JP2020082382A - Optical writing device and image formation apparatus - Google Patents

Abstract

To provide an optical writing device in a light emission arrangement system that can uniformize exposure accuracy and exposure magnification while securing image formation positional accuracy.SOLUTION: An optical writing device which is provided so as to face an image carrier face consisting of a side peripheral face of a cylindrical photoreceptor and for performing optical writing to the image carrier face includes a plurality of writing optical systems which have a light-emitting element and an image formation optical system for forming an image of light emitted by the light-emitting element to the image carrier face. The plurality of writing optical systems are arrayed in a plurality of rows along the axial direction of the photoreceptor in such a state that the optical axis is maintained in parallel. Each image formation optical system is constituted in a both-side telecentric manner such that an aperture is provided between a first lens arranged on the light-emitting element and a second lens arranged on the image carrier face. The curvatures on both side faces of the first lens and the second lens are corrected in accordance with the height position of the image carrier face in the axial direction of the writing optical system so that the image of the light from the light-emitting element is formed at the respective position of the image carrier face.SELECTED DRAWING: Figure 2

Description

The present invention relates to an optical writing device and an image forming apparatus having the optical writing device.

A light emitting array type optical writing device used in an electrophotographic image forming apparatus includes a light emitting point group, an image forming optical system, and a light emitting point group along an axial direction (hereinafter, referred to as “main scanning direction”) of a cylindrical photoconductor. Are arranged. The light emitting point group has a configuration in which the light emitting points are two-dimensionally arranged, and the imaging optical system is provided in a one-to-one correspondence with the light emitting point group. Such a light emitting array type optical writing device simultaneously exposes one entire line along the axis of the cylindrical photoconductor on the side peripheral surface of the photoconductor.

In the optical writing device as described above, a plurality of rows of the light emitting point group and the imaging optical system are arranged in the rotation direction of the photoconductor (hereinafter, referred to as "sub-scanning direction"), and light is emitted between each row. A configuration has been proposed in which the resolution of writing exposure is increased by periodically shifting the arrangement of the point group and the imaging optical system. In addition, regarding such a configuration, for example, in Patent Document 1 below, "either or both of the position of the projection surface (photoreceptor) and the light emitting element disposition surface is provided by making the projection optical system so-called telecentric on both sides. Is prevented from deviating in the optical axis direction, the positional deviation of the image forming spot does not occur, and the density unevenness between the image forming spots does not occur, thereby preventing deterioration of the formed image." There is.

JP, 2009-51194, A

However, with the configuration in which the imaging optical system (projection optical system) is telecentric on both sides, it is possible to suppress the deviation of the imaging position, but since the surface of the photoconductor is curved in the rotational direction of the photoconductor, the optical axis Since the height position of the side peripheral surface of the photoconductor with respect to the direction differs, the exposure accuracy and the exposure magnification vary at each position in the rotational direction of the photoconductor.

In view of this, the present invention provides a light-emitting array type optical writing device capable of achieving uniform exposure accuracy and exposure magnification while suppressing deviation of the image forming position with respect to the surface of a cylindrical photosensitive member, and this optical writing device. An object is to provide an image forming apparatus provided with a writing device.

The present invention for achieving such an object is an optical writing device provided to face an image bearing surface formed of a side peripheral surface of a cylindrical photoconductor and for performing optical writing on the image bearing surface. And a plurality of writing optical systems including a light emitting element and an image forming optical system for forming an image of the light emitted by the light emitting element on the image bearing surface. Are arranged in a plurality of rows along the axial direction of the photoconductor while keeping their optical axes parallel, and each of the imaging optical systems includes a first lens arranged on the light emitting element side, The telecentric lens is provided on both sides of the second lens disposed on the image bearing surface side so that a diaphragm is provided between the second lens and the second lens so that light from the light emitting element is imaged at respective positions on the image bearing surface. The curvatures of both side surfaces of the first lens and the second lens are corrected according to the height position of the image bearing surface in the axial direction of the optical system. The present invention is also an image forming apparatus having such an optical writing device.

According to the present invention, a light-emitting array type optical writing device capable of achieving uniform exposure accuracy and exposure magnification while ensuring the imaging position accuracy with respect to the surface of a cylindrical photoreceptor, and It is possible to obtain an image forming apparatus provided with an optical writing device.

It is a figure for explaining the whole composition of the image forming device concerning each embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing the configuration of the optical writing device according to the first embodiment. FIG. 3 is a schematic plan view of the optical writing device according to the first embodiment as viewed from the photoconductor side. It is a top view of the light emitting point group provided in the optical writing device. It is a schematic diagram which shows the structure of the optical writing device which concerns on 2nd Embodiment.

<<Image Forming Apparatus According to Embodiment of Present Invention>>
Prior to the description of the optical writing device and the image forming apparatus according to each embodiment to which the present invention is applied, the schematic configuration of the image forming apparatus according to each embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a diagram for explaining the overall configuration of an image forming apparatus according to each embodiment of the present invention. An electrophotographic image forming apparatus 1 having an optical writing device according to each embodiment described below will be described. It is a block diagram seen from the front (front). The image forming apparatus 1 illustrated in FIG. 1 includes a housing 10, and an image forming unit 20, a transfer unit 30, a fixing unit 40, a paper supply unit 50, and a paper conveyance unit 60 inside thereof. The configuration of each of these elements is as follows.

<Image forming unit 20>
The image forming unit 20 has, for example, four image forming units 20y, 20m, 20c, and 20k for forming toner images of yellow (Y), magenta (M), cyan (C), and black (K). Each of the image forming units 20y, 20m, 20c, 20k includes a photoconductor 21, a charging device 22, an optical writing device 23, and a developing device 24 arranged around the photoconductor 21.

Each of the photoconductors 21 has a cylindrical shape, and is rotated about a cylindrical shaft 21φ by a drive motor, and the cylindrical side peripheral surface serves as an image bearing surface 21a. Such a photoconductor 21 is arranged in contact with the intermediate transfer belt 31 of the transfer unit 30 described below. The charging device 22, the optical writing device 23, and the developing device 24 are arranged such that the charging device 22, the optical writing device 23, and the optical writing device 23 extend from the contact position between the photoconductor 21 and the transfer unit 30 toward the downstream side in the rotation direction of the photoconductor 21. The device 23 and the developing device 24 are arranged in this order.

