JP2020118854A - Image forming apparatus - Google Patents

Abstract

To prevent positional deviation of a virtual latent image line position in performing light beam irradiation at an actual latent image line position using a plurality of light emitting elements to form an electrostatic latent image at the virtual latent image line position.SOLUTION: Exposure devices 2a to 2d use a light source 21 having a plurality of light emitting elements to form an electrostatic latent image at a virtual latent image line position in an interleave scan method. A controller 31 individually corrects a light emission time per one dot of the light emitting elements when the electrostatic latent image is formed at the virtual latent image line position so that exposure energy density distributions caused by light beams from the plurality of light emitting elements match each other or come closest to each other, corresponding to the beam diameter of the light beams from the plurality of light emitting elements at main scanning direction positions.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus.

An image forming apparatus employs an interleave scanning method as a means for increasing the pseudo resolution, and physically scans a light beam at a real latent image line position to generate a virtual latent image line position between two real latent image line positions. Thus, an electrostatic latent image is formed on the photosensitive drum (see, for example, Patent Document 1). That is, an electrostatic latent image is formed at the virtual latent image line position without physically scanning the light beam at the virtual latent image line position.

JP, 2007-274098, A

An image forming apparatus uses a plurality of light emitting elements to irradiate a plurality of real latent image line positions while scanning light rays in parallel. In that case, due to the variation (individual difference) of the plurality of light emitting elements and the optical system from the light emitting element to the photoconductor drum, the light beam from the plurality of light emitting elements may cause the light beam on the photoconductor drum at each position in the main scanning direction. Beam diameters may differ from each other.

If the beam diameters of the plurality of real latent image lines are different from each other at a certain position in the main scanning direction, the light amount distribution (that is, the exposure energy) in the sub-scanning direction caused by the light beam irradiation to the plurality of real latent image lines. Density distributions) are not the same as each other, and the center (peak position) of the exposure energy density distribution formed on the virtual latent image lines is deviated instead of the center of those actual latent image lines. This deviation is not preferable because it appears in the print image as a positional deviation of the virtual latent image line.

The present invention has been made in view of the above problems, and in the case of forming an electrostatic latent image at a virtual latent image line position by irradiating light rays at a real latent image line position using a plurality of light emitting elements. An object of the present invention is to obtain an image forming apparatus that suppresses the displacement of the virtual latent image line position.

An image forming apparatus according to the present invention includes a photoconductor drum, an exposure device that emits a plurality of light beams by a plurality of light emitting elements and irradiates the photoconductor drum to form an electrostatic latent image, and the electrostatic latent image. A developing device that adheres toner to the toner to generate a toner image, and a controller that controls the exposure device. The exposure device forms the electrostatic latent image at the real latent image line position by irradiating the plurality of light rays while scanning in the main scanning direction at the real latent image line position, and at the plurality of real latent image line positions. The plurality of light beams are irradiated while scanning in the main scanning direction to form the electrostatic latent image at the virtual latent image line positions between the real latent image line positions. Then, the controller corresponds to the beam diameters of the light rays from the plurality of light emitting elements at the respective positions in the main scanning direction so that the exposure energy density distributions of the light rays from the plurality of light emitting elements match or come closest to each other. , 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.

According to the present invention, when a plurality of light emitting elements are used to irradiate a light beam at a real latent image line position to form an electrostatic latent image at a virtual latent image line position, displacement of the virtual latent image line position is suppressed. An image forming apparatus that can be obtained is obtained.

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 in the vicinity thereof. FIG. 3 is a diagram illustrating a pseudo high resolution technique. FIG. 4 is a diagram for explaining the pitch of the real latent image line position and the virtual latent image line position when the light source 21 in FIG. 2 has the same beam diameter (beam diameter in the sub-scanning direction) of the two light emitting elements. .. FIG. 5 is a diagram illustrating a difference in beam diameter between light emitting elements at each position in the main scanning direction. FIG. 6 is a diagram for explaining the correspondence between the beam diameter and the exposure energy.

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 shown in FIG. 1 is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, and a multifunction machine.

