JP2008216658A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which detects density in the midst of consecutive printing and performs density adjustment so that a result obtained by detecting the density may not give failure to an image being consecutively printed. <P>SOLUTION: In the image forming apparatus, the density of a patch formed between the images consecutively transferred to a transfer belt 3 is detected by a density sensor 8 (T1 and T2). A control part 30 compares the density of the patches 41 to 52 with predetermined reference density for every color (T3), also reads out the number of printed sheets (for example, ten) required for density correction processing (T4), and calculates the change rate of electrifying voltage every time one sheet is printed (T5). Then, the electrifying voltage of electrifiers 10, 12, 14 and 16 for respective colors is adjusted so that the density of respective color toner images consecutively transferred to the transfer belt 3 may gradually approach to the reference density until finishing print by the number of printed sheets required for the density correction processing (T6 to T9). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus, and more particularly to a color image forming apparatus capable of forming a full color image.

In a color image forming apparatus, calibration (density correction) plays an important role in matching colors. For this reason, it is necessary to improve the correction accuracy of the density correction, and it is required to perform density correction without reducing productivity.
Density correction in a conventional color image forming apparatus is performed during continuous printing, and the paper interval between the preceding paper and the subsequent paper is widened, and toner density control processing is executed at the paper interval. Known (see, for example, Patent Document 1 and Patent Document 2).

In addition, there is a prior art that proposes to reduce the sheet interval necessary for executing the density control process as much as possible (see, for example, Patent Document 3 and Patent Document 4).
Japanese Patent Laid-Open No. 2002-221888 JP 2002-258573 A JP 2003-337455 A JP 2003-337458 A

  In the image forming apparatus, when density correction is performed during continuous printing processing, it is important how the density correction result is fed back to the print contents. In particular, in a color image forming apparatus, when the density correction result is immediately fed back to the image forming density, the color of the formed image changes extremely during the continuous printing, and the same image is continuously displayed. Despite printing, there is a possibility that the color of the image will be different on the way.

  The present invention has been made based on such a background, and can perform density detection so that density detection is performed during continuous printing, and the density detection result does not cause a problem with a continuously printed image. The main object is to provide an image forming apparatus.

  In order to achieve the above object, the invention according to claim 1 is to convey an image forming unit (2) and a plurality of sheets (P) intermittently at predetermined intervals to the image forming unit. And an image forming apparatus (1) capable of continuous printing processing for continuously transferring an image (40) formed by the image forming unit on a plurality of sheets to be conveyed. The image forming unit includes means (9, 11, 13, 15) for forming an image for density detection between the images to be transferred to the sheet, and the density of the formed density detection image. A density adjusting unit that adjusts the density of the image formed by the image forming unit to be the reference density by comparing the density of the measured density detection image with a preset reference density and the means for measuring (8). Means (30, 10, 12, 14) Have the concentration adjusting means is characterized by varying the concentration of a plurality of images to be transferred continuously to gradually approach the reference density, an image forming apparatus.

The numbers in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.
The invention according to claim 2 is characterized in that the density adjusting means (30) includes a change width setting means (30) for setting a width of density change between successive images. Forming device.

The invention according to claim 3 is characterized in that the density adjusting means (30) has an image number setting means (30) for determining how many images should be formed in order to set the measured density as a reference density. The image forming apparatus according to claim 1.
According to a fourth aspect of the present invention, when the image formation to be continuously transferred during the density adjustment by the density adjusting means (30) is completed, the density adjusting means performs the first image when the next image formation is started. The image forming apparatus according to claim 1, wherein the density is adjusted to a reference density.

  According to a fifth aspect of the present invention, the image forming unit (2) is a tandem type color image forming unit, and includes a plurality of photosensitive drums (4, 5, 6, 7) and developing units (9, 11, 13. The image forming apparatus according to claim 1, further comprising: a transfer belt (3) to which an image is transferred from a plurality of photosensitive drums.

According to the first aspect of the present invention, since the density adjusting means changes the density of a plurality of images to be continuously transferred so as to gradually approach the reference density, continuous printing is performed immediately after the density measurement is performed. Therefore, all images that are continuously printed can be used as images having no color defect.
In the invention according to claim 2, since the width of the density change can be set, the user or the like can set the color change in the continuously printed image within the desired change ratio, and the type of image to be formed, etc. Accordingly, the width of density change can be adjusted to a width that does not cause a problem.

