JP2019064232A - Image formation apparatus - Google Patents

Abstract

To form an image at the correct gradation level when performing the pseudo-high resolution in the area gradation system.SOLUTION: Exposure devices 2a-2d form electrostatic latent images by emitting light at the actual latent image line positions, and form the electrostatic latent images at the virtual latent image line positions between the two actual latent image line positions by emitting the light at the two actual latent image line positions. A controller 31 adjusts the intensity or emission time of the light for each image pattern so that the density of toner images of the plurality of image patterns becomes uniform within the prescribed range based on the reference density for the plurality of image patterns in each group in the plurality of groups corresponding to the plurality of area gradation levels. All of the plurality of image patterns in the group include (a) the area gradation level corresponding to the group, and the plurality of image patterns in the group includes (b) the image pattern including both of the dots at the actual latent image line position and the dots at the virtual latent image line position.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus, an interleave scanning method is employed as a means for increasing the resolution, and laser light is physically scanned at an actual latent image line position, and a virtual latent image line between two actual latent image line positions At the position, an electrostatic latent image is formed. That is, at the virtual latent image line position, an electrostatic latent image at the virtual latent image line position is formed without physically scanning the laser light.

  In such a pseudo high resolution technology, an error in the image density may occur between the virtual latent image line position and the actual latent image line position due to the change of the use environment, the temporal change of the image forming apparatus, etc. is there.

  In one image forming apparatus, line images are formed at a plurality of actual latent image line positions, density adjustment of the plurality of actual latent image line positions is performed, and then a virtual latent image line between two actual latent image line positions A line image is formed at a position to adjust the density of the virtual latent image line position (see, for example, Patent Document 1).

JP 2002-278178 A

  However, in the case of performing gradation expression by the area gradation method, since an image pattern expressing each gradation level is formed by various dot patterns, even if density adjustment is performed with a line image as described above, Depending on the dot pattern, it may not be possible to obtain an accurate density (that is, an accurate gradation level).

  The present invention has been made in view of the above problems, and it is an object of the present invention to obtain an image forming apparatus that forms an image with an accurate gradation level when performing pseudo high resolution by an area gradation method.

  In the image forming apparatus according to the present invention, a photosensitive drum, an exposure device for irradiating the photosensitive drum with light to form an electrostatic latent image, and toner attached to the electrostatic latent image to generate a toner image And a sensor for measuring the density of the toner image, and a controller for controlling the exposure device. The exposure device emits the light at the actual latent image line position to form the electrostatic latent image at the actual latent image line position, and emits the light at two actual latent image line positions to form the two light beams. The electrostatic latent image is formed at virtual latent image line positions between actual latent image line positions. The controller is further configured to control the density of the toner image of the plurality of image patterns within a predetermined range based on the reference density for a plurality of image patterns in each of the plurality of groups corresponding to each of the plurality of area gradation levels. The light intensity or irradiation time corresponding to each of the plurality of image patterns is adjusted so as to be uniform. The plurality of image patterns in the group (a) all have an area gradation level corresponding to the group, and (b) dots of the real latent image line position and dots of the virtual latent image line position. It includes at least one image pattern including both.

  According to the present invention, it is possible to obtain an image forming apparatus that forms an image with an accurate tone level when performing pseudo high resolution by the area tone method.

  The above or 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 view showing an example of the arrangement of the exposure apparatus 2a shown in FIG. 1 and the arrangement of electronic circuits therearound. FIG. 3 is a diagram for explaining the pseudo high resolution technique. FIG. 4 is a diagram showing an example of an image pattern group in which the area gradation level is 1 among 0 to 16 in the first embodiment. FIG. 5 is a diagram showing an example of a group of image patterns in which the area gradation level is 2 out of 0 to 16 in the first embodiment. FIG. 6 is a diagram showing an example of a group of image patterns having an area gradation level of 4 in 0 to 16 in the first embodiment. FIG. 7 is a diagram showing an example of a plurality of groups of image patterns in which the area gradation level is 2 out of 0 to 16 in the second embodiment. FIG. 8 is a diagram showing an example of a plurality of groups of image patterns in which the area gradation level is 4 among 0 to 16 in the second embodiment.

