JP2003098474A - Image-formation element unit, optical writing unit and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical system and an optical writing unit capable of improving brightness more than in the conventional manner in an image- formation element unit using a roof prism lens array, and to realize an image forming device capable of high-speed printing. SOLUTION: This image-formation element unit is provided with a 1st long- length coupling lens 1, and a roof prism lens array 2 where a plurality of roof prism lenses consisting of an incident lens surface 21, a roof prism part 22 and an emitting lens surface 23 are integrally arrayed. The lens 1 has a positive power in the direction perpendicular to the lens array 2, and is arranged on the surface 21 side of the roof prism lens. It is better to arrange a 2nd long- length coupling lens having a positive power in the direction perpendicular to the array on the emission lens 23 side of the roof prism lens. The optical writing unit uses the image-formation element unit. The image forming device uses the optical writing unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming element unit, an optical writing unit and an image forming apparatus, and is applicable to digital output devices such as digital copying machines, printers and digital facsimiles.

[0002]

2. Description of the Related Art In recent years, as digital image output devices such as digital copying machines, printers and digital facsimiles have become smaller, there has been a demand for smaller optical writing units for performing digital optical writing. As a digital optical writing method,
At present, it can be roughly divided into two types.
One of them is an optical scanning method in which a light beam emitted from a light source such as a semiconductor laser is optically scanned by an optical deflector, and a light spot is formed by a scanning imaging lens.
This is a solid-state optical writing method in which a light beam emitted from a light emitting element array such as an LED array or an organic EL array forms a light spot by an imaging element array.

In the above optical scanning method, since the light is scanned by the optical deflector, the optical path length becomes large, whereas in the solid-state optical writing method, the optical path length can be made extremely short. There is an advantage that the optical writing unit can be made compact. Further, since no movable part such as an optical deflector is used, there is an advantage that noise can be suppressed (low noise).

The outline of the solid-state optical writing type optical writing unit will be described below. The solid-state optical writing type optical writing unit includes a light emitting element array including a plurality of light emitting elements and an image forming element array including a plurality of image forming elements. A general solid-state optical writing type optical writing unit uses a rod lens array as an imaging element array. FIG. 37 shows an example thereof. In FIG. 37, a rod lens array 322 is arranged between a light emitting element array 324 and an image carrier 326 composed of a photosensitive drum or the like. The rod lens array has an image forming function, and the light emitting element array 32
The on / off state of No. 4 is imaged on the surface of the image carrier 326 as, for example, an equal-magnification image.

FIG. 38 shows an example of an optical writing unit using a roof prism lens array as an example using another imaging element array. This optical writing unit has a section L
The light emitting element array 331 is arranged at the bottom of the character-shaped base 333, and the roof prism lens array 332 is arranged at the corners of the base 333.
The light from is condensed by the roof prism lens array 332, the optical path is bent at a substantially right angle, and the image of the light emitting element array 331 is formed on the image plane 334.

As the light emitting element array used in the above conventional example, an LED array in which light emitting diodes (LEDs) are arranged at a predetermined arrangement pitch is generally used as the light emitting element. In the LED array, light emitting diode array chips are mounted on a substrate, and several tens to several hundreds of light emitting diodes (LEDs) are arranged at predetermined intervals on each light emitting diode array chip. Adjacent light emitting diode array chips are mounted on the substrate so that the distance between the light emitting diodes at the ends thereof is the predetermined distance.

Other light emitting element arrays include organic E
An EL array in which L elements are arranged and a semiconductor laser (L
There is an LD array in which D) is arranged. The LD array includes a surface emitting type and an edge emitting type. Further, a high output light source such as a fluorescent tube using a shutter array such as a liquid crystal shutter can also be used as a kind of light emitting element array.

Next, as an imaging element array used in a solid-state optical writing type optical writing unit, a rod lens array in which a plurality of gradient index rod lenses are bundled is generally used. FIG. 39 shows an example thereof, in which a large number of rod lenses 341 are bundled in two rows in a bale-like shape, and the periphery thereof is held by a side plate 342. An opaque member 343 is filled in the gap between the rod lenses 341 and solidified. In addition, there is also one in which the rod lens is configured in one row (not shown).

As an example of another imaging element array, FIG.
0, a roof prism lens array (RPLA) 220 in which an incident side lens surface 221, an exit side lens surface 223, and a roof prism 223 are integrally formed.
Is proposed. A plurality of the entrance side lens surface 221, the exit side lens surface 223, and the roof prism 223 are arranged in the same direction. The roof prism 223 is
The light beam incident from the incident side lens surface 221 is obliquely provided so as to be bent at a right angle, and is reflected twice by a pair of roof-type reflecting surfaces so that an erect image of the imaging element array is formed on the imaging surface. Has become.

As a conventional example of a light emitting element array, Japanese Patent Application Laid-Open No. 1-1998
There is one described in Japanese Patent Laid-Open No. 1-78115. This is characterized by including a narrowing optical system including a reflection structure for narrowing the emission angle of each light emitting element formed integrally on the light emitting element array. By narrowing the emission angle of each light emitting element, the light emitting element is aimed to be efficiently incident on the imaging element array.

[0011]

In order to increase the density of an image to be written or an image to be formed and to improve the quality of an image to be obtained, it is necessary to form a minute structure in each light emitting element. The cost of the element array increases significantly. On the other hand, although an optical writing unit using a rod lens array is generally used as the imaging element array, an image is output in an image forming apparatus using the optical writing unit using this imaging element array. Then, density unevenness called vertical stripes (white stripes or black stripes in a monochrome image) is recognized on the output image.