The charging device 22 is for charging the image bearing surface 21a of the photoconductor 21 by corona discharge.

The optical writing device 23 is a writing unit that irradiates the image bearing surface 21a of the photoconductor 21 with laser light to form an electrostatic latent image based on image data. The image data is data generated by an image reading unit (not shown) included in the image forming apparatus 1 or data received from an external device such as a personal computer connected to the image forming apparatus 1 or another image forming apparatus. It is assumed that The detailed configuration of such an optical writing device 23 will be described in each of the following embodiments.

The developing device 24 is for adhering the toner, which is stirred and charged, to the image bearing surface 21 a of the photoconductor 21. Between the contact position between the photoconductor 21 and the transfer unit 30 and the position where the charging device 22 is arranged, a cleaner not shown here is in contact with the image bearing surface of the photoconductor 21. The toner arranged on the image bearing surface 21a of the photoconductor 21 is removed.

<Transfer unit 30>
The transfer unit 30 is arranged in parallel with the image forming unit 20. The transfer section 30 includes an intermediate transfer belt 31, a primary transfer roller 32, and a pair of secondary transfer rollers 33.

Of these, the intermediate transfer belt 31 is configured as a rotating endless belt, and the outer peripheral surface thereof serves as an image carrying surface 31a. The intermediate transfer belt 31 rotates in the direction opposite to the rotation of each photoconductor 21, and is arranged in such a state that the image bearing surface 31a is brought into contact with all the photoconductors 21 in order.

The primary transfer roller 32 is arranged such that a voltage having a polarity opposite to that of the toner is applied and the intermediate transfer belt 31 is sandwiched between the primary transfer roller 32 and each photoconductor 21. As a result, the toner attached to the image bearing surface 21 a of the photoconductor 21 is transferred to the image bearing surface 31 a of the intermediate transfer belt 31, and the toner images of the respective colors are superimposed on the image bearing surface 31 a of the intermediate transfer belt 31. An image is formed.

The pair of secondary transfer rollers 33 are arranged so as to sandwich the intermediate transfer belt 31, and the toner image formed on the image bearing surface 31 a of the intermediate transfer belt 31 is conveyed from the paper supply unit 50 described below. And is transferred to the sheet-shaped recording medium S.

<Fixing unit 40>
The fixing unit 40 includes a heating unit 41 and a pressure bonding roller 42 that is arranged to face the heating unit 41, nips the recording medium S conveyed from the secondary transfer roller 33, and transfers the toner transferred to the recording medium S. The image is fixed on the recording medium S.

<Paper supply unit 50>
The sheet supply unit 50 includes a cassette 51 that stores the recording medium S and a feed roller 52 that feeds the recording medium S stored in the cassette 51 one by one from the cassette 51, and the recording medium S from the cassette 51 to the sheet conveyance unit 60. Supply to.

<Paper transport unit 60>
The paper transport unit 60 transports the recording medium S supplied from the paper supply unit 50 along a predetermined route, and includes a plurality of roller pairs 61. The sheet transport unit 60 transports the recording medium S supplied from the sheet supply unit 50 in the order of the secondary transfer roller 33, the fixing unit 40, and a tray (not shown) outside the housing 10. As a result, the recording medium S on which the toner image is formed on the secondary transfer roller 33 is conveyed to the fixing unit 40 to fix the toner image on the recording medium S, and the recording medium S on which the toner image is fixed is removed from the housing. To the tray.

«First embodiment»
<Structure of Optical Writing Device 23>
FIG. 2 is a schematic cross-sectional view showing the configuration of the optical writing device 23 according to the first embodiment. The optical writing device 23 shown in FIG. 2 and FIG. 1 described above is of a light emitting arrangement type, and is arranged so as to face the image bearing surface 21 a constituted by the side peripheral surface of the cylindrical photoconductor 21. It is a thing.

Hereinafter, in describing the configuration of the optical writing device 23, at the position where the optical writing device 23 is arranged to face the image carrying surface 21a of the photoconductor 21, the direction of the normal line of the image carrying surface 21a will be described. The direction toward the rotation axis 21φ of the photoconductor 21 is the incident direction x of light. Further, the direction perpendicular to the incident direction x and along the rotation axis 21φ of the photoconductor 21 is defined as the main scanning direction y. The optical writing device 23 is arranged along the main scanning direction y. Further, a direction that is perpendicular to the incident direction x and the main scanning direction y and that is along the rotation direction of the photoconductor 21 is referred to as a sub-scanning direction z.

The optical writing device 23 includes a light emitting element substrate 100, a first lens array substrate 200, a diaphragm substrate 300, and a second lens array substrate 400 in order from the side farther from the image bearing surface 21a along the light incident direction x. Are arranged. The light emitting element substrate 100, the first lens array substrate 200, the diaphragm substrate 300, and the second lens array substrate 400 are arranged so as to face the image bearing surface 21a, are perpendicular to the incident direction x, and are main-scanned. It is parallel to the direction y and the sub-scanning direction z. It should be noted that between the second lens array substrate 400 and the image bearing surface 21a, a stain prevention window (not shown here) is provided.

Among these, the light emitting element substrate 100 is provided with a plurality of light emitting point groups 101 along the substrate surface. Further, the first lens array substrate 200 is provided with a plurality of first lenses 201 along the substrate surface. Further, the diaphragm substrate 300 is provided with a plurality of diaphragms 301 along the substrate surface. The second lens array substrate 400 is provided with a plurality of second lenses 401 along the substrate surface.

Then, the first lens 201, the diaphragm 301, and the second lens 401 are 1:1 about the optical axis [xφ] extending from the center of one light emitting point group 101 along the incident direction x. They are arranged in a ratio of 1:1 and one writing optical system 23a is configured by them. The structure of each writing optical system 23a is as follows.

[Writing optical system 23a]
The writing optical system 23a includes one light emitting point group 101, a first lens 201, a diaphragm 301, and a second lens 401. The optical axes [xφ] of all the writing optical systems 23a are parallel.

In each writing optical system 23a, the first lens 201, the diaphragm 301, and the second lens 401 form one imaging optical system 23b. These image forming optical systems 23b are used to form an image of light from the corresponding light emitting point group 101 on the image bearing surface 21a of the photoconductor 21, and the image bearing surface 21a of the photoconductor 21. The light from the light emitting point group 101 is imaged at different positions. Each of the image forming optical systems 23b as described above is configured to be telecentric on both sides, and has the same image forming magnification.

