JP2013125060A - Image forming apparatus, and gradation pattern image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses growth in density detection time while suppressing deterioration in density detection accuracy by density variation factors generated over a direction orthogonal to a pattern arrangement direction of gradation pattern images.SOLUTION: Gradation pattern images 50-1, 50-2 are provided so as to overlap in parallel in a shaft direction of an intermediate transfer belt 11 (or in a width direction of the intermediate transfer belt 11, or in a direction orthogonal to a pattern arrangement direction of the gradation pattern images 50-1, 50-2), and thereby, density detection time is reduced. The gradation pattern images 50-1, 50-2 have a constitution where gradation patches are arranged in such a manner that the gradations of the gradation patches are scattered in the pattern arrangement direction, and thereby, the possibility is enhanced of existence of a gradation patch not affected or less affected by density variation factors even when the density variation factors such as flaws or the like over the direction orthogonal to the pattern arrangement direction are generated, to suppress deterioration in density detection accuracy.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, a facsimile machine, a digital multifunction machine, and a gradation pattern image forming method used therefor.

  In general, in an image forming apparatus, the image density of a toner image may fluctuate due to a surrounding environment such as temperature and humidity, or due to disturbance such as a change with time of the apparatus. Therefore, in the image forming apparatus, generally, gradation correction is performed in order to stabilize the image density.

  For example, in an image forming apparatus, a gradation pattern image having a plurality of gradations is formed on a photosensitive member as a test toner image, and gradation correction is performed based on the density of the gradation pattern image. This gradation correction is performed in order to correct gradation characteristics during printing when the power is turned on, when returning from sleep, when a certain number of printed sheets is reached, or when the external environment changes significantly.

  Specifically, in the image forming apparatus, a gradation pattern image is formed on the intermediate transfer belt during gradation correction, and the density of each gradation is detected by a density sensor. A desired image density is obtained by adjusting the development bias (that is, by performing gradation correction) so that the detected density matches a preset target density. In practice, this gradation correction is based on the density detection value obtained by the density sensor, and the input gradation of the image data is converted in the gradation conversion table of the control unit so that each gradation has a predetermined density. This is done by correcting.

  Here, if the detection accuracy of the gradation pattern image is poor, the gradation correction accuracy is also deteriorated accordingly. Therefore, conventionally, many contrivances have been made to detect the density of the gradation pattern image with high accuracy. .

  Patent Documents 1 to 3 disclose techniques using a plurality of gradation pattern images. In Patent Documents 1 and 3, a plurality of gradation patterns are set to 1/2 of the above-described period so as to cancel out unevenness (periodic unevenness) that appears in the period of the developing roller, the intermediate transfer belt, and the photoreceptor. A technique is disclosed that arranges at intervals of M / N (M and N are relatively prime natural numbers).

  Further, Patent Documents 4 and 5 disclose a technique for suppressing a decrease in accuracy of gradation correction caused by density unevenness or insufficient density by devising a layout of a gradation pattern.

JP 2010-134366 A JP 2008-26551 A JP 2006-343679 A JP 2010-171689 A JP 2011-64715 A

  By the way, in order to shorten the density detection time of the gradation pattern image and shorten the time required for the entire gradation correction, the gradation pattern may be shortened. However, if each gradation patch constituting the gradation pattern is shortened, there is a high possibility that the density of the gradation patch is erroneously detected, and as a result, the precision of gradation correction is lowered.

  As in Patent Documents 1 to 5, if a plurality of gradation pattern images are formed, the total length of each gradation patch can be made relatively long, so that the density of the gradation patch may be erroneously detected. Can be lowered. However, the gradation pattern image density detection time becomes longer depending on the arrangement of the gradation pattern image.

  FIGS. 1 and 2 show examples of arrangement of the gradation pattern images 3-1 and 3-2 when a plurality of gradation pattern images 3-1 and 3-2 are formed on the intermediate transfer belt 1.

  In FIG. 1, the same gradation pattern images 3-1 and 3-2 are arranged in the moving direction of the intermediate transfer belt 1 (which may be referred to as the longitudinal direction of the intermediate transfer belt or the pattern arrangement direction of the gradation pattern). On the other hand, the example arrange | positioned in series is shown. In the illustrated example, when the intermediate transfer belt 1 moves in the direction of the arrow, the density of the gradation pattern images 3-1 and 3-2 is measured from left to right by the density sensor 2 fixed to the image forming apparatus. To go.

  2 shows that the same gradation pattern images 3-1 and 3-2 are moved in the moving direction of the intermediate transfer belt 1 (which may be referred to as the longitudinal direction of the intermediate transfer belt or the pattern arrangement direction of the gradation pattern). On the other hand, the example arrange | positioned in parallel is shown. In the illustrated example, when the intermediate transfer belt 1 moves in the direction of the arrow, the density of the gradation pattern images 3-1 and 3-2 is adjusted by the density sensors 2-1 and 2-2 fixed to the image forming apparatus. It is measured simultaneously from left to right.