We have found through experiments that, as factors causing this density unevenness, there are non-uniformity in beam characteristics due to the imaging element array and non-uniformity in light-emitting element spacing due to the light-emitting element array. . For the non-uniformity of the beam characteristics caused by the imaging element array, which is one of the factors,
It was found that the structure of the rod lens array had a great influence. That is, since the rod lens array is formed by bundling a plurality of rod lenses 341 having a refractive index distribution as shown in FIG. 39, the optical axis directions between adjacent rod lenses are likely to vary. . Since the light flux emitted from one light emitting element is imaged through a plurality of rod lenses, the optical axis of each rod lens varies and the shape of each image obtained through each rod lens is obtained. And position will vary. Therefore, the combined image depends on the optical axis variation of the rod lens. Therefore, the image formed corresponding to the plurality of light emitting elements changes according to the variation of the optical axis of the rod lens array. That is, it causes non-uniformity of beam characteristics. In addition to variations in the optical axis, variations in refractive index distribution, variations in rod diameter, etc. are also affected.

Therefore, the inventors have formed an optical writing unit using a roof prism lens as an imaging element capable of reducing variations due to processing errors such as optical axis variations by integrally forming a plurality of imaging elements. Is proposed. However, in achieving an optical writing unit using a roof prism lens array in which vertical stripes cannot be recognized, it is more disadvantageous in the brightness of the optical system than an optical writing unit using a rod lens array. I understood.

Therefore, it is an object of the present invention to realize an optical system capable of improving brightness as compared with the conventional case in an image forming element unit using a roof prism lens array. Another object of the present invention is to realize an optical writing unit using a roof prism lens array, which can improve the brightness as compared with the conventional one. It is another object of the present invention to realize an image forming apparatus using an optical writing unit using a roof prism lens array, which is capable of printing at a higher speed than conventional ones.

From the viewpoint of environment, by adopting the solid-state optical writing method, the advantage that the optical writing unit can be made compact by reducing the number of unit parts and materials as compared with the optical scanning method can be achieved. There is no moving part like a deflector, and there is an advantage that it is low noise. Further, since the brightness can be improved as compared with the conventional one, an image forming apparatus capable of high-speed printing can be realized, and if the printing speed is the same as the conventional one, the light emission power of the light emitting element array can be reduced, and the low power consumption (energy saving ) Can be realized.

[0016]

The invention according to claim 1 is
An image forming element unit comprising a first long coupling lens and a roof prism lens array in which a plurality of roof prism lenses including an entrance lens surface, a roof prism portion, and an exit lens surface are integrally arranged. The first long coupling lens has a positive power in the direction orthogonal to the arrangement of the roof prism lens array and is arranged on the incident lens surface side of the roof prism lens.

According to a second aspect of the present invention, in the first aspect of the invention, the first elongated coupling lens has a meniscus shape which is concave on the incident lens surface side of the roof prism lens. According to a third aspect of the present invention, in the first aspect of the invention, the second elongated coupling lens having a positive power in the arrangement orthogonal direction is arranged on the exit lens side of the roof prism lens, and the roof prism lens is anamorphic. It is characterized by being a lens.

According to a fourth aspect of the present invention, in the first aspect of the invention, the second elongated coupling lens having a positive power in the arrangement orthogonal direction is arranged on the exit lens side of the roof prism lens, and the arrangement orthogonal direction is provided. It is characterized in that an intermediate image is formed on the. According to a fifth aspect of the invention, in the first aspect of the invention, the second elongated coupling lens having a negative power in the arrangement orthogonal direction is disposed on the exit lens side of the roof prism lens. .

According to a sixth aspect of the invention, in an optical writing unit for forming a light spot, a light emitting element array in which a plurality of light emitting element array chips in which a plurality of light emitting elements are arranged at a predetermined interval are arranged, An image forming element unit including a first long coupling lens and a roof prism lens array, wherein the first long coupling lens has a positive power in a direction orthogonal to the array, and It is characterized in that it is arranged on the incident lens surface side.

According to a seventh aspect of the present invention, there is provided a light emitting element array comprising a plurality of light emitting element array chips in which a plurality of light emitting elements are arranged at a predetermined interval, a first elongated coupling lens and a roof prism lens array. In an image forming apparatus in which an optical writing unit including the image forming element unit including the image forming device unit is used as an exposure unit, the first long coupling lens has a positive power in a direction orthogonal to the array, and the roof. It is characterized in that it is arranged on the incident lens surface side of the prism lens.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an imaging element unit, an optical writing unit and an image forming apparatus according to the present invention will be described below with reference to the drawings. An outline of an imaging element unit composed of a first long coupling lens and a roof prism lens array is shown in FIG. 1 in a cross section in a direction orthogonal to the array. In FIG. 1, the first long coupling lens 1 has a positive power in a direction orthogonal to the array, and is on the incident lens surface 21 side of the roof prism lens array 2, that is, the object surface 3 and the roof prism lens array. It is located between two. The first elongated coupling lens 1 has a meniscus shape, and its perspective view is shown in FIG.
As shown in FIG. 2, the first long coupling lens 1 has no power in the arrangement direction.

In the roof prism lens array 2, a plurality of roof prism lenses each having an entrance lens surface 21, a roof prism portion 22, and an exit lens surface 23 are integrally arranged. The perspective view is shown in FIG. The light flux emitted from the light emitting element located on the object plane 3 is coupled by the first long coupling lens 1 in the array orthogonal direction, and is converged by the positive power in the array orthogonal direction.
After that, the light is transmitted through the incident lens surface 21 of the roof prism lens array 2, is totally reflected by the two roof prism surfaces that are substantially orthogonal to each other and forms the roof prism portion 22, and is connected to the image surface 4 via the exit lens surface 23. Image. In the arrangement direction of the roof prism lenses, the first long coupling lens 1 has no power and only transmits the light, and an image is formed on the image plane 4 by the power of the entrance lens surface 21 and the exit lens surface 23 of the roof prism lens. To do. In FIG. 1, α ′ indicates the angle of the light flux that can be taken in by the imaging element unit coupling the light flux emitted from the light emitting element located on the object plane 3 in the arrangement orthogonal direction.

FIG. 4 shows a schematic view (a cross-sectional view in the direction orthogonal to the array) of an image forming element unit which is composed of only the roof prism lens array 2 without the first elongated coupling lens 1. In FIG. 4, α represents the light flux emitted from the light emitting element located on the object plane 3 in the roof prism lens array 2
The image forming element unit formed of only the angle of the light flux that can be coupled and taken in in the array orthogonal direction.

