JP2011175068A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having an optical device arranged below a photoreceptor drum, which prevents with simple structure, deterioration in image quality due to noise generated when writing an electrostatic latent image caused by sticking of dust such as toner to transparent material such as dust-proof glass provided in an opening portion from which a beam is emitted from the optical device. <P>SOLUTION: The image forming apparatus having the optical device 2 arranged below the photoreceptor drum 11, includes the dust-proof glass 26 which is provided on a top surface of a casing 21 of the optical device 2, which prevents intrusion of dust such as the toner into the optical device 2 and causes laser beam L for writing of the electrostatic latent image with which the photoreceptor drum 11 is irradiated from the optical device 2 to pass through and which is arranged evading the vertically downward portion in a range spreading the diameter of the photoreceptor drum 11 in the horizontal direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly, an optical apparatus having an optical system for irradiating a light beam for writing an electrostatic latent image on a photosensitive drum (image carrier) within a housing. The present invention relates to an image forming apparatus disposed below a body drum.

An electrophotographic image forming apparatus such as a printer or a copying machine includes a photosensitive drum, an exposure device for writing an electrostatic latent image on the photosensitive drum, and development for developing the electrostatic latent image on the surface of the photosensitive drum as a toner image. Equipment and the like.
The exposure apparatus includes a laser light source that emits a beam light for writing an electrostatic latent image, and an optical system that scans in the rotation axis direction (main scanning direction) of the photosensitive drum while reflecting the emitted beam light. And an optical device that writes an electrostatic latent image on the surface of the photosensitive drum by a scanned beam of light. The optical system that scans the light beam is scanned by an optical scanner including a polygon mirror and its driving motor, an fθ lens that stabilizes the scanning speed of the beam light scanned in a fan shape in the main scanning direction, and the like. A reflection mirror that reflects the beam light is included.
2. Description of the Related Art Generally, an electrophotographic image forming apparatus includes a casing that accommodates the above-described optical system that scans a beam of light, and the casing and devices incorporated therein are unitized and sealed. . As a result, the optical system is prevented from being contaminated by dust such as toner, thereby causing deterioration of the image quality of the formed image and leakage of harmful laser beam light to the outside.
The housing is provided with an opening for irradiating the photosensitive drum with beam light, and the opening is closed with a transparent member such as dust-proof glass through which the beam light can pass. This prevents dust such as toner from entering the inside of the housing from the opening through which the light beam passes, thereby preventing the optical system from being contaminated.

Incidentally, in recent years, the secondary transfer type image forming apparatus X ′ having an intermediate transfer belt as shown in FIG. 1 includes a photosensitive drum 11 and a developing device, and an electrostatic latent image on the photosensitive drum 11. Is written and developed, the optical device 2 is disposed below the image forming unit 1 on which the image is transferred to the intermediate transfer belt 3.
Thus, the toner image on the intermediate transfer belt 3 is transferred from the primary transfer process in which the toner image is transferred from the image forming unit 1 to the intermediate transfer belt 3 to the recording paper that is vertically conveyed upward. The time to the next transfer process can be shortened. As a result, there is an advantage that the time from the start of the image forming process to the completion of the image forming process for the first recording sheet is shortened, and the processing efficiency is improved.
However, since the optical device 2 is disposed below the image forming unit 1, that is, below the photosensitive drum 11, dust such as toner easily falls from the photosensitive drum 11 onto the housing 21 of the optical device 2. .
In particular, the dust-proof glass that is provided on the upper surface of the housing 21 and allows the beam light irradiated toward the photosensitive drum 11 to pass therethrough is disposed vertically below the range extending across the horizontal diameter of the photosensitive drum 11. 、 Dust such as toner falls on the dust-proof glass. If dust such as the dropped toner adheres to or accumulates on the dust-proof glass, the optical path of the beam light may be partially blocked, and noise may be generated in electrostatic latent image writing. As a result, there is a concern that the image quality deteriorates.
In Patent Document 1, a dust-proof member corresponding to a dust-proof glass is exposed when light is emitted, and a shielding member that is positioned to cover the dust-proof member when not emitting light and a cleaning member that is attached to the shield member and contacts the dust-proof member An image forming apparatus including an optical writing device including a member is disclosed. According to the invention of Patent Document 1, when the light is not emitted, the dust-proof member is covered with the shielding member, thereby reducing the fall of the toner or the like onto the dust-proof member. Then, the cleaning member is moved along with the movement of the dust-proof member to remove the toner that has fallen on the dust-proof member, thereby preventing the occurrence of noise in writing of the electrostatic latent image due to the toner adhering to the dust-proof member. ing.