  In either case of FIG. 1 and FIG. 2, the average density value for each gradation patch included in the same gradation pattern image 3-1, 3-2 is calculated, and gradation correction is performed based thereon. Thus, a highly reliable concentration measurement value that is less affected by uneven density and the like can be obtained.

  By the way, when the arrangement of FIG. 1 is adopted, the gradation pattern images are arranged in series and the density is detected by one density sensor 2, so that the gradation patterns are arranged in parallel as shown in FIG. As compared with the case where the density is detected by the two density sensors 2-1, 2-2, there is a disadvantage that the density detection time becomes longer. Considering simply, in FIG. 1, the concentration detection time is twice that of FIG.

  On the other hand, considering the case where there is a scratch 4 across the axial direction of the intermediate transfer belt 1 (which may be referred to as the width direction of the intermediate transfer belt or the direction perpendicular to the pattern arrangement direction of the gradation pattern), The arrangement shown in FIG. 1 can obtain a correct density detection result than the arrangement shown in FIG. That is, in the case of the arrangement shown in FIG. 1, even if there is a gradation patch in which the scratch 4 exists in the gradation pattern image 3-1, the density detection value of the gradation patch is represented by the gradation pattern image 3. -2 can be replaced with the density detection value of the gradation patch of the same gradation. On the other hand, in the arrangement of FIG. 2, the scratch 4 appears in both of the same tone gradation patches in the gradation pattern images 3-1 and 3-2. It is difficult to obtain a correct density detection value for the patch. That is, in the case of the arrangement of FIG. 2, the influence of local scratches can be reduced, but the influence of scratches 4 and unevenness that have occurred over the entire axial direction of the intermediate transfer belt 1 is avoided. It is difficult.

  On the intermediate transfer belt 1, as in the case of the scratch 4, the density over the axial direction of the intermediate transfer belt 1 (which may be referred to as the width direction of the intermediate transfer belt or the direction perpendicular to the pattern arrangement direction of the gradation pattern). There are also fluctuation factors such as winding of the intermediate belt and streaks of the photosensitive drum.

  Conventionally, the density detection time is shortened, and the density fluctuation factor in the direction orthogonal to the pattern arrangement direction of the gradation pattern image (in the case of FIGS. 1 and 2, scratch 4 along the axial direction of the intermediate transfer belt 1). Sufficient studies have not been made on the technology that achieves both the suppression of the decrease in density detection accuracy due to the above.

  An object of the present invention is to suppress an increase in density detection time and suppress a decrease in density detection accuracy due to a density variation factor such as a scratch generated in a direction orthogonal to the pattern arrangement direction of a gradation pattern image. A forming apparatus and a gradation pattern image forming method are provided.

  One aspect of the image forming apparatus of the present invention is an image forming unit that forms a toner image on an image carrier and a density that detects the density of a gradation pattern image for gradation correction formed by the image forming unit. An image forming apparatus that performs gradation correction based on a density detection result obtained by the density sensor, wherein the image forming unit is in a direction orthogonal to a pattern arrangement direction of the gradation pattern image A plurality of gradation pattern images at least partially overlapping, and the plurality of gradation pattern images differ in at least a part of gradations between the plurality of gradation pattern images at the overlapping position.

  One aspect of the gradation pattern image forming method of the present invention is a method of forming a gradation pattern image formed on an image carrier of an image forming apparatus in order to perform gradation correction of the image forming apparatus. The gradation pattern image is a plurality of gradation pattern images at least partially overlapping in a direction orthogonal to the pattern arrangement direction of the gradation pattern image, and between the plurality of gradation pattern images in the overlapping position. Therefore, at least some of the gradations are different.

  According to the present invention, since the plurality of gradation pattern images are at least partially overlapped in the direction orthogonal to the pattern arrangement direction, the density detection time is shorter than when arranged in series in the pattern arrangement direction. Become. In addition, since the plurality of gradation pattern images have at least some of the gradations different between the plurality of gradation pattern images at overlapping positions, density fluctuations such as scratches in the direction orthogonal to the pattern arrangement direction. Even when the factor is generated, there is a gradation patch that is not influenced by the density variation factor or has little influence, and as a result, a decrease in density detection accuracy can be suppressed.

