JP2009067041A - Line head and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make sure that density unevenness caused by positional deviation of light-emitting dot images and shading does not occur, in an optical writing head in which a plurality of columnar light emitting elements are arranged correspondingly to each lens of a plurality of positive lenses arrayed in an array shape. <P>SOLUTION: The line head includes: a positive lens system 5 having the two lenses L1 and L2 with positive refractive power; a lens array in which a plurality of the positive lens systems 5 are arrayed in a first direction; a light emitter array in which the plurality of light-emitting elements are arrayed on the object side of the lens array so as to correspond to the one positive lens system 5; and an aperture plate 11 that forms an aperture diaphragm at the position of an object-side focal point of the positive lens system 5. The object-side surface of an object-side lens 1 of the positive lens system 5 is positioned close to the object-side focal point. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line head and an image forming apparatus using the line head, and more particularly to a line head that forms an imaging spot row by projecting a light emitting element row onto an irradiated surface using a microlens array. The present invention relates to an image forming apparatus.

  Conventionally, a plurality of LED array chips are arranged in the direction of the LED array, and enlarged and projected onto a photosensitive member with a positive lens in which the LED arrays of the respective LED array chips are arranged correspondingly, and the ends of adjacent LED array chips on the photosensitive member. An optical writing line head that forms images adjacent to each other at the same pitch as the pitch between the light emitting dots of the same LED array chip, and an optical reading line head with the optical path reversed. This is proposed in Japanese Patent Application Laid-Open No. H10-228707.

  Further, Patent Document 2 proposes that the positive lens is composed of two lenses in the arrangement as in Patent Document 1, and the depth of focus is made deep so that the projected light approaches the parallel light.

In addition, the LED array chips are arranged in two rows with a gap, the repetition phase is shifted by a half cycle, and the positive lens array is arranged in two rows with each LED array chip corresponding to each positive lens. Patent Document 3 proposes an optical writing line head in which images of light emitting dot arrays are arranged in a line.
Japanese Patent Laid-Open No. 2-4546 JP-A-6-344596 JP-A-6-278314

  In these conventional techniques, even if the images of the light emitting dot arrays are aligned at an equal pitch on the ideal image plane, if the image plane moves back and forth in the optical axis direction of the lens due to the shake of the photoconductor, the photoconductor As a result, the light emitting dots are displaced from each other, and the light emitting dot array moves relatively in the sub-scanning direction to cause unevenness in the pitch between scanning lines (pitch unevenness in the main scanning direction).

  Further, as the angle of view of each positive lens increases, the peripheral light amount decrease increases according to the cos 4 law (shading). In order to prevent density unevenness of the printed image due to this shading, it is necessary to make the light amount of each pixel (light emitting dot image) on the image plane constant. To do this, the light amount of the light source (light emitting dot) is changed for each light emitting dot. Shading must be corrected. However, since the light emission intensity of the light source pixel (light emitting dot) affects the life characteristics, if the shading of the optical system is increased, even if the light amount is adjusted for each light emitting dot and a uniform image surface light amount is initially obtained. The light amount unevenness of the light emitting dot pitch occurs with time, and the image density unevenness occurs.

The present invention has been made in view of such problems of the prior art, and an object thereof is to arrange a plurality of light emitting elements in a row corresponding to each lens of a plurality of positive lenses arranged in an array. In the optical writing line head thus formed, even if the writing surface fluctuates in the optical axis direction, unevenness based on the positional deviation of the light emitting dot image does not occur. Another object of the present invention is to prevent uneven density due to shading between imaging spots formed by the respective lenses.

  Another object of the present invention is to provide an image forming apparatus using such an optical writing line head and an optical reading line head in which the optical path is reversed.

The line head of the present invention that achieves the above object comprises a positive lens system having two lenses having positive refractive power,
A lens array in which a plurality of the positive lens systems are arranged in the first direction;
A light emitter array in which a plurality of light emitting elements are arranged for one positive lens system on the object side of the lens array;
An aperture plate that forms an aperture stop at the position of the object side focal point of the positive lens system;
And the object side surface of the object side lens of the positive lens system is located close to the object side focal point.

  With this configuration, even if the writing surface fluctuates in the optical axis direction, unevenness due to the positional deviation of the light emitting dot image does not occur, and the angle of view that enters the positive lens system from a plurality of light emitting elements. Can be reduced to reduce the influence of shading, and deterioration of the formed image can be prevented.

  In addition, it is desirable that the object side surface of the object side lens of the positive lens system is located within a range of ± 10% of the combined focal length of the positive lens system with respect to the object side focal point.

  With this configuration, even if the writing surface fluctuates in the optical axis direction, unevenness based on the positional deviation of the light emitting dot image does not substantially occur, and the light enters from the plurality of light emitting elements into the positive lens system. By reducing the angle of view, the influence of shading can be reduced, and deterioration of the formed image can be prevented.

  Further, the lens may be composed of a lens group.

  Such a configuration not only facilitates the production of individual lens arrays, but also facilitates aberration correction.

  In addition, the image side surface of the object side lens among the two lenses may be a flat surface.

  With this configuration, the distance between the front main surface of the image-side lens and the rear main surface of the object-side lens can be increased, so that the angle of view can be further reduced and the influence of shading can be further reduced. Further, as compared with a lens having curvatures on both sides, the object side lens has only one curved surface, and thus has an advantage of easy manufacture.

  Further, at least the object side surface of the object side lens of the positive lens system may be a convex surface, and a portion including the top of the convex surface may be arranged so as to bite into the aperture of the diaphragm plate. .

  With this configuration, the distance between the front main surface of the image-side lens and the rear main surface of the object-side lens can be increased, so that the angle of view can be further reduced and the influence of shading can be further reduced.

  In this case, the diaphragm plate can be configured by integrally forming a light-shielding member on the object-side surface of the lens array.

  With this configuration, by integrally forming the diaphragm plate on the lens surface, it becomes easy to position and assemble the diaphragm plate, and it is possible to suppress the deviation between the center of the diaphragm and the optical axis of the lens due to thermal expansion or the like.

  In addition, it is desirable that at least the image side surface of the image side lens of the positive lens system is a flat surface.

  With this configuration, the exit surface of the lens closest to the image plane can be made flat, and foreign matters such as dust and toner adhering to the exit surface can be easily cleaned, improving the cleaning performance. To do.

  Further, it is desirable that the shape of the aperture stop is a shape that restricts at least the aperture diameter in the first direction.

  With this configuration, it is possible to cope with at least the main scanning direction in which the positional deviation of the off-axis imaging spot becomes a problem.

  In addition, it is preferable that the plurality of light emitting elements form a plurality of light emitting element arrays arranged in a second direction orthogonal to the first direction.

  With this configuration, it is possible to cope with image formation with a high density of imaging spots.

  The plurality of light emitting elements are preferably arranged so as to form a group of light emitters spaced in the first direction.

  With this configuration, it is possible to cope with image formation with a high density of imaging spots. In addition, it is possible to avoid a reduction in the amount of light due to vignetting in the image of the end light emitting dots in each of the plurality of light emitting elements.

  Moreover, it is desirable that the light emitting element is an organic EL element.

  By configuring in this way, it is possible to cope with in-plane uniform image formation.

  The light emitting device may be an LED.

  By configuring in this way, it is possible to cope with a line head using an LED array.

  In addition, at least two or more image forming stations in which image forming units including a charging unit, a line head as described above, a developing unit, and a transfer unit are arranged around the image carrier are provided. By passing through the station, an image forming apparatus that forms an image by a tandem method can be configured.

  With this configuration, it is possible to configure an image forming apparatus such as a printer that is small in size and has high resolution and little image deterioration.

The present invention comprises a positive lens system having two lenses with positive refractive power;
A lens array in which a plurality of the positive lens systems are arranged in the first direction;
A light receiving array in which a plurality of light receiving elements are arranged for one positive lens system on the image side of the lens array;
An aperture plate that forms an aperture stop at the position of the image-side focal point of the positive lens system;
And a line head characterized in that the image side surface of the image side lens of the positive lens system is located close to the image side focal point.

  With this configuration, even in the optical reading line head, even if the position of the reading surface is shifted in the optical axis direction, the position of the reading spot does not occur, and a plurality of light receiving elements change to a positive lens system. By reducing the angle of view incident on the reverse optical path, the influence of shading can be reduced, and deterioration of the read image can be prevented.

  Each positive lens system constituting the lens array includes two lens units having positive refractive power, and may be a combined lens system including the two lens groups (each lens includes a lens group having positive refractive power). .)

  Before describing the optical system of the line head of the present invention in detail, the arrangement of the light emitting elements and the light emission timing will be briefly described.

