JP2012155112A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably forming a high quality image.SOLUTION: In processing for obtaining light quantity correction information, first density variation measuring patterns (MP1 to MP4) are created in synchronization with a drum home position sensor, and a first correction reference pattern is generated on the basis of an output signal of a density detector. Furthermore, second density variation measuring patterns are created in synchronization with a roller home position sensor, and a second correction reference pattern is generated on the basis of the output signal of the density detector. In forming an image, the first correction reference pattern and the second correction reference pattern are used for generating a first light quantity correction signal and a second light quantity correction signal so as to correct a drive signal of each light emitting portion for every station.

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using a laser beam.

  An image forming apparatus such as a laser printer, a digital copying machine, or a facsimile machine has a photosensitive drum as a scanning surface whose surface is photosensitive, a light source that emits laser light, a polygon mirror that deflects laser light from the light source, A scanning optical system for guiding the laser beam deflected by the polygon mirror to the photosensitive drum is provided.

  The light spot on the photosensitive drum moves in the axial direction of the photosensitive drum as the polygon mirror rotates, and scanning for one line is performed. When the scanning for one line is completed, the photosensitive drum is rotated and the next scanning is started.

  Incidentally, the scanning optical system is composed of optical elements such as a lens, a glass plate, and a mirror, and the light use efficiency (reflectance or transmittance) differs depending on the incident angle of light. The thickness of the lens varies depending on the incident position of light.

  The laser beam deflected by the polygon mirror is incident on the scanning optical system at an incident angle corresponding to the deflection angle of the polygon mirror, and when the irradiation position on the photosensitive drum is different, the incident position on the scanning optical system is also different. Therefore, the intensity of the laser beam on the photosensitive drum is not uniform and varies depending on the irradiation position.

  Such intensity of the laser light intensity according to the irradiation position is called “shading characteristics”, and causes density fluctuations in an image output from the image forming apparatus (also referred to as “output image”), thereby improving image quality. This is one of the factors that cause a decrease. Thus, various methods for correcting the shading characteristics have been proposed (see, for example, Patent Document 1 and Patent Document 2).

  Patent Document 3 discloses data conversion for converting input image data input from image input means into exposure amount data using characteristic data representing the relationship between the exposure amount to the recording medium and the color density of the recording medium. Means for correcting the input image data converted into the exposure amount data by adding shading correction data for each pixel, and converting the input image data into the exposure amount data, An image forming apparatus that performs shading correction by adding shading correction data and forms an image with an image recording unit is disclosed.

  By the way, if the photosensitive drum is eccentric or the cross section is not a perfect circle, the gap between the photosensitive drum and the developing roller varies when the photosensitive drum rotates. This variation in the gap becomes a variation in the development process, and causes an unnecessary density variation in the output image.

  In recent years, demand for image quality has increased, and it has been difficult for conventional methods to suppress fluctuations in the density of an output image due to eccentricity or shape error of the photosensitive drum to a required level.

  The present invention has been made under such circumstances, and an object thereof is to provide an image forming apparatus capable of stably forming a high-quality image.

  The present invention is an image forming apparatus for forming an image according to image information, a photosensitive drum having a longitudinal direction as a main scanning direction, a drum cycle detection sensor for detecting a rotation cycle of the photosensitive drum, A pattern creation device that creates a density detection pattern in synchronization with the drum cycle detection sensor, and a density variation in the sub-scanning direction perpendicular to the main scanning direction in the density detection pattern created by the pattern creation device is detected. An image forming apparatus including a density sensor.

  According to this, it is possible to stably form an image of higher quality than before.

1 is a diagram illustrating a schematic configuration of a color printer according to an embodiment of the present invention. It is a figure for demonstrating a roller home position sensor. It is a figure for demonstrating the output signal of a drum home position sensor, and the output signal of a roller home position sensor. It is a figure for demonstrating the density | concentration detector in FIG. It is a figure for demonstrating the structure of each optical sensor. FIG. 2 is a diagram (part 1) for describing the optical scanning device in FIG. 1; FIG. 3 is a second diagram for explaining the optical scanning device in FIG. 1; FIG. 3 is a third diagram for explaining the optical scanning device in FIG. 1; FIG. 4 is a diagram (part 4) for explaining the optical scanning device in FIG. 1; It is a block diagram for demonstrating a scanning control apparatus. It is a figure for demonstrating the state where the cross-sectional shape of a photoconductor drum is not a perfect circle. FIG. 12 is a diagram for explaining the relationship between the image density and the rotation angle of the photosensitive drum in FIG. 11. It is a flowchart (the 1) for demonstrating a light quantity correction information acquisition process. It is a flowchart (the 2) for demonstrating a light quantity correction information acquisition process. FIG. 3 is a first diagram for explaining a density chart pattern; FIG. 6 is a second diagram for explaining a density chart pattern; FIG. 17A is a diagram for explaining regular reflection light and diffuse reflection light when the detection light illumination object is a transfer belt, and FIG. 17B is a detection light illumination object. FIG. 6 is a diagram for explaining regular reflection light and diffuse reflection light when is a toner pattern. It is a figure for demonstrating the relationship between light emission power and a sensor output level. FIG. 6 is a first diagram for explaining a first density variation measurement pattern; FIG. 6 is a second diagram for explaining a first density variation measurement pattern; It is a figure for demonstrating the relationship between a light quantity setting signal and image density about several image area ratio. It is a figure for demonstrating the relationship between the formation start timing of the pattern for 1st density | concentration fluctuation | variation measurement, and the output signal of a drum home position sensor. It is a figure for demonstrating the length of the subscanning corresponding direction of each rectangular pattern of the pattern for 1st density | concentration fluctuation | variation measurement. It is a figure for demonstrating the locus | trajectory of the detection light inject | emitted from each optical sensor with respect to the pattern for 1st density | concentration fluctuation | variation measurement. It is a timing chart for demonstrating the sensor output level of each optical sensor with respect to the pattern for 1st density | concentration fluctuation | variation measurement. It is a timing chart for demonstrating the 1st period pattern extracted from FIG. It is a timing chart for explaining the 1st standard pattern. FIG. 6 is a diagram (No. 1) for describing a second density variation measurement pattern; FIG. 6 is a second diagram for explaining a second density variation measurement pattern; It is a figure for demonstrating the relationship between the formation start timing of the pattern for 2nd density | concentration fluctuation | variation measurement, and the output signal of a roller home position sensor. It is a timing chart for demonstrating the sensor output level of each optical sensor with respect to the pattern for 2nd density | concentration fluctuation | variation measurement. It is a timing chart for demonstrating the 2nd period pattern extracted from FIG. It is a timing chart for explaining the 2nd standard pattern. It is a figure for demonstrating an example of the output signal of each home position sensor, and a write start timing. It is a timing chart for demonstrating a 1st light quantity correction signal and a 2nd light quantity correction signal. It is a timing chart for demonstrating the density fluctuation of the subscanning direction after correction | amendment. It is a figure for demonstrating the case where four 1st density variation measurement patterns of the same color are formed continuously. It is a figure for demonstrating the modification of FIG. It is a figure for demonstrating the advantage of FIG.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2 show a schematic configuration of a color printer 2000 as an image forming apparatus according to an embodiment.

