JP2000249978A - Image-formation element array, and optical printing head and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-formation element array capable of improving image-formation performance and obtaining an excellent image, and an optical printing head and an image forming device using the same. SOLUTION: In this image-formation element array 1 where plural equivalent image-formation elements are integrally arrayed, the image-formation element is provided with an incident surface 1a positioned on an incident side, an emitting surface 1b positioned on an emitting side, and two total reflection surfaces 1c which are paired for guiding luminous flux from the surface 1a to the emitting side. The surfaces 1a and 1b have aspherical shape and the arraying pitch of the image-formation element is set to <=1 mm.

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 array used in a solid-state scanning writing type digital writing optical system, an optical print head using the same, and an image forming apparatus. , Digital facsimile and the like.

[0002]

2. Description of the Related Art In recent years, as digital output devices such as digital copiers, printers and digital facsimile machines have become smaller, digital writing devices have been required to be smaller. At present, digital writing systems can be roughly classified into two types. One 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 image forming lens. This is a solid-state scanning method in which a light beam emitted from an element array light source is formed into a light spot by an imaging element array.

In the above-described optical scanning method, the light path length is increased because light is scanned by an optical deflector. On the other hand, in the solid-state scanning method, the optical path length can be made very short. There is an advantage that the whole can be reduced in size, and there is also an advantage that no mechanical driving parts such as an optical deflector are required.

[0004] The imaging element array used in the solid-state scanning method is mainly composed of a gradient index lens array,
The lens array can be classified into three types: a lens array as described in JP-A-344598, an in-prism lens array or a roof mirror lens array as described in JP-A-5-232400.

However, the imaging element arrays have the following optical problems for each of the above classifications. Since the refractive index distribution type lens array is formed by bundling the individual refractive index distribution type lenses and fixing each one with an adhesive or the like, the optical axes of the individual lenses are easily shifted, and the focal points vary. There is a problem that it is easy.

In the lens array described in Japanese Patent Application Laid-Open No. 6-344598, since an erecting system is not formed in the arrangement direction, it is necessary to provide a shielding structure for each lens, so that light transmission efficiency is low. In addition, there is a problem that the light amount unevenness is large.

The in-prism lens array described in Japanese Patent Application Laid-Open No. 5-232400 has a problem that, since the lens surface is spherical, sufficient optical performance cannot be obtained in configuring a writing device. In particular, there is a problem that the variation of the beam spot diameter becomes large.

Therefore, the applicant of the present application has arranged a plurality of imaging elements each having an entrance surface, an exit surface, and two pairs of total reflection surfaces integrally, and has an incident surface and an exit surface in an aspherical shape. By applying the method, an image forming element array capable of obtaining a small-diameter and stable light spot and obtaining sufficient optical performance for forming a writing apparatus has been filed earlier. That is described in Japanese Patent Application No. 10-282295.

On the other hand, the above-described solid-state scanning method has a problem that density unevenness is easily generated on an image, and white solid lines are easily generated on a black solid image. It was clarified from the experimental analysis results that the density unevenness occurs locally due to the variation of the light emitting element and the imaging element.

In addition, the above-described solid-state scanning method has a problem that in the case of a halftone image, uniform density cannot be maintained and density unevenness is likely to occur. This density unevenness
It can be confirmed from the experimental results of frequency analysis of the density that the density unevenness that occurs periodically corresponding to the lens pitch is performed on the output image using the same-magnification imaging lens array with a pitch of several mm. did it. Also, the arrangement pitch of the imaging elements is approximately 1 to 5 mm (lower frequency region 1 cycle / mm or less)
It is known that the density unevenness that occurs when is set to is the area where humans feel most sensitive.

The applicant of the present invention has reduced the unevenness in density locally and the unevenness in periodicity by reducing the arrangement pitch of the imaging elements constituting the imaging element array to 1 mm or less. Has been filed for an imaging element array capable of obtaining good images. Japanese Patent Application No. 10-28
This is the one described in JP 7460.

