JP5884504B2 - Image forming control apparatus, image forming apparatus, and program - Google Patents

Description

  The present invention relates to an image formation control device, an image formation device, and a program.

  Various techniques are known for suppressing density unevenness caused by a plurality of rotating bodies such as a photoconductor and a developing roll included in an image forming apparatus (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). ).

JP 2007-140402 A JP 2007-187829 A JP 2006-192846 A

  In the present invention, even when periodic density unevenness including density unevenness that cannot be expressed only by a sine wave or cosine wave of a rotation cycle occurs due to rotation of a plurality of rotating bodies included in the image forming unit, the periodic density An object of the present invention is to provide an image formation control device, an image formation device, and a program capable of extracting density unevenness distribution information indicating the unevenness distribution for each rotating body.

An image formation control apparatus according to a first aspect of the present invention includes an exposure unit that performs exposure based on supplied image data and a plurality of rotating bodies, and an image is formed on a recording medium by exposure by the exposure unit and rotation of the plurality of rotating bodies. The density unevenness distribution together with an extraction image for extracting density unevenness distribution information representing a periodic density unevenness distribution for each of the rotating bodies generated by the rotation of each of the plurality of rotating bodies. A control unit that controls the image forming unit so that a synchronous image synchronized with a rotation cycle of a target rotating body that is an extraction target of information is formed; and a reading that reads the image for extraction formed by the control of the control unit contained in the image, and the position of the target rotational body the synchronization image a plurality of periodic images read with the extracted image corresponding to the rotation period of the extracted based The information of the average image obtained by averaging the combined phase in the rotation direction of the object rotating body obtained by averaging superimposed by aligning orientation and ends of a plurality of cycles images the extracted, the target rotational body Extraction means for extracting density unevenness distribution information representing density unevenness due to rotation of the image, and a correction value for correcting the density unevenness represented by the density unevenness distribution information extracted by the extraction means is generated, and the correction value is used. Correction means for correcting the image data supplied to the exposure means or the exposure amount of the exposure means.

An image forming control apparatus according to a second aspect of the present invention includes an exposure unit that performs exposure based on supplied image data and a plurality of rotating bodies, and an image is formed on a recording medium by exposure by the exposing unit and rotation of the plurality of rotating bodies. When extracting density unevenness distribution information representing a distribution of periodic density unevenness for each rotating body generated by rotation of each of the plurality of rotating bodies included in the image forming means for forming the plurality of rotating bodies, Among these, when the rotating body from which the density unevenness distribution information is extracted is a target rotating body, and the rotating body other than the target rotating body that causes density unevenness by rotation is a non-target rotating body, the density A plurality of extraction images for extracting unevenness distribution information, wherein a plurality of extraction images having a length equal to or less than a circumference of the target rotating body use a predetermined specific portion of the non-target rotating body do it Formed by controlling the image forming means and the control means so that the entire rotation direction of the target rotating body is used by forming the plurality of extraction images. A position corresponding to the phase in the rotational direction of the target rotating body is obtained by subtracting the average image of each read image from each read image obtained by reading each of the plurality of extraction images. Extracting means for extracting the information of the arrangement image arranged in the position as density unevenness distribution information for one period of the target rotating body, and correcting the density unevenness represented by the density unevenness distribution information extracted by the extracting means And a correction unit that corrects the image data supplied to the exposure unit or the exposure amount of the exposure unit using the correction value.

According to a third aspect of the present invention, in the image forming control apparatus according to the second aspect , in the case where there are a plurality of the non-target rotators that cause density unevenness, each of the plurality of non-target rotators is provided. Controls the image forming means so as to rotate synchronously.

According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: an exposure unit that performs exposure based on supplied image data; and a plurality of rotating bodies, and an image is recorded on a recording medium by the exposure by the exposing unit and the rotation of the plurality of rotating bodies. The image forming means to form and the image formation control apparatus of any one of Claims 1-3 are provided.

According to a fifth aspect of the present invention, there is provided an exposure means for exposing a computer based on supplied image data and a plurality of rotating bodies, and an image is formed on a recording medium by exposure by the exposing means and rotation of the plurality of rotating bodies. Of the density unevenness distribution information together with an extraction image for extracting density unevenness distribution information representing a distribution of periodic density unevenness for each of the rotating bodies generated by rotation of each of the plurality of rotating bodies . Included in the read image obtained by reading the extraction image formed by the control of the control means for controlling the image forming means so that a synchronous image synchronized with the rotation cycle of the target rotating body that is the extraction target is formed. is, and extracts a plurality of periodic images corresponding to the rotation cycle of the object rotating body based on the position of the synchronous image read with the extracted image, the The information of the average image obtained by averaging the combined phase in the rotation direction of the object rotating body obtained by averaging superimposed by aligning orientation and ends of a plurality of cycles images out of the target rotary body Extraction means for extracting density unevenness distribution information representing density unevenness due to rotation, and a correction value for correcting the density unevenness represented by the density unevenness distribution information extracted by the extraction means are generated, and the correction value is used to generate the correction value. This is a program for causing image data to be supplied to an exposure means or a correction means for correcting the exposure amount of the exposure means.

According to a sixth aspect of the present invention, the computer includes an exposure means for exposing the computer based on the supplied image data and a plurality of rotating bodies, and an image is formed on a recording medium by the exposure by the exposing means and the rotation of the plurality of rotating bodies. When extracting density unevenness distribution information representing a distribution of periodic density unevenness for each of the rotating bodies generated by rotation of each of the plurality of rotating bodies included in the image forming unit, the out of the plurality of rotating bodies When the rotator to be extracted from the density unevenness distribution information is a target rotator, and the rotator other than the target rotator is a non-target rotator that generates density unevenness by rotation, the density unevenness distribution is described above. A plurality of extraction images for extracting information, wherein a plurality of extraction images having a length equal to or less than a circumference of the target rotator are obtained by using a predetermined specific portion of the non-target rotator. form And a control means for controlling the image forming means so that the entire rotation direction of the target rotating body is used by forming the plurality of extraction images, and a plurality of control means formed by the control means. The average images of the read images are subtracted from the read images obtained by reading the extraction images, and the read images after the subtraction are placed at positions corresponding to the rotation direction phase of the target rotating body. Extraction means for extracting the information of the arranged image as density unevenness distribution information for one period of the target rotating body, and density unevenness represented by the density unevenness distribution information extracted by the extraction means It is a program for generating a correction value and functioning as a correction unit that corrects the image data supplied to the exposure unit or the exposure amount of the exposure unit using the correction value.

  According to the first aspect of the present invention, in the case where periodic density unevenness including density unevenness that cannot be expressed only by the sine wave or cosine wave of the rotation cycle occurs due to the rotation of the plurality of rotating bodies included in the image forming unit. In addition, density unevenness distribution information indicating the periodic density unevenness distribution can be extracted for each rotating body.

In addition, according to the first aspect of the present invention, it is possible to easily extract a periodic image corresponding to the rotation period of each rotating body, compared to a case where no synchronized image is used .

According to the second aspect of the present invention, in the case where periodic density unevenness including density unevenness that cannot be expressed only by the sine wave or cosine wave of the rotation period occurs due to the rotation of the plurality of rotating bodies included in the image forming unit. In addition, density unevenness distribution information indicating the periodic density unevenness distribution can be extracted for each rotating body.

According to the third aspect of the present invention, it is possible to suppress the influence of the non-uniformity of the non-target rotator when extracting the non-uniformity profile of the target rotator as compared to the case where this configuration is not provided.

According to the fourth aspect of the present invention, in the case where periodic density unevenness including density unevenness that cannot be expressed only by the sine wave or cosine wave of the rotation period occurs due to the rotation of the plurality of rotating bodies included in the image forming unit. In addition, density unevenness distribution information indicating the periodic density unevenness distribution can be extracted for each rotating body.

According to the fifth aspect of the present invention, in the case where periodic density unevenness including density unevenness that cannot be expressed only by the sine wave or cosine wave of the rotation period occurs due to the rotation of the plurality of rotating bodies included in the image forming unit. In addition, density unevenness distribution information indicating the periodic density unevenness distribution can be extracted for each rotating body. In addition, a periodic image corresponding to the rotation period of each rotating body can be easily extracted as compared with the case where no synchronized image is used.