  The color printer 2000 is a tandem multi-color printer that forms a full-color image by superimposing four colors (black, cyan, magenta, and yellow), and includes an optical scanning device 2010, four photosensitive drums (2030a, 2030b, 2030c, 2030d), four cleaning units (2031a, 2031b, 2031c, 2031d), four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), 4 Toner cartridges (2034a, 2034b, 2034c, 2034d), transfer belt 2040, transfer roller 2042, fixing roller 2050, paper feed roller 2054, registration roller pair 2056, paper discharge roller 2058, paper feed tray 060, paper discharge tray 2070, communication control device 2080, density detector 2245, four drum home position sensors (2246a, 2246b, 2246c, 2246d), four roller home position sensors (2247a, 2247b, 2247c, 2247d), temperature A humidity sensor (not shown) and a printer control device 2090 that controls the above-described units are provided.

  The communication control device 2080 controls bidirectional communication with a host device (for example, a personal computer) via a network or the like.

  The printer control device 2090 includes a CPU, a ROM described in a program written in code readable by the CPU, various data used when executing the program, a RAM as a working memory, an analog data An AD conversion circuit for converting the signal into digital data. The printer control device 2090 controls each unit in response to a request from the host device, and sends image information from the host device to the optical scanning device 2010.

  The temperature / humidity sensor detects the temperature and humidity in the color printer 2000 and notifies the printer controller 2090 of it.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a are used as a set and form an image forming station (hereinafter also referred to as “K station” for convenience) that forms a black image. Constitute.

  The photosensitive drum 2030b, the charging device 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b are used as a set and form an image forming station (hereinafter also referred to as “C station” for convenience) that forms a cyan image. Constitute.

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c are used as a set, and form an image forming station (hereinafter also referred to as “M station” for convenience) that forms a magenta image. Constitute.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d are used as a set, and form an image forming station (hereinafter also referred to as “Y station” for convenience) that forms a yellow image. Constitute.

  Each photosensitive drum has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductive drum is a surface to be scanned. Each photosensitive drum is rotated in the direction of the arrow in the plane of FIG. 1 by a rotation mechanism (not shown).

  In the following description, in the XYZ three-dimensional orthogonal coordinate system, the direction along the longitudinal direction of each photosensitive drum is defined as the Y-axis direction, and the direction along the arrangement direction of the four photosensitive drums is defined as the X-axis direction.

  Each charging device uniformly charges the surface of the corresponding photosensitive drum.

  Based on the multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the higher-level device, the optical scanning device 2010 charges the light flux modulated for each color correspondingly. Irradiate each surface of the photosensitive drum. As a result, on the surface of each photoconductive drum, the charge disappears only in the portion irradiated with light, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum. The latent image formed here moves in the direction of the corresponding developing roller as the photosensitive drum rotates. The configuration of the optical scanning device 2010 will be described later.

  By the way, in each photoconductor drum, areas where image information is written are called “effective scanning area”, “image forming area”, “effective image area”, and the like.

  The toner cartridge 2034a stores black toner, and the toner is supplied to the developing roller 2033a. The toner cartridge 2034b stores cyan toner, and the toner is supplied to the developing roller 2033b. The toner cartridge 2034c stores magenta toner, and the toner is supplied to the developing roller 2033c. The toner cartridge 2034d stores yellow toner, and the toner is supplied to the developing roller 2033d.

  As each developing roller rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller comes into contact with the surface of the corresponding photosensitive drum, the toner moves only to a portion irradiated with light on the surface and adheres to the surface. In other words, each developing roller causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum so as to be visualized. Here, the toner-attached image (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum rotates.

  The yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a color image. The moving direction of the toner image on the transfer belt 2040 is called a “sub direction”, and the direction orthogonal to the sub direction is called a “main direction”.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing roller 2050.

  In the fixing roller 2050, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper fixed here is sent to a paper discharge tray 2070 via a paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum. The surface of the photosensitive drum from which the residual toner has been removed returns to the position facing the corresponding charging device again.

  The drum home position sensor 2246a detects a rotation home position in the photosensitive drum 2030a.

  The drum home position sensor 2246b detects a rotation home position in the photosensitive drum 2030b.

  The drum home position sensor 2246c detects a rotation home position in the photosensitive drum 2030c.

  The drum home position sensor 2246d detects a rotation home position in the photosensitive drum 2030d.

  The roller home position sensor 2247a detects the rotation home position in the developing roller 2033a.

  The roller home position sensor 2247b detects a rotation home position in the developing roller 2033b.

  The roller home position sensor 2247c detects the rotation home position in the developing roller 2033c.

  The roller home position sensor 2247d detects the rotation home position in the developing roller 2033d.

  The relationship between the output signal of the drum home position sensor and the output signal of the roller home position sensor is shown in FIG. 3 as an example.