JP 2005-192076 A

However, in the invention of Patent Document 1, although it is possible to prevent the toner and the like from falling onto the dust-proof member when light is not emitted, the dust-proof member is disposed vertically below the range of the horizontal diameter of the photosensitive drum. When light is emitted (that is, when the dustproof member is exposed), it is not possible to prevent the toner from dropping from the photosensitive drum to the dustproof member. When dust such as toner adheres to the dust-proof member, there is a problem that it may not be removed even if the dust-proof member is cleaned when the shielding member moves.
Further, in Patent Document 1, there is a problem that an additional member such as a shielding member and a mechanism for moving the shielding member is required, and the configuration is complicated.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a beam light of an optical device in an image forming apparatus in which the optical device is disposed below an image carrier such as a photosensitive drum. With a simple structure, noise such as toner adheres to a transparent member such as dust-proof glass provided in the opening where the light is emitted, causing noise during electrostatic latent image writing and degrading the image quality. It is to prevent.

In order to achieve the above object, the present invention comprises an image carrier and an optical device positioned below the image carrier, and the optical device is disposed inside the housing of the optical device. An optical system for irradiating a beam light for writing an electrostatic latent image on the housing, and an opening for passing the beam light is provided on the upper surface of the housing, and the beam light is provided in the opening. The basic structure is that a transparent flat plate is disposed for passing the liquid and preventing foreign matter from entering the housing.
The transparent flat plate is disposed so as to avoid a vertically downward range (hereinafter simply referred to as “vertically below the image carrier”) over a range of the image carrier in the horizontal direction diameter. Configured as a device.
Accordingly, since the transparent flat plate is not vertically below the image carrier, even if dust such as toner falls from the image carrier, it is difficult to fall on the transparent flat plate.
In particular, the distance in the horizontal direction from the end on the transparent flat plate side to the end on the image carrier side of the transparent flat plate in the range of the horizontal diameter of the image carrier (hereinafter referred to as “image carrier and transparent flat plate”). The horizontal distance of the image carrier is 5% to 50% of the distance in the height direction between the rotation center of the image carrier and the transparent flat plate (hereinafter referred to as the height of the image carrier). Is preferred. Further, it is more preferable that the horizontal distance between the image carrier and the transparent flat plate is in a range of 5% to 30% of the height of the image carrier.
Since the horizontal distance between the image carrier and the transparent plate is 5% or more of the height of the image carrier, the transparent plate is arranged far from the image carrier, and even if toner or the like is scattered from the image carrier, it is transparent. It is hard to fall on a flat plate.
If the horizontal distance between the image carrier and the transparent flat plate is too large, in the case of a color image forming apparatus equipped with a plurality of image carriers, an adjacent image is formed from the end of the transparent flat plate opposite to the image carrier. The distance in the horizontal direction to the end on the transparent plate side in the range of the diameter in the horizontal direction of the carrier is shortened, and toner scattered from the adjacent image carrier may fall on the transparent plate. This is prevented by the fact that the horizontal distance between the image carrier and the transparent flat plate is 50% or less, preferably 30% or less of the height of the image carrier.
As described above, since the transparent flat plate is disposed at a position away from the image carrier with respect to the position of the image carrier, no additional member is required, and the transparent flat plate has a simple structure. It is prevented from being polluted by falling dust. As a result, dust such as toner adheres to the transparent flat plate, thereby preventing noise from being generated during the electrostatic latent image writing on the image carrier and degrading the image quality.

