JP2013195539A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the occurence of an image quality variation even when density correction processing is performed while an image having identity is continuously formed.SOLUTION: An image forming apparatus includes: acquiring means for acquiring information which indicates identify of a plurality of images; image forming means having a photoreceptor, a charging device, an exposing device, and a developing device for forming a plurality of images with an image density according to a predetermined density adjustment value; alternation means for alternating the density adjustment value; and control means for controlling the alternation means and the image forming means such that the density adjustment value is altered so that a ratio between a first potential difference which is the absolute value of the difference between charged potential and developing bias potential and a second potential difference which is the absolute value of the difference between the developing bias potential and exposing potential is kept constant when the density adjustment value is altered in a period in which a plurality of images having identity is continuously formed, and for forming an image with the image density according to the altered density adjustment value.

Description

  The present invention relates to an image forming apparatus.

  Patent Document 1 discloses an image formation control unit that controls a printing operation in which a toner image formed by an image forming system including an image carrier is transferred to a sheet and output based on image data input from an image input unit. And an image forming condition adjusting unit that adjusts an image forming condition by the image forming system every time the number of printed sheets reaches a predetermined number, wherein the image forming control unit converts a plurality of different image data into different image data. An image determination unit that determines the identity of a print image based on the number of dots constituting each image data when the continuous print operation is performed based on the image print control unit. Even when the predetermined number of images is reached, if the image determination unit determines that there is identity, the image data determined to have identity by prohibiting the operation of the image forming condition adjustment unit Continue printing operation for Image forming apparatus is disclosed that.

JP 2010-32808 A

  An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of a change in image quality even when density correction processing is executed while continuously forming images having the same identity. is there.

  In order to achieve the above object, the invention of claim 1 includes an acquisition means for acquiring information indicating the identity of a plurality of continuously formed images, a photoconductor, a charging device for charging the photoconductor to a charging potential, It has an exposure device that exposes a charged photoreceptor to form an electrostatic latent image with an exposure potential, and a developing device that develops the formed electrostatic latent image with a developing bias potential. An image forming unit that forms a plurality of images based on image information and image formation information at a corresponding image density, a changing unit that changes the density adjustment value, and a plurality of images having the sameness are formed continuously. When the density adjustment value is changed within the period, the first potential difference, which is the absolute value of the difference between the charging potential and the developing bias potential, and the second potential difference, which is the absolute value of the difference between the developing bias potential and the exposure potential. The concentration control so that the ratio is kept constant. Change the value, which is an image forming apparatus having a control means for controlling said changing means and said image forming means to form an image by an image density corresponding to the changed density adjustment value.

  According to a second aspect of the present invention, in the case where the control unit changes the density adjustment value within a period in which a plurality of identical images are continuously formed, the control unit maintains gradation characteristics and sets the density adjustment value. The image forming apparatus according to claim 1 to be changed.

  The invention of claim 3 further includes a receiving unit that receives a continuity emphasis instruction for changing the density adjustment value with emphasis on continuity of a plurality of images, and the control unit provides the continuity emphasis instruction by the receiving unit. The image forming apparatus according to claim 1, wherein the control is executed when received.

  According to a fourth aspect of the present invention, the acquisition means determines the identity of the plurality of images based on the image information and the image formation information, and determines the identity of the plurality of continuously formed images based on the determination result. The image forming apparatus according to any one of claims 1 to 3, wherein the information to be obtained is acquired.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the acquisition unit determines the identity of a plurality of images according to whether or not a plurality of the same images are formed. The image forming apparatus described.

  According to a sixth aspect of the present invention, the acquisition unit extracts a first feature amount of a first image formed before changing the density adjustment value, and a second image formed after changing the density adjustment value. And determining the identity of the plurality of images according to whether or not the degree of similarity when the extracted first feature value and the second feature value are compared is greater than or equal to a threshold value. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  According to a seventh aspect of the present invention, the acquisition unit obtains the number of first pixels in the first image formed before changing the density adjustment value, and the second image formed after changing the density adjustment value. 2. The identity of a plurality of images is determined according to whether or not a difference between the obtained first pixel number and the second pixel number is greater than a threshold value. 5. The image forming apparatus according to any one of items 4 to 4.

  According to the first aspect of the present invention, it is possible to suppress the occurrence of a change in image quality even when the density correction process is executed while images having the same identity are continuously formed.

  According to the second aspect of the present invention, the gradation characteristics are maintained before and after the density correction process, and the occurrence of a change in image quality can be further suppressed as compared with the case where this configuration is not provided.

  According to the third aspect of the present invention, processing can be performed in accordance with an instruction from the user.

  According to the fourth aspect of the present invention, it is possible to determine the identity of the image according to the contents of the image information and the image formation information.

  According to the fifth aspect of the present invention, when a plurality of the same images are formed, it can be determined that the images have the same identity.

  According to the sixth aspect of the present invention, when the similarity between two images before and after the density correction processing is equal to or greater than a threshold value, it can be determined that the images have the same identity.

  According to the seventh aspect of the present invention, when the difference in image density between the two images before and after the density correction processing is equal to or less than the threshold value, it can be determined that the images have the same identity.

