JP5716462B2 - Image forming apparatus - Google Patents

Description

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

  In an image forming apparatus such as a laser printer, a digital copying machine, or a facsimile machine, a latent image is generally formed on a scanned surface by irradiating a scanned surface with a light beam and scanning the scanned surface with the light beam. Is forming.

  Such an image forming apparatus includes a photosensitive drum as a surface to be scanned having a photosensitive surface, a light source for emitting laser light, a polygon mirror for deflecting laser light from the light source, and a laser deflected by the polygon mirror. A scanning optical system that guides light to the surface of the photosensitive drum is provided.

  The light spot on the surface of 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. The axial direction of the photosensitive drum is called “main scanning direction”, and the rotational direction of the photosensitive drum is called “sub-scanning direction”. Further, the light spot position on the surface of the photosensitive drum in the main scanning direction is called “image height”.

  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) varies 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 enters the scanning optical system at an incident angle corresponding to the deflection angle of the polygon mirror, and the incident position differs depending on the image height. The intensity varies depending on the image height.

  The intensity of the laser light intensity according to the image height is called “shading characteristics”, and is one of the factors that cause density fluctuations in the output image and lower the image quality. Accordingly, various methods for correcting the shading characteristics have been proposed (see, for example, Patent Document 1 and Patent Document 2).

  Further, Patent Document 3 discloses an image forming apparatus that controls the exposure amount according to variations in sensitivity of the photosensitive member.

  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 development, which causes unnecessary density variation in an image output from the image forming apparatus (also referred to as “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 forming a high-quality image.

According to a first aspect, the present invention is an image forming apparatus that forms an image based on image information, and includes a photosensitive drum and a light source, and main scanning is performed on the surface of the photosensitive drum by light from the light source. An optical scanning device that scans in the direction and forms a latent image on the surface of the photosensitive drum, a developing device that develops the latent image, a drum cycle detection sensor that detects a rotation cycle of the photosensitive drum, and the developing device A density sensor that detects density fluctuations in the sub-scanning direction orthogonal to the main scanning direction in the image developed in step S3, and an output signal from the density sensor and an output signal from the drum period detection sensor . extracting a periodic pattern of a sine wave at a concentration fluctuations, the so sub-scanning direction density fluctuation is suppressed, and a processing unit for correcting a driving signal of the light source in accordance with the image information An image forming apparatus.
From a second aspect, the present invention is an image forming apparatus that forms an image based on image information, and includes a photosensitive drum and a light source, and main scanning is performed on the surface of the photosensitive drum by light from the light source. An optical scanning device that scans in the direction and forms a latent image on the surface of the photosensitive drum, a developing device that develops the latent image, a drum cycle detection sensor that detects a rotation cycle of the photosensitive drum, and the developing device A density sensor that detects density fluctuations in the sub-scanning direction orthogonal to the main scanning direction in the image developed in step S3, and an output signal from the density sensor and an output signal from the drum period detection sensor. A processing unit that extracts a periodic pattern of a triangular wave in the density fluctuation and corrects the driving signal of the light source according to the image information so that the density fluctuation in the sub-scanning direction is suppressed. An image forming apparatus.
From a third aspect, the present invention is an image forming apparatus that forms an image based on image information, and includes a photosensitive drum and a light source, and main scanning is performed on the surface of the photosensitive drum by light from the light source. An optical scanning device that scans in the direction and forms a latent image on the surface of the photosensitive drum, a developing device that develops the latent image, a drum cycle detection sensor that detects a rotation cycle of the photosensitive drum, and the developing device A density sensor that detects density fluctuations in the sub-scanning direction orthogonal to the main scanning direction in the image developed in step S3, and an output signal from the density sensor and an output signal from the drum period detection sensor. A processing device that extracts a periodic pattern of trapezoidal waves in the density variation and corrects the drive signal of the light source according to the image information so that the density variation in the sub-scanning direction is suppressed. An image forming apparatus.

  According to this, density fluctuation in the sub-scanning direction due to the eccentricity and shape error of the photosensitive drum is suppressed, and a high-quality image can be formed.

