JP6380081B2 - Image forming apparatus, image forming system, and density correction method - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus, an image forming system, and a density correction method in the image forming apparatus, and more particularly to a technique for correcting density fluctuations in the sub-scanning direction.

  In general, in an image forming apparatus (printer, copying machine, facsimile, etc.) using an electrophotographic process technology, light based on image data is irradiated (exposed) to a uniformly charged photoconductor (for example, a photoconductive drum). As a result, an electrostatic latent image is formed on the surface of the photoreceptor. Then, toner is supplied to the photoconductor on which the electrostatic latent image is formed, so that the electrostatic latent image is visualized and a toner image is formed. The toner image is transferred directly or indirectly to the sheet via an intermediate transfer member, and then heated and pressed by a fixing unit, whereby an image is formed on the sheet.

  The image forming apparatus has various rotating bodies such as a photoconductor and a developer carrier, and density unevenness occurs periodically in the sub-scanning direction of the image due to the rotational shake of these rotating bodies. It is known. For example, the interval (development gap) between the photosensitive member and the developer carrying member periodically changes due to the rotational shake of the photosensitive member or the developer carrying member, so that the electric field strength is cyclic even when a constant developing bias is applied. As a result, density unevenness occurs in the image at the same cycle as the rotation cycle of the photoreceptor or developer carrier.

  In a conventional image forming apparatus, for example, based on a density profile indicating density fluctuation in the sub-scanning direction, the photosensitive member is rotated to a rotational position (phase with reference to the home position) so as to cancel out density unevenness that occurs periodically. Corresponding correction data is created. Then, with this correction data, image forming conditions such as exposure energy (exposure time or exposure output), charging voltage, developing bias voltage, rotation speed of developer carrier (for example, developing roller), and density value (tone level) of input image data Value) is corrected (for example, Patent Documents 1 and 2).

JP 2014-116711 A JP 2013-195586 A

  When forming an image on a sheet of paper, a density profile can be periodically acquired by forming a patch image that is long in the sub-scanning direction using the gap between the sheets and detecting the density of the patch image. Therefore, even if the concentration profile changes with time, it can be dealt with. However, since it is necessary to form a patch image having a length corresponding to the rotation period of the photosensitive member or developer carrier, productivity is reduced.

  Further, when images are continuously formed on long paper, there is no space between the papers, so it is not possible to periodically acquire a density profile. For this reason, density correction is performed using correction data created based on the initial density profile. However, if the density profile changes over time, there is a risk that density correction will not be performed properly.

  An object of the present invention is to provide an image forming apparatus, an image forming system, and a density correction method in an image forming apparatus that can cope with a case where the density profile changes with time and can appropriately correct periodic density fluctuations. That is.

An image forming apparatus according to the present invention includes a paper transport unit that transports paper,
An image forming unit having a rotating body including a photoconductor and a developer carrier, and forming an image on a sheet;
A density profile management unit that manages a density profile indicating density fluctuation in the sub-scanning direction in association with a phase of the density profile and a rotation position of the rotating body;
A density correction unit that creates correction data based on the density profile and performs density correction based on the correction data;
An image density detection unit for detecting a density of an image formed on the image carrier by the image forming unit;
A rotational position detector that detects the rotational position of the rotating body,
When the rotational position of the rotating body corresponds to a specific phase in the density profile and the writing position on the image carrier at this time is a non-image area, the density profile management unit Forming a correction patch image, correcting the density profile based on the detection result of the image density detection unit for the correction patch image;
The density correction unit performs density correction using correction data created based on the corrected density profile.

An image forming system according to the present invention is an image forming system including a plurality of units including an image forming apparatus,
A paper transport unit for transporting paper,
An image forming unit having a rotating body including a photoconductor and a developer carrier, and forming an image on a sheet;
A density profile management unit that manages a density profile indicating density fluctuation in the sub-scanning direction in association with a phase of the density profile and a rotation position of the rotating body;
A density correction unit that creates correction data based on the density profile and performs density correction based on the correction data;
An image density detection unit for detecting a density of an image formed on the image carrier by the image forming unit;
A rotational position detector that detects the rotational position of the rotating body,
When the rotational position of the rotating body corresponds to a specific phase in the density profile and the writing position on the image carrier at this time is a non-image area, the density profile management unit Forming a correction patch image, correcting the density profile based on the detection result of the image density detection unit for the correction patch image;
The density correction unit performs density correction using correction data created based on the corrected density profile.