  FIG. 4 is an explanatory diagram showing a correspondence relationship between the light emitter array 1 according to the embodiment of the present invention and the microlens 5 having a negative optical magnification. In the line head of this embodiment, two rows of light emitting elements correspond to one microlens 5. However, since the microlens 5 is an imaging element having a negative optical magnification (inverted imaging), the position of the light emitting element is reversed in the main scanning direction and the sub-scanning direction. That is, in the configuration of FIG. 1, even-numbered light emitting elements (8, 6, 4, 2) are arranged on the upstream side (first row) in the moving direction of the image carrier, and on the downstream side (second row). Are arranged with odd-numbered light emitting elements (7, 5, 3, 1). In addition, a light emitting element having a large number is arranged on the head side in the main scanning direction.

  1 to 3 are perspective views of a portion corresponding to one microlens of the line head of this embodiment. As shown in FIG. 2, the image spot 8a of the image carrier 41 corresponding to the odd-numbered light emitting elements 2 arranged on the downstream side of the image carrier 41 is formed at a position reversed in the main scanning direction. The R is the moving direction of the image carrier 41. Further, as shown in FIG. 3, the imaging spot 8b of the image carrier 41 corresponding to the even-numbered light emitting elements 2 arranged on the upstream side (first row) of the image carrier 41 is in the sub-scanning direction. It is formed at the inverted downstream position. However, in the main scanning direction, the positions of the imaging spots from the head side correspond to the light emitting elements 1 to 8 in order. Therefore, in this example, it is understood that the imaging spots can be formed in the same row in the main scanning direction by adjusting the timing of forming the imaging spots in the sub scanning direction of the image carrier.

  FIG. 5 is an explanatory diagram showing an example of the memory table 10 of the line buffer in which image data is stored. The memory table 10 in FIG. 5 is stored with being inverted in the main scanning direction with respect to the light emitting element numbers in FIG. 4. In FIG. 5, among the image data stored in the memory table 10 of the line buffer, first image data (1, 3, 5, 5) corresponding to the light emitting elements on the upstream side (first row) of the image carrier 41 first. 7) to read out the light emitting element. Next, after T time, the second image data (2, 4, 6, 8) corresponding to the light emitting elements on the downstream side (second row) of the image carrier 41 stored in the memory address is read and emitted. Let In this way, as indicated by the position 8 in FIG. 6, the first row of imaging spots on the image carrier is formed in the same row as the second row of imaging spots in the main scanning direction.

  FIG. 1 is a perspective view conceptually showing an example in which image data is read out at the timing of FIG. 5 to form an imaging spot. As described with reference to FIG. 5, the light emitting element on the upstream side (first row) of the image carrier 41 is first caused to emit light, thereby forming an imaging spot on the image carrier 41. Next, after a predetermined timing T has elapsed, the odd-numbered light emitting elements on the downstream side (second row) of the image carrier 41 are caused to emit light, thereby forming an imaging spot on the image carrier. At this time, the imaging spot formed by the odd-numbered light emitting elements is not formed at the position 8a described in FIG. 2, but is formed at the position 8 in the same row in the main scanning direction as shown in FIG. become.

  FIG. 7 is a schematic explanatory diagram showing an example of a light emitter array used as a line head. In FIG. 7, in the light emitter array 1, a light emitter block 4 (see FIG. 4) is formed by providing a plurality of light emitting element rows 3 in which a plurality of light emitting elements 2 are arranged in the main scanning direction. In the example of FIG. 7, the light emitter block 4 forms two light emitting element rows 3 in which four light emitting elements 2 are arranged in the main scanning direction in the sub scanning direction (see FIG. 4). A large number of the light emitter blocks 4 are arranged in the light emitter array 1, and each light emitter block 4 is arranged corresponding to the microlens 5.

  A plurality of microlenses 5 are provided in the main scanning direction and the sub-scanning direction of the light emitter array 1 to form a microlens array (MLA) 6. The MLA 6 is arranged with the leading position in the main scanning direction shifted in the sub-scanning direction. Such an arrangement of the MLA 6 corresponds to a case where the light emitting elements 1 are provided in a staggered manner in the light emitter array 1. In the example of FIG. 7, three rows of MLA 6 are arranged in the sub-scanning direction. However, for convenience of explanation, the unit blocks 4 corresponding to the respective positions of the three rows of MLA 6 in the sub-scanning direction are group A and group B. And group C.

  As described above, when the plurality of light emitting elements 2 are arranged in the microlens 5 having a negative optical magnification and the lenses are arranged in a plurality of rows in the sub-scanning direction, the main body of the image carrier 41 is used. In order to form imaging spots arranged in a line in the scanning direction, the following image data control is required. (1) Inversion in the sub-scanning direction, (2) Inversion in the main scanning direction, (3) Adjustment of light emission timing of a plurality of rows of light emitting elements in the lens, and (4) Adjustment of light emission timing of the light emitting elements between groups.

  FIG. 8 is an explanatory diagram showing an imaging position when the exposure surface of the image carrier is irradiated through the microlens 5 with the output light of each light emitting element 2 in the configuration of FIG. In FIG. 8, as described with reference to FIG. 7, the light emitter array 1 has unit blocks 4 divided into group A, group B, and group C. The light-emitting element rows of the unit blocks 4 of group A, group B, and group C are divided into the upstream side (first row) and the downstream side (second row) of the image carrier 41, and even-numbered light emission in the first row Elements are assigned, and odd-numbered light emitting elements are assigned to the second column.

  For group A, by operating each light emitting element 2 as described with reference to FIGS. 1 to 3, an image spot is formed on the image carrier 41 at a position reversed in the main scanning direction and the sub scanning direction. . In this manner, imaging spots are formed on the image carrier 41 in the order of 1 to 8 in the same row in the main scanning direction. Thereafter, the image carrier 41 is moved in the sub-scanning direction for a predetermined time, and the processing of the group B is similarly executed. Further, by moving the image carrier 41 in the sub-scanning direction for a predetermined time and executing the processing of group C, it is based on the input image data in the order of 1 to 24... In the same column in the main scanning direction. An imaging spot is formed.

FIG. 9 is an explanatory diagram showing a state of forming an imaging spot in the sub-scanning direction in FIG. S is the moving speed of the image carrier 41, d1 is the distance between the first and second light emitting elements in group A, and d2 is the second light emitting element in group A and the second light emission in group B. The element spacing, d3 is the distance between the light emitting elements in the second row of group B and the light emitting elements in the second row of group C, and T1 is the light emitting element in the first row after the light emission of the light emitting elements in the second row of group A. T2 is the time required for the image forming position of the light emitting elements in the second row of group A to move to the image forming position of the light emitting elements in the second row of group B, and T3 is the light emitting elements in the second row of group A Is the time required for the imaging position to move to the imaging position of the light-emitting elements in the second row of group C.

  T1 can be obtained as follows. T2 and T3 can be similarly obtained by replacing d1 with d2 and d3.

T1 = | (d1 × β) / S |
Here, each parameter is as follows.
d1: Distance in the sub-scanning direction of the light emitting elements S: Moving speed of the imaging surface (image carrier) β: Lens magnification In FIG. 9, T2 hours after the time when the light emitting elements in the second row of group A emit light. The light emitting elements in the second row of group B are caused to emit light. Furthermore, the light emitting elements in the second row of group C are caused to emit light after T2 to T3 hours. The first row of light emitting elements in each group emits light after T1 time after the second row of light emitting elements emits light. By performing such processing, as shown in FIG. 8, the imaging spots formed by the light emitters arranged two-dimensionally on the light emitter array 1 can be formed in a line on the image carrier. It becomes possible. FIG. 10 is an explanatory diagram showing an example in which an imaging spot is formed by inverting in the main scanning direction of the image carrier when a plurality of microlenses 5 are arranged.

  An image forming apparatus can be configured using the line head as described above. In the embodiment, a tandem color printer (exposed to four photoconductors with four line heads, simultaneously forms four color images, and transfers them to one endless intermediate transfer belt (intermediate transfer medium)). The line head as described above can be used in the image forming apparatus. FIG. 11 is a vertical side view showing an example of a tandem image forming apparatus using an organic EL element as a light emitting element. This image forming apparatus includes four line heads 101K, 101C, 101M, and 101Y having the same configuration, and corresponding four photosensitive drums (image carriers) 41K, 41C, 41M, and 41Y having the same configuration. These are respectively arranged at exposure positions, and are configured as a tandem image forming apparatus.