From a fourth aspect , the present invention is an image forming apparatus that forms an image based on image information, and includes a photosensitive drum and a light source, and the main surface of the photosensitive drum is scanned with light from the light source. An optical scanning device that scans in the direction and forms a latent image on the surface of the photosensitive drum, a developing roller that applies a developer to the photosensitive drum, and a developing device that develops the latent image, and the developing device. A density sensor that detects density fluctuations in the sub-scanning direction at the leading portion of the developed image, a leading edge detection sensor that detects a leading edge of a medium onto which the image developed by the developing device is transferred, and A processing device that corrects the driving signal of the light source according to the image information so that density fluctuation in the sub-scanning direction is suppressed based on the output signal of the tip detection sensor and the output signal of the density sensor; Be equipped That is an image forming apparatus.

  According to this, density fluctuations due to contamination of the developing roller are suppressed, and a high quality image can be formed.

1 is a diagram illustrating a schematic configuration of a color printer according to a first embodiment of the present invention. It is a figure for demonstrating the arrangement position of the density | concentration detector in FIG. It is a figure for demonstrating the structure of a density | concentration detector. 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 eccentricity of a photoconductive drum. It is a figure for demonstrating the shape error of a photoconductive drum and a developing roller. It is a flowchart for demonstrating light quantity correction information acquisition processing. It is a figure for demonstrating a density chart pattern. It is a figure for demonstrating the positional relationship of a density chart pattern and a density detector. It is a figure for demonstrating the locus | trajectory of the light for a detection inject | emitted from the density | concentration detector in the light quantity correction information acquisition process. FIG. 15A is a diagram for explaining regular reflection light and diffuse reflection light when the detection light illumination object is a transfer belt, and FIG. 15B 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. It is a figure for demonstrating the pattern for density fluctuation measurement. It is a figure for demonstrating the locus | trajectory of the detection light inject | emitted from the density detector with respect to the pattern for density fluctuation measurement. It is a timing chart for demonstrating the sensor output level of the density detector with respect to the pattern for density fluctuation measurement. It is a timing chart for demonstrating a 1st period pattern and a 2nd period pattern. It is a timing chart for explaining the 1st standard pattern. It is a timing chart for explaining the 2nd standard pattern. 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 effect of light quantity correction. It is a timing chart for explaining modification 1 of the 1st cycle pattern. It is FIG. (1) for demonstrating the difference of a triangular wave and a sine wave. It is FIG. (2) for demonstrating the difference of a triangular wave and a sine wave. It is a timing chart for explaining modification 2 of the 1st cycle pattern. It is a figure for demonstrating the trapezoid wave of the modification 2. FIG. It is a figure for demonstrating the advantage of a trapezoid wave. It is FIG. (1) for demonstrating the difference of a trapezoid wave and a sine wave. It is FIG. (2) for demonstrating the difference of a trapezoid wave and a sine wave. It is a figure for demonstrating the home position sensor of a developing roller. FIG. 6 is a diagram for explaining a relationship between an output signal of a home position sensor of a photosensitive drum and an output signal of a home position sensor of a developing roller. FIG. 6 is a diagram for explaining correction of density fluctuation caused by a photosensitive drum and correction of density fluctuation caused by a developing roller. It is a figure for demonstrating the example of the correction signal prepared beforehand as a 2nd correction signal. It is a figure for demonstrating the case where there exists a shape error only in a photoconductor drum. It is a figure which shows schematic structure of the color printer which concerns on the 2nd Embodiment of this invention. It is a block diagram for demonstrating a scanning control apparatus. It is a flowchart for demonstrating the information acquisition process with a deep tip. It is a figure for demonstrating the correction coefficient with thick tip, and correction time t4.

<< First Embodiment >>
A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a schematic configuration of a color printer 2000 as an image forming apparatus according to the first 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 ejection tray 2070, a communication control unit 2080, the concentration detector 2245,4 one home position sensor (2246a, 2246b, 2246c, 2246d) and a printer control unit 2090 for centrally controlling the above units.

  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 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. Configure.

  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. Configure.

  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. Configure.

  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. Configure.

  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 density detector 2245 is disposed on the −X side of the transfer belt 2040 and at a position facing the center of the transfer belt 2040 in the X-axis direction (see FIG. 2). Here, the center position of the density detector 2245 is Y0 with respect to the main direction (Y-axis direction).

  As shown in FIG. 3 as an example, the density detector 2245 includes an LED 11 that emits light (hereinafter also referred to as “detection light”) toward the transfer belt 2040, the transfer belt 2040, or a toner pad on the transfer belt 2040. A specular reflection light receiving element 12 that receives specular reflection light from the light source, and a diffuse reflection light receiving element 13 that receives diffuse reflection light from the transfer belt 2040 or the toner pad on the transfer belt 2040. Each of the light receiving elements outputs a signal (photoelectric conversion signal) corresponding to the amount of received light.

