JP2006065184A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image density correction pattern capable of reducing an influence of an noise from an image carrier on the mean value of the signal intensity in detecting the image density correction pattern constituted of a plurality of density patches formed on an image carrier by a sensor, and then, obtaining the mean value of the detected signal intensity. <P>SOLUTION: The image density correction pattern 80 constituted of the plurality of density patches 81a to 81j is formed on the image carrier by an image forming unit. Regarding the low-density patch formed on the image carrier while largely exposing the image carrier, and where the signal intensity detected by the sensor becomes uneven and the signal intensity is easily influenced by the noise from the image carrier, the length of the lower-density patch is made longer in the carrying direction of the image carrier, then, the influence of the image carrier is reduced in obtaining the mean value of the signal intensity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus.

  Due to recent technological advances, the formation of color images in image forming apparatuses is generally widespread, and the image quality is also improved. However, when forming a color image, a plurality of toner images output from a plurality of image forming units are overlapped, so that the output density of each color toner is not constant due to environmental changes such as temperature and humidity. It is known that the quality of images will change. In addition, it is known that the service life of the apparatus tends to be long, and the quality of the output image is also changed when the parts are changed or deteriorated due to long-term use.

  Therefore, as a method for correcting an image for outputting a stable image, a correction pattern composed of patches having different densities is formed on an intermediate transfer member such as a transfer drum or a transfer belt or an image carrier such as paper, and a sensor is used. There has been proposed a method of correcting an image by irradiating light and measuring reflected light.

In Patent Document 1, a patch pattern for density-gradation characteristic control composed of patches having different densities is formed with toner on an intermediate transfer member and paper (transfer material), and light is applied to the patch pattern by a density sensor and a color sensor. It is proposed to detect the intensity of the reflected light and correct the density and RGB output values using these values.
JP 2003-149903 A (pages 7 to 10, FIG. 3 to FIG. 6)

  The surface of the image carrier is microscopically rough, non-uniform, has a small amount of toner, and has a low density patch with many exposed parts of the image carrier. Therefore, it is difficult to detect an accurate value of the patch signal strength.

  In Patent Document 1, all of the patches constituting the density-gradation characteristic control patch pattern are formed in the same size and are affected by the roughness of the surface of the image carrier. Therefore, the low density detected by the sensor is low. The accuracy of the signal strength of the patch tends to be low, and the correction accuracy of density and RGB output values tends to be low.

  Therefore, the present invention is configured with patches having different densities so that accurate density correction can be performed in an image forming apparatus that corrects the density of an image using an image density correction pattern including a plurality of patches having different densities. In the image density correction pattern formed on the carrier, the lower the density of the patch, the longer the length of the image carrier in the conveyance direction, thereby increasing the accuracy of the signal intensity of the low density patch detected by the sensor. An object of the present invention is to provide an image forming apparatus that is improved and has improved density control accuracy.

  In order to achieve the above object, in the present invention, an image forming apparatus is configured as follows.

(1) An image forming unit, an image carrier to which a toner image formed by the image forming unit is transferred, a sensor for irradiating light onto the image carrier and detecting reflected light, and an overall operation A control unit for controlling,
In the image forming apparatus for performing image density correction by detecting reflected light of an image density correction pattern formed of a plurality of patches having different densities formed on the image carrier by the image forming unit with the sensor.
The length of the patch in the image carrier conveyance direction is such that between patches constituting one of the image density correction patterns, adjacent density patches are the same or have a lower density and the lowest density. The patch should be longer than the highest density patch.

  (2) If the density of the patch is 50% or more among the patches, the length of the image carrier in the transport direction is the same.

  (1) In the configuration of the present invention, between the patches constituting one of the image density correction patterns, the length in the image carrier conveyance direction is longer when the density of adjacent density patches is lower, and the lowest density. This patch is longer than the patch with the highest density, so that the time detected by the sensor can be made longer as the patch has a lower density. Since the low density patch has a small amount of toner and there are many exposed parts of the image carrier, the signal intensity detected by the sensor is easily affected by the surface of the image carrier, and the image carrier on which the patch is formed If the position of the sensor changes, the detected signal intensity tends to be different, but this effect can be dispersed because the detection time can be lengthened, regardless of the position of the image carrier on which the patch is formed. The detected signal intensity becomes stable. Therefore, since the accuracy of the signal intensity of the low density patch detected by the sensor can be improved, the accuracy of density control can be improved.