  As shown in FIG. 11, this image forming apparatus is provided with a driving roller 51, a driven roller 52, and a tension roller 53. The tension roller 53 applies tension to the image forming apparatus and stretches it in the direction indicated by the arrow (counterclockwise). ) Is circulated to the intermediate transfer belt (intermediate transfer medium) 50. Photosensitive members 41K, 41C, 41M, and 41Y having photosensitive layers are arranged on the outer peripheral surface as four image carriers arranged at predetermined intervals with respect to the intermediate transfer belt 50.

  K, C, M, and Y added after the above symbols mean black, cyan, magenta, and yellow, respectively, and indicate that the photoconductors are black, cyan, magenta, and yellow, respectively. The same applies to other members. The photoreceptors 41K, 41C, 41M, and 41Y are rotationally driven in the direction indicated by the arrow (clockwise) in synchronization with the driving of the intermediate transfer belt 50. Around each photoconductor 41 (K, C, M, Y), charging means (corona charger) 42 (K) for uniformly charging the outer peripheral surface of the photoconductor 41 (K, C, M, Y), respectively. , C, M, Y) and the outer peripheral surface uniformly charged by the charging means 42 (K, C, M, Y) are synchronized with the rotation of the photoconductor 41 (K, C, M, Y). Thus, the above-described line head 101 (K, C, M, Y) of the present invention for sequentially scanning the line is provided.

Further, a developing device 44 (K, C, and M) that applies a toner as a developer to the electrostatic latent image formed by the line head 101 (K, C, M, and Y) to form a visible image (toner image). M, Y) and a primary transfer roller 45 (K, Y) as transfer means for sequentially transferring the toner image developed by the developing device 44 (K, C, M, Y) to the intermediate transfer belt 50 as a primary transfer target. C, M, Y) and a cleaning device 46 (K, C, M, Y) as a cleaning means for removing the toner remaining on the surface of the photoreceptor 41 (K, C, M, Y) after being transferred. ).

  Here, in each line head 101 (K, C, M, Y), the array direction of the line head 101 (K, C, M, Y) is set to the bus of the photosensitive drum 41 (K, C, M, Y). It is installed along. The emission energy peak wavelength of each line head 101 (K, C, M, Y) and the sensitivity peak wavelength of the photoconductor 41 (K, C, M, Y) are set to substantially coincide.

  The developing device 44 (K, C, M, Y) uses, for example, a non-magnetic one-component toner as a developer, and the one-component developer is conveyed to the developing roller by a supply roller, for example, and adhered to the developing roller surface. The film thickness of the developed developer is regulated by a regulating blade, and the developing roller is brought into contact with or increased in thickness by the photosensitive body 41 (K, C, M, Y), whereby the photosensitive body 41 (K, C, M, Y). The toner is developed as a toner image by attaching a developer according to the potential level.

  The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are intermediated by the primary transfer bias applied to the primary transfer roller 45 (K, C, M, Y). The toner image, which is sequentially primary transferred onto the transfer belt 50 and sequentially superposed on the intermediate transfer belt 50 to become a full color, is secondarily transferred to a recording medium P such as paper by a secondary transfer roller 66, and serves as a fixing unit. The toner is fixed on the recording medium P by passing through the fixing roller pair 61, and is discharged onto a paper discharge tray 68 formed in the upper part of the apparatus by a paper discharge roller pair 62.

  In FIG. 11, reference numeral 63 denotes a paper feed cassette in which a large number of recording media P are stacked and held, 64 denotes a pickup roller for feeding the recording media P from the paper feed cassette 63 one by one, and 65 denotes a secondary transfer roller. A pair of gate rollers for defining the supply timing of the recording medium P to the secondary transfer portion 66, a secondary transfer roller 66 as a secondary transfer means for forming a secondary transfer portion with the intermediate transfer belt 50, 67 Is a cleaning blade as a cleaning means for removing the toner remaining on the surface of the intermediate transfer belt 50 after the secondary transfer.

  The present invention relates to the optical system of the above-described line head (optical writing line head). First, the principle will be described.

  FIG. 12 is a diagram for explaining the basic principle of the present invention. FIG. 12 shows an end light emitting element 2x of a light emitting element array arranged in a line in the line head, a microlens 5 that projects the light emitting element array, and a photoconductor (image carrier) 41 on which the light emitting element array is projected. (A) is the case of the present invention, and (b) is the case of the conventional example. In the conventional example of FIG. 12B, since the opening of the microlens 5 is generally defined by its outer shape, the imaging spot 8x that is an image of the end light emitting element 2x on the photoreceptor 41 is the end light emitting element. Since the image is formed on a straight line passing through 2x and the center of the microlens 5, the surface of the photoconductor 41, which is an image surface, is moved back and forth in the lens optical axis OO ′ direction due to the shake of the photoconductor. Is moved to the position 41 ', the position of the imaging spot 8x on the photoconductor 41 becomes the position 8x' on the straight line, the position of the imaging spot is shifted, and the imaging spot 8x is relatively sub-positioned. Unevenness occurs in the pitch between the scanning lines drawn by moving in the scanning direction (unevenness of the imaging spot in the main scanning direction).

Therefore, in the present invention, as shown in FIG. 12A, the aperture stop 11 is arranged coaxially with the optical axis OO ′ at the position of the front focal point F of the microlens 5. When such an aperture stop 11 is arranged at the front focal point F position of the microlens 5, the principal ray 12 from the end light emitting element 2x passes through the center of the aperture stop 11 and is refracted by the microlens 5 to be optical axis OO. Even if the photoconductor 41 moves to the position 41 'in the direction of the optical axis OO', the position of the imaging spot 8x on the photoconductor 41 is refracted by the microlens 5. Therefore, even if the position of the photoconductor 41 is moved back and forth, the image spot 8x is not displaced. Therefore, the uneven pitch of the imaging spot 8x in the main scanning direction does not occur as in the conventional case, and the unevenness of the pitch between the scanning lines drawn by moving the imaging spot 8x in the sub-scanning direction does not occur.

  That is, according to the present invention, a plurality of light emitting elements are arranged in a row in the main scanning direction, a single positive lens system is arranged corresponding to the plurality of light emitting elements, and an image of the row of the light emitting elements (image formation). In a line head that forms an image by projecting an array of spots onto a projection surface (photoreceptor), the projection optical system has a telecentric configuration on the image side, so that the position of the projection surface (photoreceptor) This prevents the position of the imaging spot from being shifted even if it is shifted in the optical axis direction, thereby preventing deterioration of the formed image.

  The function of the aperture stop 11 may be any shape as long as it has a shape that limits the aperture diameter in a direction (main scanning direction) at least where the positional deviation of the off-axis imaging spot is a problem. When an array of light emitting elements in one row is arranged for one positive lens system as in 3), it may be a shape that only limits the aperture diameter in the main scanning direction. Further, even when two rows of arrays are arranged in close proximity in the sub-scanning direction as in the above embodiment of the present invention (FIG. 4), the shape may limit the aperture diameter in the main scanning direction. It is good also as a shape which restrict | limits the opening diameter of a direction. For that purpose, any opening shape of a circle, an ellipse or a rectangle may be used.

  In the description of FIG. 12, the microlens 5 is assumed to be composed of a single positive lens. However, it is better to construct a lens system having a positive refractive power in which two positive lenses are coaxially arranged. It is more desirable from the viewpoint of the degree of freedom of correction.

  In this case, the two positive lenses constituting the microlens 5 are considered to be thin lenses, and the angle of view of the light beam emitted from the end light emitting element 2x of the telecentric lens system on the image side is considered.

  First, the sign of each parameter is defined as shown in FIG. That is, the angle θ measured from the optical axis OO ′ is positive in the clockwise direction, the image height h measured from the optical axis OO ′ is positive, and the distance in the optical axis OO ′ direction measured from the thin lens. , And the lowercase letter “o” after the sign means the parameter on the object side, and the lowercase letter “i” after the sign means the parameter on the image plane side.

Since the lens system (microlens) 5 including the first positive lens L1 and the second positive lens L2 is image-side telecentric, the stop 11 is disposed so that the entrance pupil is positioned at the front focal position of the lens system 5. . Accordingly, the _total focal length of the lens system is f _total , the position of the light source (light emitter array 1) with respect to the lens system object-side main surface is S _o , and the light emitting element group width (full width) between the end light emitting elements 2x in the light emitter block 4 Is W _o , and the angle of view ω of the end light emitting element 2x is expressed by the following equation (1) with reference to FIG.

ω = (W _o / 2) / (− S _o −f _total ) (1)
Here, the imaging spot group width (full width) between the imaging spots 8x, which are the images of the edge light emitting elements 2x on the photoreceptor surface (image surface) 41, is W _i , the lateral magnification is β, and the lens system image side main surface Assuming that the image plane position with respect to is S _i , W _o and S _o are expressed by the following equation (2).

