Patent Publication Number: US-2021195066-A1

Title: Image forming apparatus and non-transitory computer readable medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-228663 filed Dec. 18, 2019. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an image forming apparatus and a non-transitory computer readable medium. 
     2. Related Art 
     As a related art, JP-A-2009-288389 discloses an image forming apparatus including an image forming device that forms correction images of different colors on different sheets and outputs a correction chart, and a density unevenness corrector that sets density correction instruction information based on the correction chart and corrects density unevenness. 
     SUMMARY 
     An image forming condition may be corrected in order to reduce image density unevenness corresponding to the rotation cycle of a rotating body such as a developing roller. For example, plural test images that are different in correction amount for an image forming condition are formed on sheets, and an appropriate correction amount is determined based on the test images. Here, when the plural test images which are different in correction amount are formed on the sheets different each other, it may be difficult to determine whether the correction is insufficient and whether the correction is excessive. 
     Aspects of non-limiting embodiments of the present disclosure relate to making it possible to easily determine whether a correction amount is excessive and whether the correction amount is insufficient, as compared with a case in which test images that are different in correction amount are formed on different sheets. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However; aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided an image forming apparatus including an image forming device configured to form an image on a sheet using a rotating body under a predetermined image forming condition, a corrector configured to determine a correction amount for the image forming condition to adjust image density unevenness corresponding to a rotation cycle of the rotating body, and a controller configured to control the image forming device to form, on a single sheet, plural test images that are different in the correction amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic configuration diagram illustrating an image forming apparatus according to an exemplary embodiment; 
         FIG. 2  is a schematic view illustrating a relationship between a magnitude of a correction amount for an image forming condition and density unevenness corresponding to the rotation cycle of a rotating body that appears in a test image; 
         FIG. 3  is a block diagram illustrating a functional configuration of a control device according to the present exemplary embodiment; 
         FIG. 4  is a diagram illustrating an example of test images formed on a sheet under control of the control device according to the present exemplary embodiment; 
         FIG. 5  is a diagram illustrating another example of the test images formed on the sheet under the control of the control device according to the present exemplary embodiment; 
         FIG. 6  is a flowchart illustrating an example of a procedure for checking an appropriate correction amount for an image forming condition based on the test images; and 
         FIGS. 7A and 7B  are diagrams illustrating other forms of pointing portions. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings. 
       FIG. 1  is a schematic configuration diagram illustrating an image forming apparatus  100  according to an exemplary embodiment. The image forming apparatus  100  illustrated in  FIG. 1  is a so-called tandem color printer. The image forming apparatus  100  includes an image forming device  10 , a control device  20 , an image reader  30 , and a sheet feeder  40 . The image forming device  10  forms an image based on image data of colors. The control device  20  controls operation of the overall image forming apparatus  100 . The image reader  30  reads an image of a document. The sheet feeder  40  feeds sheets S to the image forming device  10 . 
     Here, components of the image forming apparatus  100  are accommodated in a casing  50 . A stacking unit  60  is provided below the image reader  30  and on the upper surface of the casing  50 . The sheet S on which the image is formed by the image forming device  10  is stacked on the stacking unit  60 . An operation unit  70  is provided above the image reader  30 . The operation unit  70  receives a user&#39;s operation with respect to the image forming apparatus  100 . 
     The image forming device  10  includes four image forming units  1 Y,  1 M,  1 C, and  1 K arranged in parallel at regular intervals. The image forming units  1 Y,  1 M,  1 C, and  1 K form toner images by a so-called electrophotographic process. Here, the image forming units  1 Y,  1 M,  1 C, and  1 K are similarly configured to each other, except for toners accommodated in developing devices  16  which will be described later. The image forming units  1 Y,  1 M,  1 C, and  1 K form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Therefore, in the following description, when the configurations of the image forming units  1 Y,  1 M,  1 C, and  1 K do not need to be distinguished from each other, reference signs of “Y”, “M”, “C”, and “K” will be omitted. 