In the above embodiment of the present invention, by arranging the first long coupling lens 1 having a positive power in the direction orthogonal to the arrangement of the roof prism lenses on the incident lens surface 21 side of the roof prism lens, '> Α can be achieved. In the array direction,
Since the first long coupling lens 1 has no power, the light path may be parallel-shifted due to the floating of the first long coupling lens 1, but there is no difference in the angle of taking in the light flux. Therefore, the brightness of the imaging element unit is approximately proportional to α. Therefore, by inserting the first long coupling lens 1, the brightness of the imaging element unit is improved by approximately (α ′ / α) times.

The above embodiment will be described more specifically.
As shown in FIG. 5, the first elongated coupling lens 1 has a meniscus shape having a positive power, and is arranged so as to be concave on the incident lens surface 21 side of the roof prism lens. As can be seen from FIG. 5, by inserting the first long coupling lens 1, the angle (α ′) of the luminous flux that can be taken in by the imaging element unit is increased, and the brightness of the imaging element unit is improved. Can be made.

FIG. 6 is a development view of the example shown in FIG. As shown in the figure, when each surface spacing is d ′, the radius of curvature is r, and the refractive index is N, paraxial ray tracing is performed to determine the angle (α ′) of the light beam that can be captured by the imaging element unit. Ask. In performing paraxial ray tracing, the reduced surface spacing e ′ and the surface power φ are used. Here, when the surface number is m, the reduced surface spacing e ′ and the surface power φ can be written by the following equations. FIG. 7 shows a development view represented by φ, where em ′ = dm ′ / Nm ′ φm = (Nm′−Nm) / rm e ′.

Specific examples will be shown below. The roof prism lens has the same configuration, and parameters (d0 ′, d) relating to the first long coupling lens 1 are used.
1 ′, d2 ′, r1, r2) are changed. The parameters are shown in Table 1. Table 1

From the above, Table 2 shows e ′ and φ for the imaging element unit for performing paraxial ray tracing. In addition,
In Table 2, "conventional" means that the first elongate coupling lens 1 is not provided and the imaging element unit is composed of only the roof prism lens array 2. Table 2

FIG. 8 shows an example of ray tracing for the first embodiment in the above table. The light rays in FIG. 8 are the light rays traced at the peripheral edge. The light rays at the outermost periphery are limited by the aperture diameter of the entrance lens surface or the exit lens surface of the roof prism, and in this study example, h = 0.46 mm. Table 3 shows α ′ thus obtained. Table 3 As is clear from Table 3, by inserting the first elongate coupling lens 1, α ′ becomes larger than in the conventional case (α = 0.05), and the brightness of the imaging element unit is improved.

Here, the distance from the object surface 3 to the exit lens surface of the first long coupling lens 1 is S '(= d0'
+ D1 '), the distance from the object plane 3 to the incident lens surface 21 of the roof prism lens is L (= d0' + d1 '+ d)
2 ′), and P = S ′ / L * ABS (φ1 * φ2), the relationship between P and the brightness improvement rate (α ′ / α) is as shown in Table 4. ABS (x) represents the absolute value of x. Table 4 P and (α ′ / α) are plotted in FIG. From this, it can be seen that there is an almost proportional relationship.

For the following reason, 0.03≤P≤0.1
It is desirable to satisfy 5. That is, if the distance from the object surface 3 to the first long coupling lens 1 is small, that is, S ′ is small, improvement in brightness cannot be expected. Further, when the power of the first long coupling lens 1 is small, that is, ABS (φ1 * φ2) is small, the angle of the light beam that can be taken in by the roof prism lens cannot be increased, and the improvement of brightness cannot be expected. . Therefore, in order to obtain a brightness improvement of 50% or more, (α '/ α
It is desirable that ≧ 1.5) and 0.03 ≦ P.

On the other hand, if the distance from the object surface 3 to the first long coupling lens 1 is large, that is, if S'is large, the effective diameter of the lens surface of the first long coupling lens 1 becomes large. As a result, aberration deterioration is caused, and it becomes difficult to process the first long coupling lens 1. This will be described with reference to the third embodiment. FIG. 10 shows an example of ray tracing of the third embodiment. The ray height h of the incident lens surface of the first long coupling lens 1 is about 0.8 mm. On the other hand, its radius of curvature is r1 = 1.2
mm, the ray height with respect to the radius of curvature is considerably large (h / r1> 0.5), and the deterioration of aberrations and the difficulty of processing are high. Therefore, it is desirable that P ≦ 0.15.

Table 5 shows the results of obtaining the absolute value Ms of the lateral magnification in the array orthogonal direction determined by the relationship between the object plane, the imaging element unit and the image plane in the above Examples 1 to 12. Table 5 From this, it can be seen that the lateral magnification in the direction orthogonal to the array of the roof prism lenses is increased by inserting the first long coupling lens 1. Further, the brightness improvement rate (α ′ / α) and the lateral magnification Ms are in a substantially proportional relationship.
Since the beam spot is enlarged when the lateral magnification is increased, the resolution is deteriorated when the lateral magnification is increased too much.

For example, when a rectangular planar light source having four sides of 20 μm (corresponding to 600 dpi) is considered, if Ms = 1.0, the beam spot is considered when the deterioration of the imaging characteristic due to aberration (about 20 μm) is taken into consideration. From 20 * 1.0 + 20 = 40, the diameter is about 40 μm level, and a beam spot diameter almost equal to the pixel size of 600 dpi (42.3 μm) can be obtained. If Ms = 3.0, then 20 * 3.0 + 20 = 80, so that the level is about 80 μm, the beam spot diameter is about twice, and twice the 600 dpi pixel size. If it is about twice the pixel size, it can be practically used. Therefore, in view of the brightness improvement of 50% or more and the deterioration of the resolution due to the beam spot expansion, it is preferable that 1.5 ≦ Ms ≦ 3.0 is satisfied.

At least one of the lens surfaces constituting the image forming element unit may have a non-arcuate shape in the array orthogonal direction. By having a non-arcuate shape, aberration correction can be performed in the direction orthogonal to the array. For example, the entrance lens surface or the exit lens surface of the roof prism lens may be a coaxial aspherical surface, and aberrations may be corrected in the arrangement direction as well.