1 is a configuration diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a configuration diagram illustrating an example of a configuration of an image forming unit according to an embodiment of the present invention. FIG. 3 is a schematic configuration diagram illustrating an example of a positional relationship between a density sensor and a reference toner image included in an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating an example of an electrical configuration of an image forming apparatus according to an embodiment of the present invention. It is a schematic diagram which shows an example of the structure of the change amount derivation | leading-out table in the density | concentration correction process of a standard mode. 6 is a graph illustrating an example of a transition state of a surface potential of a photosensitive drum in a density correction process in a standard mode. It is a graph which shows the gradation characteristic change before and behind correction | amendment in the density correction process of a standard mode. It is a schematic diagram which shows an example of the structure of the change amount derivation | leading-out table in the density | concentration correction process of continuity emphasis mode. 6 is a graph showing an example of a transition state of the surface potential of the photosensitive drum in the density correction processing in the continuity priority mode. It is a graph which shows the gradation characteristic change before and behind correction | amendment in the density correction process of continuity emphasis mode. It is a schematic diagram which shows an example of the reception screen displayed on a UI panel. 4 is a flowchart illustrating an example of a process flow of “image forming process” according to the first exemplary embodiment of the present invention. It is a flowchart which shows an example of the flow of the process of the "image identity determination process" which concerns on 1st Embodiment. It is a flowchart which shows an example of the flow of the process of the "image identity determination process" which concerns on 2nd Embodiment. It is a flowchart which shows an example of the flow of the process of the "image identity determination process" concerning 3rd Embodiment.

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

<Image forming apparatus>
(Schematic configuration of image forming apparatus)
First, the configuration of the image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram showing a main configuration of an image forming apparatus 10 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 10 includes an endless belt-like intermediate transfer belt 14 that is wound around a plurality of rolls 12 and conveyed in the direction of arrow E by driving a motor (not shown). A plurality of image forming units 15 are arranged along the longitudinal direction of the intermediate transfer belt 14.

  The image forming apparatus 10 according to the present embodiment also supports color image formation, and toner images corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K) are displayed. Image forming units 15Y, 15M, 15C, and 15K to be formed are respectively disposed. Hereinafter, the members provided for each color are shown by adding alphabets (Y / M / C / K) indicating the respective colors at the end of the reference numerals. The description will be made by omitting the alphabet at the end of the code.

  The different color toner images formed by the image forming units 15 are transferred onto the intermediate transfer belt 14 so as to overlap each other on the belt surface of the intermediate transfer belt 14. As a result, a color toner image is formed on the intermediate transfer belt 14. In this embodiment, the toner image in which the four color toner images are transferred in a superimposed manner is referred to as a final toner image.

  On the downstream side of the four image forming units 15 in the transport direction of the intermediate transfer belt 14, a transfer device 26 having two opposed rolls 26A and 26B is provided. The final toner image formed on the intermediate transfer belt 14 is sent between the rolls 26A and 26B, taken out from a paper tray 29 provided at the bottom of the image forming apparatus 10, and similarly between the rolls 26A and 26B. Is transferred to the paper 28 that has been conveyed to the paper.

  In addition, a fixing device 30 including a pressure roll 30A and a heating roll 30B is provided in the conveyance path of the paper 28 to which the final toner image has been transferred. The paper 28 conveyed to the fixing device 30 is nipped and conveyed by the pressure roll 30A and the heating roll 30B, whereby the final toner image is melted and fixed by being pressed against the paper 28. As a result, a desired image (color image) is formed on the paper 28. The paper 28 on which the image is formed is discharged out of the apparatus.

  On the other hand, a cleaner 32 that collects toner remaining on the intermediate transfer belt 14 without being transferred onto the paper 28 by the transfer device 26 is provided downstream of the transfer device 26 in the transport direction of the intermediate transfer belt 14. The cleaner 32 is provided with a blade 34 so as to be in contact with the intermediate transfer belt 14, and collects residual toner by rubbing it.

  A density sensor 36 is provided on the downstream side of the image forming unit 15 in the conveyance direction of the intermediate transfer belt 14. The density sensor 36 irradiates the image forming area on the surface of the intermediate transfer belt 14 (for example, a predetermined area on the surface of the intermediate transfer belt 14 where an image is to be formed) with light. The density of the reference toner image transferred to the image forming area on the surface of the intermediate transfer belt 14 is measured by detecting the reflected light.

(Image forming unit)
Next, the configuration of the image forming unit will be described.
FIG. 2 shows the configuration of the image forming unit 15. Since the configuration of each image forming unit 15 is not different, the description is omitted here by omitting the last symbol indicating each color. As shown in the figure, the image forming unit 15 includes a photosensitive drum 16 that is disposed in contact with the intermediate transfer belt 14 and rotates in a direction indicated by an arrow F at a predetermined speed.

  A charging roll 18 for charging the photosensitive drum 16 is disposed on the peripheral surface (surface) of each photosensitive drum 16. The charging roll 18 is a conductive roll, and its circumferential surface is in contact with the circumferential surface of the photosensitive drum 16, and is arranged so that the axial direction of the charging roll 18 and the axial direction of the photosensitive drum 16 substantially coincide with each other. Has been.

