JP2008216700A - Image forming apparatus and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus achieving higher image quality without lowering throughput in image forming. <P>SOLUTION: Based on an image forming starting position and an image forming finishing position in a real image forming area in a subscanning direction derived from image data formed on an image carrier, the image forming apparatus forms a patch image in a blank area existing in a leading edge area ahead of the image forming starting position or in a trailing edge area astern of the image forming finishing position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that suppresses image quality degradation when images are continuously formed, and a control method thereof.

  In an image forming apparatus, when images are continuously formed, the image quality may change. Normally, in order to correct a change in image quality, the image forming apparatus interrupts image formation and performs correction processing when a predetermined condition (for example, the number of sheets to be formed) is satisfied. In the correction process, information such as density is detected by forming a patch image, and, for example, correction is performed so as to maintain a constant toner density ratio with respect to the carrier (developer) in the developing device. Is called. However, since the correction process is performed while image formation is interrupted, the throughput of image formation is reduced.

  Patent Document 1 shows an image forming apparatus that calculates a toner replenishment amount, integrates a replenishment error amount, and forms a patch image when the accumulated value of the error amount reaches a predetermined value. The image forming apparatus described in Patent Document 1 suppresses a decrease in throughput by reducing the frequency of patch image formation.

Patent Document 2 shows an image forming apparatus that forms a patch image at a position where an image is not formed on an intermediate transfer body capable of simultaneously supporting B images. Specifically, this image forming apparatus forms a patch image in an empty area of the intermediate transfer member when a fraction is generated in A ÷ B (when it is not divisible) assuming that the number of continuously formed sheets is A. On the other hand, when the fraction does not occur (when it is divisible), the image forming apparatus forms a patch image in a vacant area with the number of image bearings of the intermediate transfer member being B-1 at a predetermined formation interval. The image forming apparatus described in Patent Document 2 suppresses a decrease in throughput by minimizing the empty area necessary for forming a patch image.
JP 09-34242 A JP 2005-165079 A

  Image forming apparatuses are required to achieve both higher productivity (throughput) and higher image quality. For this reason, it is necessary to increase the frequency of patch image formation without causing a reduction in productivity. Therefore, the above-described method for reducing the patch image formation frequency and the method for providing a minimum empty area for forming a patch image are insufficient. Since these methods keep the formation of patch images to the minimum necessary, higher image quality cannot be realized.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that realizes higher image quality without reducing the throughput of image formation.

  The present invention can be realized as an image forming apparatus, for example. The image forming apparatus includes an acquisition unit that acquires data of an image formed on a recording material, and a formation start position in the sub-scanning direction and a formation in the sub-scanning direction from the data when forming an electrostatic latent image on the image carrier. Deriving means for deriving the end position. The image forming apparatus includes a specifying unit that specifies a blank area in which an electrostatic latent image is not formed in the image forming area on the image carrier corresponding to the size of the recording material from the derived formation start position and formation end position. . The image forming apparatus includes an image forming unit that forms a patch image for correcting the image quality in the specified blank area, and a density detecting unit that detects the density of the patch image formed on the image carrier. The image forming apparatus includes a correcting unit that adjusts image forming conditions for forming an image based on the detected density to correct the image quality.

  The present invention can provide an image forming apparatus that realizes higher image quality without reducing the throughput of image formation.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. The following embodiments do not limit the invention described in the claims, and all the combinations of features described in the embodiments are essential to the solution means of the present invention. Not exclusively. Here, the description is described using a printer as the image forming apparatus. However, the image forming apparatus according to the present invention may be an apparatus that forms an image on a recording material, such as a multifunction machine, a copier, or a FAX. The present invention is realized by an electrophotographic printer as an application example. However, the present invention may be realized by a printer that employs another image printing method, such as an inkjet printer.

  The present invention provides an image forming apparatus that realizes stable image quality without reducing the throughput of image formation. For example, in a printer, when continuous printing is performed, the image quality changes. In order to keep the image quality constant, for example, it is necessary to keep the toner density ratio with respect to the carrier (developer) in the developing device constant. In order to suppress a change in image quality due to continuous printing, the printer according to the present invention forms a patch image on the image carrier, detects the density of the patch image, and executes a correction process for correcting the image quality. Further, the image forming apparatus according to the present invention is characterized in that the correction process is executed without interrupting continuous printing. Specifically, during continuous printing, a patch image is formed in a blank area where an electrostatic latent image is not formed on the image carrier, and correction processing is performed.

[First Embodiment]
The first embodiment will be described below with reference to FIGS. In the printer according to the present embodiment, based on the formation start position and the formation end position in the sub-scanning direction derived from image data formed on the image carrier, the front end region or the formation end position in front of the formation start position is used. A patch image is formed in a blank area existing in the rear end area. FIG. 1 is a cross-sectional view illustrating an example of a printer according to the first embodiment. The printer 100 includes a reader unit 150 that forms the upper part of the housing and a printer unit 170 that forms the lower part of the housing, and has an image reading function and an image forming function. The reader unit 150 reads image data to be formed from a document.

  A document feeder 180 for supplying a recording material to be a document is attached to the upper part of the reader unit 150. The printer 100 transmits and receives data to and from an external device such as a host computer via a network communication interface unit (not shown). Therefore, the printer 100 may receive image data formed from an external device. The reader unit 150 includes a scanner unit 102, scanning mirrors 105 and 106, a lens 107, a full-color image sensor unit 108, and the like. The scanner unit 102 includes a document table glass 101, a document illumination lamp 103, and a scanning mirror 104.

  On the platen glass 101, a document fed by the document feeding device 180 or a document set manually is placed. The scanner unit 102 is driven by a motor (not shown), and reciprocates in a predetermined direction. The document illumination lamp 103 is a light source that emits light that irradiates the document. When the scanner unit 102 scans a document placed on the platen glass 101, the reflected light image of the light irradiated on the document by the document illumination lamp 103 is input to the lens 107 via the scanning mirrors 104, 105, and 106. Is done. The input reflected light image is formed on the CCD sensor in the full-color image sensor unit 108 formed integrally with the RGB three-color separation filter through the lens 107. As a result, the full-color image sensor unit 108 obtains an analog signal of an image separated for each color. This analog signal is amplified and digitized by an amplifier circuit.