The density correction method according to the present invention includes a sheet transport unit that transports a sheet, and a rotating body including a photosensitive member and a developer carrier, and includes an image forming unit that forms an image on the sheet. A method,
Managing a density profile indicating density fluctuation in the sub-scanning direction in association with the phase of the density profile and the rotational position of the rotating body;
When the rotational position of the rotating body corresponds to a specific phase in the density profile and the writing position on the image carrier at this time is a non-image area, a correction patch image is formed on the image carrier. ,
Detecting the image density of the correction patch image;
Based on the detected image density, the density profile is corrected,
Create correction data based on the corrected density profile,
It is characterized in that density correction is performed with the created correction data.

  According to the present invention, since the density profile is efficiently corrected, it is possible to cope with a case where the density profile changes with time, and it is possible to appropriately correct periodic density fluctuations.

1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an overall configuration of an image forming apparatus main body. FIG. 3 is a diagram illustrating a main part of a control system of the image forming apparatus main body. It is a figure which shows an example of a density profile. It is a flowchart which shows an example of a density profile correction process. It is a figure which shows an example of arrangement | positioning of the patch image for correction | amendment. It is a figure which shows the density profile after correction based on the detection result of the highest density and the lowest density. It is a figure which shows another example of arrangement | positioning of the patch image for correction | amendment. It is a figure which shows the density | concentration profile after correction | amendment based on the detection result of the highest density | concentration and an average density | concentration.

FIG. 1 is a diagram showing an image forming apparatus 1 according to an embodiment of the present invention.
An image forming apparatus 1 illustrated in FIG. 1 includes a paper feeding device 1A, an image forming device main body 1B, and a winding device 1C. The image forming apparatus 1 forms an image on roll paper. However, the present invention continuously forms roll paper and continuous paper including continuous paper, that is, a plurality of images continuously on paper with no gap. This is suitable for image formation.

  The sheet feeding device 1A includes a roll sheet feeding unit 91, a sheet feeding side buffer unit 94, and the like, and feeds roll paper in accordance with an instruction from the image forming apparatus main body 1B. In the paper supply side buffer unit 94, for example, a slack of the roll paper is absorbed by a tension roller movable in the vertical direction, a blower that blows air onto the roll paper, or an air supply device that sucks the roll paper. Tension is applied.

  Roll paper fed from the paper feeding device 1 </ b> A is conveyed along the paper passing path 93. The image forming apparatus main body 1B forms an image on the roll paper fed from the paper feeding device 1A using electrophotographic process technology.

  The winding device 1C includes a roll winding unit 92 and a winding side buffer unit 95, and winds the roll paper on which an image is formed by the image forming apparatus main body 1B. The take-up buffer unit 95 has the same configuration as the paper feed buffer unit 94.

FIG. 2 is a diagram illustrating an overall configuration of the image forming apparatus main body 1B. FIG. 3 is a diagram illustrating a main part of a control system of the image forming apparatus main body 1B.
An image forming apparatus main body 1B shown in FIGS. 2 and 3 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. In the image forming apparatus main body 1B, photosensitive drums 213 corresponding to four colors of CMYK are arranged in series in the running direction (vertical direction) of the intermediate transfer belt 221, and each color toner image is sequentially applied to the intermediate transfer belt 221 in one procedure. A vertical tandem system for transfer is used.

  That is, the image forming apparatus main body 1B primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) toner images formed on the photosensitive drum 213 to the intermediate transfer belt 221. After the four color toner images are superimposed on the intermediate transfer belt 221, the image is formed by secondary transfer onto a sheet.

  As shown in FIGS. 2 and 3, the image forming apparatus main body 1 </ b> B includes an operation display unit 12, an image processing unit 13, an image forming unit 20, a paper introduction unit 14, a paper discharge unit 15, a main transport unit 16, and a control unit 17. Is provided.

  The control unit 17 includes a CPU (Central Processing Unit) 171, a ROM (Read Only Memory) 172, a RAM (Random Access Memory) 173, and the like. The CPU 171 reads out a program corresponding to the processing content from the ROM 172 or the storage unit 182 and develops it in the RAM 173. In cooperation with the developed program, each block of the image forming apparatus main body 1B, the sheet feeder 1A, and the winding device Centrally control the operation of 1C.

  The communication unit 181 has various interfaces such as a NIC (Network Interface Card), MODEM (MOD-DE Modulator), and USB (Universal Serial Bus), and is connected to the sheet feeding device 1A, the winding device 1C, or other external devices. Enables information communication.

  The storage unit 182 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive. The storage unit 182 stores, for example, a lookup table that is referred to when controlling the operation of each block.

  The control unit 17 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 181. Do. For example, the control unit 17 receives image data (input image data) in a page description language (PDL) transmitted from an external device, and forms an image on a sheet based on the received image data.

  The control unit 17 functions as a density profile management unit 17A and a density correction unit 17B. The density profile management unit 17A manages the density profile indicating the density fluctuation in the sub-scanning direction in association with the phase of the density profile and the rotation position of the rotating body (for example, the photosensitive drum 213 and the developer carrier 212a). The density correction unit 17B creates correction data based on the density profile, and controls the image density based on the correction data. The density profile and the correction data are stored in the storage unit 182, for example. Further, the density profile management unit 17A corrects this when the density profile changes with time. A method for correcting the density profile will be described later.