     The image forming device  10  includes an intermediate transfer belt  13  to which toner images of the respective colors formed on photoconductor drums  12  of the image forming units  1  are transferred. The image forming device  10  includes primary transfer rollers  17  that sequentially transfer (primarily transfer) the toner images of the respective colors formed by the image forming units  1  to the intermediate transfer belt  13 . The image forming device  10  includes a secondary transfer roller  19 , a fixing device  21 , and discharge rollers  23 . The secondary transfer roller  19  collectively transfers (secondarily transfers) the toner images of the colors, which are formed on the intermediate transfer belt  13  in a superimposed manner, to a sheet S. The fixing device  21  fixes the secondarily transferred toner images of the colors onto the sheet S. The discharge rollers  23  discharge the sheet S. 
     Each image forming unit  1  includes the photoconductor drum  12 , a charging device  14 , an exposure device  15 , and a developing device  16 . The photoconductor drum  12  carries a toner image. The charging device  14  charges the photoconductor drum  12 . The exposure device  15  forms an electrostatic latent image by exposure of the surface of the charged photoconductor drum  12 . The developing device  16  develops the electrostatic latent image formed on the photoconductor drum  12  to form the toner image. 
     The developing device  16  includes a rotatable developing roller  16   a  that faces the photoconductor drum  12 . Each developing device  16  accommodates a developer containing a toner of a corresponding color (for example, yellow toner in the yellow image forming unit  1 Y) therein. Magnets are built in the developing roller  16   a . The developing roller  16   a  carries the developer containing the toner on the surface thereof by a magnetic force. In the developing device  16 , a predetermined developing bias is applied to the developing roller  16   a  by a developing power source (not illustrated), so that the toner is transferred from the surface of the developing roller  16   a  to an image portion of the electrostatic latent image formed on the photoconductor drum  12 . 
     The image forming apparatus  100  executes a series of image forming processing under control of the control device  20 . That is, an image processor (not illustrated) performs image processing on image data acquired from a PC (not illustrated) or the image reader  30  to obtain image data of the colors, and sends the image data of each color to the exposure device  15  of the corresponding image forming unit  1 . Then, the exposure device  15  performs the exposure and the developing device  16  performs the development, so that the toner image is formed on the photoconductor drum  12 . 
     The toner images of the respective colors formed on the photoconductor drums  12  of the respective image forming units  1  are primarily transferred onto the intermediate transfer belt  13  by the respective primary transfer rollers  17  in sequence. As a result, a superimposed toner image in which the toners of the colors are superimposed is formed on the intermediate transfer belt  13 . The superimposed toner image is transported toward the secondary transfer roller  19  with traveling of the intermediate transfer belt  13 . 
     The sheet S fed from the sheet feeder  40  is transported to the secondary transfer roller  19  in accordance with a transportation timing of the superimposed toner image on the intermediate transfer belt  13 . Then, the superimposed toner image on the intermediate transfer belt  13  is secondarily transferred onto the sheet S by the secondary transfer roller  19 . The superimposed toner image transferred to the sheet S is fixed onto the sheet S by the fixing device  21 , and then discharged to the stacking unit  60  by the discharge rollers  23 . 
     In the image forming apparatus  100 , each image forming unit  1  includes a rotating body such as the developing roller  16   a  of the developing device  16  and the photoconductor drum  12 . In the image formed on the sheet S by the image forming apparatus  100 , density unevenness corresponding to the rotation cycle of the rotating body may occur due to eccentricity of the rotating body or unevenness of the outer peripheral surface of the rotating body. Here, the “density unevenness corresponding to the rotation cycle of the rotating body” is a variation in image density that occurs in a sub-scanning direction of the sheet S when an image is formed on the sheet S at a uniform image density. 