  The density detector 2245 is disposed on the −X side of the transfer belt 2040. The density detector 2245 has five optical sensors (2245a, 2245b, 2245c, 2245d, 2245e) as shown in FIG. 4 as an example.

  The optical sensor 2245a is disposed at a position facing the vicinity of the −Y side end in the effective image region of the transfer belt 2040, and the optical sensor 2245e is opposed to the vicinity of the + Y side end of the effective image region in the transfer belt 2040. The optical sensors 2245b to 2245d are arranged at positions, and the optical sensors 2245a and 2245d are arranged between the optical sensors 2245a and 2245e so that the intervals between the five optical sensors are substantially equal. Here, regarding the main direction (Y-axis direction), the center position of the optical sensor 2245a is Y1, the center position of the optical sensor 2245b is Y2, the center position of the optical sensor 2245c is Y3, the center position of the optical sensor 2245d is Y4, and the optical sensor. The center position of 2245e is set to Y5.

  As shown in FIG. 5 as an example, each optical sensor includes an LED 11 that emits light (hereinafter also referred to as “detection light”) toward the transfer belt 2040, the toner on the transfer belt 2040, or the toner on the transfer belt 2040. A regular reflection light receiving element 12 that receives regular reflection light from the pad and a diffuse reflection light receiving element 13 that receives diffuse reflection light from the toner belt on the transfer belt 2040 or the transfer belt 2040 are provided. Each light receiving element outputs a signal (photoelectric conversion signal) corresponding to the amount of received light.

  Next, the configuration of the optical scanning device 2010 will be described.

  The optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), four openings, as shown in FIGS. Plate (2202a, 2202b, 2202c, 2202d), four cylindrical lenses (2204a, 2204b, 2204c, 2204d), polygon mirror 2104, four scanning lenses (2105a, 2105b, 2105c, 2105d), six folding mirrors (2106a) 2106b, 2106c, 2106d, 2108b, 2108c) and a scanning control device 3022 (not shown in FIGS. 6 to 9, see FIG. 10). These are assembled at predetermined positions of an optical housing (not shown).

  Each light source includes a surface emitting laser array in which a plurality of light emitting units are two-dimensionally arranged. The plurality of light emitting portions of the surface emitting laser array are arranged such that the intervals between the light emitting portions are equal when all the light emitting portions are orthogonally projected onto a virtual line extending in the sub-scanning corresponding direction. In this specification, the “light emitting portion interval” refers to the distance between the centers of two light emitting portions.

  The coupling lens 2201a is disposed on the optical path of the light beam emitted from the light source 2200a, and makes the light beam a substantially parallel light beam.

  The coupling lens 2201b is disposed on the optical path of the light beam emitted from the light source 2200b, and makes the light beam a substantially parallel light beam.

  The coupling lens 2201c is disposed on the optical path of the light beam emitted from the light source 2200c, and makes the light beam a substantially parallel light beam.

  The coupling lens 2201d is disposed on the optical path of the light beam emitted from the light source 2200d, and makes the light beam a substantially parallel light beam.

  The aperture plate 2202a has an aperture and shapes the light beam that has passed through the coupling lens 2201a.

  The aperture plate 2202b has an aperture and shapes the light beam that has passed through the coupling lens 2201b.

  The aperture plate 2202c has an aperture and shapes the light beam that has passed through the coupling lens 2201c.

  The aperture plate 2202d has an aperture and shapes the light beam that has passed through the coupling lens 2201d.

  The cylindrical lens 2204 a forms an image of the light beam that has passed through the opening of the aperture plate 2202 a in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204b forms an image of the light beam that has passed through the opening of the aperture plate 2202b in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204 c forms an image of the light beam that has passed through the opening of the aperture plate 2202 c in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  The cylindrical lens 2204d forms an image of the light flux that has passed through the opening of the aperture plate 2202d in the vicinity of the deflection reflection surface of the polygon mirror 2104 in the Z-axis direction.

  An optical system including the coupling lens 2201a, the aperture plate 2202a, and the cylindrical lens 2204a is a pre-deflector optical system of the K station.

  An optical system including the coupling lens 2201b, the aperture plate 2202b, and the cylindrical lens 2204b is a pre-deflector optical system of the C station.

  An optical system including the coupling lens 2201c, the aperture plate 2202c, and the cylindrical lens 2204c is a pre-deflector optical system of the M station.

  An optical system including the coupling lens 2201d, the aperture plate 2202d, and the cylindrical lens 2204d is a pre-deflector optical system of the Y station.

  The polygon mirror 2104 has a four-stage mirror having a two-stage structure that rotates around an axis parallel to the Z axis, and each mirror serves as a deflecting reflection surface. The light beam from the cylindrical lens 2204b and the light beam from the cylindrical lens 2204c are respectively deflected by the first-stage (lower) tetrahedral mirror, and the light beam from the cylindrical lens 2204a and the cylindrical light are deflected by the second-stage (upper) tetrahedral mirror. It arrange | positions so that the light beam from lens 2204d may be deflected, respectively.

  Further, the light beams from the cylindrical lens 2204 a and the cylindrical lens 2204 b are deflected to the −X side of the polygon mirror 2104, and the light beams from the cylindrical lens 2204 c and the cylindrical lens 2204 d are deflected to the + X side of the polygon mirror 2104.

  Each scanning lens has an optical power for condensing a light beam in the vicinity of the corresponding photosensitive drum, and a light spot on the surface of the corresponding photosensitive drum at a constant speed in the main scanning direction as the polygon mirror 2104 rotates. It has optical power to move.

  The scanning lens 2105 a and the scanning lens 2105 b are disposed on the −X side of the polygon mirror 2104, and the scanning lens 2105 c and the scanning lens 2105 d are disposed on the + X side of the polygon mirror 2104.

  The scanning lens 2105a and the scanning lens 2105b are stacked in the Z-axis direction, the scanning lens 2105b is opposed to the first-stage four-sided mirror, and the scanning lens 2105a is opposed to the second-stage four-sided mirror. The scanning lens 2105c and the scanning lens 2105d are stacked in the Z-axis direction, the scanning lens 2105c is opposed to the first-stage four-sided mirror, and the scanning lens 2105d is opposed to the second-stage four-sided mirror.