  Hereinafter, embodiments of the present invention will be described based on the drawings.

Embodiment 1

  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 shown in FIG. 1 is an apparatus having a printing function of an electrophotographic system, such as a printer, a facsimile machine, a copier, a multifunction machine, and the like.

  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 photoreceptor drums 1a to 1d are photoreceptors of four colors of cyan, magenta, yellow and black.

  The exposure devices 2a to 2d irradiate laser light to the photosensitive drums 1a to 1d to form electrostatic latent images. The exposure devices 2a to 2d include a laser diode which is a light source of laser light, and an optical element (a lens, a mirror, a polygon mirror or the like) for guiding the laser light to the photosensitive drums 1a to 1d.

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

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

  The development of magenta is performed by the photosensitive drum 1a, the exposure device 2a, and the developing device 3a, and the development of cyan is performed by the photosensitive drum 1b, the exposure device 2b, and the developing device 3b, so that the photosensitive drum 1c is exposed. The yellow development is performed by the device 2c and the developing device 3c, and the black development is performed by the photosensitive drum 1d, the exposure device 2d, and the developing device 3d.

  The intermediate transfer belt 4 is an annular image carrier that contacts the photosensitive drums 1 a to 1 d and primarily transfers the toner image on the photosensitive drums 1 a to 1 d. The intermediate transfer belt 4 is stretched around the drive roller 5 and revolves in the direction from the contact position with the photosensitive drum 1 d to the contact position with the photosensitive drum 1 a by the driving force from the drive 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 onto the sheet. The sheet to which the toner image has been transferred is conveyed to the fixing unit 9, and the toner image is fixed to the sheet.

  The roller 7 has a cleaning brush and brings the cleaning brush into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the sheet.

  The sensor 8 is an optical sensor for measuring the density of the developed toner image, and irradiates the intermediate transfer belt 4 with a light beam to detect the reflected light. For example, at the time of toner concentration adjustment, the sensor 8 irradiates a predetermined area of the intermediate transfer belt 4 with a light beam, detects the reflected light, and outputs an electric signal according to the light amount.

  The registration roller 10 temporarily stops the sheet conveyed as a primary sheet feed from a sheet feed tray or the like, and conveys the sheet to a transfer position by the intermediate transfer belt 4 and the transfer roller 6 at a secondary sheet feed timing. The secondary sheet feeding timing is designated so that the toner image on the intermediate transfer belt 4 is transferred to the designated position on the sheet. The resist sensor 11 is a sensor that is disposed in the vicinity of the resist roller 10 and optically detects that the sheet has reached the resist roller 10 (registration position).

  FIG. 2 is a view showing an example of the arrangement of the exposure apparatus 2a shown in FIG. 1 and the arrangement of electronic circuits therearound. The exposure device shown in FIG. 2 is the exposure device 2a for the photosensitive drum 1a, and the exposure devices 2b to 2d for the photosensitive drums 1b to 1d have the same configuration.

  In FIG. 2, a laser diode 21 is a light source for emitting a laser beam. The optical system 22 is various lens groups disposed between the laser diode 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 polygon mirror 23 is an element having an axis perpendicular to the axis of the photosensitive drum 1a, a cross section perpendicular to the axis being a polygon, and a side surface thereof being a mirror. The polygon mirror 23 rotates about its axis, and scans the laser beam emitted from the laser diode 21 along the axial direction (main scanning direction) of the photosensitive drum 1a.

  The polygon motor unit 23 a rotates the polygon mirror 23 in accordance with a control signal from the controller 31.

  Further, the PD sensor 24 is a sensor for receiving the laser beam scanned by the polygon mirror 23 at a predetermined position in order to generate a main scanning synchronization signal. When light enters, the PD sensor 24 induces an output voltage according to the amount of light. The PD sensor 24 is disposed at a predetermined position on a line on which light is scanned, detects the timing when the 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 application specific integrated circuit (ASIC), a computer, and the like, controls internal devices of the image forming apparatus, performs data processing, and the like, and controls the exposure device 2a (laser diode 21, driver circuit 32, etc.) The photosensitive drum 1a is exposed to laser light for image formation. At this time, gradation is expressed by an area gradation method.