  The operation display unit 12 includes, for example, a liquid crystal display (LCD) with a touch panel, and functions as the display unit 121 and the operation unit 122. The display unit 121 displays various operation screens, an image status display, an operation status of each function, and the like according to a display control signal input from the control unit 17. The operation unit 122 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 17. The user can operate the operation display unit 12 to perform settings relating to image formation such as document setting, image quality setting, magnification setting, application setting, output setting, and paper setting.

  The image processing unit 13 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 13 performs gradation correction based on the gradation correction data under the control of the control unit 17. The image processing unit 13 performs various correction processes such as color correction and shading correction on the input image data. The image forming unit 20 is controlled based on the image data subjected to these processes.

  The image forming unit 20 is formed by a toner image forming unit 21 and a toner image forming unit 21 for forming a toner image with colored toners of Y component, M component, C component, and K component based on input image data. An intermediate transfer unit 22 for transferring the toner image onto the paper, a fixing unit 23 for fixing the toner image transferred onto the paper, and the like.

  The toner image forming unit 21 includes four toner image forming units 21Y, 21M, 21C, and 21K for Y component, M component, C component, and K component. Since the toner image forming units 21Y, 21M, 21C, and 21K have the same configuration, for convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and the Y, M, It shall be shown with C and K attached. In FIG. 2, only the components of the Y component toner image forming unit 21 </ b> Y are denoted by reference numerals, and the symbols of the other toner image forming units 21 </ b> M, 21 </ b> C, and 21 </ b> K are omitted.

  The toner image forming unit 21 includes an exposure device 211, a developing device 212, a photosensitive drum 213, a charging device 214, a drum cleaning device 215, and the like. The toner image forming unit 21 may include a charge eliminating device for removing residual charges remaining on the surface of the photosensitive drum 213 after the primary transfer.

  The photosensitive drum 213 includes, for example, an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) on a peripheral surface of an aluminum conductive cylindrical body (aluminum tube). : A negatively charged organic photoconductor (OPC) in which Charge Transport Layers are sequentially stacked. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges upon exposure by the exposure device 211. The charge transport layer consists of a hole transport material (electron donating nitrogen-containing compound) dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  A home position mark indicating a reference position is provided on the photosensitive drum 213, and a sensor S <b> 1 (see FIG. 3, a rotational position detection unit) is disposed in the vicinity of the photosensitive drum 213. The rotational position of the photosensitive drum 213 is specified based on the time after the home position mark is detected by the sensor S1.

  The charging device 214 is constituted by a corona discharge generator such as a scorotron charging device or a corotron charging device. The charging device 214 uniformly charges the surface of the photosensitive drum 213 to a negative polarity by corona discharge.

  The exposure apparatus 211 includes, for example, an LED array in which a plurality of light emitting diodes (LEDs) are linearly arranged, an LPH driving unit (driver IC) for driving individual LEDs, and emitted light from the LED array Is formed by an LED print head having a lens array or the like that forms an image on the photosensitive drum 213. One LED of the LED array corresponds to one dot of the image.

  The exposure device 211 irradiates the photosensitive drum 213 with light corresponding to the image of each color component. The positive charge generated in the charge generation layer of the photosensitive drum 213 upon being irradiated with light is transported to the surface of the charge transport layer, so that the surface charge (negative charge) of the photosensitive drum 213 is neutralized. Thereby, an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 213 due to a potential difference from the surroundings.

  The developing device 212 contains a developer for each color component (for example, a two-component developer composed of toner and a magnetic carrier). The developing device 212 visualizes the electrostatic latent image by forming toner of each color component on the surface of the photosensitive drum 213 to form a toner image. Specifically, a developing bias voltage is applied to the developer carrier 212a (for example, a developing roller), and an electric field is formed between the photosensitive drum 213 and the developer carrier 212a. Due to the potential difference between the photosensitive drum 213 and the developer carrier 212a, the charged toner on the developer carrier 212a moves to and adheres to the exposed portion of the surface of the photosensitive drum 213.

  The developer carrier 212a is provided with a home position mark indicating a reference position, and a sensor S2 (see FIG. 3, rotation position detector) is disposed in the vicinity of the developer carrier 212a. Based on the time after the home position mark is detected by the sensor S2, the rotational position of the developer carrier 212a is specified.

  The drum cleaning device 215 includes a drum cleaning blade that is slidably contacted with the surface of the photosensitive drum 213, and removes transfer residual toner remaining on the surface of the photosensitive drum 213 after primary transfer.