The image forming apparatus of this embodiment has a tandem type color developing device. This color developing device has photoconductor 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 photoconductor drums 1a to 1d with a laser beam to form electrostatic latent images. Each of the exposure devices 2a to 2d has a laser diode that is a light source of a laser beam and an optical element (lens, mirror, polygon mirror, etc.) that guides the laser beam to the photoconductor drums 1a to 1d.

Each of the exposure devices 2a to 2d causes a plurality of light emitting elements to emit a plurality of light rays and irradiates the photoconductor drums 1a to 1d to form an electrostatic latent image.

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

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

In this way, the developing devices 3a to 3d generate toner images by attaching toner to the electrostatic latent images on the photoconductor drums 1a to 1d.

The photosensitive drum 1a, the exposure device 2a, and the developing device 3a perform magenta development, and the photosensitive drum 1b, the exposure device 2b, and the developing device 3b perform cyan development, and the photosensitive drum 1c and exposure are performed. The device 2c and the developing device 3c develop yellow, and the photosensitive drum 1d, the exposure device 2d, and the developing device 3d develop black.

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

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

The roller 7 has a cleaning brush, and the cleaning brush is brought 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 to 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 light rays, 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 the reflected light thereof, and responds to a patch image (a toner image having a uniform density and a predetermined shape) passing through the predetermined portion. Output electrical signal.

The registration roller 10 temporarily stops the sheet conveyed by the primary sheet feeding from the sheet feed tray or the like, and conveys the sheet to the transfer position by the intermediate transfer belt 4 and the transfer roller 6 at the secondary sheet feeding timing. The secondary paper feed timing is designated so that the toner image on the intermediate transfer belt 4 is transferred to the designated position on the paper. The registration sensor 11 is a sensor that is installed in the vicinity of the registration roller 10 and optically detects that the paper 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 in the vicinity thereof. The exposure device shown in FIG. 2 is the exposure device 2a for the photoconductor drum 1a, and the exposure devices 2b to 2d for the photoconductor drums 1b to 1d have the same configuration.

In FIG. 2, the light source 21 is a light source having a plurality of light emitting elements that emit a plurality of light rays.
Here, the light source 21 is a monolithic two-beam semiconductor laser. 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. An fθ lens or the like is used for the optical system 22.

The polygon mirror 23 is an element that has an axis perpendicular to the axis of the photosensitive drum 1a, has a polygonal cross section perpendicular to the axis, and has 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 along 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 to generate a main scanning synchronization signal at a predetermined position. When light is incident on the PD sensor 24, the PD sensor 24 induces an output voltage according to the amount of light. The PD sensor 24 is arranged at a predetermined position on the line where the light is scanned, detects the timing when the spot of the light passes through that position, and outputs the pulse formed at that timing as the main scanning synchronization signal.

The controller 31 includes an ASIC (Application Specific Integrated Circuit), a computer, and the like, controls the internal devices of the image forming apparatus, performs data processing, and the like, and exposes the exposure apparatuses 2a to 2d (the light source 21) according to the image data of the image to be printed. , The driver circuit 32) to expose the photosensitive drums 1a to 1d with a laser beam for image formation.

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 to emit light in a temporal pattern designated by the controller 31, in synchronization with the main scanning synchronization signal. The driver circuit 32 individually controls light emission of a plurality of light emitting elements of the light source 21 (ON/OFF of light emission at a constant light amount) 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 technique. Specifically, the exposure device 2a irradiates a plurality of laser beams at a plurality of real latent image line positions to form an electrostatic latent image at the real latent image line positions, and also a plurality (here, two) of real latent image line positions. A laser beam is irradiated at the latent image line position to form an electrostatic latent image at the virtual latent image line positions between the plurality of (two in this case) 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 the toner image is developed at the virtual latent image line position. , An electrostatic latent image is formed.

Further, the controller 31 corresponds to the beam diameters of the light rays from the plurality of light emitting elements of the light source 21 at each position in the main scanning direction, and the exposure energy density distribution (particularly in the sub-scanning direction) by the light rays from the plurality of light emitting elements. 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 exposure energy density distributions in the directions match or come closest to each other.