  The document feeder 180 includes a document stacking unit on which a document bundle to be copied is stacked, and a feeding mechanism that feeds documents one by one from the document bundle loaded in the document stacking unit. Specifically, the document feeder 180 feeds documents one by one from the document bundle onto the document table glass 101 and discharges the documents when reading of the documents is completed. The document feeder 180 repeats this series of processes for the number of documents.

  The printer unit 170 includes an image forming unit 110 that functions as an image forming unit that forms an image on a recording material. The image forming unit 110 includes an exposure unit 109, a photosensitive drum 111, a cleaning unit 112, a pre-exposure lamp 113, a primary charger 114, a black developing unit 115, a color developing unit 116, an intermediate transfer belt 117, a primary transfer roller 118, and A cleaning unit 121 is provided. The exposure unit 109 includes a semiconductor laser that is a laser beam generation unit, a polygon scanner, and the like. As a result, the exposure unit 109 irradiates the photosensitive drum 111 with laser light modulated based on the image signal output from the full-color image sensor unit 108. The photosensitive drum 111 is rotationally driven in the direction of the arrow shown in FIG. 1, is neutralized by the pre-exposure lamp 113, and is uniformly charged at a predetermined potential by the primary charger 114. Thereafter, an electrostatic latent image is formed by the laser light emitted from the exposure unit 109. The electrostatic latent image formed on the photosensitive drum 111 is developed with toner by a black developing unit 115 and a color developing unit 116 that function as a developer carrier. The color developing unit 116 includes developing units 122, 123, and 124 corresponding to yellow, magenta, and cyan, respectively, and rotates as necessary to develop the electrostatic latent image.

  According to the present embodiment, the printer 100 includes a contact / separation mechanism that contacts or separates the photosensitive drum 111 and the primary transfer roller 118. This is necessary in order to properly use the case where the image is transferred to the intermediate transfer belt 117 functioning as a transfer body and the case where the image is not transferred when the image formed on the photosensitive drum 111 reaches the transfer position. Specifically, when a patch image is formed on the photosensitive drum 111, the printer 100 separates the photosensitive drum 111 from the primary transfer roller 118. As a result, the patch image developed on the photosensitive drum 111 is not primarily transferred to the intermediate transfer belt 117 but sent to the density detection sensor 119. The density detection sensor includes, for example, an optical sensor, and detects reflected light that irradiates the patch image with light. As a result, the printer 100 detects the density of the patch image. Further, the patch image developed on the photosensitive drum 111 is conveyed to the cleaning unit 112, and is scraped off and discarded by a blade provided in the cleaning unit 112. The cleaning unit 121 scrapes and discards the patch image transferred to the intermediate transfer belt 117 in the same manner as the cleaning unit 112.

  On the other hand, when the actual image to be transferred to the recording material is formed on the photosensitive drum 111, the printer 100 brings the photosensitive drum 111 and the primary transfer roller 118 into contact with each other. As a result, the actual image formed on the photosensitive drum 111 is transferred to the intermediate transfer belt 117 and transferred to the recording material at the secondary transfer position. The contact / separation mechanism is configured to control whether an image developed on the photosensitive drum 111 is transferred to the intermediate transfer belt 117 depending on whether a primary transfer bias is applied to the primary transfer roller 118. Also good. Further, the contact / separation mechanism may have another mechanism for controlling whether or not the image developed on the photosensitive drum 111 is transferred to the intermediate transfer belt 117.

  In addition to the components described above, the printer unit 170 includes a registration roller, a secondary transfer roller, a conveyance belt, a heat roller fixing device (hereinafter abbreviated as a fixing device), a paper discharge flapper, a recording material cassette, a refeed roller, and a discharge roller. And a manual feed tray. However, these constituent elements are not necessary constituent elements for explaining the present invention, and the description thereof will be omitted.

  FIG. 2 is a diagram illustrating a control block of the printer according to the first embodiment. The reader control unit 200 is a processing unit that controls the document feeder 180 and the reader unit 150, and is a processing unit that mainly performs document feeding and image reading. The reader control unit 200 includes a CPU 201, ROM 202, RAM 203, EEPROM 204, I / O 205, and image processing unit 206.

  The CPU 201 is a central processing unit that controls the entire reader unit. The ROM 202 is a read-only memory that stores a control procedure (control program) for the document feeder 180 and the reader unit 150. The CPU 201 controls each component of the document feeder 180 and the reader unit 150 according to the control procedure stored in the ROM 202. A RAM 203 is a main storage device used as a storage area for input data and a work area. The EEPROM 204 is an erasable read-only memory that holds control parameters and the like of each component included in the reader unit 150. An I / O 205 is an input / output IC that inputs a control signal output from the CPU 201 to a load such as a motor and a signal from a sensor or the like and sends the signal to the CPU 201. The image processing unit 206 performs shading correction on the image data read by the CCD sensor in the full-color image sensor unit 108 and performs control for transmission to the controller unit 220 described later.

  The controller unit 220 performs overall control related to a print job while issuing an image reading or image forming instruction to the reader unit 150 and the printer unit 170. The controller unit 220 includes a CPU 221, ROM 222, RAM 223, SRAM 224, image processing unit 225, image memory 226, and network I / F 227. The CPU 221 is connected to an operation unit 260 that receives input from the operator.

  The CPU 221 is a central processing unit that controls the entire printer 100. In addition, the CPU 221 includes an acquisition unit 271 that functions as an acquisition unit. The acquisition unit 271 acquires image data formed on the recording material from the external device via the reader control unit 200 or the network I / F 227. The ROM 222 is a read-only memory that stores a control procedure (control program) of the printer 100. The CPU 221 controls each component of the printer 100 according to the control procedure stored in the ROM 222. The RAM 223 is a main storage device used as a storage area for input data or work. The CPU 221 accepts input from various keys provided in the operation unit 260 via the bus and appropriate I / O, and further displays necessary information on the display on the panel. The SRAM 224 is a RAM that holds data such as adjustment values and the total number of prints that must be held even after the main power is turned off. The SRAM 224 is connected to a battery (not shown) and stores the held information. Back up.