  (2) Since the lengths of the patches having the density of 50% or more of the applied toner amount in the image carrier conveyance direction are the same, the lengths of these patches are set to the minimum length necessary for detecting the density. If the entire length of the image density correction pattern is the same, the area that can be allocated to the low density patch can be expanded. Thereby, by dispersing the influence of the image carrier, the accuracy of the signal intensity of the low density patch detected by the sensor can be improved, and the accuracy of density control can be improved.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a printer according to an embodiment of an image forming apparatus of the present invention. A paper discharge tray 11 is provided on the upper surface of the main body 10. Inside the main body 10, a control unit 12, a paper feeding unit 40, an image forming unit 50, and a fixing unit 70 are provided. The control unit 12 controls the operation of the entire printer.

  Next, the paper feed unit 40 will be described. The paper feed unit 40 includes a paper feed cassette 41, a paper feed roller 42, a transport roller pair 43 and a registration roller pair 44. The paper feed cassette 41 accommodates the paper P and is disposed in the lower part of the main body 10. From here, the paper P is sent one by one to the paper transport path 46 by the paper feed roller 42 and transported by the transport roller pair 43, the registration roller pair 44, and the like.

  Next, the image forming unit 50 will be described. FIG. 2 is a schematic configuration diagram of the image forming unit 50 according to the embodiment of the present invention. The image forming unit 50 includes magenta, cyan, yellow, and black image forming units 60a, 60b, 60c, and 60d, a primary transfer roller 51, a paper transport belt 52, a sensor 54, and a belt cleaner 56.

  The paper transport belt 52 is stretched and supported by support rollers 55a and 55b. All the image forming units 60 a, 60 b, 60 c, and 60 d are in contact with the outer surface on the upper side of the sheet conveying belt 52. The support roller 55a drives the paper transport belt 52, and the paper transport belt 52 rotates counterclockwise (arrow direction) in FIG. Here, two support rollers 55 a and 55 b are used in the present embodiment, but three or more support rollers may be used as long as the image forming units 60 a, 60 b, 60 c and 60 d are in contact with the paper transport belt 52.

  The image forming units 60a, 60b, 60c and 60d are arranged in tandem, and the arrangement order can be changed. One primary transfer roller 51 is arranged at a position facing each of the image forming units 60a, 60b, 60c and 60d across the paper transport belt 52.

  As shown in the schematic configuration diagram of the sensor 54 in FIG. 3, the sensor 54 includes an LED light-emitting portion 54a and a light-receiving portion 54b composed of a phototransistor. Is used to detect the signal intensity of an image density correction pattern formed of toner on a sheet conveying belt 52 as will be described later. .

  The belt cleaner 56 removes the image density correction pattern detected by the sensor 54 from the paper transport belt 52 and includes a blade in contact with the paper transport belt 52.

  The image forming units 60 a, 60 b, 60 c, and 60 d have the same structure, and the image forming units 60 a, 60 b, 60 c, and 60 d have the same structure. According to the rotation direction (arrow direction), the cleaning device 65 and the static eliminator 66 are arranged as peripheral elements across the contact portion with the charger 62, the LED print head 63, the developing device 64, and the paper transport belt 52.

  Finally, the fixing unit 70 will be described. In the fixing unit 70, the fixing roller 71 and the pressure roller 72 are pressed against each other, and the toner image transferred onto the paper P is heated and pressed to be fixed on the paper P.

  Next, an image forming operation will be described. When a user issues an image formation instruction from an external computer (not shown) connected to the main body 10 directly or via a network, the control unit 12 receives the instruction and operates each unit. The sheet conveying belt 52 rotates counterclockwise (in the direction of the arrow) in FIG. 2, and the photosensitive drum 61 of each of the image forming units 60a, 60b, 60c, and 60d that contacts this rotates correspondingly in the clockwise direction (in the direction of the arrow). To do. When the photosensitive drum 61 rotates, the surface of the photosensitive drum 61 is first uniformly charged by the charger 62. Next, it corresponds to the portion of the image formed on the paper P or the portion other than the image by the light irradiated from the optical scanning unit 63 composed of a number of LEDs based on the electrical signal of the original image sent from the external computer. The charged electric charge is erased, and an electrostatic latent image is formed on the surface of the photosensitive drum 61. Then, toner is supplied to the electrostatic latent image on the photosensitive drum 61 by the developing device 64 and visualized as a toner image.