The image forming magnification of each image forming optical system 23b is [−1], and the second lens 401 and the first lens 201 have symmetrical shapes with respect to the diaphragm 301 as described below. There is. Thereby, the first lens array substrate 200 having the first lens 201 and the second lens array substrate 400 having the second lens 401 can be commonly used.

FIG. 3 is a schematic plan view of the optical writing device 23 according to the first embodiment as viewed from the photoconductor 21 side. As shown in this figure, the optical writing device 23 has a plurality of writing columns [L] in which a plurality of writing optical systems 23a are arranged along the main scanning direction y. Here, as an example, it is assumed that a plurality of writing optical systems 23a are arranged along the main scanning direction y at predetermined intervals to have three writing columns [L]. Note that FIG. 2 corresponds to the A-A′ cross section in FIG. 3.

The writing optical system 23a arranged in each writing row [L] overlaps the writing optical system 23a arranged in another writing row [L] in the main scanning direction y at a predetermined pitch. They are arranged in a staggered manner. As a result, the resolution of the electrostatic latent image written on the image bearing surface 21a of the photoconductor 21 is ensured by the writing optical system 23a of each writing row [L].

As shown in FIGS. 2 and 3, one of these writing lines [L] is the normal to the image bearing surface 21a of the photoconductor 21 and the optical axis [xφ] of the writing optical system 23a. Is the central column [Lφ] that matches. Further, the remaining two of the writing rows [L] are upstream rows [L- which are located on the upstream side in the sub-scanning direction z in the rotation direction of the image bearing surface 21a with respect to the central row [Lφ]. ] And a downstream side row [L+] located downstream of the central row [Lφ] in the sub-scanning direction z in the rotation direction of the image bearing surface 21a. The upstream side row [L−] and the downstream side row [L+] are arranged at equal intervals with respect to the central row [Lφ].

In each writing optical system 23a arranged in this way with respect to the image bearing surface 21a of the cylindrical photoconductor 21, the image points [Pφ], [P−], [P+] on the image bearing surface 21a. Have different heights in the optical axis [xφ] direction. That is, the image point [Pφ] on the image bearing surface 21a in the writing optical system 23aφ in the central row [Lφ] and the image point on the image bearing surface 21a in the writing optical system 23a− in the upstream row [L−]. [P-] and the image point [P+] on the image bearing surface 21a in the writing optical system 23a+ of the downstream side row [L+] do not exist on the same plane.

Of the three image points [Pφ], [P-], and [P+], the normal line of the photoconductor 21 to the image bearing surface 21a and the optical axis [xφ] of the writing optical system 23a coincide with each other. The image point [Pφ] of the writing optical system 23aφ of the column [Lφ] is arranged closer to the light emitting element substrate 100 side than the other two image points [P−] and [P+].

Further, as described below, the center of each second lens 401, that is, the center of the core thickness [t2] of each second lens 401 is arranged on the same plane perpendicular to the incident direction x. Therefore, the conjugate length of the writing optical system 23aφ in the central row [Lφ] is greater than the conjugate length of the writing optical system 23a− in the upstream row [L−] and the writing optical system 23a+ in the downstream row [L+]. Is also short.

Of the writing optical systems 23a arranged in this way, the writing optical system 23aφ arranged in the central column [Lφ], the writing optical system 23a− arranged in the upstream column [L−], and the downstream. The writing optical system 23a+ arranged in the side row [L+] is characterized in that the first lens 201 and the second lens 401 have different shapes, as described in detail below.

Hereinafter, the details of the configurations of the light emitting point group 101, the first lens 201, the diaphragm 301, and the second lens 401 which configure each writing optical system 23a will be described.

[Light emitting point group 101]
The light emitting point group 101 is a light emitting element provided two-dimensionally along the substrate surface of the light emitting element substrate 100. These light emitting point groups 101 have the same configuration in all the writing optical systems 23a.

FIG. 4 is a plan view of the light emitting point group 101. As shown in this figure, each light emitting point group 101 has a configuration in which a plurality of light emitting points 102 are arranged in a rectangular region that is long in the main scanning direction y and short in the sub scanning direction z, for example. Each light emitting point 102 is configured by, for example, an LED (light emitting diode) or an OLED (Organic Light Emitting Diode).

Returning to FIG. 2, in the light emitting element substrate 100, each light emitting point group 101 is a bottom emission type OLED covered with a transparent substrate material such as a silicon oxide substrate. As a result, the light emitting surface 101a of each light emitting point group 101 is located on the surface of the light emitting element substrate 100 and deeper than the light emitting surface 100a. However, the center points of all the light emitting point groups 101 are substantially on the same plane, and the plane formed by the center points of the light emitting point groups 101 and the plane perpendicular to the optical axis [xφ] (incident direction x) are formed. The angle is 0 degrees.

[First lens 201]
The first lens 201 is two-dimensionally provided along the substrate surface of the first lens array substrate 200. Each of these first lenses 201 is a biconvex lens. Each of the first lenses 201 as described above has a resin-made convex lens portion formed on both side surfaces of a common first lens array substrate 200 made of a transparent material such as glass. By forming the first lens 201 as a biconvex lens, the refracting power of the first lens 201 can be allocated to both the light incident surface 202 and the light exit surface 203, which suppresses the occurrence of aberrations, The difficulty is also reduced.

In addition, each first lens 201 has the same core thickness [t1], the center of the core thickness [t1] is arranged on the same plane, and the plane where the center is arranged and the optical axis [xφ]. The angle formed by the plane perpendicular to the (incident direction x) is 0 degree. Further, in each of the first lenses 201, the distance [d1] between the light emitting surface 101a of the light emitting point group 101 and the incident surface 202 is the same. By making the core thickness [t1] the same, when the first lens 201 is resin-molded on a common substrate, the resin volume of the lens portion can be made uniform, so that the moldability of the lens is improved.

The above-described first lens 201 is characterized in that the curvature ratios of the light incident surface 202 and the light emitting surface 203 are different for each writing column [L]. Here, the curvature of the entrance surface 202 with respect to the curvature of the exit surface 203 of the first lens 201 is defined as a first curvature ratio [R1].