The figure which shows the example which has arrange | positioned the same gradation pattern image in series The figure which shows the example which has arrange | positioned the same gradation pattern image in parallel 1 schematically shows an entire configuration of an image forming apparatus according to an embodiment. The figure which shows the gradation characteristic which is the relationship of the density between the input original image and the actual print image Diagram for explaining gradation pattern and gradation patch A figure showing the density detection value of the gradation pattern detected by the density sensor, corresponding to the original image density data The figure which shows the relationship between density sensor output value and density The figure which shows the mode of a gradation conversion table (curve L3 in the figure) The figure which shows the structural example 1 of a gradation pattern image. The figure which shows the structural example 2 of a gradation pattern image. The figure which shows the structural example 3 of a gradation pattern image. The figure which shows the structural example 4 of a gradation pattern image. Flow chart for explaining density detection processing example 1 Flow chart for explaining density detection processing example 2 Flow chart for explaining density detection processing example 3 The figure which shows the output value of the density | concentration sensor obtained by the structure of this Embodiment The figure which shows the output value of the density sensor which is obtained with the conventional constitution

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[1] Overall Configuration FIG. 3 is a schematic diagram showing the overall configuration of the image forming apparatus 100 of the embodiment. The image forming apparatus 100 shown in FIG. 3 is a tandem color laser printer.

  The image forming apparatus 100 in FIG. 3 includes an image forming apparatus 10 that forms an image by attaching unfixed toner to the recording paper S, and a fixing apparatus 20 that melts the toner and fixes the recording paper S on the recording paper S.

  The image forming apparatus 10 includes an intermediate transfer belt 11, four image forming units 12-1 to 12-4, a primary transfer roller 13, and a secondary transfer roller 14. The image forming units 12-1 to 12-4 are arranged along the intermediate transfer belt 11 and form a toner image. The primary transfer roller 13 is disposed at a position facing the photoconductor 31 via the intermediate transfer belt 11, and the toner images formed by the image forming units 12-1 to 12-4 are placed on the intermediate transfer belt 11. Transcript. The secondary transfer roller 14 transfers the image transferred to the intermediate transfer belt 11 to the recording paper S.

  The intermediate transfer belt 11 is wound around a plurality of rollers 15-1 to 15-4. A cleaning device 16 is disposed at a position facing the intermediate transfer belt 11, and the cleaning device 16 collects toner remaining on the intermediate transfer belt 11.

  A density sensor 17 is disposed at a position facing the intermediate transfer belt 11. The density sensor 17 detects the density of the gradation pattern (toner image) formed on the intermediate transfer belt 11 during gradation correction. Note that the gradation pattern formed on the intermediate transfer belt 11 during gradation correction is removed as waste toner by the cleaning device 16 when the density detection is completed.

  A configuration example of the density sensor 17 will be described. The density sensor 17 is an optical sensor. The density sensor 17 includes a light emitting unit that emits light and a light receiving unit that receives light, emits light from the light emitting unit toward the toner patch, and receives light reflected on the toner patch by the light receiving unit. The light receiving unit has a light receiving element, and obtains a sensor output by converting the amount of light received by the light receiving element into an electric signal. The toner patch is composed of a belt surface and a toner surface, and the density sensor 17 detects the concealment rate by the toner (the ratio of the toner to the total area of the patch). The less the light reflected from the belt surface, the smaller the sensor output. As the toner patch density increases, the concealment rate of the belt surface by the toner increases and the sensor output decreases. Therefore, the concealment rate of the belt surface by the toner, that is, the density of the toner patch can be detected based on the magnitude of the sensor output (see FIG. 7). The configuration of the density sensor 17 is not limited to the above-described configuration, and any configuration that can detect the concentration may be used.

  The image forming unit 12-1 forms a yellow (Y) toner image, the image forming unit 12-2 forms a magenta (M) toner image, and the image forming unit 12-3 forms a cyan (C) toner image. The image forming unit 12-4 forms a black (BK) toner image. These image forming units 12-1 to 12-4 are sequentially arranged from the upstream side to the downstream side of the intermediate transfer belt 11.

  Each of the image forming units 12 (12-1 to 12-4) includes a photoreceptor 31, a charging device 32 for uniformly charging the photoreceptor 31, and exposure for performing image exposure on the charged photoreceptor 31. And a developing device 34 for developing the electrostatic latent image formed by exposure with each color toner.

  The developing device 34 includes a developing roller 35 and causes the toner to adhere to the photoreceptor 31 from the developing roller 35. A cleaner 36 is disposed at a position facing the photoconductor 31, and the cleaner 36 collects toner remaining on the photoconductor 31. All the image forming units 12-1 to 12-4 are controlled by the control unit 40.

  Next, the operation of the image forming apparatus 100 will be described.

  The toner images developed on the photoconductors 31 of the image forming units 12-1 to 12-4 are primarily transferred onto the intermediate transfer belt 11 by the primary transfer roller 13 at the contact position with the intermediate transfer belt 11.

  Each time the toner image transferred onto the intermediate transfer belt 11 passes through each of the image forming units 12-1 to 12-4, each color is superimposed thereon. As a result, a full-color toner image is finally formed on the intermediate transfer belt 11.