At this time, the optical axis of the beam light passing through the transparent flat plate is inclined by 10 ° to 30 °, preferably 10 ° to 20 °, toward the image carrier with respect to the vertical direction of the transparent flat plate.
When the inclination of the optical axis of the beam light with respect to the vertical direction of the transparent flat plate (hereinafter referred to as the optical axis inclination) is less than 10 °, the transparent flat plate through which the beam light scanned by the image carrier passes is the vertical of the image carrier. In order to avoid the downward position, the height of the image carrier must be considerably high. However, if the height of the image carrier is high, there is a high possibility that the dust such as toner falling from the image carrier will spread over a wide range, and the possibility that the dust such as toner will fall on the transparent flat plate becomes high. End up.
In the image forming apparatus according to the present invention, by setting the inclination of the optical axis to 10 ° or more, the transparent flat plate is disposed avoiding the vertically lower side of the image carrier while the height of the image carrier is not so high. ing. For this reason, the range in which the dust such as toner falls does not reach a wide range, and the possibility that the dust such as toner falls on the surface of the transparent flat plate is low.
However, if the tilt of the optical axis is too large, it is likely to be affected by reflection and refraction by the transparent flat plate, which may lead to a decrease in the writing accuracy of the electrostatic latent image formed on the image carrier. Is 30 ° or less, preferably 20 ° or less.

In addition to the above configuration, it is preferable that the transparent flat plate is disposed to be inclined to the image carrier side or the side opposite to the image carrier with respect to the horizontal direction.
Since the transparent flat plate is inclined, even if dust such as toner scatters from the image carrier and falls on the transparent flat plate, the dust such as toner easily moves to the lower side of the inclined transparent flat plate. Therefore, dust such as toner is hard to collect on the transparent flat plate. As a result, dust such as toner can be more effectively prevented from adhering to the transparent flat plate.
Further, a recess lower than the transparent flat plate may be provided around the transparent flat plate, and a cleaning mechanism for cleaning the surface of the transparent flat plate may be provided. In particular, it is desirable that a cleaning range of the cleaning mechanism is wider than that of the transparent flat plate, and the concave portion is formed continuously to the cleanable range or overlapping the cleanable range.
Since the periphery of the transparent flat plate is a recess that is lower than the transparent flat plate, it falls from the image carrier, etc., and the dust such as toner on the upper surface of the optical device other than the transparent flat plate vibrates the image forming apparatus itself. Even if it moves by such as, it can be prevented from sticking to the transparent flat plate.
Further, by providing a cleaning mechanism for cleaning the surface of the transparent flat plate, these can be removed even if dust such as toner falls on the transparent flat plate.
If the cleaning mechanism has a wider cleanable range than the transparent flat plate and the recess is formed continuously with the cleanable range or overlapping the cleanable range, the surface of the transparent flat plate is removed by the cleaning mechanism. Dust such as toner removed from the toner can be dropped into the recesses. For this reason, it is possible to prevent the dust such as toner once removed from the transparent flat plate from moving due to the vibration of the image forming apparatus itself and being placed on the transparent flat plate again to be contaminated.

In addition, it is preferable that an optical axis of the beam light irradiated on the image carrier is inclined with respect to a normal line at an irradiation point where the beam light on the image carrier is irradiated.
As a result, the light beam irradiated to the image carrier is regularly reflected by the image carrier and returned to the optical device, causing irregular reflection in the optical device, and changing the light amount of the beam light irradiated to the image carrier. Can be prevented.