According to the sixth aspect of the present invention, in the case where periodic density unevenness including density unevenness that cannot be expressed only by the sine wave or cosine wave of the rotation cycle occurs due to the rotation of the plurality of rotating bodies included in the image forming unit. In addition, density unevenness distribution information indicating the periodic density unevenness distribution can be extracted for each rotating body.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment and a second embodiment. FIG. 2 is a diagram illustrating a schematic configuration of an image forming unit. 2 is a configuration diagram illustrating a configuration of a control system of the image forming apparatus. FIG. The hardware block diagram of the computer which implement | achieves a control part is shown. It is a flowchart which shows the flow of the density | concentration nonuniformity extraction process routine performed with the control part of 1st Embodiment. (A) is an explanatory view for explaining processing for extracting the density unevenness profile of the photoconductor in the first embodiment, and (B) is a process for extracting the density unevenness profile of the developing roll in the first embodiment. It is explanatory drawing explaining these. It is a flowchart of the conversion information generation process routine which produces | generates the conversion information performed with a control part. It is a figure which shows the example of formation of the image for conversion information generation. (A) is a figure which shows an example of the conversion information which shows the relationship between the pixel value of a read image, and an exposure correction value, (B) is the conversion which shows the relationship between the pixel value of a read image, and an image data correction value. It is a figure which shows an example of information. It is a flowchart of a density unevenness correction processing routine in the case of correcting based on an exposure correction value. It is a flowchart which shows the flow of the synthetic | combination process performed by step 500 of FIG. It is a flowchart of a density unevenness correction processing routine in the case of correcting based on the image data correction value. It is a flowchart which shows the flow of the density | concentration nonuniformity extraction process routine performed with the control part of 2nd Embodiment. It is a figure which illustrates typically the procedure at the time of extracting the density nonuniformity profile of a rotary body in 2nd Embodiment. It is explanatory drawing explaining an example of the method of deriving the formation amount at the time of forming the some image for extraction equivalent to 1 period of the object rotary body which is density | concentration nonuniformity extraction object. An example of a method for deriving the formation amount when forming a plurality of extraction images corresponding to one cycle of the target rotating body when the peripheral length of the target rotating body is shorter than the peripheral length of the non-target rotating body It is explanatory drawing to do. When the circumference of the target rotator is longer than the circumference of the non-target rotator, the specific part of the non-target rotator used when forming the image for extraction is the entire circumferential direction of the non-target rotator. It is a figure which shows the example of formation of the image for extraction. FIG. 3 is a diagram illustrating an example of an image forming unit provided with a rotary developing device.

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

  [First Embodiment]

  FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 5 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 5 includes an image forming unit 100 that forms an image, an image reading unit 200 that reads an image, an operation unit for a user to input an operation, a display unit that displays an operation screen, and the like. The operation panel unit 250 including the above is provided. Also. The image forming apparatus 5 controls the operations of the image forming unit 100 and the image reading unit 200, performs display control on the operation panel unit 250, and receives information input through the operation panel unit 250. The unit 300 is also provided.

  FIG. 2 is a diagram illustrating a schematic configuration of the image forming unit 100. The image forming unit 100 generates image data for each color of yellow (Y), magenta (M), cyan (C), and black (K), and based on each image data, a recording medium (in this embodiment, recording paper). An image is formed on P). Hereinafter, image formation performed by the image forming unit 100 may be referred to as printing. The image forming unit 100 includes an image forming fixing unit 102, a paper feeding unit 104, and a paper discharge unit 106.

  The image forming fixing unit 102 includes image forming units 10Y, 10M, 10C, and 10K that form toner images of colors Y, M, C, and K.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in a line in the traveling direction W of the endless intermediate transfer belt 30 supported by the support roll 34 and the plurality of rolls 32. The intermediate transfer belt 30 is disposed to face the photoreceptors 12Y, 12M, 12C, and 12K of the image forming units 10Y, 10M, 10C, and 10K, and the photoreceptors 12Y, 12M, 12C, and 12K, respectively. The primary transfer rolls 16Y, 16M, 16C, and 16K are inserted.

  In the following, when it is necessary to distinguish YMCK, any one of Y, M, C, and K is added after the sign, and when it is not necessary to distinguish YMCK, Y, M, C, and K are omitted. (Same for FIG. 3).

  Each image forming unit 10 includes a photoreceptor 12, a charger 13, an exposure unit 14, a developing device 15, and a primary transfer roll 16.

  The photoreceptor 12 is driven to rotate, and the surface thereof is charged by the charger 13. In the present embodiment, the charger 13 is configured by a charging brush, but may be configured by a charging roll that is a rotating body.

  The exposure unit 14 includes a laser light source that emits laser light by driving an exposure control unit 164 (see also FIG. 3), which will be described later, and exposes the charged photoconductor 12 by irradiating the laser beam with the laser beam. An electrostatic latent image is formed on the surface. In the present embodiment, the exposure unit 14 provided with a laser light source will be described as an example. However, the present invention is not limited to this. The exposure unit 14 includes an LED (light emitting diode) and exposes the photosensitive member 12 from the LED. The exposure part which irradiates light may be sufficient.

  The electrostatic latent image formed on the photoconductor 12 is developed by the developer 15 using a developer, and becomes a toner image of any color of YMCK. In this embodiment, the case where the developer is a two-component developer including toner and carrier will be described. However, the developer may be a one-component developer, and further, the one-component developer may be Magnetic toner or non-magnetic toner may be used.

  The developing device 15 according to this embodiment includes a developing sleeve that rotates outward, and includes a developing roller that includes a magnetic pole inside the developing sleeve, rotates while holding toner, and transports the toner to the developing region. Yes.

  The primary transfer roll 16 conveys the intermediate transfer belt 30 between the primary transfer roll 16 and the photosensitive drum 12, and generates a toner image formed on the photosensitive drum 12 by generating an electrostatic adsorption force when a transfer bias is applied. Primary transfer is performed on the intermediate transfer belt 30. After the primary transfer, untransferred residual toner remaining on the photoconductor 12 is removed by a cleaning device (not shown). The surface of the photoconductor 12 is neutralized by a neutralizing device (not shown) and then charged again by the charger 13 for the next image forming cycle.

  In the image forming unit 100, the image forming process is performed for each of the image forming units 10Y, 10M, 10C, and 10K at a timing that considers the relative position difference between the image forming units 10Y, 10M, 10C, and 10K. The Y, M, C, and K color toner images are sequentially superimposed on the intermediate transfer belt 30 to form a color toner image. When a black and white image is formed, a single color toner image of K color is transferred onto the intermediate transfer belt 30.

  The toner image formed on the intermediate transfer belt 30 is secondarily transferred to the recording paper P by the secondary transfer roll 36. The secondary transfer roll 36 sandwiches the recording paper P conveyed to the secondary transfer position A between the intermediate transfer belt 30 supported by the support roll 34 and generates an electrostatic adsorption force by the applied transfer bias. The toner image on the intermediate transfer belt 30 is secondarily transferred to the recording paper P.

  The recording paper P is stored in the paper feed cassettes 60 and 61 of the paper feed unit 104 arranged in the preceding stage of the image forming and fixing unit 102. Then, the recording paper P is fed from one of the paper feed cassettes 60 and 61 to the image forming and fixing unit 102. The fed recording paper P is sent to the secondary transfer position A by a plurality of transport rolls 66 and an alignment roll 68 of the transport mechanism 64. Then, as described above, the toner images are transferred from the intermediate transfer belt 30 to the recording paper P all at once by the support roll 34 and the secondary transfer roll 36.

  Untransferred residual toner on the intermediate transfer belt 30 that has not been transferred to the recording paper P during the secondary transfer is scraped off and removed by the cleaning blade 42 of the cleaning device 40.

  The recording paper P on which the toner image has been transferred from the intermediate transfer belt 30 is separated from the intermediate transfer belt 30 and then conveyed to the fixing unit 50 by the conveyance belt 38 disposed on the downstream side of the secondary transfer position A. .

  The fixing unit 50 includes a heat fixing roll 52 having a heating element such as a halogen lamp inside a metallic core having thermal conductivity. Further, a pressure roll 56 that applies pressure to the recording paper P conveyed in pairs with the heat fixing roll 52 is also provided.

  Then, the surface of the recording paper P onto which the unfixed toner image is transferred becomes the heat fixing roll 52 side, and when the recording paper P is gripped and conveyed by the heat fixing roll 52 and the pressure roll 56, heat and The toner image is fixed on the recording paper P by the pressure.

  The recording paper P on which the toner image is fixed by the fixing unit 50 is sent to the paper discharge unit 106. Then, the recording paper P is discharged to the paper discharge tray 72 by the paper discharge mechanism 110 of the paper discharge unit 106.

  Further, the main image forming unit 100 reverses the front and back of the recording paper P on which the toner image is fixed on one side, transports the recording paper P to the secondary transfer position A again, and performs intermediate transfer on the other side as well. A mechanism for transferring a new toner image from the belt 30 and printing on both sides of the recording paper P is provided.

  Specifically, the recording paper P is reversed by the reverse conveyance mechanism 70 of the paper discharge unit 106, and then conveyed to the conveyance mechanism 64 via the conveyance path 74. The other surface of the recording paper P is again conveyed by the conveyance mechanism 64. Is transferred to the secondary transfer position A on the intermediate transfer belt 30 side.

  Then, after the toner image is transferred to the other surface of the recording paper P, the toner image is similarly fixed to the other surface by the fixing device 50, and the sheet is discharged onto the discharge tray 72 by the discharge mechanism 110 of the discharge portion 106. Discharged.

  In the vicinity of the intermediate transfer belt 30 on the downstream side of the four image forming units 10Y, 10M, 10C, and 10K, light receiving elements are arranged in a line along the direction intersecting the rotation direction of the intermediate transfer belt 30. A line sensor 120 is also provided. The line sensor 120 has a light source as well as a light receiving element, reads the image formed on the intermediate transfer belt 30 by causing the light source to emit light, irradiating the image with read light, and receiving the reflected light by the light receiving element. The line sensor 120 outputs image data for each color of RGB as a reading result. As will be described later, the line sensor 120 may be used when reading an image for extraction when extracting density unevenness distribution information indicating a two-dimensional distribution of density unevenness.