  The driver circuit 32 is a circuit that controls the laser diode 21 to emit laser light. The driver circuit 32 controls the laser diode 21 so as to be exposed by the laser beam in a pattern according to the image to be formed in synchronization with the main scanning synchronization signal.

  FIG. 3 is a diagram for explaining the pseudo high resolution technique. As shown in FIG. 3, the exposure apparatus 2a forms an electrostatic latent image using a pseudo-resolution technique. Specifically, the exposure device 2a irradiates laser light at an actual latent image line position to form an electrostatic latent image at an actual latent image line position, and irradiates laser light at two actual latent image line positions. An electrostatic latent image is formed at the virtual latent image line position between the two real latent image line positions. The toner image is developed at the virtual latent image line position without developing the toner image at the actual latent image line position by adjusting the light amount (intensity or irradiation time) of the laser light at the actual latent image line position. You can do so.

  Furthermore, the controller 31 causes the exposure device 2a to form electrostatic latent images of the image patterns corresponding to each of the plurality of area gradation levels, and the measured density of the toner image of the image pattern corresponding to the electrostatic latent image is Identification is made based on the sensor output of the sensor 8, and the intensity or irradiation time (that is, light emission time) of the laser light of the exposure device 2a is adjusted based on the measured concentration, thereby performing density adjustment.

  Specifically, for the plurality of image patterns in each group in the plurality of groups corresponding to each of the plurality of area gradation levels, the controller 31 determines that the density of the toner image of the plurality of image patterns is based on the reference density. The intensity or irradiation time of the laser beam corresponding to each of the plurality of image patterns is adjusted to be uniform within the range. That is, the controller 31 determines whether the density of toner images of a plurality of image patterns is uniform within the above-described predetermined range, and the density of toner images of a plurality of image patterns is uniform within the above-described predetermined range If not, change the intensity or the irradiation time of the above-mentioned laser light, and determine again whether the density of the toner image of the plurality of image patterns is uniform within the predetermined range. The density of the toner image of the image pattern is made uniform within the above-described predetermined range.

  In the first embodiment, as the condition # 1, a plurality of image patterns in each of the groups (a) all have an area gradation level corresponding to the group, and (b) dots of the actual latent image line position And at least one image pattern including both of the latent image line position dots.

  Furthermore, as the condition # 2, the plurality of image patterns in each group include a reference image pattern including only dots of the actual latent image line position, and the controller 31 sets the density of the toner image of the reference image pattern to the above-described reference It is the concentration. The intensity or irradiation time of the laser beam for the reference image pattern is a predetermined fixed value. Alternatively, the above-mentioned reference concentration may be a predetermined fixed concentration.

  FIG. 4 is a diagram showing an example of an image pattern group in which the area gradation level is 1 among 0 to 16 in the first embodiment. In the example shown in FIG. 4, two image patterns 51-1 and 51-2 are included in the group when the area gradation level is 1. The image pattern 51-1 has one dot at the real latent image line position. The image pattern 51-2 has one dot at the virtual latent image line position.

  FIG. 5 is a diagram showing an example of a group of image patterns in which the area gradation level is 2 out of 0 to 16 in the first embodiment. In the example shown in FIG. 5, five image patterns 52-1 to 52-5 are included in the group when the area gradation level is two. The image pattern 52-1 has one dot at each of two different real latent image line positions. The image pattern 52-2 has two dots continuous in the main scanning direction at one virtual latent image line position. The image pattern 52-3 has one dot at each of two different virtual latent image line positions. The image pattern 52-4 has two continuous dots in the main scanning direction at one real latent image line position. The image pattern 52-5 has two dots continuous in the sub-scanning direction at real latent image line positions and virtual latent image line positions adjacent to each other.