  The image processing unit 225 processes image data to be formed acquired by the acquisition unit 271. For example, the image processing unit 225 performs processing such as scaling in accordance with an instruction from the operator, and further transmits image data to be formed on the printer unit 170 described later through writing and reading of image data to and from the image memory 226. In addition, the image processing unit 225 includes a derivation unit 272, a specification unit 273, and a determination unit 274. The deriving unit 272 functions as deriving means, and derives a formation start position in the sub-scanning direction and a formation end position in the sub-scanning direction from the acquired image data when forming an electrostatic latent image on the photosensitive drum 111. The specifying unit 273 functions as a specifying unit, and specifies a blank area where an electrostatic latent image is not formed in the image forming area on the photosensitive drum 111 corresponding to the size of the recording material from the derived formation start position and formation end position. To do. The determination unit 274 functions as a determination unit, and determines whether the size of the specified blank area is larger than the size of the patch image. The image memory 226 stores the acquired image data and the derived formation start position and formation end position.

  The printer control unit 240 is a processing unit that controls the printer unit 170. The printer control unit 240 is a series of processes related to image formation on a recording material, that is, recording material conveyance control, electrostatic latent image formation and development, and recording material. Transfer to and fix on. The printer control unit 240 controls patch image formation, reading, and cleaning. The printer control unit 240 includes a CPU 241, ROM 243, RAM 244, I / O 245, EEPROM 246, pattern generator 247, and exposure control unit 248.

  The CPU 241 is a central processing unit that controls the entire printer unit 170. The CPU 241 includes a density detection unit 275 and a correction unit 276. The density detection unit 275 functions as density detection means, and detects the density of the patch image formed on the photosensitive drum 111 using the density detection sensor 119. The correction unit 276 functions as a correction unit, and adjusts image formation conditions for forming an image based on the density of the patch image detected by the density detection unit 275 to correct the image quality of the formed image. For example, when the toner consumed by image formation is replenished, the correction unit 276 replenishes the toner (carrier) so as to maintain a constant ratio. The ROM 243 is a read-only memory that stores a control procedure (control program) of the printer unit 170. The CPU 241 controls each component of the printer unit 170 according to the control procedure stored in the ROM 243. The RAM 244 is a main storage device used as a storage area for input data and work. The I / O 245 is an input / output IC that inputs a control signal output from the CPU 241 to a load such as a motor and a signal from a sensor or the like and sends the signal to the CPU 241. The exposure control unit 248 controls the laser emission of the exposure unit 109 based on the image data transmitted from the image processing unit 225 in the controller unit 220 to form an electrostatic latent image.

  The image data of the patch image is generated by a pattern generator 247 provided in the printer control unit 240, and the generated image data is transmitted to the exposure control unit 248. Thereafter, the exposure control unit 248 forms an electrostatic latent image as a patch image on the photosensitive drum 111 based on the transmitted image data. Note that the CPU 201 and the CPU 221 are connected to the CPU 221 and the CPU 241 by serial connection. Thus, necessary data such as document size, recording material size, and color information can be exchanged between the CPUs.

  Next, a method for specifying a blank area where an electrostatic latent image is not formed will be described with reference to FIGS. FIG. 3 is a diagram illustrating how the acquired image data is stored in the image memory. Here, as shown in FIG. 3, the image to be formed is a document image 301 including photographic data x and character data y.

  When the document image 301 is acquired, the document image 301 is decomposed into image data 302, 303, 304, and 305 of each component of yellow (Y), magenta (M), cyan (C), and black (K). And stored in the image memory 226. Here, the image forming area in the sub-scanning direction in which the photosensitive drum 111 rotates is an area having a width a shown in FIG. However, the area of the electrostatic latent image that is actually formed (that is, the area where the toner image is actually formed on the photosensitive drum 111, hereinafter referred to as the actual image forming area) is indicated by b and b ′ in the figure. It becomes an area. The image forming area refers to an area having a size for image formation designated by the operator or an area corresponding to the size of the recording material. According to the present embodiment, a patch image is formed in an area (blank area) where no electrostatic latent image is formed in this image forming area.

  FIG. 4 is a diagram for explaining a method for deriving the formation start position and the formation end position in the sub-scanning direction of the image data separated for each color component. Here, a method of deriving the formation start position Ca and the formation end position Cb of the electrostatic latent image actually formed from the image data is shown. These derivations are performed by the derivation unit 272.

  First, the image processing unit 225 stores the image data sequentially sent from the image processing unit 206 in the image memory 226. The image data is two-dimensionally stored in the image memory 226 in correspondence with the main scanning direction and the sub-scanning direction. The image data is stored after being decomposed into image data 302, 303, 304, and 305 for each of the Y component, M component, C component, and K component. Here, the main scanning direction corresponds to the axial direction of the photosensitive drum 111, and the sub-scanning direction corresponds to the rotational direction of the photosensitive drum 111.

  The formation start position Ca and the formation end position Cb of the electrostatic latent image are determined from the storage addresses in the sub-scanning direction of the image memory 226 stored for the image data 302 to 305 for each color component. For example, in the case of Y component image data 302, a value of 0 is stored in a portion where there is no image and a value other than 0 is stored in a portion where the image is present, corresponding to the main scanning direction and the sub-scanning direction. Is done. The formation start position Ca and the formation end position Cb of the Y component image data 302 are determined from the first address and the last address in the sub-scanning direction in which values other than 0 of a certain part of the image are stored. Deriving unit 272 derives. The specifying unit 273 specifies the actual image forming area and the blank area from the derived formation start position Ca and formation end position Cb. Similarly, the deriving unit 272 derives the formation start position Ca and the formation end position Cb for each image for the M component, the C component, and the K component. The formation start position Ca and the formation end position Cb for each color component image are latched until the image formation is completed.

  Furthermore, the formation start position Ca and the formation end position Cb may be derived by the method described below. Here, the Y component image data 302 input to the deriving unit 272 will be described. When an image writing timing signal is input as a trigger, the deriving unit 272 starts counting the number of input lines from the leading edge Cs, which is the Y component image forming area, using a clock synchronized with the image (line) in the sub-scanning direction. . At the same time, the deriving unit 272 determines the presence / absence of image data (pixels), and latches the count value when the first image-formed line appears in the register in the image processing unit 225 as CTa. The counter value CTa at this time becomes the formation start position Ca. The deriving unit 272 continues counting thereafter and detects a line in which image formation disappears. Upon detection, the deriving unit 272 subtracts a clock corresponding to one line from the count value CTb + 1 to obtain CTb, and latches it in a register in the image processing unit 225. The deriving unit 272 continues counting thereafter, and clears the count when a count value corresponding to the rear end Ce of the image forming area is reached. The count value, which is the rear end Ce of the image forming area, stores in advance a value corresponding to an area designated for image formation by the operator or an area corresponding to the size of the recording material. The count values CTa and CTb for each color component are latched until the image formation is completed. Similar processing is performed on the image data 303 to 305 of other color components.