  Next, the full-color toner image on the intermediate transfer belt 11 is secondarily transferred onto the recording sheet S by the secondary transfer roller 14 downstream of the intermediate transfer belt 11.

  Next, the recording sheet S passes through the fixing device 20 downstream of the conveyance path of the recording sheet S, whereby the toner image is fixed and discharged onto a discharge tray (not shown). The recording paper S is stored in a cassette (not shown), and is conveyed from the cassette to the secondary transfer roller 14 one by one.

  The toner remaining on the photoreceptor 31 after the primary transfer is removed by a cleaner 36 disposed downstream and collected in a waste toner box (not shown). Further, the toner remaining on the intermediate transfer belt 11 after the secondary transfer is collected by the cleaning device 16.

  Here, in the image forming apparatus 100, the image density of the toner image may be different due to an environment around the apparatus such as temperature and humidity and disturbance such as durability of the apparatus. Therefore, in the image forming apparatus 100, in order to stabilize the image density, a test toner image is formed on the intermediate transfer belt 11, and the image forming unit 12-1 is based on the density of the test toner image. The toner adhesion amount at ˜12-4 is controlled.

  Specifically, the toner adhesion amount of the toner image formed on the intermediate transfer belt 11 is changed by the developing device 34. The circumferential length of the intermediate transfer belt 11 in the toner image formed on the intermediate transfer belt 11 is changed by the developing device 34 and the exposure device 33.

  The control unit 40 controls the developer 34 and the exposure device 33 to control the toner adhesion amount and the length of the toner image. In practice, the image forming apparatus 100 forms a test toner image on the intermediate transfer belt 11 during gradation correction, and the density sensor 17 detects the density of the toner image. The image forming apparatus 100 performs gradation correction by correcting the gradation conversion table provided in the control unit 40 in accordance with the density detection result. The image forming apparatus 100 controls the developing device 34 using the corrected gradation conversion table when printing on the recording paper S (that is, at the time of actual printing), so that the density on the intermediate transfer belt 11 is controlled. Forms a toner image corrected for.

[2] Gradation correction Next, gradation correction will be described in detail. In this specification, “gradation” may be rephrased as “density”, and conversely, “density” may be rephrased as “gradation”.

  FIG. 4 shows the density OD and density ID when the density indicated by the input original image data is OD (Original Density) and the density of the print image output on the recording paper S is ID (Image Density). It is a figure which shows the gradation characteristic which is the relationship. In the relationship between the density O.D. and the density I.D., an ideal print image can be obtained if a linear relationship is maintained as shown by the gradation characteristic line L1 in FIG.

  However, in practice, the relationship between the concentration OD and the concentration ID is as indicated by the gradation curve L2 in FIG. 4 depending on the environment surrounding the device such as temperature and humidity, and the variation factors such as device durability and manufacturing variations. It becomes a non-linear relationship. As a result, the density of the print image changes greatly for each gradation with respect to the input original image data. As can be seen from the gradation curve L2, since the print image density ID is usually lower than the original image density OD in the low density area of the original image data, a color skip occurs and the print image has a very low density. Is difficult to reproduce on the recording paper S. Further, since the print image density ID is higher than the original image density OD in the area where the original image data is high density, color collapse occurs and it is difficult to reproduce the density difference near the maximum density on the recording paper S. It becomes.

  Therefore, in order to make the density of the print image coincide with the density indicated by the input original image data, it is necessary to correct the gradation characteristics. Specifically, the relationship between the density O.D. and the density I.D. is made stable and linear in all gradations by gradation correction. In practice, gradation correction is performed by correcting a gradation conversion table provided in the control unit 40.

  A method for creating a gradation conversion table will be described. The image forming apparatus 100 forms a gradation pattern image (toner image) 50 as shown in FIG. 5 on the intermediate transfer belt 11 during gradation correction, and the density sensor 17 detects the density of the gradation pattern image 50. To do. The gradation pattern image 50 is composed of a plurality of gradation patches P1 to P11 having different gradations. For example, the gradation of each gradation patch P1 to P11 is 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, with the maximum gradation being 100%. , 0%. The lengths of the gradation patches P1 to P11 are set such that the density sensor 17 can accurately detect the gradation patches P1 to P11. The width of each gradation patch (which may be referred to as the width of the gradation pattern 50) is sufficiently detected even if the diameter of the density sensor 17, the attachment of the density sensor 17, the image forming position in the main scanning direction of the image, etc. fluctuate. Use as wide as possible.