  The light beam from the cylindrical lens 2204a deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030a through the scanning lens 2105a and the folding mirror 2106a, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030a as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030a is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030a, and the rotational direction of the photosensitive drum 2030a is the “sub-scanning direction” on the photosensitive drum 2030a.

  The light beam from the cylindrical lens 2204b deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030b through the scanning lens 2105b, the folding mirror 2106b, and the folding mirror 2108b, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030b as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030b is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030b, and the rotational direction of the photosensitive drum 2030b is the “sub-scanning direction” on the photosensitive drum 2030b.

  The light beam from the cylindrical lens 2204c deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030c through the scanning lens 2105c, the folding mirror 2106c, and the folding mirror 2108c, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030c as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030c is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030c, and the rotational direction of the photosensitive drum 2030c is the “sub-scanning direction” on the photosensitive drum 2030c.

  The light beam from the cylindrical lens 2204d deflected by the polygon mirror 2104 is irradiated onto the photosensitive drum 2030d through the scanning lens 2105d and the folding mirror 2106d, thereby forming a light spot. This light spot moves in the longitudinal direction of the photosensitive drum 2030d as the polygon mirror 2104 rotates. That is, the photosensitive drum 2030d is scanned. The moving direction of the light spot at this time is the “main scanning direction” on the photosensitive drum 2030d, and the rotational direction of the photosensitive drum 2030d is the “sub-scanning direction” on the photosensitive drum 2030d.

  Each folding mirror is arranged so that the optical path lengths from the polygon mirror 2104 to each photosensitive drum coincide with each other, and the incident position and the incident angle of the light flux on each photosensitive drum are equal to each other. ing.

  An optical system disposed on the optical path between the polygon mirror 2104 and each photosensitive drum is also called a scanning optical system. Here, the scanning optical system of the K station is composed of the scanning lens 2105a and the folding mirror 2106a. Further, the scanning optical system of the C station is composed of the scanning lens 2105b and the two folding mirrors (2106b, 2108b). The scanning lens 2105c and the two folding mirrors (2106c, 2108c) constitute a scanning optical system for the M station. Further, the scanning optical system of the Y station is composed of the scanning lens 2105d and the folding mirror 2106d. In each scanning optical system, the scanning lens may be composed of a plurality of lenses.

  As shown in FIG. 10 as an example, the scanning control device 3022 includes a CPU 3210, a flash memory 3211, a RAM 3212, an IF (interface) 3214, a pixel clock generation circuit 3215, an image processing circuit 3216, a writing control circuit 3219, and a light source driving circuit. 3221 and the like. Note that the arrows in FIG. 10 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block.

  An IF (interface) 3214 is a communication interface that controls bidirectional communication with the printer control apparatus 2090. Image data from the host device is supplied via an IF (interface) 3214.

  The pixel clock generation circuit 3215 generates a pixel clock signal. The pixel clock signal can be phase-modulated with a resolution of 1/8 clock.

  The image processing circuit 3216 performs predetermined halftone processing or the like on the image data rasterized for each color by the CPU 3210, and then creates dot data for each light emitting unit of each light source.

  The writing control circuit 3219 obtains a writing start timing for each image forming station based on an output signal of a synchronization detection sensor (not shown). Then, the dot data of each light emitting unit is superimposed on the pixel clock signal from the pixel clock generating circuit 3215 in accordance with the writing start timing, and independent modulation data is generated for each light emitting unit.

  The light source driving circuit 3221 outputs a driving signal for each light emitting unit to each light source in accordance with each modulation data from the writing control circuit 3219.

  The flash memory 3211 stores various programs described in codes readable by the CPU 3210 and various data necessary for executing the programs.

  The RAM 3212 is a working memory.

  The CPU 3210 operates according to a program stored in the flash memory 3211 and controls the entire optical scanning device 2010.

  By way of example, as exaggeratedly shown in FIG. 11, when the circularity of the photosensitive drum is low, there is a gap variation due to the rotational position, and as an example, exaggeratedly shown in FIG. 12, As the photosensitive drum rotates, the image density also varies. In FIG. 11, the photosensitive drum has a portion having a larger diameter and a portion having a smaller diameter than those of a perfect circle, whereby the image density for one cycle of the photosensitive drum is a sine wave having two inflection points. It has a fluctuation close to.

  Therefore, the CPU 3210 acquires light amount correction information for suppressing unnecessary density fluctuations in the sub-scanning direction at a predetermined timing. Hereinafter, the process of acquiring the light quantity correction information is abbreviated as “light quantity correction information acquisition process”.

  In addition, as the predetermined timing, when the power is turned on, (1) when the photosensitive drum stop time is 6 hours or more, (2) when the temperature in the apparatus changes by 10 ° C. or more, (3) in the apparatus When the relative humidity of the ink is changed by 50% or more, during printing, (4) when the number of printed sheets reaches a predetermined number, (5) when the number of rotations of the developing roller reaches a predetermined number, (6) When the travel distance of the transfer belt reaches a predetermined distance, a light amount correction information acquisition process is performed.

  Here, the light quantity correction information acquisition processing will be described with reference to FIGS. 13 and 14. The flowcharts of FIGS. 13 and 14 correspond to a series of processing algorithms executed by the CPU 3210 during the light amount correction information acquisition processing.

  In the first step S401, as shown in FIG. 15 as an example, density chart patterns (DP1 to DP4) are created for each color.

  The density chart pattern DP1 is formed of black toner, and the density chart pattern DP2 is formed of magenta toner. The density chart pattern DP3 is formed with cyan toner, and the density chart pattern DP4 is formed with yellow toner.

  Hereinafter, when it is not necessary to distinguish the density chart patterns DP1 to DP4, they are also collectively referred to as “density chart pattern DP”.

