JP2010173297A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device forming a uniform large spot, on a photoreception face. <P>SOLUTION: This image forming device includes a light emitting element 74b and a light emitting element 74d juxtaposed unidirectionally, and an image focusing optical system 60 having a plurality of focal points for projecting a light emitted from the light emitting element 74b and a light emitted from the light emitting element 74d respectively to the photoreception face 111, and the image focusing optical system 60 is constituted to make an optical-axis-directional shift amount between an image focusing point FPf positioned in the most distant position from a lens and an image focusing point FPn positioned in the nearest position out of the plurality of image focusing points, get greater than an optical-axis-directional shift amount between an image focusing point of the light emitted from the light emitting element 74b and an image focusing point of the light emitted from the light emitting element 74d. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  Conventionally, an image forming apparatus is used to form an image on a recording medium. Such an image forming apparatus includes a columnar (cylindrical) photoconductor, a charging unit that uniformly charges the light receiving surface of the photoconductor, a laser for a desired position on the uniformly charged light receiving surface, and the like. An exposure unit (line head) that forms an electrostatic latent image on the light receiving surface by irradiating the light is provided.

Further, the exposure unit (line head) included in the image forming apparatus includes a plurality of LED chip arrays arranged in a line in the axial direction of the photosensitive member, and a plurality of lens elements provided corresponding to the LED chip arrays. An optical information writing device having an optical lens system is known (for example, see Patent Document 1).
In the optical information writing apparatus described in Patent Document 1, an optical lens system is formed so that light from each LED chip array forms an image on the light receiving surface of the photosensitive member (that is, the spot diameter on the light receiving surface is minimized). For example, a desired latent image can be formed on the light receiving surface by independently controlling the ON / OFF timing of driving (light emission) of each LED.

  Here, it is technically and costly difficult to make the cross-sectional shape of the photosensitive member a perfect circle. Even if the cross-sectional shape of the photosensitive member can be made a perfect circle, the usage environment ( Depending on the ambient temperature, external force), deterioration of the light-receiving surface, etc., the shape may change and the cross-sectional shape may not be a perfect circle. As described above, when the cross-sectional shape of the photoconductor is not a perfect circle, the light receiving surface coincides with the imaging point at the first point on the light receiving surface, but the second point is different from the first point. At this point, the light receiving surface and the imaging point do not coincide. As described above, the difference in spot size between the first point and the second point makes it impossible to form a spot having a uniform size over the entire light receiving surface.

Further, as described above, the exposure unit is provided so that the spot diameter on the light receiving surface is minimized. However, when the installation position of the exposure unit is deviated from the predetermined position (that is, the exposure unit and the photosensitive unit When the distance from the body is deviated from a predetermined value), the spot diameter on the light receiving surface is larger than the predetermined diameter.
As described above, in the optical information writing apparatus of Patent Document 1, it is difficult to form a spot having a desired diameter on the light receiving surface, and thus it is difficult to form a desired latent image. There's a problem.

Japanese Patent Laid-Open No. 2-4546

  An object of the present invention is to provide an image forming apparatus capable of forming a spot having a uniform size on a light receiving surface.

Such an object is achieved by the present invention described below.
The image forming apparatus of the present invention includes a latent image carrier on which a latent image is formed,
A first light emitting element and a second light emitting element arranged in a first direction, and a first light emitting element and a second light emitting element arranged in a second direction orthogonal or substantially orthogonal to the first direction of the first light emitting element and the second light emitting element. A line head having an imaging optical system that projects light emitted from the first light emitting element and the second light emitting element onto the latent image carrier;
A developing unit for developing the latent image carrier,
The imaging optical system is configured to cause the light emitted from the first light emitting element to emit light emitted from the latent image carrier on the imaging optical system side, and the latent image carrier. An image is formed at a second imaging point located on the opposite side of the imaging optical system, and the light emitted from the second light emitting element is positioned on the imaging optical system side of the latent image carrier. Forming an image at a third imaging point and a fourth imaging point located on the opposite side of the imaging optical system of the latent image carrier;
The amount of shift in the second direction between the first image point and the second image point is greater than the amount of shift in the second direction between the first image point and the third image point. Features.

The image forming apparatus of the present invention includes an aperture stop,
The first light emitting element and the second light emitting element are disposed at different distances in the first direction with respect to an axis that passes through the geometric center of gravity of the aperture shape of the aperture stop and extends in the second direction. It is preferable.
In the image forming apparatus according to the aspect of the invention, it is preferable that the imaging optical system includes a multifocal lens having regions having different lens surface shapes.
In the image forming apparatus of the present invention, it is preferable that the multifocal lens has a rotationally symmetric lens surface.

In the image forming apparatus according to the aspect of the invention, the rotationally symmetric lens surface of the multifocal lens is provided in a first region provided in a central portion of the lens surface in the first direction and around the first region. A second region provided, and a third region provided around the second region,
Of the light emitted from the first light emitting element, the light passing through the first region passes through the fifth imaging point, and the light passing through the second region passes through the sixth imaging point and the third region. The imaged light is imaged at the seventh image point,
The sixth imaging point is located on the latent image carrier surface on the imaging optical system side, the seventh imaging point is located on the latent image carrier surface on the opposite side of the imaging optical system, Preferably, the fifth imaging point is located between the sixth imaging point and the seventh imaging point in the second direction.
In the image forming apparatus according to the aspect of the invention, it is preferable that the first area, the second area, and the third area are defined by different definition formulas.
In the image forming apparatus of the present invention, it is preferable that the area of the first region, the area of the second region, and the area of the third region are equal or substantially equal.

The image forming apparatus of the present invention includes a first light emitting element and a second light emitting element arranged in the first direction,
Light radiated from the first light emitting element and the second light emitting element is disposed in a second direction orthogonal or substantially orthogonal to the first direction of the first light emitting element and the second light emitting element. And an imaging optical system for projecting onto the exposed surface,
The imaging optical system is configured to provide light emitted from the first light emitting element, a first imaging point located on the imaging optical system side of the exposed surface, and the imaging of the exposed surface. An image is formed at a second imaging point located on the opposite side of the optical system, and the light emitted from the second light emitting element is irradiated with a third coupling located on the imaging optical system side of the exposed surface. Forming an image at an image point and a fourth imaging point located on the opposite side of the imaging optical system from the exposed surface;
The amount of shift in the second direction between the first image point and the second image point is greater than the amount of shift in the second direction between the first image point and the third image point. Features.

  According to the present invention, even if the relative positional relationship (separation distance) with the light receiving surface is deviated from a predetermined value or the distance from the light receiving surface changes with driving, A uniform spot having a desired size can be formed on the light receiving surface, and a desired latent image can be formed.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus of the present invention. FIG. 2 is a partial cross-sectional perspective view of a line head included in the image forming apparatus illustrated in FIG. 1. It is the sectional view on the AA line in FIG. FIG. 3 is a plan view of the line head shown in FIG. 2. It is sectional drawing and a top view of the multifocal lens with which the line head shown in FIG. 2 is provided. It is a figure which shows the focus of the multifocal lens shown in FIG. It is a figure which shows the focus of the imaging optical system with which the line head shown in FIG. 2 is provided. It is a figure which shows the focus of the imaging optical system with which the line head shown in FIG. 2 is provided. It is a figure which shows the focus of the imaging optical system with which the line head shown in FIG. 2 is provided. FIG. 3 is a diagram illustrating a positional relationship between the line head illustrated in FIG. 2 and a photosensitive drum included in the image forming apparatus illustrated in FIG. 1. FIG. 3 is a schematic perspective view showing an operation state of the line head shown in FIG. 2 with time. FIG. 3 is a schematic perspective view showing an operation state of the line head shown in FIG. 2 with time. FIG. 3 is a schematic perspective view showing an operation state of the line head shown in FIG. 2 with time. FIG. 3 is a schematic perspective view showing an operation state of the line head shown in FIG. 2 with time. FIG. 3 is a schematic perspective view showing an operation state of the line head shown in FIG. 2 with time. FIG. 3 is a schematic perspective view showing an operation state of the line head shown in FIG. 2 with time. It is a figure which shows the Example of this invention. It is a graph which shows the longitudinal aberration which the imaging optical system of an Example and a comparative example has. It is a graph which shows the field curvature which the imaging optical system of an Example and a comparative example has. It is a graph which shows the change in the optical axis direction of a spot diameter about the imaging optical system of an Example and a comparative example.

Hereinafter, an image forming apparatus of the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.
FIG. 1 is a schematic view showing the overall configuration of the image forming apparatus of the present invention, FIG. 2 is a partial cross-sectional perspective view of a line head included in the image forming apparatus shown in FIG. 1, and FIG. 3 is AA in FIG. 4 is a plan view of the line head shown in FIG. 2, FIG. 5 is a cross-sectional view and a plan view of a multifocal lens included in the line head shown in FIG. 2, and FIG. 6 is a multi-focus shown in FIG. FIG. 7, FIG. 8, and FIG. 9 are diagrams showing the focal point of the lens. FIGS. 10, 8, and 9 are diagrams showing the focal point of the imaging optical system provided in the line head shown in FIG. FIG. 11 to FIG. 16 are schematic perspective views showing the operational states of the line head shown in FIG. 2 over time, and FIG. 17 is a diagram showing the positional relationship with the photosensitive drum included in the image forming apparatus shown in FIG. FIG. 18 is a diagram showing an embodiment of the present invention, and FIG. 19 is a graph showing longitudinal aberration, FIG. 19 is a graph showing curvature of field of the imaging optical systems of the example and the comparative example, and FIG. 20 is an optical axis of a spot diameter for the imaging optical systems of the example and the comparative example. It is a graph which shows the change in a direction. In the following, for convenience of explanation, the upper side in FIGS. 1 to 3 and FIGS. 11 to 16 is referred to as “upper” or “upper”, and the lower side is referred to as “lower” or “lower”.