  A predetermined voltage in which a DC (direct current) component and an AC (alternating current) component are superimposed is applied to the charging roll 18, and the photosensitive drum 16 rotates while following the rotation of the photosensitive drum 16. Is charged to a predetermined potential.

  Further, an exposure device 20 for forming an electrostatic latent image on the photosensitive drum 16 is provided on the circumferential surface on the downstream side of the charging roll 18 in the rotation direction (arrow F direction) of each photosensitive drum 16. It has been.

  The exposure device 20 includes an LED array in which a plurality of LEDs (light emitting diodes) 20A are arranged along the main scanning direction (the front-rear direction in FIG. 2) during image formation. Irradiation is performed while scanning with a light beam based on the input image information in the axial direction of the photosensitive drum 16 charged in a positive direction. The potential of the region irradiated with the light beam by the exposure device 20 rises, and an electrostatic latent image is formed on the photosensitive drum 16.

  Further, an electrostatic latent image formed on the photosensitive drum 16 is arranged in a predetermined color (yellow / magenta / cyan / black) around the exposure device 20 in the rotation direction of each photosensitive drum 16. A developing device 22 is provided for developing with a toner of any one color) to form a toner image. A toner box 44 that contains toner is connected to the developing device 22 via a pipe (not shown). The amount of toner replenished from the toner box 44 to the developing device 22 is adjusted by the rotation time of a dispense motor (not shown).

  In the present embodiment, as the toner, a developer containing two components of toner particles (colored particles) having negative polarity and carriers (magnetic particles) having positive polarity is applied. In order to improve development efficiency and transfer efficiency described later, the toner particles are preferably spherical. Further, in the present embodiment, the developer 22 is not replenished, but only toner particles are replenished.

  As shown in the drawing, the developing device 22 is configured to include a developing roll 38 and a blade 40 that are disposed in proximity to the photosensitive drum 16. The developing roll 38 has a DC (DC) component (developing bias potential component) of the same polarity (negative polarity in the present embodiment) and an AC (AC) component preliminarily superimposed on the surface of the photosensitive drum 16. A predetermined voltage is applied, and the toner particles are transported to the peripheral surface together with the positive polarity carrier loaded in the developing device 22. Further, the developing roll 38 is driven to rotate in the same direction as the rotation direction of the photosensitive drum 16 (in the direction of arrow G in the figure), and the toner particles and the carrier that are excessively attached to the developing roll 38 are dropped by the blade 40 so 38 evenly.

  As the developing roll 38 rotates in the direction of arrow G, the toner attached to the developing roll 38 is supplied to the surface of the photosensitive drum 16.

  On the other hand, a transfer roll 25 for transferring the toner image on each photoconductive drum 16 to the intermediate transfer belt 14 is provided around the downstream side of the developing device 22 in the rotation direction of each photoconductive drum 16. The transfer roll 25 rotates in the direction of arrow H, conveys the intermediate transfer belt 14 at a predetermined speed, and sequentially opposes the photosensitive drum 16. Further, a power source 42 is connected to the transfer roll 25, and a positive bias voltage is applied to the transfer roll 25 to transfer the toner on the photosensitive drum 16 onto the intermediate transfer belt 14.

  Here, the transfer roll 25 cannot transfer all of the toner on the photoconductive drum 16 to the intermediate transfer belt 14, and the toner is transferred onto the photoconductive drum 16 that has passed the position where the transfer roll 25 is disposed. Slightly remains (transfer residual toner).

  There is also toner (retransfer toner) whose polarity is reversed to plus by the transfer roll 25 and reattached on the photosensitive drum 16. Note that if the toner image of another color has already been transferred onto the intermediate transfer belt 14 when passing through the position where the transfer roll 25 is disposed, the toner of the other color is included in the retransfer toner.

  Therefore, a cleaning roll 24 that temporarily holds the transfer residual toner or the retransfer toner on the photosensitive drum 16 is disposed downstream of the transfer roll 25 on the peripheral surface of the photosensitive drum 16. The cleaning roll 24 has conductive brush bristles planted on the surface thereof, and is arranged so that the bristles come into contact with the photosensitive drum 16 so that a bias voltage is applied and the brush roll is driven to rotate. It has become.

  The cleaning roll 24 is rotated in the same direction as the rotation direction of the photosensitive drum 16 while a bias voltage having a negative polarity (-500 V in the present embodiment) is applied during a period in which image formation is performed. As a result, the positive polarity retransfer toner adhering to the surface of the photosensitive drum 16 is attracted to the brush hair and collected.

  The cleaning roller 24 does not collect the negative transfer residual toner, and the photosensitive drum 16 is charged and exposed while adhering to the photosensitive drum 16, so that the transfer residual adhering to the non-image portion is performed. The toner is collected in the developing device 22 by rubbing with the carrier and toner attached to the developing roll 38 of the developing device 22.

  The retransfer toner collected by the cleaning roll 24 is discharged onto the photosensitive drum 16 in a cleaning mode executed during non-image formation.