  As shown in FIG. 16 as an example, the density chart pattern DP has ten square patterns (p1 to p10, hereinafter referred to as “rectangular pattern” for convenience). The rectangular patterns are arranged in a line along the traveling direction of the transfer belt 2040 at substantially equal intervals, and the gradation of toner density differs when viewed as a whole. Here, p1, p2, p3, p4, p5, p6, p7, p8, p9, and p10 are selected from a rectangular pattern having a low toner density. That is, the rectangular pattern p1 has the lowest toner density, and the rectangular pattern p10 has the highest toner density.

  Further, the lighting time of the light emitting portion when forming the density chart pattern DP is constant regardless of the toner concentration, and only the light emission power is varied according to the toner concentration. The light emission power when forming the rectangular pattern p1 is P1, the light emission power when forming the rectangular pattern p2 is P2,..., And the light emission power when forming the rectangular pattern p10 is P10.

  In the next step S403, the LED 11 of each optical sensor is turned on. The light from the LED 11 (detection light) is sequentially irradiated from the rectangular pattern p1 to the rectangular pattern p10 as the transfer belt 2040 rotates, that is, as time elapses.

  And the output signal of the regular reflection light receiving element 12 and the diffuse reflection light receiving element 13 in each optical sensor is acquired.

  By the way, when the toner does not adhere to the transfer belt 2040, the detection light reflected by the transfer belt 2040 has more regular reflection light components than diffuse reflection light components. Therefore, much light is incident on the regular reflection light receiving element 12, but almost no light is incident on the diffuse reflection light receiving element 13 (see FIG. 17A).

  On the other hand, when the toner adheres to the transfer belt 2040, the specular reflection light component decreases and the diffuse reflection light component increases compared to the case where the toner does not adhere. Therefore, the light incident on the regular reflection light receiving element 12 decreases, and the light incident on the diffuse reflection light receiving element 13 increases (see FIG. 17B).

  That is, it is possible to detect the density of the toner adhering to the transfer belt 2040 based on the output levels of the regular reflection light receiving element 12 and the diffuse reflection light receiving element 13.

  In the next step S405, the output level of the diffuse reflected light receiving element 13 is normalized for each rectangular pattern using the following equation (1). Hereinafter, the standardized output level L of the diffusely reflected light receiving element 13 is also referred to as “sensor output level” for convenience.

L = (Output level of diffuse reflection light receiving element 13) ÷ {(Output level of specular reflection light receiving element 12) + (Output level of diffuse reflection light receiving element 13)} (1)

  In the next step S407, the correlation between the sensor output level and the light emission power is obtained for each color (see FIG. 18). Here, the correlation is approximated by a polynomial, and the polynomial is stored in the flash memory 3211.

  In the present embodiment, the correlation between the sensor output level and the light emission power is adjusted so as not to vary between the optical sensors.

  In the next step S411, as shown in FIG. 19 as an example, first density variation measurement patterns (MP1 to MP4) are created for each color.

  The first density fluctuation measurement pattern MP1 is formed of black toner, and the first density fluctuation measurement pattern MP2 is formed of magenta toner. The first density fluctuation measurement pattern MP3 is formed of cyan toner, and the first density fluctuation measurement pattern MP4 is formed of yellow toner. Hereinafter, when it is not necessary to distinguish the first density variation measurement patterns MP1 to MP4, they are collectively referred to as a “first density variation measurement pattern MP”.

  As shown in FIG. 20, as an example, the first density variation measurement pattern MP has 30 rectangular patterns arranged in a matrix of 5 columns and 6 rows. Hereinafter, for convenience, the rectangular pattern of the first density variation measurement pattern MP is also referred to as a “rectangular pattern mp”.

  Each rectangular pattern mp has the same toner density. As shown in FIG. 21 as an example, in the relationship between the image density D and the light quantity setting signal V, the image density D is equal to the variation ΔV of the light quantity setting signal V. It is created at the image area ratio (70% in FIG. 21) when the variation ΔD is maximized. The light amount setting signal V corresponds to the light emission power of the light source.

  As an example, as shown in FIG. 22, the first density variation measurement pattern MP1 is transferred to the transfer belt 2040 at a timing after Δt1 from the falling edge of the output signal of the drum home position sensor 2246a, and the first density variation is measured. The measurement pattern MP2 is transferred to the transfer belt 2040 at a timing after Δt1 from the fall of the output signal of the drum home position sensor 2246b. The first density fluctuation measurement pattern MP3 is transferred to the transfer belt 2040 at a timing Δt1 after the fall of the output signal of the drum home position sensor 2246c, and the first density fluctuation measurement pattern MP4 is transferred to the drum home position sensor. The toner image is transferred to the transfer belt 2040 at a timing Δt1 after the trailing edge of the output signal 2246d. That is, each first density variation measurement pattern is created in synchronization with the corresponding drum home position sensor. In the conventional image forming apparatus, even if the drum home position sensor is provided, the density variation measurement pattern is created regardless of the drum home position sensor.

  Incidentally, the response characteristics of the optical sensor are shown in FIG. In the optical sensor, time Ts1 is required until a stable level signal is obtained. Further, a time Ts2 is required from when the signal is stabilized until a signal corresponding to the toner density is obtained. This time Ts2 is the minimum time set according to the sampling speed and the number of samplings.

  The length w in the X-axis direction of the rectangular pattern mp is determined from the relative moving speed of the transfer belt 2040 with respect to the optical sensor so that the time during which the light from the optical sensor is illuminated is “Ts1 + Ts2”. The

  That is, the length w in the X-axis direction of the rectangular pattern mp is determined from the response characteristic of the optical sensor and the relative moving speed of the transfer belt 2040 with respect to the optical sensor. As a result, toner consumption can be reduced.

  In the next step S413, the LED 11 of each optical sensor is turned on. The detection light from each LED 11 illuminates the first density variation measurement pattern along the sub-scanning corresponding direction as the transfer belt 2040 rotates, that is, as time elapses (see FIG. 24).

  For each optical sensor, output signals of the regular reflection light receiving element 12 and the diffuse reflection light receiving element 13 are obtained at predetermined time intervals.

  In the next step S415, the sensor output level is calculated for each rectangular pattern using the above equation (1). FIG. 25 shows each sensor output level when the first density variation measurement pattern MP1 is illuminated, together with the output signal of the drum home position sensor 2246a. Hereinafter, the time change of the sensor output level is also referred to as “sensor output level waveform”.