     The image forming apparatus  100  corrects an image forming condition in order to reduce such density unevenness corresponding to the rotation cycle of the rotating body. As will be described later in detail, the image forming apparatus  100  performs predetermined correction on the image forming condition, forms test images on the sheet S, and determines an appropriate correction amount based on the test images. More specifically, the image forming apparatus  100  forms, on the sheet S, plural test images that are different in correction amount for the image forming condition. Then, a user visually checks the plural test images, which are different in correction amount and are formed on the sheet S, to determine an appropriate correction amount. 
     The test images are not particularly limited to specific ones, but may be any test images that make it possible to check the density unevenness corresponding to the rotation cycle of the rotating body. Examples of the test images include rectangular or strip-shaped images each having a length, in the sub-scanning direction, equal to or longer than a length corresponding to the rotation cycle of the rotating body. 
       FIG. 2  is a schematic diagram illustrating a relationship between the magnitude of the correction amount for the image forming condition and the density unevenness corresponding to the rotation cycle of the rotating body that appears in the test image. 
     As illustrated in  FIG. 2 , in the test image, a high density portion (a portion having a dark color) and a low density portion (a portion having a pale color) alternately appear in the sub-scanning direction in accordance with the rotation cycle of the rotating body. A density difference between the high density portion and the low density portion corresponds to the density unevenness corresponding to the rotation cycle of the rotating body that appears in an image. The smaller the density difference between the high density portion and the lower density portion is, the more appropriate the correction amount for the image forming condition is. In the following description, a correction amount for an image forming condition that generate no density difference in a test image may be referred to as an “appropriate correction amount”. 
     Here, as illustrated in  FIG. 2 , phases of a high density portion and a low density portion that appear in accordance with the rotation cycle of the rotating body in a case where a correction amount for an image forming condition is smaller than an appropriate correction amount (that is, in a case where the correction amount is insufficient for the appropriate correction amount) are opposite to those in a case where the correction amount for the image forming condition is larger than the appropriate correction amount (that is, in a case where the correction amount is excessive for the appropriate correction amount). However, when a user looks at a test image that is insufficient in correction amount and a test image that is excessive in correction amount individually, it is difficult for him or her to check the phases of a high density portion and a low density portion so as to determine (i) whether the correction amount is insufficient for the appropriate correction amount and (ii) whether the correction amount is excessive for the appropriate correction amount. 
     In contrast, in the present exemplary embodiment, plural test images that are different in correction amount for an image forming condition are formed on a single sheet S. This enables the user to easily determine, based on the plural test images formed on the sheet S, whether the phases of the high density portion and the low density portion that appear in accordance with the rotation cycle of the rotating body are equal to each other or opposite to each other. Then, this also enables the user to easily determine whether the correction amount is insufficient for the appropriate correction amount or whether the correction amount is excessive for the appropriate correction amount. 
     In the following description, phases of a high density portion and a low density portion that appear in a test image in accordance with the rotation cycle of a rotating body may be referred to as a “phase of density unevenness”. 
     Next, description will be given on the configuration of the control device  20  and test images formed on a sheet S under control of the control device  20 . Hereinafter, a case where two test images that are different in correction amount for an image forming condition are formed on the sheet S as plural test images will be described as an example. More specifically, a case where a first test image T 1  in which the correction amount for the image forming condition is a first correction amount a 1  and a second test image T 2  in which the correction amount for the image forming condition is a second correction amount a 2  are formed on a single sheet S will be described as an example. 
       FIG. 3  is a block diagram illustrating a functional configuration of the control device  20  according to the present exemplary embodiment. Further,  FIGS. 4 and 5  are diagrams illustrating examples of test images formed on the sheet S under the control of the control device  20  according to the present exemplary embodiment.  FIG. 4  illustrates a case where both the first correction amount a 1  of the first test image T 1  and the second correction amount a 2  of the second test image T 2  are smaller than the appropriate correction amount.  FIG. 5  illustrates a case where the first correction amount a 1  of the first test image T 1  is smaller than the appropriate correction amount, while the second correction amount a 2  of the second test image T 2  is larger than the appropriate correction amount. 