(Image forming device)
An image forming apparatus 1 shown in FIG. 1 is an electrophotographic printer that records an image on a recording medium P through a series of image forming processes including a charging process, an exposure process, a developing process, a transfer process, and a fixing process. In the present embodiment, the image forming apparatus 1 is a color printer that employs a so-called tandem method.
As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 10 for a charging process, an exposure process, and a developing process, a transfer unit 20 for a transfer process, and a fixing unit for a fixing process. 30, a transport mechanism 40 for transporting a recording medium P such as paper, and a paper feed unit 50 that supplies the recording medium P to the transport mechanism 40.

The image forming unit 10 includes an image forming station 10Y that forms a yellow toner image, an image forming station 10M that forms a magenta toner image, an image forming station 10C that forms a cyan toner image, and a black toner image. Four image forming stations including an image forming station 10K to be formed are provided.
Each of the image forming stations 10Y, 10C, 10M, and 10K has a photosensitive drum (photosensitive member) 11 that carries an electrostatic latent image, and a charging unit 12 and a line head are provided around (outer peripheral side). An (exposure unit) 13, a developing device 14, and a cleaning unit 15 are provided. Since these apparatuses constituting the image forming stations 10Y, 10C, 10M, and 10K have the same configuration, only one apparatus will be described below.

  The photosensitive drum 11 has a cylindrical shape as a whole. The outer peripheral surface (cylindrical surface) of the photosensitive drum 11 constitutes a light receiving surface 111 that receives light L (emitted light) from the line head 13 (lens array 6). That is, a photosensitive layer (not shown) is formed on the outer peripheral surface of the photosensitive drum 11. Further, the photosensitive drum 11 is rotatable around the axis in the direction of the arrow in FIG. Further, portions (both ends) of the outer peripheral surface of the photosensitive drum 11 excluding the light receiving surface 111 are non-photosensitive regions 112 that are not sensitive to the light L.

The charging unit 12 uniformly charges the light receiving surface 111 of the photosensitive drum 11 by corona charging or the like.
The line head 13 receives image information from a host computer such as a personal computer (not shown) and irradiates the light L toward the light receiving surface 111 of the photosensitive drum 11 in response to the image information. On the other hand, the light receiving surface 111 of the photosensitive drum 11 is in a uniformly charged state, and a latent image corresponding to the irradiation pattern of the light L is formed. The configuration of the line head 13 will be described in detail later.

The developing device 14 has a storage unit (not shown) that stores toner, and supplies toner from the storage unit to the light receiving surface 111 of the photosensitive drum 11 that carries an electrostatic latent image. To do. Thereby, the latent image on the photosensitive drum 11 is visualized (developed) as a toner image.
The cleaning unit 15 has a rubber cleaning blade 151 that abuts on the light receiving surface 111 of the photosensitive drum 11, so that the toner remaining on the photosensitive drum 11 after the primary transfer described later is scraped off and removed by the cleaning blade 151. It has become.

The transfer unit 20 collectively transfers the toner images of the respective colors formed on the photosensitive drums 11 of the image forming stations 10Y, 10M, 10C, and 10K as described above to the recording medium P.
In each of the image forming stations 10Y, 10C, 10M, and 10K, the charging unit 12 charges the light receiving surface 111 of the photosensitive drum 11 and the line head 13 exposes the light receiving surface 111 while the photosensitive drum 11 rotates once. Then, supply of toner to the light receiving surface 111 by the developing device 14, primary transfer to the intermediate transfer belt 21 by pressure contact with a primary transfer roller 22 described later, and cleaning of the light receiving surface 111 by the cleaning unit 15 are sequentially performed.

The transfer unit 20 includes an endless belt-like intermediate transfer belt 21, and the intermediate transfer belt 21 includes a plurality of (four in the configuration shown in FIG. 1) primary transfer rollers 22, drive rollers 23, and driven rollers 24. It is stretched, and is driven to rotate in the direction of the arrow shown in FIG.
Each primary transfer roller 22 is disposed opposite to the corresponding photosensitive drum 11 via an intermediate transfer belt 21, and transfers a single color toner image on the photosensitive drum 11 to the intermediate transfer belt 21 (primary transfer). It is like that. At the time of primary transfer, the primary transfer roller 22 is applied with a primary transfer voltage (primary transfer bias) having a polarity opposite to the charging polarity of the toner.

On the intermediate transfer belt 21, a toner image of at least one of yellow, magenta, cyan, and black is carried. For example, when a full-color image is formed, four color toner images of yellow, magenta, cyan, and black are sequentially transferred onto the intermediate transfer belt 21 to form a full-color toner image as an intermediate transfer image.
Further, the transfer unit 20 includes a secondary transfer roller 25 disposed to face the driving roller 23 via the intermediate transfer belt 21, and a cleaning unit 26 disposed to face the driven roller 24 via the intermediate transfer belt 21. have.

  The secondary transfer roller 25 transfers a single-color or full-color toner image (intermediate transfer image) formed on the intermediate transfer belt 21 to a recording medium P such as paper, film, or cloth supplied from the paper supply unit 50. (Secondary transfer). The secondary transfer roller 25 is pressed against the intermediate transfer belt 21 and applied with a secondary transfer voltage (secondary transfer bias) during secondary transfer. During such secondary transfer, the drive roller 23 also functions as a backup roller for the secondary transfer roller 25.

The cleaning unit 26 has a rubber cleaning blade 261 that contacts the surface of the intermediate transfer belt 21, and the toner remaining on the intermediate transfer belt 21 after the secondary transfer is scraped off and removed by the cleaning blade 261. It has become.
The fixing unit 30 includes a fixing roller 301 and a pressure roller 302 that is pressed against the fixing roller 301, and is configured such that the recording medium P passes between the fixing roller 301 and the pressure roller 302. Yes. The fixing roller 301 has a built-in heater for heating the outer peripheral surface of the fixing roller, and can heat and press the recording medium P passing therethrough. The fixing unit 30 having such a configuration heats and presses the recording medium P that has received the secondary transfer of the toner image, and fuses the toner image to the recording medium P to fix it as a permanent image.

The conveyance mechanism 40 includes a registration roller pair 41 that conveys the recording medium P while feeding the recording medium P to the secondary transfer portion between the secondary transfer roller 25 and the intermediate transfer belt 21 described above, and fixing by the fixing unit 30. Conveying roller pairs 42, 43, and 44 for nipping and conveying the processed recording medium P are provided.
When such a transport mechanism 40 forms an image on only one surface of the recording medium P, the transport mechanism 40 sandwiches and transports the recording medium P fixed on one surface by the fixing unit 30 by the transport roller pair 42. Then, it is discharged outside the image forming apparatus 1. When forming an image on both surfaces of the recording medium P, the recording medium P fixed on one surface by the fixing unit 30 is once sandwiched by the conveying roller pair 42 and then the conveying roller pair 42 is driven to reverse. Then, the pair of conveying rollers 43 and 44 are driven, the recording medium P is turned upside down and returned to the registration roller pair 41, and an image is formed on the other surface of the recording medium P by the same operation as described above.
The paper feeding unit 50 includes a paper feeding cassette 51 that stores unused recording media P, and a pickup roller 52 that feeds the recording media P from the paper feeding cassette 51 to the registration roller pair 41 one by one. .

(Line head)
Here, the line head 13 will be described in detail. Hereinafter, for convenience of explanation, the longitudinal direction of the long line head 13 (first lens array 6, second lens array 6 ′ described later) is referred to as “main scanning direction”, and the width direction is “ "Sub-scanning direction".
As shown in FIG. 3, the line head 13 is disposed below the photosensitive drum 11 so as to face the light receiving surface 111. The line head 13 is arranged so that the main scanning direction is parallel to the rotation axis of the photosensitive drum 11.

The line head 13 includes a second lens array 6 ′, a spacer 84, a first lens array 6, a spacer 83, a diaphragm (aperture diaphragm) 82, a light shielding member 81, and a light emitting element array 7 from the photosensitive drum 11 side. These members are arranged in order, and these members are accommodated in the casing 9.
In the line head 13, after the light L emitted from the light emitting element array 7 is stopped by the stop 82, the light L passes through the first lens array 6 and the second lens array 6 ′, and the light receiving surface 111 of the photosensitive drum 11. It is comprised so that it may condense.

As shown in FIGS. 2 to 4, the first lens array 6 is composed of a plate-like body whose outer shape is long. A plurality of convex curved surfaces (lens surfaces) 62 are formed on the surface of the first lens array 6 on the light emitting element array 7 side (incident surface on which the light L is incident). On the other hand, the surface of the first lens array 6 on the photoconductor 11 side (the exit surface from which the light L is emitted) is a flat surface.
That is, in the first lens array 6, a plurality of lenses 64, which are plano-convex lenses in which the light L incident side surface is a convex curved surface 62 and the light L emission side surface is a flat surface, are arranged. A portion of the first lens array 6 other than each lens 64 (mainly a portion around each lens 64) constitutes a lens support portion 65 that supports each lens 64.
Each lens 64 is a multifocal lens having a plurality of focal points as will be described later, and the configuration of the lens 64 will be described in detail later.