  In the next step S417, a sine wave having the same period as the rotation period of the photosensitive drum is used as the first period pattern from each sensor output level waveform based on the output signal of the drum home position sensor for each color and for each optical sensor. Extract (see FIG. 26).

  In the next step S419, an inverted periodic pattern obtained by vertically inverting the first periodic pattern is obtained for each color and for each optical sensor, and the vertical axis indicates the correlation between the sensor output level and the light emission power. The light level is converted from the output level to obtain the first reference pattern. FIG. 27 shows a first reference pattern corresponding to the sine wave of FIG.

  In the next step S421, the first reference patterns of the five optical sensors are averaged for each color to obtain a correction first reference pattern. Instead of averaging, the largest first reference pattern among the first reference patterns of the five optical sensors may be used as the first reference pattern for correction.

  In the next step S423, the first reference pattern for correction for each color is stored in the flash memory 3211.

  In the next step S425, a first light amount correction signal having a vertical axis as a correction coefficient is generated for each color based on the first reference pattern for correction (see FIG. 27), and the light emission power of the light source is corrected.

  In the next step S431, as shown in FIG. 28 as an example, second density variation measurement patterns (SP1 to SP4) are created for each color.

  The second density fluctuation measurement pattern SP1 is formed of black toner, and the second density fluctuation measurement pattern SP2 is formed of magenta toner. The second density fluctuation measurement pattern SP3 is formed of cyan toner, and the second density fluctuation measurement pattern SP4 is formed of yellow toner. Hereinafter, when it is not necessary to distinguish between the second density variation measurement patterns SP1 to SP4, they are also collectively referred to as “second density variation measurement patterns SP”.

  As shown in FIG. 29 as an example, the second density variation measurement pattern SP has 25 rectangular patterns arranged in a matrix of 5 columns and 5 rows. Hereinafter, for convenience, the rectangular pattern of the second density variation measurement pattern SP is also referred to as a “rectangular pattern sp”.

  Each rectangular pattern sp has the same toner density and is created under the same conditions as the rectangular pattern mp.

  As an example, as shown in FIG. 30, the second density fluctuation measurement pattern SP1 is transferred to the transfer belt 2040 at a timing Δt2 after the fall of the output signal of the roller home position sensor 2247a, and the second density fluctuation measurement pattern SP1 is transferred. The measurement pattern SP2 is transferred to the transfer belt 2040 at a timing Δt2 after the fall of the output signal of the roller home position sensor 2247b. The second density fluctuation measurement pattern SP3 is transferred to the transfer belt 2040 at a timing Δt2 after the fall of the output signal of the roller home position sensor 2247c. The second density fluctuation measurement pattern SP4 is transferred to the roller home position sensor. The toner image is transferred to the transfer belt 2040 at a timing Δt2 after the fall of the output signal 2247d. That is, each second density variation measurement pattern is created in synchronization with the corresponding roller home position sensor. Note that Δt2 ≠ Δt1.

  In the next step S433, the LED 11 of each optical sensor is turned on. The detection light from each LED 11 illuminates the second density variation measurement pattern along the sub-scanning corresponding direction as the transfer belt 2040 rotates, that is, as time elapses.

  For each optical sensor, output signals of the regular reflection light receiving element 12 and the diffuse reflection light receiving element 13 are obtained at predetermined time intervals.

  In the next step S435, the sensor output level is calculated for each rectangular pattern using the above equation (1). FIG. 31 shows each sensor output level when the second density variation measuring pattern SP1 is illuminated, together with the output signal of the roller home position sensor 2247a.

  In the next step S437, a sine wave having the same cycle as the rotation cycle of the developing roller is extracted as a second cycle pattern from each sensor output level waveform based on the output signal of the roller home position sensor for each color and for each optical sensor. To do. FIG. 32 shows a sine wave extracted from the sensor output level waveform of the optical sensor 2245a in FIG.

  In the next step S439, an inverted periodic pattern obtained by vertically inverting the second periodic pattern is obtained for each color and for each optical sensor, and the vertical axis indicates the correlation between the sensor output level and the light emission power. Conversion from the output level to the light emission power is made the second reference pattern. FIG. 33 shows a second reference pattern corresponding to the sine wave of FIG.

  In the next step S441, the second reference patterns of the five optical sensors are averaged for each color to obtain a correction second reference pattern. Instead of averaging, the largest second reference pattern among the second reference patterns of the five optical sensors may be used as the second reference pattern for correction.

  In the next step S443, the second reference pattern for correction for each color is stored in the flash memory 3211. Then, the light quantity correction information acquisition process ends.

  When image formation is performed, the CPU 3210 performs writing start timing obtained from the output signal of the drum home position sensor, the output signal of the roller home position sensor, and the output signal of a synchronization detection sensor (not shown) for each station. Based on the above, the phase of the first reference pattern for correction stored in the flash memory 3211 is shifted to generate a first light quantity correction signal, and the phase of the second reference pattern for correction is shifted to A two-light quantity correction signal is generated (see FIGS. 34 and 35). Here, the vertical axis of each light quantity correction signal is converted into a coefficient with an average value of 1.0.

  Then, the drive signal is corrected by multiplying the drive signal of each light emitting unit corresponding to the image information by the coefficient.

  FIG. 36 shows the density fluctuation in the sub-scanning direction after correction. The density fluctuation is suppressed by the correction.

  As described above, according to the color printer 2000 according to the present embodiment, the optical scanning device 2010, the four photosensitive drums (2030a, 2030b, 2030c, 2030d), and the four developing rollers (2033a, 2033b, 2033c, 2033d). , Transfer belt 2040, transfer roller 2042, density detector 2245, four drum home position sensors (2246a, 2246b, 2246c, 2246d), four roller home position sensors (2247a, 2247b, 2247c, 2247d), and printer control device 2090 and the like.

  The density detector 2245 has five optical sensors (2245a, 2245b, 2245c, 2245d, 2245e).