     The control device  20  includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). The ROM stores a control program to be executed by the CPU. The CPU reads out the control program stored in the ROM, and executes the control program using the RAM as a work area. The CPU executes the control program to control the elements of the image forming apparatus  100 . 
     As illustrated in  FIG. 3 , the control device  20  includes a corrector  201  and an image controller  203 . The corrector  201  determines correction amounts for an image forming condition under which the image forming device  10  forms an image on a sheet S. The image controller  203  is an example of a controller. The image controller  203  controls the image forming device  10  to form plural test images that are different in correction amount on a single sheet S using the correction amounts for the image forming condition determined by the corrector  201 . The corrector  201  is not limited to one implemented by the CPU executing the control program. The corrector  201  may be implemented, for example, by an electronic circuit. 
     The corrector  201  determines the correction amount for the image forming condition to adjust density unevenness corresponding to the rotation cycle of the rotating body. Examples of the image forming condition for which the corrector  201  determines the correction amount include an exposure amount by the exposure device  15 , the magnitude of a developing bias applied to the developing roller  16   a  of the developing device  16 , and the magnitude of a charging bias of the charging device  14 . The image forming condition for which the corrector  201  determines the correction amount is not particularly limited to the above examples, but may be any image forming condition that can adjust image density unevenness corresponding to the rotation cycle of a rotating body. 
     The corrector  201  determines plural correction amounts to be applied to respective test images when the plural test images are formed on a single sheet S. In this example, the corrector  201  determines the first correction amount a 1  and the second correction amount a 2  as plural correction amounts. The second correction amount a 2  is larger than the first correction amount a 1  (that is, the first correction amount a 1 &lt;the second correction amount a 2 ). 
     Here, it may be clear whether at least one correction amount among the plural correction amounts determined by the corrector  201  is smaller than the appropriate correction amount or larger than the appropriate correction amount. In this example, it is assumed that the corrector  201  sets the first correction amount a 1  to 0 (that is, no correction) such that it is clear that the first correction amount a 1  is smaller than the appropriate correction amount. 
     The image controller  203  controls the image forming device  10  to form plural test images on a single sheet S with toner of predetermined colors under image forming conditions to which the plural correction amounts determined by the corrector  201  are applied, respectively. More specifically, the image controller  203  controls the elements of the image forming device  10  using the correction amounts determined by the corrector  201 , so as to cancel the density unevenness corresponding to the rotation cycle of the rotating body. 
     In this example, the image controller  203  applies the first correction amount a 1  to the image forming condition to form the first test image T 1  on the sheet S, and applies the second correction amount a 2  to the same sheet S to form the second test image T 2 . 
     The image controller  203  forms the plural test images on the single sheet S side by side in the sub-scanning direction in which the density unevenness corresponding to the rotation cycle of the rotating body occurs. In this example, as illustrated in  FIGS. 4 and 5 , the first test image T 1  and the second test image T 2  are formed side by side in the sub-scanning direction. For example, the image controller  203  controls the image forming device  10  to change the correction amount to be applied to the image forming condition from the first correction amount a 1  to the second correction amount a 2  during formation of the test images on the single sheet S. In this case, the first test image T 1  and the second test image T 2  are continuously formed in the sub-scanning direction on the sheet S. 
     In the present exemplary embodiment, the plural test images are formed side by side on the single sheet S, so that the user can easily compare the plural test images with each other. When the plural test images are formed side by side on the single sheet S, the plural test images may be formed continuously or intermittently. 
     The image controller  203  may form the first test image T 1  and the second test image T 2  so as to each include an image corresponding to at least one rotation cycle of the rotating body. That is, as illustrated in  FIGS. 4 and 5 , the image controller  203  may form the first test image T 1  and the second test image T 2  such that each of the first test image T 1  and the second test image T 2  includes at least one high density portion that is generated in accordance with the rotation cycle of the rotating body and at least one low density portion that is generated in accordance with the rotation cycle of the rotating body. 