  According to the present embodiment, the specifying unit 273 blanks an area between the leading edge Cs of the image forming area and the formation start position Ca, or an area between the trailing edge Ce of the image forming area and the formation end position Cb. Specify as an area. Further, the image forming unit 110 forms a patch image in the specified blank area.

  Next, a method of forming an electrostatic latent image from the formation start position Ca and the formation end position Cb of the image data 302 to 305 of each color component shown in FIG. The CPU 241 determines the operation timing of image formation based on the formation start position Ca and the formation end position Cb of the derived image data 302 to 305 for each color. At that time, the image data to be output to the printer unit 170 is processed by the image processing unit 225, but is not output to the printer unit 170 as it is, but is temporarily stored in the image memory 226. Thereafter, the image data is read again from the image memory 226 using the image writing timing signal as a trigger and output to the printer control unit 240. The image formation for the image data 302 is started after a time corresponding to the formation start position Ca from the front end Cs has elapsed. Thereafter, the image formation ends after a time corresponding to the end point Cs to the formation end position Cb has elapsed. Similarly, image formation is performed on the image data 303 to 305 in a section corresponding to the actual image formation area.

  FIG. 5 is a diagram for explaining a method by which the specifying unit according to the first embodiment specifies the size of the blank area. Here, a method in which the specifying unit 273 specifies a blank area and a method in which the determination unit 274 determines whether the specified blank area is larger than the size of the patch image will be described. The area for forming the patch image is generally 1 to 4 cm 2. Therefore, the determination unit 274 determines whether or not the width (length) Dt between the leading edge Cs of the image forming area and the leading edge Ca of the actual image forming area has a predetermined length (for example, 2 cm). .

  More specifically, the specifying unit 273 specifies the length Dt of the blank area which is the tip area as Dt = | Cs−Ca |. On the other hand, the specifying unit 273 specifies the length Db of the blank area as the rear end area as Db = | Cb−Ce |. Further, according to the present embodiment, the length D necessary for forming a patch image is predetermined as D = dp + dr. Here, dp indicates the number of lines in the sub-scanning direction of the patch image, and dr indicates the number of lines on which the toner image on the photosensitive drum 111 advances while the primary transfer roller 118 is separated from the photosensitive drum 111. In other words, the predetermined length D is the size of the patch image and until the photosensitive drum 111 and the primary transfer roller 118 are separated from the contact state so that the patch image is not transferred to the intermediate transfer belt 117. It is set in consideration of time. Therefore, the determination unit 274 determines whether or not at least one of Dt and Db is longer than D. This is performed for the image data of each color component.

  In the case where the primary transfer roller 118 and the photosensitive drum 111 are not provided with a contact / separation mechanism and only the bias value of the primary transfer bias is switched, the predetermined length D is the bias length. It is set in consideration of the value switching time. That is, assuming that the number of lines on which the toner image on the photosensitive drum 111 travels from ON to OFF and from OFF to ON is dv, a predetermined length D is obtained as D = dp + dv.

  Next, control when forming a patch image will be described with reference to FIG. FIG. 6 is a flowchart illustrating a procedure for forming a patch image according to the first embodiment. The procedure described below is performed for each color. Here, the Y component will be described as an example.

  In step S <b> 601, the CPU 221 acquires image data by the acquisition unit 271, stores the image data in the image memory 226, and derives the formation start position and the formation end position. Subsequently, in step S602, the specifying unit 273 specifies the blank area of the front end area and the blank area of the rear end area from the derived formation start position and formation end position.

  Next, the determination unit 274 determines whether or not the length Dt of the blank area of the tip area exceeds a predetermined length D. Here, it is desirable that the determination unit 274 also determines whether or not m or more images have been formed since the previous patch image formation for the same component. This is a determination that is made to reduce useless correction processing, whereby toner for forming a patch image can be reduced. When Dt> D is satisfied, in step S604, the image forming unit 110 first starts forming a patch image in the blank area of the leading end area in accordance with the image forming timing of the component of the page. Subsequently, in step S605, the image forming unit 110 forms a real image in the real image forming area. Details of these image forming procedures will be described later with reference to FIG.

  On the other hand, if Dt> D is not satisfied, that is, if a patch image cannot be formed with the size of the blank area existing in the front end area, in step S607, the determination unit 274 determines the length Db of the blank area existing in the rear end area. Is longer than a predetermined length D. As in S603, the determination unit 274 desirably determines whether m or more images have been formed since the previous patch image formation with the same component. If Db> D is satisfied, in step S608, the image forming unit 110 forms a real image in the real image forming area. Subsequently, in step S609, the image forming unit 110 forms a patch image in the blank area of the rear end area. Details of these image forming procedures will be described later with reference to FIG.

On the other hand, if Db> D is not satisfied, that is, if the patch image cannot be formed with the size of the blank area in the leading end area and the trailing end area, in step S610, the image forming unit 110 does not form a patch image and Perform image formation. Here, when the number of sheets formed since the previous patch image is formed exceeds the predetermined number m, it is desirable that the image forming unit 110 interrupts the formation of the actual image and forms the patch image. . Specifically, the image forming unit 110 forms a patch image by extending an image forming interval on continuous recording materials to a range where a patch image can be formed. That is, the image forming unit 110 temporarily interrupts the formation of the actual image and forms the patch image. Thereafter, the same processing is performed in the order of M component data, C component data, and K component data, which are the next color components.
Thereafter, the density detector 275 detects the density of the formed patch image. Further, the correction unit 276 corrects the image quality by adjusting image forming conditions for forming an image based on the detected density. Here, the image forming conditions are, for example, the replenishment amount of consumed toner and the amount of light at the time of exposure in order to keep the developer and toner at a constant ratio.

  FIG. 7 is a diagram illustrating a control procedure for forming a patch image in the blank area of the tip area according to the first embodiment. Here, the vertical axis indicates the positions of the exposure unit 109, the black development unit 115, the color development unit 116, the primary transfer roller 118, the density detection sensor 119, and the cleaning unit 112 in the image forming unit 110. The abscissa represents time, and shows the movement from exposure to development, primary transfer, density detection, and cleaning over time. A broken line 701 indicates the rear end of the image forming area in the previous image. A solid line 702 indicates the tip of the image forming area in the current image. An alternate long and short dash line 703 indicates a formation start position, and an alternate long and short dash line 704 indicates a formation end position. A broken line 705 indicates the rear end of the image forming area in the current image. Here, it is assumed that the patch image 721 is formed in the tip region between the solid line 702 and the alternate long and short dash line 703. Furthermore, as shown in FIG. 7, it is assumed that image data 700 is formed.