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

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

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

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

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

  As shown in FIGS. 4 to 7 as an example, the optical scanning device 2010 includes four light sources (2200a, 2200b, 2200c, 2200d), four coupling lenses (2201a, 2201b, 2201c, 2201d), and four apertures. 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), a scanning control device 3022 (not shown in FIGS. 4 to 7, see FIG. 8), and the like. 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, light beams from the cylindrical lens 2204a and the cylindrical lens 2204b are deflected to the −X side of the polygon mirror 2104A, and light beams from the cylindrical lens 2204c and the cylindrical lens 2204d 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. 8 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. 8 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.

  Incidentally, as described above, if the photosensitive drum has an eccentricity or a shape error, an unnecessary density fluctuation in the sub-scanning direction occurs in the output image. Also, if there is an eccentricity or a shape error in the developing roller, unnecessary density fluctuation in the sub-scanning direction occurs in the output image (see FIGS. 9 and 10).

  Therefore, the CPU 3210 suppresses density fluctuation in the sub-scanning direction due to the eccentricity and shape error of the photosensitive drum and density fluctuation in the sub-scanning direction caused by the eccentricity and shape error of the developing roller at a predetermined timing. Obtain light quantity correction information. 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 FIG. The flowchart in FIG. 11 corresponds to a series of processing algorithms executed by the CPU 3210 during the light amount correction information acquisition processing. The light amount correction information acquisition process is performed for each station, but is performed in the same manner at each station. Here, the light amount correction information acquisition process at the K station will be described as a representative.

  In the first step S401, as shown in FIG. 12 as an example, a density chart pattern having a plurality of regions having different toner densities with respect to black is displayed as an example, and the center position in the Y-axis direction is displayed as shown in FIG. Is formed to be Y0.

  Here, as an example, the density chart pattern has 10 types of density (n1 to n10) regions. The density n1 is the lowest density and the density n10 is the highest density. When the density chart pattern is formed, the lighting time of the light emitting unit is constant regardless of the density, and only the light emission power is varied according to the density. Here, the light emission power corresponding to the density n1 is p1, the light emission power corresponding to the density n2 is p2,..., And the light emission power corresponding to the density n10 is p10.

  In the next step S403, the LED 11 of the concentration detector 2245 is turned on. Light from the LED 11 (referred to as “detection light”) is sequentially irradiated from the density n1 area to the density n10 area in the density chart pattern as the transfer belt 2040 rotates, that is, as time passes. 14).

  Then, output signals from the regular reflection light receiving element 12 and the diffuse reflection light receiving element 13 are 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. 15A).

  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. 15B).

  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 reflection light receiving element 13 is normalized using the following equation (1) for each density in the density chart pattern. Hereinafter, the standardized output level 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)

  Then, a correlation between the sensor output level and the light emission power is obtained (see FIG. 16). Here, the correlation is approximated by a polynomial, and the polynomial is stored in the flash memory 3211.

  In the next step S407, a density variation measurement pattern is created. Here, a black solid pattern is formed in A3 vertical size as the density variation measurement pattern (see FIG. 17).

  In the next step S409, the LED 11 of the concentration detector 2245 is turned on. The detection light from the LED 11 illuminates the pattern for density fluctuation measurement along the sub-scanning corresponding direction as the transfer belt 2040 rotates, that is, as time elapses (see FIG. 18).

  Then, output signals of the regular reflection light receiving element 12 and the diffuse reflection light receiving element 13 are acquired at predetermined time intervals, and the sensor output level is calculated using the above equation (1) (see FIG. 19). FIG. 19 also shows an output signal of the home position sensor 2246a.

  As shown in FIG. 19, the sensor output level is not constant. Hereinafter, the time change of the sensor output level is also referred to as “sensor output level waveform”.

  In the next step S411, based on the output signal of the home position sensor 2246a, a sine wave having the same cycle as the rotation cycle of the photosensitive drum 2030a is extracted from the sensor output level waveform as a first cycle pattern (see FIG. 20).