According to the third aspect of the invention, since it is possible to set how many images the density change is gradually changed, in this case as well, an image having no sudden color change can be continuously formed.
In the invention according to claim 4, when the number of printed sheets is finished during the continuous printing, the next image is printed from the reference density because the image density is adjusted to the reference density at the start of the next printing. Is started and a good image can be obtained.

As in the fifth aspect of the present invention, when the image forming unit is a tandem type color image forming unit, the present invention can be suitably used.
Specifically, the density adjustment in the image forming apparatus can be performed by controlling the amount of toner used for printing. The toner amount is controlled by an image forming engine such as a charging voltage, a developing bias, an exposure intensity, and a transfer voltage. This can be realized by changing a parameter relating to control or controlling a parameter relating to image processing such as gradation control.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view schematically showing the main configuration of a color printer 1 which is an example of an image forming apparatus according to the present invention. The color printer 1 includes a tandem type image forming unit 2 for forming a color image.
The image forming unit 2 includes a transfer belt 3, a cleaning device 28 for cleaning the surface of the transfer belt 3, and magenta for magenta arranged in contact with the transfer belt 3 along the moving direction of the transfer belt 3. A photosensitive drum 4, a cyan photosensitive drum 5, a yellow photosensitive drum 6, and a black photosensitive drum 7 are provided. Further, as viewed from the moving direction of the transfer belt 3, on the downstream side of the black photosensitive drum 7, a patch density for measuring the density of patches 41 to 52 (see FIG. 4) which are density detection images. A sensor 8 is arranged.

  The magenta photosensitive drum 4 includes a magenta developing unit 9 for developing an electrostatic latent image formed on the peripheral surface of the magenta photosensitive drum 4 with magenta toner, and a periphery of the photosensitive drum 4. Adjacent is a magenta charger 10 for charging the surface. Similarly, the cyan photosensitive drum 5 includes a cyan developing device 11 for developing the electrostatic latent image with cyan toner, and a cyan charging device 12 for charging the peripheral surface of the photosensitive drum 5. Is located next to it. The yellow photosensitive drum 6 is provided with a yellow developing device 13 for developing the electrostatic latent image with yellow toner and a yellow charging device 14 for charging the peripheral surface of the photosensitive drum 6 adjacent thereto. Has been. Adjacent to the black photosensitive drum 7 are a black developing device 15 for developing the electrostatic latent image with black toner, and a black charging device 16 for charging the peripheral surface of the photosensitive drum 7. Has been. Further, in order to transfer the toner images carried on the peripheral surfaces of the photosensitive drums 4 to 7 to the transfer belt 3, transfer rollers are provided on the peripheral surfaces of the photosensitive drums 4 to 7 with the transfer belt 3 interposed therebetween. 17, 18, 19, and 20 are arranged.

The transfer belt 3 is stretched between the driving roller 21 and the driven roller 22 and is given a predetermined tension by the tension roller 23. The transfer belt 3 moves in the direction of the arrow 24, and therefore, the four photosensitive drums 4 to 7 rotate counterclockwise in FIG.
Each of the photosensitive drums 4 to 7 is charged at a predetermined potential by the chargers 10, 12, 14, and 16, respectively, and an image corresponding to the original image is written therein by an LSU (laser scanning unit) or the like. Thereby, an electrostatic latent image is formed. The electrostatic latent images are developed into toner images of different colors by the developing devices 9, 11, 13, and 15, respectively. The toner images of the respective colors are transferred onto the transfer belt 3 by the transfer rollers 17 to 20, and the toner images are superimposed on the transfer belt 3.

On the other hand, the paper P is drawn out by a drawing roller (not shown) from a cassette (not shown) that can store a plurality of sheets P. A plurality of sheets P are conveyed toward the image forming unit 2 at a predetermined interval by the conveyance roller 26. The toner image transferred to the transfer belt 3 is transferred onto the paper P conveyed to the image forming unit 2 by the transfer roller 27.
The control unit 30 has each image in the image forming unit 2 including each photoconductive drum 4 to 7, each developing device 9, 11, 13, 15, each charger 10, 12, 14, 16 and each transfer roller 17 to 20. Controls the operation control of the forming member. Further, operation control of the transport mechanism including the transport roller 26 is performed. Furthermore, the detection output of the density sensor 8 is given to the control unit 30, and thus the control unit 30 can detect the density of the patches 41 to 52 that are density detection images. .