As shown in FIG. 4, the lenses 64 are arranged in a plurality of rows in the main scanning direction, and are arranged in a plurality of rows in the sub-scanning direction orthogonal to the main scanning direction and the optical axis direction of the lens 64.
More specifically, the plurality of lenses 64 are arranged in a matrix of 3 rows and n columns (n is an integer of 2 or more). Hereinafter, among the three lenses 64 belonging to one row (lens row), the lens 64 located at the center is referred to as a “lens 64b” and is located on the left side in FIG. 3 (upper side in FIG. 4). The lens 64 is referred to as “lens 64a”, and the lens 64 positioned on the right side in FIG. 3 (lower side in FIG. 4) is referred to as “lens 64c”.

In the present embodiment, among the plurality of lenses 64 (64a to 64c) belonging to one row, the lens 64b closest to the center side in the sub-scanning direction is closest to the light receiving surface 111 of the photosensitive drum 11. Then, the line head 13 is installed in the image forming apparatus. This facilitates setting of optical characteristics of the imaging optical system 60 described later.
Further, as shown in FIG. 4, in each lens row, the lenses 64a to 64c are sequentially arranged at an equal distance in the main scanning direction (right direction in FIG. 4). That is, in each lens row, the line connecting the lens centers of the lenses 64a to 64c is inclined at a predetermined angle with respect to the main scanning direction and the sub-scanning direction.

When viewed in the cross section shown in FIG. 3, in the three lenses 64 belonging to one lens row, that is, the lenses 64a to 64c, the optical axes of the lenses 64a and 64c pass through the optical axis of the lens 64b. They are arranged symmetrically. The lenses 64a to 64c are arranged so that their optical axes are parallel to each other.
As shown in FIG. 3, the second lens array 6 ′ is installed on the light L emission side of the first lens array 6 via a spacer 84. The second lens array 6 ′ has substantially the same configuration as the first lens array 6. That is, a plurality of convex curved surfaces (lens surfaces) 62 ′ are formed on the surface of the second lens array 6 ′ on the first lens array 6 side, and the surface on the photoreceptor 11 side is a flat surface. It consists of
Thereby, in the second lens array 6 ′, a plurality of lenses 64 ′, which are plano-convex lenses in which the light L incident side surface is a convex curved surface 62 ′ and the light L emission side surface is a flat surface, are arranged. I can say that. However, each lens 64 ′ is a single focus lens having a single focal point, unlike the lens 64.

  The plurality of lenses 64 ′ are arranged in a matrix of 3 rows and n columns (n is an integer of 2 or more) spaced apart from each other, corresponding to the plurality of lenses 64 described above. That is, the plurality of lenses 64 'are arranged in a matrix as shown in FIG. Further, one lens 64 ′ is arranged so as to face one lens 64 and so that its optical axis coincides with the optical axis of the opposite lens 64.

  The top surface of the second lens array 6 ′ (a flat surface exposed to the outside of the line head 13) may be subjected to antifouling treatment. Examples of the antifouling treatment include a treatment for preventing or suppressing the adhesion of dirt on the upper surface and a process capable of easily removing the dirt even if the dirt adheres to the upper surface. Examples of such antifouling treatment include a method in which a fluorine-containing silane compound is applied to the upper surface by, for example, a dipping method (see, for example, JP-A-2005-3817).

Further, the upper surface of the second lens array 6 ′ may be subjected to a scratch-proofing process. Examples of the flaw-proofing treatment include a method of forming a layer mainly composed of C ₆ H ₁₄ and C ₂ F _{6 on the} upper surface by a vapor deposition method such as a high-frequency plasma CVD method (for example, JP 2006-133420 gazette).
Further, when such antifouling treatment or scratch prevention treatment is performed on the upper surface of the second lens array 6 ', the upper surface is a flat surface, so that the operation can be easily performed. Further, since the upper surface is a flat surface, the layer formed by the antifouling treatment or the flaw-proofing treatment can be uniformly formed on the upper surface.

The constituent material of each of the lenses 64 and 64 ′ is not particularly limited as long as it can exhibit the optical characteristics as described above. For example, a resin material and / or a glass material is preferably used.
As this resin material, various resin materials can be used. For example, a liquid crystal polymer such as polyamide, thermoplastic polyimide, polyamideimide aromatic polyester, polyolefin such as polyphenylene oxide, polyphenylene sulfide, polyethylene, modified polyolefin, polycarbonate, acrylic (Methacrylic), Polymethylmethacrylate, Polyethylene terephthalate, Polybutylene terephthalate and other polyesters, Polyether, Polyetheretherketone, Polyetherimide, Polyacetal and other thermoplastic resins, Epoxy resins, Phenol resins, Urea resins, Melamine resins Thermosetting resins such as saturated polyester resins and polyimide resins, photocurable resins, etc. are mentioned, and one or more of these are combined. It is possible to have.
Among such resin materials, when a thermosetting resin or a photocurable resin is used, the following effects can be obtained. That is, such a resin material is advantageous in that it has a relatively high refractive index, has a relatively low thermal expansion coefficient, and is unlikely to be expanded (deformed), modified, or deteriorated by heat.

  Examples of the glass material include various glass materials such as soda glass, crystalline glass, quartz glass, lead glass, potassium glass, borosilicate glass, and alkali-free glass. The light emitting element array 7 described later is configured. When the support plate 72 is made of a glass material, a relative displacement between the light emitting element and each lens due to temperature fluctuation can be prevented by using a glass material having a linear expansion coefficient substantially equal to the glass material. .

For example, in the case where the first and second lens arrays 6 and 6 ′ are composed by combining the resin material and the glass material as described above, one surface of the glass substrate made of the glass material is made of the resin material. In the laminated structure in which the resin layer is formed, convex curved surfaces 62 and 62 ′ may be formed on the surface of the resin layer opposite to the glass substrate. In addition, the first and second lens arrays 6 and 6 ′ have, for example, a plurality of convex portions protruding in a convex curved shape on one surface of a flat plate-like member (substrate) whose upper surface and lower surface each form a flat surface. It can also be formed by applying. In this case, from the viewpoint of ease of manufacturing and securing the rigidity of the first and second lens arrays 6 and 6 ', the flat plate member is made of, for example, a glass material, and each convex portion is made of a resin material. Is preferred.
Hereinafter, among the three lenses 64 ′ belonging to one row (lens row), the lens 64 ′ facing the lens 64a is referred to as “lens 64a ′”, and the lens 64 ′ facing the lens 64b is referred to as “lens 64b”. The lens 64 ′ facing the lens 64c is referred to as “lens 64c ′” (see FIG. 3).

  The first lens array 6 having a plurality of lenses 64 and the second lens array 6 ′ having a plurality of lenses 64 ′ have been described above. In the line head 13 of the present embodiment, a corresponding set of The lenses 64 and 64 ′ constitute one imaging optical system 60. Hereinafter, for convenience of explanation, the imaging optical system 60 configured by a set of lenses 64a and 64a ′ is referred to as an “imaging optical system a”, and is formed by a set of lenses 64b and 64b ′. The image optical system 60 is referred to as “image forming optical system b”, and the image forming optical system 60 including a pair of lenses 64c and 64c ′ is referred to as “image forming optical system c” (see FIG. 3).

As shown in FIG. 3, the light emitting element array 7 is installed on the light L incident side of the first lens array 6 via a spacer 83, a diaphragm 82 and a light shielding member 81. The light emitting element array 7 includes a plurality of light emitting element groups (light emitting element groups) 71 and a support plate (head substrate) 72.
The support plate 72 supports each light emitting element group 71, and is configured by a plate-like body having a long outer shape. The support plate 72 is disposed in parallel with the first lens array 6.
The support plate 72 has a length in the main scanning direction that is longer than the length of the first lens array 6 in the main scanning direction. The length of the support plate 72 in the sub-scanning direction is also set longer than the length of the first lens array 6 in the sub-scanning direction.

  The constituent material of the support plate 72 is not particularly limited, but when the light emitting element group 71 is provided on the back side of the support plate 72 as in the present embodiment (that is, when a bottom emission type light emitting element is used as the light emitting element 74). ), Transparent materials such as various glass materials and various plastics are preferably used. In addition, when using a top emission type light emitting element as the light emitting element 74, the constituent material of the support plate 72 is not limited to a material having transparency, for example, various metal materials such as aluminum and stainless steel, and various glasses. A material, various plastics, etc. can be used individually or in combination. When the support plate 72 is made of various metal materials or various glass materials, heat generated by light emission of each light emitting element 74 can be efficiently radiated through the support plate 72. Further, when the support plate 72 is made of various plastics, it contributes to weight reduction of the support plate 72.

A box-shaped storage portion 73 that opens to the support plate 72 side is installed on the back side of the support plate 72. In this housing portion 73, a plurality of light emitting element groups 71, conductive wires (not shown) electrically connected to these light emitting element groups 71 (each light emitting element 74), or each light emitting element 74 is driven. A circuit (not shown) is housed.
The plurality of light emitting element groups 71 are arranged in a matrix of 3 rows and n columns (n is an integer of 2 or more) spaced apart from each other, corresponding to the plurality of lenses 64 (imaging optical system 60) described above. (See, for example, FIG. 4). Each light emitting element group 71 is composed of a plurality (eight in this embodiment) of light emitting elements 74.

  As shown in FIG. 3, the eight light emitting elements 74 constituting each light emitting element group 71 are arranged along the lower surface 721 of the support plate 72. The light L emitted from each light-emitting element 74 is stopped by the stop 82, passes through the imaging optical system 60 (the lens 64 and the lens 64 ′), and reaches the light receiving surface 111 of the photosensitive drum 11. Condensate. As will be described in detail later, the light L emitted from each light emitting element 74 exposes the light receiving surface 111, thereby forming a spot SP on the light receiving surface 111.