Further, on the entrance lens surface of the first long coupling lens, a non-arcuate shape can be formed in the direction orthogonal to the arrangement. As shown in FIG. 8 and FIG. 10, among the lens surfaces forming the imaging element unit, the effective diameter of the entrance lens surface of the first long coupling lens is the largest. Since the deterioration of the aberration is large on the lens surface having a large effective diameter, the aberration can be more effectively corrected by using a non-arcuate shape for this lens surface.

In Examples 1 to 12, the roof prism lens has a substantially erecting equal-magnification system in the arrangement direction and a substantially inverted equal-magnification system in the arrangement orthogonal direction in relation to the object plane and the image plane. Further, the entrance lens surface and the exit lens surface of the roof prism lens are a coaxial system, and are more workable than the anamorphic surface.

Further, the roof prism lens has a substantially erecting equal-magnification system in the arrangement direction in the relationship between the object plane and the image plane, and the entrance lens surface and / or the exit lens surface is an anamorphic surface. can do. The anamorphic surface is a surface in which the power in the array direction and the power in the array orthogonal direction are different, and represents a surface shape such as a cylindrical surface, a toroidal surface, or a free-form surface. Therefore,
In the array orthogonal direction, the powers of the four surfaces of the entrance lens surface and the exit lens surface of the first long coupling lens and the entrance lens surface and the exit lens surface of the roof prism lens can be set, and the degree of freedom in design can be increased. Can be large.

A specific example of such an embodiment is shown below. As shown in FIG. 11, the first long coupling lens 11 has a cylindrical shape, and the roof prism lens 12 is an anamorphic lens, that is, a lens having an anamorphic surface. FIG. 12 shows the first elongated coupling lens 11 having a cylindrical shape. The first long coupling lens 11 has a cylindrical surface on one side and a flat surface on the other side in the array orthogonal direction. Further, as shown in FIG. 13, since the roof prism lens array 12 has a substantially erecting equal-magnification system in the array direction, in the array orthogonal direction of the roof prism lenses,
Either the incident lens surface 13 or the exit lens surface 14 has a power different from the power in the arrangement direction, and forms an anamorphic surface.

As can be seen from FIG. 11, by inserting the first elongate coupling lens 11, the brightness of the imaging element unit, that is, the angle (α ') of the luminous flux which can be taken in by the imaging element unit. Grows.

FIG. 14 shows a development view of the embodiment shown in FIG. 11, and concrete examples will be shown below. Parameters (d0 ′, d) related to the first long coupling lens 11
1 ′, d2 ′, r1, r2) and the parameters (r3, r4) relating to the roof prism lens are changed. The parameters are shown in Table 6. In addition, Example 1 shown in this table
In Examples 9 to 9, the incident lens surface of the first long coupling lens 11 was a cylindrical surface, and the radius of curvature of the exit lens surface was r2 = ∞, that is, a flat surface. Of course, the entrance lens surface may be a flat surface and the exit lens surface may be a cylindrical surface. Table 6 From the above, Table 7 shows e ′ and φ for the imaging element unit for performing paraxial ray tracing.

Table 7

FIG. 15 shows an example of ray tracing for the first embodiment in the above table. The rays in FIG. 15 are traces of the rays at the outermost periphery. The light rays at the outermost periphery are limited by the aperture diameter of the entrance lens surface or the exit lens surface of the roof prism, and in this study example, h = 0.46 mm. Table 8 shows α ′ thus obtained. Table 8 Therefore, by inserting the first long coupling lens 11, α ′ is increased and the brightness of the imaging element unit is improved.

Here, the distance from the object plane 3 to the incident lens surface of the first long coupling lens is S (= d0 '),
When the distance from the object surface to the entrance lens surface of the roof prism lens is L (= d0 '+ d1' + d2 '), Q = S / L * φ12 is set, and Q and brightness improvement rate (α' / Table 9 shows the relationship of α). Table 9 Q and (α ′ / α) are plotted in FIG. From this, it can be seen that there is an almost proportional relationship.

For the following reason, 0.009≤Q≤0.
It is desirable to satisfy 033. That is, if the distance from the object surface to the first long coupling lens is small, that is, S is small, improvement in brightness cannot be expected. Further, if the power of the first long coupling lens is small, that is, φ12 is small, the angle of the light beam that can be taken in by the roof prism lens cannot be increased, and improvement in brightness cannot be expected. Therefore, in order to obtain a brightness improvement of 50% or more, it is desirable that 0.009 ≦ Q. On the other hand, when the distance from the object surface to the first long coupling lens is large, that is, S is large, the effective diameter of the lens surface of the first long coupling lens becomes large, which causes aberration deterioration and It becomes difficult to process the first long coupling lens. Further, when the exit lens surface of the roof prism lens has a large negative power, the lateral magnification of the imaging element units in the direction orthogonal to the array becomes large.

This will be described with reference to Examples 8 and 9. First, FIG. 17 shows an example of ray tracing for Example 9.
Shown in. The power of the exit lens surface of the roof prism lens is φ4 = 0, and the absolute value Ms of the lateral magnification in the array orthogonal direction of the imaging element unit is 2.7 times. 18 shows an example of ray tracing of the eighth embodiment. The power of the exit lens surface of the roof prism lens is φ4 = −0.06 <0
The absolute value Ms of the lateral magnification in the array orthogonal direction of the imaging element unit is 3.2 times. Therefore, in order to suppress the lateral magnification in the array orthogonal direction to about 3 times or less, Q ≦ 0.03
It is desirable to set it to 3.

Table 10 shows the results of obtaining the absolute value Ms of the lateral magnification in the array orthogonal direction determined by the relationship between the object plane, the imaging element unit and the image plane in the above Examples 1 to 9. Table 10 It can be seen from Table 10 that the lateral magnification in the array orthogonal direction is increased by inserting the first long coupling lens. Since the beam spot is enlarged when the lateral magnification is increased, the resolution is deteriorated when the lateral magnification is increased too much.