According to the present invention, since the transparent flat plate is arranged so as to avoid the vertically lower part of the range extending over the horizontal diameter of the image carrier, even if dust such as toner falls from the image carrier, it falls on the transparent flat plate. Hard to do.
In particular, the distance in the horizontal direction from the end on the transparent flat plate side to the end of the transparent flat plate on the side of the image carrier in the range of the horizontal diameter of the image carrier (hereinafter referred to as “the horizontal distance between the image carrier and the transparent flat plate”). Is 5% or more of the distance in the height direction between the rotation center of the image carrier and the transparent flat plate (hereinafter referred to as “the height of the image carrier”), and the transparent flat plate from the image carrier. However, even if toner or the like is scattered from the image carrier, it is difficult to fall on the transparent flat plate.
If the horizontal distance between the image carrier and the transparent flat plate is too large, in the case of a color image forming apparatus equipped with a plurality of image carriers, an adjacent image is formed from the end of the transparent flat plate opposite to the image carrier. The distance in the horizontal direction to the end on the transparent plate side in the range of the diameter in the horizontal direction of the carrier is shortened, and toner scattered from the adjacent image carrier may fall on the transparent plate. This is prevented by the fact that the horizontal distance between the image carrier and the transparent flat plate is 50% or less, preferably 30% or less of the height of the image carrier.
As described above, since the transparent flat plate is arranged with respect to the position of the image carrier, no additional members are required, and the transparent flat plate is contaminated by the fall of dust such as toner. It is prevented. As a result, the dust such as toner adheres to the transparent flat plate, so that it is possible to prevent the image quality from being deteriorated due to the generation of noise when the electrostatic latent image is written on the image carrier.
Further, since the transparent flat plate is inclined, even if toner dust or the like is scattered from the image carrier and falls on the transparent flat plate, the toner dust moves to the lower side of the inclined transparent flat plate. Since it is easy, dust such as toner is hard to collect on the transparent flat plate. As a result, dust such as toner can be more effectively prevented from adhering to the transparent flat plate.
In addition, since the periphery of the transparent flat plate is a concave portion lower than the transparent flat plate, toner or other dust that has fallen from the image bearing member or the like to the portion other than the transparent flat plate on the upper surface of the optical device vibrates the image forming apparatus itself. Even if it is moved due to, etc., it can be placed on the transparent flat plate to prevent the transparent flat plate from being contaminated, and by providing a cleaning mechanism that cleans the surface of the transparent flat plate, even if dust such as toner falls on the transparent flat plate, these Can be removed.
In addition, when the cleaning mechanism has a wider cleanable range than the transparent flat plate and the concave portion is formed continuously or overlaps with the cleanable range, the cleaning mechanism removes the surface of the transparent flat plate from the surface. Dust such as toner to be removed can be dropped into the recess. Therefore, it is possible to prevent the dust such as the toner once removed from the transparent flat plate from being put on the transparent flat plate again due to the vibration of the image forming apparatus itself, and the transparent flat plate being contaminated.

1 is a schematic diagram showing an internal structure of a general image forming apparatus. FIG. 3 is a partially enlarged view showing one of image forming units of a general image forming apparatus. 1 is a perspective view showing an optical device of an image forming apparatus according to the present invention. 1 is a schematic diagram showing an internal structure of an optical device of an image forming apparatus according to the present invention. 1 is a schematic diagram illustrating an optical device and an image carrier of an image forming apparatus according to the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

First, the outline of the image forming apparatus X according to the embodiment of the present invention will be described. The image forming apparatus X will be described by taking a color printer as an example, but is not limited to this, and may be a copying machine, a facsimile, a monochrome printer, or the like.
The image forming apparatus X includes four image forming units 1, two optical devices 2, and an intermediate transfer belt 3, similar to the general intermediate transfer type image forming apparatus X ′ shown in FIGS. . Further, a secondary transfer roller 4, a paper feeding device 5, a fixing device 6, a paper discharge unit 7 and the like are provided.
Here, the four image forming units 1 execute an image forming process for transferring toner images of black, yellow, cyan, and magenta to the intermediate transfer belt 3, respectively. 3 in the order of black, yellow, cyan, and magenta. The image forming process of the image forming unit 1 is not different for each color but has the same configuration. Therefore, the image forming unit 1 is generally referred to as an image forming unit 1 and only when particularly necessary, the image forming unit 1B (black), They are referred to as 1Y (yellow), 1C (cyan), and 1M (magenta). Further, the two optical devices 2 have the same configuration as each other, and hence are collectively referred to as the optical device 2.
The image forming unit 1 includes a photosensitive drum 11 that carries a toner image (an embodiment of an image carrier), a charging device 12 that charges the surface of the photosensitive drum 11, and a laser beam on the surface of the charged photosensitive drum 11. A developing device 13 for developing the electrostatic latent image written by light irradiation (exposure) with toner; a primary transfer roller 14 for transferring the toner image developed and formed on the photosensitive drum 11 to the intermediate transfer belt 3; A cleaning device 15 for removing toner remaining on the photosensitive drum 11 is provided. In the case where the configuration of the image forming unit 1 of a specific color is described, B, Y, C which means black, yellow, cyan, magenta, like the image forming units 1B, 1Y, 1C, 1M described above. , M are added to each code (for example, in the case of a black photosensitive drum, the photosensitive drum 11B is used).
The two optical devices 2 are arranged below the image forming unit 1, and one of them is a laser beam light (an example of beam light) for writing an electrostatic latent image on the black and yellow photosensitive drums 11. The other outputs laser beam light for writing an electrostatic latent image to the photosensitive drums 11 for cyan and magenta. Although the configuration of the optical device 2 will be described later, the configuration of the optical device 2 also shows B, Y, which means black, yellow, cyan, and magenta, as in the image forming unit 1, when a configuration related to a specific color is shown. C and M are added to each code.
The intermediate transfer belt 3 is an endless belt made of a material such as rubber or urethane. The intermediate transfer belt 3 is supported by a drive roller 31 and a driven roller 32 so as to be rotated and driven, and the photosensitive drum 11 and the primary transfer roller. 14 passes.