  In the next step S413, the rotation period of the developing roller 2033a is obtained based on the diameter of the photosensitive drum 2030a, the diameter of the developing roller 2033a, and the output signal of the home position sensor 2246a, and the rotation of the developing roller 2033a is determined from the sensor output level waveform. A sine wave having the same period as that of the period is extracted as the second period pattern (see FIG. 20).

  In the next step S415, as shown in FIG. 21, a first density correction pattern in which the phase of the first period pattern is shifted by ½ wavelength is obtained, and the sensor output level and light emission power are obtained for that period. , The vertical axis is converted from the sensor output level to the light emission power to obtain the first reference pattern.

  In the next step S417, as shown in FIG. 22, a second density correction pattern in which the phase of the second period pattern is shifted by ½ wavelength is obtained, and the sensor output level and light emission power are obtained for one period. , The vertical axis is converted from the sensor output level to the light emission power to obtain the second reference pattern.

  In the next step S419, the first reference pattern and the second reference pattern are stored in the flash memory 3211, and the light amount correction information acquisition process is ended.

  When image formation is performed, the CPU 3210, for each station, based on the home position sensor output signal and the write start timing obtained from the output signal of the synchronization detection sensor (not shown), starts the home position and write start. And the phases of the first reference pattern and the second reference pattern are shifted according to the time difference to generate the first light amount correction signal and the second light amount correction signal (see FIG. 23). 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. 24 shows sensor output levels of the density detector 2245 before and after correction. As described above, the density fluctuation in the sub-scanning direction due to the eccentricity and shape error of the photosensitive drum and the density fluctuation in the sub-scanning direction due to the eccentricity and shape error of the developing roller can be suppressed.

  The horizontal axis (time) of each light quantity correction signal corresponds to the length of the formed image in the sub-scanning direction. Therefore, each light amount correction signal is a first light amount correction signal when the time corresponding to the length of the formed image in the sub-scanning direction is shorter than the rotation period of the photosensitive drum. Generated from parts. On the other hand, when the time corresponding to the length of the formed image in the sub-scanning direction is longer than the rotation cycle of the photosensitive drum, the first light quantity correction signal is generated from a plurality of cycles of the first reference pattern.

  In addition, when an image area enable signal whose signal level is “high” is generated only when image formation is being performed, the image area enable signal is used as a mask signal for each light amount correction signal. (See FIG. 23).

  As described above, according to the color printer 2000 according to the first embodiment, the optical scanning device 2010, the four photosensitive drums (2030a, 2030b, 2030c, 2030d), the four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), a transfer belt 2040, a density detector 2245, four home position sensors (2246a, 2246b, 2246c, 2246d), and the like.

  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 sub-scanning direction due to eccentricity or shape error of the photosensitive drum based on the output signal of the density detector 2245 and the output signal of the corresponding home position sensor at each station at every predetermined timing. The first periodic pattern showing the density fluctuations of the color and the second periodic pattern showing the density fluctuations in the sub-scanning direction due to the eccentricity and shape error of the developing roller. Then, data for one period of each pattern obtained by shifting the phase of the first period pattern and the second period pattern by ½ period is stored in the memory as the first reference pattern and the second reference pattern. Then, when image formation is performed, the first light amount correction signal and the second light amount correction signal are generated for each station using the first reference pattern and the second reference pattern, and the drive signal of each light emitting unit is corrected. To do.

  In this case, 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 formed.

  In the first embodiment, the case where a sine wave is extracted as the first periodic pattern has been described. However, the present invention is not limited to this.

  For example, as shown in FIG. 25, a triangular wave close to the sine wave may be extracted as the first periodic pattern. In this case, the first light quantity correction signal is also a triangular wave. The first light quantity correction signal can be generated if the phase shift time with respect to the drum cycle and the correction range amount are known, and the data amount can be reduced. Thus, cost reduction can be achieved.

  FIG. 26 shows a sine wave and a triangular wave approaching the sine wave. In FIG. 26, the amplitude of the sine wave is 1.

  FIG. 27 shows the difference in value between the sine wave and the triangular wave approaching the sine wave. As can be seen from FIG. 27, the difference from the sine wave shows a steep fluctuation at the apex portion of the triangular wave. Even if the triangular wave is approximated to a sine wave, the difference in the amount of light from the sine wave is approximately 15%.