  The intermediate transfer unit 22 includes an intermediate transfer belt 221, a primary transfer roller 222, a plurality of support rollers 223, a secondary transfer roller 224, a belt cleaning device 225, and the like.

  The intermediate transfer belt 221 is an endless belt, and is stretched around a plurality of support rollers 223 in a loop shape. At least one of the plurality of support rollers 223 is configured by a driving roller, and the other is configured by a driven roller. As the drive roller rotates, the intermediate transfer belt 221 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 222 is disposed on the inner peripheral surface side of the intermediate transfer belt 221 so as to face the photosensitive drum 213 of each color component. The primary transfer roller 222 is pressed against the photosensitive drum 213 with the intermediate transfer belt 221 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 213 to the intermediate transfer belt 221 (hereinafter referred to as “primary”). Referred to as “transfer section”).

  The secondary transfer roller 224 is disposed on the outer peripheral surface side of the intermediate transfer belt 221 so as to face one of the plurality of support rollers 223. Of the plurality of support rollers 223, the support roller 223 disposed to face the intermediate transfer belt 221 is referred to as a backup roller. The secondary transfer roller 224 is pressed against the backup roller with the intermediate transfer belt 221 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 221 to the sheet (hereinafter “secondary”). Referred to as “transfer section”). Instead of the secondary transfer roller 224, a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller is adopted. Also good.

  In the primary transfer portion, the toner image on the photosensitive drum 213 is primarily transferred to the intermediate transfer belt 221 in order. Specifically, a primary transfer bias is applied to the primary transfer roller 222, and a charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 221 (the side in contact with the primary transfer roller 222). It is electrostatically transferred to the intermediate transfer belt 221.

  Thereafter, when the sheet passes through the secondary transfer portion, the toner image on the intermediate transfer belt 221 is secondarily transferred to the sheet. Specifically, by applying a secondary transfer bias to the secondary transfer roller 224 and applying a charge having a polarity opposite to that of the toner to the back side of the paper (the side in contact with the secondary transfer roller 224), the toner image becomes It is electrostatically transferred to the paper. The sheet on which the toner image is transferred is conveyed toward the fixing unit 23.

  The belt cleaning device 225 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 221 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 221 after the secondary transfer. The belt cleaning device 225 is also used in a toner refresh operation for forcibly discharging the deteriorated toner in the developing device 212.

  An image density detection unit that detects the density of the toner image formed on the intermediate transfer belt 221 in a region downstream of the primary transfer unit in the belt traveling direction and upstream of the secondary transfer unit in the belt traveling direction. 226 is arranged. The image density detection unit 226 includes, for example, a light emitting element such as a light emitting diode (LED) and a light receiving element such as a photodiode (PD), and a reflection type optical sensor that detects the reflection intensity of the toner image. Consists of. The image density detection unit 226 is used when creating a density profile and correcting the density profile. The image density detection unit 226 may be a line type sensor. Further, the image density detection unit 226 may be disposed on the downstream side of the sheet conveyance of the fixing unit 23 to detect the image density after fixing.

  The fixing unit 23 is disposed on the upper fixing unit 231 having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) side of the paper, and on the back surface (surface opposite to the fixing surface) side of the paper. A lower fixing unit 232 having a back side supporting member, a heating source 233 for heating the fixing side member, a fixing temperature detecting unit 234 for detecting a temperature (fixing temperature) in the vicinity of the fixing side member, and a back side supporting member Is provided with a press-contact separation portion (not shown) or the like that presses against the fixing surface side member.

  For example, when the upper fixing unit 231 is a roller heating method, the fixing roller is a fixing surface side member, and when the upper fixing portion 231 is a belt heating method, the fixing belt is a fixing surface side member. Further, for example, when the lower fixing unit 232 is a roller pressurization method, the pressure roller is a backside support member, and when the lower fixing unit 232 is a belt pressurization method, the pressure belt is a backside support member. FIG. 2 shows a case where the upper fixing unit 231 is configured by a roller heating method and the lower fixing unit 232 is configured by a roller pressing method.

  The upper fixing unit 231 includes an upper fixing unit driving unit (not shown) for rotating the fixing surface side member. When the operation of the upper fixing unit driving unit is controlled by the control unit 17, the fixing surface side member rotates (runs) at a predetermined speed. The lower fixing unit 232 includes a lower fixing unit driving unit (not shown) for rotating the back side support member. When the operation of the lower fixing unit driving unit is controlled by the control unit 17, the back side support member rotates (runs) at a predetermined speed. When the fixing surface side member is driven by the rotation of the back surface side support member, the upper fixing portion driving unit is not necessary.

