JP2020006540A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately suppress density unevenness due to variations in light emission amounts of a plurality of light source elements. An exposure device 2a forms a electrostatic latent image by causing a light emitting element array to emit a plurality of light rays and irradiating the light ray on a photosensitive drum 1a. The exposure device 2a irradiates the light beam while scanning the light beam in the main scanning direction at the real latent image line position to form an electrostatic latent image at the real latent image line position, and also performs the main scanning light beam at the two real latent image line positions. Irradiate while scanning in the direction to form an electrostatic latent image at a virtual latent image line position between two real latent image line positions. Then, the controller 31 sequentially causes the plurality of light emitting elements in the light emitting element array to emit light to measure the amount of emitted light, and based on the amount of emitted light measured for the plurality of light emitting elements, the virtual latent image line position The light emission time per dot of the light emitting element when the electrostatic latent image is formed at the virtual latent image line position is individually corrected so that the density unevenness is suppressed. [Selection diagram]

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus, a periodic jitter may occur at a scanning position of a laser beam due to a surface tilt of a polygon mirror in an exposure apparatus, and a pitch between scanning positions may fluctuate. When the pitch between the scanning positions fluctuates, density unevenness and color shift in the sub-scanning direction occur. Therefore, some image forming apparatuses use a plurality of light sources to shift the peak of the exposure light amount distribution or select a light emitting light source to suppress density unevenness and color shift (for example, Patent Document 1, 2). In another image forming apparatus, the density unevenness is suppressed by changing the exposure light amount in accordance with the jitter (for example, refer to Patent Document 3).

JP-A-7-174995 JP 2013-097034 A JP 2000-238330 A

  On the other hand, an image forming apparatus employs an interleaved scanning method as a means for increasing the pseudo-resolution, in which a laser beam is physically scanned at a real latent image line position, and a virtual latent image between two real latent image line positions is formed. An electrostatic latent image is formed at the line position. That is, an electrostatic latent image is formed at the virtual latent image line position without physically scanning the laser beam at the virtual latent image line position.

  By changing the exposure light amount in accordance with the jitter as described above, the density unevenness at the actual latent image line position can be suppressed. Since the amount of exposure light at the line position is involved, the density unevenness at the virtual latent image line position may not be appropriately suppressed by the above method. Further, when the density unevenness is suppressed by using a plurality of light sources as described above, the cost of the light source, and eventually the cost of the image forming apparatus, increase.

  However, when a multi-beam light source having an array of a plurality of light source elements is used as the light source of the above-mentioned laser beam, the actual latent image line position does not fluctuate even if the light emission amount of the plurality of light source elements fluctuates, but the interleaving is performed. Since the exposure amount at a plurality of real latent image line positions is related to the density at the virtual latent image line position in the scanning method, the virtual latent image line position may be reduced due to the variation in the light emission amount of a plurality of light source elements. It may fluctuate, and density unevenness may occur due to the fluctuation of the virtual latent image line position.

  The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus that appropriately suppresses density unevenness caused by variations in the amount of light emitted from a plurality of light source elements.

  An image forming apparatus according to the present invention includes a photosensitive drum, an exposure device that emits a plurality of light beams by a light emitting element array and irradiates the photosensitive drum to form an electrostatic latent image. The image forming apparatus includes a developing device that generates a toner image by attaching toner, and a controller that controls the exposure device. The exposure device irradiates the light beam while scanning it in the main scanning direction at the actual latent image line position to form the electrostatic latent image at the actual latent image line position, and at the two actual latent image line positions, Is irradiated while scanning in the main scanning direction to form the electrostatic latent image at a virtual latent image line position between the two real latent image line positions. The controller measures the amount of emitted light by sequentially emitting light from the plurality of light emitting elements in the light emitting element array, and, based on the amount of emitted light measured for the plurality of light emitting elements, the density at the position of the virtual latent image line. The light emission time per dot of the light emitting element when forming the electrostatic latent image at the virtual latent image line position is individually corrected so that unevenness is suppressed.

  According to the present invention, it is possible to obtain an image forming apparatus that appropriately suppresses density unevenness caused by variations in the light emission amounts of a plurality of light source elements.