  As an example, as shown in FIG. 28, a trapezoidal wave close to the sine wave may be extracted as the first periodic pattern. In this case, the first light quantity correction signal is also a trapezoidal wave. As shown in FIG. 29 as an example, the first light quantity correction signal is assumed to be an increment time T1, a peak time T2, a decrement time T3, a correction range amount, and a phase shift time (T4 with respect to the drum cycle). 30)) can be generated, and the amount of data can be reduced as compared with a sine wave.

  The increment time T1 is obtained from the sensor output level waveform. The peak time T2 may be obtained from the sensor output level waveform or may be obtained from T1 / 2. The decrement time T3 is basically equal to T1. The phase shift time T4 is used to adjust the phase between the photosensitive drum cycle and the writing start timing. When the photosensitive drum rotates for the first time, it is defined by a preset default value cycle.

  Unlike the triangular wave, the trapezoidal wave has a feature that the concentration fluctuation at the peak position is small. Further, the trapezoidal wave has a feature that even if the drum cycle varies, there is no joint, so that correction is possible (see FIG. 30).

  FIG. 31 shows a sine wave and a trapezoidal wave close to the sine wave. Further, FIG. 32 shows a difference in values between a sine wave and a trapezoidal wave approaching the sine wave.

  In the case of a trapezoidal wave, a slightly steep fluctuation is observed in the difference from the sine wave at the corner of the trapezoid, but the fluctuation is smaller than that in the case of a triangular wave. Further, the difference from the sine wave as a whole is about 7% or less, and the sine wave can be simulated with higher accuracy than in the case of the triangular wave.

  In the first embodiment, the case where the rotation period of the developing roller is obtained based on the diameter of the photosensitive drum, the diameter of the developing roller, and the output signal of the home position sensor of the photosensitive drum has been described. It is not limited to.

  As an example, as shown in FIG. 33, home position sensors (2247a to 2247d) are also provided for each developing roller, and the rotation period of each developing roller can be obtained based on the output signal of the home position sensors (2247a to 2247d). good.

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

  As an example, as shown in FIG. 35, after correcting the driving signal of each light emitting unit with the first light amount correction signal, the density detector 2245 obtains the density fluctuation residue, and the density fluctuation residue and the developing roller Based on the output signal of the home position sensor, the drive signal of each light emitting unit may be corrected with the second light quantity correction signal.

  Incidentally, the density fluctuation caused by the developing roller has a considerably shorter period than the density fluctuation caused by the photosensitive drum. If the density variation is finely corrected at a very high frequency, banding may occur due to the residual component of the correction.

  Therefore, it is preferable to correct the density fluctuation caused by the developing roller with a simple triangular wave signal, sine wave signal, and trapezoidal wave signal having a signal period of one or two cycles of the developing roller. FIG. 35 shows an example of a triangular wave signal. Alternatively, linear approximation may be performed on the sampling data of the density detector 2245, and the drive signal of each light emitting unit may be corrected with a correction signal (second light amount correction signal) corresponding thereto.

  In addition, a plurality of correction signals having different phases are prepared in advance as the second light quantity correction signal (see FIG. 36), and the correction signal having the phase that minimizes the density fluctuation detected by the density detector 2245 is selected. May be. In FIG. 36, three correction signals (correction signal A, correction signal B, and correction signal C) whose phases are different by 120 degrees are shown, but the present invention is not limited to this.

  Alternatively, the photosensitive drum and the developing roller may be mechanically connected using a gear, and the rotation period of the developing roller may be obtained based on the gear ratio and the output signal of the home position sensor of the photosensitive drum.

  Incidentally, there is a case where the developing roller is slid during development. In this case, the rotation period of the developing roller is obtained in consideration of the sliding ratio.

  In the first embodiment, when the eccentricity or shape error of the developing roller is small, the second reference pattern may not be obtained (see FIG. 37).

<< Second Embodiment >>
Hereinafter, a second embodiment of the present invention will be described with reference to FIGS. The color printer 2000A according to the second embodiment is characterized in that it includes a paper leading edge detection sensor 2247 as shown in FIG. Other configurations are the same as those of the first embodiment described above. Therefore, in the following, the description will focus on the differences from the first embodiment, and the same reference numerals are used for the same or equivalent components as in the first embodiment described above, and the description is simplified or Shall be omitted.

  By the way, as one of the density fluctuations in the sub-scanning direction, a density deviation band corresponding to the length of one round of the developing roller is generated at the tip of the image immediately after the pattern switching at the position where the image pattern is switched. There is a phenomenon (hereinafter also referred to as “deep tip”). In particular, when the image is output continuously from the background area, there is a problem that the image density at the front end of the paper increases uniformly. The cause of this will be described below.