In this embodiment, the controller 31 causes the plurality of light emission of the light source 21 so that the exposure energy density distribution by the light rays from the plurality of light emitting elements of the light source 21 coincides with or comes closest to the exposure energy density distribution at the predetermined reference diameter. Correct the light emission time of each element. As a result, the exposure energy density distributions (particularly, the exposure energy density distributions in the sub-scanning direction) due to the light rays from the plurality of light emitting elements match or come closest to each other.

FIG. 4 is a diagram for explaining the pitch of the real latent image line position and the virtual latent image line position when the light source 21 in FIG. 2 has the same beam diameter (beam diameter in the sub-scanning direction) of the two light emitting elements. .. As shown in FIG. 4, when the beam diameter is the same, the pitch between the real latent image line position and the virtual latent image line position becomes uniform. On the other hand, when the beam diameters are not the same, the exposure energy density distribution differs between the light emitting elements, and the center (peak position) of the exposure energy density distribution of the virtual latent image line obtained by combining them is the virtual latent image line. Offset from the center between two adjacent real latent image lines. That is, 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.

Therefore, the controller 31 makes the light emission time per dot of the light emitting element having a large beam diameter longer than the light emission time of the light emitting element having a small beam diameter so that the light emission amounts of the both are close to each other.

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

FIG. 5 is a diagram illustrating a difference in beam diameter between light emitting elements at each position in the main scanning direction. FIG. 6 is a diagram for explaining the correspondence between the beam diameter and the exposure energy. Usually, the intensity distribution of light rays in the main scanning direction and the sub-scanning direction (that is, the exposure energy density distribution) is a substantially Gaussian distribution, and the width at which the light intensity reaches a predetermined value (for example, 13.5% of the peak) is the beam. It is considered to be the diameter. For example, as shown in FIG. 5, due to the optical system 22, the beam diameters of the beams #1 and #2 of the respective light emitting elements change along the main scanning direction.

Further, due to differences in the characteristics of the light emitting elements, there is a difference in beam diameter (beam diameter in the sub-scanning direction) between the light emitting elements. Then, for example, as shown in FIG. 6, the exposure energy E decreases from the reference energy Er as the beam diameter increases from the reference diameter Dr. Here, this exposure energy E is a spatial (here, along the sub-scanning direction) integrated value of the exposure energy density that contributes to toner development (that is, equal to or greater than the development threshold in FIG. 4), as shown in FIG. (That is, the area of the hatched portion in FIG. 4).

In this embodiment, the above-mentioned reference diameter Dr is the minimum value in the main scanning direction of the beam diameter of the light emitting element (the light emitting element of beam #1 in FIG. 5) having the smallest beam diameter among the plurality of light emitting elements ( In FIG. 5, a predetermined value (here, the minimum value) equal to or smaller than the beam diameter D1(Xr) at the reference position Xr is set. Then, the light emission time of each light emitting element is corrected at each position in the main scanning direction so as to approach the reference energy Er corresponding to the reference diameter Dr. That is, as shown in FIG. 6, a decrease dEi(X) of the exposure energy E from the reference energy Er corresponding to the beam diameter Di(X) (i=1, 2) at the position X in the main scanning direction. The light emission time is extended by the time length for increasing the exposure energy E.

Further, in this embodiment, a plurality of light rays from a plurality of light emitting elements are irradiated onto the photosensitive drum 1a at different positions in the main scanning direction at each time at the actual latent image line position. A plurality of light emitting elements may be arranged in the light source 21. In that case, the controller 31 specifies (a) the light emitting element of the light beam emitted to the most preceding position in the main scanning direction among the irradiation positions of the plurality of light rays as the preceding light emitting element, and (b) the preceding light emitting element. For the light emitting element, the correction amount of the light emission time per dot when forming the electrostatic latent image at the virtual latent image line position is specified, and the light emission time of the preceding light emitting element is corrected by the correction amount, (c) When the correction amount of the light emission time of the preceding light emitting element is specified, the correction amount of the light emission time of the remaining light emitting element at the most preceding position in the main scanning direction is also specified, and (d) the remaining When the irradiation position of the light beam from the light emitting element reaches the most advanced position in the main scanning direction, the emission time of the remaining light emitting element is corrected by the correction amount of the remaining light emitting element already specified. You may do so.