W _o = −W _i / β = −W _i · S _o / S _i (2)
From paraxial imaging,
1 / S _i = 1 / S _o + 1 / f _total (3)
And write, and solving for S _{o,
S o = S i · f total} / (f total -S i) ··· (4)
It becomes. Substituting the formulas (2) and (4) into the formula (1) and rearranging them,
ω = W _i / (2f _total ) (5)
Can be written.

Here, the combined focal length f _total is the focal distance f ₁ of the first positive lens L1, the focal distance f ₂ of the second positive lens L2, a first positive lens L1 a distance between the second positive lens L2 Assuming d ₁ , the following expression (6) is obtained.

f _total = f ₁ · f ₂ / (f ₁ + f ₂ −d ₁ ) (6)
Substituting equation (6) into equation (5),
ω = W _i (f ₁ + f ₂ −d ₁ ) / (2f ₁ · f ₂ ) (7)
It becomes.

When attention is paid to d ₁ in equation (7), when (f ₁ + f ₂ ) ≧ d ₁ , ω is smaller as d ₁ is as large as possible. When the arrangement of the diaphragm 11 is limited to the object side with respect to the first positive lens L1 due to structural restrictions or the like, the lens distance d ₁ is limited as shown in the following equation (8) in order to achieve image-side telecentricity. Is done.

0 ≦ d ₁ ≦ f ₂ (8)
In order to make the angle of view ω represented by the equation (7) as small as possible within the range of the equation (8), taking d ₁ as large as possible sets the d ₁ as close to f ₂ as possible. . At this time, the distance between the diaphragm 11 and the first positive lens L1 approaches zero. Substituting d ₁ = f ₂ into equation (6) and rearranging results in f _total = f ₂ (FIG. 15).

  As described above, in the study as a thin lens of the two-lens positive lens optical system 5 in which the diaphragm 11 is disposed on the light emitter array 1 side from the first positive lens L1, the peripheral light amount is reduced according to the cos 4 power law in image side telecentricity. In order to reduce the increasing shading phenomenon as much as possible, in order to reduce the angle of view of this optical system, a stop 11 is disposed on the front focal plane of the lens system 5 comprising two positive lenses L1 and L2, and It is desirable to dispose the first positive lens L1 close to the diaphragm 11, and at this time, the diaphragm 11 and the first positive lens L1 approach the front focal plane of the second positive lens L2, as shown in FIG.

  The above is a study as a thin lens, but a study will be made on a case where the lens is composed of a thick lens system that actually constitutes the lens.

  In the lens system 5 in which the diaphragm 11 is disposed in front (object side) of the first positive lens L1, even when the two positive lenses L1 and L2 are thick lenses, the lens system 5 is on the image side. In order to be telecentric, it is only necessary that the diaphragm 11 be disposed at the front focal position of the combining optical system of the two positive lenses L1 and L2. Furthermore, from the result of the study as the thin lens described above, by arranging the first positive lens L1 and the stop 11 close to each other, the angle of view can be reduced and the influence of shading can be reduced. In the first numerical example, which will be described later, the distance between the surface of the diaphragm 11 and the surface of the first positive lens L1 on the object side is zero.

Further, in the thick lens, the principal surface position changes depending on the power distribution of the incident surface (object side surface) and the exit surface (image surface side surface), but the first positive lens L1 is a convex flat positive lens having a convex incident surface. Since the rear main surface of the first positive lens L1 is closer to the incident surface side than the biconvex positive lens, the distance between the rear main surface of the first positive lens L1 and the front main surface of the second positive lens L2 can be increased. it can. In this case, there is also an advantage that the lens forming surface (curved surface) of the first positive lens L1 becomes one surface, which facilitates manufacture. The second numerical example described below is different from the first exemplary embodiment in the first positive lens L1.
Is a convex positive lens while keeping the focal length as it is, and the maximum angle of view is smaller than that in the first embodiment.

  Further, when the incident surface of the first positive lens L1 is a convex surface, the first positive lens L1 is arranged so that the incident surface of the first positive lens L1 bites into the aperture of the diaphragm 11, that is, the first positive lens L1. Is arranged so that the apex of the incident surface is closer to the object side than the surface of the stop 11, so that the distance between the rear main surface of the first positive lens L1 and the front main surface of the second positive lens L2 is increased. (Example 3). In this case, the arrangement position of the diaphragm 11 is the front focal position of the combining optical system of the positive lenses L1 and L2, but the front focal point is embedded in the first positive lens L1, and the parallel light is projected from the image side. Is converged in the first positive lens L1, then becomes divergent light that diverges from the condensing point, and the divergence angle is weakened on the incident surface of the first positive lens L1, and then exits to the object side. . The image viewed from the object side of the condensing point (diverging light) is a virtual image, but the surface where the virtual image exists is the front focal plane of the entire lens system. Therefore, by disposing the stop 11 on the front focal plane, a configuration telecentric on the image side is obtained.

  The stop 11 is not located at the position of the entrance surface of the first positive lens L1, and is not disposed so that the entrance surface of the first positive lens L1 bites into the opening of the stop 11, but instead of the first positive lens L1. Even if it is arranged in the very vicinity of the incident surface, as long as the diaphragm 11 is arranged on the front focal plane of the lens system 5 composed of the two positive lenses L1 and L2, the angle of view of this optical system can be reduced. , The shading phenomenon based on the cos 4 power law can be reduced (Example 4).

  As described above, the microlens 5 is composed of a positive refracting lens system in which two positive lenses are coaxially arranged, and the front focal point of the combined optical system is positioned in the vicinity of the incident surface of the first positive lens L1. By arranging the aperture stop 11 at the front focal position, a telecentric configuration is formed on the image side, and even if the position of the projection surface (photosensitive member) 41 is shifted in the optical axis direction, the position of the imaging spot is not shifted. In addition, the shading phenomenon in which the decrease in the amount of light at the periphery increases as much as the lens cos 4th law is minimized, and the density unevenness of the imaging spot 8 of the light emitting element array arranged in a line on the light emitter array 1 hardly occurs.

  Therefore, when the optical system of the above-described line head according to the present invention is used for an optical writing line head, the unevenness of the pitch of the imaging spot 8 in the main scanning direction does not occur as in the prior art, and the imaging spot 8 moves in the sub-scanning direction. Thus, there is no unevenness in the pitch between the scanning lines drawn.

  Further, the density unevenness between the imaging spots 8 due to the shading of the microlens 5 as in the prior art hardly occurs, and the density unevenness between the scanning lines drawn by moving the imaging spot 8 in the sub-scanning direction hardly occurs.

In the above description, the front focal position of the combining optical system of the positive lenses L1 and L2 is positioned close to (in the vicinity of) the incident surface of the first positive lens L1, but in the present invention, the combining optical system includes The case where the incident surface of the first positive lens L1 is located within ± 10% of the combined focal length f _total is assumed to be close or close.

By the way, in the case where the optical system of the line head has a configuration in which only one row of the telecentric microlenses 5 is arranged in the main scanning direction on the image side as described above, the optical system is arranged in a line by the specific microlens 5. The distance between the imaging spot 8x which is an image of the end light emitting element 2x of the light emitting element array and the adjacent imaging spot 8x by the adjacent microlens 5 is an image of the imaging spot array formed by one microlens 5. In order to make it the same as the pitch, the imaging spot 8x of the image of the end light emitting element 2x has to be lowered by the influence of vignetting as compared with the amount of light of the other imaging spots in the imaging spot row. In order to avoid this, as shown in FIGS. 1 to 10, the light emitter blocks 4 are arranged at intervals in the main scanning direction, and a plurality of light emitter blocks 4 are arranged in the sub scanning direction. In addition, the microlens array 6 corresponding to the arrangement of the light emitter blocks 4 is also two-dimensionally arranged with the microlenses 5 in the main scanning direction and the sub-scanning direction. The problem that the light quantity of the imaging spot 8x of the 2x image is reduced can be solved.

  As described above, according to the present invention, a plurality of light emitting elements are arranged in a row in the main scanning direction, one positive lens system is arranged corresponding to the plurality of light emitting elements, and an image of the row of the light emitting elements. In a line head that forms an image by projecting an (imaging spot array) onto a projection surface (photoreceptor), the projection optical system is composed of two positive lenses and is telecentric on the image side, By arranging the entrance surface of the positive lens as close as possible to the aperture stop, even if the position of the projection surface (photosensitive member) shifts in the optical axis direction, the position of the imaging spot does not occur. The density unevenness between the imaging spots is reduced to prevent deterioration of the formed image.