  FIG. 6 shows the density (print image density) detection value of the gradation pattern image 50 detected by the density sensor 17 in correspondence with the original image density data. The black circles in the figure represent the density detection values of the respective gradation patches P1 to P11 (FIG. 5). As shown in FIG. 7, the density detection value is obtained by converting the sensor output value to the density using a conversion table showing the relationship between the sensor output value and the density of the density sensor 17 prepared in advance. Can do. As can be seen from FIG. 6, the detected density value exists on the gradation curve L2 and deviates from the target gradation characteristic line L1. Therefore, gradation correction that corrects this shift is necessary.

  FIG. 8 shows a state of the gradation conversion table provided in the control unit 40. The data of the gradation conversion table in which the curve L3 in FIG. 8 is corrected is shown. The correction data indicated by the curve L3 is a value that cancels out the deviation of the gradation curve L2 from the target gradation characteristic line L1. That is, when the original image data is input, the toner image forming operation of the image forming units 12-1 to 12-4 is controlled using the correction control data on the curve L3 corresponding to the original image data. The density of the image can be set to the density on the target gradation curve L1.

[3] Gradation pattern image according to this embodiment Next, the configuration of the gradation pattern image according to this embodiment will be described in detail.

[3-1] Configuration example 1 of gradation pattern image
FIG. 9 shows a configuration example 1 of a gradation pattern image. As shown in FIG. 9, the gradation pattern images 50-1 and 50-2 are arranged in parallel. Each of the gradation pattern images 50-1 and 50-2 includes a plurality of gradation patches P1 to P11 having different gradations.

  The gradation pattern images 50-1 and 50-2 are obtained by arranging gradation patches P1 to P11 so that gradations of gradation patches are dispersed in the pattern arrangement direction. In other words, the gradation pattern images 50-1 and 50-2 are each configured such that the arrangement of the gradation patches is random in terms of gradation.

  When the intermediate transfer belt 11 moves in the direction of the arrow, the density of the gradation pattern images 50-1 and 50-2 is detected from left to right by density sensors 17-1 and 17-2 fixed to the image forming apparatus 100. It will be done.

  Here, over the axial direction of the intermediate transfer belt 11 (which may be referred to as a width direction of the intermediate transfer belt 11 or a direction orthogonal to the pattern arrangement direction of the gradation pattern images 50-1 and 50-2), Consider the case where there is a scratch 60. Even in such a case, the gradation patch P7 where the scratch 60 is located and the gradation patch P9 are different in gradation, so that a gradation patch of a certain gradation is present in both of the gradation pattern images 50-1 and 50-2. It is possible to avoid being affected by the scratch 60. That is, even if the gradation patch P7 of the gradation pattern image 50-1 is adversely affected by the scratch 60, the gradation patch P7 of the gradation pattern image 50-2 is not adversely affected by the scratch 60. A value can be obtained. Similarly, even if the gradation patch P9 of the gradation pattern image 50-2 is adversely affected by the scratch 60, the gradation patch P9 of the gradation pattern image 50-1 is not adversely affected by the scratch 60, so that the correct density is obtained. A detection value can be obtained.

  Further, since the gradations of the gradation patches P7 and P9 having the scratch 60 are different, the influence of the scratch 60 is also different, and the density detection values of the gradation patches P7 and P9 that are less influenced by the scratch 60 can be adopted. become. The method of using the density detection value will be described in detail later.

The characteristics of the gradation pattern images 50-1 and 50-2 in FIG. 9 are as follows.
(I) The gradation pattern images 50-1 and 50-2 are in the axial direction of the intermediate transfer belt 11 (in the width direction of the intermediate transfer belt 11 or in the pattern arrangement direction of the gradation pattern images 50-1 and 50-2). (It may be said that the directions are orthogonal to each other.) Thereby, the density detection time is shortened.

  (Ii) The gradation pattern images 50-1 and 50-2 are configured by arranging gradation patches so that gradations of gradation patches are dispersed in the pattern arrangement direction. As a result, even when a density variation factor such as a scratch occurs in a direction orthogonal to the pattern arrangement direction, there is a high possibility that there is a gradation patch that is not affected by the density variation factor or has little influence. Therefore, it is possible to suppress a decrease in density detection accuracy.

[3-2] Configuration example 2 of gradation pattern image
FIG. 10 shows a configuration example 2 of the gradation pattern image.
The characteristics of the gradation pattern images 50-1 and 50-2 in FIG. 10 are as follows.

  (I) The gradation pattern images 50-1 and 50-2 are arranged in parallel so that they all overlap in the axial direction of the intermediate transfer belt 11. Thereby, the density detection time is shortened.

  (Ii) The gradation pattern image 50-1 is a pattern in which gradation gradually decreases. Note that the gradation pattern image 50-1 may be a pattern in which gradation gradually increases. The gradation pattern image 50-2 is a pattern in which the first half portion and the second half portion are interchanged from substantially the center position of the gradation pattern 50-1. As a result, even when there is a scratch 60 in the axial direction of the intermediate transfer belt 11, a gradation patch of a certain gradation is affected by the scratch in both of the gradation pattern images 50-1 and 50-2. As a result, a decrease in density detection accuracy can be suppressed.

