JP4351503B2 - Image forming apparatus - Google Patents

Description

  The present invention includes an image forming unit for each color, an intermediate transfer body, and a density detection sensor that reads the density of an image density detection pattern on the intermediate transfer body, and an image density based on the read image density detection pattern information. The present invention relates to an electrophotographic image forming apparatus that performs control.

  In general, in an electrophotographic color image forming apparatus such as a color copying machine or a color printer, an electrostatic latent image corresponding to image information is formed on a latent image carrier made of a photosensitive member or a photosensitive belt, This is visualized by a developing device and transferred to an intermediate transfer member or transfer paper. In an image forming apparatus using a two-component developer, the density of each color toner image is detected by a density sensor provided on the photosensitive member or the intermediate transfer member in order to adjust the image density, thereby controlling density correction. By performing the above, the image density is maintained constant.

As an image forming apparatus for performing such density correction, the “tandem type image forming apparatus” disclosed in Patent Document 1 has a good image formation based on the result of detecting a larger number of density patterns than in the past. An image forming apparatus that determines conditions is disclosed.
JP 2002-62708 A

  Since the color image forming apparatus forms a four-color visible image and performs color superposition, it is necessary to adjust the density for four colors, and it takes time to adjust the density. It is necessary to shorten the warm-up time and the image adjustment time, and it is an issue to shorten the image adjustment time. Further, in the color image forming apparatus, it is necessary to align the density characteristics of the four color developers used for image formation, and this variation causes a problem that the gray balance is not matched.

  In addition, in order to match the above gray balance, accurate density control is required. When performing accurate density control, it has been found that it is necessary to extremely reduce the outer shape fluctuation and sensitivity variation in the rotation direction of the photosensitive member, and it has been found that the gray balance cannot be adjusted unless four colors are aligned.

  The invention described in Patent Document 1 performs density control with high accuracy because a pattern block is repeatedly formed on a transfer conveyance belt and an image forming condition is determined based on a result of detecting a density pattern of each reference pattern image. I can. However, since the density pattern detection is repeatedly executed, the image adjustment time becomes long, and the demand for energy saving by shortening the image adjustment time cannot be met.

  An object of the present invention is to provide an image forming apparatus capable of detecting an image density with high accuracy in a short time and obtaining a good color image with good gray balance.

In order to achieve the above object, the invention described in claim 1 includes an image forming unit for each color, an intermediate transfer member, and a density detection sensor that reads the density of an image density detection pattern on the intermediate transfer member. In the image forming apparatus that controls the image density based on the image density detection pattern information, before the creation of the image density detection pattern, the position of the photoconductor of the image forming portion of each color is adjusted, and then the image density detection of each color is performed. the use patterns created so that the same pattern is repeated in a cycle of laps photoreceptor 1, characterized in row Ukoto the density detection.

According to a second aspect of the invention, in the image forming apparatus according to claim 1, wherein the image density detection pattern is aligned on the colors the photosensitive member, wherein the same pattern is repeatedly generated.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus includes a developing sleeve, and a product of a linear velocity ratio of the photosensitive member and the developing sleeve and the developing sleeve diameter is an integral multiple of the photosensitive member diameter. It is characterized by.

  According to the present invention, the image forming unit of each color, the intermediate transfer body, and the density detection sensor that reads the density of the image density detection pattern on the intermediate transfer body are provided, and based on the read image density detection pattern information. In the image forming apparatus that performs image density control, the same pattern is repeated in the cycle of the photoreceptor around the image density detection pattern, so that the intended purpose can be achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of a main part of an image forming apparatus according to an embodiment of the present invention. Four image forming units each including a drum-shaped photosensitive member and an electrophotographic process unit such as a charging unit, a developing unit, and a transfer unit are arranged (first image forming unit 1 for yellow, second image for cyan). Forming unit 2, magenta third image forming unit 3, black fourth image forming unit 4). An optical unit 5 that performs optical writing is disposed in each of the image forming units 1 to 4.

  A belt-like intermediate transfer member 6 is disposed so as to be in contact with the photosensitive member of each of the image forming units 1 to 4, and a density detection sensor 7 is provided around the belt-like intermediate transfer member 6. A paper transfer belt 8 is disposed so as to partially contact the intermediate transfer member 6. A fixing device 9 is disposed on the downstream side of the nip portion between the intermediate transfer member 6 and the paper transfer belt 8.