  The function of the aperture stop 11 may be any shape as long as it has a shape that limits the aperture diameter in a direction (main scanning direction) at least where the positional deviation of the off-axis imaging spot is a problem. When an array of light emitting elements in one row is arranged for one positive lens system as in 3), it may be a shape that only limits the aperture diameter in the main scanning direction. Further, even when two rows of arrays are arranged in close proximity in the sub-scanning direction as in the above embodiment of the present invention (FIG. 4), the shape may limit the aperture diameter in the main scanning direction. It is good also as a shape which restrict | limits the opening diameter of a direction. For that purpose, any opening shape of a circle, an ellipse or a rectangle may be used.

  In the description of FIG. 15, each of the positive lenses L1 and L2 constituting the microlens 5 is composed of one lens. However, each lens has a positive refracting power in which two or more lenses are coaxially arranged. It may consist of a lens system.

  In the above description, the microlens 5 is premised on an axially symmetric lens system in which the focal length and the focal position in the main scanning direction and the sub-scanning direction match, but the lens system constituting the microlens 5 is an anamorphic lens. It is possible to use a system that has different focal lengths and magnifications in the main scanning direction and the sub-scanning direction. In that case, in the main scanning direction (main scanning section), the aperture stop 11 is disposed so as to be image-side telecentric, and at the position of the aperture stop 11 (the front focal position of the combining optical system in the main scanning direction). What is necessary is just to comprise so that the surface on the most object side of a synthetic | combination optical system may be located close.

  The optical system of the optical writing line head has been described so far. A plurality of light receiving elements are arranged in a row in the main scanning direction with the optical path reversed, and one light receiving element is provided corresponding to the plurality of light receiving elements. Even in the case of an optical reading line head in which a positive lens is arranged and an image (array of reading spots) of the light receiving element array is back projected onto the reading surface, the projection optical system is separated from the two positive lenses. If the incident surface of the positive lens on the image plane side is as close to the aperture stop as possible, the reading spot position shifts even if the reading surface position shifts in the optical axis direction. In addition, the density unevenness between readings can be reduced to prevent deterioration of the formed read image. In this case, in FIGS. 12A and 15, reference numeral 41 denotes a reading surface, and reference numeral 2x denotes an end light receiving element, and the principle is the same as that of the optical system of the optical writing line head.

  Next, an optical writing line head according to one embodiment to which the principle of the present invention is applied will be described.

FIG. 16 is a partially broken perspective view showing the configuration of the optical writing line head of this embodiment, and FIG. 17 is a sectional view taken along the sub-scanning direction. FIG. 18 is a plan view showing the arrangement of the light emitter array and the microlens array in this case. Further, FIG. 19 is a diagram showing a correspondence relationship between one microlens and a corresponding light emitter block.

  In this embodiment, as in the case of FIGS. 4 and 7, four light emitting element rows 3 in which four light emitting elements 2 made of organic EL elements are arranged in the main scanning direction are formed in the sub scanning direction. Thus, one light emitter block 4 is provided, and a plurality of the light emitter blocks 4 are provided in the main scanning direction and the sub scanning direction to form the light emitter array 1. The light emitter block 4 is in the main scanning direction in the sub scanning direction. They are arranged in a staggered pattern by shifting the top position of. In the example of FIG. 16, the light emitter blocks 4 are arranged in three rows in the sub-scanning direction. Such a light emitter array 1 is formed on the back surface of the glass substrate 20 and is driven by a drive circuit formed on the back surface of the same glass substrate 20. The organic EL element (light emitting element 2) on the back surface of the glass substrate 20 is sealed with a sealing member 27.

  The glass substrate 20 is fitted into a receiving hole 22 provided in a long case 21, covered with a back cover 23, and fixed by a fixing bracket 24. The positioning pins 25 provided at both ends of the long case 21 are fitted into the positioning holes of the opposing image forming apparatus main body, and the fixing screws are inserted through the screw insertion holes 26 provided at both ends of the long case 21. The optical writing line head 101 is fixed at a predetermined position by being screwed into the screw hole.

  An opening 31 (FIGS. 20 and 21) is provided on the surface side of the glass substrate 20 of the case 21 through the first spacer 71 so as to be aligned with the center of each light emitter block 4 of the light emitter array 1. The positive lens L1 is used as a constituent element so that the center of each light emitter block 4 of the light emitter array 1 and the positive lens L1 are aligned via the second spacer 72 thereon. The first microlens array 61 is disposed, and the positive lens L2 is configured so that the positive lens L2 is aligned with the center of each light emitter block 4 of the light emitter array 1 via the third spacer 73 thereon. The second microlens array 62 is fixed.

  As described above, the lens array of the microlens 5 that projects the light emitting element array of each light emitter block 4 includes a combination of the first microlens array 61 and the second microlens array 62.

  In accordance with the present invention, the diaphragm plate coincides with the object side (front side) focal position of the composite lens system of the positive lens L1 constituting the first microlens array 61 and the positive lens L2 constituting the second microlens array 62. 30 and the first spacer 71, the second spacer 72, and the second spacer 72 so that the object-side focal point of the microlens 5 (positive lens L1 + positive lens L2) coincides with or is close to the object-side surface of the positive lens L1. The thickness of the three spacers 73 is set. Details of the diaphragm plate 30 are shown in FIGS. FIG. 20 is a plan view of the diaphragm plate 30 arranged corresponding to the light emitter block 4 of the light emitter array 1, and FIG. 21 is a view showing the opening 31 of the diaphragm plate 30 for one light emitter block 4. . The aperture plate 30 is provided with openings 31 aligned with the center (optical axis) of each of the microlenses 5 including the positive lens L1 and the positive lens L2 and the center of the light emitter block 4. In this embodiment, each opening is provided. The shape of 31 is configured to be a substantially elliptical shape that limits the opening diameter in the main scanning direction to be larger than the subscanning direction, but may be a circular, elliptical, rectangular, or other opening shape as described above. .

  The above embodiment is an optical writing line head 101 having a so-called bottom emission arrangement using an organic EL element provided on the back surface of the glass substrate 20 as the light emitting element 2 and using light emitted on the front surface side of the glass substrate 20. However, an EL element or LED in which the light emitting element 2 is arranged on the surface side of the substrate may be used.

By the way, in the above description, as shown in FIGS. 7 and 18, the light emitter array 1 includes one or more light emitting element rows 3 in which a plurality of light emitting elements 2 are arranged in the main scanning direction. It has been assumed that the light emitter blocks 4 are formed and the microlenses 5 are arranged corresponding to the respective light emitter blocks 4. However, the light emitting elements 2 are arranged in a long continuous row at fine intervals in the main scanning direction, and control is performed so that only the light emitting element groups corresponding to the light emitter blocks 4 in the light emitting blocks 4 emit light. By controlling the light emitting element so as not to emit light, the light emitter block 4 similar to the case of FIGS. 7 and 18 can be configured. FIG. 22 shows a diagram corresponding to FIG. 18 in that case. That is, as the light emitter array 1, the light emitting elements 2 are arranged as long light emitting element rows 3 ′ that are continuous at fine equal intervals in the main scanning direction, and the imaging spots 8 are formed through the microlenses 5 therein. Only the group of light emitting elements 2 ′ (indicated by ◯) to be involved is controlled to emit light, and the group of light emitting elements 2 ″ (indicated by ●) existing between the groups of the light emitting elements 2 ′ is not allowed to emit light. Each of the body blocks 4 can be configured as shown in Fig. 22. In the case of Fig. 22, three rows of microlenses 5 are arranged in the main scanning direction, and two rows of light emitting element rows 3 'are provided so as to correspond to each row of the microlenses 5. Are formed in two rows in the sub-scanning direction, and the light emitting elements 2 in the two light emitting element rows 3 ′ are arranged in a staggered manner, and the four light emitting elements in each light emitting element row 3 ′ are arranged. Only the element 2 ′ emits light, and 8 elements among the four light emitting elements 2 ′ Emitting element 2 "is controlled not to emit light.

  In the above description, when all the light-emitting elements 2 and 2 ′ in all the light-emitting body blocks 4 are turned on with the timing adjusted to draw one straight line extending in the main scanning direction, The imaging spots 8 arranged in a row are arranged adjacent to each other between the light emitter blocks 4 without excess or deficiency. However, the number and position of the light emitting elements 2, 2 ′ constituting the light emitter block 4 are set such that the imaging spot 8 overlaps on the image carrier 41 between the light emitting elements 2, 2 ′ constituting the light emitter block 4. It may be set to have redundancy. In this way, for example, even if density unevenness occurs in the imaging spot 8 which is an image of the light emitting elements 2 and 2 ′ in the vicinity of the end of the light emitter block 4, they are corrected by overlapping each other. be able to.