In this case, the first curvature ratio [R1φ] of the first lens 201φ forming the central row [Lφ] is equal to the first curvature ratio [R1-] of the first lens 201− forming the upstream row [L−] and It is different from the first curvature ratio [R1+] of the first lens 201+ that constitutes the downstream side row [L+]. Specifically, as the position of the image bearing surface 21a in the optical axis [xφ] direction of the imaging optical system 23b is closer to the light emitting element substrate 100 side, the first curvature ratio [R1] of the first lens 201 is smaller, The first curvature ratio [R1φ]<first curvature ratios [R1-], [R1+].

That is, the first curvature ratio [R1φ] of the first lens 201φ of the central column [Lφ] whose image point [Pφ] is close to the light emitting point group 101 and whose conjugate length is short is the same as that of the upstream column [L−] whose conjugate length is long. It is smaller than the first curvature ratio [R1-] of the first lens 201- and the first curvature ratio [R1+] of the first lens 201+ in the downstream side row [L+]. Further, the first curvature ratio [R1-] of the first lens 201- of the upstream side row [L-] is equal to the first curvature ratio [R1+] of the first lens 201+ of the downstream side row [L+].

In each of the first lenses 201 as described above, the light [hφ] that has passed through the first lens 201φ in the central row [Lφ] becomes parallel light or convergent light, and the upstream row [L−] and the downstream row It is assumed that the lights [h−] and [h+] that have passed through the [L+] first lenses 201− and 201+ are arranged to be divergent light. However, the light [hφ] that has passed through the first lens 201φ in the central row [Lφ] becomes convergent light, and also passes through the first lenses 201− and 201+ in the upstream side row [L−] and the downstream side row [L+]. The lights [h−] and [h+] may be arranged so as to be parallel light or divergent light.

[Aperture 301]
The diaphragm 301 is provided two-dimensionally along the substrate surface of the diaphragm substrate 300. These diaphragms 301 are openings provided in the diaphragm substrate 300 made of a light shielding film. The light shielding film may be formed on one main surface of a transparent substrate such as glass. Such a diaphragm 301 has the same aperture shape in all the writing optical systems 23a.

The center points of the respective diaphragms 301 are substantially on the same plane, and the angle between the plane where the center points of the diaphragms 301 are present and the plane perpendicular to the optical axis [xφ] (incident direction x) is 0 degree. ..

The diaphragm 301 is arranged between the first lens 201 and the second lens 401 at a position where each imaging optical system 23b is telecentric on both sides.

[Second lens 401]
The second lens 401 is two-dimensionally provided along the substrate surface of the second lens array substrate 400. Each of these second lenses 401 is a biconvex lens. Each of the second lenses 401 as described above has a resin-made convex lens portion formed on both side surfaces of a common second lens array substrate 400 made of a transparent material such as glass. Second lens 4
By using 01 as a biconvex lens, it is possible to allocate the refracting power of the second lens 401 to both the light incident surface 402 and the light exit surface 403, which suppresses the occurrence of aberrations and also has difficulty in processing. It has a reduced configuration.

The second lenses 401 have the same core thickness [t2], the centers of the core thickness [t2] are arranged on the same plane, and the plane on which the center is arranged and the optical axis [xφ]. The angle formed by the plane perpendicular to the (incident direction x) is 0 degree. By setting the core thickness [t2] to be the same, when the second lens 401 is resin-molded on a common substrate, the resin volume of the lens portion can be made uniform, so that the lens moldability is improved.

Further, in each second lens 401, the distances [d2φ], [d2-], [d2+] between the exit surface 403 and the image points [Pφ], [P−], [P+] on the image bearing surface 21a are different. That is, the distance [d2φ] between the exit surface 403 of the second lens 401φ in the central row [Lφ] and the image point [Pφ] is equal to the distance between the exit surface 403 and the image point of the second lens 401− in the upstream row [L−]. It is smaller than the distance [d2-] from [P-] and the distance [d2+] between the exit surface 403 and the image point [P+] of the second lens 401+ in the downstream side row [L+]. Further, the distance [d2-] of the upstream side row [L-] is equal to the distance [d2+] of the downstream side row [L+].

In the writing optical system 23aφ in the central column [Lφ], the distance [d2φ]≦distance [d1] is set. In this case, if the distance [d2φ]<distance [d1], the light [hφ] that has passed through the first lens 201φ becomes convergent light. As a result, the image forming position of the light passing through the second lens 401φ moves toward the second lens 401φ, the conjugate length becomes short, and the image point [Pφ] is formed on the image bearing surface 21a located closer to the second lens 401φ. It is configured so that an image can be formed. If the image point [Pφ] can be formed on the image bearing surface 21a, the distance [d2φ]=distance [d1] may be used. In this case, the light [hφ] that has passed through the first lens 201φ is parallel. Become light.

Further, in the writing optical system 23- of the upstream side row [L-] and the writing optical system 23+ of the downstream side row [L+], the distances [d2-], [d2+]>distance [d1] are set. .. In this case, the lights [h-] and [h+] that have passed through the first lenses 201- and 201+ are divergent lights. As a result, the image forming position of the light that has passed through the second lenses 401- and 401+ moves in a direction away from the second lenses 401- and 401+, the conjugate length extends, and the image is formed on the image carrying surface 21a at the farther position. The point [P-][P] can be imaged.

The second lens 401 as described above is arranged symmetrically with respect to the first lens 201 with respect to the diaphragm 301 in each imaging optical system 23b and has a symmetrical shape, and the write column [L]. It is characteristic that the curvature ratios of the entrance surface 402 and the exit surface 403 are different for each. Here, contrary to the definition of the first lens 201, the curvature of the exit surface 403 with respect to the curvature of the entrance surface 402 of the second lens 401 is defined as the second curvature ratio [R2].

In this case, the second curvature ratio [R2φ] of the second lens 401φ forming the central row [Lφ] is equal to the second curvature ratio [R2-] of the second lens 401− forming the upstream row [L−] and It is different from the second curvature ratio [R2+] of the second lens 401+ that constitutes the downstream side row [L+]. Specifically, as the position of the image bearing surface 21a in the optical axis [xφ] direction of the imaging optical system 23b is closer to the light emitting element substrate 100 side, the second curvature ratio [R2] of the second lens 401 is smaller, Second curvature ratio [R2φ]<first curvature ratio [R2-], [R2+].