  Although not shown, a density detection sensor is also provided in the vicinity of the intermediate transfer belt 30. The density detection sensor includes a light source and a light receiving unit, emits the light source, irradiates the image with reading light, and receives the reflected light by the light receiving unit, thereby reading the image formed on the intermediate transfer belt 30. The density detection sensor outputs image data for each color of RGB as a read result. The density detection sensor is used, for example, when performing color misregistration adjustment or adjustment processing for adjusting the developer supply amount. Specifically, in the adjustment process, a predetermined adjustment image is formed by the image forming unit 10, the formed image is read by the density detection sensor, and the degree of color misregistration, density, etc. are analyzed. This refers to processing for adjusting the exposure timing of the four exposure units 14 and adjusting the amount of developer supplied to the developing device 15. Further, the density detection sensor may be used in place of the line sensor 120 as a reading unit when reading the extraction image when extracting the density unevenness distribution information.

  FIG. 3 is a configuration diagram showing the configuration of the control system of the image forming apparatus 5.

  As shown in FIG. 3, the image forming unit 100 includes a charging control unit 160, a photoreceptor control unit 162, a developing roll control unit 170, a primary transfer roll control unit 174, a secondary transfer roll control unit 176, a fixing control unit 178, A conveyance control unit 180 and a sensor control unit 184 are provided. Each of the charging control unit 160, the photoconductor control unit 162, the developing roll control unit 170, the primary transfer roll control unit 174, the secondary transfer roll control unit 176, the fixing control unit 178, the conveyance control unit 180, and the sensor control unit 184 includes , Connected to the control unit 300 and operated by a control signal from the control unit 300.

  The charging controller 160 applies a charging bias voltage to the charger 13. When the charger 13 includes a charging roll that is a rotating body, the charging controller 160 is provided with a motor that rotates the charging roll.

  The photoconductor control unit 162 includes a photoconductor motor. The photoreceptor motor is provided for each image forming unit 10 and is connected to the photoreceptor 12 in each corresponding image forming unit 10. When the photoconductor motor is driven, the rotational force is transmitted to the photoconductor 12, and the photoconductor 12 is rotated in the direction of the arrow shown in FIG.

  The exposure control unit 164 is provided for each image forming unit 10 and is connected to the exposure unit 14 in the corresponding image forming unit 10. The exposure control unit 164 includes a drive unit 166 and an exposure amount control unit 168. The control unit 300 includes a storage unit for storing image data representing an image to be formed by the image forming unit 100, and the image forming unit 100 forms an image from the image data stored in the storage unit. Is supplied to the drive unit 166 of the exposure control unit 164.

  Based on the image data supplied from the control unit 300, the driving unit 166 generates a modulation signal that defines timing for turning on and off the light beam emitted from the laser light source of the exposure unit 14, and according to the generated modulation signal At the same timing, the laser light source of the exposure unit 14 is turned on / off. Further, the drive unit 166 generates a drive current for changing the light amount (exposure amount) of the light beam at the time of ON to a setting signal supplied from the exposure amount control unit 168, and supplies the drive current to the laser light source. .

  The exposure amount control unit 168 includes a storage unit for storing correction value data for correcting the exposure amount of the drive unit 166. The control unit 300 inputs the correction value data to the exposure amount control unit 168, and stores the correction value data in the storage unit. The exposure amount control unit 168 corrects the exposure amount of the exposure unit 14 according to the correction value data stored in the storage unit. The exposure amount control unit 168 generates a drive amount setting signal obtained by changing the drive amount setting signal according to the reference exposure amount according to the correction value data, and supplies the drive amount setting signal to the drive unit 166. The drive unit 166 supplies a drive current corresponding to the supplied drive amount setting signal to the exposure unit 14.

  Here, when correcting the exposure amount, the correction value indicated by the correction value data may be subtracted from the value indicating the reference exposure amount, or may be corrected to the value indicating the reference exposure amount. May be multiplied, added, or divided, and the correction method is not limited. However, each correction value of the correction value data needs to be determined according to the correction method. The exposure amount control unit 168 generates a drive amount setting signal so as to be exposed with the exposure amount corrected with the correction value, and supplies the drive amount setting signal to the drive unit 166.

  The exposure amount may be adjusted according to the amount of drive current, but may be adjusted by changing the pulse width when driven by a pulse signal. Further, the exposure amount may be adjusted by a voltage value.

  The developing roll control unit 170 includes a developing motor that applies a rotational force to the developing roll included in the developing device 15 and a bias applying unit that applies a developing bias voltage to the developing roll.

  The primary transfer roll control unit 174 is provided for each image forming unit 10 and includes a transfer motor that applies a rotational force to the primary transfer roll 16. During printing, the primary transfer roll 16 in the corresponding image forming unit 10 is pressed and brought into contact with the peripheral surface of the photoconductor 12 by the rotation of the transfer motor. The primary transfer roll control unit 174 also includes a bias application unit. A bias voltage for primary transfer is applied to the primary transfer roll 16 by the bias application unit.

  The secondary transfer roll control unit 176 includes a transfer motor that applies a rotational force to the secondary transfer roll 36 and a bias application unit that applies a secondary transfer bias voltage to the secondary transfer roll 36. During printing, the secondary transfer roll 36 is pressed and brought into contact with the peripheral surface of the intermediate transfer belt 30 by the rotation of the transfer motor of the secondary transfer roll control unit 176. Further, a bias voltage for secondary transfer is applied to the secondary transfer roll 36 by the bias applying unit of the secondary transfer roll control unit 176.

  Further, the fixing control unit 178 controls the fixing unit 50. Specifically, the heating element included in the heat-fixing roll 52 is caused to generate heat, and the heat-fixing roll 52 and the pressurizing roll 56 are heated so that the recording paper P is sandwiched and conveyed. The pressure roll 56 is driven.

  The conveyance control unit 180 includes a conveyance motor. The conveyance control unit 180 is connected to the conveyance system 182 such as the conveyance roll 60, the alignment roll 68, and the support roll 34 described with reference to FIG. 2, and when the conveyance motor is driven, the rotational force is transmitted to the conveyance system. 2, a series of recording sheets P along the conveyance path until the intermediate transfer belt 30 moves in the direction of arrow W shown in FIG. 2 and is discharged from the discharge unit 106 via the secondary transfer roll 36. Is carried out.

  The sensor control unit 184 controls the line sensor 120 to read an image formed on the intermediate transfer belt 30. The read result is supplied to the control unit 300.

  Although not shown in FIG. 2, as shown in FIG. 3, the image forming unit 100 rotates to detect the rotational position (also referred to as phase) of a rotating body such as the photosensitive member 12 or the developing roll. A position detector (encoder) 186 is provided for each rotating body. Each of the rotational position detectors 186 generates a pulse signal in synchronization with the rotational period of the rotating body. The pulse signal is input to the control unit 300.

  The image reading unit 200 includes a reading control unit 202 and a reading unit 204. The reading unit 204 includes a light source and a light receiving unit, and is controlled by the reading control unit 202. The reading unit 204 emits a light source, irradiates the image with reading light, and receives the reflected light by the light receiving unit, whereby a predetermined portion of the image forming apparatus 5 (for example, a platen glass (not shown)). The image of the original set by the user is read. The image reading unit 200 outputs image data for each color of RGB as a reading result. If a transport mechanism that transports the document to the reading position of the reading unit 204 is provided, the transport mechanism is controlled by the control of the reading control unit 202 to transport the document to the reading position. Read the original image. The read result is supplied to the control unit 300.

  The control unit 300 can be realized by an electronic circuit or the like, for example. The control unit 300 may be realized by, for example, a semiconductor integrated circuit, more specifically, an ASIC (Application Specific Integrated Circuit) or the like. Furthermore, the control unit 300 may be realized by a computer. In the present embodiment, a case where the control unit 300 is realized by a computer will be described.

  FIG. 4 shows a hardware configuration diagram of a computer 302 that implements the control unit 300. The computer 302 includes a CPU (Central Processing Unit) 304, a ROM (Read Only Memory) 306, a RAM (Random Access Memory) 306, an image forming unit IF (Interface) 310, an image reading unit IF 312, an operation panel unit IF 314, and a communication IF 316. Are connected via a bus 318.

  The CPU 304 executes programs stored in the ROM 306 (including programs for density unevenness extraction processing, conversion information generation processing, and density unevenness correction processing described later). The ROM 306 stores programs executed by the CPU 304, data necessary for processing by the CPU 304, and the like. The RAM 308 is used as a work memory or the like.

  Note that the storage medium for storing the program executed by the CPU 304 is not limited to the ROM 306. For example, it may be an HDD (Hard Disk Drive), a flexible disk, a DVD disk, a magneto-optical disk, a USB (Universal Serial Bus) memory, or the like (not shown), or may be connected to the computer 302 via a communication IF 316. It may be a storage device.

  The image forming unit IF 310 is an interface for connecting to the image forming unit 100. The image reading unit IF 312 is an interface for connecting to the image reading unit 200. The operation panel unit IF 314 is an interface for connecting to the operation panel unit 250. The communication IF 316 is an interface for communicating with other devices connected to communication means (for example, a network such as a telephone line or a LAN).

  In the image forming apparatus 5 of the present embodiment, density unevenness caused by rotation of a plurality of rotating members (for example, the photosensitive member 12, the developing roll in the developing device 15, the primary transfer roll 16) included in the image forming unit 100 is corrected. Density unevenness correction processing is performed.