The image forming operation on the transfer material such as recording paper by the image forming apparatus X is not particularly different from that of the general image forming apparatus X ′, and the outline thereof is a photosensitive charged uniformly by the charging device 12 first. The photosensitive drum 11 is exposed by irradiating the body drum 11 with the laser beam light from the optical device 2, and an electrostatic latent image is written on the surface of the photoreceptor drum 11. This electrostatic latent image is developed by the developing device 13 to form a toner image on the surface of the photosensitive drum 11. This is performed in the image forming unit 1 for each color.
The toner images formed on the surface of the photosensitive drum 11 of each color are sequentially transferred and laminated on the intermediate transfer belt 3 pressed against the photosensitive drum 11 by the respective primary transfer rollers 14, and the full-color toner image is formed on the intermediate transfer belt 3. A toner image is formed. The full-color toner image formed on the intermediate transfer belt 3 is transferred by the secondary transfer roller 4 onto the recording paper fed one by one from the paper feeding device 5. Thereafter, the toner is fixed on the recording paper by the fixing device 6, and the recording paper on which the image is formed is discharged to the paper discharge unit 7.
After the toner image is transferred to the intermediate transfer belt 3, the toner remaining on the surface of the photosensitive drum 11 is removed by the cleaning device 15.
Thus, the image forming apparatus X forms a color image on a transfer material such as recording paper.

Next, the optical device 2 of the image forming apparatus X according to the present invention will be described with reference to FIGS.
The optical device 2 includes a light source (not shown) such as a laser diode that emits a laser beam light L (see FIG. 5) for writing an electrostatic latent image, and a laser beam light L in the direction of the rotation axis of the photosensitive drum 11 (mainly). The optical system 20 includes various optical devices for scanning in the scanning direction), a housing 21 that houses the optical system 20, and the like. The optical device constituting the optical system 20 includes a collimator lens (not shown) that collimates the laser beam L emitted from the light source, a cylindrical lens (not shown) that collects the collimated light in a linear shape, and laser beam light. An optical scanner 22 including a polygon mirror that rotates while reflecting and a motor for driving the mirror, an fθ lens 23 that stabilizes the scanning speed in the main scanning direction of the laser beam L scanned in a fan shape, and the laser beam L that is scanned. And the like, and these are accommodated in the casing 21. The light source may be housed in the housing 21, but may be housed in a holding member dedicated to the light source attached to the outer surface of the housing 21.
As shown in FIG. 5, the upper surface of the housing 21 is arranged substantially horizontally. As described above, the optical device 2 is disposed below the image forming unit 1, that is, the upper surface of the housing 21 faces the photosensitive drum 11. In the present embodiment, the casing 21 has a substantially rectangular parallelepiped shape as shown in FIG. 3, but is not limited to this.
As shown in FIG. 4, an opening 25 is formed on the upper surface of the housing 21. The opening 25 is for passing the laser beam L emitted from the light source and passing through the optical system 20 in order to irradiate the photosensitive drum 11.
The opening 25 is closed by a dustproof member such as a dustproof glass 26 in order to prevent foreign matter from entering the housing 21 and contaminating the optical system. The dust-proof member is not limited to a glass-made material such as the dust-proof glass 26 as long as the upper and lower surfaces are parallel and a transparent flat plate that allows the laser beam L to pass therethrough.
The optical device 2 of the present embodiment is an optical device that scans the laser beam L on two photosensitive drums 11 (in FIG. 5, a black photosensitive drum 11B and a yellow photosensitive drum 11Y) by one optical scanner 22. Each of the optical devices 2 is provided with two openings 25 and dust-proof glasses 26 (in FIG. 5, openings 25B and 25Y and dust-proof glasses 26B and 26Y). However, the optical apparatus in the image forming apparatus of the present invention is not limited to the above-described one, and one that scans the laser beam light on four photosensitive drums by one optical scanner or one for each toner color. , Each may be an optical device provided with an optical scanner.