  In the cleaning mode, a positive bias voltage (+500 V in the present embodiment) is applied to the cleaning roll 24, and the rotation of the photosensitive drum 16 is followed in a direction different from the rotational direction of the photosensitive drum 16. To be rotated. As a result, the positive polarity retransfer toner held on the cleaning roll 24 is discharged onto the photosensitive drum 16.

  The retransfer toner discharged on the photosensitive drum 16 in this way is conveyed to the transfer position by the rotation of the photosensitive drum 16.

  In the cleaning mode, a negative bias voltage is applied to the transfer roll 25, and the retransfer toner transported to the transfer position is transferred onto the intermediate transfer belt 14 by the transfer roll 25, and the intermediate transfer belt. 14 to the cleaner 32 and scraped off by the blades 34 of the cleaner 32.

(Density sensor)
Next, the density sensor will be described.
FIG. 3 is a schematic configuration diagram illustrating an example of an aspect in which the density sensor 36 measures the density of the reference toner image. As shown in FIG. 3, first, a single reference toner image is formed by an image forming unit 15 in an image forming region on the surface of the intermediate transfer belt 14 (in the example shown in FIG. 2, the central portion in the width direction of the intermediate transfer belt 14). Alternatively, the plurality of reference toner images are formed under different conditions (for example, under the condition that the amount of toner per unit area of a specific color is different). The density sensor 36 irradiates each of the single reference toner image or the plurality of reference toner images with light with a predetermined amount of light, and detects the reflected light at the time of irradiation, thereby detecting the density of the reference toner image. Measure.

(Electrical configuration of image forming apparatus)
Next, the electrical configuration of the image forming apparatus will be described.
FIG. 4 is a block diagram showing a main configuration of the electrical system of the image forming apparatus 10 according to the present embodiment. As shown in the figure, the image forming apparatus 10 includes a density sensor 36, a CPU (Central Processing Unit) 60, a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 64, a secondary storage unit (a flash memory as an example). ) 66, a UI (user interface) panel 68, a communication interface 70, and an image forming unit 74.

  The CPU 60 controls the overall operation of the image forming apparatus 10. The ROM 62 functions as a storage unit that stores in advance a control program for controlling the operation of the image forming apparatus 10 and various parameters. An example of a program stored in the ROM 62 is an “image formation processing program” described later. The RAM 64 is used as a work area when executing various programs. The secondary storage unit 66 stores various types of information that must be retained even when the power switch of the apparatus is turned off.

  The UI panel 68 includes a touch panel display or the like in which a transmissive touch panel is superimposed on a display. Various information is displayed on the display surface of the display, and various information and instructions are input by the user touching the touch panel. The

  The communication interface 70 is connected to an external device 72 such as a personal computer and receives various information from the external device 72 and transmits various information to the external device 72. For example, the image forming apparatus 10 receives image information and image formation information of an electronic document to be printed together with an image formation instruction from the external device 72. Note that the image formation information includes print parameters representing print attributes such as page, number of copies, and color mode.

  The image forming unit 74 forms an image on the paper 28 by the LED xerography method. The image forming unit 15, the transfer device 26, and the fixing device 30 (for example, other than the density sensor 36 shown in FIG. 1). It is comprised including the structural member which is a structural member and is electrically controlled.

  The density sensor 36, CPU 60, ROM 62, RAM 64, secondary storage unit 66, UI panel 68, communication interface 70, and image forming unit 74 are electrically connected to each other via a bus BUS such as a control bus. Therefore, the CPU 60 accesses the ROM 62, the RAM 64, and the secondary storage unit 66. Further, the CPU 60 displays various information on the UI panel 68 and grasps the contents of user operation instructions on the UI panel 68. In addition, the CPU 60 receives various information from the external device 72 via the communication interface 70. Further, the CPU 60 controls the operation of the density sensor 36 and the image forming unit 74, grasps the operation state of the image forming unit 74, and grasps the density measured by the density sensor 36.

  Further, when the CPU 60 according to the present embodiment receives an “image formation instruction” requesting execution of one unit of image formation processing from the external device 72 via the communication interface 70, the CPU 60 of the electronic document received together with the image formation instruction One unit of image forming processing for forming an image on a sheet based on the image information is executed. This image forming process is realized by the CPU 60 executing an image forming process program to be described later.

<Density correction processing>
Next, the density correction process will be described.
In the image forming apparatus 10 according to the present embodiment, the “density correction” is performed to correct the output image density by changing the density adjustment value so that the density of the image formed on the paper 28 (output image density) becomes the target density. Processing "is performed. The image forming apparatus 10 starts the density correction process when a predetermined condition is satisfied. A normal image forming operation is not performed during the density correction process. In the present embodiment, a case where the density correction process is started when a predetermined period has elapsed will be described.

  The conditions for starting the density correction process may be other conditions. For example, the density correction process may be started when the number of image formations is counted and the number of image formations exceeds the limit number. Further, when at least one of humidity and temperature has changed significantly beyond the presumption, or when a member (for example, the photosensitive drum 16 or the developing device 22) of the image forming unit 74 is replaced with a new one. Alternatively, the density correction process may be started.