  As shown in FIG. 4, the eight light emitting elements 74 are spaced apart from each other, arranged in four columns in the main scanning direction, and arranged in two rows in the sub scanning direction. As described above, the eight light emitting elements 74 are arranged in a matrix of 2 rows and 4 columns. Two adjacent light emitting elements 74 belonging to one row (light emitting device row) are shifted from each other in the main scanning direction. In the eight light emitting elements 74 having a matrix of 2 rows and 4 columns as described above, the light emitting elements 74 adjacent in the main scanning direction are complemented by one light emitting element 74 in the next row.

For example, there is a limit to arranging the eight light emitting elements 74 in one row as densely as possible. However, by arranging the eight light emitting elements 74 to be shifted as described above, the arrangement density of these light emitting elements 74 is reduced. Can be higher. Thereby, when an image is recorded on the recording medium P, the recording density on the recording medium P can be further increased. Therefore, it is possible to obtain the recording medium P having a high resolution, a multi-gradation and a clear image.
The eight light emitting elements 74 belonging to one light emitting element group 71 are arranged in a matrix of 2 rows and 4 columns in the present embodiment, but the present invention is not limited to this, and for example, a matrix of 4 rows and 2 columns. May be arranged.

As described above, the plurality of light emitting element groups 71 are spaced apart from each other and arranged in a matrix of 3 rows and n columns. As shown in FIG. 4, the three light emitting element groups 71 belonging to one row (light emitting element group row) are arranged at equal intervals in the main scanning direction (right direction in FIG. 4).
In the light emitting element group 71 having a matrix of 3 rows and n columns in this way, the interval between the adjacent light emitting element groups 71 is set so that the light emitting element group 71 in the next row and the light emitting element group 71 in the next row have the same distance. Complements sequentially.

For example, there is a limit in arranging the plurality of light emitting element groups 71 in one row as densely as possible. However, by arranging the plurality of light emitting element groups 71 so as to be shifted as described above, these light emitting element groups 71 are arranged. The arrangement density of can be made higher. Thereby, coupled with the fact that the eight light-emitting elements 74 in one light-emitting element group 71 are shifted and arranged, when an image is recorded on the recording medium P, the recording density on the recording medium P can be increased. Therefore, it is possible to obtain the recording medium P having higher resolution, multi-gradation, good color reproducibility and carrying a clearer image.
Each light emitting element 74 is an organic EL element (organic electroluminescence element) having a bottom emission structure. Note that the light emitting element 74 is not limited to an element having a bottom emission structure, and may be an element having a top emission structure. In this case, as described above, the support plate 72 is not required to have optical transparency.

  When each light emitting element 74 is an organic EL element, the interval (pitch) between the light emitting elements 74 can be set to be relatively small. Thereby, when an image is recorded on the recording medium P, the recording density on the recording medium P becomes relatively high. In addition, each light emitting element 74 can be formed with highly accurate dimensions and positions by using various film forming methods. Therefore, the recording medium P carrying a clearer image can be obtained.

In the present embodiment, each light emitting element 74 is configured to emit red light. Here, examples of the constituent material of the light emitting layer that emits red light include (4-dicyanomethylene) -2-methyl-6- (paradimethylaminostyryl) -4H-pyran (DCM) and Nile red. It is done. In addition, each light emitting element 74 is not limited to being configured to emit red light, and may be configured to emit monochromatic light of other colors or white light. Thus, in the organic EL element, the light L emitted from the light emitting layer can be appropriately set to monochromatic light of an arbitrary color according to the constituent material of the light emitting layer.
In general, the spectral sensitivity characteristics of a photosensitive drum used in an electrophotographic process is set to have a peak in the region from red to the near infrared, which is the emission wavelength of a semiconductor laser. It is preferable to use materials.

As shown in FIG. 3, between the first lens array 6 and the light emitting element array 7, a light shielding member 81, a diaphragm 82, and a spacer 83 are installed in this order from the light emitting element array 7 side.
The light blocking member 81 prevents crosstalk of the light L between the adjacent light emitting element groups 71. The light shielding member 81 is configured by a block body having a long outer shape. A plurality of through-holes 811 are formed in the light shielding member 81 formed of the block body so as to penetrate the light shielding member 81 in the vertical direction (thickness direction) in FIG. Each of these through holes 811 is disposed at a position corresponding to each lens 64 described above, and forms a part of an optical path from the light emitting element group 71 to the corresponding lens 64. Each through hole 811 has a circular shape in plan view, and includes eight light emitting elements 74 of the light emitting element group 71 corresponding to the through hole 811 inside. In addition, although each through-hole 811 has comprised the cylindrical shape in the structure shown in FIG. 3, it is not limited to this, For example, you may comprise the truncated cone shape expanded toward upper direction.
Such a light shielding member 81 also functions as a spacer that regulates the distance (gap) between the light emitting element array 7 and the diaphragm 82.

The diaphragm 82 is configured to allow only a part of the light L emitted from each light emitting element group 71 to reach the imaging optical system 60. The diaphragm 82 is composed of a plate member having a long outer diameter. A plurality of openings 821 penetrating the diaphragm in the vertical direction in FIG. 3 are formed in the diaphragm 82 formed of the plate member.
Each of these openings 821 is formed at a position corresponding to the lens 64 (through hole 811) described above. Further, each opening 821 has a circular shape with a diameter smaller than the diameter of the through hole 811 in plan view, and the center thereof substantially coincides with the center of the corresponding through hole 811.
Due to the function of the diaphragm 82, as will be described later, each lens 64 is formed with a light passing region through which the light L emitted from the corresponding light emitting element group 71 passes and a light non-passing region that does not pass through. Is done.

The spacer 83 regulates the distance (gap) between the stop 82 and the first lens array 6. The spacer 83 is configured by forming a plurality of through-holes 831 penetrating in the vertical direction (thickness direction) in FIG. 3 in a block body having a long outer shape, like the light shielding member 81 described above. These through holes 831 are arranged at positions corresponding to the respective lenses 64, and together with the corresponding through holes 811, form an optical path from the light emitting element group 71 to the lens 64.
The light emitting element array 7 and the light shielding member 81, the light shielding member 81 and the diaphragm 82, the diaphragm 82 and the spacer 83, and the spacer 83 and the first lens array 6 are fixed by, for example, adhesion (adhesion with an adhesive or a solvent). It may be.

In addition, it is preferable that the light shielding member 81 and the spacer 83 have at least the inner peripheral surfaces of the through holes 811 and 831 have a dark color such as black, brown, or amber. Further, it is preferable that at least the inner peripheral surface of each opening 821 and the portion exposed to the optical path on the lower surface of the diaphragm 82 have a dark color such as black, brown, or amber. Thereby, when the light L passes through the through holes 811, 831 and the opening 821, it can be prevented from being reflected on the inner peripheral surface thereof.
In addition, although it does not specifically limit as a constituent material of the light-shielding member 81, the diaphragm 82, and the spacer 83, respectively, For example, the same constituent material as the support plate 72 can be used.

As shown in FIG. 3, a spacer 84 is installed between the first lens array 6 and the second lens array 6 ′. The spacer 84 regulates a gap length which is a distance between the first lens array 6 and the second lens array 6 ′. Since such a spacer 84 has the same configuration as the spacer 83 described above, description thereof is omitted.
As shown in FIGS. 2 and 3, the first lens array 6, the second lens array 6 ′, the light emitting element array 7, the light shielding member 81, the diaphragm 82, and the spacers 83 and 84 are collectively formed in the casing 9. It is stored in. The casing 9 includes a frame member (casing body) 91, a lid member (back cover) 92, and a plurality of clamp members 93 that fix the lid member 92 to the frame member 91 (see FIG. 3).

As shown in FIG. 2, the frame member 91 has a long overall shape.
Further, the frame member 91 has a frame shape, and as shown in FIG. 3, the frame member 91 is formed with a lumen portion 911 that opens to the upper side and the lower side thereof. The width of the lumen portion 911 gradually decreases from the lower side to the upper side in FIG.
In the lumen portion 911, the second lens array 6 ′, the spacer 84, the first lens array 6, the spacer 83, the diaphragm 82, the light shielding member 81, and the light emitting element array 7 are fitted, respectively. These are fixed with an adhesive, for example. Accordingly, the second lens array 6 ′, the spacer 84, the first lens array 6, the spacer 83, the diaphragm 82, the light shielding member 81, and the light emitting element array 7 are collectively held by the frame member 91. Positioning of the second lens array 6 ′, the spacer 84, the first lens array 6, the spacer 83, the diaphragm 82, the light shielding member 81, and the light emitting element array 7 in the main scanning direction and the sub scanning direction. Is made.

Here, the upper surface 722 of the support plate 72 of the light emitting element array 7 is in contact with (contacts with) the stepped portion 915 formed on the wall surface of the lumen portion 911 and the lower end surface of the first light shielding member 81. ) A lid member 92 is fitted into the lumen portion 911 from below.
The lid member 92 is formed of a long member having a recess 922 into which the storage portion 73 is inserted. The upper end surface of the lid member 92 sandwiches the edge portion of the support plate 72 of the light emitting element array 7 between the step portion 915 of the frame member 91.

  Further, the lid member 92 is pressed upward by each clamp member 93. Thereby, the lid member 92 is fixed to the frame member 91. Further, the pressed lid member 92 causes the second lens array 6 ′, the spacer 84, the first lens array 6, the spacer 83, the diaphragm 82, the light shielding member 81, and the light emitting element array 7 to be main components. The positional relationship between the scanning direction, the sub-scanning direction, and the vertical direction in FIG. 3 is fixed.