Here, most of the foreign matter that is prevented from entering the inside of the housing 21 by the dust-proof glass 26 is dust such as toner falling from the image forming unit 1 (particularly the photosensitive drum 11) (hereinafter referred to as dust T). It is. Needless to say, if the dust T penetrates into the housing 21 and the optical system is contaminated, the image quality is likely to deteriorate. However, the dust T adheres to the surface of the dust-proof glass 26 or is deposited. Even if it does, since the optical path of the laser beam L is partially blocked, there is a possibility that noise may be generated at the time of electrostatic latent image writing. As a result, there is a concern that the image quality deteriorates.
Therefore, in the image forming apparatus X, as shown in FIG. 5, the dust-proof glass 26 (opening 25) is disposed at a portion that is out of the vertical lower portion of the range W over the horizontal diameter of the photosensitive drum 11. The dust T is prevented from falling from the photosensitive drum 11 to the dust-proof glass 26.
The dust-proof glass 26 has a horizontal distance D from a portion deviated from the vertically lower side of the range W, that is, from the end of the range W on the dust-proof glass 26 side to the end of the dust-proof glass 26 on the photosensitive drum 11 side. However, the distance D is 5% to 50% of the distance in the height direction (height H) between the rotation center of the photosensitive drum 11 and the dust-proof glass 26. It is preferable to arrange in the following range. Furthermore, it is more preferable that the distance D is arranged in a range of 5% to 30% of the height H.
It is conceivable that the toner on the surface of the photosensitive drum 11 not only falls but also scatters due to the influence of a slight air flow and vibration that may occur inside the image forming apparatus X. Therefore, the dust-proof glass 26 is disposed at a position where the distance D is 5% or more of the height H, and is away from the photosensitive drum 11. As a result, even if the dust T is slightly scattered from the photosensitive drum 11, it is difficult to fall on the surface of the dust-proof glass 26.
However, if the distance D is too large, the end of the photosensitive drum 11 (11B) of the adjacent image forming unit 1 (1B) from the end of the dust-proof glass 26 (26Y) opposite to the photosensitive drum 11 (11Y). The distance D2 in the horizontal direction to the end of the dust-proof glass 26 (26Y) in the range W over the horizontal diameter is shortened, and dust T scattered from the adjacent photosensitive drum 11 (11B) becomes dust-proof glass 26 ( 26Y) may fall. This is prevented by disposing the dustproof glass 26 at a position where the distance D is 50% or less of the height H, preferably 30% or less.
FIG. 5 shows the relationship between the yellow photosensitive drum 11Y, the dustproof glass 26Y corresponding thereto, and the black photosensitive drum 11B adjacent thereto, but the magenta photosensitive drum 11M and the dustproof glass. The relationship between the photosensitive drum 26C and the cyan photosensitive drum 11C and the relationship between the cyan photosensitive drum 11C, the dustproof glass 26C and the yellow photosensitive drum 11Y are the same.

