensor 23.
The control unit 9 and the magnetic sensor are an example of a developer remaining amount detecting means, and the control unit 9, the densitometer 21, and the magnetic sensor 23 are used to adjust the development density adjusting device according to the embodiment of the present invention. Is configured.

The procedure of the development density adjustment process by the development density adjustment device (the control unit 9) according to the embodiment of the present invention will be described below with reference to the flowchart shown in FIG. The processing shown in FIG. 3 is executed at an appropriate timing such as when the power to the control unit 9 is turned on or when a predetermined number of images are formed. S201, S202,... Represent step (processing procedure) identification symbols.
First, the toner remaining amount in the developing device 19 is estimated from the detected value of the magnetic force around the toner tank by the magnetic sensor 23 (S201).
Next, the first density adjustment is performed (S202), and then it is determined whether or not the remaining amount of toner estimated in step S201 is equal to or greater than a predetermined threshold (S203). If the remaining amount of toner is equal to or greater than the threshold (YES in S203), the second density adjustment is performed (S204), and then the development density adjustment process ends. On the other hand, when the remaining amount of toner is less than the threshold (NO in S203), the developing density adjustment process is terminated without performing the second density adjustment. Note that there is no problem even if the procedures of S201 and S202 are interchanged.
As described above, the control unit 9 (an example of the density adjustment switching unit) determines the remaining amount of the toner (an example of the developer) from the detection value of the magnetic sensor 23 (an example of a part of the developer remaining amount detection unit). Based on the estimation result, only the first density adjustment (development bias adjustment) is performed, or the density adjustment is performed by both the first density adjustment and the second density adjustment (halftone density adjustment). Or switching control.

The present invention can also be applied to a color image forming apparatus such as a color printer or a color copying machine for forming a color image. In that case, a plurality of types (a plurality of colors) of the toner (developer) are used, and the first density adjustment and the second density adjustment are performed independently for each of them.
Therefore, in the color image forming apparatus, for example, when one-component magnetic toner is used, the remaining amount of each toner is detected by using the magnetic sensor 23 (developer remaining amount detecting means), and the control. The unit 9 may switch whether or not to appropriately perform the second density adjustment for each type (color) of the toner according to the remaining amount of the toner.
Further, in a general image forming apparatus, as shown in FIG. 4, a gradation table, which is a correspondence relationship between an input image density and an output image density, is stored in advance in a storage unit. Image density conversion (gradation conversion) is performed according to the table. In the above-described embodiment, an example in which halftone density adjustment (second density adjustment) is performed by adjusting the output level of the laser light amount (correspondence between the output image density and the output level of the laser light). As described above, the same halftone density adjustment can be performed by adjusting the gradation table. For example, as described above, patch image data for halftone density adjustment for several different gradations is generated, and a toner image developed based on them is transferred onto the intermediate transfer belt 22, and the toner images are transferred. It is also possible to use a method of determining the adjustment value of each gradation in the gradation table from the detected density value and adjusting the gradation table. In this case, the method for determining the adjustment value based on the density detection value is to select an appropriate one of gamma curves stored in advance according to the density detection result, and to calculate each level based on the selected gamma curve. A conventionally known method such as adjusting the gradation table by determining a tone adjustment value may be used.
A configuration in which both the output level of the laser beam and the gradation table are adjusted by the control unit 9 is also considered as an example.

In the above-described embodiment, the description has been given by taking the one-component development type image forming apparatus as an example. However, the scope of application of the present invention is not limited to this, and a two-component development type image forming apparatus can also be used. is there.
In that case, it is known that there is a high correlation between the magnetic permeability in the developing tank of the developing device 19 and the toner concentration (occupation ratio of toner in the mixed layer of carrier and toner). It is conceivable to use a magnetic flux sensor for detecting toner as a means for detecting the remaining amount of toner.
In the above-described embodiment, the copying machine has been described as a specific example. However, the present invention can naturally be applied to an image forming apparatus such as a printer, a facsimile machine, or a multifunction machine having a plurality of functions.

1 is a schematic configuration diagram of a copying machine A including a developing density adjusting device according to an embodiment of the present invention. 6 is a flowchart showing procedures of first density adjustment (solid image density adjustment) and second density adjustment (halftone density adjustment) in the development density adjustment apparatus according to the embodiment of the present invention. 6 is a flowchart showing a procedure of development density adjustment processing in the development density adjustment apparatus according to the embodiment of the present invention. The graph which shows an example of a gradation table.

Explanation of symbols

A ... Copier X1 equipped with the development density adjusting device according to the embodiment of the present invention ... Document reading section X2 ... Paper feeding section X3 ... Printing section X4 ... Paper discharge section 1 ... Document setting section 2 ... Automatic document feeder 3 ... Original platen 4 ... Original discharge part 5 ... Exposure device 6 ... Light guide mirror 7 ... Optical lens 8 ... CCD
DESCRIPTION OF SYMBOLS 9 ... Control part 10 ... Paper feed cassette 11 ... Paper feed roller 12 ... Paper remaining amount meter 13 ... Conveyance roller 14 ... Photoconductor drum 15 ... LSU unit 16 ... Various mirrors 17 ... Polygon mirror 18 ... Charging unit 19 ... Developing device 20 ... Fixing device 21 ... Density meter 22 ... Intermediate transfer belt 23 ... Magnetic sensor

Claims (3)

A development density adjusting device in an image forming apparatus,
Image density detection means for detecting the density of a development bias adjustment test pattern image comprising a solid image transferred to the intermediate transfer belt;
Development bias adjusting means for transferring the development bias adjusting test pattern image to the intermediate transfer belt and adjusting the developing bias based on the detected density of the developing bias adjusting test pattern image by the image density detecting means;
The intermediate transfer belt halftone density adjusting test pattern image halftone density is transferred to the image density detecting means according to the halftone density adjusting test pattern image of the gradation conversion table of the image based on the detected concentration and / Or halftone density adjusting means for adjusting the halftone density at the time of development by adjusting the light quantity of the laser beam for writing the electrostatic latent image on the image carrier;
A developer remaining amount detecting means for detecting the remaining amount of developer;
Wherein when the developer remaining amount is detected result of the developer remaining amount detecting means is smaller than a predetermined threshold may have rows concentration adjustment by only the developing bias adjusting means, if large, the developing bias adjusting Density adjustment switching control means for performing switching control so as to perform density adjustment by both means and the halftone density adjustment means;
A development density adjusting device comprising: The developer remaining amount detecting means detects the remaining amount of each of a plurality of color developers in a color image forming apparatus;
The developing density adjusting apparatus according to claim 1, wherein the density adjustment switching control unit performs the switching control for each color of the developer. An image forming apparatus characterized by being provided with a development density adjusting device according to claim 1 or 2.

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