[3-3] Configuration example 3 of gradation pattern image
FIG. 11 shows a configuration example 3 of the gradation pattern image.
The characteristics of the gradation pattern images 50-1 and 50-2 in FIG. 11 are as follows.

  (I) The gradation pattern images 50-1 and 50-2 are arranged in parallel so that they all overlap in the axial direction of the intermediate transfer belt 11. Thereby, the density detection time is shortened.

  (Ii) The gradation pattern image 50-1 is a pattern in which gradation is sequentially decreased, and the gradation pattern image 50-2 is a pattern in which gradation is sequentially increased in contrast to the gradation pattern. Note that the gradation pattern image 50-1 may be a pattern in which the gradation is sequentially increased, and the gradation pattern image 50-2 may be a pattern in which the gradation is sequentially decreased. As a result, even when there is a scratch 60 in the axial direction of the intermediate transfer belt 11, a gradation patch of a certain gradation is affected by the scratch in both of the gradation pattern images 50-1 and 50-2. As a result, a decrease in density detection accuracy can be suppressed.

[3-4] Configuration example 4 of gradation pattern image
FIG. 12 shows a configuration example 4 of a gradation pattern image.
The characteristics of the gradation pattern images 50-1 and 50-2 in FIG. 12 are as follows.

  (I) The gradation pattern images 50-1 and 50-2 have the same gradation pattern. That is, the arrangement order of the gradation patches P1 to P11 is the same.

  (Ii) The gradation pattern image 50-1 and the gradation pattern image 50-2 are arranged so as to be shifted from each other in the pattern arrangement direction so that they partially overlap each other in the pattern arrangement direction. With this arrangement, the density detection time is shortened by the amount of overlap. Further, since they are arranged shifted in the pattern arrangement direction, the gradations of the gradation patches that overlap in the direction orthogonal to the pattern arrangement direction are different. As a result, even when there is a scratch 60 in the axial direction of the intermediate transfer belt 11, a gradation patch of a certain gradation is affected by the scratch in both of the gradation pattern images 50-1 and 50-2. As a result, a decrease in density detection accuracy can be suppressed.

[4] Density Detection Processing Next, concentration detection processing according to the present embodiment will be described. In the present embodiment, three processes are given as examples.

[4-1] Density detection processing example 1
FIG. 13 is a flowchart for explaining the density detection processing example 1.

  In step S0, the image forming apparatus 100 performs the gradation correction timing (that is, when the power is turned on, when returning from sleep, when a certain number of printed sheets is reached, or when the external environment changes significantly). The processing is started, and gradation pattern images 50-1 and 50-2 are formed on the intermediate transfer belt 11 in the subsequent step S1. In subsequent step S2, the density sensors 17-1 and 17-2 detect the densities of the gradation pattern images 50-1 and 50-2.

  Although the density detection processing example 1 shown in FIG. 13 can be applied to any of the arrangements shown in FIGS. 9 to 12, a case where the density detection processing example 1 is applied to the arrangement of FIG. 9 will be described here.

  In step S3, the image forming apparatus 100 determines whether the density difference of the corresponding gradation patch is equal to or greater than a threshold value. That is, the density of each gradation patch P1 to P11 detected by the density sensor 17-1 and the density of each gradation patch P1 to P11 detected by the density sensor 17-2 are compared between corresponding gradation patches, and It is determined whether or not the density difference is greater than or equal to a threshold value.

  If the image forming apparatus 100 obtains a positive result in step S3, it proceeds to step S4, and if it obtains a negative result, it proceeds to step S5.

  In step S4, the image forming apparatus 100 sets the density detection value of the gradation patch having a large difference from the previous and subsequent density average values as invalid data. In step S5, density data is collected (that is, stored in a memory). In step S6, it is determined whether or not all the gradation patches have been processed. If it is determined that the processing has ended, the process proceeds to step S7. If it is determined that the processing has not ended, the process returns to step S3.

  Here, the processing of step S3 and step S4 will be specifically described with reference to FIG.

  For the gradation patches other than the gradation patches P7 and P9 where the scratch 60 exists, the density sensors 17-1 and 17-2 can obtain almost the same density detection value with the corresponding gradation patches. A negative result is obtained. On the other hand, the density of the gradation patch P7 detected by the density sensor 17-1 and the density of the gradation patch P7 detected by the density sensor 17-2 are the gradation detected by the density sensor 17-1. Since the patch P7 is affected by scratches, the density difference becomes equal to or greater than the threshold value, and a positive result is obtained in step S3. The same applies to the gradation patch P9.