  The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of the configuration of the exposure apparatus 2a in FIG. 1 and the configuration of electronic circuits around it. FIG. 3 is a diagram illustrating a pseudo high resolution technique. FIG. 4 is a diagram for explaining pitches of a real latent image line position and a virtual latent image line position when there is no difference between the light emission amounts of the two light emitting elements when the light source 21 in FIG. 2 is an array including two light emitting elements. It is. FIG. 5 is a diagram for explaining the pitch between the real latent image line position and the virtual latent image line position when the light source 21 in FIG. 2 includes two light emitting elements and there is a difference in the amount of emitted light between the two light emitting elements. FIG. 6 is a flowchart illustrating the operation of the image forming apparatus illustrated in FIGS. 1 and 2.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus illustrated in FIG. 1 is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copier, and a multifunction peripheral.

  The image forming apparatus of this embodiment has a tandem type color developing device. This color developing device has photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are photoconductors of four colors of cyan, magenta, yellow and black.

  The exposure devices 2a to 2d irradiate the photosensitive drums 1a to 1d with laser beams to form electrostatic latent images. Each of the exposure devices 2a to 2d has a laser diode as a light source of a laser beam, and an optical element (a lens, a mirror, a polygon mirror, etc.) for guiding the laser beam to the photosensitive drums 1a to 1d.

  Each of the exposure devices 2a to 2d emits a plurality of light beams from the light emitting element array and irradiates the photosensitive drum with the light beams to form an electrostatic latent image.

  Further, a charger such as a scorotron, a cleaning device, a static eliminator, and the like are arranged around the photosensitive drums 1a to 1d. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the charge remover removes electricity from the photosensitive drums 1a to 1d after the primary transfer.

  To the developing devices 3a to 3d, toner cartridges filled with toners of four colors of cyan, magenta, yellow and black are respectively mounted, and the toner is supplied from the toner cartridges to constitute a developer together with a carrier. The developing devices 3a to 3d form toner images by attaching the toner to the electrostatic latent images on the photosensitive drums 1a to 1d.

  As described above, each of the developing devices 3a to 3d generates a toner image by attaching toner to the electrostatic latent image on the photosensitive drums 1a to 1d.

  Magenta development is performed by the photosensitive drum 1a, the exposure device 2a, and the developing device 3a, and cyan development is performed by the photosensitive drum 1b, the exposure device 2b, and the developing device 3b. The developing device 2c and the developing device 3c develop yellow, and the photosensitive drum 1d, the exposing device 2d, and the developing device 3d develop black.

  The intermediate transfer belt 4 is an annular image carrier that comes into contact with the photoconductor drums 1a to 1d and primarily transfers a toner image on the photoconductor drums 1a to 1d. The intermediate transfer belt 4 is stretched around a driving roller 5 and circulates in a direction from a contact position with the photosensitive drum 1d to a contact position with the photosensitive drum 1a by a driving force from the driving roller 5.

  The transfer roller 6 brings the conveyed sheet into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the sheet. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, contacts the cleaning brush with the intermediate transfer belt 4, and removes the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 is an optical sensor that measures the density of the developed toner image, irradiates the intermediate transfer belt 4 with a light beam, and detects the reflected light. For example, at the time of various adjustments, the sensor 8 irradiates a predetermined portion of the intermediate transfer belt 4 with a light beam, detects its reflected light, and responds to a patch image (a toner image of uniform density and a predetermined shape) passing through the predetermined portion. Output an electrical signal.

  The registration roller 10 temporarily stops the paper conveyed by the primary paper supply from a paper supply tray or the like, and conveys the paper to a transfer position by the intermediate transfer belt 4 and the transfer roller 6 at the secondary paper supply timing. The secondary paper feed timing is specified so that the toner image on the intermediate transfer belt 4 is transferred to a specified position on the paper. The registration sensor 11 is a sensor that is installed near the registration roller 10 and optically detects that the sheet has reached the registration roller 10 (registration position).