  In the two-component development method, toner adhesion occurs on the developing roller in the background area, and the effective developing potential for one rotation of the developing roller after the background area increases. Thereafter, the toner attached to the developing roller in the image area returns to the carrier side, and the toner returns, so that the developing roller is clean and the developing potential is restored. This difference in development potential is considered to increase the density by one rotation of the developing roller at the front end of the paper.

  FIG. 39 shows the configuration of the scanning control device 3022. Note that the arrows in FIG. 39 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block.

  The CPU 3210 obtains “dark tip” information at a predetermined timing. Hereinafter, the process of acquiring the “dark tip information” is abbreviated as “the dark tip information acquisition process”.

  Here, the processing for acquiring information with a dark tip will be described with reference to FIG. The flowchart in FIG. 40 corresponds to a series of processing algorithms executed by the CPU 3210 in the process of acquiring information with a dark tip. It should be noted that the dark tip information acquisition process is performed for each station, but is performed in the same manner at each station, and therefore, the dark tip information acquisition process at the K station will be described as a representative.

  In the first step S501, for black, a density chart pattern similar to that in the first embodiment described above is formed so that the center position is Y0 in the Y-axis direction.

  In the next step S503, the LED 11 of the concentration detector 2245 is turned on. Light from the LED 11 (“detection light”) sequentially irradiates from the density n1 area to the density n10 area in the density chart pattern as the transfer belt 2040 rotates, that is, as time elapses.

  Then, output signals from the regular reflection light receiving element 12 and the diffuse reflection light receiving element 13 are acquired.

  In the next step S505, the output level of the diffuse reflected light receiving element 13 is normalized using the above equation (1) for each density in the density chart pattern. Then, a correlation between the sensor output level and the light emission power is obtained. Here, the correlation is approximated by a polynomial, and the polynomial is stored in the flash memory 3211.

  In the next step S507, a density variation measurement pattern is created. Here, a black solid pattern is formed in A3 vertical size as the density fluctuation measurement pattern.

  In the next step S509, the LED 11 of the concentration detector 2245 is turned on. The detection light from the LED 11 illuminates the pattern for density fluctuation measurement along the sub-scanning corresponding direction as the transfer belt 2040 rotates, that is, as time elapses.

  Then, the sensor output level (referred to as V1) when the time t1 has elapsed from the falling timing of the output signal of the paper leading edge detection sensor 2247 is obtained (see FIG. 41).

  In the next step S511, a sensor output level (referred to as V2) is obtained when time t2 (t2> t1) has elapsed from the falling timing of the output signal of the paper leading edge detection sensor 2247 (see FIG. 41).

  In the next step S513, the correlation between the sensor output level and the light emission power is referred to, the light emission power corresponding to V1-V2 is obtained, and converted into a correction coefficient (referred to as “high-end correction coefficient”). Here, the value when correction is unnecessary is 1.0.

  In the next step S515, a correction time t4 is obtained based on the outer peripheral size of the developing roller and the printing speed (see FIG. 41).

  In the next step S517, the dark tip correction coefficient and the correction time t4 are stored in the flash memory 3211, and the tip dark information acquisition process is terminated.

  When the CPU 3210 detects the falling edge of the output signal of the paper leading edge detection sensor 2247 during image formation, the correction time t4 is synchronized with the writing start timing obtained from the output signal of the synchronization detection sensor (not shown). In the meantime, the driving signal is corrected by multiplying the driving signal of each light emitting unit corresponding to the image information by a correction coefficient with a deep tip. FIG. 41 shows sensor output levels before and after correction. As described above, the density fluctuation in the sub-scanning direction due to the contamination of the developing roller can be suppressed.

  As described above, according to the color printer 2000A according to the second embodiment, the optical scanning device 2010, the four photosensitive drums (2030a, 2030b, 2030c, 2030d), the four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), a transfer belt 2040, a density detector 2245, a paper leading edge detection sensor 2247, and the like.