  First, in the exposure unit 109, an electrostatic latent image of the patch image 721 is formed. Subsequently, when the formation of the patch image 721 is completed, the exposure unit 109 performs exposure to form an electrostatic latent image of the real image 720 between the formation start position and the formation end position. The development units (115, 116) are driven between the solid line 702 and the alternate long and short dash line 704 to develop the patch image 721 and the real image 720, as indicated by a timing 711. The primary transfer roller 118 is driven between the alternate long and short dash line 703 and the alternate long and short dash line 704 to transfer only the actual image 720 to the intermediate transfer belt 117 as indicated by timing 712. This driving means that the primary transfer roller 118 contacts the photosensitive drum 111 as described above. On the other hand, when not driven, the primary transfer roller 118 is separated from the photosensitive drum 111. The density detection sensor 119 detects the density of the patch image 721 formed on the photosensitive drum 111 between the solid line 702 and the alternate long and short dash line 703, as indicated by the timing 713. As indicated by timing 714, the cleaning unit 112 is driven between the solid line 702 and the one-dot chain line 704, and scrapes and collects all the toner that forms the patch image 721 with a blade. Further, the cleaning unit 112 collects residual toner of the actual image 720 remaining on the photosensitive drum 111 after being transferred to the intermediate transfer belt 117 by scraping with a blade.

  FIG. 8 is a diagram illustrating a control procedure for forming a patch image in the blank area of the rear end area according to the first embodiment. Here, the vertical axis indicates the positions of the exposure unit 109, the black development unit 115, the color development unit 116, the primary transfer roller 118, the density detection sensor 119, and the cleaning unit 112 in the image forming unit 110. The abscissa represents time, and shows the movement from exposure to development, primary transfer, density detection, and cleaning over time. A solid line 801 indicates the tip of the image forming area in the current image. An alternate long and short dash line 802 indicates the formation start position, and an alternate long and short dash line 803 indicates the formation end position. A broken line 804 indicates the rear end of the image forming area in the current image. A solid line 805 indicates the tip of the image forming area in the next image. Here, it is assumed that the patch image 821 is formed in the rear end region between the alternate long and short dash line 803 and the broken line 804. Furthermore, as shown in FIG. 8, it is assumed that a real image 820 is formed.

  First, an electrostatic latent image of the real image 820 is formed in the exposure unit 109. Subsequently, when the formation of the real image 820 is completed, the exposure unit 109 performs exposure to form an electrostatic latent image of the patch image 821 in the rear end region. The development units (115, 116) are driven between the alternate long and short dash line 802 and the broken line 804 as shown in the timing 811 to develop the actual image 820 and the patch image 821. The primary transfer roller 118 is driven between the alternate long and short dash line 802 and the alternate long and short dash line 803 as shown at a timing 812, and transfers only the actual image 820 to the intermediate transfer belt 117. The density detection sensor 119 detects the density of the patch image 821 formed on the photosensitive drum 111 between the alternate long and short dash line 803 and the broken line 804 as indicated by a timing 813. As indicated by timing 814, the cleaning unit 112 is driven between the solid line 801 and the broken line 804, and scrapes and collects all the toner forming the patch image 821 with a blade. Further, the cleaning unit 112 collects residual toner of the actual image 820 remaining on the photosensitive drum 111 after being transferred to the intermediate transfer belt 117 by scraping with a blade.

  As described above, in this embodiment, as an application example, a patch image is applied to the leading end region from the leading end of the image forming region to the forming start position, or the trailing end region from the forming end position to the trailing end of the image forming region. An example of forming was described. However, the front end area may be from the rear end of the previous image formation area to the current formation start position, and the rear end area may be from the current formation end position to the front end of the next image formation area. Thereby, a sufficient size of the blank area can be secured.

  As described above, the image forming apparatus according to the present embodiment identifies a blank area in the image forming area and forms a patch image in the blank area. Further, the image forming apparatus detects the density of the formed patch image and corrects the image quality based on the detected density. As a result, the image forming apparatus can achieve higher image quality without reducing the throughput of image formation.

  The present invention is not limited to the above embodiment, and various modifications are possible. The image forming apparatus may determine whether the size of the specified blank area is larger than the size of the patch image. As a result, the image forming apparatus forms a patch image in a blank area when it is determined to be large, and the image forming interval on a continuous recording material when it is determined as small is within a range where a patch image can be formed. A patch image may be formed by spreading it. Therefore, since the image forming apparatus changes the patch image forming position to the optimum position in accordance with the image data to be formed, the image quality can always be kept constant.

  The image forming apparatus may specify a blank area between the previous image formation end position and the next image formation start position. Thus, the image forming apparatus can specify the blank area beyond the image forming area to be formed this time, and can easily secure the area for forming the patch image.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS. 9 to 14. In the present embodiment, a patch image is formed in an intermediate area between a plurality of electrostatic latent images formed in the image forming area. In addition, below, the description which overlaps with 1st Embodiment is abbreviate | omitted. FIG. 9 is a diagram illustrating how the acquired image data is stored in the image memory.

  When the image data 901 of the document image is acquired, the document image is image data 902, 903, 904, 905 of each component of yellow (Y), magenta (M), cyan (C), and black (K), respectively. And stored in the image memory 226. Here, the image forming area in the sub-scanning direction in which the photosensitive drum 111 rotates is an area having a width a shown in FIG. However, the actual image forming areas are areas b and b 'in the drawing. The specifying unit 273 according to the present embodiment specifies an intermediate area 906 between the electrostatic latent image having the width b and the electrostatic latent image having the width b ′ in the K component image data 905 as a blank area.

  FIG. 10 is a diagram illustrating a method for deriving the formation start position and the formation end position in the sub-scanning direction of the image data separated for each color component. Here, a method of deriving the formation start positions Ca and Cc and the formation end positions Cb and Cd of the electrostatic latent image actually formed from the image data is shown. These derivations are performed by the derivation unit 272.