  When the photosensitive drum 61 further rotates and the toner image comes to a position facing the primary transfer roller 51 with the paper conveying belt 52 interposed therebetween, the photosensitive drum 61 is interposed between the photosensitive drum 61 and the paper conveying belt 52 accordingly. The paper P is conveyed. At this time, a voltage having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roller 51, and the toner image is transferred from the photosensitive drum 61 to the paper P. The residual toner that has not been transferred is removed from the photosensitive drum 61 by a cleaning device 65 having a blade in contact with the photosensitive drum 61, and then the surface charge of the photosensitive drum 61 is removed by light irradiation by the static eliminator 66, so that the next image A forming process takes place.

  With the above operation, the toner images of the respective colors are stacked on the paper P in order of the image forming units 60a to 60b, 60c, and 60d. The paper P on which the toner image has been transferred is then conveyed to the fixing unit 70 where the toner image is fixed and discharged onto the paper discharge tray 11 as described above.

  Next, the conventional image density correction pattern 180 and the detection result by the sensor 54 will be described. As shown in the perspective view showing the positional relationship between the image forming unit 50 and the image density correction pattern 180 in FIG. 7, the control unit 12 controls the image forming units 60a, 60b, 60c and 60d to correct the image density. An image density correction pattern 180 based on a toner image is formed on a sheet conveying belt 52 as an image carrier and is detected by a sensor 54. In FIG. 7, the image forming units 60b, 60c, and 60d are omitted for easy understanding of the drawing.

  The image density correction pattern 180 formed by any of the image forming units 60a, 60b, 60c, or 60d is as shown in the plan view of the image density correction pattern 180 formed on the paper transport belt 52 in FIG. In addition, the patch is composed of ten patches 181a to 181j whose density is from 10% to 10% in terms of toner loading. In the present embodiment, the order in which the patches 181a to 181j are formed is the order of 181j, 181i, ..., 181a, but may be reversed. The length of each patch in the rotation direction of the sheet conveying belt 52 is the same. This image density correction pattern 180 is similarly formed for magenta, cyan, yellow and black by the image forming units 60a, 60b, 60c and 60d.

  The amount of applied toner will be described with reference to FIGS. This is the same for magenta, cyan, yellow and black. FIGS. 9A to 9J are enlarged views of the patches 181a to 181j, respectively. FIGS. 10A and 10B are partial cross-sectional views of the patch 181b and the patch 181i on the paper transport belt 52. FIG. In the present embodiment, the state in which the toner 90 is placed on 10% of the virtual meshes on the paper transport belt 52 is the toner loading amount of 10% in FIG. The state where 90 is loaded is the toner loaded amount of 100% in FIG. As can be seen from FIGS. 10A and 10B, the patch 181i having a toner application amount of 90% has a large amount of toner 90, so that the portion where the paper transport belt 52 is exposed is small, and the toner application amount is 20%. In 181b, since the toner 90 is small, there are many portions where the sheet conveying belt 52 is exposed. For this reason, in a low-density patch with a small amount of applied toner, the signal intensity detected by the sensor 54 is more susceptible to the non-uniform surface of the paper transport belt 52 than in a high-density patch.

  FIG. 11 is a graph of signal intensity obtained by detecting the image density correction pattern 180 by the sensor 54. It can be seen that the signal from the low-density patch 181a having a toner application amount of 10% is affected by the paper transport belt 52 having a non-uniform surface. For the image density correction, average values va to vj of the signal intensities of the patches 181a to 181j detected by the sensor 54 are used as detection results of the patches. Since the value of the high density patch is close to the signal intensity of the patch itself, it can be used for correction as it is. However, since the value of the low-density patch is easily affected by the paper conveying belt 52 as described above, the value tends to be far from the value of the patch signal itself.