The dust-proof glass 26 is preferably inclined by an angle θ1 with respect to the horizontal direction as shown in FIGS.
Even if the dust T scatters from the photosensitive drum 11 and falls on the surface of the dust-proof glass 26, the dust T easily moves toward the lower slope given by the angle θ1, so that the dust T is deposited on the surface of the dust-proof glass 26. It is because it is hard to accumulate. As a result, the dust T is more effectively prevented from adhering to the dustproof glass 26.
In addition, although angle (theta) 1 is not specifically limited, For example, about 1-30 degrees is preferable. In the present embodiment, the dust-proof glass 26 is inclined so that the photosensitive drum 11 side is lowered, but may be inclined in the opposite direction.

Around the dust-proof glass 26, it is preferable that a recess 27 lower than the surface of the dust-proof glass 26 is provided as shown in FIG.
Even if the dust T falls from the photosensitive drum 11 or the like and the dust T on the portion other than the dust-proof glass 26 on the upper surface of the optical device 2 moves due to vibration of the image forming apparatus X itself or the like. The dust T collects in the recess 27 lower than the dust-proof glass 26. Further, when the dust-proof glass 26 is tilted as described above, the dust T once placed on the surface of the dust-proof glass 26 also moves to the lower tilt side and accumulates in the concave portion 27. Therefore, dust T on the upper surface of the optical device 2 other than the surface of the dust-proof glass 26 is moved by the vibration of the image forming apparatus X and placed on the surface of the dust-proof glass 26, so that the dust-proof glass 26 is contaminated. Is prevented.
In FIG. 5, the concave portion 27 is formed in a shape in which the upper surface of the casing 21 is recessed integrally with the casing 21, but is not limited thereto. For example, a portion of the housing 21 where the dust-proof glass 26 is disposed is raised with respect to the surroundings, and a protruding line surrounding the protruding portion is provided slightly outside the protruding portion, and a recess is formed between the protruding portion and the protruding line. Alternatively, a fitting hole may be provided around the dust-proof glass 26, and the recess may be formed by a member different from the casing 21 such as a receiving tray fitted to the fitting hole.
The image forming apparatus X may include a cleaning mechanism 28 that cleans the surface of the dust-proof glass 26. This is because even if dust T is placed on the surface of the dust-proof glass 26, it can be easily removed.
The cleaning mechanism 28 is not particularly limited, and is schematically shown in FIG. 4. For example, as shown in FIG. 3, the cleaning brush 28 a is main-scanned on the surface of the dust-proof glass 26 by the screw shaft 28 b. And the like reciprocated in the direction.
As shown in FIG. 4, the cleanable range of the cleaning mechanism 28 is wider than the dust-proof glass 26, and the concave portion 27 is formed overlapping the cleanable range.
Needless to say, the dust T is reliably removed from the surface of the dust-proof glass 26 by the fact that the cleanable range is wider than the dust-proof glass 26, but the recess 27 is provided overlapping the cleanable range of the cleaning mechanism 28. As a result, the dust T removed from the surface of the dust-proof glass 26 is reliably dropped into the recess 27. Therefore, the dust T once removed from the transparent flat plate is prevented from being put on the transparent flat plate again due to vibration of the image forming apparatus X itself. As a result, the transparent flat plate can be prevented from being contaminated.
The recess 27 may be provided continuously in the cleanable range without overlapping the cleanable range of the cleaning mechanism 28.