A plurality of clamp members 93 are preferably arranged at equal intervals along the main scanning direction. Thereby, the frame member 91 and the lid member 92 can be uniformly clamped along the main scanning direction.
The clamp member 93 has a substantially U shape in the cross section shown in FIG. 3 and is formed by bending a metal plate. Both end portions of the clamp member 93 form claw portions 931 that are bent inward. Each claw portion 931 is engaged with the shoulder portion 916 of the frame member 91.

A curved portion 932 that is curved upward in an arch shape is formed in the intermediate portion of the clamp member 93. The top portion of the curved portion 932 is in pressure contact with the lower surface of the lid member 92 in a state where each claw portion 931 is engaged with the shoulder portion 916 as described above. Thereby, the lid member 92 is biased upward in a state where the bending portion 932 is elastically deformed.
In addition, when each clamp member 93 holding the frame member 91 and the lid member 92 is removed, the lid member 92 can be removed from the frame member 91. Thereby, maintenance such as replacement and repair of the light emitting element array 7 can be performed.

Moreover, it does not specifically limit as a constituent material of the frame member 91 and the cover member 92, For example, the constituent material similar to the support plate 72 can be used. It does not specifically limit as a constituent material of the clamp member 93, For example, aluminum and stainless steel are mentioned. The clamp member 93 may be made of a hard resin material.
Furthermore, although not shown, spacers that protrude upward are provided at both ends of the frame member 91 in the longitudinal direction. This spacer regulates the distance between the light receiving surface 111 of the photoconductor 11 and the first and second lens arrays 6 and 6 '.

(Imaging optics)
Next, the imaging optical system 60 provided in the line head 13 will be described. As described above, in the line head 13, one imaging optical system 60 is configured by one lens 64 and one lens 64 ′ facing the lens 64, and the imaging optical system 60 is arranged in a matrix. Several are arranged. In the present embodiment, each imaging optical system 60 is a telecentric imaging optical system on the light emission side (photosensitive member 11 side).
Since the imaging optical system 60 having such a configuration has the same configuration, for convenience of explanation, one imaging optical system 60 will be described as a representative and the other imaging optical systems 60 will be described below. The description is omitted.

First, the lenses 64 and 64 ′ will be described.
As described above, the lens 64 is a multifocal lens having a plurality of focal points.
As shown in FIG. 5, the lens 64 has a circular shape in plan view and is rotationally symmetric with respect to the optical axis. Thereby, the lens 64 can exhibit the same optical characteristics in any cross section including the optical axis of the lens 64.

Such a convex curved surface (lens surface) 62 of the lens 64 is positioned so as to surround a circular first region 621 located at the center of the convex curved surface 62 and the periphery (outer periphery) of the first region 621. An annular second region 622, an annular third region located so as to surround the second region 623, and a fourth region 624 located so as to surround the third region It consists of These four regions 621 to 624 are formed concentrically (concentrically) around the optical axis of the lens 64.
Of these four regions 621 to 624, the first to third regions 621 to 623 are light passing regions through which the light L emitted from the light emitting element group 71 passes, and the fourth region 624 is the light L. This is a light non-passing area where no light passes. Therefore, the shape (particularly the surface shape) of the fourth region 624 is not particularly limited. Further, the fourth region 624 may be omitted.

  The surface shapes of the first to third regions 621 to 623 are designed so that their focal lengths are different from each other. Specifically, as shown in FIG. 6, among the light L irradiated from infinity, the focal point FP621 of the light that has passed through the first region 621 is more than the focal point FP623 of the light that has passed through the third region 623. Also, the focal point FP 622 of the light passing through the second region 622 is located closer to the lens 64 than the focal point FP 621.

The focal point FP621 is located between the focal point FP622 and the focal point FP623. Note that the focal point FP621 may not be located between the focal point FP622 and the focal point FP623 as long as it is located between the focal point FP622 and the focal point FP623.
In addition, the first region 621, the second region 622, and the third region 623 each have a substantially equal area in a plan view of the lens 64. As a result, the amount of light passing through the first region 621, the amount of light passing through the second region 622, and the amount of light passing through the third region 623 can be made substantially the same.

  Each of the three regions 621, 622, and 623 is an aspheric surface and is defined by different definition formulas. Specifically, the three regions 621, 622, and 623 are represented by the following formula (1), and at least one of c, K, A, B, C, and Δ in the formula (1), respectively. The values are different. In this way, the lens 64 having a plurality of focal points (FP621 to FP623) as described above can be designed precisely and easily by defining the three regions 621, 622, and 623 with different definition formulas. it can.

［ただし、式（１）中のｒは、光軸からの距離であり、ｃは、光軸上曲率であり、Ｋは、コーニック定数であり、Ａ、Ｂ、ＣおよびΔは、それぞれ、非球面係数である。］

[Where r in the formula (1) is a distance from the optical axis, c is a curvature on the optical axis, K is a conic constant, and A, B, C and Δ are non- Spherical coefficient. ]

On the other hand, the lens 64 ′ is a lens having one focal point. The lens surface 62 ′ of the lens 64 ′ is a free-form surface (xy polynomial surface).
Next, how the light emitted from the light emitting element group 71 is condensed (imaged) by the imaging optical system 60 will be described with reference to FIG. FIG. 7 is a cross-sectional view in the main scanning direction including the optical axis of the imaging optical system 60.

  In the following, four light emitting elements 74 arranged in the main scanning direction (first direction) are arranged in order from the left side in FIG. 7 as “light emitting element 74a”, “light emitting element 74b”, “light emitting element 74c”, “light emitting element 74d”. " The four light emitting elements 74a to 74d have different distances from the optical axis 601 of the imaging optical system 60 (separation distance in the main scanning direction), and the light emitting element 74b is closest to the optical axis 601. Next, the light emitting element 74c and the light emitting element 74a are continued, and the light emitting element 74d is the most distal from the optical axis 601. In the present embodiment, the optical axis 601 is perpendicular to the substrate surface of the light emitting element array 7 and passes through the geometric center of gravity of the light emitting element group 71.

First, light emitted from the light emitting element (first light emitting element) 74b closest to the optical axis 601 will be described.
As shown in FIG. 6, the lens 64 has three focal points. Therefore, as shown in FIG. 7, the imaging point of the light L emitted from the light emitting element 74b and passing through the first region 621 of the lens 64 is FP11, and the light L passing through the second region 622 is The imaging point is FP12, and the imaging point of the light L that has passed through the third region 623 is FP13.

  The three image forming points FP11 to FP13 are arranged apart from each other in the optical axis direction (second direction; hereinafter, also simply referred to as “optical axis direction”) of the image forming optical system 60. The imaging point FP11 is located closer to the imaging optical system 60 than the imaging point FP13, and the imaging point FP12 is located closer to the imaging optical system 60 than the imaging point FP11. That is, with the intersection of the final surface of the imaging optical system 60 and the optical axis as a reference position, the optical axis direction distance to the imaging point FP11 is L11, the optical axis direction distance to the imaging point FP12 is L12, and the imaging point When the distance in the optical axis direction to the FP 13 is L13, the relationship of L12 <L11 <L13 is satisfied.

As described above, when the imaging optical system 60 in which the three imaging points FP11 to FP13 are shifted from each other in the optical axis direction is used, the light L emitted from the light emitting element 74b and passed through the imaging optical system 60 is obtained. An area where the spot diameter is relatively small and does not change much (hereinafter, also simply referred to as “small spot diameter area T”) can be formed over a wide area along the optical axis direction.
Here, the “small spot diameter region T” in the present specification differs depending on the required image quality (resolution) and the like, and is not particularly limited. For example, it can be defined as an area having a spot diameter of 35 μm or less. Alternatively, it can be defined as an area where the spot diameter is 1.5 times or less of the minimum spot diameter.

The separation distance (shift amount in the optical axis direction) between the imaging point FP12 and the imaging point FP13 is not particularly limited, but is preferably about 0.02 to 0.05 mm, and preferably about 0.03 to 0.04 mm. It is more preferable that As a result, the small spot diameter region T can be formed over a wide area in the optical axis direction.
The imaging point FP11 is located between the imaging point FP12 and the imaging point FP13. As a result, the small spot diameter region T can be formed over a wide area in the optical axis direction, and the change in spot diameter (difference between the maximum spot diameter and the minimum spot diameter) within the small spot diameter region T can be reduced. Can do. Note that the imaging point FP11 may not be located between the imaging point FP12 and the imaging point FP13 as long as the imaging point FP11 is located between the imaging point FP12 and the imaging point FP13.
As described above, the first to third regions 621 to 623 of the lens 64 have substantially the same area. Therefore, of the light L emitted from the light emitting element 74b, the amount of light passing through the first region 621, the amount of light passing through the second region 622, and the amount of light passing through the third region 623 The amount is almost the same. As a result, the effect of expanding the small spot diameter region T is enhanced.

Hereinafter, the point with the smallest spot diameter in the small spot diameter region T is referred to as a “beam waist”. In addition, when this point (the point with the smallest spot diameter) extends in the optical axis direction of the imaging optical system, the intermediate point is called a “beam waist”. A point close to the optical system 60 is referred to as a “beam waist”. The definition of such “beam waist” is the same for light emitted from other light emitting elements (for example, light emitting elements 74a, 74c, and 74d).
In the present embodiment, since the imaging point FP11 is positioned between the imaging point FP12 and the imaging point FP13, the beam waist of the light emitted from the light emitting element 74b and passing through the imaging optical system 60 is It substantially coincides with the imaging point FP11.