That is, the second curvature ratio [R2φ] of the second lens 401φ of the central column [Lφ], which has a short conjugate length and whose image point [Pφ] is close to the light emitting point group 101 side, has a long conjugate length in the upstream column [L−]. ] Smaller than the second curvature ratio [R2-] of the second lens 401− and the second curvature ratio [R2+] of the second lens 401+ in the downstream side row [L+]. Further, the second curvature ratio [R2-] of the second lens 401- in the upstream side row [L-] is equal to the second curvature ratio [R2+] of the second lens 201+ in the downstream side row [L+].

Further, in such a central row [Lφ], the second curvature ratio [R2φ]=first curvature ratio [R1φ]. In the upstream side row [L-] and the downstream side row [L+], the second curvature ratios [R2-], [R2+] = the first curvature ratios [R1-], [R1+].

<Specific Example of Optical Writing Device 23>
Next, a specific example of the above-mentioned optical writing device 23 will be shown. Table 1 below shows coordinate data of the writing optical system 23aφ of the central column [Lφ] of the writing optical system 23a in the optical writing device 23 of the first embodiment. Table 2 below shows coordinate data of the writing optical system 23a- of the upstream row [L-] of the writing optical system 23a in the optical writing device 23 of the first embodiment. Since the incident data x of the coordinate data of the downstream side column [L+] is the same as that of the coordinate data of the upstream side line [L-], the signs of the main scanning direction y and the sub scanning direction z may be reversed. Omitted.

In the coordinate data shown in Tables 1 and 2 below, the center position [O] of the light emitting surface 101a of the light emitting point group 101 provided in the central column [Lφ] is defined as the incident direction x=0, the main scanning direction y=0, This is coordinate data when the sub-scanning direction z=0. Regarding the entrance surface 202 and the exit surface 203 of the first lens 201, the diaphragm 301, and the entrance surface 402 and the exit surface 403 of the second lens 401, the respective central values are shown. In addition, the center coordinates of the writing optical system 23aφ in the central column [Lφ] are commonly used for the respective substrates. Further, the coordinate data of the photoconductor 21 is the coordinate data at the image points [Pφ] and [P−] on the image bearing surface 21 a of the photoconductor 21. The photoconductor 21 has a cylindrical shape with a radius of 22 mm.

In Table 1, the incident surface 202 and the exit surface 203 of the first lens 201φ, the diaphragm 301, the incident surface 402 and the exit surface 403 of the second lens 401φ have the same values in the main scanning direction y and the sub-scanning direction z, It can be seen that these are arranged in a straight line along the incident direction x.

Further, in Table 2, the values of the entrance surface 202 and the exit surface 203 of the first lens 201-, the diaphragm 301, the entrance surface 402 and the exit surface 403 of the second lens 401- in the main scanning direction y and the sub-scanning direction z are the same. It can be seen that these are arranged in a straight line along the incident direction x.

Further, the angle formed by the first lens 201, the diaphragm 301, the second lens 401, and the substrate provided with these with respect to the plane perpendicular to the optical axis [xφ] (incident direction x) is 0 degree. Further, the photoconductor 21 has a cylindrical shape. For this reason, comparing Tables 1 and 2, in the incident direction x of the image bearing surface 21a, the writing optical system 23aφ in the central column [Lφ] is closer to the writing optical system 23a in the upstream column [L−]. -It is smaller than. The angle of the image bearing surface 21a is 0° in the writing optical system 23aφ in the central row [Lφ] and is oblique in the writing optical system 23a− in the flow side row [L−].

The following Tables 3 (1) to (4) show the aspherical coefficients of the first lens 201φ and the second lens 401φ that form the writing optical system 23aφ of the central column [Lφ]. Further, Tables 4 (1) to (4) below show the aspherical surface coefficients of the first lens 201- and the second lens 401- that configure the writing optical system 23a- of the upstream side row [L-]. Note that the data of the writing optical system 23a+ in the downstream side column [L+] is common and is therefore omitted.

The surface shapes of the first lens 201 and the second lens 401 shown here are axisymmetric aspherical surfaces, there is no spherical term, and the shape formula is as shown in the following formula (1).

The curvature in this case is a paraxial curvature. In an axisymmetric aspherical surface, paraxial curvature=2×[second-order aspherical coefficient]. In Tables 3 and 4, the second-order aspherical coefficient is an aspherical coefficient of [i=2]. The first lens 201 and the second lens 401 are configured such that convex lens portions made of resin having a refractive index of 1.5285 are provided on both main surfaces of a glass substrate having a refractive index of 1.5145. Further, the imaging magnification of each writing optical system 23a configured by using the first lens 201 and the second lens 401 is [-1] times.

Table 5 below shows the first curvature ratio [R1φ] for the first lens 201φ and the second curvature ratio [R2φ] for the second lens 401φ in the center column [Lφ] shown in Table 3 above. Moreover, the 1st curvature ratio [R1-] regarding the 1st lens 201- of the upstream side row [L-] and the 2nd curvature ratio [R2-] regarding the 2nd lens 401- which are shown in the said Table 4 are shown. The first curvature ratio [R1] and the second curvature ratio [R2] are shown as absolute values. Further, the first curvature ratio [R1+] for the first lens 201+ and the second curvature ratio [R2+] for the second lens 401+ in the downstream row [L+] are the same as the values in the upstream row [L-]. Omitted.

As shown in Table 5, the first curvature ratio [R1φ] of the central row [Lφ] where the image point [Pφ] is close to the light emitting point group 101 and the conjugate length is short, the first curvature ratio [R1φ] of the upstream row [L−] having the long conjugate length is large. It is smaller than the first curvature ratio [R1-]. Similarly, the second curvature ratio [R2[phi]] of the central row [L[phi]] is smaller than the second curvature ratio [R2-] of the upstream row [L-].

Further, as shown in the coordinate data of Table 1, in the center column [Lφ], the distance [d1] between the light emitting surface 101a and the entrance surface 202 of the first lens 201φ is [d1]=3.882. The distance [d2φ] between the exit surface 403 of the second lens 401φ and the image point [Pφ] on the image bearing surface 21a is [d2φ]=19.747-16.118=3.629. Therefore, in the center column [Lφ], the distance [d1]>distance [d2φ] is satisfied, and the light [hφ] that has passed through the first lens 201φ is convergent light.