  As an example, FIG. 23 shows that when the light emitter array 1 has the structure shown in FIG. 22, the number of light emitting elements 2 ′ constituting each light emitter block 4 is increased by one (light emitting element 2a) to 4 × 2. FIG. 4 is a diagram illustrating an example in which adjacent microlenses 5 expose a row of imaging spots 8 arranged on an image carrier 41 so as to overlap each other at the end by one imaging spot 8. However, FIG. 23 shows the light emitting element 2a on the light emitter array 1 side so as to overlap at the opposite end of the adjacent light emitter block 4 (light emitting element between dotted lines), but this figure is correct. Is when the imaging magnification of the microlens 5 is -1.

  Incidentally, the microlens arrays 61 and 62 used in the optical writing line head 101 of the present invention can be used in any conventionally known configuration. FIG. 24 shows the first microlens array 61 and the second microlens array. 62 is a cross-sectional view taken along the main scanning direction when an array of microlenses 5 is configured by combining 62 so that the microlenses L1 and L2 are coaxially aligned (FIGS. 16 and 17). In this example, the microlens L1 and L2 are formed by integrally molding a lens surface portion 35 made of a transparent resin in alignment with one side (object side) of the glass substrate 34 of each of the microlens arrays 61 and 62. is there. In this case, by setting the image side surface of the second microlens array 62 to be a flat surface, for example, when used as a microlens array of a line head of an image forming apparatus, the toner of the developer scatters and the flat surface of the microlens array. Even if it adheres to the surface, it can be easily cleaned and the cleaning performance is improved.

  Next, specific numerical examples of the optical system used in the above examples are shown as Examples 1 to 4.

25A and 25B are cross-sectional views of the optical system corresponding to one microlens 5 of Example 1 in the main scanning direction and the sub-scanning direction, respectively, and a glass substrate is provided on the emission side of the light emitting element 2. In this case, the microlens 5 is a composite lens system composed of a biconvex positive lens L1 and a biconvex positive lens L2, and the diaphragm plate 30 is an object of a composite lens system composed of the biconvex positive lens L1 and the biconvex positive lens L2. It is arranged at the side (front) focal point and is telecentric on the image side, and the surface top of the object side lens surface (convex surface) of the biconvex positive lens L1 on the object side coincides with the object side focal point. This is an example of the microlens 5.

Numerical data of this example are shown below. In order from the light emitter block 4 side to the photoconductor (image surface) 41 side, r ₁ , r _2, ... Are curvature radii (mm), d ₁ , d of each optical surface. ₂ ... Is the distance (mm) between the optical surfaces, n _d1 , n _d2 ... Is the refractive index of the d-line of each transparent medium, and ν _d1 , ν _d2 . Here, r ₁ , r ₂ ... Also represent optical surfaces, the optical surface r ₁ is the light emitter block (object surface) 4, and the optical surface r ₂ is the apertures 31, r ₃ , r ₄ of the diaphragm plate 30. The object-side surface, the image-side surface, and the optical surfaces r ₅ and r ₆ of the positive lens L 1 are the object-side surface and the image-side surface of the biconvex positive lens L, and the optical surface r ₇ is a photoreceptor (image surface) 41. It is. Further, the object side surface of the biconvex positive lens L1 is aspherical, but the aspherical shape has a distance from the optical axis as r,
cr ² / [1 + √ {1- (1 + K) c ² r ² }] + Ar ⁴
It is represented by However, c is a curvature (1 / r) on the optical axis, K is a conic coefficient, and A is a fourth-order aspheric coefficient. In the following numerical data, K ₃ and A ₃ are the conic coefficient and the fourth-order aspheric coefficient of the object side surface of the biconvex positive lens L1, respectively.

  26A and 26B are cross-sectional views of the optical system corresponding to one microlens 5 of Example 2 in the main scanning direction and the sub-scanning direction, respectively, and a glass substrate is provided on the emission side of the light emitting element 2. Not disposed, the micro lens 5 is a synthetic lens system composed of a convex positive lens L1 and a biconvex positive lens L2, and the diaphragm plate 30 is an object side of the synthetic lens system composed of the convex positive lens L1 and the biconvex positive lens L2 ( Example of a microlens 5 that is arranged at the front side focal point and is telecentric on the image side, and the top surface of the object side lens surface (convex surface) of the convex flat lens L1 coincides with the object side focal point. It is.

  This embodiment is different from the first embodiment in that the first positive lens L1 is a convex positive lens while maintaining the focal length, and the maximum angle of view is smaller than that of the first embodiment. The distance from the light emitter block 4 to the diaphragm plate 30 is adjusted so that the image formation state of the image plane is improved.

  In this way, by forming the first positive lens L1 as a convex flat lens, there is an advantage that the lens forming surface to be formed as the first microlens array 61 is only one surface, and the manufacture thereof is facilitated.

Numerical data of this example are shown below. In order from the light emitter block 4 side to the photoconductor (image surface) 41 side, r ₁ , r _2, ... Are curvature radii (mm), d ₁ , d of each optical surface. ₂ ... Is the distance (mm) between the optical surfaces, n _d1 , n _d2 ... Is the refractive index of the d-line of each transparent medium, and ν _d1 , ν _d2 . Here, r ₁ , r ₂ ... Also represent optical surfaces, the optical surface r ₁ is the light emitter block (object surface) 4, the optical surface r ₂ is the aperture 31, r ₃ , r ₄ of the diaphragm plate 30. The object-side surface, the image-side surface, and the optical surfaces r ₅ and r ₆ of the lens L 1 are the object-side surface and the image-side surface of the biconvex positive lens L, and the optical surface r ₇ is a photoconductor (image surface) 41. is there. Further, the object-side surface of the convex flat positive lens L1 is an aspherical surface, but the aspherical shape is obtained when the distance from the optical axis is r.
cr ² / [1 + √ {1- (1 + K) c ² r ² }] + Ar ⁴
It is represented by However, c is a curvature (1 / r) on the optical axis, K is a conic coefficient, and A is a fourth-order aspheric coefficient. In the following numerical data, K ₃ and A ₃ are the conic coefficient and the fourth-order aspheric coefficient, respectively, of the object side surface of the convex positive lens L1.

27A and 27B are cross-sectional views of the optical system corresponding to one microlens 5 of Example 3 in the main scanning direction and the sub-scanning direction, respectively, and a glass substrate is provided on the emission side of the light emitting element 2. Not disposed, the micro lens 5 is a synthetic lens system composed of a convex positive lens L1 and a biconvex positive lens L2, and the diaphragm plate 30 is an object side of the synthetic lens system composed of the convex positive lens L1 and the biconvex positive lens L2 ( This is an example of the microlens 5 which is disposed at the focal point and is telecentric on the image side, and the convex surface on the object side of the convex flat lens L1 bites into the opening 31 of the diaphragm plate 30. .

  That is, the rear surface of the convex positive lens L1 and the front side of the biconvex positive lens L2 are arranged so that the vertex of the incident surface (convex surface) of the convex flat lens L1 is closer to the object side than the surface of the diaphragm plate 30. The space | interval of a main surface can be taken more widely. In this case, the position of the diaphragm plate 30 is the front focal position of the composite lens system composed of the convex positive lens L1 and the biconvex positive lens L2, but the front focal point is embedded in the convex positive lens L1. When collimated light is incident from the image side, the light is condensed in the convex flat lens L1, and then diverged light diverges from the converging point, and the divergence angle is weakened on the incident surface (convex surface) of the convex positive lens L1. And go out to the object side. The image viewed from the object side of the condensing point (diverging light) is a virtual image, but the surface where the virtual image exists is the front focal plane of the entire lens system. Therefore, by arranging the diaphragm plate 30 on the front focal plane, a telecentric configuration is provided on the image side.