  First, the image processing unit 225 stores the image data sequentially sent from the image processing unit 206 in the image memory 226. The image data is two-dimensionally stored in the image memory 226 in correspondence with the main scanning direction and the sub-scanning direction. The image data is stored after being decomposed into image data 902, 903, 904, and 905 for each color component of Y, M, C, and K. Here, the main scanning direction corresponds to the axial direction of the photosensitive drum 111, and the sub-scanning direction corresponds to the rotational direction of the photosensitive drum 111.

  The electrostatic latent image formation start positions Ca and Cc and the formation end positions Cb and Cd are determined from the storage addresses in the sub-scanning direction of the image memory 226 stored for each color component image data 902 to 905. The Y component, M component, and C component image data 902, 903, and 904 are the same as the image data 302, 303, and 304, and thus description thereof is omitted. On the other hand, in the case of the K component image data 905, since the intermediate region 906 exists, the deriving unit 272 derives two formation start positions Ca and Cc and formation end positions Cb and Cd, respectively.

Furthermore, the formation start positions Ca and Cc and the formation end positions Cb and Cd may be derived by the method described below. Here, the K component image data 302 input to the deriving unit 272 will be described. When an image writing timing signal is input as a trigger, the deriving unit 272 starts counting the number of input lines from the leading edge Cs, which is the K component image forming area, using a clock synchronized with the image (line) in the sub-scanning direction. . At the same time, the deriving unit 272 determines the presence / absence of image data (pixels), and latches the count value when the first image-formed line appears in the register in the image processing unit 225 as CTa. The count value CTa at this time is the formation start position. The deriving unit 272 continues counting thereafter and detects a line in which image formation disappears. Upon detection, the deriving unit 272 subtracts a clock corresponding to one line from the count value CTb + 1 to obtain CTb, and latches it in a register in the image processing unit 225. The deriving unit 272 continues counting thereafter and determines the presence or absence of image data. Here, the count value when a line on which an image is formed again appears is latched in the register in the image processing unit 225 as CTc. The counter value CTc at this time is the second formation start position. Thereafter, the deriving unit 272 detects a line in which image formation disappears again. Upon detection, the deriving unit 272 subtracts a clock corresponding to one line from the count value CTd + 1 to obtain CTd, and latches it in a register in the image processing unit 225. The deriving unit 272 continues counting thereafter, and clears the count when a count value corresponding to the rear end Ce of the image forming area is reached. The count values CTa, CTb, CTc, CTd are latched until the image formation is completed. Accordingly, the actual image forming area in the image data 905 is two areas between the formation start position Ca and the formation end position Cb and between the formation start position Cc and the formation end position Cd. The intermediate area 906 is between these two areas.

  As described above, the deriving unit 272 according to the present embodiment determines the presence / absence of image data from the front end Cs to the rear end Ce on the assumption that there are a plurality of real image areas in the image forming area. Latch the count value when the status changes. Here, when the state changes, the case where the image data changes from a state showing a zero value to a state showing a non-zero value and the state where the image data shows a non-zero value change to a state where a zero value is shown. Indicates the case.

  FIG. 11 is a diagram for explaining a method by which the specifying unit according to the second embodiment specifies the size of the blank area. Here, a method in which the specifying unit 273 specifies a blank area and a method in which the determination unit 274 determines whether the specified blank area is larger than the size of the patch image will be described.

  As illustrated in FIG. 11, in the case of the Y component, the M component, and the C component, the specifying unit 273 specifies the length Dm of the blank area as Dm = | Cb−Ce |. On the other hand, in the case of the K component, the specifying unit 273 specifies the length Dn of the blank area as Dn = | Cb−Cc |. Similar to the first embodiment, the length D required to form a patch image is predetermined as D = dp + dr. Therefore, the determination unit 274 determines whether or not the lengths Dm and Dn of the blank area in each color component are longer than the predetermined length D. Thereby, the determination unit 274 determines that the patch image can be formed in the blank area when the length Dm or Dn is longer than the length D, and the patch image is formed in the blank area when the length Dm or Dn is shorter. Judge that it is impossible.

The specifying unit 273 also obtains the length Dt = | Cs−Ca | of the blank area that is the front end area and the length Db = | Cd−Ce | of the blank area that is the other rear end area. The description is omitted because it can be applied.

Next, control when forming a patch image will be described with reference to FIG. FIG. 12 is a flowchart illustrating a procedure for forming a patch image according to the second embodiment. Here, as an example, a case where the image data 901 described with reference to FIGS. 9 to 11 is formed will be described.

  In step S1201, the CPU 221 acquires image data by the acquisition unit 271 and stores the image data in the image memory 226, and derives the formation start positions Ca and Cc and the formation end positions Cb and Cd. Subsequently, in step S1202, the specifying unit 273 specifies blank areas of the leading end area, the intermediate area, and the trailing end area from the derived formation start positions Ca and Cc and formation end positions Cb and Cd.

  Next, the determination unit 274 determines whether or not the length Dn of the blank area in the intermediate area is longer than a predetermined length D. In addition, the determination unit 274 determines whether or not the lengths of the front end region and the rear end region are also longer than a predetermined length D. Here, it is desirable that the determination unit 274 also determines whether or not images have been formed on m sheets or more since the previous patch image formation for the same component. This is a determination that is made to reduce useless correction processing, whereby toner for forming a patch image can be reduced. If Dn, Dm, Dt, and Db> D are not satisfied, in step S1211, the image forming unit 110 forms a normal image without forming a patch image.

  On the other hand, when Dn, Dm, Dt, and Db> D are satisfied, in step S1204, the image forming unit 110 determines whether the formation of the actual image is first or the formation of the patch image is first. If the real image is formed first, in step S1205, the image forming unit 110 first starts forming the real image in accordance with the image formation timing of the color component of the page. In step S1206, the image forming unit 110 forms a patch image in the specified blank area (here, the intermediate area or the rear end area). Thereafter, the image forming unit 110 shifts the process to step S1207. On the other hand, if the patch image is formed first, in step S1209, the image forming unit 110 forms a patch image in the specified blank area (here, the leading end area). Subsequently, in step S1210, the image forming unit 110 forms an actual image in accordance with the image formation timing of the color component of the page. Thereafter, the image forming unit 110 shifts the process to step S1207.