As shown in the coordinate data of Table 2, in the upstream side row [L-], the distance [d1] between the light emitting surface 101a and the entrance surface 202 of the first lens 201- is [d1]=3.882. Is. The distance [d2-] between the exit surface 403 of the second lens 401- and the image point [P-] on the image bearing surface 21a is [d2-]=20.253-16.118=4.135. is there. Therefore, in the upstream side row [L-], the distance [d1]<distance [d2-], and the light [h-] that has passed through the first lens 201- is divergent light.

Further, since the imaging magnification of each writing optical system 23a is [−1] times, as can be seen from the coordinates and aspherical coefficients of the construction data in Tables 1 to 5, the central column [Lφ] and the upstream column [Lφ] The first lens 201 and the second lens 401 of L−] are arranged symmetrically with respect to the diaphragm 301, and the surface shapes are also symmetrical, and have the configuration shown in the second embodiment.

<Effects of First Embodiment>
According to the optical writing device 23 of the first embodiment described above, the image forming optical systems 23b are both-side telecentric, so that the image forming position accuracy on the image carrying surface 21a is ensured. Moreover, each writing optical system 23a corrects the curvature ratios [R1] and [R2] of the first lens 201 and the second lens 204 according to the height position of the image bearing surface 21a in the optical axis [xφ] direction. By doing so, the conjugate length is adjusted so that the image points [Pφ], [P−], and [P−] are imaged on the image bearing surface 21a. Therefore, it is possible to suppress variations in the exposure amount at each position on the image bearing surface 21a of the cylindrical photoconductor 21. Furthermore, by correcting the curvature ratios [R1] and [R2] of both the first lens 201 and the second lens 204, it is possible to keep the magnification of each imaging optical system 23b uniform.

Further, according to the image forming apparatus 1 including the optical writing device 23, it is possible to improve the image forming accuracy.

«Second embodiment»
<Configuration of optical writing device 23'>
FIG. 5 is a schematic cross-sectional view showing the configuration of the optical writing device 23′ according to the second embodiment. The optical writing device 23' shown in this figure differs from the optical writing device 23 described in the first embodiment in that the arrangement state of the light emitting point group 101, the first lens 201, the diaphragm 301, and the second lens 401 is different. The other optical configuration is the same as the configuration described in the first embodiment. For example, the relationship among the light emitting point group 101, the first lens 201, the diaphragm 301, and the second lens 401 in each writing device 23′ is similar to the relationship shown in the first embodiment.

That is, in the optical writing device 23′ of the second embodiment, the planes in which the centers of the light emitting point group 101, the first lens 201, the diaphragm 301, and the second lens 401 are arranged respectively, and the optical axis [xφ]( The angle formed by a plane perpendicular to the incident direction x) is not 0 degrees, but has the following inclination.

[Light emitting point group 101]
The light emitting point groups 101 are two-dimensionally provided along the substrate surface of the light emitting element substrate 100, and each light emitting point group 101 faces the image bearing surface 21a and is perpendicular to the incident direction x. , Is provided on a plane parallel to the main scanning direction y and the sub scanning direction z.

Further, the center points of all the light emitting point groups 101 exist on substantially the same plane. The angle [θ1] formed by the plane 107 where the center point of the light emitting point group 101 exists and the plane 108 perpendicular to the optical axis [xφ] (incident direction x) is not 0 degrees but has an inclination.

In the light emitting element substrate 101′ on which the light emitting point groups 101 are arranged, the light emitting point groups 101 are provided for each of the central row [Lφ], the upstream row [L−], and the downstream row [L+]. A substrate is provided, and these substrates are stacked in the optical axis [xφ] (incident direction x) direction.

[First lens 201]
The first lens 201 is two-dimensionally provided along the substrate surface of the first lens array substrate 200. The core thicknesses [t1] of the first lenses 201 are parallel to the incident direction x and have the same size.

The centers of the core thicknesses [t1] of all the first lenses 201 are arranged on the same plane. The angle [θ2] formed by the plane 207 on which the center of the core thickness [t1] is arranged and the plane 208 perpendicular to the optical axis [xφ] (incident direction x) is in the range of angle [θ2]<[θ1]. Have a slope. Even in this case, the position of the image bearing surface 21a in the optical axis [xφ] direction of the imaging optical system 23b constitutes the central row [Lφ] closer to the light emitting element substrate 100′ side. The first curvature ratio [R1φ] of the first lens 201+ of the first lens 201+ forming the upstream side row [L−] and the first curvature ratio [R1φ] of the first lens 201+ forming the downstream side row [L+] of Similar to the first embodiment, it is smaller than one curvature ratio [R1+].

[Aperture 301]
The diaphragm 301 is provided two-dimensionally along the substrate surface of the diaphragm substrate 300. The center points of these diaphragms 301 are substantially on the same plane. The angle [θ3] formed by the plane 307 where the center point of the diaphragm 301 exists and the plane 308 perpendicular to the optical axis [xφ] (incident direction x) has an inclination in the range of angle [θ3]<[θ2]. ..

[Second lens 401]
The second lens 401 is two-dimensionally provided along the substrate surface of the second lens array substrate 400. The core thicknesses [t2] of the respective second lenses 401 are parallel to the incident direction x and have the same size.

The centers of the core thicknesses [t2] of all the second lenses 401 are arranged on the same plane. The angle [θ4] formed by the plane 407 in which the center of the core thickness [t2] is arranged and the plane 408 perpendicular to the optical axis [xφ] (incident direction x) is in the range of angle [θ4]<[θ3]. Have a slope. Even in this case, the position of the image bearing surface 21a in the optical axis [xφ] direction of the imaging optical system 23b constitutes the central row [Lφ] closer to the light emitting element substrate 100′ side. The second curvature ratio [R2φ] of the second lens 401+ of the second lens 401+ forming the upstream side row [L−] and the second curvature ratio [R2−] of the second lens 401+ forming the downstream side row [L+]. It is smaller than the second curvature ratio [R2+], as in the second embodiment.

<Specific Example of Optical Writing Device 23'>
Next, a specific example of the above-described optical writing device 23' will be shown. Table 6 below shows coordinate data of the writing optical system 23aφ of the central column [Lφ] in the optical writing device 23′ of the second embodiment. Table 7 below shows coordinate data of the writing optical system 23a- of the upstream side row [L-] in the optical writing device 23' of the second embodiment. Further, Table 8 below shows coordinate data of the writing optical system 23a+ of the downstream side column [L+] in the optical writing device 23' of the second embodiment.