Furthermore, a memory (not shown) of the control unit 30 stores the number of printed sheets (number of images) required for density correction processing described later. The number of printed sheets required for the density correction process may be set by the user operating an operation panel (not shown), or may be set during maintenance.
FIG. 2 is a flowchart illustrating an example of print control in the color printer 1.

  When there is a print job in a memory (not shown) of the control unit 30 (YES in step S1), image formation is performed by the image forming unit 2 and printing by the color printer 1 is performed (step S2). Printing is performed continuously until printing of one print job is completed (step S4). In other words, images are formed by continuous printing until printing of one print job is completed.

When the number of printed sheets from the previous density correction (calibration) process has reached a predetermined number (for example, 1000 sheets) (YES in step S3), the density correction process (calibration) is performed. In the density correction process, the density of the toner image of each color (magenta, cyan, yellow, black) transferred to the transfer belt 3 is corrected.
FIG. 3 is a flowchart showing control during density correction processing. FIG. 4 is a diagram illustrating an example of a patch used during the density correction process.

The density correction process is performed during continuous printing so as not to reduce the productivity of the color printer 1. The density correction of the toner image of each color performed in the density correction process is based on the control of the charging voltage of each of the chargers 10, 12, 14, 16 by the control unit 30 to control the amount of toner of each color transferred to the transfer belt 3. Is done.
In the density correction process, patches 41 to 52 are formed between continuously printed images (step T1). The patches 41 to 52 are continuously transferred (continuous printing) to the transfer belt 3. As shown in FIG. 4, the patches 41 to 52 have a total of 12 images in which magenta, cyan, yellow, and black are each provided with three levels of density (30%, 50%, and 70%). Is provided.

  In this embodiment, patch groups P <b> 1 to P <b> 6 including two patches are formed between a pair of consecutive images 40 and 40. The first patch group P1 conveyed first includes a patch 41 made of a 30% dark magenta toner image and a patch 42 made of a 30% dark cyan toner image. The second patch group P2 transported second is provided with a patch 43 made of a 30% dark yellow toner image and a patch 44 made of a 30% dark black toner image.

The third patch group P3 transported third includes a patch 45 made of a 50% dark magenta toner image and a patch 46 made of a 50% dark cyan toner image. The fourth patch group P4 conveyed fourth includes a patch 47 made of a 50% dark yellow toner image and a patch 48 made of a 50% dark black toner image.
The fifth patch group P5 conveyed fifth includes a patch 49 made of a magenta toner image having a density of 70% and a patch 50 made of a cyan toner image having a density of 70%. The sixth patch group P6 transported last includes a patch 51 made of a 70% dark yellow toner image and a patch 52 made of a 70% dark black toner image.

  Referring to FIG. 3 again, the density sensor 8 detects the density of each of the patches 41 to 52 conveyed on the transfer belt 3 (step T2). The control unit 30 compares the density of the patches 41 to 52 with a predetermined reference density for each color (step T3). Thereafter, in the process of printing a predetermined number of prints (for example, 10 times) required for the density correction process, the density of the continuously printed image (the density of the image continuously transferred to the transfer belt 3) is used as a reference. The charging voltages of the chargers 10, 12, 14, and 16 for each color are adjusted so as to gradually approach the density (steps T4 to T9).

  Specifically, the number of printed sheets (for example, 10 sheets) required for density correction processing stored in a memory (not shown) of the control unit 30 is read (step T4), and the image to be changed for each printing is read. A density change width is calculated. Based on this, the change rate of the charging voltage for each printing is calculated (step T5). After the charging voltages of the chargers 10, 12, 14, and 16 for each color are controlled based on this change ratio (step T6), one sheet is printed (step T7). Thereafter, the control of the charging voltage in step T5 and the printing operation in step T6 are repeated until the number of prints required for the density correction process is printed. As a result, a plurality of images printed during that time approaches the reference density. When the number of prints required for the density correction process is printed (YES in step T9), the density correction process ends. At this time, the density of the image printed at the end is almost adjusted to the reference density.