  The heat source 233 is disposed in or near the fixing surface side member. The control unit 17 controls the output of the heating source 233 so that the fixing temperature becomes the fixing control temperature based on the detection result of the fixing temperature detecting unit 234 disposed in the vicinity of the fixing surface side member. By controlling the output of the heating source 233 by the control unit 17, the fixing surface side member is heated and held at a fixing control temperature (for example, a fixing target temperature and an idling temperature).

  A press-contact separation portion (not shown) presses the back surface side support member toward the fixing surface side member. For example, the press-separation portion abuts on both end portions of the shaft that supports the back-side support member, and presses both ends of the shaft independently. Thereby, the balance of the axial nip pressure in the fixing nip can be adjusted. The control unit 17 controls the operation of the press contact / separation unit (not shown), and the back surface side support member is pressed against the fixing surface side member, thereby forming a fixing nip for nipping and transporting the sheet.

  The sheet on which the toner image is secondarily transferred and conveyed along the sheet passing path is heated and pressurized when passing through the fixing unit 23. As a result, the toner image is fixed on the paper.

The paper introduction unit 14 includes, for example, a paper introduction roller unit 141 and the like, and feeds the roll paper fed from the paper feeding device 1 </ b> A to the main transport unit 16.
The paper discharge unit 15 includes, for example, a paper discharge roller unit 151 and the like, and feeds the roll paper sent from the main transport unit 16 to the winding device 1C.

  The main conveyance unit 16 includes a plurality of conveyance roller units including an entrance roller unit 161 disposed on the upstream side of the secondary transfer unit in the sheet conveyance direction as a sheet conveyance element for nipping and conveying the sheet. The main transport unit 16 transports the roll paper introduced from the paper introduction unit 14 and passes the roll paper to the image forming unit 20 (secondary transfer unit, fixing unit 23), and from the image forming unit 20 (fixing unit 23). The sent paper is conveyed toward the paper discharge unit 15.

  When image formation is performed on roll paper, the roll paper fed from the paper feeding device 1 </ b> A is introduced via the paper introduction unit 14. The introduced roll paper is conveyed to the image forming unit 20 by the main conveying unit 16. When the roll paper passes through the secondary transfer portion, the toner image on the intermediate transfer belt 221 is secondarily transferred to the roll paper all at once, and fixing processing is performed in the fixing portion 23. The roll paper on which the image is formed is discharged from the paper discharge unit 15 to the outside of the apparatus, and is taken up by the roll take-up unit 92 of the take-up device 1C. As described above, the paper introduction unit 14, the paper discharge unit 15, and the main conveyance unit 16 constitute a paper conveyance unit of the image forming apparatus main body 1B.

  In the image forming apparatus 1, density unevenness occurs periodically in the sub-scanning direction due to the rotational shake of the rotating body such as the photosensitive drum 213 and the developer carrier 212 a. The density unevenness differs for each gradation and also for each of Y, M, C, and K colors. Here, the case where density unevenness occurs due to the rotational shake of the developer carrier 212a for the K component will be described. However, other rotary bodies (for example, the developer carrier 212a, Y, M, C component developer carrier 212a, The same applies to the case where density unevenness occurs due to the rotational shake of the photosensitive drum 213) for Y, M, C, and K components.

  FIG. 4 is a diagram illustrating an example of a density profile. The density profile shown in FIG. 4 shows density fluctuations in the sub-scanning direction due to the rotational shake of the developer carrier 212a. This density profile has a length equal to or longer than the period length of the developer carrier 212a (a length corresponding to the rotation period of the developer carrier 212a) in advance, and a patch image (halftone density) for density correction on the intermediate transfer belt 221. And the density of the patch image is detected by the image density detection unit 226. The created density profile is stored in the storage unit 18 in association with the phase of the density profile and the rotation position of the developer carrier 212a (density profile management unit 17A). The density profile is created for each rotating body (for example, the developer carrier 212a for each color component and the photosensitive drum 213).

  As shown in FIG. 4, the density profile can be approximated by a sine curve (Y = Asin (θ + α) + B). Here, A is the amplitude, (θ + α) is the phase of the density profile, and B is the average density. As shown in FIG. 4, the average density is obtained when the phase is 0 ° and 180 °, the highest density is obtained when the phase is 90 °, and the lowest density is obtained when the phase is 270 °. That is, an image formed when the rotation position of the developer carrying member 212a corresponds to the phase (90 °, 270 °) at which the maximum density and the minimum density are obtained appears as density unevenness.

  Based on this density profile, correction data corresponding to the phase of the density profile (rotation position of the developer carrier 212a) is created and stored in the storage unit 182 so as to cancel out the density unevenness that occurs periodically. The Based on this correction data, density correction is performed (density correction unit 17B).