Next, the light L emitted from the light emitting element (second light emitting element) 74d farthest from the optical axis 601 will be described.
The light L emitted from the light emitting element 74d and passing through the imaging optical system 60 is the same as that of the light emitting element 74b described above. That is, as shown in FIG. 8, the imaging point of the light L emitted from the light emitting element 74d and passing through the first region 621 of the lens 64 is FP21, and the light L passing through the second region 622 is The imaging point is FP22, and the imaging point of the light L that has passed through the third region 623 is FP23. The three imaging points FP21 to FP23 are shifted in the optical axis direction, the imaging point FP21 is located closer to the imaging optical system 60 than the imaging point FP23, and the imaging point FP22 is the imaging point FP21. It is located closer to the imaging optical system 60 side. Similar to the light emitting element 74b, the beam waist of the light emitted from the light emitting element 74d and passed through the imaging optical system 60 coincides with the imaging point FP21.

  The light L emitted from the other light emitting elements 74a and 74c is the same as the light L emitted from the light emitting elements 74b and 74d described above. Therefore, the description of the light L emitted from the light emitting elements 74a and 74c and passing through the imaging optical system 60 is omitted. In the following, the imaging point of the light L emitted from the light emitting element 74a and passing through the first region 621 of the lens 64 is “FP31”, and the imaging point of the light L passing through the second region 622 is “ “FP32”, the imaging point of the light L that has passed through the third region 623 is “FP33”. Further, an imaging point of the light L emitted from the light emitting element 74c and passing through the first region 621 of the lens 64 is “FP41”, and an imaging point of the light L passing through the second region 622 is “FP42”. The imaging point of the light L that has passed through the third region 623 is referred to as “FP43”. In this embodiment, the beam waist of the light emitted from the light emitting element 74a and passed through the imaging optical system 60 coincides with the imaging point FP31, and is emitted from the light emitting element 74c and passes through the imaging optical system 60. The beam waist of the light coincides with the imaging point FP41.

  FIG. 9 is a diagram illustrating a positional relationship between image forming points (FP11 to FP13, FP21 to FP23, FP31 to FP33, and FP41 to FP42) of light emitted from the light emitting elements 74a to 74d. As shown in FIG. 9, the intersection between the optical axis 601 and the curve connecting the imaging points FP13, FP23, FP33, and FP43 (that is, the imaging point of the light L that has passed through the third region 623). The intersection point of the optical axis 601 and the curve connecting the imaging points FP12, FP22, FP32, and FP42 (that is, the imaging point of the light L that has passed through the second region 622) is defined as the imaging point FPf. The intersection of the optical axis 601 and the curve connecting the imaging points FP11, FP21, FP31, and FP41 (that is, the imaging point of the light L that has passed through the first region 621) is defined as the imaging point FPm. .

  As shown in FIG. 9, when the imaging points FP11, FP21, FP31, and FP41 of the light that has passed through the first region 621 of the lens 64 are compared, the imaging point FP21 in the optical axis direction of the imaging optical system 60 is The image forming point FP31 and the image forming point FP41 are next closest to the image forming optical system 60, and the image forming point FP11 is the farthest from the image forming optical system 60. This relationship is the same for the imaging points FP12, FP22, FP32, and FP42 of the light L that has passed through the second region 622 of the lens 64, and the focal point FP13 of the light L that has passed through the third region 623, The same applies to FP23, FP33, and FP43.

  The separation point (shift amount) in the optical axis direction between the imaging point FP21 located farthest from the optical axis 601 and the imaging point FPm on the optical axis 601 is G1, and the imaging point FPf (that is, the optical axis) Among the imaging points of the plurality of imaging optical systems 60 on 601, the imaging point farthest from the imaging optical system 60 and the imaging point FPn (that is, a plurality of imaging optical systems on the optical axis) The imaging optical system 60 satisfies the relationship of G1 <G2, where G2 is the separation distance of the 60 imaging points closest to the imaging optical system 60).

  According to the line head 13 including the imaging optical system 60 that satisfies such a relationship (G1 <G2), the separation distance of the photosensitive drum 11 from the light receiving surface 111 is deviated from a predetermined value, or the photosensitive member. Even if the separation distance from the light receiving surface 111 is changed with the rotation of the light 11 or the like, a spot SP having a substantially uniform and desired size is formed on the light receiving surface 111 along the main scanning direction. Can be formed. That is, the spot diameters of the spots SP arranged along the main scanning direction on the light receiving surface 111 can be made substantially equal to each other and can be made to have a desired size. As a result, a desired latent image can be formed on the light receiving surface 111.

  More specific description will be given below. As shown in FIG. 10, in the optical axis direction of the imaging optical system 60, a small spot diameter region Ta of the light L emitted from the light emitting element 74a, a small spot diameter region Tb of the light L emitted from the light emitting element 74b, The light receiving surface 111 is positioned in a region S where all of the small spot diameter region Tc of the light L emitted from the light emitting element 74c and the small spot diameter region Td of the light L emitted from the light emitting element 74d exist. The line head 13 is installed. At this time, as shown in FIG. 10, it is preferable to install the line head 13 so that the light receiving surface 111 is positioned approximately in the middle of the optical axis direction of the region S.

When the line head 13 is installed in this way, the spot diameter of the spot SP formed by the light L emitted from the light emitting element 74a and the spot formed by the light L emitted from the light emitting element 74b on the light receiving surface 111. The spot diameter of the SP, the spot diameter of the spot SP formed by the light L emitted from the light emitting element 74c, and the spot diameter of the spot SP formed by the light L emitted from the light emitting element 74d are substantially equal. That is, the spot diameters of the plurality of spots SP arranged in the main scanning direction (the rotation axis direction of the photosensitive drum 11) can be made substantially equal to each other. Also, all these spot diameters can be made to a desired size.
Thereby, the spot diameters of all the spots SP formed on the light receiving surface 111 can be made substantially equal, and a desired latent image free from distortion, unevenness, blur, etc. can be formed on the light receiving surface 111.

  Further, even when the line head 13 is installed (attached), even if the installation position is slightly deviated from the predetermined position in the optical axis direction (the direction in which the line head 13 and the light receiving surface 111 are separated from each other, the direction in which they are approached). The light receiving surface 111 can be positioned in the region S. As described above, since the spot diameter is substantially constant in the optical axis direction in the small spot diameter region T, even if the deviation in the optical axis direction as described above has occurred, the light receiving surface 111. The spot diameter of the spot SP formed on the light receiving surface 111 can be made substantially equal to the spot diameter of the spot SP formed on the light receiving surface 111 when no deviation occurs. Thereby, a desired latent image can be formed on the light receiving surface 111 and the installation of the line head 13 is simplified. In addition, the yield is improved.

  Further, if the cross-sectional shape of the photoconductor 11 is slightly distorted from the perfect circle, or if the rotation axis of the photoconductor 11 is deviated from the center of the true circle, the light receiving surface 111 is accompanied by the rotation of the photoconductor 11. The distance between the line heads 13 changes over time. As described above, even if the separation distance between the light receiving surface 111 and the line head 13 changes with time, the light receiving surface 111 can be constantly positioned in the region S by installing the line head 13 as described above. . Therefore, the spot diameter can be made almost equal for all the spots SP formed on the light receiving surface 111 (can be kept at a desired size), and a desired latent image free from distortion, unevenness, blur, etc. can be obtained. It can be formed on the light receiving surface 111.

The optical characteristics of the imaging optical system 60 when viewed in a cross section in the main scanning direction including the optical axis 601 of the imaging optical system 60 have been described above. The imaging optical system 60 includes the optical axis 601. Other (arbitrary) cross sections have similar optical characteristics. Thereby, the freedom degree of arrangement | positioning of the several light emitting element 74 which comprises the light emitting element group 71 improves, and the design freedom degree of the line head 13 improves with this.
In the latent image writing by the line head, it is important that the spot diameter in the main scanning direction is uniform rather than the sub scanning direction in which the surface of the latent image carrier as the light receiving surface is sent. The effect is obtained by being exhibited in a cross section in the main scanning direction.

  Next, the operation of the line head 13, that is, an example of the light emission timing of each light emitting element 74 will be described with reference to FIGS. In addition, since the operation | movement of each light emitting element group row | line is the same, below, the operation | movement of the light emitting element group row | line | column (light emitting element group 71a-71c) located in the 1st row | line is demonstrated typically. Further, as described above, numbers 1 to 8 are assigned to the eight light emitting elements 74 belonging to the light emitting element group 71a. Similarly, the numbers from 9 to 16 are assigned to the eight light emitting elements 74 belonging to the light emitting element group 71b. Similarly, the numbers 17 to 24 are assigned to the eight light emitting elements 74 belonging to the light emitting element group 71c. In the following description, each number assigned to the light emitting element 74 corresponds to each number assigned to the spot (latent image) SP.

When the line head 13 operates, the photosensitive drum 11 rotates at a constant speed at a predetermined peripheral speed.
First, as shown in FIG. 11, the first, third, fifth, and seventh light emitting elements 74 emit light at the same time for a predetermined time (instantaneously). By the light emission of these light emitting elements 74, four spots SP corresponding to the respective light emitting elements 74 are formed on the light receiving surface 111 of the photosensitive drum 11. Each spot SP has a very small area.

The four spots SP are respectively formed at positions inverted from the first, third, fifth, and seventh light emitting elements 74 through the lens 64a.
In other words, the first spot SP corresponding to the first light emitting element 74 located on the rightmost side in FIG. 11 is located on the leftmost side in FIG. The third spot SP is located adjacent to the first spot SP on the right side in the main scanning direction via a gap. The fifth spot SP is located adjacent to the third spot SP on the right side in the main scanning direction via a gap. The No. 7 spot SP is located adjacent to the No. 5 spot SP on the right side in the main scanning direction via a gap.