  FIG. 2 is a diagram showing an example of the configuration of the exposure apparatus 2a in FIG. 1 and the configuration of electronic circuits around it. The exposure apparatus shown in FIG. 2 is an exposure apparatus 2a for the photosensitive drum 1a, and the exposure apparatuses 2b to 2d for the photosensitive drums 1b to 1d have the same configuration.

  In FIG. 2, a light source 21 is a light source that emits a laser beam. The optical system 22 is a group of various lenses arranged between the light source 21 and the polygon mirror 23 and / or between the polygon mirror 23 and the photosensitive drum 1 a and the PD sensor 24. For the optical system 22, an fθ lens or the like is used.

  The light source 21 includes a light emitting element array that emits a plurality of laser beams. In this embodiment, the light emitting element array is a monolithic laser diode array.

  The polygon mirror 23 is an element having an axis perpendicular to the axis of the photosensitive drum 1a, a section perpendicular to the axis being a polygon, and a side surface serving as a mirror. The polygon mirror 23 rotates about its axis, and scans the laser beam emitted from the light source 21 in the axial direction (main scanning direction) of the photosensitive drum 1a. The polygon motor unit 23a rotates the polygon mirror 23 according to a control signal from the controller 31.

  The PD sensor 24 is a sensor that receives a laser beam scanned by the polygon mirror 23 at a predetermined position to generate a main scanning synchronization signal. When light enters, the PD sensor 24 induces an output voltage corresponding to the amount of light. The PD sensor 24 is arranged at a predetermined position on a line on which light is scanned, detects a timing at which a light spot passes through the position, and outputs a pulse formed at that timing as a main scanning synchronization signal.

  The controller 31 includes an ASIC (Application Specific Integrated Circuit), a computer, and the like, controls an internal device of the image forming apparatus, performs data processing, and controls the exposure apparatus 2a (the light source 21, the driver circuit 32, and the like). The photosensitive drum 1a is exposed with a laser beam for forming.

  The driver circuit 32 is a circuit that controls the light source 21 to emit a laser beam. The driver circuit 32 controls the light source 21 so as to be exposed by a laser beam in a pattern corresponding to an image to be formed in synchronization with the main scanning synchronization signal. The driver circuit 32 individually performs light emission control (light emission on / off) for a plurality of light emitting elements of the light source 21 according to a control signal from the controller 31.

  FIG. 3 is a diagram illustrating a pseudo high resolution technique. As shown in FIG. 3, the exposure device 2a forms an electrostatic latent image using a pseudo high resolution technology. Specifically, the exposure device 2a irradiates a laser beam at the actual latent image line position to form an electrostatic latent image at the actual latent image line position, and irradiates a laser beam at the two actual latent image line positions. An electrostatic latent image is formed at a virtual latent image line position between the two real latent image line positions. By adjusting the light amount (intensity or irradiation time) of the laser beam at the actual latent image line position, the toner image is not developed at the actual latent image line position but is developed at the virtual latent image line position. Can be

  Further, the controller 31 measures the amount of emitted light by sequentially emitting light from the plurality of light emitting elements in the light emitting element array of the light source 21, and based on the amount of emitted light measured for the plurality of light emitting elements, the position of the virtual latent image line. The light emission time per dot of the light emitting element is individually corrected so that the density unevenness is suppressed.

  FIG. 4 is a diagram for explaining pitches of a real latent image line position and a virtual latent image line position when there is no difference between the light emission amounts of the two light emitting elements when the light source 21 in FIG. 2 is an array including two light emitting elements. It is. FIG. 5 is a diagram for explaining the pitch between the real latent image line position and the virtual latent image line position when the light source 21 in FIG. 2 includes two light emitting elements and there is a difference in the amount of emitted light between the two light emitting elements.

  When there is no difference in the amount of emitted light, as shown in FIG. 4, the pitch between the actual latent image line position and the position of the imaginary latent image line are uniform, but, for example, as shown in FIG. For example, as shown in FIG. 5, when the amount of light emitted from the first light emitting element is lower than the amount of light emitted from the second light emitting element), one of the pitches between the actual latent image line position and the adjacent actual latent image line position becomes narrower, and the other. Becomes wider.