  Here, the density unevenness caused by the rotation of the rotating body will be described. For example, the rotating body such as the photoconductor 12 or the primary transfer roll 16 is shifted between the rotation center of the rotating body and the cross-sectional center of the rotating body (deviation of the rotation axis), and the cross-sectional shape of the rotating body is deviated from a perfect circle. It is difficult to manufacture in a state in which (uneven shape) or the like is completely eliminated. Due to such unevenness, the density of an image to be formed varies, resulting in two-dimensional unevenness. Further, density unevenness may occur due to the attachment accuracy when attaching the rotating body to the image forming unit 100. Such density unevenness periodically occurs according to the rotation of the rotating body. In the present embodiment, the image forming unit 100 does not perform control for rotating the rotating members in synchronization with each other during normal image formation. Accordingly, during normal image formation, each rotating body rotates asynchronously.

  In this embodiment, in order to correct this periodic density unevenness, first, a density unevenness extraction image (hereinafter referred to as an extraction image) for extracting density unevenness is formed, and each rotating body is formed from the extraction image. Each density unevenness distribution information (hereinafter, density unevenness profile) representing the density unevenness distribution for each is extracted. Then, a correction value for each rotator is generated from the extracted density unevenness profile, and each correction value is synthesized so as to match the phase of each rotator at the start of image formation, and is corrected by the synthesized value. The density unevenness may be corrected, for example, by correcting the image data, or by correcting the exposure amount of the exposure unit 14.

  Hereinafter, each process performed in the present embodiment will be described in detail.

  FIG. 5 is a flowchart showing the flow of the concentration unevenness extraction processing routine executed by the control unit 300.

  Note that the image forming unit 100 of the present embodiment includes a plurality of image forming units and is configured to be able to print a color image, but in this embodiment, the density unevenness profile is extracted for each color. Therefore, an extraction image is formed for each image forming unit 10, and a density unevenness profile is extracted for each rotating body of each image forming unit.

  In step 400, it is determined whether the user has operated the operation panel unit 250 and selected the density unevenness extraction mode. If the determination is affirmative, the process shifts to the density unevenness extraction mode and proceeds to step 402.

  Here, although an example in which the user selects the density unevenness extraction mode by operating the operation panel unit 250 has been described, the present invention is not limited to this. For example, when a predetermined condition is satisfied (preliminary) It is determined that the density unevenness extraction mode is selected every time a predetermined number of sheets are printed, every time a predetermined time interval elapses, or when a density unevenness monitoring result exceeds a predetermined density unevenness threshold value). Alternatively, when the customer engineer or the like of the image forming apparatus 5 performs maintenance, the operation panel unit 250 may be operated and selected.

  In step 402, the image forming unit 100 is controlled so that an extraction image is formed. As described above, in the image forming unit 100, since each rotating body in the image forming unit 10 is not controlled to rotate synchronously in a normal image forming operation, each rotating body rotates asynchronously. Further, in the present embodiment, in the density unevenness extraction mode, as in the case of the normal image forming operation, the extraction image is formed in a state in which each rotating body rotates asynchronously. In the density unevenness extraction mode, the control unit 300 sends control signals similar to those in a normal image forming operation to each control unit of the rotating body such as the photoconductor control unit 162, the developing roll control unit 170, and the primary transfer roll control unit 174. And an instruction signal for instructing application of a bias voltage necessary for image formation is also output to the charging control unit 160, the developing roll control units 170 and 172, the primary transfer roll control unit 174, the secondary transfer roll control unit 176, and the like. To do. The control unit 300 also supplies image data for forming an extraction image to the drive unit 166. Further, the control unit 300 controls the exposure amount so that a drive amount setting signal for exposure with a predetermined reference (that is, uncorrected) exposure amount is supplied from the exposure amount control unit 168 to the drive unit 166. A control signal is output to the unit 168. That is, when forming the extraction image, control is performed so that density unevenness is not corrected.

  Here, the extraction image may be, for example, a single-color (Y, M, C, or K) halftone image of the entire A3 size. Moreover, other sizes (for example, A4 size) different from A3 size may be sufficient. Further, it is assumed that image data for forming an image for extraction is stored in advance in the ROM 306 of the control unit 300. When the control unit 300 is realized by hardware such as an ASIC or a semiconductor integrated circuit, the control unit 300 may be held in advance in an internal circuit constituting the control unit 300.

  Further, the density of the image for extraction may be plural or only one specific density. In the former case, a plurality of image data having different densities (pixel values) are supplied to the drive unit 166, and a plurality of extraction images having different densities are formed.

  Forming multiple extraction images corresponding to multiple densities and acquiring density unevenness profiles for multiple densities can deal more precisely with changes in density unevenness, sensitivity changes, etc. The correction effect is higher than when only the density is formed.

  Here, an image corresponding to the circumferential length (for one cycle) of each rotating body included in the formed extraction image is referred to as a periodic image. In this embodiment, the control unit 300 performs control so that a plurality of periodic images are formed for each of the rotating bodies in which density unevenness occurs. For example, when an A3 size extraction image can include a periodic image of one cycle of the photoconductor 12 and a periodic image of four cycles of the developing roll of the developing device 15, the photoconductor 12 having a long circumference is used. As a reference, at least two A3 size extraction images are formed. As the number of extracted images formed increases, the density unevenness correction accuracy increases. However, if the number of formed images is too large, the amount of consumption of consumables such as toner increases. The number of sheets to be formed is set in advance and formed according to the setting, or the upper and lower limits of the number of sheets to be formed are determined, and the user extracts within the range of the upper and lower limits when starting the density unevenness extraction mode. The number of images to be formed may be set and formed according to the setting. In any case, it is set so that two or more periodic images of each rotating body that cause density unevenness are included.

  Furthermore, in the present embodiment, the control unit 300 extracts a synchronization image (hereinafter referred to as a synchronization mark) formed at a position synchronized with the rotation cycle of the target rotating body that is a target rotating body from which density unevenness is extracted. The image forming unit 100 is controlled so as to be formed together. The synchronization mark is used for alignment of periodic images. The control unit 300 receives a pulse signal from the rotational position detection unit 186 during the formation of the extraction image. The control unit 300, based on the pulse signal, every time each rotating body rotates once. Image data is generated and supplied to the exposure control unit 164 so that a predetermined synchronization mark for each rotating body is formed on the extraction image. The image for extraction formed between two consecutive synchronization marks becomes a periodic image for one round.

  The synchronization mark is formed in a format that can be identified for each rotating body. For example, in FIG. 6A, the synchronization mark synchronized with the rotation period of the photosensitive member 12 is the rotation direction of the rotating body (hereinafter referred to as “rotating body”). , Which is formed at the left end in a direction intersecting with the sub-scanning direction (hereinafter referred to as main scanning direction), and is synchronized with the rotation cycle of the developing roll of the developing device 15 at the right end. Further, not only the position of the synchronization mark but also the shape, size, and density of each rotator may be made different so as to identify which rotator each sync mark corresponds to. In any case, the position, size, and shape of the synchronization mark are set to a position, size, and shape that do not affect the extraction of the density unevenness profile.

  After the set number of extraction images are formed, in step 404, the formed image is read. Here, a control signal is output from the control unit 300 to the image reading unit 200, and the extraction image formed on the recording paper is read. When an image having a plurality of densities is formed, each image is read.

  In this way, when the image for reading is read by the image reading unit 200, in order for the user to read the image formed on the recording paper, the recording paper is set in an original reading unit such as a platen glass. It is necessary to operate the operation panel unit 250 to give a reading instruction. For this reason, a user or a customer engineer operates the operation panel unit 250 to determine whether or not an image reading is instructed. When it is determined that an instruction is given, the image is read.

  Here, an example in which an image is read by the image reading unit 200 has been described. However, other than the image reading unit 200 mounted on the image forming apparatus 5, for example, other on a communication unit connected by the communication IF 316. You may make it read with a reading apparatus.

  For example, the extraction image formed on the intermediate transfer belt 30 may be read by the line sensor 120 provided in the image forming unit 100. In this case, the control unit 300 inputs a control signal to the sensor control unit 184 so that the extraction image transferred onto the intermediate transfer belt 30 by the line sensor 120 is read, and is formed on the intermediate transfer belt 30. The line sensor 120 is caused to read the extracted image. The read result is supplied to the control unit 300. In this case, there is no need for secondary transfer onto the recording paper. As a result, the recording paper is not wasted. Further, for example, a line sensor may be provided on the downstream side of the developing device 15 in the vicinity of the photoconductor 12 to read the developed image formed on the photoconductor 12 (in this case, primary transfer). The density unevenness profile of the roll 16 is not extracted.) Image data of the read image is input to the control unit 300.

  In step 406, 1 is set to the variable n. This variable n is a variable for identifying a rotator to be extracted with uneven density, and each of the rotators is assigned any number from 1 to N (N is the total number of rotators to be extracted). It shall be.

  In step 408, a synchronization mark of the nth rotating body (hereinafter referred to as the nth rotating body) is detected from the read image read in step 404.

  In step 410, the synchronization marks of the n-th rotator are aligned to match the phases of the plurality of periodic images of the n-th rotator, and an average image is generated by averaging these phases. Information representing this average image is a density unevenness profile representing a distribution of periodic density unevenness due to rotation of the n-th rotating body. In addition, when the image for extraction is formed with a plurality of densities, an average image is generated for each density and a density unevenness profile is extracted.