     In addition to the plural test images, the image controller  203  forms pointing portions B indicating the boundary between the plural test images, on the sheet S. In this example, the image controller  203  forms, on the sheet S, the pointing portions B indicating the boundary between the first test image T 1  and the second test image T 2 , which are formed side by side in the sub-scanning direction. 
     The pointing portion B is not particularly limited to specific one, but may be any pointing portion that enables a user who visually recognizes the sheet S to know the position of the boundary between the first test image T 1  and the second test image T 2 . In this example, as illustrated in  FIGS. 4 and 5 , triangular notches are formed at the boundary between the first test image T 1  and the second test image T 2  so as to remove portions at both ends in the main scanning direction. The vertexes of the notches indicate the position of the boundary between the first test image T 1  and the second test image T 2 . 
     Here, as illustrated in  FIG. 4 , when the phases of the density unevenness of the first test image T 1  and the second test image T 2  are equal to each other, intervals (pitch) at which the high density portion (or the low density portion) appear are equal across the boundary between the first test image T 1  and the second test image T 2 . On the other hand, as illustrated in  FIG. 5 , when the phases of the density unevenness of the first test image T 1  and the second test image T 2  are different from each other, the intervals (pitch) at which the high density portion (or the low density portion) appears change at the boundary between the first test image T 1  and the second test image T 2 . 
     In the present exemplary embodiment, the pointing portions B formed on the sheet S enables the user who visually recognizes the sheet S to easily know the position of the boundary between the first test image T 1  and the second test image T 2 . Thus, it is easy for the user to understand whether an interval between high density portions (or an interval between low density portions) changes at the boundary between the first test image T 1  and the second test image T 2 . As a result, it is easy for the user to determine whether the first test image T 1  and the second test image T 2  are different in phase of the density unevenness appearing in accordance with the rotation cycle of the rotating body. 
     Next, an example of a procedure for forming test images on a sheet S in the image forming apparatus  100  of the present exemplary embodiment and checking an appropriate correction amount for an image forming condition based on the test images will be described.  FIG. 6  is a flowchart illustrating the example of the procedure for checking the appropriate correction amount for the image forming condition based on the test images. 
     When checking the appropriate correction amount for the image forming condition, the user instructs the image forming apparatus  100 , for example, via the operation unit  70  to output test images. When the user instructs the image forming apparatus  100  to output the test images, the corrector  201  of the control device  20  determines correction amounts for the image forming condition to be applied to the test images (step  101 ). In this example, the corrector  201  determines the first correction amount a 1  (=0) to be applied to the first test image T 1  and the second correction amount a 2  (&gt;a 1 ) to be applied to the second test image T 2 . 
     Next, the image forming apparatus  100  forms plural test images that are different in correction amount on a single sheet S and outputs the test images under control of the image controller  203  (step  102 ). In this example, the image forming apparatus  100  forms the first test image T 1  to which the first correction amount a 1  (=0) is applied and the second test image T 2  to which the second correction amount a 2  (&gt;first correction amount a 1 ) is applied, and outputs the first and second test images T 1 , T 2 . 
     Next, the user visually checks the first test image T 1  formed on the sheet S, and determines whether density unevenness occurs in the first test image T 1  (step  103 ). 
     When the user determines that no density unevenness occurs in the first test image T 1  (NO in step  103 ), the user inputs to the image forming apparatus  100  via the operation unit  70  that no density unevenness occurs in the first test image T 1 . Then, the corrector  201  of the control device  20  determines that the first correction amount a 1  is the appropriate correction amount (step  104 ). 
     On the other hand, when the user determines that the density unevenness occurs in the first test image T 1  (YES in step  103 ), the user visually checks the second test image T 2  formed on the sheet S, and determines whether density unevenness occurs in the second test image T 2  (step  105 ). 
     When the user determines that no density unevenness occurs in the second test image T 2  (NO in step  105 ), the user inputs to the image forming apparatus  100  via the operation unit  70  that no density unevenness occurs in the second test image T 2 . Then, the corrector  201  of the control device  20  determines that the second correction amount a 2  is the appropriate correction amount (step  106 ). 