[0012]

As described above, the device disclosed in Japanese Patent Application No. 10-282295 has a plurality of imaging elements each having an entrance surface, an exit surface, and a pair of two total reflection surfaces. Since they are arranged integrally and the entrance surface and the exit surface are aspherical, a lens array as described in JP-A-6-344598 or an in-prism as described in JP-A-5-232400 is disclosed. Although the above problems with the lens array or the roof mirror lens array can be solved, there is still room for improvement.

That is, in the device disclosed in Japanese Patent Application No. 10-282295, the arrangement pitch of the imaging elements constituting the imaging element array is 1.8 mm.
It is difficult to reduce locally generated density unevenness and periodically generated density unevenness as in the invention described in Japanese Patent Application No. 0-287460. In addition, the above-mentioned Japanese Patent Application No. Hei 10-2822
In the device disclosed in Japanese Patent Publication No. 95, as shown in FIG. 12, the deviation of the aspherical surface between the incident surface and the outgoing surface from the spherical shape has an extreme value, and the aspherical shape is complicated.

The present invention is a further improvement of the invention described in Japanese Patent Application No. 10-282295 previously filed by the applicant of the present invention, which has an entrance surface, an exit surface and a pair of two total reflection surfaces. A plurality of imaging elements are integrally arranged, and the incident surface and the emission surface are aspherical, and further, by setting the arrangement pitch of the imaging elements to 1 mm or less, the imaging performance is further improved, It is an object of the present invention to provide an imaging element array capable of obtaining a good image, an optical print head using the same, and an image forming apparatus. Further, the present invention provides an imaging element array capable of improving workability and mass productivity by making the entrance surface and the exit surface into monotonous aspherical shapes, an optical print head using the same, and an image forming apparatus. The purpose is to provide.

[0015]

According to the first aspect of the present invention,
An imaging element array in which a plurality of equivalent imaging elements are integrally arranged, wherein each of the imaging elements has an entrance surface located on an incident side, an exit surface located on an exit side, and It has two pairs of total reflection surfaces for guiding the light beam to the emission side, the incident surface and the emission surface are aspherical, and the arrangement pitch of each imaging element is 1 mm or less. .

The invention according to claim 2 provides the invention according to claim 1.
In the light, the lens height is H, the paraxial radius of curvature is R, and the cone is
When the constant is K and the constants are A, B, C, and D, the aspheric surface
State X _ASP(H) is X_ASP(H) = H^Two/ [R + R√ ｛1
-(1 + K) (H / R)^Two｝] + AH^Four+ BH⁶+ CH⁸+
DH^Ten+ ... satisfied, spherical shape X_SPH(H) is X_SPH(H) = H^Two/ [R + R√ ｛1- (H / R)^Two｝], And the above-mentioned aspherical shape X_ASP(H) spherical shape X_SPH
Δ (H) = X_ASP(H)
-X_SPH(H), the lens height H becomes large
So that the deviation Δ (H) decreases monotonically as
Surface shape X_ASP(H) is set.
You.

According to a third aspect of the present invention, in the second aspect of the present invention, the entrance surface and the exit surface have the same aspherical shape, and each imaging element is an erecting unit in the arrangement direction. It is characterized by the following.

According to a fourth aspect of the present invention, in the third aspect of the invention, the angle formed by the incident optical axis and the outgoing optical axis is 90 degrees.
Degrees or more.

The invention according to claim 5 is the invention according to claims 1, 2,
5. An imaging element array according to 3 or 4, and a light-emitting element array, and a light beam from each light-emitting element constituting the light-emitting element array emits light of each imaging element constituting the imaging element array. The present invention relates to an optical print head that forms a light spot on a surface to be scanned via at least two or more imaging elements.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, an image is formed between at least one of between the light emitting element array and the imaging element array and between the imaging element array and the surface to be scanned. An opening means is provided so as to correspond to the arrangement pitch of the image element array.

According to a seventh aspect of the present invention, in the sixth aspect, the beam spot diameter is smaller than the light emitting element pitch.