  “Density adjustment value” means an adjustment value for adjusting a control parameter for controlling the output image density. Examples of the method for correcting the output image density include gradation correction processing, TC (toner concentration) control processing, and surface potential control processing. At least one of gradation correction processing, TC control processing, and surface potential control processing is performed. Normally, all of gradation correction processing, TC control processing, and surface potential control processing are performed. Note that these processes are performed by executing an image forming process program to be described later.

  The gradation correction processing refers to processing for acquiring image information indicating an image to be formed on the paper 28 and performing gradation correction on the acquired image information. In this case, the correction amount applied in the gradation correction process corresponds to the density adjustment value. The TC control process refers to control for adjusting the ratio of toner particles contained in the toner to the toner in the developing device 22. In this case, the TC control parameter used to adjust the toner particle ratio corresponds to the density adjustment value.

  The surface potential control process refers to a process for adjusting the image density by controlling the potential applied to the surface of the photosensitive drum 16. In this case, the charge amount on the surface of the photosensitive drum 16, the light amount of the light beam emitted from the exposure device 20, the magnitude of the voltage applied to the developing roll 38, and the magnitude of the bias voltage applied to the transfer roll 25. A control parameter that controls the image uniformly corresponds to the density adjustment value.

  When the time of density correction processing arrives, each of the plurality of reference toner images is formed on the intermediate transfer belt 14 with the density adjusted according to the current density adjustment value, and the density of each of the formed plurality of reference toner images. Is measured by the density sensor 36. Then, a deviation (deviation amount) between the measured density of the reference toner image (current density) and the target density of the reference toner image (target density) is acquired. The basic change amount of the density adjustment value is derived from a predetermined table or arithmetic expression so that the deviation amount between the current density and the target density is reduced, and the density adjustment value is changed by the derived basic change amount. .

  However, when the density correction process is executed within a period in which a plurality of images having the same identity are continuously formed, a change in image quality before and after the density correction process is more conspicuous than when a plurality of different images are formed. It becomes like this. Here, “sequentially forming a plurality of images having the same identity” means performing one unit of image forming processing for continuously printing a plurality of images having the same image, the same image density for each color, and the like. It is. Therefore, in the present embodiment, in addition to the “standard mode” in which density correction processing is performed as in the conventional case, a “continuity importance mode” in which density correction processing is performed with emphasis on continuity of a plurality of images is provided. Hereinafter, each mode will be described.

(Standard mode)
First, the “standard mode” density correction processing will be described.
FIG. 5 is a schematic diagram showing an example of the structure of the change amount derivation table in the standard mode. FIG. 6 is a graph showing an example of the transition state of the surface potential of the photosensitive drum in the standard mode. FIG. 7 is a graph showing the gradation characteristic change before and after correction in the standard mode.

  In the density correction process in the “standard mode”, all of the gradation correction process, the TC control process, and the surface potential control process are performed as in the conventional case. For the density adjustment value of each process, the basic change amount of the density adjustment value is derived from a predetermined table or arithmetic expression so that the deviation amount between the current density and the target density is reduced, and the derived basic change amount The density adjustment value is changed with.

  For example, as shown in FIG. 5, the basic change amount is derived using a change amount derivation table 90 in which the basic change amount An is assigned to the density Xn of the reference toner image. In the change amount derivation table 90, a basic change amount An is assigned to a plurality of densities Xn. Here, “the density Xn of the reference toner image” is a density Xn assumed as a density obtained by measuring the density of the reference toner image.

  Usually, in the situation where the density correction process is performed, the developability (for example, the charge amount of the developer) changes. As shown in FIGS. 6 and 7, when the developability changes greatly, the control parameter (density) of the surface potential control process is set so that the output image density at the maximum density (area ratio 100%) becomes the target density. Adjustment value) is changed. As a result, the gradation characteristics at the halftone density (area ratio 25%, 50%, 75%, etc.) change between before and after correction. For the halftone density whose tone characteristics have changed, the correction amount (density adjustment value) of the tone correction control process is changed to bring the output image density closer to the target density.

(Continuity-oriented mode)
Next, density correction processing in the “continuity priority mode” will be described.
FIG. 8 is a schematic diagram showing an example of the structure of the change amount derivation table in the density correction processing in the continuity priority mode. FIG. 9 is a graph showing an example of the transition state of the surface potential of the photosensitive drum in the density correction processing in the continuity priority mode. FIG. 10 is a graph showing the gradation characteristic change before and after correction in the density correction processing in the continuity priority mode.

  In density correction processing in the “continuity priority mode”, at least surface potential control processing is performed. Each of the gradation correction process and the TC control process may not be performed. As will be described later, in the density correction processing in the “continuity priority mode”, the density adjustment value is changed so that the gradation characteristics are maintained before and after correction. By performing the gradation correction process, the gradation characteristics may be impaired. Therefore, the tone correction process may be omitted.

As shown in FIG. 9, in the surface potential control process, the density adjustment value is set so that the ratio (ΔV _CF : ΔV _deve ) between “first potential difference ΔV _CF ” and “second potential difference ΔV _deve ” is kept constant. To change. Here, the “first potential difference ΔV _CF ” refers to a potential at which the surface of the photosensitive drum 16 is charged (charging potential) and a developing bias potential (developing bias potential) used when developing with the developing device 22. Is the absolute value of the difference. The “second potential difference ΔV _deve ” is the absolute value of the difference between the developing bias potential and the potential (exposure potential) of the region irradiated with the light beam from the exposure device 20.