  Next, in step S1207, the image forming unit 110 further determines whether or not the formation of the actual image remains. If not, the image forming unit 110 ends the process and shifts to the next color component or next page process. On the other hand, if still remaining, in step S1208, the image forming unit 110 forms a second real image. Thereafter, the image forming unit 110 ends the processing and shifts to the processing of the next color component or the next page. Thereafter, the density detector 275 detects the density of the formed patch image. Further, the correction unit 276 corrects the image quality by adjusting image forming conditions for forming an image based on the detected density. Here, the image forming conditions are, for example, the replenishment amount of consumed toner and the amount of light at the time of exposure in order to keep the developer and toner at a constant ratio.

  In the case of forming a patch image in the tip region, the process is performed in the order of S1209, S1210, and S1207, and the process ends. When a patch image is formed in the intermediate area, the process is performed in the order of S1205, S1206, S1207, and S1208, and the process ends. In the above-described example, the K component image data 905 corresponds to this procedure. When a patch image is formed in the rear end area, the process is performed in the order of S1205, S1206, and S1207, and the process ends. In the above-described example, the image data of the Y component, M component, and C component image data 902, 903, and 904 corresponds to this procedure.

  FIG. 13 is a diagram illustrating a control procedure for forming a patch image in the blank area of the rear end area according to the second embodiment. Here, the control procedure of the Y component image data 902 will be described. Also, the M component and C component image data 903 and 904 are similar to the procedure described below. Here, the vertical axis indicates the positions of the exposure unit 109, the black development unit 115, the color development unit 116, the primary transfer roller 118, the density detection sensor 119, and the cleaning unit 112 in the image forming unit 110. The abscissa represents time, and shows the movement from exposure to development, primary transfer, density detection, and cleaning over time. A solid line 1301 indicates the tip of the image forming area in the current image. An alternate long and short dash line 1302 indicates a formation start position, and an alternate long and short dash line 1303 indicates a formation end position. A broken line 1304 indicates the rear end of the image forming area in the current image. A solid line 1305 indicates the tip of the image forming area in the next image. Here, it is assumed that the patch image 1321 is formed in the rear end region between the alternate long and short dash line 1303 and the broken line 1304. Furthermore, it is assumed that image data 902 is formed as shown in FIG.

  First, an electrostatic latent image of the actual image 1320 is formed in the exposure unit 109. Subsequently, when the formation of the actual image 1320 is completed, the exposure unit 109 performs exposure to form an electrostatic latent image of the patch image 1321 in the rear end region. The development units (115, 116) are driven between the alternate long and short dash line 1302 and the broken line 1304 as shown at a timing 1311 to develop the actual image 1320 and the patch image 1321. The primary transfer roller 118 is driven between an alternate long and short dash line 1302 and an alternate long and short dash line 1303 as shown at timing 1312, and transfers only the actual image 1320 to the intermediate transfer belt 117. The density detection sensor 119 detects the density of the patch image 1321 formed on the photosensitive drum 111 between the alternate long and short dash line 1303 and the broken line 1304 as indicated by a timing 1313. The cleaning unit 112 is driven between a solid line 1301 and a broken line 1304 as indicated by a timing 1314, and scrapes and collects all the toner forming the patch image 1321 with a blade. Further, the cleaning unit 112 collects residual toner of the actual image 1320 remaining on the photosensitive drum 111 after being transferred to the intermediate transfer belt 117 by scraping with a blade.

  FIG. 14 is a diagram illustrating a control procedure for forming a patch image in the blank area of the intermediate area according to the second embodiment. Here, a control procedure of the K component image data 905 will be described. Here, the vertical axis indicates the positions of the exposure unit 109, the black development unit 115, the color development unit 116, the primary transfer roller 118, the density detection sensor 119, and the cleaning unit 112 in the image forming unit 110. The abscissa represents time, and shows the movement from exposure to development, primary transfer, density detection, and cleaning over time. A broken line 1401 indicates the rear end of the image forming area in the previous image. A solid line 1402 indicates the tip of the image forming area in the current image. An alternate long and short dash line 1407 indicates the formation start position of the actual image 1420. An alternate long and short dash line 1403 indicates the position where the actual image 1420 is formed. An alternate long and short dash line 1404 indicates the formation start position of the actual image 1422. An alternate long and short dash line 1408 indicates the position where the actual image 1422 is formed. A solid line 1405 indicates the rear end of the image forming area in the current image. A broken line 1406 indicates the tip of the image forming area in the next image. Here, it is assumed that the patch image 1421 is formed in an intermediate region between the alternate long and short dash line 1403 and the alternate long and short dash line 1404.

  First, an electrostatic latent image of the actual image 1420 is formed in the exposure unit 109. Subsequently, when the formation of the actual image 1420 is completed, the exposure unit 109 performs exposure to form an electrostatic latent image of the patch image 1421 in the intermediate area. Further, when the formation of the patch image 1421 is completed, the exposure unit 109 performs exposure to form an electrostatic latent image of the actual image 1422. The development units (115, 116) are driven between the alternate long and short dash line 1407 and the alternate long and short dash line 1408 as shown at timing 1411 to develop the actual image 1420, the patch image 1421, and the actual image 1422. The primary transfer roller 118 is driven between the one-dot chain line 1407 and the one-dot chain line 1403 and between the one-dot chain line 1404 and the one-dot chain line 1408 as shown in the timing 1412, and only the actual images 1420 and 1422 are intermediately transferred. Transfer to belt 117. The density detection sensor 119 detects the density of the patch image 1321 formed on the photosensitive drum 111 between the one-dot chain line 1403 and the one-dot chain line 1404 as indicated by a timing 1413. The cleaning unit 112 is driven between the solid line 1402 and the solid line 1405 as indicated by a timing 1414, and scrapes and collects all the toner forming the patch image 1421 with a blade. Further, the cleaning unit 112 collects residual toner of the actual images 1420 and 1422 remaining on the photosensitive drum 111 after being transferred to the intermediate transfer belt 117 by scraping with a blade.

  As described above, the printer 100 according to the present embodiment identifies a blank area as an intermediate area and forms a patch image. However, the image forming apparatus may be realized in combination with the first embodiment. That is, the image forming apparatus first sets at least one of the blank areas specified in the leading edge area and the trailing edge area when at least one of the blank areas specified in the leading edge area and the trailing edge area is larger than the size of the patch image. A patch image is formed. Further, the image forming apparatus is configured when both the blank area specified in the front end area and the rear end area are smaller than the size of the patch image, and the blank area specified in the intermediate area is larger than the size of the patch image. The patch image may be formed in the blank area specified by the intermediate area. Further, the image forming apparatus is configured so that a patch image can be formed at a continuous image forming interval when a blank area specified by the leading edge area, the intermediate area, and the trailing edge area is smaller than the size of the patch image. A patch image may be formed by spreading the image. As a result, the image forming apparatus can always perform correction processing with optimum throughput according to the image data to be formed.