In the coordinate data shown in Tables 6 to 8 below, the center position [O] of the light emitting surface 101a of the light emitting point group 101 provided in the central column [Lφ] is defined as incident direction x=0, main scanning direction y=0, This is coordinate data when the sub-scanning direction z=0. Regarding the entrance surface 202 and the exit surface 203 of the first lens 201, the diaphragm 301, and the entrance surface 402 and the exit surface 403 of the second lens 401, the respective central values are shown. As for the substrate material of the first lens array substrate 200 and the second lens array substrate 400, the center coordinates on the incident surface side in the writing optical system 23aφ of the central column [Lφ] are used in common. The coordinates of the exit surfaces of the substrate materials of the first lens array substrate 200 and the second lens array substrate 400 are the coordinates in the direction normal to the entrance surface at the center coordinates on the entrance surface side. Since the light emitting element substrate 100′ has a configuration in which the substrates provided with the light emitting point groups 101 are stacked for the central row [Lφ], the upstream row [L−], and the downstream row [L+], respectively, the coordinates are also Showing each

Further, the coordinate data of the photoconductor 21 is the coordinate data at the image points [Pφ], [P−], [P+] on the image bearing surface 21 a of the photoconductor 21. The photoconductor 21 has a cylindrical shape with a radius of 22 mm.

As shown in Tables 6 to 8, in each of the writing optical systems 23aφ, 23a−, 23a+, the entrance surface 202 and the exit surface 203 of the first lens 201, the diaphragm 301, the entrance surface 402 and the exit of the second lens 401. It can be seen that the values of the main scanning direction y and the sub scanning direction z of the surface 403 are the same, and these are arranged in a straight line along the incident direction x.

Further, the angle formed by the first lens 201, the diaphragm 301, the second lens 401, and the substrate provided with these with respect to the plane perpendicular to the optical axis [xφ] (incident direction x) is not 0 degrees but is inclined. ing. Further, the photoconductor 21 has a cylindrical shape. Therefore, comparing the coordinates of the image bearing surface 21a in Tables 6 to 8, with respect to the incident direction x, the writing optical system 23aφ in the central column [Lφ] writes in the upstream column [L−]. It is smaller than the optical system 23a− and the writing optical system 23a+ of the downstream side row [L+]. The angle of the image bearing surface 21a is 0° in the writing optical system 23aφ of the central row [Lφ], and the writing optical system 23a− of the flow side row [L−] and the writing of the downstream side row [L+]. The optical system 23a+ is oblique.

Tables 9(1) to 9(4) below show aspherical surface coefficients of the first lens 201φ and the second lens 401φ that form the writing optical system 23aφ of the central column [Lφ]. Further, Tables 10 (1) to (4) below show aspherical surface coefficients of the first lens 201- and the second lens 401- that configure the writing optical system 23a- of the upstream side row [L-]. Further, Tables 11(1) to 11(4) below show aspherical surface coefficients of the first lens 201+ and the second lens 401+ that form the writing optical system 23a+ of the downstream side column [L+].

The surface shapes of the first lens 201 and the second lens 401 shown here are axisymmetric aspherical surfaces similar to those shown in the first embodiment, and the curvature is a paraxial curvature. In an axisymmetric aspherical surface, paraxial curvature=2×[second-order aspherical coefficient]. In Tables 9 to 11, the secondary aspherical coefficient is an aspherical coefficient of i=2. The first lens 201 and the second lens 401 are configured such that convex lens portions made of resin having a refractive index of 1.5285 are provided on both main surfaces of a glass substrate having a refractive index of 1.5145. Further, the imaging magnification of each writing optical system 23a configured by using the first lens 201 and the second lens 401 is [-1] times.

Table 12 below shows the first curvature ratio [R1] for each first lens 201 and the second curvature ratio [R2] for the second lens 401 shown in Tables 9 to 11 above. The first curvature ratio [R1] and the second curvature ratio [R2] are shown as absolute values.

As shown in Table 12, the first curvature ratio [R1φ] of the central row [Lφ] where the image point [Pφ] is close to the light emitting element substrate 100 and the conjugate length is short, the first curvature ratio [R1φ] of the upstream row [L−] is long. It is smaller than the first curvature ratio [R1-] and the first curvature ratio [R1+] of the downstream side row [L+]. Similarly, the second curvature ratio [R2φ] of the central row [Lφ] is the second curvature ratio [R2-] of the upstream row [L-] and the second curvature ratio [R2+] of the downstream row [L+]. Smaller than.

Further, as shown in the coordinate data of Table 6, in the center column [Lφ], the distance [d1φ] between the light emitting surface 101a and the incident surface 202 of the first lens 201φ is [d1φ]=4.257. The distance [d2φ] between the exit surface 403 of the second lens 401φ and the image point [Pφ] on the image bearing surface 21a is [d2φ]=21.247-17.243=4.004. Therefore, in the center column [Lφ], the distance [d1φ]>distance [d2φ], and the light [hφ] that has passed through the first lens 201φ is convergent light.

As shown in the coordinate data of Table 7, in the upstream side row [L-], the distance [d1-] between the light emitting surface 101a and the entrance surface 202 of the first lens 201- is [d1-]=5. .381-1.500=3.881. The distance [d2-] between the exit surface 403 of the second lens 401- and the image point [P-] on the image bearing surface 21a is [d2-] = 21.753-17.619 = 4.134. is there. Therefore, in the upstream side row [L-], the distance [d1-]<distance [d2-], and the light [h-] that has passed through the first lens 201- is divergent light.

As shown in the coordinate data of Table 8, in the downstream side row [L+], the distance [d1+] between the light emitting surface 101a and the incident surface 202 of the first lens 201+ is [d1+]=3.132−( −1.500)=4.632. The distance [d2+] between the exit surface 403 of the second lens 401+ and the image point [P+] on the image bearing surface 21a is [d2+]=21.753-16.868=4.885. Therefore, in the downstream side row [L+], the distance [d1+]<distance [d2+], and the light [h-] that has passed through the first lens 201+ is divergent light.

Further, since the imaging magnification of each writing optical system 23a is [-1] times, as can be seen from the coordinates and aspherical coefficients of the construction data in Tables 6 to 12, the central column [Lφ], the upstream column [Lφ], The first lens 201 and the second lens 401 of L−] and the downstream side row [L+] are arranged symmetrically with respect to the diaphragm 301, and the surface shapes are also symmetrical, and the configuration shown in the second embodiment is used. It has become.