  The optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four pre-deflector optical systems, a polygon mirror 2104, four scanning optical systems, and a scanning control device 3022.

  The scanning control device 3022 performs light amount correction information acquisition processing for each station at every predetermined timing. In this light amount correction information acquisition process, a first density variation measurement pattern is created in synchronization with the drum home position sensor, and a correction first reference pattern is generated based on the output signal of the density detector 2245. In the light amount correction information acquisition process, a second density variation measurement pattern is created in synchronization with the roller home position sensor, and a correction second reference pattern is generated based on the output signal of the density detector 2245.

  Then, when image formation is performed, the scanning control device 3022 generates a first light amount correction signal and a second light amount correction signal for each station using the correction first reference pattern and the correction second reference pattern. Then, the drive signal of each light emitting unit is corrected.

  In this case, the correction first reference pattern and the correction second reference pattern can be accurately obtained with a small amount of toner. Further, density unevenness in the sub-scanning direction in the output image can be reduced as compared with the conventional case. As a result, a high quality image can be stably formed.

  In the above-described embodiment, the case where sine waves are extracted as the first periodic pattern and the second periodic pattern has been described. However, the present invention is not limited to this. For example, a triangular wave or a trapezoidal wave that is close to the sine wave may be extracted as the first periodic pattern. Similarly, a triangular wave or a trapezoidal wave close to the sine wave may be extracted as the second periodic pattern.

  In the above-described embodiment, a plurality of first density variation measurement patterns of the same color may be continuously generated. For example, four first density variation measurement patterns of the same color may be created in succession (see FIG. 37). The accuracy can be improved by averaging the measurement results.

  In this case, the first density variation measurement patterns may be transferred to the transfer belt 2040 with different delay times with respect to the falling timing of the output signal of the drum home position sensor (see FIG. 38). In this case, as shown in FIG. 39 as an example, the periodic pattern can be extracted with high accuracy.

  In the above embodiment, a plurality of second density variation measuring patterns of the same color may be continuously created.

  Moreover, although the said embodiment demonstrated the case where the drive signal of each light emission part was correct | amended based on the 1st correction reference pattern and the 2nd correction reference pattern, it is not restricted to this, The 1st correction reference pattern The developing bias may be corrected based on the second correction reference pattern. Even in this case, density unevenness in the sub-scanning direction in the output image can be reduced as compared with the conventional case. The developing bias may be corrected based on the first correction reference pattern, and the drive signal of each light emitting unit may be corrected based on the second correction reference pattern.

  In the above embodiment, the case where the concentration detector 2245 includes five optical sensors has been described. However, the present invention is not limited to this. In short, the density detector 2245 only needs to have a plurality of optical sensors arranged along the Y-axis direction.

  In the above embodiment, the printer control device 2090 may perform at least a part of the processing in the scanning control device 3022. Further, the scanning control device 3022 may perform at least a part of the processing in the printer control device 2090.

  In the above embodiment, at least a part of the processing according to the program by the CPU 3210 may be configured by hardware, or all may be configured by hardware.

  In the above embodiment, the case where the density detector 2245 detects the toner pattern on the transfer belt 2040 has been described. However, the present invention is not limited to this, and the toner pattern on the surface of the photosensitive drum may be detected. good. Note that the surface of the photosensitive drum is close to a regular reflector like the transfer belt 2040.

  In the above embodiment, the toner pattern may be transferred to a recording sheet, and the toner pattern on the recording sheet may be detected by the density detector 2245.

  In each of the above-described embodiments, the case where the optical scanning device is integrally configured has been described. However, the present invention is not limited to this. For example, an optical scanning device may be provided for each image forming station, or an optical scanning device may be provided for every two image forming stations.

  In each of the above embodiments, the case where there are four photosensitive drums has been described, but the present invention is not limited to this. For example, five or six photosensitive drums may be provided.

  In each of the above embodiments, the case of the color printer 2000 as the image forming apparatus has been described, but the present invention is not limited to this.

  Further, the image forming apparatus may be an image forming apparatus other than a printer, for example, a copier, a facsimile, or a complex machine in which these are integrated.

  As described above, the image forming apparatus of the present invention is suitable for stably forming a high-quality image.

  2000 ... color printer (image forming apparatus), 2010 ... optical scanning device, 2030a to 2030d ... photosensitive drum, 2033a to 2033d ... developing roller (part of developing device), 2040 ... transfer belt (moving body), 2090 ... printer Control device, 2200a to 2200d ... light source, 2245a to 2245e ... optical sensor, 2246a to 2246d ... drum home position sensor (drum cycle detection sensor), 2247a to 2247d ... roller home position sensor (roller cycle detection sensor), 3022 ... scanning control Device (processing device), MP ... first density fluctuation measurement pattern (first density detection pattern), SP ... second density fluctuation measurement pattern (second density detection pattern).

JP 2007-135100 A JP 2009-262344 A JP 2003-127454 A

Claims (29)