  FIG. 6 is a diagram showing an example of a group of image patterns having an area gradation level of 4 in 0 to 16 in the first embodiment. In the example shown in FIG. 6, five image patterns 53-1 to 53-5 are included in the group when the area gradation level is four. The image pattern 53-1 has two discontinuous dots respectively at two different real latent image line positions. The image pattern 53-2 has four continuous dots in the sub-scanning direction at two continuous real latent image line positions and two virtual latent image line positions. The image pattern 53-3 has two discontinuous dots respectively at two different virtual latent image line positions. The image pattern 53-4 has four dots which are discontinuous in both the main scanning direction and the sub scanning direction, one each at two continuous real latent image line positions and two virtual latent image line positions. The image pattern 53-5 has two sets of two continuous dots in the sub-scanning direction at real latent image line positions and virtual latent image line positions adjacent to each other.

  Furthermore, the controller 31 applies the intensity or irradiation time of the adjusted laser beam corresponding to a certain image pattern to another image pattern of the same area gradation level. However, the other image pattern does not change the dot pattern in the image pattern where the intensity or irradiation time of the laser light is adjusted, the number of dots in the actual latent image line position and the number of dots in the virtual latent image line position. It shall have the dot pattern obtained by making it move.

  Next, the operation of the image forming apparatus according to the first embodiment will be described.

  At predetermined adjustment timings, the controller 31 performs density adjustment of each gradation level (that is, area gradation level).

  In the density adjustment, the controller 31 controls the exposure devices 2a to 2d and the developing devices 3a to 3d to form a toner image of the image pattern for each image pattern in each group, and the sensor 8 measures the density If the density is not within the predetermined range based on the reference density, the intensity or irradiation time of the laser light of the exposure devices 2a to 2d is changed according to the density, and the density of the toner image of the image pattern The formation of the toner image of the image pattern, the measurement of the density, and the change of the intensity or irradiation time of the laser light are repeated until the predetermined range based on the reference density is reached.

  For example, assuming that the laser emission time can be adjusted with a resolution of 256 steps and the reference density is 1.0, the density adjustment for the group (area gradation level = 1) shown in FIG. When the laser emission time is 100/256 and the laser emission time is 50/256 for the image pattern 51-2, the image patterns 51-1 and 51-2 are formed. When the measured density value of the image pattern 51-2 is 1.1, the laser emission time of the image pattern 51-2 is changed to 49/256, and the image pattern 51-2 is formed again. The density adjustment can be similarly performed for other area gradation levels.

  As described above, according to the first embodiment, the exposure devices 2a to 2d irradiate light at the actual latent image line position to form an electrostatic latent image at the actual latent image line position, and Light is emitted at the latent image line position to form an electrostatic latent image at the virtual latent image line position between the two real latent image line positions. The controller 31 makes the density of the toner image of the plurality of image patterns uniform within a predetermined range based on the reference density for the plurality of image patterns in each group in the plurality of groups corresponding to each of the plurality of area gradation levels. Thus, the light intensity or irradiation time corresponding to each of the plurality of image patterns is adjusted. Then, the plurality of image patterns in the group (a) all have an area gradation level corresponding to the group, and (b) both the dots of the real latent image line position and the dots of the virtual latent image line position. Include at least one image pattern.

  As a result, density adjustment is individually performed for various image patterns of each area gradation level, and therefore, when performing pseudo high resolution by the area gradation system, it is possible to form an image with an accurate gradation level. .

Second Embodiment

  In the second embodiment, in addition to the conditions of the first embodiment (conditions # 1 and # 2 described above), in the dot pattern of a plurality of image patterns in each group as the condition # 3, the main scanning direction or the sub scanning direction The numbers of consecutive dots are identical to one another.

  That is, in the second embodiment, a plurality of groups are set for one area gradation level for at least one of the plurality of area gradation levels, and the density of the toner image of the plurality of image patterns is set for each group. The light intensity or irradiation time corresponding to each of the plurality of image patterns is adjusted so as to be uniform within a predetermined range based on the reference density.

  FIG. 7 is a diagram showing an example of a plurality of groups of image patterns in which the area gradation level is 2 out of 0 to 16 in the second embodiment. In the example shown in FIG. 7, two groups 61 and 62 are set. The group 61 has an image pattern 61-1 and 61-2 having two dots (that is, two discontinuous dots) in which the number of continuous dots is 1 in both the main scanning direction and the sub scanning direction. Including. The group 62 includes image patterns 62-1, 62-2, and 62-3 having two dots in which the number of continuous dots in the main scanning direction or the sub scanning direction is two. Then, concentration adjustment is performed for each group.