  The “continuity priority mode” is a mode that is set or selected when the density correction process is executed within a period in which a plurality of images having the same identity are continuously formed. In a situation where a plurality of images having the same identity are continuously formed, toner replacement is very stable, and it is predicted that an event in which the developing property fluctuates rapidly does not occur. Therefore, as shown in FIG. 10, the control parameter (density adjustment value) of the surface potential control process is changed so that the gradation characteristics are maintained before and after the correction.

As described above, by changing the density adjustment value so that the ratio (ΔV _CF : ΔV _deve ) between the first potential difference and the second potential difference is constant, the gradation characteristics are maintained before and after the correction. . Although the overall density changes by performing the density correction process so that the gradation characteristics are maintained, for example, from the output images before and after the density correction process, such as maintaining the texture of the hair in the photographic image The visual impression you receive will not change. That is, the occurrence of a change in image quality due to the density correction process is suppressed.

For example, as shown in FIG. 9, when a single image A and a single image A ′ having a reduced density of the single image A are successively formed, the ratio (ΔV _CF : ΔV _deve ) is The control value is changed within a range maintained at 1: 3. For example, the density adjustment value is changed so as to widen the difference between the charging potential and the exposure potential so that the ratio (ΔV _CF : ΔV _deve ) is maintained at 1: 3 while the developing bias potential is fixed. It should be _noted that the ratio (ΔV _CF : ΔV _deve ) is 1: 3 even in the reverse case in which a single image A ′ and a single image A having a higher density of the single image A ′ are continuously formed. The control value may be changed within a range that is maintained.

  The change amount of the density adjustment value may also be a change amount smaller than the basic change amount of the density adjustment value in the standard mode (hereinafter, referred to as “minute change amount”). The minute change amount of the density adjustment value is derived from a predetermined table or calculation formula so that the deviation amount between the current density and the target density is reduced, and the density adjustment value is changed with the derived minute change amount. . For example, as shown in FIG. 8, in the change amount derivation table 92 used for deriving the minute change amount, the minute change amount an is assigned to each of the densities Xn of the plurality of reference toner images.

The ratio (ΔV _CF : ΔV _deve ) between the first potential difference and the second potential difference may be constant before and after the correction, and the ratio may be a normal range used in the surface potential control process. The ratio (ΔV _CF : ΔV _deve ) may be in the range of 1: (X ± 0.1). Here, “X” represents an integer of 2 or more. “X” may be an integer of 2 or more and 4 or less. Further, the reason why the upper and lower limits are allowed for X is that it is very difficult to visually determine the gradation change if the change is within this range. That is, the ratio (ΔV _CF : ΔV _deve ) only needs to be constant including an error within the allowable range. For example, as shown in FIG. 9, the ratio (ΔV _CF : ΔV _deve ) may be about “1: 3”.

(Reception screen)
The selection of the standard mode or the continuity priority mode may be performed by displaying a reception screen on the UI panel 68 and receiving an instruction (continuity priority instruction) from a user performing density correction processing in the continuity priority mode. Good. FIG. 11 is a schematic diagram illustrating an example of a reception screen displayed on the UI panel 68. As shown in FIG. 11, density mode selection options such as “standard mode” and “continuity priority mode” are displayed on the reception screen along with color mode options such as “black and white” and “color”. . In addition, an “OK” button and a “Cancel” button are displayed on the reception screen.

  When the user selects each of the color mode and the density correction mode from the options displayed on the reception screen and designates the “OK” button, the mode designation is accepted. As shown in FIG. 11, for example, when “color” is selected as the color mode, “continuity emphasis mode” is selected as the density correction mode, and the “OK” button is designated, the continuity emphasis instruction is accepted.

  In the following, the case where the user selects the density correction mode before instructing the image formation will be described. However, the density correction mode may be selected based on image information or image formation information. For example, when performing one unit of image forming processing for printing a plurality of the same images continuously, the continuity priority mode is selected based on the “number of images” of the image information and the “number of copies” of the image forming information. Is done. In addition, when a high-quality image or a color image is formed, the continuity priority mode may be selected.

<Image formation processing>
Next, the “image forming process” operation of the image forming apparatus 10 according to the present embodiment will be described.
FIG. 12 is a flowchart illustrating an example of a processing flow of an image forming processing program executed by the CPU 60 when the main power supply of the image forming apparatus 10 is turned on. As described above, in the present embodiment, when a predetermined period has elapsed since the previous density correction process, the “density correction process” is started assuming that the time of the density correction process has arrived. As described above, the density correction mode is selected by the user before the image formation instruction is received.

  In step 100 of FIG. 12, the reception of an image formation instruction is waited. That is, in step 100, it is repeatedly determined whether or not an image formation instruction has been received until the image formation instruction is received. When an image formation instruction for instructing one unit of image formation processing is received, an affirmative determination is made and the routine proceeds to step 102. In the next step 102, the image information and the image formation information received together with the image formation instruction are acquired, and the process proceeds to step 104.