An image forming apparatus that forms an image according to image information,
A photosensitive drum having a longitudinal direction as a main scanning direction;
A drum cycle detection sensor for detecting a rotation cycle of the photosensitive drum;
A pattern creation device that creates a density detection pattern in synchronization with the drum cycle detection sensor;
An image forming apparatus comprising: a density sensor configured to detect a density variation in a sub-scanning direction orthogonal to the main scanning direction in the density detection pattern created by the pattern creating apparatus. The drum cycle detection sensor outputs a pulse signal corresponding to the rotation cycle of the photosensitive drum,
The image forming apparatus according to claim 1, wherein the pattern creating apparatus starts creating the density detection pattern at a timing delayed by a preset time with respect to the pulse signal. The drum cycle detection sensor outputs a pulse signal corresponding to the rotation cycle of the photosensitive drum,
2. The image formation according to claim 1, wherein the pattern generation device starts generation of the density detection pattern at a timing delayed by a different time for each of the plurality of continuous pulse signals. apparatus.   The said pattern production apparatus produces the said several pattern for a density | concentration detection at substantially equal intervals, while the said photoconductive drum rotates 1 time. Image forming apparatus.   The image forming apparatus according to claim 4, wherein the pattern creating apparatus creates at least five density detection patterns at substantially equal intervals while the photosensitive drum rotates once. The density detection pattern is formed on a moving body,
The pattern creating apparatus determines a length of the density detection pattern in the sub-scanning direction based on a response characteristic of the density sensor and a moving speed of the moving body with respect to the density sensor. The image forming apparatus according to claim 1. The pattern creating device includes a light source,
For a plurality of image area ratios different from each other, the relationship between the light emission power of the light source and the image density is acquired in advance,
In the above relationship, the pattern creating apparatus creates the density detection pattern with an image area ratio when the variation of the image density is maximum with respect to the variation of the light emission power of the light source. The image forming apparatus according to claim 1. The density sensor has a plurality of optical sensors arranged at different positions with respect to the main scanning direction,
8. The pattern generation device according to claim 1, wherein the pattern generation device generates the density detection patterns at positions different from each other in the main scanning direction, corresponding to the plurality of optical sensors. The image forming apparatus described.   The image forming apparatus according to claim 8, wherein the plurality of optical sensors are arranged at substantially equal intervals in the main scanning direction.   The image forming apparatus according to claim 8, wherein the plurality of optical sensors is at least five optical sensors.   The image forming apparatus according to claim 8, wherein an average of outputs of the plurality of optical sensors is used as a detection result of the density sensor.   The image forming apparatus according to claim 8, wherein the largest output among the outputs of the plurality of optical sensors is set as a detection result of the density sensor. The pattern creating device includes an optical scanning device that forms a latent image on the surface of the photosensitive drum, and a developing device that develops the latent image,
The developing device includes a developing roller facing the photosensitive drum, and a roller cycle detection sensor that detects a rotation cycle of the developing roller,
The pattern creation device creates the density detection pattern as a first density detection pattern in synchronization with the drum cycle detection sensor, and synchronizes with the roller cycle detection sensor. The image forming apparatus according to claim 1, wherein different second density detection patterns are created. The roller cycle detection sensor outputs a pulse signal corresponding to the rotation cycle of the developing roller,
The image forming apparatus according to claim 13, wherein the pattern creating apparatus starts creating the second density detection pattern at a timing delayed by a preset time with respect to the pulse signal. . The roller cycle detection sensor outputs a pulse signal corresponding to the rotation cycle of the developing roller,
14. The pattern generation device starts generating the second density detection pattern at a timing delayed by a different time for each of the plurality of continuous pulse signals. Image forming apparatus. The drum cycle detection sensor outputs a first pulse signal corresponding to the rotation cycle of the photosensitive drum, and the roller cycle detection sensor outputs a second pulse signal corresponding to the rotation cycle of the developing roller. ,
The pattern creation device starts creating the first density detection pattern at a timing delayed by a first time set in advance with respect to the first pulse signal, and the preset first pattern 14. The image formation according to claim 13, wherein the creation of the second density detection pattern is started at a timing delayed with respect to the second pulse signal by a second time different from the first time. apparatus.   17. The pattern creating apparatus creates a plurality of the second density detection patterns at substantially equal intervals while the developing roller makes one rotation. The image forming apparatus described.   The image forming apparatus according to claim 17, wherein the pattern creating apparatus creates at least five second density detection patterns at substantially equal intervals while the developing roller rotates once.   The pattern creating device creates a plurality of first density detection patterns at a first interval during one rotation of the photosensitive drum, and a plurality of patterns during one rotation of the developing roller. The image forming apparatus according to claim 13, wherein the second density detection pattern is created at a second interval different from the first interval. The second density detection pattern is formed on a moving body,
The pattern generation device determines a length of the second density detection pattern in the sub-scanning direction based on a response characteristic of the density sensor and a moving speed of the moving body with respect to the density sensor. The image forming apparatus according to claim 13, wherein the image forming apparatus is an image forming apparatus. The pattern creating device includes a light source,
For a plurality of image area ratios different from each other, the relationship between the light emission power of the light source and the image density is acquired in advance,
In the above relationship, the pattern creating device creates the second density detection pattern at an image area ratio when the variation of the image density is maximum with respect to the variation of the light emission power of the light source. The image forming apparatus according to claim 13, wherein the image forming apparatus is an image forming apparatus. The density sensor has a plurality of optical sensors arranged at different positions with respect to the main scanning direction,
The pattern generation device according to any one of claims 13 to 21, wherein the pattern generation device generates the second density detection patterns corresponding to the plurality of optical sensors at positions different from each other in the main scanning direction. The image forming apparatus according to one item.   The image forming apparatus according to claim 22, wherein the plurality of optical sensors are arranged at substantially equal intervals in the main scanning direction.   The image forming apparatus according to claim 22, wherein the plurality of optical sensors is at least five optical sensors.   25. The image forming apparatus according to claim 22, wherein an average of outputs of the plurality of optical sensors is set as a detection result of the density sensor.   25. The image forming apparatus according to claim 22, wherein the largest output among the outputs of the plurality of optical sensors is set as a detection result of the density sensor.   Based on the detection result of the density sensor with respect to the first density detection pattern and the output signal of the drum cycle detection sensor, the light emission power of the light source is controlled so that density fluctuations caused by the photosensitive drum are suppressed. Alternatively, the density fluctuation caused by the developing roller is corrected based on the detection result of the density sensor for the second density detection pattern and the output signal of the roller cycle detection sensor while correcting the developing bias in the developing device. 27. The image forming apparatus according to claim 13, further comprising a processing device that corrects a light emission power of the light source or a developing bias in the developing device so as to be suppressed.   The pattern creating apparatus corrects the second density after the light emission power of the light source or the developing bias in the developing apparatus is corrected by the processing apparatus so that density fluctuation caused by the photosensitive drum is suppressed. 28. The image forming apparatus according to claim 27, wherein a detection pattern is created.   The processing device is configured to suppress density fluctuation caused by the developing roller based on a detection result of the density sensor with respect to the second density detection pattern and an output signal of the roller cycle detection sensor. 29. The image forming apparatus according to claim 27, wherein the light emission power of the light source is corrected.