Therefore, the brightness is improved by 50% or more (α '
/Α≧1.5), and it is desirable that 1.5 ≦ Ms ≦ 3.0 is satisfied in view of the deterioration of the resolution due to the beam spot expansion.

At least one of the lens surfaces constituting the image forming element unit may have a non-arcuate shape in the arrangement orthogonal direction. By having a non-arcuate shape, aberration correction can be performed in the direction orthogonal to the array. Furthermore, the cylindrical surface of the first long coupling lens can have a non-arcuate shape in the array orthogonal direction. In the examples shown in FIGS. 17 and 18, the effective diameter of the cylindrical surface of the first long coupling lens is large. Since the deterioration of the aberration is large on the lens surface having a large effective diameter, the aberration can be more effectively corrected by using a non-arcuate shape for this lens surface.

A specific example of this embodiment will be shown below.
As shown in FIG. 19, the second long coupling lens 15 having a positive power in the arrangement orthogonal direction is arranged on the exit lens surface 17 side of the roof prism lens array 16. The roof prism lens array 16 is an anamorphic lens (a lens having an anamorphic surface). In this embodiment, the first and second elongated coupling lenses 15 and 20 are cylindrical lenses, and the exit lens surface 18 of the roof prism lens array 16 is a flat surface in the array orthogonal direction. Of course, the first and second elongated coupling lenses 15 and 20 may be biconvex lenses or meniscus lenses. The entrance lens surface of the roof prism lens may be an anamorphic surface, or the exit lens surface may be provided with power.

As can be seen from FIG. 19, the first and second
By inserting the long coupling lenses 15 and 20, the brightness of the imaging element unit, that is, the angle (α ′) of the light beam that can be taken in by the imaging element unit is increased.

FIG. 20 shows a development view of the embodiment shown in FIG. 19, and concrete examples will be shown below. Parameters (d0 ′, d) related to the first long coupling lens 15
1 ′, d2 ′, r1), the parameter (r3) for the roof prism lens, and the parameters (d4 ′, d5 ′, d6 ′, r for the second long coupling lens 20).
6) is changed. The parameters are shown in Table 11. In Examples 1 to 12, the exit lens surface of the first long coupling lens 15 and the roof prism lens array 16 are used.
Exit lens surface 18 of the second long coupling lens 20
Is assumed to be a plane (r2 = r4 = r5
= 0). Table 11

From the above, Table 12 shows e ′ and φ for the imaging element unit for performing paraxial ray tracing. Table 12

FIG. 21 shows an example of ray tracing for Example 1 in Table 12. The light rays in FIG. 21 trace the light rays at the outermost periphery. The light rays at the outermost periphery are limited by the aperture diameter of the entrance lens surface 17 or the exit lens surface 18 of the roof prism, and in this study example, h = 0.46 mm. Table 13 shows α ′ thus obtained. Table 13 As can be seen from Table 13, by inserting the first long coupling lens, α ′ becomes large and the brightness of the imaging element unit is improved.

Here, the distance from the object surface to the entrance lens surface of the first long coupling lens is S (= d0 '), and the distance from the object surface to the entrance lens surface of the roof prism lens is L (= d0'). + D1 ′ + d2 ′), where R = S / L * φ2, where R is the power of the first long coupling lens, and R is the brightness improvement rate (α ′ / α).
It becomes like 4. (Note that φ = φ1 + φ2-e1 ′ * φ
1 * φ2, and in this embodiment φ2 = 0, so φ
= Φ1) Table 14 R and (α ′ / α) are plotted in FIG. From this, it can be seen that it can be expressed by a quadratic function, and it can be seen that R and (α ′ / α) have a correlation.

For the following reason, 0.01≤R≤0.0
It is desirable to satisfy 45. That is, when the power of the first long coupling lens is small, that is, φ2 is small, it is not possible to increase the angle of the light beam that the roof prism lens can capture, and it is not possible to improve the brightness. Therefore, in order to obtain a brightness improvement of 50% or more, it is desirable that 0.01 ≦ R. On the other hand, the first
The power of the long coupling lens is large, that is, φ
If 2 is large, the radius of curvature becomes small, the ray height with respect to the radius of curvature becomes large, and the deterioration of aberration,
And the difficulty of processing becomes high.

This will be described with reference to the fourth embodiment. FIG. 23 shows an example of ray tracing for the fourth embodiment. The ray height h of the entrance lens surface of the first long coupling lens is about 0.71 mm. On the other hand, the radius of curvature is r1 = 1.35 mm, the ray height with respect to the radius of curvature is considerably large (h / r1> 0.5), and the deterioration of aberration and the difficulty of processing are high. In addition, Example 3
In the ray tracing result of, h = 0.63 mm, r1 = 1.4
mm, and h / r1 <0.5. Therefore, it is desirable that R ≦ 0.045.

Table 15 shows the results of obtaining the absolute value Ms of the lateral magnification in the array orthogonal direction determined by the relationship between the object plane, the imaging element unit, and the image plane in the above Examples 1 to 12. Table 15 Since the beam spot is enlarged when the lateral magnification is increased, the resolution is deteriorated when the lateral magnification is increased too much. For the following reasons, 1.0 ≦ Ms ≦ 3.0
It is desirable to satisfy. In order to obtain a brightness improvement of 50% or more, it is desirable that Ms ≧ 1.0. In Example 5, α ′ / α = 1.4 and Ms = 0.8, which is outside the above range. It is desirable that Ms ≦ 3.0 as a range that does not cause deterioration of resolution due to expansion of the beam spot.

A ray tracing example of the second embodiment is shown in FIG.
4 shows. By configuring the imaging element unit to be a symmetric system in the optical axis direction, the absolute value Ms of lateral magnification in the array orthogonal direction can be set to Ms = 1, and the imaging element can be formed without expanding the beam spot. The brightness of the unit can be improved.

At least one of the lens surfaces constituting the image forming element unit may have a non-arcuate shape in the array orthogonal direction. By having a non-arcuate shape, aberration correction can be performed in the direction orthogonal to the array. Further, at least one surface of the first long coupling lens can have a non-arcuate shape in the arrangement orthogonal direction.