     On the other hand, when the user determines that the density unevenness occurs in the second test image T 2  (YES in step  105 ), the user visually checks the relationship between the phase of the density unevenness of the first test image T 1  and the phase of the density unevenness of the second test image T 2 . That is, the user determines whether the phase of the density unevenness of the first test image T 1  is equal to that of the second test image T 2  (step  107 ). 
     When the user determines that the phase of the density unevenness of the first test image T 1  is equal to that of the second test image T 2  (YES in step  107 ), the user inputs to the image forming apparatus  100  via the operation unit  70  that the phase of the density unevenness of the first test image T 1  is equal to that of the second test image T 2 . 
     As described above, when the phase of the density unevenness of the first test image T 1  is equal to that of the second test image T 2 , both the first correction amount a 1  and the second correction amount a 2  are smaller than the appropriate correction amount. Therefore, the corrector  201  of the control device  20  determines that the second correction amount a 2  is insufficient (step  108 ), and ends the series of processes. In this case, the corrector  201  may newly set a first correction amount a 1 ′ and a second correction amount a 2 ′ that are larger than the second correction amount a 2 , and return to the step  102  to continue the processing using the first correction amount a 1 ′ and the second correction amount a 2 ′. 
     On the other hand, when the user determines that the phase of the density unevenness of the first test image T 1  is different from that of the second test image T 2  (NO in step  107 ), the user inputs to the image forming apparatus  100  via the operation unit  70  that the phase of the density unevenness of the first test image T 1  is different from that of the second test image T 2 . 
     As described above, when the phase of the density unevenness of the first test image T 1  is different from that of the second test image T 2 , the first correction amount a 1  is smaller than the appropriate correction amount, and the second correction amount a 2  is larger than the appropriate correction amount. Therefore, the corrector  201  of the control device  20  determines that the second correction amount a 2  is excessive (step  109 ), and ends the series of processes. In this case, the corrector  201  may newly set a second correction amount a 2 ″ smaller than the second correction amount a 2 , and return to step  102  to continue the processing using the first correction amount a 1  and the second correction amount a 2 ″. 
     Next, another form of the pointing portion B formed on the sheet S will be described.  FIGS. 7A and 7B  are diagrams illustrating other forms of the pointing portion B.  FIGS. 7A and 7B  illustrate examples of the first test image T 1 , the second test image T 2 , and the pointing portions B formed on a single sheet S. 
     As described above, the form of the pointing portion B is not particularly limited to the above described exemplary embodiment, but may be any pointing portion that indicates the position of the boundary between plural test images formed on a single sheet S. 
     The pointing portions B illustrated in  FIGS. 4 and 5  are provided at both ends in the main scanning direction. Alternatively, the pointing portion B may have a linear shape extending continuously in the main scanning direction at the boundary between the first test image T 1  and the second test image T 2  as illustrated in  FIG. 7A . Since the pointing portion B is continuous in the main scanning direction, the user can easily know the position of the boundary between the first test image T 1  and the second test image T 2 , even in a center area in the main scanning direction of the sheet S, for example. 
     As illustrated in  FIG. 7B , in addition to the pointing portion B, information C on a correction amount for an image forming condition applied to each test image may be indicated on the sheet S. In this example, (i) information on the first correction amount a 1  applied to the first test image T 1  and (ii) information on the second correction amount a 2  applied to the second test image T 2  are indicated on the sheet S. 
     As described above, the image forming apparatus  100  of the present exemplary embodiment forms, on a single sheet S, plural test images that are different in correction amount for an image forming condition. This enables a user to easily determine, based on the plural test images formed on the sheet S, whether the correction amount is insufficient for an appropriate correction amount or whether the correction amount is excessive for the appropriate correction amount. 
     The present disclosure is not limited to the above-described exemplary embodiment. For example, the present disclosure may be applied to an intermediate transfer body of an inkjet printer. Various modifications and combinations may be made to the exemplary embodiment described above without departing from the spirit of the present disclosure. 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.