According to this embodiment, the density of a plurality of continuously printed images is changed so as to gradually approach the reference density. As a result, immediately after the density measurement of the patches 41 to 52 is performed, the continuously printed image density does not change abruptly, and all the continuously printed images are used as images having no color defect. Can do.
Also, when all printing of the print job is completed during the density adjustment process, that is, when all printing of the print job is completed before the printing of the number of prints required for the density correction process is completed. (YES in step T8), the charging voltages of the chargers 10, 12, 14, and 16 are controlled so that the image density becomes the reference density (step T10). For this reason, at the start of the next printing, the image density is adjusted to the reference density. Therefore, printing of the next image is started from the reference density, and a good image can be obtained.

In addition, this invention is not limited to the above-mentioned embodiment.
In the above description, the number of prints required for the density correction processing is set. However, instead of this, the width of the density change between continuously printed images can be set. In this case, the number of prints required for the density correction process is calculated based on the density and density change width of the patches 41 to 52. The density change width can be set, for example, by operating an operation panel (not shown). In this case, the user can set the color change in the continuously printed images within a desired change rate.

Further, instead of performing density correction before and after the printing operation, density correction may be performed continuously during image formation.
Furthermore, in the above-described embodiment, the toner amount of each toner image is controlled by adjusting the charging voltage of the chargers 10, 12, 14, and 16, but the toner amount is controlled in addition to this. This can be done by adjusting the developing bias applied to the developing rollers of the developing units 9, 11, 13, and 15, the exposure intensity of the exposure unit, the transfer voltage, and the like. The toner amount control can be realized not only by image formation control but also by control of parameters relating to image processing such as image control gradation.

The density sensor 8 detects not the patches 41 to 52 on the transfer belt 3 but the density of patches on the peripheral surface of the photosensitive drums 4 to 7 and the density of patches formed on the paper P. It may be.
In the above description, a color printer has been described as an example of the image forming apparatus. However, the present invention can also be applied to a monochrome printer, and can also be applied to other image forming apparatuses such as a copying machine and a multifunction machine. .

  In addition, various design changes can be made within the scope of matters described in the claims.

1 is a cross-sectional view schematically showing an internal configuration of a color printer which is an example of an image forming apparatus according to the present invention. 3 is a flowchart illustrating an example of print control in a color printer. It is a flowchart which shows the control at the time of a density correction process. It is a figure which shows the example of the patch used at the time of a density | concentration correction process.

Explanation of symbols

1 Color printer (image forming device)
2 Image forming unit 3 Transfer belt 4, 5, 6, 7 Photosensitive drum 8 Density sensor 9, 11, 13, 15 Developer 10, 12, 14, 16 Charger (density adjusting means)
17, 18, 19, 20 Transfer roller 30 controller (density adjusting means, change width setting means, number of images setting means)
40 images 41 to 52 patches (images for density detection)
P paper

Claims (5)

An image forming unit; and a conveying unit that intermittently conveys a plurality of sheets with a predetermined interval to the image forming unit. In an image forming apparatus capable of continuous printing processing for continuously transferring formed images,
The image forming unit includes:
Means for forming an image for density detection between the images to be transferred to the paper;
Means for measuring the density of the formed density detection image;
A density adjusting unit that compares the density of the measured density detection image with a preset reference density and adjusts the density of the image formed by the image forming unit to be the reference density;
The image forming apparatus, wherein the density adjusting unit changes the density of a plurality of images to be continuously transferred so as to gradually approach a reference density.   The image forming apparatus according to claim 1, wherein the density adjusting unit includes a change width setting unit that sets a width of a density change between successive images.   The image forming apparatus according to claim 1, wherein the density adjusting unit includes an image number setting unit that determines how many images should be formed in order to set the measured density to a reference density.   When the image formation to be continuously transferred during the density adjustment by the density adjustment unit is completed, the density adjustment unit adjusts the first image density to be the reference density at the next image formation to be started. The image forming apparatus according to claim 1, wherein: The image forming unit is a tandem color image forming unit,
A plurality of photosensitive drums and developing units;
A transfer belt on which images are transferred from a plurality of photosensitive drums;
The image forming apparatus according to claim 1, further comprising:

Images