In the example shown in FIG. 23, the effective diameter of the cylindrical surface of the first long coupling lens is large. In this type, that is, the type including the first long coupling lens + roof prism lens array + second long coupling lens, the effective diameter of the first long coupling lens tends to be large. Therefore, since the deterioration of the aberration is large on the lens surface having a large effective diameter, the aberration can be more effectively corrected by using a non-arcuate shape on at least one surface of the lens.

Another embodiment of the present invention will be described. In FIG. 25, the second long coupling lens 35 having a positive power in the direction orthogonal to the arrangement of the roof prism lens array is the roof prism lens array 32.
Is arranged on the side of the exit lens surface 34 and is configured to form an intermediate image in the array orthogonal direction. Figure 25
In the example shown in (1), the first and second long coupling lenses 31 and 35 are cylindrical lenses.
Of course, the cylindrical surface may be directed to the roof prism lens array 32 side, or a biconvex lens 36 as shown in FIG. 26 may be used.

As can be seen from FIG. 25, the first and second
By inserting the long coupling lenses 31 and 35, the brightness of the imaging element unit, that is, the angle of the light beam that can be taken in by the imaging element unit is increased.

FIG. 27 shows a developed view of the embodiment shown in FIG. The imaging element unit is an optical system (d0 ′ = d6 ′, d1 ′ = d5 ′, d2 ′ = d) that is symmetrical in the optical axis direction.
4 ′, r1 = −r6, r2 = −r5, r3 = −r4), and by forming an intermediate image inside the roof prism lens, it becomes a substantially erecting equal-magnification system in the direction orthogonal to the array and enlarges the beam spot. The brightness can be improved without causing the occurrence.

Specific examples of the above embodiment will be shown below. Parameters (d) relating to the first long coupling lens 31 and the second long coupling lens 35.
0 ', d1', d2 ', r1) are changed. The parameters are shown in Table 16. In the present embodiment, the first
The exit lens surface of the long coupling lens 31 and the entrance lens surface of the second long coupling lens 35 are flat surfaces (r2 = r5 = 0). Table 16

From the above, Table 17 shows e ′ and φ for the imaging element unit for performing paraxial ray tracing. Table 17

FIG. 28 shows an example of ray tracing for the first embodiment in the above table. The rays in FIG. 28 are traces of the rays at the outermost periphery. It should be noted that the outermost peripheral ray is limited by the height of the ray passing through the first long coupling lens or the second long coupling lens, and in this study, h = 0.5 *
r1. Table 18 shows α ′ thus obtained. Table 18

Further, the brightness can be improved by allowing the ray height to be large. h = 0.7 * r
FIG. 29 shows an example in which ray tracing is performed for Example 1 when the number is 1. Table 19 shows the obtained α ′. Table 19 However, since the ray height is allowed to be large, the aberration deterioration becomes large and the lens processing difficulty becomes high.

At least one of the lens surfaces constituting the image forming element unit may have a non-arcuate shape in the direction orthogonal to the arrangement. By having a non-arcuate shape, aberration correction can be performed in the direction orthogonal to the array. Further, at least one surface of the first long coupling lens and at least one surface of the second long coupling lens can have a non-arcuate shape in a direction orthogonal to the arrangement, and more preferably, symmetrical with respect to the optical axis. It is preferable to provide the optical system such that the optical system is a system. As shown in FIG. 28, in order to greatly improve the brightness, the effective diameter of the first elongate coupling lens 31 becomes considerably larger than the radius of curvature, so aberration correction using a non-arc shape is performed. Is required.

In Examples 1 to 3 shown in the above table, the roof prism lens has the following relationship between the object plane and the image plane.
A substantially erecting equal-magnification system is arranged in the array direction, and an approximately inverted equal-magnification system is formed in the array orthogonal direction. Further, the entrance lens surface and the exit lens surface of the roof prism lens are a coaxial system, and are more workable than the anamorphic surface.

The roof prism lens has a substantially erecting equal-magnification system in the arrangement direction in the relationship between the object plane and the image plane, and the entrance lens surface and / or the exit lens surface is an anamorphic surface. can do. Therefore, in the array orthogonal direction, the entrance lens surface and the exit lens surface of the first long coupling lens, the entrance lens surface and the exit lens surface of the roof prism lens, and the entrance lens surface and the exit lens surface of the second long coupling lens. The power of six surfaces can be set, and the degree of freedom in design can be increased. Even when the optical system is symmetrical in the optical axis direction, the first long coupling lens (that is, the second long coupling lens has the same shape) and the entrance lens surface (that is, the exit lens surface) of the roof prism lens. The power of the three surfaces having the same shape) can be set, and the degree of freedom in design can be increased.

Another embodiment of the present invention will be described. 30, the roof prism lens array 4
The second long coupling lens 41 having negative power in the direction orthogonal to the two arrays is arranged on the exit lens surface 43 side of the roof prism lens array 42. In this embodiment, the first long coupling lens 41 is a cylindrical lens having a positive power, and the second long coupling lens 45 is a cylindrical lens having a negative power as shown in FIG. . Of course, it goes without saying that the first and second long coupling lenses 41 and 45 are not limited to cylindrical lenses.

As can be seen from FIG. 30, the first and second
By inserting the long coupling lenses 41 and 45, the brightness of the imaging element unit, that is, the angle (α ′) of the light beam that can be taken in by the imaging element unit is increased.