For example, in FIG. 5, when the light emitting position of the preceding light emitting element is X1 and the light emitting position of the remaining light emitting element is X2 at a certain time t1, the light emitting time of the preceding light emitting element is the beam diameter D1 (X1). The correction amount of the emission time of the remaining light emitting elements at the position X1 (that is, the correction amount corresponding to the beam diameter D2(X1)) is also derived. Then, at time t1, the light emission time of the remaining light emitting elements is corrected according to the beam diameter D2 (X2), but at the subsequent time t2, the light beam irradiation position of the remaining light emitting elements becomes X1. In addition, the emission time of the remaining light emitting elements is corrected by the above-described correction amount derived in advance when the irradiation position of the preceding light emitting element is X1.

In that case, main correction data indicating the correction amount of the light emission time of the preceding light emitting element at each position in the main scanning direction, the correction amount of the light emission time of the preceding light emitting element at each position in the main scanning direction, and the remaining light emission. The sub-correction data indicating the difference or ratio with the correction amount of the light emission time of the element is previously acquired by an experiment or the like, and is stored in a storage device (not shown, such as a built-in non-volatile storage device). A temperature sensor for measuring the environmental temperature of 2a to 2d is installed, and the controller 31 specifies (a) the correction amount of the light emission time of the preceding light emitting element based on the main correction data, and (b) the temperature sensor. The correction amount of the light emission time of the preceding light emitting element is corrected by the temperature correction coefficient corresponding to the environmental temperature of the exposure apparatuses 2a to 2d detected by, and the temperature correction coefficient is corrected based on the sub correction data (c). The correction amount of the light emission time of the remaining light emitting elements may be specified from the correction amount of the light emission time of the preceding light emitting element. By doing so, the temperature correction is reflected only in the light emission time of the preceding light emitting element, and the temperature correction is reflected in the light emission time of the remaining light emitting elements, so that the calculation amount for the temperature correction can be small. ..

Next, the operation of the image forming apparatus will be described.

After executing the image processing of the image to be printed, the controller 31 controls the exposure devices 2a to 2d according to the image data of the image, exposes the photosensitive drums 1a to 1d with a laser beam for image formation, and prints. An electrostatic latent image corresponding to the image to be formed is formed. The developing device 3a develops the electrostatic latent image with toner to form a toner image. The toner image is primarily transferred to the intermediate transfer belt 4, then secondarily transferred to a print sheet, and fixed by the fixing device 9.

When forming the electrostatic latent image, the controller 31 uses the driver circuit 32 to control the light emission time of each light emitting element of the light source 21. That is, as shown in FIG. 2, the light rays from the respective light emitting elements of the light source 21 are scanned in the main scanning direction, and the controller 31 determines that the dots should be formed according to the image data (that is, the scanning position or the irradiation position). Determine the light emission time.

At that time, the controller 31 controls the light emitting elements of the light source 21 from the plurality of light emitting elements of the light source 21 in accordance with the beam diameter Di(X) (i=1, 2) at each position X in the main scanning direction. 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 exposure energy density distributions of the light beams coincide with or come closest to each other.

In this embodiment, the irradiation positions of the plurality of light emitting elements in the main scanning direction are different from each other, and as described above, when the correction amount of the emission time of the preceding light emitting element with respect to the irradiation position X1 of the preceding light emitting element is derived, At the same time, the correction amount of the light emission time of the remaining light emitting elements at the position X1 is derived and held in a memory (not shown) or the like until the irradiation position of the remaining light emitting elements reaches the position X1.

As described above, according to the above-described embodiment, the exposure apparatuses 2a to 2d irradiate a plurality of light rays while scanning them in the main scanning direction at the actual latent image line position to irradiate the electrostatic latent image at the actual latent image line position. And a plurality of light rays are emitted while scanning in the main scanning direction at a plurality of real latent image line positions to form an electrostatic latent image at a virtual latent image line position between the real latent image line positions. Then, the controller 31 adjusts the exposure energy density distributions of the light rays from the plurality of light emitting elements so as to match or come closest to each other in accordance with the beam diameters of the light rays from the plurality of light emitting elements at the respective positions in the main scanning direction. , 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.