Numerical data of this example are shown below. In order from the light emitter block 4 side to the photoconductor (image surface) 41 side, r ₁ , r _2, ... Are curvature radii (mm), d ₁ , d of each optical surface. ₂ ... Is the distance (mm) between the optical surfaces, n _d1 , n _d2 ... Is the refractive index of the d-line of each transparent medium, and ν _d1 , ν _d2 . Here, r ₁ , r ₂ ... Also represent optical surfaces, the optical surface r ₁ is the light emitter block (object surface) 4, the optical surface r ₂ is the aperture 31, r ₃ , r ₄ of the diaphragm plate 30. The object-side surface, the image-side surface, and the optical surfaces r ₅ and r ₆ of the lens L 1 are the object-side surface and the image-side surface of the biconvex positive lens L, and the optical surface r ₇ is a photoconductor (image surface) 41. is there. Further, the object-side surface of the convex flat positive lens L1 is an aspherical surface, but the aspherical shape is obtained when the distance from the optical axis is r.
cr ² / [1 + √ {1- (1 + K) c ² r ² }] + Ar ⁴
It is represented by However, c is a curvature (1 / r) on the optical axis, K is a conic coefficient, and A is a fourth-order aspheric coefficient. In the following numerical data, K ₃ and A ₃ are the conic coefficient and the fourth-order aspheric coefficient, respectively, of the object side surface of the convex positive lens L1.

  In Example 3, even when it is difficult to form an aperture stop inside the lens L1, the stop 30 is integrally formed on the surface around the convex surface of the incident surface of the first positive lens L1. it can. That is, as shown in FIG. 28, in the lens array (FIGS. 16, 17, and 24) of the microlens 5 that is a combination of the first microlens array 61 and the second microlens array 62, the first microlens array For example, a light-shielding film is selectively applied along the skirt (valley) between the convex surfaces of the incident surface of the first positive lens L1 on the object side of the object 61, so that the diaphragm is integrated with the first microlens array 61. 30 can be formed. Further, in this embodiment, the distance between the rear main surface of the first positive lens L1 and the front main surface of the second positive lens L2 can be separated as much as possible, and the angle of view can be further reduced. More ideal.

  29A and 29B are cross-sectional views of the optical system corresponding to one microlens 5 of Example 4 in the main scanning direction and the sub-scanning direction, respectively, and a glass substrate is provided on the emission side of the light emitting element 2. In this case, the microlens 5 is a synthetic lens system including the convex flat lens L1 and the convex flat lens L2, and the diaphragm plate 30 is the object side (front side) of the synthetic lens system including the convex flat lens L1 and the convex flat lens L2. Example of the microlens 5 that is disposed at the focal point and is telecentric on the image side, and the convex surface on the object side of the convex positive lens L1 is positioned slightly away from the aperture plate 30 toward the object side It is.

As in this example (same as in Example 3), in the present invention, the object side focal point of the composite lens system including the first positive lens L1 and the second positive lens L2 is the object side surface of the first positive lens L1. Not only coincides with the object-side focal point of the surface of the lens but also in the vicinity thereof, the lens cos 4
The shading phenomenon in which the decrease in the amount of light at the periphery increases in accordance with the power law is minimized, and uneven density of the imaging spots 8 of the light emitting element arrays arranged in a line on the light emitter array 1 is less likely to occur.

  Further, as in this embodiment, the image-side surface of the second positive lens L2 is a flat surface, so that the entire image-side surface of the second microlens array 62 constituting the lens array of the microlens 5 is a flat surface. For example, when used as a microlens array of a line head of an image forming apparatus, even if the toner of the developer scatters and adheres to the plane of the microlens array, it can be easily cleaned and the cleaning performance is improved. Become.

Numerical data of this example are shown below. In order from the light emitter block 4 side to the photoconductor (image surface) 41 side, r ₁ , r _2, ... Are curvature radii (mm), d ₁ , d of each optical surface. ₂ ... Is the distance (mm) between the optical surfaces, n _d1 , n _d2 ... Is the refractive index of the d-line of each transparent medium, and ν _d1 , ν _d2 . Here, r ₁ , r ₂ ... Also represent optical surfaces, the optical surface r ₁ is the light emitter block (object surface) 4, the optical surface r ₂ is the aperture 31, r ₃ , r ₄ of the diaphragm plate 30. The object-side surface, the image-side surface, and the optical surfaces r ₅ and r ₆ of the lens L 1 are the object-side surface and the image-side surface of the biconvex positive lens L, and the optical surface r ₇ is a photoconductor (image surface) 41. is there. Further, the object-side surfaces of the convex flat lens L1 and the convex flat lens L2 are both aspherical surfaces, but the aspherical shape has a distance from the optical axis as r.
cr ² / [1 + √ {1- (1 + K) c ² r ² }] + Ar ⁴
It is represented by However, c is a curvature (1 / r) on the optical axis, K is a conic coefficient, and A is a fourth-order aspheric coefficient. In the following numerical data, K ₃ and A ₃ are conic coefficients of the object side surface of the convex flat positive lens L1, respectively, a fourth-order aspheric coefficient, and K ₅ and A ₅ are each of the object side surface of the convex flat positive lens L2. The conic coefficient and the fourth-order aspheric coefficient.

Example 1
r ₁ = ∞ (object plane) d ₁ = 6.6460
r ₂ = ∞ (aperture) d ₂ = 0.0000
r ₃ = 3.4613 (aspherical surface) d ₃ = 1.0000 n _d1 = 1.5168 ν _d1 = 64.2
K ₃ = 0.0
A ₃ = -0.0195
r ₄ = -3.4613 d ₄ = 2.4564
r ₅ = 3.3896 d ₅ = 1.0000 n _d2 = 1.5168 ν _d2 = 64.2
r ₆ = -3.3896 d ₆ = 1.5000
r ₇ = ∞ (image plane)
Use wavelength 632.5nm
First lens focal length 3.5333mm
Second lens focal length 3.4639mm
Imaging spot group width (full width) 0.4mm
Distance from the first lens rear main surface to the second lens front main surface 3.1512mm
Maximum angle of view 3.608 °.

Example 2
r ₁ = ∞ (object plane) d ₁ = 6.9201
r ₂ = ∞ (aperture) d ₂ = 0.0000
r ₃ = 1.8200 (aspherical surface) d ₃ = 1.0000 n _d1 = 1.5168 ν _d1 = 64.2
K ₃ = 0.0
A ₃ = -0.03493
r ₄ = ∞ d ₄ = 2.4564
r ₅ = 3.3896 d ₅ = 1.0000 n _d2 = 1.5168 ν _d2 = 64.2
r ₆ = -3.3896 d ₆ = 1.5000
r ₇ = ∞ (image plane)
Use wavelength 632.5nm
First lens focal length 3.5333mm
Second lens focal length 3.4639mm
Imaging spot group width (full width) 0.4mm
The distance from the first lens rear main surface to the second lens front main surface 3.4639mm
Maximum angle of view 3.308 °.

Example 3
r ₁ = ∞ (object plane) d ₁ = 7.0578
r ₂ = ∞ (aperture) d ₂ = -0.1300
r ₃ = 1.8200 (aspherical surface) d ₃ = 1.0000 n _d1 = 1.5168 ν _d1 = 64.2
K ₃ = 0.0
A ₃ = -0.0420
r ₄ = ∞ d ₄ = 2.5499
r ₅ = 3.3896 d ₅ = 1.0000 n _d2 = 1.5168 ν _d2 = 64.2
r ₆ = -3.3896 d ₆ = 1.5000
r ₇ = ∞ (image plane)
Use wavelength 632.5nm
First lens focal length 3.5333mm
Second lens focal length 3.4639mm
Imaging spot group width (full width) 0.4mm
The distance from the first lens back main surface to the second lens front main surface 3.5740mm
Maximum angle of view 3.201 °.

Example 4
r ₁ = ∞ (object plane) d ₁ = 5.1280
r ₂ = ∞ (aperture) d ₂ = 0.1871
r ₃ = 1.3472 (aspherical surface) d ₃ = 1.0000 n _d1 = 1.5168 ν _d1 = 64.2
K ₃ = 0.0000
A ₃ = -0.04946
r ₄ = ∞ d ₄ = 1.9000
r ₅ = 1.4225 (aspherical surface) d ₅ = 0.8500 n _d2 = 1.5168 ν _d2 = 64.2
K ₃ = 0.0000
A ₃ = -0.1123
r ₆ = ∞ d ₆ = 0.7500
r ₇ = ∞ (image plane)
Use wavelength 632.5nm
First lens focal length 2.6154mm
Second lens focal length 2.7616mm
Imaging spot group width (full width) 0.4mm
The distance from the first lens rear main surface to the second lens front main surface 2.5600mm
Maximum angle of view 4.46 °.

By the way, in the optical system of the optical writing line head according to the present invention as described above, the light from the light emitter block 4 entering the specific microlens 5 of the microlens array enters the optical path of the adjacent microlens 5. In order to prevent generation of flare, it is desirable to arrange one or more flare diaphragm plates between the light emitter array 1 and the diaphragm plate 30. FIG. 30 shows a cross-sectional view taken along the main scanning direction of one example in that case. In this case, six flare diaphragm plates 32 are arranged in parallel with the diaphragm plate 30 at intervals, and each flare diaphragm plate 32 is provided with an opening 33 corresponding to the opening 31 of the diaphragm plate 30. The aperture stop intended in the present invention refers to the opening 31 of the diaphragm plate 30, and does not refer to such an opening 33 of the flare stop plate 32.