Here, as shown in FIG. 5, the optical axis LA of the laser beam L passing through the dust-proof glass 26 and irradiating the photosensitive drum 11 is angled toward the photosensitive drum 11 with respect to the vertical direction of the dust-proof glass 26. It is tilted by θ2. The angle θ2 is 10 ° to 30 °, preferably 10 ° to 20 °.
If the angle θ2 is less than 10 °, the dust-proof glass 26 through which the laser beam L scanned by the photosensitive drum 11 passes is arranged at the height H in order to dispose the dust-proof glass 26 at a portion outside the range W. Must be considerably higher. However, if the height H is high, there is a high possibility that the dust T falling from the photosensitive drum 11 extends over a wide range. That is, the possibility that the dust T is placed on the surface of the dust-proof glass 26 is increased.
In the image forming apparatus X, since the angle θ2 is 10 ° or more, the dust-proof glass 26 is disposed at a portion outside the range W from the vertically lower side with the height H not so high. Therefore, the range in which the dust T falls does not reach a wide range, and the possibility that the dust T is placed on the surface of the dust-proof glass 26 is low.
This also prevents the height H from becoming so high that the image forming apparatus X can be prevented from becoming unnecessarily large.
However, if the angle θ2 is too large, the laser beam L is likely to be affected by reflection and refraction by the dust-proof glass 26, and the writing accuracy of the electrostatic latent image formed on the surface of the photosensitive drum 11 may be reduced. There is. Therefore, the angle θ2 is set to 30 ° or less, preferably 20 ° or less.
Furthermore, it is preferable that the optical axis LA is inclined by an angle θ3 (1 to 30 °) with respect to the normal line N of the photosensitive drum 11 at the irradiation point where the laser beam L on the photosensitive drum 11 is irradiated.
As a result, the laser beam L applied to the photosensitive drum 11 is regularly reflected on the surface of the photosensitive drum 11 and returns to the optical device 2, causing irregular reflection in the optical device 2, and being applied to the photosensitive drum 11. It is possible to prevent the amount of laser beam light L from being changed.

1 Image forming section 11 Photosensitive drum (image carrier)
2 Optical device 20 Optical system 21 Case 22 Optical scanner (component of optical system)
23 fθ lens (component of optical system)
24 Reflection mirror (component of optical system)
25 Opening 26 Dust-proof glass (transparent flat plate)
27 Concave portion 28 Cleaning mechanism X Image forming apparatus

Claims (10)

An image carrier;
An optical device positioned below the image carrier,
The optical device has an optical system for irradiating a beam for writing an electrostatic latent image on the image carrier inside the housing of the optical device;
An image forming apparatus provided with an opening through which the light beam passes on the top surface of the housing,
The opening is provided with a transparent flat plate for allowing the beam light to pass therethrough and preventing foreign matter from entering the housing,
An image forming apparatus, wherein the transparent flat plate is disposed so as to avoid a vertically lower portion in a range extending over a horizontal diameter of the image carrier.   The distance in the horizontal direction from the end on the transparent plate side to the end on the image carrier side of the transparent plate within the range of the horizontal diameter of the image carrier is the rotation center of the image carrier and the transparent plate. The image forming apparatus according to claim 1, wherein the distance in the height direction is 5% to 50%.   The distance in the horizontal direction from the end on the transparent plate side to the end on the image carrier side of the transparent plate within the range of the horizontal diameter of the image carrier is the rotation center of the image carrier and the transparent plate. The image forming apparatus according to claim 1, wherein the distance is 5% to 30% of the distance in the height direction.   The image forming apparatus according to claim 1, wherein an optical axis of the beam light passing through the transparent flat plate is inclined by 10 ° to 30 ° toward the image carrier with respect to a vertical direction of the transparent flat plate. .   The image forming apparatus according to claim 1, wherein an optical axis of the beam light passing through the transparent flat plate is inclined by 10 ° to 20 ° toward the image carrier with respect to a vertical direction of the transparent flat plate. .   The image forming apparatus according to claim 1, wherein the transparent flat plate is disposed to be inclined to the image carrier side or the side opposite to the image carrier with respect to a horizontal direction.   The image forming apparatus according to claim 1, wherein a concave portion lower than the transparent flat plate is provided around the transparent flat plate.   The image forming apparatus according to claim 1, further comprising a cleaning mechanism that cleans a surface of the transparent flat plate. A cleaning mechanism for cleaning the surface of the transparent flat plate;
The range that can be cleaned by the cleaning mechanism is wider than the transparent flat plate,
The image forming apparatus according to claim 7, wherein the concave portion is formed continuously with the cleanable range or overlapping the cleanable range.   The optical axis of the beam light irradiated to the image carrier is inclined with respect to a normal line at an irradiation point on the image carrier where the beam light is irradiated. Image forming apparatus.