Next, in synchronism with (in conjunction with) the rotation of the photosensitive drum 11, the second, fourth, sixth and eighth light emitting elements 74 simultaneously emit light for a predetermined time (instantaneously) (see FIG. 12). . Due to the light emission of these light emitting elements 74, four spots SP corresponding to the respective light emitting elements 74 are further formed on the light receiving surface 111 of the photosensitive drum 11.
At this time, as the photosensitive drum 11 rotates, the above-mentioned spots SP of No. 1, No. 3, No. 5, and No. 7 are moving, and therefore, No. 4 of No. 2, No. 4, No. 6, No. 8, and No. 8 are moved. Two spots SP are formed so as to fill the space between the first, third, fifth and seventh spots SP, respectively. Thus, the first to eighth spots SP are arranged in a straight line along the main scanning direction in order from the left side in FIG.

Next, in synchronization with the rotation of the photosensitive drum 11, the 9th, 11th, 13th, and 15th light emitting elements 74 emit light at the same time (instantaneously) for a predetermined time (see FIG. 13). Due to the light emission of these light emitting elements 74, four spots SP corresponding to the respective light emitting elements 74 are further formed on the light receiving surface 111 of the photosensitive drum 11.
Each of these four spots SP is formed on the right side of the eighth spot SP in the main scanning direction. The ninth spot SP is located adjacent to the right spot in the main scanning direction of the eighth spot SP. The eleventh spot SP is located adjacent to the ninth spot SP on the right side in the main scanning direction via a gap. The number 13 spot SP is located adjacent to the number 11 spot SP on the right side in the main scanning direction via a gap. The 15th spot SP is located adjacent to the 13th spot SP on the right side in the main scanning direction via a gap.

  Next, as described above, the 10th, 12th, 14th, and 16th light emitting elements 74 emit light at the same time (instantaneously) for a predetermined time (see FIG. 14). Due to the light emission of these light emitting elements 74, four spots SP corresponding to the respective light emitting elements 74 are further formed on the light receiving surface 111 of the photosensitive drum 11. Thereby, the 1st to 16th spots SP are arranged in a straight line along the main scanning direction in order from the left side in FIG.

Next, similarly to the above, the 17th, 19th, 21st, and 23rd light emitting elements 74 emit light at the same time (instantaneously) for a predetermined time (see FIG. 15). Due to the light emission of these light emitting elements 74, four spots SP corresponding to the respective light emitting elements 74 are further formed on the light receiving surface 111 of the photosensitive drum 11.
The 17th spot SP is located adjacent to the right side of the 16th spot SP in the main scanning direction. The 19th spot SP is located adjacent to the 17th spot SP on the right side in the main scanning direction via a gap. The No. 21 spot SP is located adjacent to the No. 19 spot SP on the right side in the main scanning direction via a gap. The 23rd spot SP is located adjacent to the 21st spot SP on the right side in the main scanning direction via a gap.

  Next, in the same manner as described above, the 18th, 20th, 22nd, and 24th light emitting elements 74 emit light at the same time (instantaneously) for a predetermined time (see FIG. 16). Further, by the light emission of these light emitting elements 74, four spots SP corresponding to the respective light emitting elements 74 are further formed on the light receiving surface 111 of the photosensitive drum 11. Accordingly, the first to 24th spots SP are arranged in a straight line along the main scanning direction in order from the left side in FIG.

As described above, the line head 13 operates the light emitting elements 74 of the two light emitting element rows belonging to the light emitting element group 71 while shifting the light emission timing in one light emitting element group 71. The light emitting element groups 71 are operated at different light emission timings.
Further, as described above, the plurality of light emitting element groups 71 are arranged with high density, and even within one light emitting element group 71, the plurality of light emitting elements 74 belonging thereto are arranged with high density.

The image forming apparatus according to the present invention has been described above with reference to the illustrated embodiment. However, the present invention is not limited to this, and each part of the line head and the image forming apparatus can exhibit the same function. Any configuration can be substituted. Moreover, arbitrary components may be added.
Further, the lens array is not limited to a plurality of lenses arranged in a matrix of 3 rows and n columns, and may be arranged in a matrix of 3 rows and n columns, 4 rows and n columns, for example.

Further, in the lens array, at least two of the lenses belonging to one column have different focal lengths. The means for changing the focal length is not limited to the means for changing the radius of curvature (shape) of the convex curved surfaces of the lenses as described above.
In addition, the lens protection member is not limited to one made of a glass material, and may be made of any material as long as it is a substantially transparent material.

In the embodiment described above, the case where there are a plurality of light emitting elements corresponding to one lens has been described. However, the present invention is not limited to this, and one light emitting element may be provided for one lens.
In addition, the number of light emitting elements constituting one light emitting element group is not limited to eight, for example, two, three, four, five, six, seven, nine or more. Also good.

In each light emitting element group, the light emitting elements are not limited to being arranged in a matrix, and may be arranged in an arbitrary shape different from the matrix, for example. For example, when one light emitting element group is comprised by three light emitting elements, these three light emitting elements may be arrange | positioned so that the line which connected each center may make a triangle.
Moreover, each light emitting element is not limited to being comprised by the organic EL element, respectively, For example, you may be comprised by the light emitting diode (LED).

Next, examples of the present invention will be described.
1. Production of image forming apparatus (Example 1)
[Create Lens 64]
A resin layer made of a resin material is formed on one surface of a flat glass substrate made of a glass material, and a convex curved surface (lens surface) 62 is formed on the surface of the resin layer opposite to the glass substrate. As a result, a lens 64 having a circular shape in a plan view was obtained.
At this time, in the lens surface 62 of the lens 64, a range of radius 0.0 to 0.493 mm with the optical axis as the center is defined as a first region 621, and a range of radius 0.493 to 0.604 mm is defined as a second region. The region outside the radius of 0.604 mm was defined as a third region 623.

The shape of the first region 621 is an aspherical shape, and c = 1 / 1.50321, K = −1.31757, A = 0.010344, B = 0, C = 0 and Δ = 0 were defined by definition formulas substituted respectively.
The shape of the second region 622 is an aspherical shape, and c = 1 / 1.493326, K = −0.60017, A = −0.01626, B = 0 in the above-described formula (1). , C = 0, and Δ = −0.00054875 are defined by the substituted definition formulas.
In addition, the shape of the third region 622 is an aspheric shape, and c = 1 / 1.517423, K = −1.10004, A = 0.007269, B = 0, C = 0 and Δ = 0.00130944 were defined by the substituted definition formulas.

[Create lens 64 ']
A resin layer made of a resin material is formed on one surface of a flat glass substrate made of a glass material, and a convex curved surface (lens surface) 62 ′ is formed on the surface of the resin layer opposite to the glass substrate. To obtain a lens 64 '.
The shape of the lens surface 62 ′ is a free-form surface (xy polynomial surface), and c = 1 / 1.41337, K = −3.889446025, A = 0.039595998, B = 0 in the following equation (2). 0.035508266, C = 0.1256865, D = 0.3034097, E = 0.1094741, F = −0.07921190, G = −0.2126654, H = −0.2376198, I = −0.078115926, respectively. Defined by the assigned definition formula.

［ただし、ｒ^２＝ｘ^２＋ｙ^２である。また、式（２）中のｘは、主方向（主走査方向）座標であり、ｙは、副方向（副走査方向）座表であり、ｃは、光軸上曲率であり、Ｋは、コーニック係数であり、Ａ〜Ｉは、それぞれ、非球面係数である。］

[However, r ² = x ² + y ² . X in the equation (2) is a main direction (main scanning direction) coordinate, y is a sub direction (sub scanning direction) coordinate, c is a curvature on the optical axis, and K is It is a conic coefficient, and A to I are aspherical coefficients. ]

[Create line head]
The line head 13 as shown in FIG. 17 is formed by combining the lenses 64 and 64 ′ having the above shapes. In FIG. 17, one imaging optical system is representatively shown, and the other imaging optical systems are not shown. FIG. 17 is a cross-sectional view of the imaging optical system 60 and shows a cross section in the main scanning direction including the optical axis of the imaging optical system 60.

As shown in FIG. 17, the line head 13 includes, in order from the left side, a light emitting element array 7 provided with a light emitting element group 71 (a plurality of light emitting elements 74), a diaphragm 82, a lens 64, and a lens 64 ′ (imaging optical system). 60). Note that the object-side numerical aperture of the imaging optical system 60 is 0.153, and the magnification is −0.5039.
In this embodiment, the light emitting element group 71 is composed of three light emitting elements 74, and one of the light emitting elements 74 (light emitting element 741) is provided on the optical axis 601 of the imaging optical system 60, and the other two Two light-emitting elements 74 (light-emitting elements 742 and 743) were provided on the opposite sides of the light-emitting element 741 and at equal distances from the light-emitting element 741 (optical axis 601). In addition, the diameter of each light emitting element 74 was 40 micrometers.

The wavelength of light emitted from each light emitting element 74 was set to 690 nm (hereinafter, this wavelength is also referred to as “reference wavelength”). The full width w (length in the main scanning direction) of the light emitting element group 71 was 1.176 mm.
Such a line head 13 was incorporated into the image forming apparatus shown in FIG. At this time, the photoconductor 11 was provided such that its light receiving surface 111 was positioned in the small spot diameter region T as described above.