  As described above, the image forming apparatus according to the present embodiment specifies a blank area in an intermediate area existing between a plurality of electrostatic latent images in image data formed on one recording material. . Therefore, the present image forming apparatus can display a patch image for correcting the image quality even when the blank area existing in the front end area and the rear end area does not have a sufficient size to form a patch image. Can be formed. As a result, the image forming apparatus can maintain a constant image quality without reducing the image forming throughput.

1 is a cross-sectional view illustrating an example of a printer according to a first embodiment. It is a figure which shows the control block of the printer which concerns on 1st Embodiment. It is a figure which shows a mode that the acquired image data is stored in an image memory. It is a figure explaining the method to derive | lead out the formation start position and the formation end position in the subscanning direction of the image data decomposed | disassembled for every color component. It is a figure explaining the method the specific part which concerns on 1st Embodiment specifies the size of a blank area | region. It is a flowchart which shows the procedure which forms the patch image which concerns on 1st Embodiment. It is a figure which shows the control procedure which forms a patch image in the blank area | region of the front-end | tip area | region which concerns on 1st Embodiment. It is a figure which shows the control procedure which forms a patch image in the blank area | region of the rear-end area | region which concerns on 1st Embodiment. It is a figure which shows a mode that the acquired image data is stored in an image memory. It is a figure explaining the method to derive | lead out the formation start position and the formation end position in the subscanning direction of the image data decomposed | disassembled for every color component. It is a figure explaining the method the specific part which concerns on 2nd Embodiment specifies the size of a blank area | region. It is a flowchart which shows the procedure which forms the patch image which concerns on 2nd Embodiment. It is a figure which shows the control procedure which forms a patch image in the blank area | region of the rear-end area | region which concerns on 2nd Embodiment. It is a figure which shows the control procedure which forms a patch image in the blank area | region of the intermediate area which concerns on 2nd Embodiment.

Explanation of symbols

200: Reader control unit 220: Controller unit 240: Printer control unit 260: Operation units 201, 221, 241: CPU
202, 222, 243: ROM
203, 223, 244: RAM
204, 246: EEPROM
205, 245: I / O
224: SRAM
206, 225: Image processing unit 226: Image memory 247: Pattern generator 248: Exposure control unit 271: Acquisition unit 272: Derivation unit 273: Identification unit 274: Determination unit 275: Density detection unit 276: Correction unit

Claims (9)

An image forming apparatus,
Acquisition means for acquiring image data to be formed on the recording material;
Deriving means for deriving a formation start position in the sub-scanning direction and a formation end position in the sub-scanning direction from the data when forming an electrostatic latent image on the image carrier;
Specifying means for specifying a blank area where an electrostatic latent image is not formed in the image forming area on the image carrier corresponding to the size of the recording material from the derived formation start position and formation end position;
Image forming means for forming a patch image for correcting the image quality in the specified blank area;
Density detecting means for detecting the density of the patch image formed on the image carrier;
An image forming apparatus comprising: correction means for adjusting an image forming condition for forming an image based on the detected density and correcting an image quality. Determination means for determining whether the size of the identified blank area is larger than the size of the patch image;
The image forming unit includes:
A patch image can be formed in the specified blank area when it is determined to be large by the determination unit, and a patch image can be formed on the continuous recording material when it is determined to be small by the determination unit The image forming apparatus according to claim 1, wherein the patch image is formed in a wide range. The specifying means is:
From the formation start position and the formation end position in the current electrostatic latent image, the formation end position in the previous electrostatic latent image, and the formation start position in the next electrostatic latent image, the image carrier 3. The image forming apparatus according to claim 1, wherein a blank area where no electrostatic latent image is formed is specified. The specifying means is:
The image forming apparatus according to claim 3, wherein a blank area is specified in a tip area from the previous electrostatic latent image formation end position to the current electrostatic latent image formation start position. The specifying means is:
5. The image formation according to claim 3, wherein the blank area is specified in a rear end area from the current electrostatic latent image formation end position to the next electrostatic latent image formation start position. apparatus. The specifying means is:
6. The image forming apparatus according to claim 3, wherein a blank area is specified in an intermediate area existing between a plurality of electrostatic latent images in the image forming area. The image forming unit includes:
When at least one of the blank areas specified in the leading edge area and the trailing edge area is larger than the size of the patch image, a patch image is formed in at least one of the blank areas specified in the leading edge area and the trailing edge area. ,
If both the blank area specified in the leading edge area and the trailing edge area are smaller than the size of the patch image, and the blank area specified in the intermediate area is larger than the size of the patch image, the intermediate area A patch image is formed in the blank area specified in
When all the blank areas specified by the leading edge area, the intermediate area, and the trailing edge area are smaller than the size of the patch image, the patch is formed by expanding the image forming interval on a continuous recording material to a range where a patch image can be formed. The image forming apparatus according to claim 6, wherein an image is formed. A contact / separation mechanism that contacts or separates the image carrier and a transfer body onto which the image formed on the image carrier is transferred;
The contact and separation mechanism is
When the actual image transferred to the recording material formed on the image carrier reaches the transfer position, the image carrier and the transfer body are brought into contact with each other,
The image according to any one of claims 1 to 6, wherein when the patch image formed on the image carrier reaches the transfer position, the image carrier and the transfer member are separated from each other. Forming equipment. A method for controlling an image forming apparatus, comprising:
Acquiring image data to be formed on the recording material by an acquisition unit;
Deriving a formation start position in the sub-scanning direction and a formation end position in the sub-scanning direction by the deriving unit from the data when forming the electrostatic latent image on the image carrier;
Identifying a blank area where an electrostatic latent image is not formed in the image forming area on the image carrier corresponding to the size of the recording material from the derived formation start position and formation end position by a specifying unit;
Forming a patch image for correcting the image quality in the specified blank area by an image forming unit;
Detecting the density of the patch image formed on the image carrier by density detecting means;
Adjusting the image forming conditions for forming an image based on the detected density and correcting the image quality by a correcting unit.

Images