  For example, the gradation value (input image value) of the input image data is corrected by the correction data, and image formation is performed based on the corrected input image data. Depending on the correction data, the exposure energy (exposure time or exposure output) in the exposure device 211, the charging voltage in the charging device 214, the developing bias voltage in the developing device 212, the rotational speed of the developer carrier 212a (for example, the developing roller), and the like. The image forming conditions may be corrected.

  In the image forming apparatus 1, the initial density profile is created in advance, but there is a possibility that it will change over time. In the present embodiment, the density profile that changes with time is efficiently corrected by the following method.

  FIG. 5 is a flowchart illustrating an example of the density profile correction process. This processing is realized, for example, by the CPU 171 executing a predetermined program stored in the ROM 172 when the image forming apparatus 1 receives a print job.

  In step S101, the control unit 17 acquires a density profile created in advance. When the density profile is corrected by the previous density profile correction process, the latest density profile is acquired.

  In step S102, the control unit 17 acquires input image data included in the print job. The input image data includes an arrangement pattern of the label image on the roll paper.

  In step S103, the control unit 17 determines the arrangement of the patch image for correcting the density profile, based on the acquired density profile and input image data. Specifically, when the rotation position of the developer carrier 212a corresponds to a specific phase in the density profile and the writing position on the intermediate transfer belt 221 is a non-image area, a correction patch image is displayed in this area. Let it form. Here, a case where the specific phase is 90 ° (corresponding to the highest density) and 270 ° (corresponding to the lowest density) will be described.

  Note that the correction patch image is an image formed in order to grasp the density fluctuation in the sub-scanning direction, and therefore the position in the main scanning direction needs to be the same. Here, it is assumed that a correction patch image is formed in the center of the main scanning direction. Further, the length of the correction patch image in the sub-scanning direction is a length corresponding to a phase range of ± 45 ° or less so that a desired phase is at the center.

  Here, the correction patch image formation interval does not exceed a predetermined time. In other words, a state in which the correction patch image writing position becomes a non-image area appears within a predetermined time (for example, every minute). As a result, the accuracy of the current density profile can be appropriately determined in a short time, and can be corrected as necessary. In the case of forming a label image on roll paper, the formation interval of the correction patch images can be adjusted by adjusting the interval (margin) of the label image, for example.

  FIG. 6 is a diagram illustrating an example of the arrangement of correction patch images. As shown in FIG. 6, when the label image L is arranged in a predetermined pattern, a margin where the label image L is not formed becomes a non-image area. As shown in FIG. 6, when the rotation position of the developer carrier 212a corresponds to the phases of 90 ° and 270 ° in the density profile, the writing position at this time does not overlap with the label image L, that is, non- In the case of an image area, a patch image P is formed.

  In step S104, the control unit 17 executes the image forming process instructed by the print job, and forms a correction patch image at the position determined in step S103. This correction patch image has the same density as the patch image used when creating an initial density profile, and is formed in a state where density correction by correction data is not performed.

  In step S <b> 105, the control unit 17 acquires the density of the correction patch image detected by the image density detection unit 226. When the density profile has not changed, the difference between the density value read from the original density profile and the detected density becomes small. When the density profile has changed, the difference between the density value read from the original density profile and the detected density. Will grow.

  In step S106, the control unit 17 compares the density value read from the original density profile with the detected density, and determines whether or not the density change is larger than a predetermined value (for example, the density difference is 5%). When the density change is larger than the predetermined value, the process proceeds to step S107. If the density change is less than or equal to the predetermined value, the original density profile is retained, and the process proceeds to step S109.

  Here, as the detected density, it is preferable to use the nearest predetermined number of average values among the detected densities of the correction patch images formed at the positions corresponding to the same phase. Alternatively, the most recent predetermined number of weighted average values (the newer the detection timing, the larger the weight) may be used. As a result, irregular density fluctuations are eliminated, so that the necessity of density profile correction can be determined appropriately.

  In step S107, the control unit 17 corrects the original density profile based on the comparison result in step S106. Specifically, based on the detected density (maximum density) corresponding to the 90 ° phase of the density profile and the detected density (lowest density) corresponding to the 270 ° phase, the amplitude of the density profile ((maximum density−minimum) Density) / 2) and average density (vibration center, (highest density + lowest density) / 2). The corrected density profile is specified by the calculated amplitude A and average density B. At this time, the period of the density profile is maintained. FIG. 7 shows a density profile Y1 (amplitude: A1, average density: B1) after correction based on the detection results of the highest density and the lowest density.

  In step S108, the control unit 17 creates correction data based on the corrected density profile so that density unevenness is canceled out. In the subsequent image forming process, density correction is performed using the correction data created in step S108. Since the correction data reflects changes over time in the density profile, appropriate density correction is performed. Therefore, good image quality is ensured. If the density profile is not corrected (“NO” in step S106), the density correction is performed using the current correction data.