An eighth aspect of the present invention relates to an image forming apparatus for forming an image, wherein the optical print head according to the fifth, sixth or seventh aspect is used as an exposure unit.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an imaging element array, an optical print head using the same, and an image forming apparatus according to the present invention will be described with reference to the drawings. As shown in FIGS. 1 to 3, the imaging element array 1
Is for imaging a light beam from each light emitting element of the light emitting element array 2 as a light spot on the surface to be scanned of the photoconductor 3, and the incident surface 1 a located on the incident side which is the light emitting element array 2 side And an emission surface 1b located on the emission side, which is the surface to be scanned of the photoconductor 3, and a pair of total reflection surfaces 1c that form a substantially right angle for guiding the light flux from the incidence surface 1a to the emission side. A plurality of equivalently formed imaging elements are integrally arranged and form an erecting unit-size system in the arrangement direction of the imaging elements.

The two pairs of total reflection surfaces 1c are 9
The roof prism forms an angle of 0 degrees, does not act on an image, and is inclined at 45 degrees with respect to the incident optical axis. In addition, a boundary portion between the entrance surface 1a and the exit surface 1b of the imaging element, and each edge of the entrance surface 1a and the exit surface 1b of the imaging device, which are parallel to the arrangement direction of the imaging device. ,
A rod-shaped rib portion 1d for enhancing positional accuracy during reinforcement and assembly is integrally formed. The shape of the rib 1d shown in FIG. 1 is an example. The angle between the incident optical axis and the outgoing optical axis is approximately 90 degrees.

The imaging element array 1 shown in FIGS. 1 to 3 has a roof prism lens array (RPLA) formed integrally with a roof prism lens array, an entrance lens array, and an exit lens array. Used.

As described above, the imaging element array 1 is an erecting equal-magnification system in the arrangement direction of the imaging elements. That is, the entrance surface 1a and the exit surface 1b are formed in the same aspherical shape, are optically equivalent, and extend from the object point of the light emitting element surface of the light emitting element array 2 to the incident surface 1a of the imaging element array 1. The distance and the distance from the exit surface 1b of the imaging element array 1 to the photoconductor 3
Are equal to the image point on the surface to be scanned. Accordingly, the distortion can be reduced to zero, the light transmission efficiency can be increased, and a brighter imaging system can be obtained. The specific description of the aspherical shape of the entrance surface 1a and the exit surface 1b will be described later.

A light beam emitted from one point on the light emitting element surface of the light emitting element array 2 enters the incident surface 1a of the imaging element array 1, is reflected by two pairs of total reflection surfaces 1c in order, and is emitted from the light emitting surface 1b. And reaches the scanning surface of the photoconductor 3. By the image forming action of the entrance surface 1a and the exit surface 1b, an image of one point on the light emitting element surface is changed to one image on the surface to be scanned of the photoconductor 3 corresponding thereto.
Tied to a point. In this manner, the images of a large number of light emitting element surfaces arranged in the light emitting element array 2 are formed in a line on the scanned surface of the photoconductor 3. This line direction is the main scanning direction. By controlling the on / off of a large number of light emitting elements arranged in the light emitting element array 2 while rotating the photosensitive member 3 and performing sub scanning, an image is formed on the surface to be scanned. Can be formed.

The imaging element array 1 is set so that the arrangement pitch of each imaging element is 1 mm or less as shown in FIG. As mentioned in the background section,
Density unevenness that occurs when the array pitch of the imaging elements is set to approximately 1 to 5 mm (low-frequency region 1 cycle / mm or less) is a region where humans feel most sensitive. Therefore, by setting the arrangement pitch of each imaging element to 1 mm or less and shifting the arrangement pitch from a region where human beings are most sensitive, even if periodic density unevenness occurs, it is not noticeable to human eyes. Density unevenness can be suppressed. Further, if the arrangement pitch of the imaging elements is set to 0.5 mm or less, it is possible to greatly shift the frequency range from the most sensitive frequency region to which human beings are most sensitive, and it is possible to suppress the density unevenness to be less noticeable.

As described above, the imaging element array 1 has
Each imaging element is formed integrally. An equal-magnification imaging element array such as a gradient-index lens array is formed by arranging respective imaging elements in the array arrangement direction and connecting the respective imaging elements by bonding or the like. There is a problem that local variations are apt to occur, such as an optical axis shift of each imaging element due to an error, and the assembling accuracy is lowered. In this way, the imaging elements are integrally formed. Thus, occurrence of local variation can be prevented, and assembling accuracy can be increased.