  Here, the formed extraction image includes unevenness in the density of a rotating body other than the n-th rotating body. However, as described above, each rotating body rotates asynchronously, and the circumferential lengths of the rotating bodies are also mutually different. Therefore, when the phases of the periodic images of the n-th rotator are overlapped (ie, added) and averaged, the density unevenness of the rotator that rotates asynchronously with respect to the n-th rotator is averaged in the average image. Each phase is shifted and dispersed (that is, density unevenness is reduced). Therefore, by the averaging process in step 410, the influence of the density unevenness of the rotating body other than the n-th rotating body is reduced, and the density unevenness profile of the n-th rotating body can be extracted.

  In step 414, 1 is added to n.

  In step 416, it is determined whether or not n exceeds the total number (N) of rotators to be extracted with uneven density. If a negative determination is made in step 416, the process returns to step 408 and the same processing as described above is repeated. As a result, the density unevenness profile due to the rotation of each of the rotating bodies to be subjected to density unevenness extraction is extracted.

  Here, with reference to FIG. 6, the extraction of the density unevenness profile of the present embodiment will be specifically described. Here, the extraction target of the density unevenness profile is the photoconductor 12 and the developing device 15, and the primary transfer roll 16 is excluded from the density unevenness extraction target. Here, a case will be described in which density unevenness extraction is performed by forming three A3 size extraction images.

  6 (A) and 6 (B) show the image formation results for three sheets in which each of the synchronization mark of the photoconductor 12 and the synchronization mark of the developing roll of the developing device 15 is formed together with the image for extraction. Yes. Each of FIGS. 6A and 6B is a schematic diagram, and illustration of density unevenness generated in the formed extraction image is omitted. First, the extraction of the density unevenness profile of the photoreceptor 12 will be described with reference to FIG.

  As shown in FIG. 6A, three periodic images p_1, p_2, and p_3 are extracted from the three image formation results based on the synchronization mark of the photoconductor 12. When these periodic images are overlapped and averaged, the influence of the density unevenness of the developing roll of the developing device 15 is reduced, and a density unevenness profile indicating the density unevenness distribution of the photoconductor 12 is extracted.

  Next, extraction of the density unevenness profile of the developing roll will be described with reference to FIG.

  As shown in FIG. 6B, 15 periodic images m_1_1 to m_1_5, m_2_1 to m_2_5, and m_3_1 to m_3_5 are extracted from the above three image formation results based on the synchronization marks on the developing roll of the developing device 15. Is done. Since the circumferential length of the developing roll is shorter than the circumferential length of the photoconductor 12, the number of periodic images of the developing roll included in the three extraction images is larger than the number of periodic images of the photoconductor 12. When the periodic images of the developing rolls are overlapped and averaged, the influence of the density unevenness of the photoconductor 12 is reduced, and a density unevenness profile indicating the density unevenness distribution of the developing roll of the developing device 15 is extracted.

  If the determination in step 416 is affirmative, the process proceeds to step 418.

  In step 418, each extracted density unevenness profile is converted into correction value data which is distribution information of correction values for correcting the density unevenness indicated by the density unevenness profile. The correction value here refers to a correction value (exposure correction value) for correcting the exposure amount of the exposure unit 14 or a correction value (image data correction value) for correcting image data. Conversion to the correction value is information indicating the relationship between the pixel value of the read image and the exposure correction value (see also FIG. 9A), or the relationship between the pixel value of the read image and the image data correction value (FIG. 9 ( (See also B)). Such information is referred to as conversion information. As described above, in this embodiment, the conversion information is used when converting the pixel value of the average image of the periodic images extracted from the read image into the correction value. At this time, the “read image” of the conversion information is used. Is applied to the pixel value of the average image. The conversion information is obtained in advance or every time the density unevenness profile is extracted.

  FIG. 7 shows a flowchart of a conversion information generation processing routine for generating conversion information. Here, a case where conversion information indicating a relationship between a pixel value of a read image and a correction value for correcting an exposure amount is generated will be described as an example.

  In step 600, the control unit 300 supplies image data for forming a conversion information generation image to the exposure control unit 164 to cause the image formation unit 100 to form a conversion information generation image. It is assumed that image data for forming the conversion information generation image is held in advance in the ROM 306 of the control unit 300. When the control unit 300 is realized by hardware such as an ASIC or a semiconductor integrated circuit, the control unit 300 may be held in advance in an internal circuit constituting the control unit 300.

  For example, as illustrated in FIGS. 8A and 8B, the conversion information generation image includes a plurality of small images (hereinafter referred to as patches) each having the same pixel value (density) in the image data. Images. Note that the pixel values (density) on the image data of each patch are the same, but here the exposure value correction value is varied to vary the density. If the pixel value on the image data for forming the density unevenness extraction image is represented by the halftone dot area ratio Cin of 50%, as shown in FIG. The density on the image data of each patch of the conversion information generation image is also set to Cin 50% (according to the density of the image for extracting uneven density). In this way, the exposure value correction values of the patches are made different from each other without changing the density of the base image data. In the example shown in FIG. 8C, the correction values of the patches P1 to P5 are -10, -5, 0, +5, and +10. Basically, as shown in FIG. 8C, each correction value has a plurality of correction values in the vertical direction with a correction value (in this case, 0) when no correction is performed as a reference (center). Is preferably assigned to a plurality of patches, but the assignment method is not limited to this.

  The control unit 300 supplies the image data of the conversion information generation image to the drive unit 166 to the exposure control unit 164, and at the same time, the exposure amount of each patch included in the conversion information generation image is different. A control signal indicating the correction value is supplied to the exposure amount control unit 168.

  Note that the arrangement of patches in the conversion information generation image shown in FIGS. 8A and 8B is merely an example, and is not particularly limited to this example. Also, the number of patches need not be five. If the number of patches is large, the toner consumption increases, but the correction accuracy increases. Further, as described above, the exposure correction value is set to a value corresponding to the exposure correction method. As described above, the correction value indicated by the correction value data may be subtracted from the value indicating the reference exposure amount, or the value indicating the reference exposure amount may be multiplied, added, or divided by the correction value. However, the correction method is not limited. Therefore, the correction value needs to be determined so as to be a value according to the correction method.

  Here, the correction value when no correction is made is 0, but the correction value when no correction is made may be 100, and is not particularly limited. Furthermore, in the above example, the correction value of each patch has been described as an example in which correction values are assigned to a plurality of patches at equal intervals, such as -10, -5, 0, +5, and +10. There is no need to allocate correction values at even intervals.

  In step 602, it is determined whether the user or customer engineer has operated the operation panel unit 250 to instruct image reading. If an affirmative determination is made in step 602, in step 604, a control signal is output from the control unit 300 to the image reading unit 200, and each image formed on the recording paper is read. The read result (data representing the read image) is image data expressed as a distribution of pixel values for each RGB color, and is supplied to the control unit 300. Here, an example in which the conversion information generation image formed on the recording paper is read has been described. However, the conversion information generation image formed on the intermediate transfer belt 30 may be read by the line sensor 120.

  In step 606, conversion information indicating the relationship between the pixel value of the read image and the correction value is generated (see also FIG. 9A). Specifically, first, the control unit 300 obtains an average value obtained by averaging the read pixel values of each patch area from the obtained reading result. Then, if the correction value given at the time of patch formation is plotted on the horizontal axis (X-axis) and the obtained average value is plotted on the vertical axis (Y-axis) as the pixel value of the read image, the correction value and the pixel value A relationship is required. Note that this conversion information may be stored in a lookup table format, or may be expressed in a function format if it can be expressed in a function format. In addition, since the patch is formed by changing the correction value stepwise, the correction value and the pixel value obtained by reading may be discrete values, and data in the meantime may be insufficient. In this case, the missing data may be interpolated by performing an interpolation process or the like.

  Here, an example in which a conversion information generation image including a plurality of patches is formed has been described. However, as shown in FIG. 8D, the conversion information generation image is converted into a full-tone image (pixels of image data). Multiple images (images of one page having the same value for all pixels) may be formed (five G1 to G5 are illustrated in the figure). In this case, the correction value is varied so that the exposure amount is different for each sheet. In step 606, an average value obtained by averaging the pixel values is obtained from the reading result of the entire halftone image, and the relationship between the average value and the correction value may be obtained.

  Through the processing described above, conversion information indicating the relationship between the pixel value and the correction value is generated. Although the case where the correction value is the exposure correction value has been described here, the present invention is not limited to this. For example, even if the correction value is an image data correction value, each patch (or each half-surface Pixel values obtained by changing the pixel value of the image data of the tone image) stepwise according to the image data correction value and supplying the pixel value to the drive unit 166 to form a conversion information generation image and reading the formed image Conversion information indicating the relationship between the value and the correction value may be generated (see also FIG. 9B). When correcting the image data, the image data correction value may be subtracted from the output image data for correction, or the output image data may be multiplied, added, or divided by the image data correction value. The correction method is not limited. However, the image data correction value needs to be a value corresponding to the correction method.

  As described above, the conversion information generation process is performed in advance (for example, when a predetermined number of recording media are manufactured at the time of manufacture and shipment of the image forming apparatus 5 or every time a predetermined time elapses from the start of use of the image forming apparatus 5). Each time it is formed, it may be generated when a predetermined time arrives, or when density unevenness exceeding a predetermined threshold occurs, etc. Therefore, it may be performed every time the density unevenness extraction mode is executed. When the conversion information generation process is performed every time the density unevenness extraction mode is executed, the conversion information generation process may be executed before step 418 in FIG. Therefore, for example, the conversion information generation process may be executed between step 400 and step 402, or the conversion information generation process may be executed between step 414 and step 418. .