  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 density fluctuation in the sub-scanning direction due to contamination of the developing roller based on the output signal of the density detector 2245 and the output signal of the paper leading edge detection sensor 2247 at each station at every predetermined timing. A correction coefficient with a thick tip for suppressing the correction is obtained. When image formation is performed, each light emission corresponding to the image information is corrected for each station during a correction time t4 calculated from the outer peripheral size of the developing roller and the printing speed in accordance with the writing start timing. The drive signal is corrected by multiplying the drive signal of the unit by a correction coefficient with a thick tip.

  In this case, it is possible to reduce the density fluctuation in which the leading edge in the output image becomes darker than before. As a result, a high quality image can be formed.

  In each of the above embodiments, the case where there is one concentration detector 2245 has been described, but the present invention is not limited to this. A plurality of density detectors 2245 may be arranged along the Y-axis direction.

  In each of the above embodiments, the printer control device 2090 may perform at least 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 each of the above embodiments, 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 is detected. Also good. Note that the surface of the photosensitive drum is close to a regular reflector like the transfer belt 2040.

  In each of the above embodiments, 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.

  For example, an image forming apparatus that directly irradiates laser light onto a medium (for example, paper) that develops color with laser light may be used.

  Further, an image forming apparatus using a silver salt film as the image carrier may be used. In this case, a latent image is formed on the silver salt film by optical scanning, and this latent image can be visualized by a process equivalent to a developing process in a normal silver salt photographic process. Then, it can be transferred to photographic paper by a process equivalent to a printing process in a normal silver salt photographic process. Such an image forming apparatus can be implemented as an optical plate making apparatus or an optical drawing apparatus that draws a CT scan image or the like.

  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 forming a high quality image.

  2000 ... color printer (image forming apparatus), 2000A ... color printer (image forming apparatus), 2010 ... optical scanning device, 2030a-2030d ... photoconductor drum, 2033a-2033d ... developing roller, 2040 ... transfer belt, 2090 ... printer control Device (part of processing device), 2200a to 2200d ... light source, 2245 ... density detector (density sensor), 2246a to 2246d ... photosensitive drum home position sensor (rotation cycle detection sensor), 2247a to 2247d ... developing roller Home position sensor (roller cycle detection sensor), 2247... Paper tip detection sensor (tip detection sensor), 3022... Scanning control device (part of processing device).

JP 2007-135100 A JP 2009-262344 A JP 2008-065270 A

Claims (23)