FIG. 32 shows a development view of the embodiment shown in FIG. 30, and concrete examples will be shown below. Here, d
0 '= d6' = 4.033, d1 '= d2' = d4 '=
d5 ′ = 3.0, and the first long coupling lens 41
The parameter (r1) related to the roof prism lens, the parameter (r4) related to the roof prism lens, and the parameter (r6) related to the second long coupling lens 45 are changed.
The parameters are shown in Table 20. The exit lens surface of the first long coupling lens 41 and the entrance lens surface of the second long coupling lens 45 are flat surfaces. Table 20

From the above, Table 21 shows e ′ and φ for the imaging element unit for performing paraxial ray tracing. Table 21

FIG. 33 shows an example of ray tracing for Example 1 in the above table. The light rays in FIG. 33 are the light rays traced at the peripheral edge. The light rays at the outermost periphery are limited by the aperture diameter of the entrance lens surface or the exit lens surface of the roof prism, and in this study, h = 0.46 mm. Table 22 shows α ′ thus obtained. Table 22

At least one of the lens surfaces constituting the imaging element unit can be formed in a non-arcuate shape in the array orthogonal direction. By having a non-arcuate shape, aberration correction can be performed in the direction orthogonal to the array. Further, at least one surface of the first long coupling lens can have a non-arcuate shape in the arrangement orthogonal direction. As shown in FIG. 33, in this type, that is, the type including the first long coupling lens (positive power) + the roof prism lens array + the second long coupling lens (negative power), The effective diameter of the two long coupling lenses can be made very small. Therefore, by using a non-arcuate shape on at least one surface of the first long coupling lens, which is advantageous in processing, rather than the entrance lens surface and the exit lens surface of the roof prism lens, aberration correction can be performed more effectively. it can.

By using the imaging element array described above, an optical writing unit can be configured together with the light emitting element array. FIG. 34 shows an example of an optical writing unit using the imaging element unit according to the present invention. This example
The imaging element unit shown in FIGS. 1 to 3 is used.
In FIG. 34, the roof prism lens array 2 forming the imaging element array is held by a holding member (not shown),
It is fixed to the frame 50 by an appropriate holder. The light emitting element array 51, which is, for example, an LED array, is also positioned with respect to the roof prism lens array 2 and fixed to the frame 50. The light emitting surface of the light emitting element array 51 coincides with the object plane 3. The light emitted from each light emitting element (LED element or the like) of the light emitting element array 51 is converged by the roof prism lens array 2 onto the image surface 4, for example, the surface of an image carrier such as a photoconductor, to form a light spot. .

In the light emitting element array 51, a plurality of light emitting elements are arranged while keeping a constant interval. A light emitting diode (LED) array is used as a typical light emitting element array. As an example, FIG.
Shown in. FIG. 35 (a) is a front view of the LED array, and FIG.
(B) is a cross-sectional view. A plurality of LED array chips 54 are arranged on a substrate 53, and a driver IC 55 for driving LEDs on both sides in the arrangement direction is mounted. The driver IC 55 may be arranged only on one side of the LED array chip 54 in the arrangement direction. Further, a connector portion 56 for connecting a signal cable for giving information such as an image signal to the driver IC 55 is provided.

FIG. 35C is a schematic view of the LED array chip 54, and a plurality of LEDs 57 are arranged on the chip 54. Generally, several tens to several hundreds of LEDs 57 are arranged on one chip 54, and several tens of LED array chips 54 are arranged on the substrate 53. For example, to print A4 size at 600 dpi, 1
128 LEDs are arranged on the chip 54, and the substrate 53
Forty LED array chips 54 are arranged on the upper side, and 128 × 40 = 5120 LEDs are arranged in total.

An optical writing unit can be constructed as described above by using the imaging element array described so far, and an image forming apparatus can be constructed using this optical writing unit as an exposure unit. it can. An electrophotographic process is one of the processes for forming an image in an image forming apparatus. An image forming apparatus can be constructed by using the optical writing unit for executing the writing process or the exposing process in the electrophotographic process. Hereinafter, an example of an image forming apparatus using an electrophotographic process will be outlined with reference to FIG.

In FIG. 36, a charging unit 61, an optical writing unit 62, a developing unit 63, a transfer unit 64, a cleaning unit 66, a charge eliminating unit are provided around the image carrier 60 made of a photosensitive drum in a clockwise direction in the figure. 67 is arranged, and a fixing unit 65 for fixing the toner image transferred to the recording paper 70 is arranged beside the transfer unit 64. As is well known, the charging unit 61 applies a uniform potential (charging) to the image carrier 60 that is rotated clockwise, and the optical writing unit 62 is used.
A latent image is formed (exposure) by irradiating the image carrier 60 with a light spot from the developing unit 63.
The toner is attached by means of to form a toner image (development), the transfer unit 64 transfers the toner image onto the recording paper 70 (transfer), and the fixing unit 65 applies pressure or heat to the recording paper 70.
To fuse (fix). Further, the cleaning unit 66 removes the residual toner on the surface of the image bearing member, and the charge eliminating unit 67 removes the remaining electric charge, thus ending a series of electrophotographic processes.

As the optical writing unit 62, the image forming element unit according to each of the above-described embodiments is used.
For example, this imaging element unit has a light emitting element array in which a plurality of light emitting element array chips in which a plurality of light emitting elements are arranged at a predetermined interval are arranged, a first elongated coupling lens, and a roof prism lens array. The first long coupling lens has a positive power in the direction orthogonal to the array and is arranged on the incident lens surface side of the roof prism lens. Further, it may have a second long coupling lens, and may use any one of the embodiments of the imaging element unit described above.

The optical writing unit of the present invention can also be applied to an image forming apparatus called a tandem type, which is advantageous for high-speed color image output.

[0085]

According to the first aspect of the invention, by arranging the coupling lens having a positive power in the direction orthogonal to the arrangement, the light flux emitted from the light source can be effectively taken into the roof prism lens. The brightness of the imaging element unit can be improved.

According to the second aspect of the invention, the brightness of the imaging element unit can be improved by adding only one lens, and the desired effect can be obtained, but the cost increase is minimized. Can be suppressed.

According to the third aspect of the invention, by adding two long coupling lenses, aberration correction can be performed better than when one long coupling lens is added. The brightness of the imaging element unit can be improved. Further, when the first and second long coupling lenses are cylindrical lenses, it is possible to obtain an image forming element unit which is advantageous in processing parts.

According to the fourth aspect of the present invention, the image forming diameter becomes substantially upright and equal in the direction orthogonal to the arrangement direction of the roof prism lens array, the beam spot is not expanded, and the brightness of the image forming element unit is increased. Can be improved.