  Next, in step 104, the image forming unit 74 is instructed to start one unit of image forming processing at a density corresponding to a predetermined density adjustment value. The image forming unit 74 starts one unit of image forming processing based on the image information and the image forming information, and an image is formed on the sheet.

  Next, in step 106, it is repeatedly determined whether or not it is time to execute density correction processing. When it is time to execute the density correction process, an affirmative determination is made in step 106, and the process proceeds to step 108. In the next step 108, it is determined whether or not one unit of image forming processing has been completed. If the determination in step 108 is affirmative, the “image forming process” processing routine is terminated. On the other hand, if a negative determination is made in step 108, the process proceeds to step 110, and the image forming unit 74 is instructed to interrupt one unit of image forming processing. The image forming unit 74 interrupts one unit of image forming processing in response to the instruction.

  Next, in step 112, “image identity determination processing” is executed to determine the identity of a plurality of images that are successively formed across the density correction processing. Details of the “image identity determination process” will be described later. Next, in step 114, it is determined based on the determination result of “image identity determination processing” in step 112 whether or not it is determined that there is image identity. If it is determined that the images are identical, an affirmative determination is made in step 114 and the process proceeds to step 116. If it is determined that the images are not identical, a negative determination is made at step 114 and the process proceeds to step 124.

  Next, in step 116, it is determined whether or not “continuity priority mode” is selected as the density correction processing mode. If the continuity priority mode is selected, an affirmative determination is made at step 116 and the routine proceeds to step 118. If the standard mode is selected, a negative determination is made at step 116 and the routine proceeds to step 124.

Next, in step 118, density correction processing is executed in the continuity priority mode. In the present embodiment, as shown in FIG. 9, the gradation correction process is not performed, and the ratio (ΔV _CF : ΔV _deve) between the “first potential difference ΔV _CF ” and the “second potential difference ΔV _deve ” in the surface potential control process. ) Is kept constant so that the density adjustment value is changed. When it is determined that the images are identical and the continuity emphasis mode is selected, the tone characteristics are maintained in the continuity emphasis mode, so that the gradation characteristics are maintained before and after the correction. That is, the occurrence of a change in image quality due to the density correction process is suppressed.

  For example, a reference toner image is formed on the surface of the intermediate transfer belt 14, and the density of the formed reference toner image is measured by the density sensor 36. A minute change amount of the density adjustment value is derived so that a deviation amount between the measured current density and the target density is reduced. For example, the minute change amount an is assigned to the density Xn of the reference toner image using the change amount derivation table 92 shown in FIG. The density adjustment value is changed by the derived minute change amount. When the density correction process in the continuity priority mode is completed, the process proceeds to the next step 120.

  On the other hand, in step 124, density correction processing is executed in the standard mode. For example, a reference toner image is formed on the surface of the intermediate transfer belt 14, and the density of the formed reference toner image is measured by the density sensor 36. The basic change amount of the density adjustment value is derived so that the deviation amount between the measured current density and the target density is reduced. For example, the basic change amount An is assigned to the density Xn of the reference toner image using the change amount derivation table 90 shown in FIG. The density adjustment value is changed by the derived basic change amount. When the density correction process in the standard mode ends, the process proceeds to the next step 120.

  In step 120, the image forming unit 74 is instructed to restart one unit of image forming processing at a density corresponding to the reset density adjustment value. Next, in step 122, it is determined whether or not one unit of image forming processing has been completed. If the determination in step 122 is affirmative, the “image forming process” processing routine is terminated. On the other hand, if a negative determination is made in step 122, the process returns to step 106, and the processing from step 106 to step 122 is repeated.

(Image identity determination processing)
Here, the “image identity determination process” executed in step 112 will be described.
FIG. 13 is a flowchart illustrating an example of a process flow of “image identity determination process” according to the first embodiment. In step 200, it is determined whether or not the same image is to be formed continuously based on the “number of images” in the image information and the “number of copies” in the image formation information. If an affirmative determination is made in step 200, it is determined in next step 202 that the images are identical, and the routine is terminated. On the other hand, if a negative determination is made in step 200, it is determined in the next step 204 that the images are not identical, and the routine is terminated.

<Modification>
In this embodiment, an example in which it is determined that the same image is identical when it is determined that the same image is continuously formed is described. However, the image identity determination process is based on another standard. May be based on.

(Modification 1 of image identity determination processing)
Next, Modification 1 of the “image identity determination process” will be described.
FIG. 14 is a flowchart illustrating an example of a process flow of “image identity determination process” according to the first modification. In the second modification, image identity is determined by a so-called pattern matching technique.

  In step 300, image information of the pre-interruption image formed before interrupting one unit of image formation processing is acquired. Next, in step 302, the feature amount of the image before interruption is extracted based on the image information of the image before interruption. For example, feature points of the object are extracted as feature amounts. Next, in step 304, image information of a resuming image formed after resuming one unit of image forming processing is acquired. Next, in step 306, the feature amount of the restart image is extracted based on the image information of the restart image.