In the embodiment of the present invention, as shown in the plan view of the image density correction pattern 80 formed on the paper conveyance belt 52 in FIG. 10 patches 81a to 81j in increments of 10% to 100%. The lengths of the patches 81a to 81j in the rotation direction of the sheet conveying belt 52 are a, b, c, d, e, f, g, h, i, and j, respectively.
a ≧ b ≧ c ≧ d ≧ e ≧ f ≧ g ≧ h ≧ i ≧ j and a> j
It is. Here, the number of patches constituting the image density correction pattern 80 is not limited to 10 and may be more or less than 10 depending on the accuracy of desired density correction, etc., but each density is different. There must be.

  FIG. 5 shows a graph of signal intensity obtained by detecting the patch 81a and the patch 181a with the sensor 54. Since the width of the patch 181a is narrow, as shown in FIG. 5B, the average value va of the signal intensity of the patch 181a is easily influenced by the belt 52, and varies depending on the position of the paper conveying belt 52 on which the patch is formed. Although the patch 81a is wide, the average value Va of the signal intensity of the patch 81a is small due to the influence of the paper transport belt 52 as shown in FIG. 5A, and the patch is formed. Since the difference in value depending on the position of the paper transport belt 52 is small, the density correction accuracy can be increased by using this value.

Further, in the embodiment of the present invention, as shown in FIG. 6, the image density correction pattern 80 has the same length in the rotational direction of the paper conveyance belt 52 of the patches 81e to j with the applied toner amount of 50% or more. e = f = g = h = i = j
It may be. In this case, it is assumed that the lengths e to j are long enough to detect the signals of the patches 81e to j.

  As a result, when the area where the image density correction pattern 80 of the paper or the paper transport belt 52 can be formed is limited, the area where the low density patch can be formed can be widened, so that the signal intensity of the high density patch can be ensured. , The accuracy of the signal intensity of the detected low density patch can be improved. By using this value, the accuracy of density correction can be improved.

  The image density correction pattern according to the present invention may be formed on a sheet as an image carrier. In this case, it is necessary to provide the sensor 54 at a position where the sheet can be detected. Further, it can also be used for a color image forming apparatus that transfers a toner image onto a sheet via an intermediate transfer belt, by forming it on an intermediate transfer belt as an image carrier. Further, it can be used not only for density correction but also for correction using a plurality of patches with different densities formed on an image carrier, such as RGB correction. It can also be used for monochrome image forming apparatuses. The image forming apparatus is not limited to a copying machine, and can be used for a printer and a multifunction machine of these.

1 is a schematic configuration diagram of a printer according to an embodiment of an image forming apparatus of the present invention. 1 is a schematic configuration diagram of an image forming unit according to an embodiment of the present invention. The schematic block diagram of a sensor. FIG. 3 is a plan view of an image density correction pattern according to the embodiment of the present invention. The graph of the signal strength of the patch which concerns on embodiment of this invention, and the conventional patch. Another form of the image density correction pattern. The perspective view which shows the positional relationship of an image formation part and the conventional image density correction pattern. FIG. 6 is a plan view of a conventional image density correction pattern. The enlarged view of the patch which comprises the pattern for image density correction. The fragmentary sectional view of a patch and a paper conveyance belt. The graph of the signal strength of the conventional image density correction pattern.

Explanation of symbols

12 Control Unit 52 Paper Conveying Belt (Image Carrier)
54 Sensor 60a-d Image forming unit 80 Image density correction pattern 81a-j Patch

Claims (2)

An image forming unit, an image carrier to which a toner image formed by the image forming unit is transferred, a sensor for irradiating light on the image carrier and detecting reflected light, and a control for controlling the entire operation With
In the image forming apparatus for performing image density correction by detecting reflected light of an image density correction pattern formed of a plurality of patches having different densities formed on the image carrier by the image forming unit with the sensor.
The length of the patch in the image carrier conveyance direction is such that between patches constituting one of the image density correction patterns, adjacent density patches are the same or have a lower density and the lowest density. An image forming apparatus characterized in that the patch is longer than the highest density patch.   2. The image forming apparatus according to claim 1, wherein the length of the image carrier in the transport direction is the same when the density of the patch is 50% or more among the patches.

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