  The controller 31 makes the light emitting time per dot of the light emitting element with a low light emitting amount longer than the light emitting time of the light emitting element with a high light emitting amount, and makes the light emitting amounts of both light closer to each other.

  The light emission time (time length) per dot (one pixel) is specified by the driver circuit 32 by the controller 31 using, for example, an 8-bit signal, and can be adjusted in 256 steps.

  Specifically, the controller 31 selects (a) one light-emitting element from the plurality of light-emitting elements described above, and (b) changes the light-emitting time (that is, the light-emission light amount) of the selected light-emitting element to change the electrostatic capacity. A latent image is formed, the density of the toner image corresponding to the formed electrostatic latent image is measured by the sensor 8, the amount of emitted light is specified from the measured density, and (c) measurement is performed for the plurality of light emitting elements. Based on the amount of emitted light and the corresponding emission time, one dot of the light emitting element when forming an electrostatic latent image at the position of the virtual latent image line is controlled so that density unevenness at the position of the virtual latent image line is suppressed. Are individually corrected.

  For example, the controller 31 specifies, for each light emitting element, a light emitting time at which the measured density becomes a predetermined density, specifies a ratio of the specified light emitting time, and based on the ratio, (a) a light emitting element having a low light emitting amount. (B) by shortening the light emitting time of the light emitting element having a high light emitting amount, or (c) by performing both of them, so that the light emitting amounts of the plurality of light emitting elements coincide with each other. As close as possible.

  The controller 31 also forms (a) an electrostatic latent image at the actual latent image line position without forming an electrostatic latent image at the virtual latent image line position, and determines the density of the toner image at the actual latent image line position. (B) forming an electrostatic latent image at the virtual latent image line position without forming an electrostatic latent image at the actual latent image line position, and measuring the toner image density based on the virtual latent image line position; The sensor 8 measures the density of the toner image based on the actual latent image line position and the toner image density based on the imaginary latent image line position with respect to a certain density designation value (a certain pixel value in the image data). (C1) Emission time per dot of the light emitting element when forming an electrostatic latent image at a virtual latent image line position or (c2) Formation of an electrostatic latent image at a real latent image line position so that The light emission time per dot of the light emitting element when .

  Next, the operation of the image forming apparatus will be described. FIG. 6 is a flowchart illustrating the operation of the image forming apparatus illustrated in FIGS. 1 and 2.

  At the time of the adjustment, first, as described above, the controller 31 causes the sensor 8 to measure the density of the toner image (patch image) based on (a) the actual latent image line position, and (b) the toner based on the imaginary latent image line position. The sensor 8 measures the density of the image (patch image), and (c) adjusts the imaginary latent image so that the density of the toner image at the actual latent image line position matches the density of the toner image at the imaginary latent image line position. Emission time per dot of the light emitting element when forming an electrostatic latent image at the image line position or (c2) Emission time per dot of the light emitting element when forming an electrostatic latent image at the actual latent image line position Are individually corrected (step S1).

  Next, the controller 31 selects one light emitting element from the plurality of light emitting elements of the light source 21 (step S2), and changes the light emitting time of the selected light emitting element by using only the selected light emitting element. The light emitting element emits light corresponding to the image (step S3). The controller 31 measures the toner density of the patch image at each light emission time with the sensor 8, and specifies the light emission time at which the toner density becomes the predetermined density (step S4).

  Then, the controller 31 determines whether or not the light-emitting characteristics of all the light-emitting elements of the light source 21 (that is, the light-emitting time when the toner density becomes the predetermined density) are determined (step S5), and the light-emitting characteristics are not specified. If there is a light emitting element, the process returns to step S2, selects one light emitting element for which the light emission characteristics are not specified (step S2), and executes the same processing.

  After specifying the light emission characteristics of all the light emitting elements in this way, the controller 31 individually corrects the light emission time of the light emitting elements as described above (step S6).