  In this way, the density data of the gradation patches P7 and P9 where the scratch 60 is present becomes the processing target in step S4. In step S4, the density detection value of the gradation patch P7 from the density average value before and after the gradation patch P7, that is, the density average value obtained from the density detection value of the gradation patch P6 and the density detection value of the gradation patch P8. Find the value minus. Further, the density detection value of the gradation patch P9 is subtracted from the density average value before and after the gradation patch P9, that is, the density average value obtained from the density detection value of the gradation patch P8 and the density detection value of the gradation patch P10. Find the value. Then, of the density data of the gradation patch P7 and the density data of the gradation patch P9, the one with the larger value (difference) is deleted as invalid data.

  In other words, the density detection value of the first gradation patch included in the first gradation pattern image 50-1 and the first gradation patch P7 included in the second gradation pattern image 50-2. If the difference value between the density detection value of the second gradation patch of the same gradation and the threshold value is equal to or greater than the threshold value, the density detection value of the first gradation patch and the density detection value of the second gradation patch Among them, the density detection value having the larger difference from the density detection average value of the gradation patch of the preceding and succeeding gradations with respect to the gradation is treated as invalid data.

  In this way, it is possible to avoid using density data that has a large influence on the density detection value due to the scratch 60.

[4-2] Concentration detection processing example 2
FIG. 14, in which the same reference numerals are assigned to the parts corresponding to those in FIG.

  In processing example 2 in FIG. 14, step S <b> 10 is added after step S <b> 4 as compared to processing example 1 in FIG. 13. In step S10, the gradation patch data at the same position in the axial direction of the intermediate transfer belt 11 with respect to the invalid data is also invalidated. In other words, the density detection value of the gradation patch arranged at a position overlapping in the direction orthogonal to the pattern arrangement direction with respect to the gradation patch treated as invalid data is also treated as invalid data. Specifically, when one of the gradation patch P7 and the gradation patch P9 is determined to be invalid data, the other is also regarded as invalid data. By doing so, it is possible to avoid using the density detection value of the gradation patch in which the scratch 60 or the like exists.

[4-3] Example 3 of density detection processing
FIG. 15, in which parts corresponding to those in FIG. 14 are assigned the same reference numerals, is a flowchart for explaining density detection processing example 3.

  Processing example 3 in FIG. 15 is different from processing example 2 in FIG. 14 in that step S20 is added between step S4 and step S10. In step S20, it is determined whether or not the invalid data and the gradation patch at the same position in the axial direction of the intermediate transfer belt 11 have a low density. If it is determined that the density is low, the process proceeds to step S10, and is determined not to have a low density. If so, the process proceeds to step S5.

  Here, it is known that the influence on the density detection value by the scratch 60 or the like becomes larger as the density is lower. Therefore, in this example, a density threshold value is set in advance, and in the case of a density detection value of a tone patch whose density is lower than the threshold value, the process proceeds to step S10 to make invalid data, and a gradation having a density equal to or higher than the threshold value. In the case of the detected density value of the patch, the process proceeds to step S5 and is adopted as density data. In short, when the gradation patch arranged at a position overlapping in the direction orthogonal to the pattern arrangement direction with respect to the gradation patch treated as invalid data is a gradation patch whose density is lower than a predetermined density, The density detection value of this gradation patch is also handled as invalid data. By doing in this way, it becomes possible to accurately select density data in which the influence on the density detection value due to the scratch 60 or the like is largely invalid and density data to be adopted with a small influence.

[5] Effect As described above, according to the present embodiment, the gradation pattern images 50-1 and 50-2 are at least partially in the direction orthogonal to the pattern arrangement direction (the axial direction of the intermediate transfer belt 11). Alternatively, the gradation pattern images 50-1 and 50-2 having different gradations are formed at the overlapping positions, and the gradation pattern images 50-1 and 50-2 are formed with different gradations while suppressing an increase in density detection time. A decrease in density detection accuracy due to a density variation factor such as a scratch 60 extending in a direction orthogonal to the pattern arrangement direction can be suppressed.

  FIG. 16 shows the output value of the density sensor 17 obtained by the configuration of the present embodiment. As shown in the figure, in a certain gradation, the density detection value of the gradation pattern image 50-2 becomes an incorrect value at the position of the scratch, but the density detection value of the gradation pattern image 50-1 is affected by the scratch. Therefore, the correct density detection value for the gradation can be obtained.

  FIG. 17 shows an output value of the density sensor 17 when the configuration shown in FIG. 2 is adopted as a comparative example with respect to the present embodiment. Since the position of the flaw exists in the same gradation in the gradation pattern images 50-1 and 50-2, the density detection value of the flawed gradation is obtained from either of the gradation pattern images 50-1 and 50-2. Can not get the correct value.

  In the above example, the gradation patterns 50-1 and 50-2 including the 11 gradation patches P1 to P11 having different gradations are used as the gradation pattern for detecting the density. The number of gradation patches constituting the pattern image is not limited to eleven.