According to the fifth aspect of the present invention, the brightness of the imaging element unit can be improved and the effective diameter of the second long coupling lens can be reduced, which is advantageous in processing optical parts. It is possible to obtain a different imaging element unit.

According to the sixth aspect of the invention, a bright optical writing unit can be realized by forming the optical writing unit by using the imaging element unit capable of obtaining the above effects.

According to the seventh aspect of the invention, the image forming apparatus can be configured to have a higher printing speed by configuring the image forming apparatus using the optical writing unit capable of obtaining the above effects. Can be realized.

[Brief description of drawings]

FIG. 1 is an optical layout diagram showing an embodiment of an imaging element unit according to the present invention.

FIG. 2 is a perspective view showing a first long coupling lens in the above embodiment.

FIG. 3 is a perspective view showing a roof prism lens array in the embodiment.

FIG. 4 is an optical layout diagram showing an example of a conventional imaging element unit.

FIG. 5 is an optical layout diagram for explaining a function and effect of the embodiment.

FIG. 6 is a development view of the above embodiment.

FIG. 7 is a development view showing the above embodiment in terms of reduced surface spacing and power of each surface.

FIG. 8 is a ray tracing diagram of the above embodiment.

FIG. 9 is a graph showing a distribution of brightness improvement rates obtained by the above embodiment.

FIG. 10 is a ray tracing diagram of another embodiment of the imaging element unit according to the present invention.

FIG. 11 is an optical layout diagram of the same embodiment.

FIG. 12 is a perspective view showing a first long coupling lens in the same embodiment.

FIG. 13 is a perspective view showing a roof prism lens array in the same embodiment.

FIG. 14 is a development view of the above embodiment.

FIG. 15 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 16 is a graph showing a distribution of brightness improvement rates obtained by the above embodiment.

FIG. 17 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 18 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 19 is an optical layout diagram of the above embodiment.

FIG. 20 is a development view of the above embodiment.

FIG. 21 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 22 is a graph showing a distribution of brightness improvement rates obtained by the above embodiment.

FIG. 23 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 24 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 25 is an optical layout diagram showing still another embodiment of the imaging element unit according to the present invention.

FIG. 26 is a perspective view showing another example of the long coupling lens applicable to the above embodiment.

FIG. 27 is a development view of the above embodiment.

FIG. 28 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 29 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 30 is an optical layout diagram of the above embodiment.

FIG. 31 is a perspective view showing a second long coupling lens in the same embodiment.

FIG. 32 is a development view of the above embodiment.

FIG. 33 is a ray tracing diagram of still another embodiment of the imaging element unit according to the present invention.

FIG. 34 is a sectional view showing an embodiment of an optical writing unit according to the present invention.

35A is a front view, FIG. 35B is a sectional view, and FIG. 35C is a schematic side view showing an example of a light emitting element array that can be used in an optical writing unit according to the invention.

FIG. 36 is a front view schematically showing an example of an image forming apparatus according to the present invention.

FIG. 37 is a front view showing an example of a conventional solid writing type writing unit.

FIG. 38 is a cross-sectional view showing another example of a conventional solid writing type writing unit.

FIG. 39 is a plan view showing an example of a rod lens array used in a conventional solid-state writing type writing unit.

FIG. 40 is a perspective view showing an example of a roof prism lens array.

[Explanation of symbols]

1 First long coupling lens 2 Roof prism lens array 3 Object plane 4 image plane 21 Incident side lens surface 22 Roof prism part 23 Outgoing side lens surface 15 First long coupling lens 20 Second long coupling lens

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/028 1/04 101 F term (reference) 2C162 AE04 AE21 AE28 AE47 FA17 FA44 FA50 2H087 KA08 KA18 KA19 LA01 PA02 PA03 PA17 PB02 PB03 QA02 QA07 QA12 QA13 QA21 QA25 QA26 QA33 QA38 QA41 QA45 RA07 RA41 5C051 AA01 BA03 DA03 DB22 DB29 DE30 5C072 AA01 BA05 CA05 CA14 DA02 DA10 DA21 EA04

Claims (7)

[Claims] 1. A combination comprising a first elongate coupling lens and a roof prism lens array in which a plurality of roof prism lenses including an entrance lens surface, a roof prism portion, and an exit lens surface are integrally arranged. In the image element unit, the first long coupling lens has a positive power in a direction orthogonal to the arrangement of the roof prism lens array, and is arranged on the incident lens surface side of the roof prism lens. Image forming element unit. 2. The imaging element unit according to claim 1, wherein the first elongated coupling lens has a meniscus shape that is concave toward the incident lens surface side of the roof prism lens. 3. The imaging element unit according to claim 1, wherein the second elongated coupling lens having a positive power in the arrangement orthogonal direction is arranged on the exit lens side of the roof prism lens, and the roof prism lens is anamorphic. An image forming element unit characterized by being a lens. 4. The imaging element unit according to claim 1, wherein a second long coupling lens having a positive power in the arrangement orthogonal direction is arranged on the exit lens side of the roof prism lens, and an intermediate image is formed in the arrangement orthogonal direction. An image forming element unit, wherein the image forming element unit is configured to be formed. 5. The imaging element unit according to claim 1, wherein a second long coupling lens having a negative power in a direction orthogonal to the arrangement is arranged on the exit lens side of the roof prism lens. Imaging element unit. 6. An optical writing unit for forming a light spot, a light emitting element array comprising a plurality of light emitting element array chips in which a plurality of light emitting elements are arranged at a predetermined interval, and a first elongated coupling. An image forming element unit including a lens and a roof prism lens array, wherein the first long coupling lens has a positive power in a direction orthogonal to the array, and is arranged on the incident lens surface side of the roof prism lens. The optical writing unit is characterized by being. 7. An imaging element comprising a light emitting element array in which a plurality of light emitting element array chips in which a plurality of light emitting elements are arranged at predetermined intervals are arranged, and a first long coupling lens and a roof prism lens array. In an image forming apparatus in which an optical writing unit including a child unit is used as an exposure unit, the first long coupling lens has a positive power in the direction orthogonal to the array, and the incident lens surface of the roof prism lens. An image forming apparatus, which is disposed on the side.