As a result, the exposure energy density distribution due to the light irradiation at the real latent image line position adjacent to the virtual latent image line position becomes substantially the same, and the light irradiation is performed at the real latent image line position by using a plurality of light emitting elements to create a virtual latent image. The position shift of the virtual latent image line position when the electrostatic latent image is formed at the image line position (that is, the position shift caused by the difference in beam diameter of the light rays of the plurality of light emitting elements of the light source 21) is 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 covered by the appended claims.

For example, in the above-described embodiment, the scanning width in the main scanning direction (or the width of the photosensitive drums 1a to 1d) is divided by a predetermined number of divisions, and each of the sections in the main scanning direction is obtained by the division. The above-described correction amount may be derived, and the light emission time at that position in the main scanning direction may be corrected with the correction amount corresponding to the section including each position in the main scanning direction.

Further, in the above embodiment, the number of light emitting elements of the light source 21 is two, but it may be three or more.

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 Developing device 31 Controller

Claims (4)

A photoconductor drum,
An exposure device that forms a latent electrostatic image by irradiating a plurality of light rays with a plurality of light emitting elements and irradiating the photosensitive drum.
A developing device that adheres toner to the electrostatic latent image to generate a toner image;
A controller for controlling the exposure apparatus,
The exposure device forms the electrostatic latent image at the real latent image line position by irradiating the plurality of light rays while scanning in the main scanning direction at the real latent image line position, and at the plurality of real latent image line positions. Forming the electrostatic latent image at the virtual latent image line positions between the real latent image line positions by irradiating the plurality of light beams while scanning in the main scanning direction,
The controller corresponds to the beam diameters of the light rays from the plurality of light emitting elements at the respective positions in the main scanning direction, so that the exposure energy density distributions of the light rays from the plurality of light emitting elements coincide with each other or are closest to each other. Individually correcting the light emission time per dot of the light emitting element when the electrostatic latent image is formed at the latent image line position,
An image forming apparatus characterized by. A plurality of light rays from the plurality of light emitting elements are irradiated on the photoconductor drum at different positions in the main scanning direction at each actual latent image line position,
The controller identifies (a) the light emitting element of the light beam emitted at the most preceding position in the main scanning direction among the irradiation positions of the plurality of light rays as the preceding light emitting element, and (b) the preceding light emitting element. For this reason, the correction amount of the light emission time per dot when the electrostatic latent image is formed at the virtual latent image line position is specified, and the light emission time is corrected by the correction amount, and (c) the preceding light emission is performed. When the correction amount of the light emission time of the element is specified, the correction amount of the light emission time of the remaining light emitting element at the most preceding position in the main scanning direction is also specified, and (d) the remaining When the irradiation position of the light beam from the light emitting element reaches the most advanced position in the main scanning direction, the light emission of the remaining light emitting element is performed with the correction amount of the remaining light emitting element that has already been specified. Compensating for time,
The image forming apparatus according to claim 1, wherein: The controller specifies (a) a correction amount of the light emission time of the preceding light emitting element based on main correction data indicating a correction amount of the light emission time of the preceding light emitting element at each position in the main scanning direction, (B) The correction amount of the light emission time of the preceding light emitting element is corrected by a temperature correction coefficient corresponding to the environmental temperature of the exposure apparatus detected by a predetermined temperature sensor, and (c) at each position in the main scanning direction. The preceding light emitting element corrected by the temperature correction coefficient based on sub-correction data indicating a difference or ratio between a correction amount of the light emitting time of the preceding light emitting element and a correction amount of the light emitting time of the remaining light emitting elements. The image forming apparatus according to claim 2, wherein the correction amount of the light emission time of the remaining light emitting elements is specified from the correction amount of the light emission time of. The controller, the exposure energy density distribution by the light rays from the plurality of light emitting elements, so as to match or closest to the exposure energy density distribution at a predetermined reference diameter, respectively, correct the light emission time of the plurality of light emitting elements,
The reference diameter is a predetermined value equal to or less than a minimum value in the main scanning direction of the beam diameter of the light emitting element having the smallest beam diameter among the plurality of light emitting elements,
The image forming apparatus according to any one of claims 1 to 3, wherein:

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