  FIG. 8 is a diagram showing an example of a plurality of groups of image patterns in which the area gradation level is 4 among 0 to 16 in the second embodiment. In the example shown in FIG. 8, three groups 71 and 72 are set. The group 71 has image patterns 71-1, 71-2, having four dots (that is, four discontinuous dots) in which the number of continuous dots is 1 in both the main scanning direction and the sub scanning direction. 71-3. The group 72 includes image patterns 72-1 and 72-2 having four dots in which the number of continuous dots in the main scanning direction or the sub scanning direction is two. The group 73 includes image patterns 73-1 and 73-2 having four dots in which the number of continuous dots in the main scanning direction or the sub scanning direction is four. Then, concentration adjustment is performed for each group.

  The other configuration and operation of the image forming apparatus according to the second embodiment are the same as in the first embodiment, and thus the description thereof is omitted.

  As described above, according to the second embodiment, density adjustment is performed for each image pattern in which the number of continuous dots in the main scanning direction or the sub scanning direction is the same. To be executed.

  Note that 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 the intended advantages. That is, such changes and modifications are intended to be included in the scope of the claims.

  For example, in the above embodiment, the number of changes of the laser light intensity or irradiation time at the time of adjustment of the laser light intensity or irradiation time may be equal to or less than a predetermined upper limit value.

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

1a to 1d Photosensitive drum 2a to 2d Exposure device 3a to 3d Development device 8 Sensor 31 Controller

Claims (5)

Photosensitive drum,
An exposure device that irradiates light to the photosensitive drum to form an electrostatic latent image;
A developing device for attaching toner to the electrostatic latent image to generate a toner image;
A sensor that measures the density of the toner image;
And a controller for controlling the exposure device,
The exposure device emits the light at the actual latent image line position to form the electrostatic latent image at the actual latent image line position, and emits the light at two actual latent image line positions to form the two light beams. Forming the electrostatic latent image at virtual latent image line positions between actual latent image line positions;
The controller is configured to make the density of the toner image of the plurality of image patterns uniform within a predetermined range based on the reference density for a plurality of image patterns in each group in a plurality of groups corresponding to a plurality of area gradation levels. Adjusting the intensity or irradiation time of the light corresponding to each of the plurality of image patterns so that
The plurality of image patterns in the group (a) all have an area gradation level corresponding to the group, and (b) dots of the real latent image line position and dots of the virtual latent image line position. Including at least one image pattern including both;
An image forming apparatus characterized by The plurality of image patterns in the group include a reference image pattern including only dots of the actual latent image line position,
The controller sets the density of the toner image of the reference image pattern as the reference density.
The image forming apparatus according to claim 1, wherein A plurality of groups are set corresponding to one area gradation level, and dot patterns of the plurality of image patterns in each group in the plurality of groups set corresponding to the one area gradation level are main scanning The number of consecutive dots in the direction or sub-scanning direction being identical to each other,
The image forming apparatus according to claim 1 or 2, wherein The controller applies the adjusted intensity or irradiation time of the light corresponding to the image pattern to another image pattern of the same area gradation level,
The other image pattern does not change the dot pattern in the image pattern whose light intensity or irradiation time has been adjusted, the number of dots in the actual latent image line position and the number of dots in the virtual latent image line position Having a dot pattern obtained by moving
The image forming apparatus according to any one of claims 1 to 3, characterized in that The controller determines whether the density of the toner image of the plurality of image patterns is uniform within the predetermined range, and the density of the toner image of the plurality of image patterns is uniform within the predetermined range If not, it is determined again whether the density of the toner image of the plurality of image patterns is uniform within the predetermined range by changing the intensity or irradiation time of the light.
The number of times of change of the light intensity or the irradiation time is equal to or less than a predetermined upper limit value.
The image forming apparatus according to any one of claims 1 to 4, characterized in that

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