  In step 418, the uneven density profile is converted into a correction value using the generated conversion information. Correction value data which is distribution information of the corrected correction value is stored in a predetermined storage means. Here, the correction value data may be thinned out to be stored at a low resolution. This is because the storage capacity is reduced and there is almost no high-frequency density unevenness.

  In step 420, the density unevenness extraction mode is terminated.

  Thereafter, when printing specified by the user is performed, the control unit 300 forms an image by correcting density unevenness using the generated correction value data. FIG. 10 shows a flowchart of a density unevenness correction processing routine in the case of correcting based on the exposure correction value.

  In step 500, the control unit 300 synthesizes correction value data for each rotating body (factor) to generate one correction value data. Details of the synthesis process will be described later.

  In step 502, the control unit 300 writes the combined light amount correction value data into the exposure control unit 164 (the storage unit of the exposure amount control unit 168). Details of the composition processing in step 502 will be described later with reference to FIG.

  In step 504, the control unit 300 supplies image data for printing specified by the user to the driving unit 166 to cause the image forming unit 100 to start image formation. In image formation, the exposure amount control unit 168 generates a drive amount setting signal according to the written correction value data and supplies the drive amount setting signal to the drive unit 166. Thereby, the exposure amount of the drive unit 166 is corrected.

  FIG. 11 specifically describes an example of the synthesis process in step 500 described above.

  In step 550, correction value data corresponding to the rotating body is read.

  In step 552, by performing two-dimensional interpolation processing (interpolation processing in the main scanning direction and sub-scanning direction) on the correction value data, the resolution of the image data to be output (printed) with low resolution correction value data. Convert to a resolution suitable for.

  In step 554, it is determined whether or not the two-dimensional interpolation processing has been completed for each factor (rotating body). If a negative determination is made in step 554, the process returns to step 550, the correction value data is read for the remaining rotating bodies, and the above processing is repeated.

  On the other hand, if an affirmative determination is made in step 554, the process proceeds to step 558.

  In step 556, the rotational position detection unit 186 detects the current rotational position (phase) of the rotating body corresponding to the read correction value data, and the correction value data is set so that the correction value data corresponds to the current phase. The head address of each correction value is determined (hereinafter, this process is referred to as position synchronization).

  In step 558, the correction value data of each of the rotating bodies is combined with the start address of each correction value data aligned. Thereby, final correction value data is obtained. Note that the time from the position synchronization to the start of image formation may cause a positional deviation between the actual density unevenness and the correction value data. Therefore, the time needs to be sufficiently short. Even in the case of synthesizing with software, there is a mode in which the synthesized data can be sent to image formation sequentially by pipeline processing (mode of sequential processing) instead of batch processing (type of batch processing collectively). desirable. Here, for the same reason, position synchronization is performed immediately before the synthesis of correction value data for each factor.

  Here, an example in which the control unit 300 performs position synchronization, composition, and writing to the exposure control unit 164 has been described, but the present invention is not limited to this. For example, a circuit for performing position synchronization, composition, and writing may be provided separately and processed by hardware. Further, this circuit may be provided in the exposure control unit 164. In addition, an electronic circuit for performing each process shown in FIGS. 10 and 11 may be provided, and the above-described processes may be realized by the electronic circuit. Further, the above processing may be realized by a semiconductor integrated circuit, more specifically, an ASIC (Application Specific Integrated Circuit) or the like.

  In addition, when correcting image data instead of exposure amount, it carries out as follows. FIG. 12 shows a flowchart of a density unevenness correction processing routine in the case of correcting based on the image data correction value.

  In step 520, the control unit 300 synthesizes correction value data for each rotator (factor) to generate one correction value data. The synthesis method is as described above.

  In step 522, the control unit 300 corrects the pixel value of the output image data with the combined correction value data. The image data to be output is image data designated for printing by the user (for example, image data transmitted from another apparatus and designated for printing, or image data obtained by reading a document designated for copying). Yes, the control unit 300 performs correction by subtracting the correction value data synthesized from the image data.

  In step 524, the control unit 300 supplies the corrected image data to the driving unit 166 and causes the image forming unit 100 to start image formation. Thereby, exposure is performed based on the corrected image data.

  Also in this case, as described above, the position synchronization, composition, and correction of the image data by the correction value data may be hardware processed by an electronic circuit or the like. Similarly, an electronic circuit for performing each process shown in FIGS. 11 and 12 may be provided, and each process described above may be realized by the electronic circuit. Further, the above processing may be realized by a semiconductor integrated circuit, more specifically, an ASIC (Application Specific Integrated Circuit) or the like.

  When correction value data is obtained by forming only an entire halftone extraction image in which pixels of a specific density (specific pixel value) are arranged, correction value data of other densities other than the specific density exists. do not do. In this case, the correction value of the same correction value data may be used for each pixel value in the image data designated to be printed by the user, but a coefficient predetermined for the correction value is determined according to the pixel value. You may multiply and use. The coefficient to be multiplied by the correction value is to form a gradation image including a plurality of small images having different densities from each other separately from the full-screen halftone image for extraction, read each small image, and use the full-screen halftone image as a reference Each coefficient corresponding to the ratio between the specific density and the density of each small image is set as a coefficient to be multiplied by the correction value of the density of each small image. Then, the correction value is used by multiplying a coefficient set corresponding to each pixel value (density value) when the image data designated for printing by the user is printed.

  In addition, when a plurality of density extraction images are formed and correction value data corresponding to each of the plurality of densities is obtained, if coefficients other than the formed density are obtained in advance in the same manner as described above, coefficients are used. Good.

  [Second Embodiment]

  The configuration of the image forming apparatus of the second embodiment, the configuration of the image forming unit, and the hardware configuration of the control unit are the same as the configuration of the image forming apparatus 5 of the first embodiment, the configuration of the image forming unit 100, and the control unit. The hardware configuration is the same as that of 300.

  FIG. 13 is a flowchart showing the flow of the concentration unevenness extraction processing routine executed by the control unit 300 of the second embodiment.

  In this embodiment as well, the density unevenness profile is extracted for each color. That is, an extraction image is formed for each image forming unit 10 and a density unevenness profile is extracted for each rotating body of each image forming unit. Here, it is assumed that the density unevenness caused by the secondary transfer roll 36 hardly occurs and can be ignored.

  In step 450, it is determined whether or not the user has operated the operation panel unit 250 to select the density unevenness extraction mode. If the determination is affirmative, the process shifts to the density unevenness extraction mode and proceeds to step 452. As in step 400 of the first embodiment, the selection method and timing of the density unevenness extraction mode are not limited to the example in which the user operates the operation panel unit 250 to select, and various selection methods and timings are available. Conceivable.

  In step 452, 1 is set to the variable n. This variable n is a variable for identifying a rotator to be extracted with uneven density, and each of the rotators is assigned any number from 1 to N (N is the total number of rotators to be extracted). It shall be.

  In step 454, the image forming unit 100 is controlled so that the density non-uniformity extraction image is formed using the n-th rotator as the rotation target (target rotator). Here, for each of the rotators (non-target rotators) other than the n-th rotator, control is performed so that only a specific portion predetermined for each rotator is used for forming the extraction image. Note that the length of the specific portion in the sub-scanning direction (circumferential direction) is less than the circumferential length of the n-th rotating body. In addition, the length of the extraction image in the sub-scanning direction is equal to the length of the specific portion. The control unit 300 rotates each rotating body by intermittently supplying image data for forming an extraction image having a length equal to the circumferential length of the specific portion to the exposure control unit 164. However, control is performed so that only a specific portion of the non-target rotating body is used for forming the extraction image.

  In addition, although the n-th rotating body and the non-target rotating bodies other than the n-th rotating body rotate asynchronously, when there are a plurality of non-target rotating bodies in which density unevenness occurs, each of the plurality of non-target rotating bodies However, the rotation is controlled so that the length in the sub-scanning direction of the specific portion used when forming the extraction image is synchronized with each other in each non-target rotator (control unit). A control signal for controlling the rotation is supplied from 300 to the image forming unit 100).

  For example, when the photosensitive member 12 is a rotator to be extracted and each of the developing roll and the primary transfer roll 16 of the developing device 15 is a non-target rotator, the control unit 300 may control the developing roll and the primary transfer roll 16. Each rotates asynchronously with respect to the photoreceptor 12, and the developing roll and the primary transfer roll 16 are controlled to rotate in synchronization with each other. For example, the control unit 300 controls the rotation speed of the developing roll so as to rotate in synchronization with each other. In addition, the control unit 300 controls the charger 13 so that only the part of the photosensitive member 12 that contacts the specific part of the developing roll is charged, and the part of the photosensitive member 12 that contacts the specific part of the developing roll is exposed. As described above, the image data of the extraction image is supplied to the exposure control unit 164.

  For example, when the density unevenness hardly occurs in the primary transfer roll 16, it is not necessary to synchronize the rotation of the developing roll and the primary transfer roll 16.

  Thus, since the n-th rotating body and the non-target rotating body rotate asynchronously, the n-th rotating body used for forming the extraction image every time each rotating body rotates to form the extraction image. The surface position of gradually shifts. By rotating each rotator to some extent, a plurality of extraction images are formed, and when at least the entire area in the sub-scanning direction of the nth rotator is used for forming the extraction image, the formation of the extraction image is completed ( Step 456, Y).

  In step 456, it is determined whether or not an extraction image of at least the circumference of the n-th rotator (one cycle) has been formed. If a negative determination is made in step 456, the process returns to step 454 and the formation of the extraction image is continued. If an affirmative determination is made in step 456, the process proceeds to step 458.