  Further, the number of gradation pattern images 50 to be formed is not limited to two and may be three or more. In short, a plurality of gradation pattern images that overlap at least partially in a direction orthogonal to the pattern arrangement direction of the gradation pattern images are formed, and the plurality of gradation pattern images are located between the gradation pattern images at the overlapping positions. Therefore, it is sufficient that at least some of the gradations are different.

  In the above-described example, the image forming apparatus 100 in which the intermediate transfer belt 11 is an image carrier has been described as an example. However, the image forming apparatus in which the photosensitive belt, the photosensitive drum, or the intermediate transfer drum is an image carrier. The same applies to the above.

  Furthermore, the image forming apparatus of the present invention can be applied to any of a full-color copying machine, a printer, a FAX, or a complex machine thereof.

  The embodiments of the present invention have been described above. The above description is an illustration of a preferred embodiment of the present invention, and the scope of the present invention is not limited to this. That is, the description of the configuration and operation of each of the above devices is an example, and it is obvious that various modifications and additions to these examples are possible within the scope of the present invention.

1, 11 Intermediate transfer belt 2, 17, 17-1, 17-2 Density sensor 3-1, 3-2, 50 Gradation pattern image 4, 60 Scratch 10 Imaging device 12-1, 12-2, 12- 3, 12-4 Image forming unit 31 Photoconductor 32 Charging device 33 Exposure device 34 Developer 35 Developing roller 40 Control unit 100 Image forming device S Recording paper P1 to P11 Gradation patch

Claims (9)

An image forming unit that forms a toner image on the image carrier, and a density sensor that detects the density of a gradation pattern image for gradation correction formed by the image forming unit, and is obtained by the density sensor. An image forming apparatus that performs gradation correction based on the density detection result,
The image forming unit forms a plurality of gradation pattern images at least partially overlapping in a direction orthogonal to a pattern arrangement direction of the gradation pattern images;
The plurality of gradation pattern images are different in at least some of the gradations between the plurality of gradation pattern images in overlapping positions.
Image forming apparatus. Each gradation pattern image is
It is composed of multiple gradation patches with different gradations.
The gradation patches are arranged so that the gradations of the gradation patches are dispersed in the pattern arrangement direction.
The image forming apparatus according to claim 1. The plurality of gradation pattern images formed by the image forming unit include first and second gradation pattern images arranged in parallel in the pattern arrangement direction,
The first gradation pattern image is a pattern in which gradation gradually increases or decreases sequentially,
The second gradation pattern image is a pattern in which the first half part and the second half part are interchanged from substantially the center position of the first gradation pattern.
The image forming apparatus according to claim 1. The plurality of gradation pattern images formed by the image forming unit include first and second gradation pattern images arranged in parallel in the pattern arrangement direction,
The first gradation pattern image is a pattern in which gradation gradually increases or decreases sequentially,
The second gradation pattern image is a pattern in which gradation gradually decreases or sequentially increases in the reverse order to the first gradation pattern.
The image forming apparatus according to claim 1. The plurality of gradation pattern images formed by the image forming unit include first and second gradation pattern images having the same gradation pattern,
The first gradation pattern image and the second gradation pattern image are arranged so as to be shifted from each other in the pattern arrangement direction so that a part thereof overlaps in the pattern arrangement direction.
The image forming apparatus according to claim 1. The density detection value of the first gradation patch included in the first gradation pattern image and the second gradation value included in the second gradation pattern image and having the same gradation as the first gradation patch. If the difference between the gradation patch density detection value and the threshold is greater than or equal to the threshold,
Of the density detection value of the first gradation patch and the density detection value of the second gradation patch, the difference from the density detection average value of the gradation patch of the preceding and succeeding gradations with respect to the gradation Treat the detected density value with the larger value as invalid data.
The image forming apparatus according to any one of claims 1 to 5. Concerning the gradation patch treated as the invalid data, the density detection value of the gradation patch arranged at a position overlapping in the direction orthogonal to the pattern arrangement direction is also treated as invalid data.
The image forming apparatus according to claim 6. When the gradation patch arranged at a position overlapping the gradation patch treated as invalid data in a direction orthogonal to the pattern arrangement direction is a gradation patch having a density lower than a predetermined density, this Treat density patch density detection values as invalid data.
The image forming apparatus according to claim 6. A method of forming a gradation pattern image formed on an image carrier of an image forming apparatus in order to perform gradation correction of the image forming apparatus,
The gradation pattern image is
A plurality of gradation pattern images at least partially overlapping in a direction orthogonal to the pattern arrangement direction of the gradation pattern image;
And, at the overlapping position, at least some of the gradations differ between the plurality of gradation pattern images.
Gradation pattern image forming method.

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