  As described above, the line head and the image forming apparatus using the same according to the present invention have been described based on the principle and the embodiments, but the present invention is not limited to these embodiments and can be variously modified.

It is a perspective view of the part corresponding to one micro lens of the line head concerning one embodiment of the present invention. It is a perspective view of the part corresponding to one micro lens of the line head concerning one embodiment of the present invention. It is a perspective view of the part corresponding to one micro lens of the line head concerning one embodiment of the present invention. It is explanatory drawing which shows the correspondence of the light-emitting body array which concerns on one Embodiment of this invention, and the micro lens with minus optical magnification. It is explanatory drawing which shows the example of the memory table of the line buffer in which image data is stored. It is explanatory drawing which shows a mode that the imaging spot by the light emitting element of an odd number and an even number is formed in the same row in the main scanning direction. It is explanatory drawing of the outline which shows the example of the light-emitting body array used as a line head. It is explanatory drawing which shows the image formation position at the time of irradiating the exposure surface of an image carrier through a micro lens with the output light of each light emitting element by the structure of FIG. FIG. 9 is an explanatory diagram illustrating a state of forming an imaging spot in the sub-scanning direction in FIG. 8. It is explanatory drawing which shows the example in which an imaging spot is reversed and formed in the main scanning direction of an image carrier when a plurality of microlenses are arranged. 1 is a schematic cross-sectional view illustrating an overall configuration of an embodiment of an image forming apparatus using an electrophotographic process according to the present invention. It is a figure for demonstrating the basic principle of this invention. It is a figure which shows the definition of the code | symbol of each parameter. It is a figure which shows the angle of view of an edge part light emitting element when the lens system which consists of a 1st positive lens and a 2nd positive lens is image side telecentric. It is a figure which shows the structure in the case of comprising the optical system by this invention with a thin lens system. It is the perspective view which fractured | ruptured a part which shows the structure of the optical writing line head of one Example of this invention. It is sectional drawing taken along the subscanning direction of FIG. It is a top view which shows arrangement | positioning of the light-emitting body array in the case of FIG. 16, and a micro lens array. It is a figure which shows the correspondence of one micro lens and the light-emitting body block corresponding to it. It is a top view of the aperture plate arrange | positioned corresponding to the light-emitting body block of a light-emitting body array. It is a figure which shows opening of the aperture plate with respect to one light-emitting body block. FIG. 19 is a diagram corresponding to FIG. 18 in a case where light emitting elements are arranged in a long line in the main scanning direction and a light emitter block is configured by controlling light emission of a part thereof. It is the figure which illustrated the example which increased the number of the light emitting elements which comprise a light-emitting body block, and was made to expose so that the row | line | column of the imaging spot of the light-emitting body block adjacent on an image carrier might overlap with an edge part. It is sectional drawing taken along the main scanning direction in the case of comprising a microlens array with two microlens arrays. 2 is a cross-sectional view of an optical system corresponding to one microlens of Example 1 in a main scanning direction and a sub-scanning direction. FIG. 6 is a cross-sectional view of an optical system corresponding to one microlens of Example 2 in a main scanning direction and a sub-scanning direction. FIG. 6 is a cross-sectional view of an optical system corresponding to one microlens of Example 3 in a main scanning direction and a sub scanning direction. FIG. FIG. 10 is a cross-sectional view taken along the main scanning direction of an example in which a diaphragm is integrally formed on the object-side surface of the first microlens array constituting the lens array of the microlens in Example 3. FIG. 6 is a cross-sectional view of an optical system corresponding to one microlens in Example 4 in the main scanning direction and the sub-scanning direction. It is sectional drawing taken along the main scanning direction of the example which arrange | positions a flare aperture plate separately from an aperture plate in the optical system of the optical writing line head of this invention.

Explanation of symbols

OO ′: lens optical axis, F: front focal point of microlens, 1 ... light emitter array, 2 ... light emitting element, 2x ... edge light emitting element or edge light receiving element, 2 '... involved in formation of imaging spot A light emitting element to be turned on, 2 ″ a light emitting element that does not emit light, 2a a light emitting element in which imaging spots overlap on the image carrier, 3 a light emitting element row, 3 ′ a light emitting element row in a long row continuous in the main scanning direction, 4 ... light emitter block, 5 ... microlens, 6 ... microlens array, 8, 8a, 8b ... imaging spot, 8x ... imaging spot of the end light emitting element, 8x '... end when the photoconductor is displaced The position of the imaging spot of the light emitting element, 8x "... the position of the imaging spot of the end light emitting element when the light emitting element placement surface is displaced, 10 ... the memory table, 11 ... the aperture stop, 12 ... the principal ray, 20 ... the glass Substrate, 21 ... long case, 22 ... receiving hole, DESCRIPTION OF SYMBOLS 23 ... Back cover, 24 ... Fixing metal fitting, 25 ... Positioning pin, 26 ... Insertion hole, 27 ... Sealing member, 30 ... Diaphragm plate (diaphragm), 31 ... Opening of an aperture plate, 32 ... Flare diaphragm plate, 33 ... Flare Opening of aperture plate, 34 ... Glass substrate, 35 ... Lens surface part, 41 ... Photoconductor (image carrier) or reading surface, 41 '... Positive position of photoconductor (image carrier), 41 (K, C, M, Y) ... photosensitive drum (image carrier), 42 (K, C, M, Y) ... charging means (corona charger), 44 (K, C, M, Y) ... developing device, 45 (K, C) , M, Y) ... primary transfer roller, 50 ... intermediate transfer belt, 51 ... driving roller, 52 ... driven roller, 53 ... tension roller, 55 ... light emitting element arrangement surface, 55 '... deviation position of light emitting element arrangement surface, 61 ... first microlens array, 62 ... second microlens array, 66 ... secondary rotation Roller, 71 ... first spacer, 72 ... second spacer, 73 ... third spacer, 101, 101K, 101C, 101M, 101Y ... line head (optical writing line head), L1 ... first (positive) lens, L2 ... Second (positive) lens

Claims (14)

A positive lens system having two lenses of positive refractive power;
A lens array in which a plurality of the positive lens systems are arranged in the first direction;
A light emitter array in which a plurality of light emitting elements are arranged for one positive lens system on the object side of the lens array;
An aperture plate that forms an aperture stop at the position of the object side focal point of the positive lens system;
A line head, wherein an object side surface of an object side lens of the positive lens system is positioned close to the object side focal point. 2. The object side surface of the object side lens of the positive lens system is located within a range of ± 10% of a combined focal length of the positive lens system with respect to the object side focal point. The line head described. 3. The line head according to claim 1, wherein the lens includes a lens group. 4. The line head according to claim 3, wherein the image side surface of the object side lens is a flat surface among the two lenses. 2. The object side lens of at least the object side lens of the positive lens system is a convex surface, and a portion including the top of the convex surface is arranged so as to bite into the aperture of the diaphragm plate. 5. The line head according to any one of 1 to 4. 6. The line head according to claim 5, wherein the diaphragm plate is formed by integrally forming a light shielding member on the object side surface of the lens array. 7. The line head according to claim 1, wherein at least an image side surface of the image side lens of the positive lens system is a flat surface. 8. The line head according to claim 1, wherein the shape of the aperture stop is a shape that restricts at least the aperture diameter in the first direction. 9. 9. The line head according to claim 1, wherein the plurality of light emitting elements form a plurality of the light emitting element rows arranged in a second direction orthogonal to the first direction. The line head according to any one of claims 1 to 9, wherein the plurality of light emitting elements are arranged so as to form a group of light emitters spaced in a first direction. The line head according to claim 1, wherein the light emitting element is an organic EL element. The line head according to claim 1, wherein the light emitting element is an LED. At least two or more image forming stations in which image forming units including a charging unit, a line head according to any one of claims 1 to 12, a developing unit, and a transfer unit are arranged around an image carrier. An image forming apparatus characterized in that an image is formed by a tandem method when the transfer medium passes through each station. A positive lens system having two lenses of positive refractive power;
A lens array in which a plurality of the positive lens systems are arranged in the first direction;
A light receiving array in which a plurality of light receiving elements are arranged for one positive lens system on the image side of the lens array;
An aperture plate that forms an aperture stop at the position of the image-side focal point of the positive lens system;
A line head, wherein an image side surface of an image side lens of the positive lens system is located close to the image side focal point.

Images