  In step S109, the control unit 17 determines whether the image forming process instructed by the print job is finished. When the image forming process is finished, the density profile correction process is finished. If the image forming process is not completed, the process proceeds to step S104.

  As described above, the image forming apparatus 1 includes a paper conveyance unit (a paper introduction unit 14, a paper discharge unit 15, and a main conveyance unit 16) that conveys paper, a photosensitive drum 213 (photosensitive member), and a developer carrier 212a. An image forming unit 20 that has a rotator and forms an image on a sheet, and a density profile that indicates density fluctuation in the sub-scanning direction, and manages the density profile phase and the rotation position of the rotator in association with each other An image formed on the intermediate transfer belt 221 (image carrier) by the profile management unit 17A, a density correction unit 17B that generates correction data based on the density profile, and performs density correction based on the correction data, and the image forming unit 20. An image density detecting unit 226 for detecting the density of the rotating body, and a rotational position detecting unit (not shown) for detecting the rotational position of the rotating body. In the density profile management unit 17A, the rotation position of the rotating body (for example, developer carrier 212a) corresponds to a specific phase (for example, 90 ° and 270 °) in the density profile, and writing to the intermediate transfer belt 221 at this time is performed. When the position is a non-image area, a correction patch image is formed on the intermediate transfer belt 221 and the density profile is corrected based on the detection result of the image density detection unit 226 for the correction patch image. The density correction unit 17B performs density correction using correction data created based on the corrected density profile.

  According to the image forming apparatus 1, since the density profile is efficiently corrected, it is possible to cope with a case where the density profile changes with time, and it is possible to appropriately correct periodic density fluctuations. Further, since a correction patch image is formed only when the rotational position of the rotating body (for example, developer carrier 212a) corresponds to a specific phase (for example, 90 ° and 270 °) in the density profile, a small amount of toner is consumed. An appropriate concentration profile can be maintained.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.

  For example, in the density profile correction processing, at least one of 90 ° (corresponding to the highest density) and 270 ° (corresponding to the lowest density) and one of 0 ° or 180 ° may be set as the specific phase. Good. When the specific phase is 0 °, 90 °, and 180 °, patch images are arranged as shown in FIG.

  In this case, based on the detected density (maximum density) corresponding to the 90 ° phase of the density profile and the detected density (average density) corresponding to the phases of 0 ° and 180 °, the amplitude of the density profile (maximum density−average). Concentration) is calculated. Based on the calculated amplitude A and the detected average density B, a corrected density profile is specified. At this time, the period of the density profile is maintained. FIG. 9 shows a density profile Y2 (amplitude: A2, average density: B2) after correction based on the detection results of the maximum density and the average density.

  Further, for example, when the density value read from the original density profile is compared with the detected density in step S106 in FIG. 5 and the density change is remarkably large (for example, the density difference for either the maximum density or the minimum density is 10% or more), development θ (rotational speed of the developer carrier 212a / rotational speed of the photosensitive drum 213) may fluctuate, and the period of the density profile may change. Therefore, it is preferable to recreate the density profile. For example, a patch image for density profile creation is formed in a non-image area that appears intermittently during image formation, and these detection results are combined to recreate the density profile while continuing the image formation process. You can also.

  Furthermore, in step S106 of FIG. 5, when the density value read from the original density profile is compared with the detected density, the density change is extremely small and no significant difference is observed (for example, the maximum density and the minimum density). The density difference may be 3% or less), and the correction patch image formation interval may be increased. For example, every time it is determined that the density change is extremely small, the formation of one correction patch image is skipped. When the density change is continuously small, the correction patch image formation interval gradually increases. Thereby, an appropriate density profile can be maintained by consuming a smaller amount of toner. When a significant difference is recognized in the density change, the correction patch image formation interval may be reset.

  In the embodiment, a half image (halftone) is employed as the correction patch image. However, a gradation pattern may be employed in the patch image in order to cope with the difference in density unevenness for each gradation.

  Although the case where image formation is performed on roll paper has been described in the embodiment, the present invention can also be applied to the case where image formation is performed on a sheet of paper. In this case, an area corresponding to the space between the preceding sheet and the succeeding sheet is a non-image area.