  In step 458, the plurality of formed extraction images are read. Since the reading method may be performed in the same manner as Step 404 described in the first embodiment, the description is omitted here.

  In step 460, an average image is generated by aligning and superimposing the ends of the read images obtained by reading the plurality of extraction images. Since the plurality of extraction images are formed using the fixed positions (specific portions) of the non-target rotating body and using different positions of the n-th rotating body (target rotating body), each of the read images The average image obtained by averaging is an image representing the density unevenness profile of a specific part of the non-target rotating body from which the influence of the density unevenness caused by the rotation of the n-th rotating body is substantially removed.

  In step 462, the average image is subtracted from each read image (the pixel value of the average image is subtracted from the pixel value of each pixel of the read image). Thereby, the influence of density unevenness caused by the non-target rotating body in each read image is reduced.

  In step 464, each of the read images subtracted from the average image is aligned. Specifically, each of the read images is arranged at a position corresponding to the phase (rotation position) of the n-th rotator in the sub-scanning direction. Note that the formation position of the extraction image is determined in advance, and the arrangement position of the read image corresponds to the formation position of the extraction image. Therefore, the extraction image may be arranged according to the formation position of the corresponding extraction image. Position information indicating the formation position of the extraction image is stored in advance in a storage unit such as the ROM 306, and the position information is read out and used not only when the extraction image is formed but also when the step 464 is executed. Good. Information on the arrangement image generated by arranging a plurality of read images in this way is stored as a density unevenness profile for one round of the n-th rotating body. When a plurality of read images are aligned and there is an overlapping portion (overlap portion) that overlaps in the sub-scanning direction between adjacent read images, the average of the images in the overlapping portion is taken. To do.

  Note that there is no need for an overlap portion, but when reading the extraction image, reading the edge portion of the extraction image is prone to errors, so non-target rotation is performed so that an overlap portion is intentionally generated. The length of the specific part of the body in the sub-scanning direction (the length of the extraction image in the sub-scanning direction) may be determined in advance, and a plurality of extraction images may be formed.

  Here, the procedure for extracting the density unevenness profile of the n-th rotating body will be described with reference to the schematic diagram of FIG. Here, a case where the rotating body (n-th rotating body) from which density unevenness is to be extracted is the photosensitive body 12 and the non-target rotating body is the developing roll of the developing device 15 will be described.

(1) Only a specific portion is used in the developing roll, and an image for extraction is formed on the photosensitive member 12 using a portion in contact with the specific portion of the developing roll. FIG. 14 illustrates an extraction image formation state when the circumferential length of the photoconductor 12 is 190 mm, the circumferential length of the developing roll is 40 mm, and the length of a specific portion of the developing roll in the sub-scanning direction is 10 mm. . As shown in FIG. 14, each extraction image is formed using a different part of the photoconductor 12. In this example, if 19 extraction images are formed from the circumferences of the photoconductor 12 and the developing roll and the size of the specific portion, a density unevenness profile for one cycle of the photoconductor 12 can be generated. An extraction image is not formed on a portion of the photoreceptor 12 that does not contact a specific portion of the developing roll.

(2) After the extraction image is formed, a plurality (19 in this case) of the extraction images formed are read. The image is not read for the portion where the extraction image is not formed.

(3) An average image R_ave of the read images R_1... R_19 obtained by reading is obtained. In other words, the average image R_ave is obtained by averaging density profiles of specific portions of the developing roll.

(4) The average image R_ave is subtracted from each of the read images R_1... R_19 obtained by reading. Thereby, the density unevenness of the developing roll is removed from each read image.

(5) The images R_1-R_ave and R_2-R_ave ... R_19-R_ave obtained by subtracting the average image R_ave from each of the read images R_1 ... R_19 are aligned. As shown in FIG. 14, each of the images R_1-R_ave, R_2-R_ave... R_19-R_ave is arranged at a position corresponding to the phase of the photoconductor 12 in the sub-scanning direction.

  As described above, when images R_1-R_ave, R_2-R_ave... R_19-R_ave are aligned, if there are overlapping portions (overlap portions) that overlap in the sub-scanning direction between adjacent images, For the overlap portion, the average of each image is taken.

(6) The arrangement image data obtained by arranging (arranging) the images R_1-R_ave, R_2-R_ave... R_19-R_ave is stored as a density unevenness profile for one cycle of the photoconductor 12.

  The processing from step 454 to step 464 corresponds to extraction processing of the density unevenness profile of the n-th rotating body. When a plurality of extraction images having different densities are formed, the density unevenness profile of the n-th rotating body is extracted (generated) for each density.

  Next, in step 466, the density unevenness profile of the n-th rotator is converted into correction value data that is correction value distribution information for correcting the density unevenness indicated by the density unevenness profile. Conversion to the correction value is performed using the conversion information generated as described in the first embodiment. Correction value data which is distribution information of the corrected correction value is stored in a predetermined storage means.

  In step 468, 1 is added to n.

  In step 470, it is determined whether or not n exceeds the total number (N) of rotators to be extracted with uneven density. If a negative determination is made in step 470, the process returns to step 454 and the same processing as described above is repeated. As a result, the density unevenness profile due to the rotation of each of the rotating bodies to be subjected to density unevenness extraction is extracted.

  In step 472, the density unevenness extraction mode is terminated.

  Thereafter, when printing specified by the user is performed, the control unit 300 forms an image by correcting density unevenness using the generated correction value data. Since the correction method may be performed in the same manner as the processing described with reference to FIGS. 10 to 12 in the first embodiment, description thereof is omitted here.

  Next, a technique for deriving the formation amount when forming a plurality of extraction images corresponding to one cycle of the target rotating body will be described with reference to FIG. Here, the peripheral length of the photoconductor 12 is 264 mm, the peripheral length of the developing roll is 54 mm, the peripheral length of the primary transfer roll 16 is 70 mm, and the rotating body from which density unevenness is extracted is the photoconductor 12. It will be explained as being. Since the non-target rotating body is the developing roll and the primary transfer roll 16, the rotational speed of at least one of the developing roll and the primary transfer roll 16 is changed so that the periods of the two rotating bodies are equal, and the rotating is synchronized. Let For example, the rotation speed of the developing roll is decreased, and the cycle of the developing roll is adjusted to the cycle of the primary transfer roll 16.

  In this example, each extraction image is formed so that the distance between the leading end positions of two extraction images adjacent in the sub-scanning direction is 70 mm in accordance with the circumferential length of the primary transfer roll 16. On the other hand, since the circumferential length of the photosensitive member 12 is 264 mm, if the rotation speed of the primary transfer roll 16 is C (C is an integer), the minimum C value that satisfies at least “264 mm <70 mm × C” (C = 4 ), The usage area of the primary transfer roll 16 becomes an area of one cycle or more of the photoconductor 12.

  Here, a difference of 16 mm between 280 mm, which is four times the circumference of the primary transfer roll 16, and 264 mm of the circumference of the photoconductor 12 is a deviation amount of the formation position of the extraction image with respect to the photoconductor surface position per circumference of the photoconductor. . Therefore, if the length of the image for extraction in the sub-scanning direction (the length of the specific portion of the primary transfer roll 16 in the sub-scanning direction) is set to 16 mm, every time the photoconductor 12 rotates, the image for extraction on the photoconductor 12 is extracted. The image forming position is shifted by the length of the extraction image in the sub-scanning direction, and data corresponding to one rotation of the photoreceptor 12 is collected without a gap. The number of extraction images formed is 264/16 = 16.5, and if a total of 17 extraction images are formed, a density unevenness profile for one rotation of the photoreceptor 12 can be generated. The method for generating (extracting) the density unevenness profile is as described with reference to FIG.

  In addition, since an edge portion (edge portion) of the extraction image may have poor reading accuracy, for example, about 2 mm may be added as an overlap portion. That is, the extraction image may be formed with a width of 16 + 2 = 18 mm.

  Here, the case where the circumference of the target rotating body is longer than the circumference of the non-target rotating body has been described, but even when the circumference of the target rotating body is shorter than the circumference of the non-target rotating body, the same control is performed, A density unevenness profile may be extracted. For example, consider the case where the primary transfer roll 16 described above is a target rotating body and the photoconductor 12 is a non-target rotating body. Also in this case, as shown in FIG. 16, a difference of 16 mm between 280 mm, which is four times the circumference of the primary transfer roll 16, and 264 mm of the circumference of the photosensitive member 12 is the length in the sub-scanning direction of the image for extraction (photosensitive member 12 The length of the specific portion in the sub-scanning direction). In this case, extraction images are formed at intervals of 264 mm in accordance with the circumferential length of the photoreceptor 12. As a result, every time an image for extraction is formed, the formation position of the image for extraction on the primary transfer roll 16 is shifted by the length of the image for extraction in the sub-scanning direction (the image for extraction shown in FIG. 16). See also B_1 to B_5). As a result, as shown in FIG. 16, if a total of five extraction images are formed at 70/16 = 4.4, a density unevenness profile for one round of the primary transfer roll 16 can be generated. The method for generating (extracting) the density unevenness profile is as described with reference to FIG.