  Next, in step 308, the feature amount of the pre-interruption image is compared with the feature amount of the resumption image, and the similarity between the pre-interruption image and the resumption image is obtained. For example, feature point types, orientations, coordinates, and the like are compared. Next, in step 310, it is determined whether or not the obtained similarity is greater than or equal to a preset threshold value. If the similarity is greater than or equal to the threshold value, an affirmative determination is made in step 310 and the process proceeds to step 312 where it is determined that the images are identical and the routine is terminated. On the other hand, if the similarity is less than the threshold, a negative determination is made in step 310 and the process proceeds to step 314, where it is determined that there is no image identity, and the routine is terminated.

(Modification 2 of image identity determination processing)
Next, a second modification of the “image identity determination process” will be described.
FIG. 15 is a flowchart illustrating an example of a process flow of “image identity determination process” according to the second modification. In step 400, image information of the pre-interruption image formed before interrupting one unit of image formation processing is acquired. Next, in step 402, the count value _Xn-1 of the number of pixels of the image before interruption is acquired. In step 404, image information of a restarting image formed after restarting one unit of image forming processing is acquired. Next, in step 406, the count value X _n−1 of the number of pixels of the restarting image is acquired.

Next, at step 408, the count value X _n-1 number of pixels before interruption image, the absolute value of the difference between the count value X _n of the number of pixels of resuming image, whether below a preset threshold value Determine. If the determination in step 408 is affirmative, the process proceeds to step 410 to determine that the images are identical, and the routine is terminated. If a negative determination is made in step 408, the process proceeds to step 412 to determine that the images are not identical, and the routine is terminated.

  In the above example, the colors of the pre-interrupt image and the restart image are not specified, but the difference between the number of pixels of the pre-interrupt image and the number of pixels of the restart image is obtained for each color. Here, the “number of pixels” refers to the number of ON pixels on which toner is placed. The number of ON pixels per unit area is called “image density”. That is, in the second modification, the image density is compared for each color, and the identity of the image is determined.

  In the above example, the example of obtaining the difference in the number of pixels of the entire image has been described. However, the image before interruption and the image at the time of resumption may be divided into a plurality of blocks, and the difference in the number of pixels may be obtained for each block. When obtaining the difference in the number of pixels for each block, it is determined that there is no image identity if there is even one block whose absolute value of the difference in the number of pixels exceeds the threshold. Since the absolute value of the difference in the number of pixels is obtained for each block and the image identity is determined, the determination accuracy is improved.

  Note that the configuration of the image forming apparatus described in the above embodiment is merely an example, and it is needless to say that the configuration may be changed without departing from the gist of the present invention. For example, in the image forming apparatus according to the present embodiment, the image forming process is realized by executing a program using a computer, but is realized by a hardware configuration or a combination of a hardware configuration and a software configuration. Also good.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 14 Intermediate transfer belt 16 Photosensitive drum 18 Charging roll 22 Developer 36 Density sensor 60 CPU
68 UI panel

Claims (7)

Acquisition means for acquiring information indicating the identity of a plurality of images formed in succession;
A photoconductor, a charging device that charges the photoconductor to a charging potential, an exposure device that exposes the charged photoconductor to form an electrostatic latent image at the exposure potential, and develops the formed electrostatic latent image at a developing bias potential An image forming unit that forms a plurality of images based on image information and image formation information at an image density according to a predetermined density adjustment value;
Changing means for changing the density adjustment value;
When the density adjustment value is changed within a period in which a plurality of images having the same identity are continuously formed, the first potential difference, the development bias potential, and the exposure potential, which are absolute values of the difference between the charging potential and the development bias potential. The density adjustment value is changed so that the ratio to the second potential difference, which is the absolute value of the difference between the two and the second voltage difference, is kept constant, and the change is made so as to form an image with an image density corresponding to the changed density adjustment value. And control means for controlling the image forming means;
An image forming apparatus.   2. The control unit according to claim 1, wherein, when the density adjustment value is changed within a period in which a plurality of images having the same identity are continuously formed, the control unit maintains gradation characteristics and changes the density adjustment value. Image forming apparatus.   The apparatus further includes a receiving unit that receives a continuity priority instruction for changing the density adjustment value with emphasis on continuity of a plurality of images, and the control unit performs the control when the reception unit receives the continuity priority instruction. The image forming apparatus according to claim 1, wherein the image forming apparatus is executed.   The acquisition unit determines identity of a plurality of images based on image information and image formation information, and acquires information indicating the identity of the plurality of continuously formed images based on a determination result. The image forming apparatus according to any one of claims 1 to 3.   The image forming apparatus according to claim 1, wherein the acquisition unit determines the identity of a plurality of images according to whether or not a plurality of the same images are formed.   The acquisition unit extracts a first feature amount of a first image formed before changing the density adjustment value, and extracts a second feature amount of a second image formed after changing the density adjustment value. The identity of the plurality of images is determined according to whether the similarity when the extracted first feature value and the second feature value are compared is greater than or equal to a threshold value. The image forming apparatus according to claim 1.   The acquisition means obtains a first pixel number in the first image formed before changing the density adjustment value, and calculates a second pixel number in the second image formed after changing the density adjustment value. 5. The identity of a plurality of images is determined according to whether the difference between the obtained first pixel number and the obtained second pixel number is greater than a threshold value. The image forming apparatus described in 1.