  The present invention can also be applied to an image forming system including a plurality of units including an image forming apparatus. The plurality of units include, for example, external devices such as post-processing devices and network-connected control devices.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Image forming apparatus 1A Paper feeding device (paper feeding unit)
1B Image forming apparatus body 1C Winding device (winding part)
12 Operation display section 13 Image processing section 14 Paper introduction section (paper transport section)
15 Paper discharge unit (paper transport unit)
16 Main transport section (paper transport section)
17 control unit 17A density profile management unit 17B density correction unit 20 image forming unit 21 toner image forming unit 22 intermediate transfer unit 221 intermediate transfer belt (image carrier)
226 Image density detection unit 23 Fixing unit S1, S2 Sensor (rotation position detection unit)

Claims (14)

A paper transport unit for transporting paper,
An image forming unit having a rotating body including a photoconductor and a developer carrier, and forming an image on a sheet;
A density profile management unit that manages a density profile indicating density fluctuation in the sub-scanning direction in association with a phase of the density profile and a rotation position of the rotating body;
A density correction unit that creates correction data based on the density profile and performs density correction based on the correction data;
An image density detection unit for detecting a density of an image formed on the image carrier by the image forming unit;
A rotational position detector that detects the rotational position of the rotating body,
When the rotational position of the rotating body corresponds to a specific phase in the density profile and the writing position on the image carrier at this time is a non-image area, the density profile management unit Forming a correction patch image, correcting the density profile based on the detection result of the image density detection unit for the correction patch image;
The image forming apparatus, wherein the density correction unit performs density correction based on correction data created based on a corrected density profile. The concentration profile is Y = Asin (θ + α) + B
A: Density fluctuation range θ + α: Phase B: Average density
The image forming apparatus according to claim 1, wherein the density profile management unit sets at least θ + α = 90 ° and 270 ° as the specific phase. The concentration profile is Y = Asin (θ + α) + B
A: Density fluctuation range θ + α: Phase B: Average density
2. The image according to claim 1, wherein the density profile management unit sets at least one of θ + α = 90 ° and 270 ° and one of θ + α = 0 ° and 180 ° as the specific phase. Forming equipment.   The density profile management unit compares the detection result of the image density detection unit for the correction patch image formed at the position corresponding to the same phase with the density value in the original density profile, and compares the comparison result. The image forming apparatus according to claim 1, wherein the density profile is corrected based on the image quality.   The density profile management unit calculates a nearest predetermined number of average values based on the detection result of the image density detection unit for the correction patch image formed at a position corresponding to the same phase, The image forming apparatus according to claim 4, wherein the image forming apparatus is compared with a density value in a density profile.   The density profile management unit calculates a nearest predetermined number of weighted average values based on the detection result of the image density detection unit for the correction patch image formed at a position corresponding to the same phase, The image forming apparatus according to claim 5, wherein the image forming apparatus compares the density value with a density value in the density profile.   The image forming apparatus according to claim 4, wherein the density profile management unit creates the density profile anew based on the comparison result.   The image forming apparatus according to claim 4, wherein the density profile management unit changes an interval for forming the correction patch image based on the comparison result.   The image forming apparatus according to claim 1, wherein the density profile management unit manages the density profile for each rotating body. The paper transport unit is capable of transporting long paper,
10. The correction profile image according to claim 1, wherein the density profile management unit forms the correction patch image in a margin between label images formed periodically on the long paper. The image forming apparatus described in the item.   The density profile management unit is configured so that a rotation position of the rotating body corresponds to a specific phase in the density profile and a state where a writing position to the image carrier is a non-image area appears within a predetermined time. The image forming apparatus according to claim 10, wherein an interval between the label images is adjusted. A paper feed unit for feeding roll paper to the paper transport unit;
The image forming apparatus according to claim 1, further comprising: a winding unit that winds the roll paper fed from the paper transport unit. An image forming system including a plurality of units including an image forming apparatus,
A paper transport unit for transporting paper,
An image forming unit having a rotating body including a photoconductor and a developer carrier, and forming an image on a sheet;
A density profile management unit that manages a density profile indicating density fluctuation in the sub-scanning direction in association with a phase of the density profile and a rotation position of the rotating body;
A density correction unit that creates correction data based on the density profile and performs density correction based on the correction data;
An image density detection unit for detecting a density of an image formed on the image carrier by the image forming unit;
A rotational position detector that detects the rotational position of the rotating body,
When the rotational position of the rotating body corresponds to a specific phase in the density profile and the writing position on the image carrier at this time is a non-image area, the density profile management unit Forming a correction patch image, correcting the density profile based on the detection result of the image density detection unit for the correction patch image;
The image forming system, wherein the density correction unit performs density correction based on correction data created based on a corrected density profile. A density correction method in an image forming apparatus including a sheet transport unit that transports a sheet, and a rotating body including a photosensitive member and a developer carrier, and an image forming unit that forms an image on the sheet.
Managing a density profile indicating density fluctuation in the sub-scanning direction in association with the phase of the density profile and the rotational position of the rotating body;
When the rotational position of the rotating body corresponds to a specific phase in the density profile and the writing position on the image carrier at this time is a non-image area, a correction patch image is formed on the image carrier. ,
Detecting the image density of the correction patch image;
Based on the detected image density, the density profile is corrected,
Create correction data based on the corrected density profile,
A density correction method, wherein density correction is performed using created correction data.

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