<Effects of Second Embodiment>
Even in the optical writing device 23′ according to the second embodiment described above, the relationship between the light emitting point group 101, the first lens 201, the diaphragm 301, and the second lens 401 is the same as the relationship shown in the first embodiment. It is the same. Therefore, similar to the optical writing device 23 of the first embodiment, the accuracy of the image forming position on the image bearing surface 21a is ensured, and the variation of the exposure amount at each position on the image bearing surface 21a of the cylindrical photoconductor 21. Can be suppressed, and the magnification of each imaging optical system 23b can be kept uniform. Further, according to the image forming apparatus 1 including the optical writing device 23', it is possible to improve the image forming accuracy.

DESCRIPTION OF SYMBOLS 1... Image forming apparatus 21... Photosensitive body 21a... Image carrying surface 21φ... Photosensitive body axis 23, 23'... Optical writing device 23a, 23aφ, 23a−, 23a+... Writing optical system 23b, 23bφ, 23b−, 23b+ ... Imaging optical system 101 ... Light emitting element group (light emitting element)
102... Emission point 107... Plane where the center point of the light emitting element exists 108, 208, 308, 408... Plane perpendicular to the optical axis 201, 201φ, 201−, 201+... First lens 202... Light incident surface (first lens) )
203... Light exit surface (first lens)
207... Plane in which the center point of the first lens exists 301... Stop 307... Plane in which the center point of the stop exists 401, 401φ, 401−, 401+... Second lens 402... Light incident surface (second lens)
403... Light exit surface (second lens)
407... Plane in which the center of the second lens exists [R1], [R1φ], [R1-], [R1+]... First curvature ratio [R2], [R2φ], [R2-], [R2+]... 2 Curvature ratio [t1]... Core thickness (first lens)
[T2]... Core thickness (second lens)
[Xφ]... Optical axis

Claims (12)

An optical writing device provided to face an image bearing surface formed of a side peripheral surface of a cylindrical photosensitive member, for performing optical writing on the image bearing surface,
A plurality of writing optical systems including a light emitting element and an image forming optical system for forming an image of the light emitted by the light emitting element on the image bearing surface, the plurality of writing optical systems being optical axes. Are arranged in a plurality of rows along the axial direction of the photoconductor while keeping the
Each of the imaging optical systems,
A double-sided telecentric structure is provided in which a diaphragm is provided between a first lens arranged on the light emitting element side and a second lens arranged on the image bearing surface side,
According to the height position of the image carrying surface in the axial direction of the writing optical system, the light from the light emitting element is focused on the respective positions of the image carrying surface, and the first lens and the An optical writing device in which the curvature of both side surfaces of the second lens is corrected. Each of the light emitting elements comprises a light emitting point group in which light emitting points are two-dimensionally arranged,
The center points of the respective light emitting elements are on substantially the same plane,
The center points of the respective first lenses are substantially on the same plane,
The center points of the respective diaphragms are on substantially the same plane,
The optical writing device according to claim 1, wherein the center points of the respective second lenses are substantially on the same plane. The optical writing device according to claim 2, wherein a plane where the center point of the light emitting element exists is parallel to a plane perpendicular to the optical axis. The optical writing device according to claim 2, wherein a plane where the center point of the light emitting element exists is inclined with respect to a plane perpendicular to the optical axis. A plane where the center point of the first lens exists, a plane where the center point of the diaphragm exists, and a plane where the center of the second lens exists have an inclination with respect to a plane perpendicular to the optical axis,
An angle [θ1] between a plane where the center point of the light emitting element is present and a plane perpendicular to the optical axis, and an angle between a plane where the center point of the first lens is present and a plane perpendicular to the optical axis [ [theta]2], an angle [[theta]3] between a plane where the center point of the diaphragm is present and a plane perpendicular to the optical axis, and a plane where the center of the second lens is present and a plane perpendicular to the optical axis. The optical writing device according to claim 4, wherein the angle [θ4] is [θ1]>[θ2]>[θ3]>[θ4]. In each of the imaging optical systems, the curvature of the light incident surface with respect to the curvature of the light emitting surface of the first lens is a first curvature ratio, and the curvature of the light exit surface with respect to the curvature of the light incident surface of the second lens is second. Given the curvature ratio,
6. The values of the first curvature ratio and the second curvature ratio are smaller as the position of the image bearing surface in the optical axis direction of each of the writing optical systems is closer to the light emitting element side. 2. The optical writing device according to item 1. In the writing optical system, a distance [d1] between the light emitting element and the light incident surface of the first lens and a distance [d1] between the light emitting surface of the second lens and the image bearing surface on each of the optical axes. In the writing optical system whose relationship with [d2] is [d1]>[d2], the light passing through the first lens is converged light, and the writing optical system is [d1]<[d2]. The optical writing device according to claim 1, wherein the system is configured such that the light that has passed through the first lens becomes divergent light. The optical writing device according to claim 1, wherein the first lens and the second lens are convex lenses on both sides. The core thickness of the first lens is the same between the imaging optical systems,
The optical writing device according to claim 1, wherein the core thickness of the second lens is the same between the imaging optical systems. The imaging magnification of each of the imaging optical systems is [−1] times, and the first lens and the second lens in each of the imaging optical systems are symmetrical with respect to the diaphragm. 9. The optical writing device according to any one of 9. A cylindrical photoconductor whose side peripheral surface is an image bearing surface,
And an optical writing device provided to face the image bearing surface for performing optical writing on the image bearing surface,
The optical writing device,
A plurality of writing optical systems including a light emitting element and an image forming optical system for forming an image of the light emitted by the light emitting element on the image bearing surface, the plurality of writing optical systems being optical axes. Are arranged in a plurality of rows along the axial direction of the photoconductor while keeping the
Each of the imaging optical systems,
A first lens arranged on the light emitting element side and a second lens arranged on the image carrying surface side are provided with a diaphragm between the two lenses and are telecentric.
According to the height position of the image carrying surface in the axial direction of the writing optical system, the first lens and the light so that the light from the light emitting element is imaged at respective positions of the image carrying surface. An image forming apparatus in which the curvature of both side surfaces of the second lens is corrected. The image forming apparatus according to claim 11, wherein the photoconductor rotates about the cylindrical shaft.

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