An image forming apparatus that forms an image based on image information,
A photosensitive drum;
An optical scanning device that includes a light source, scans the surface of the photosensitive drum in the main scanning direction with light from the light source, and forms a latent image on the surface of the photosensitive drum;
A developing device for developing the latent image;
A drum cycle detection sensor for detecting a rotation cycle of the photosensitive drum;
A density sensor for detecting density fluctuations in a sub-scanning direction orthogonal to the main scanning direction in an image developed by the developing device;
Based on the output signal of the density sensor and the output signal of the drum period detection sensor, a periodic pattern of a sine wave in the density fluctuation in the sub-scanning direction is extracted so that the density fluctuation in the sub-scanning direction is suppressed. An image forming apparatus comprising: a processing device that corrects a driving signal of the light source according to the image information. An image forming apparatus that forms an image based on image information,
A photosensitive drum;
An optical scanning device that includes a light source, scans the surface of the photosensitive drum in the main scanning direction with light from the light source, and forms a latent image on the surface of the photosensitive drum;
A developing device for developing the latent image;
A drum cycle detection sensor for detecting a rotation cycle of the photosensitive drum;
A density sensor for detecting density fluctuations in a sub-scanning direction orthogonal to the main scanning direction in an image developed by the developing device;
Based on the output signal of the density sensor and the output signal of the drum period detection sensor, a periodic pattern of triangular waves in the density fluctuation in the sub-scanning direction is extracted, and the density fluctuation in the sub-scanning direction is suppressed. And a processing device that corrects the driving signal of the light source according to image information. An image forming apparatus that forms an image based on image information,
A photosensitive drum;
An optical scanning device that includes a light source, scans the surface of the photosensitive drum in the main scanning direction with light from the light source, and forms a latent image on the surface of the photosensitive drum;
A developing device for developing the latent image;
A drum cycle detection sensor for detecting a rotation cycle of the photosensitive drum;
A density sensor for detecting density fluctuations in a sub-scanning direction orthogonal to the main scanning direction in an image developed by the developing device;
Based on the output signal of the density sensor and the output signal of the drum period detection sensor, a periodic pattern of trapezoidal waves in the density fluctuation in the sub-scanning direction is extracted, and the density fluctuation in the sub-scanning direction is suppressed. An image forming apparatus comprising: a processing device that corrects a driving signal of the light source according to the image information. Period of the periodic pattern, the image forming apparatus according to claim 1, wherein the the same as the rotation period of the photosensitive drum. 5. The image forming apparatus according to claim 4 , wherein the processing apparatus stores, as a reference pattern, data for one period of a pattern obtained by shifting the phase of the periodic pattern by ½ period in a memory. The image forming apparatus according to claim 5 , wherein the processing device adjusts a phase of the reference pattern based on a timing of starting writing of the image information. The image forming apparatus according to claim 6 , wherein the processing device corrects a driving signal of the light source according to the image information using a reference pattern in which the phase is adjusted. The sub-scanning direction density variation, the photosensitive drum eccentricity and the image forming apparatus according to any one of claims 1 to 7, characterized in that it comprises a density variation due to at least one of the shape error of. The developing device has a developing roller facing the photosensitive drum,
The image forming apparatus according to claim 8 , wherein the density fluctuation in the sub-scanning direction includes density fluctuation caused by at least one of an eccentricity and a shape error of the developing roller. The processing device further obtains a periodic pattern indicating a density variation caused by the developing roller based on an output signal of the density sensor and a rotation period of the developing roller, and corrects the driving signal of the light source. The image forming apparatus according to claim 9 . The image forming apparatus according to claim 10 , wherein the signal for correcting the driving signal of the light source is a sine wave signal in order to correct the density variation caused by the developing roller. The image forming apparatus according to claim 10 , wherein the signal for correcting the driving signal of the light source in order to correct the density fluctuation caused by the developing roller is a triangular wave signal. The image forming apparatus according to claim 10 , wherein the signal for correcting the driving signal of the light source is a trapezoidal wave signal in order to correct the density fluctuation caused by the developing roller. The developing device has a roller period detection sensor that detects a rotation period of the developing roller,
The image forming apparatus according to claim 10 , wherein the processing device obtains a rotation cycle of the developing roller based on an output signal of the roller cycle detection sensor. The processing device is obtained from the output signal of the density sensor after correcting the drive signal of the light source according to the image information based on the output signal of the density sensor and the output signal of the drum cycle detection sensor. 15. The image forming apparatus according to claim 14 , wherein a drive signal of the light source is corrected based on a density variation residue and an output signal of the roller cycle detection sensor. The image forming apparatus according to claim 15 , wherein the processing apparatus linearly approximates a residue of density fluctuation based on an output signal of the density sensor. The photosensitive drum and the developing roller are set so that a fixed relationship is maintained during each rotation period,
The image forming apparatus according to claim 10 , wherein the processing device obtains a rotation cycle of the developing roller based on an output signal of the drum cycle detection sensor and the predetermined relationship. The image forming apparatus according to claim 17 , wherein the photosensitive drum and the developing roller are connected via a gear. The image forming apparatus according to claim 10 , wherein the processing device obtains a rotation period of the developing roller based on a diameter of the photosensitive drum and a diameter of the developing roller. In order to correct the density fluctuation caused by the developing roller, the processing device prepares a plurality of correction signals having different phases in advance as correction signals for correcting the driving signal of the light source, and the density fluctuation is minimized. The image forming apparatus according to claim 10 , wherein a phase correction signal is selected. An image forming apparatus that forms an image based on image information,
A photosensitive drum;
An optical scanning device that includes a light source, scans the surface of the photosensitive drum in the main scanning direction with light from the light source, and forms a latent image on the surface of the photosensitive drum;
A developing device for developing the latent image, including a developing roller for applying a developer to the photosensitive drum;
A density sensor that detects density fluctuations in the sub-scanning direction at the head portion of the image developed by the developing device;
A leading edge detection sensor for detecting a leading edge of a medium onto which an image developed by the developing device is transferred before the transfer;
A processing device that corrects the driving signal of the light source according to the image information so that density fluctuation in the sub-scanning direction is suppressed based on the output signal of the tip detection sensor and the output signal of the density sensor; And an image forming apparatus. The image forming apparatus according to claim 21 , wherein the processing device determines a length of time for correcting the driving signal of the light source based on a size of the developing roller and a printing speed. The image forming apparatus according to any one of claims 1 to 22 , wherein the light source is a vertical cavity surface emitting laser.