  Further, when the perimeter of the target rotator is longer than the perimeter of the non-target rotator, the density unevenness profile may be extracted by forming an extraction image as follows. Here, the entire circumferential direction of the non-target rotating body is used as the specific portion, and the length of the extraction image in the sub-scanning direction is set equal to the peripheral length of the non-target rotating body. Then, the non-target rotation body is rotated by the minimum C value satisfying at least “the circumference of the target rotation body <the circumference of the non-target rotation body × C”, and C extraction images are continuously formed. . Then, as described with reference to FIG. 13, the read images obtained by reading the C extraction images are averaged, and the average image is subtracted from each read image. Then, if the read image is aligned in accordance with the phase of the non-target rotating body, a density unevenness profile of the target rotating body is generated. An example is shown in FIG. When the peripheral length of the primary transfer roll 16 is 70 mm and the peripheral length of the photosensitive member 12 is 264 mm, an extraction image is formed using the entire circumferential direction of the primary transfer roll 16 as the specific portion. In this case, if four extraction images are formed, the entire circumferential direction of the photoconductor 12 is covered.

  Moreover, although 2nd Embodiment demonstrated the example which forms the some image for extraction intermittently using the specific part of the said non-object rotary body, it is not limited to this. For example, a halftone image for extracting density unevenness is continuously formed, and each of the image portions corresponding to the specific portion is extracted from the entire read image obtained by reading the entire formed image. The average image of the plurality of read images may be subtracted from each of the plurality of read images, and these may be aligned to generate a density unevenness profile of the target rotating body. Further, for example, a halftone image for extracting density unevenness is continuously formed, and among the formed images, each of the image portions corresponding to the specific portion is selectively read, and the read plural images An average image of each read image may be generated, subtracted from the plurality of read images, and these may be aligned to generate a density unevenness profile of the target rotating body.

  In the first embodiment and the second embodiment, the tandem type image forming unit 100 has been described as an example. However, the image forming unit 100 is not limited to the tandem type configuration. For example, as shown in FIG. 18, an image forming unit 710 provided with a rotary developing device 718 may be used.

  The photoreceptor 712 is provided to be rotated in the direction of arrow A by a motor (not shown). Around the photoreceptor 712, a charging roll 714, an exposure device 716, a developing device 718, a primary transfer device 732, and a cleaning device 722 are arranged.

  The charging roll 714 charges the surface of the photoconductor 712, and the exposure device 716 forms an electrostatic latent image by exposing the surface of the charged photoconductor 712 with a laser beam according to image data.

  In the developing device 718, developing devices 718Y, 718M, 718C, and 718K using C, M, Y, and K color toners are arranged along the circumferential direction, and are provided with developing rollers 720, respectively, M, Y, and K toners are stored. Each developing unit 718Y, 718M, 718C, 718K develops the electrostatic latent image on the photoreceptor 712 with C, M, Y, and K color toners, respectively. When developing, the developing device 718 is rotated by a motor (not shown), and the developing device is aligned so as to face the latent image on the photoreceptor 712.

  The toner images developed on the photoconductor 712 are sequentially transferred to the intermediate transfer belt 724 rotated in the direction of arrow B by the primary transfer unit 732, and the toner images are superimposed.

  The recording paper P drawn from the recording paper storage unit 734 to the conveyance path by the drawing roll 736 is conveyed to the transfer position of the secondary transfer roll 742 by the roll pairs 738 and 740. The toner image formed on the intermediate transfer belt 724 is transferred onto the recording paper P at this transfer position, thermally fixed by the fixing device 744, and discharged to a discharge unit (not shown).

  In the above-described embodiment, the image forming unit 100 capable of forming a color image has been described. However, the present invention is not limited to this. For example, the image forming unit 100 includes only one image forming unit and can perform monochrome printing. May be.

  Note that the control unit 300 provided in the image forming apparatus 5 is not limited to the above example in which the function of extracting the uneven density profile and generating the correction value data is executed. For example, the image forming apparatus 5 is connected to the image forming apparatus 5 via a communication unit. A communicable external device may function as the control unit 300, and the external device may extract the density unevenness profile and generate correction value data.

100, 710 Image forming unit 200 Image reading unit 300 Control unit 302 Computer 304 CPU
306 ROM
308 RAM

Claims (6)

The plurality of rotations are provided by an image forming unit that includes an exposure unit that performs exposure based on the supplied image data and a plurality of rotating bodies, and that forms an image on a recording medium by exposure by the exposure unit and rotation of the plurality of rotating units. The rotation cycle of the target rotating body from which the density unevenness distribution information is to be extracted, together with an extraction image for extracting density unevenness distribution information representing the distribution of density unevenness for each of the rotating bodies generated by each rotation of the body Control means for controlling the image forming means so as to form a synchronized image synchronized with
The position of the synchronized image that is included in the read image obtained by reading the extraction image formed by the control of the control unit and that is read together with the extraction image, a plurality of periodic images corresponding to the rotation cycle of the target rotating body The average image information obtained by averaging the phases in the rotation direction of the target rotator obtained by aligning the directions and edges of the extracted plurality of periodic images and averaging them Extracting means for extracting density unevenness distribution information representing density unevenness due to rotation of the target rotating body;
A correction value for correcting the density unevenness represented by the density unevenness distribution information extracted by the extracting unit is generated, and the correction value is used to correct the image data supplied to the exposure unit or the exposure amount of the exposure unit. Correction means to
An image forming control device. An exposure unit that performs exposure based on the supplied image data and a plurality of rotating bodies, and the plurality of rotating units included in the image forming unit that forms an image on a recording medium by exposure by the exposing unit and rotation of the plurality of rotating bodies. When extracting density unevenness distribution information representing a periodic density unevenness distribution for each of the rotating bodies generated by the rotation of each rotating body, the rotating body from which the density unevenness distribution information is to be extracted among the plurality of rotating bodies. Is a target rotator, and a rotator other than the target rotator is a non-target rotator that causes density unevenness due to rotation. A plurality of extraction images having a length equal to or less than a circumference of the target rotator are formed using predetermined specific portions of the non-target rotator, and the plurality of extraction images The As the rotation direction entire area of the target rotating body is used by forming a control means for controlling said image forming means,
The average image of each of the read images is subtracted from each of the read images obtained by reading each of the plurality of extraction images formed under the control of the control means, and each of the read images after the subtraction is used as the target rotating body. Extracting means for extracting the information of the arrangement image arranged at a position corresponding to the phase in the rotation direction as density unevenness distribution information for one cycle of the target rotating body;
A correction value for correcting the density unevenness represented by the density unevenness distribution information extracted by the extracting unit is generated, and the correction value is used to correct the image data supplied to the exposure unit or the exposure amount of the exposure unit. Correction means to
An image forming control device. The control unit controls the image forming unit so that each of the plurality of non-target rotating bodies rotates in synchronization when there are a plurality of the non-target rotating bodies that cause density unevenness.
The image formation control device according to claim 2 . Image forming means for forming an image on a recording medium by exposure by the exposure means and rotation of the plurality of rotating bodies, the exposure means for exposing based on the supplied image data and a plurality of rotating bodies;
An image formation control device according to any one of claims 1 to 3 ,
An image forming apparatus. Computer
The plurality of rotations are provided by an image forming unit that includes an exposure unit that performs exposure based on the supplied image data and a plurality of rotating bodies, and that forms an image on a recording medium by exposure by the exposure unit and rotation of the plurality of rotating units. The rotation cycle of the target rotating body from which the density unevenness distribution information is to be extracted, together with an extraction image for extracting density unevenness distribution information representing the distribution of density unevenness for each of the rotating bodies generated by each rotation of the body Control means for controlling the image forming means so as to form a synchronized image synchronized with
The position of the synchronized image that is included in the read image obtained by reading the extraction image formed by the control of the control unit and that is read together with the extraction image, a plurality of periodic images corresponding to the rotation cycle of the target rotating body The average image information obtained by averaging the phases in the rotation direction of the target rotator obtained by aligning the directions and edges of the extracted plurality of periodic images and averaging them Extraction means for extracting density unevenness distribution information representing density unevenness due to rotation of the target rotating body, and a correction value for correcting the density unevenness represented by the density unevenness distribution information extracted by the extraction means, A program for functioning as correction means for correcting the image data supplied to the exposure means or the exposure amount of the exposure means using the correction value. Computer
An exposure unit that performs exposure based on the supplied image data and a plurality of rotating bodies, and the plurality of rotating units included in the image forming unit that forms an image on a recording medium by exposure by the exposing unit and rotation of the plurality of rotating bodies. When extracting density unevenness distribution information representing a periodic density unevenness distribution for each of the rotating bodies generated by the rotation of each rotating body, the rotating body from which the density unevenness distribution information is to be extracted among the plurality of rotating bodies. Is a target rotator, and a rotator other than the target rotator is a non-target rotator that causes density unevenness due to rotation. A plurality of extraction images having a length equal to or less than a circumference of the target rotator are formed using predetermined specific portions of the non-target rotator, and the plurality of extraction images The As the rotation direction entire area of the target rotating body is used by forming a control means for controlling said image forming means,
The average image of each of the read images is subtracted from each of the read images obtained by reading each of the plurality of extraction images formed under the control of the control means, and each of the read images after the subtraction is used as the target rotating body. Extracting means for extracting the information of the arrangement image arranged at a position corresponding to the phase in the rotation direction as density unevenness distribution information for one period of the target rotating body, and the density unevenness distribution extracted by the extracting means A program for generating a correction value for correcting density unevenness represented by information and functioning as correction means for correcting image data supplied to the exposure means or exposure amount of the exposure means using the correction value.