  In such a configuration, as is well known, each color toner image formed in each image forming unit 1 to 4 is superimposed and transferred onto the intermediate transfer member 6 and transferred to a transfer sheet fed from a sheet feeding unit (not shown). At the nip portion between the intermediate transfer member 6 and the paper transfer belt 8, the superimposed and transferred toner images are collectively transferred. Thereafter, the transfer paper is conveyed to the fixing device 9 where the unfixed toner image is melted and fixed on the transfer paper. Thereafter, the transfer paper is discharged to a paper discharge unit (not shown).

  The density detection sensors 7 are provided at four positions in the rotational direction of the intermediate transfer body 6 and on the downstream side of the nip portion between the intermediate transfer body 6 and the paper transfer belt 8 substantially in parallel with a rotation drive shaft (not shown). The detection sensor 7 simultaneously reads the densities of the four color image density detection patterns, and performs image density control based on the read information.

  FIG. 2 is a diagram showing a first example of an image density detection pattern on the intermediate transfer member. When the image density detection pattern 10 is created on the intermediate transfer member 6, the pattern is created in accordance with the period of the photosensitive member.

  In this embodiment, since a drum-shaped photosensitive member having a diameter of 40 mm is used as the photosensitive member, the image density detection pattern 10 is created with a period of 125.664 mm. The image density detection pattern 10 is composed of eight types of density of a rectangular pattern of 15 mm in the rotation direction of the photosensitive member and 20 mm in the axial direction, and is a pattern of 120 mm in the rotation direction. By repeating this pattern at the photosensitive member cycle, errors in the density detection of the image density detection pattern 10 due to the sensitivity of the photosensitive member and the outer diameter fluctuation of the photosensitive member can be eliminated, and accurate density control detection is performed. be able to.

  In Embodiment 2, the error can be reduced when detecting the continuous pattern density by matching the period of the photoconductor when creating the image density detection pattern. Thus, the pattern writing is not performed at the same position with respect to the surface of the photosensitive member each time.

  Therefore, in the second embodiment, in order to eliminate this error, projections indicating rotation reference positions are attached to the four photoconductors, and the positions of the projections of all the photoconductors are detected by the density detection sensor 7. Thereafter, the positions of the four photoconductors are matched by changing the speed of the photoconductor to match the four reference positions, and the positions on the photoconductor for creating the image density detection pattern are always matched. As a result, it is possible to eliminate density detection errors due to variations in the sensitivity of the photoreceptor and fluctuations in the outer diameter of the photoreceptor.

  FIG. 3 is a diagram showing a second example of the image density detection pattern on the intermediate transfer member. By always matching the positions where the image density detection patterns for the respective colors are created on the photoconductor, an error in color balance is eliminated.

  Specifically, as shown in the figure, by aligning the position on the photoconductor and aligning the start of creating the image density detection pattern for each color, errors due to variations in sensitivity of the photoconductor and outer diameter fluctuation on the photoconductor are eliminated. Thus, variations in the colors in the photoconductor rotation direction can be eliminated. Thereby, a good gray balance can be obtained.

  The fourth embodiment suppresses density variation due to the outer diameter fluctuation of the developing sleeve. When developing the image density detection pattern, the development gap may change due to the outer diameter fluctuation of the development through groove, resulting in variations in the development amount of the density pattern.

  Therefore, by making the product of the linear velocity ratio of the photosensitive member and the developing sleeve and the developing sleeve diameter an integral multiple of the photosensitive member diameter, the collecting position of the developing sleeve and the position of the pattern can be made coincident with each other. It is possible to eliminate an error due to radial flutter.

1 is a main part configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the 1st example of the pattern for an image density detection on an intermediate transfer body. It is a figure which shows the 2nd example of the pattern for an image density detection on an intermediate transfer body.

Explanation of symbols

1 to 4 First to fourth image forming units 6 Intermediate transfer member 7 Density detection sensor 10 Image density detection pattern

Claims (3)

An image having an image forming unit for each color, an intermediate transfer member, and a density detection sensor for reading the density of the image density detection pattern on the intermediate transfer member, and performing image density control based on the read image density detection pattern information In the forming device,
Before creating the image density detection pattern, align the photoconductor of the image forming section for each color,
An image forming apparatus characterized in that density detection is performed by creating an image density detection pattern for each color so that the same pattern is repeated in one cycle of the photoreceptor. 2. The image forming apparatus according to claim 1, wherein the image density detection pattern is formed repeatedly by aligning each color on the photoconductor . 2. The image forming apparatus according to claim 1 , further comprising a developing sleeve, wherein a product of a linear velocity ratio between the photosensitive member and the developing sleeve and the developing sleeve diameter is an integral multiple of the photosensitive member diameter. Forming equipment.

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