  As described above, according to the above embodiment, the exposure apparatuses 2a to 2d emit a plurality of light beams from the light emitting element arrays and irradiate the photosensitive drums 1a to 1d to form electrostatic latent images. Further, the exposure devices 2a to 2d form the electrostatic latent image at the actual latent image line position by irradiating light beams while scanning in the main scanning direction at the actual latent image line position, and at the two actual latent image line positions. Light rays are emitted while scanning in the main scanning direction to form an electrostatic latent image at a virtual latent image line position between two real latent image line positions. Then, the controller 31 measures the amount of emitted light by sequentially emitting light from the plurality of light emitting elements in the above-described light emitting element array, and based on the measured amount of emitted light for the plurality of light emitting elements, the controller 31 at the position of the virtual latent image line. The light emission time per dot of the light emitting element when forming an electrostatic latent image at the virtual latent image line position is individually corrected so that the density unevenness is suppressed.

  Thereby, the density unevenness due to the variation in the light emission amount of the plurality of light source elements in the light source 21 is appropriately suppressed.

  Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. That is, such changes and modifications are intended to be included in the scope of the claims.

  For example, in the above-described embodiment, the above-described light emission amount is measured by measuring the toner concentration with the sensor 8, but a part of the light emission light is branched at a predetermined ratio by an optical element such as a beam splitter, and the light is branched. The light emission amount described above may be measured by receiving a part of the emitted light beam with a light receiving element such as a photodiode and measuring the amount of received light.

  In the above embodiment, after the adjustment in step S6, the same processing as in step S1 is performed so that the toner image density based on the actual latent image line position matches the toner image density based on the imaginary latent image line position. Alternatively, the light emission time per dot of the light emitting element when forming an electrostatic latent image at the actual latent image line position may be individually corrected.

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

1a-1d Photoconductor drum 2a-2d Exposure device 3a-3d Developing device 31 Controller

Claims (4)

A photosensitive drum,
An exposure apparatus that forms a latent electrostatic image by irradiating the photosensitive drum with a plurality of light rays emitted by a light emitting element array,
A developing device that generates a toner image by attaching toner to the electrostatic latent image;
A controller for controlling the exposure apparatus,
The exposure device irradiates the light beam while scanning it in the main scanning direction at the actual latent image line position to form the electrostatic latent image at the actual latent image line position, and the light beam at the two actual latent image line positions. Irradiating while scanning in the main scanning direction to form the electrostatic latent image at a virtual latent image line position between the two real latent image line positions,
The controller measures the amount of emitted light by sequentially emitting light from the plurality of light emitting elements in the light emitting element array, and, based on the amount of emitted light measured for the plurality of light emitting elements, the density at the position of the virtual latent image line. Individually correcting the light emission time per dot of the light emitting element when forming the electrostatic latent image at the virtual latent image line position so that unevenness is suppressed;
An image forming apparatus comprising: Further comprising a sensor for measuring the density of the toner image,
The controller is configured to (a) select one light emitting element from the plurality of light emitting elements one by one, and (b) change the light emission time of the selected light emitting element to form the electrostatic latent image. Causing the sensor to measure the density of the toner image corresponding to the electrostatic latent image; identifying the amount of emitted light from the measured density; and (c) determining the amount of emitted light corresponding to the plurality of light emitting elements. And based on the light emission time, so that the density unevenness at the virtual latent image line position is suppressed, so that the light emitting element per dot of the light emitting element when forming the electrostatic latent image at the virtual latent image line position Correcting the emission time individually,
The image forming apparatus according to claim 1, wherein:   The controller (a) forms the electrostatic latent image at the actual latent image line position without forming the electrostatic latent image at the virtual latent image line position, and controls the toner based on the actual latent image line position. (B) forming the electrostatic latent image at the virtual latent image line position without forming the electrostatic latent image at the actual latent image line position; Causing the sensor to measure the density of the toner image based on the image line position, and (c) adjusting the density of the toner image based on the actual latent image line position to match the density of the toner image based on the imaginary latent image line position. (A) a light emission time per dot of the light emitting element when forming the electrostatic latent image at the virtual latent image line position, or (b) forming the electrostatic latent image at the real latent image line position The light emitting time per dot of the light emitting element Another corrected image forming apparatus according to claim 2, characterized in that.   The image forming apparatus according to any one of claims 1 to 3, wherein the light emitting element array is a monolithic laser diode array.

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