  Here, as shown in FIG. 17, the left side surface of the light emitting element array 7 (the surface on which the light emitting element group 71 is formed) is S1, the right side surface of the light emitting element array 7 is S2, and the surface of the diaphragm 82 Is S3, the lens surface 62 of the lens 64 is S4, the boundary surface between the glass substrate and the resin layer of the lens 64 is S5, the flat surface (right surface) of the lens 64 is S6, and the lens surface 62 of the lens 64 ′. When S ′ is S7, the boundary surface between the glass substrate and the resin layer of the lens 64 ′ is S8, the flat surface (right surface) of the lens 64 ′ is S9, and the light receiving surface 111 of the photosensitive drum 11 is S10, Each of S1 to S10 has a configuration as shown in Table 1 below.

  Further, the distance between the surfaces S1 and S2 (distance) is d1, the distance between the surfaces S2 and S3 is d2, the distance between the surfaces S3 and S4 is d3, and the distance between the surfaces S4 and S5. Is d4, the distance between the surfaces S5 and S6 is d5, the distance between the surfaces S6 and S7 is d6, the distance between the surfaces S7 and S8 is d7, and the distance between the surfaces S8 and S9 is d8. Assuming that the distance between the surfaces S9 and S10 is d9, each of d1 to d9 has a value as shown in Table 1 below.

(Comparative Example 1)
Comparative Example 1 is the same as Example 1 except that a lens 64 ″ is used instead of the lens 64 and d9 = 0.888896.

[Create lens 64 "]
A lens 64 ″ is formed by forming a resin layer made of a resin material on one surface of a flat glass substrate made of a glass material, and a convex curved surface (on the surface of the resin layer opposite to the glass substrate ( Lens surface) 62 "was formed. Such a lens 64 ″ is a lens having one focal point.
The shape of the lens surface 62 ″ is an aspherical surface that is rotationally symmetric with respect to the optical axis, and c = 1 / 1.50321, K = −1.432045, A = 0.008079811, B in the above equation (1). = 0.01631843, C = -0.01348224, and Δ = 0.

2. Various Measurements (2-1) Measurement of Longitudinal Aberration in Main Scanning Direction For each of Example 1 and Comparative Example 1, longitudinal aberration in the main scanning direction (positioned farthest from the lens among the plurality of focal points). The amount of deviation between the focal point and the most proximal focal point in the optical axis direction) was measured. The result is shown in FIG. The vertical axis in FIG. 18 represents the light beam passing position on the aperture stop in relative coordinates, with 0 corresponding to the optical axis and 1 corresponding to the aperture end of the aperture stop.

(2-2) Measurement of field curvature in main scanning direction For Example 1 and Comparative Example 1, the field curvature in the main scanning direction was measured. The result is shown in FIG. The vertical axis in FIG. 19 represents the position of the spot in the main direction on the light receiving surface in relative coordinates. 0 corresponds to the optical axis, and 1 is emitted from the light emitting element farthest from the optical axis. This corresponds to the position of a spot formed by collecting light. Further, “1” in FIG. 19 corresponds to 0.2963 mm.
(2-3) Change in spot diameter in optical axis direction For Example 1 and Comparative Example 1, the change in spot diameter in the optical axis direction was measured. The result is shown in FIG.

3. Results As shown in FIG. 20, the light emitted from the light emitting element 741 located on the optical axis and the light emitted from the other light emitting elements 742 and 743 in Example 1 are compared to Comparative Example 1. In any case, a region having a spot diameter of 35 nm or less (small spot diameter region) is formed in a wide area in the optical axis direction.
In addition, as shown in FIG. 20, the light emitted from the light emitting element 741 positioned on the optical axis and the light emitted from the other light emitting elements 742 and 743 in Example 1 are compared with Comparative Example 1. In either case, there is little change in the spot diameter within the small spot diameter region.

  In particular, in Example 1, in the light irradiated from the light emitting element 741, the spot diameter is substantially constant in the section of −20 to 10 on the horizontal axis, and in the light irradiated from the light emitting elements 742 and 743, The spot diameter is almost constant in the section of -20 to 20 on the axis. That is, in Example 1, both the spot diameter of the light emitted from the light emitting element 741 and the spot diameter of the light emitted from the light emitting elements 742 and 743 are constant in the section of −20 to 10 on the horizontal axis. .

Further, as shown in FIG. 20, the difference between the spot diameter of the light emitted from the light emitting element 741 and the spot diameter of the light emitted from the light emitting elements 742 and 743 in the section of −20 to 10 on the horizontal axis is Compared to Comparative Example 1, Example 1 is smaller.
For this reason, when an image is recorded on the recording medium P, Example 1 is expected to produce a clearer image with less density unevenness than Comparative Example 1.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Image forming unit 10Y, 10M, 10C, 10K ... Image forming station 11 ... Photosensitive drum (photoconductor) 111 ... Light receiving surface 112 ... Non-photosensitive area 12 ... Charging unit 13 ...... Line head (exposure unit) 14 ...... Developing device 15 ...... Cleaning unit 151 ...... Cleaning blade 20 ...... Transfer unit 21 ...... Intermediate transfer belt 22 ...... Primary transfer roller 23 …… Drive roller 24 …… Drive roller 25 …… Secondary transfer roller 26 …… Cleaning unit 261 …… Cleaning blade 30 …… Fixing unit 301 …… Fixing roller 302 …… Pressure roller 40 …… Conveying mechanism 41 …… Registration roller pair 42, 43, 44… ... Conveying roller pair 50 ... Feeding unit 51 ... Feed Paper cassette 52 ... Pickup roller 6 ... First lens array 6 '... Second lens array 60, 60a, 60b, 60c ... Imaging optical system 601 ... Optical axis 62, 62' ... Convex curved surface (Lens surface) 621... First region 622... Second region 623... Third region 64, 64a, 64b, 64c, 64 ′, 64a ′, 64b ′, 64c ′. Lens support part 7... Light emitting element array 71, 71 a, 71 b, 71 c... Light emitting element group (light emitting element group) 72 ....... Support plate (head substrate) 721 ... Lower face 722 ... Upper face 73 ... Storage part 74 74a, 74b, 74c, 74d, 741, 742, 743 ... Light emitting element 81 ... Light shielding member 811 ... Through hole 82 ... Aperture 821 ... Opening 83, 84 ... Spacer 831: Through hole 9: Casing 91: Frame member (casing body) 911 ... Lumen 915 ... Stepped portion 916 ... Shoulder 92 ... Lid member (rear cover) 922 ... Recess 93 ... Clamp member 931 ... Claw part 932 ... Curved part FP11 to FP13, FP21 to 23, FP31 to 33, FP41 to 43, FP621 to FP623, FPf, FPn ... Imaging point L ... Light P ... Recording medium SP …… Spot T …… Small spot diameter area

Claims (8)

A latent image carrier on which a latent image is formed;
A first light emitting element and a second light emitting element arranged in a first direction, and a first light emitting element and a second light emitting element arranged in a second direction orthogonal or substantially orthogonal to the first direction of the first light emitting element and the second light emitting element. A line head having an imaging optical system that projects light emitted from the first light emitting element and the second light emitting element onto the latent image carrier;
A developing unit for developing the latent image carrier,
The imaging optical system is configured to cause the light emitted from the first light emitting element to emit light emitted from the latent image carrier on the imaging optical system side, and the latent image carrier. An image is formed at a second imaging point located on the opposite side of the imaging optical system, and the light emitted from the second light emitting element is positioned on the imaging optical system side of the latent image carrier. Forming an image at a third imaging point and a fourth imaging point located on the opposite side of the imaging optical system of the latent image carrier;
The amount of shift in the second direction between the first image point and the second image point is greater than the amount of shift in the second direction between the first image point and the third image point. An image forming apparatus. With an aperture stop,
The first light emitting element and the second light emitting element are disposed at different distances in the first direction with respect to an axis that passes through the geometric center of gravity of the aperture shape of the aperture stop and extends in the second direction. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the imaging optical system includes a multifocal lens having regions having different lens surface shapes.   The image forming apparatus according to claim 3, wherein the multifocal lens has a rotationally symmetric lens surface. The rotationally symmetric lens surface of the multifocal lens includes a first region provided in a central portion of the lens surface in the first direction, a second region provided around the first region, A third region provided around the second region,
Of the light emitted from the first light emitting element, the light passing through the first region passes through the fifth imaging point, and the light passing through the second region passes through the sixth imaging point and the third region. The imaged light is imaged at the seventh image point,
The sixth imaging point is located on the latent image carrier surface on the imaging optical system side, the seventh imaging point is located on the latent image carrier surface on the opposite side of the imaging optical system, 5. The image forming apparatus according to claim 3, wherein the fifth imaging point is located between the sixth imaging point and the seventh imaging point in the second direction.   The image forming apparatus according to claim 5, wherein the first area, the second area, and the third area are defined by different definition formulas.   The image forming apparatus according to claim 5, wherein an area of the first region, an area of the second region, and an area of the third region are equal or substantially equal. A first light emitting element and a second light emitting element arranged in a first direction;
Light radiated from the first light emitting element and the second light emitting element is disposed in a second direction orthogonal or substantially orthogonal to the first direction of the first light emitting element and the second light emitting element. And an imaging optical system for projecting onto the exposed surface,
The imaging optical system is configured to provide light emitted from the first light emitting element, a first imaging point located on the imaging optical system side of the exposed surface, and the imaging of the exposed surface. An image is formed at a second imaging point located on the opposite side of the optical system, and the light emitted from the second light emitting element is irradiated with a third coupling located on the imaging optical system side of the exposed surface. Forming an image at an image point and a fourth imaging point located on the opposite side of the imaging optical system from the exposed surface;
The amount of shift in the second direction between the first image point and the second image point is greater than the amount of shift in the second direction between the first image point and the third image point. An image forming apparatus.

Images