Although not shown, an image is formed between at least one of between the light emitting element array 2 and the imaging element array 1 and between the imaging element array 1 and the surface to be scanned of the photosensitive member 3. An aperture array as aperture means is provided so as to correspond to the arrangement pitch of the image element array 1. The aperture array is mainly for removing flare light,
It also has the role of beam shaping.

Each of the apertures of the aperture array is, for example, as shown in FIG.
As shown in the figure, the width of the imaging element array 1 in the direction orthogonal to the arrangement direction can be formed in a rectangular shape that is longer than the width in the arrangement direction, and the center of each aperture and the optical axis of each lens can be defined. They are provided to match. The opening is not limited to the rectangular shape, and may be formed in an elliptical shape, a rectangular shape in which four corners are formed in a round shape, or the like.

Next, the aspherical shapes of the entrance surface 1a and the exit surface 1b will be described. The aspherical shape X _ASP (H) of the entrance surface 1a and the exit surface 1b is given by: X _ASP (H) = H ² / [R + R√ ｛1− (1 + K) (H /
R) ² }] + AH ⁴ + BH ⁶ + CH ⁸ + DH ¹⁰ +... Where H: lens height, R: paraxial radius of curvature, K: conical constant, A, B, C, D: constant Is formed.

Here, the spherical shape X _SPH (H) is expressed as X _SPH (H) = H ² / [R + R {1- (H / R) ² }], and the aspherical shape X _ASP (H) Spherical shape X
_{When the} deviation Δ (H) with respect to _SPH (H) is Δ (H) = X _ASP (H) −X _SPH (H), the deviation Δ (H) monotonously decreases as the lens height H increases. Aspherical shape X
_ASP (H) is set. More specifically, the shift Δ (H) is determined by a certain lens height H, as shown in FIG.
Spherical shape X _SPH (H) and aspherical shape X _ASP (H)
Is the difference.

Hereinafter, a description will be given with specific optical data. As shown in FIG. 3, the distance from the object point on the light emitting element surface of the light emitting element array 2 to the incident surface 1a of the imaging element array 1 is L1, and the distance from the emission surface 1b of the imaging element array 1 to the photosensitive member 3 is L1. L2, the distance to the image point on the surface to be scanned
Is the distance on the optical axis from the pair of total reflection surfaces 1c to D
The distance on the optical axis from the pair of total reflection surfaces 1c and the exit surface 1b is D2.

(Unit: mm) L1 = L2 = 9.0 D1 = D2 = 1.6 Refractive index = 1.525 Array pitch = 0.9 (Aspherical shape of incident surface 1a) R = 4.721 K = 14.28887 A = -2.2693E-2 B = 0.0 C = 0.0 D = 0.0 (Aspherical shape of exit surface 1b) ) R = −4.721 K = 14.2888 A = 2.2693E−2 B = 0.0 C = 0.0 D = 0.0

Next, the beam spot diameter (1/1 /
shows data e ² diameter). As shown in FIG. 5, the lens height H is at two locations, H = 0.0 and H = 0.45, and H = 0.0 is on the optical axis of a certain imaging element 10. , H = 0.45 is a joint position between the imaging element 10 and the imaging element 11 adjacent to the imaging element 10.
As described above, a plurality of imaging elements of the imaging element array 1 are integrally arranged at a pitch of 0.9 mm in the arrangement direction. Reference numeral 5 denotes an aperture array formed in a flat plate shape. Further, the light emitting element array 2 has a capacity of 600 dp.
Assuming an i-th LED array, a 20 μm × 20 μm planar perfect diffusion light source is used.

<Data of Beam Spot Diameter (1 / e ² Diameter)> (array direction) (array orthogonal direction) H = 0.0 H = 0.45 H = 0.0 H = 0.45 29 μm 30 μm 30 μm 30 μm

As shown in the above data, the beam spot diameter has substantially the same value in both the array arrangement direction and the direction orthogonal to the array arrangement direction.
The values are almost the same at the two lens heights.
In addition, the beam spot diameter also depends on the light emitting element pitch (42.3μ).
m). Therefore, the toner image on the image can be formed into an image close to the pitch of the light emitting elements, and a stable and small beam spot diameter can be obtained.

FIG. 6 shows the spherical aberration at this time. As shown in FIG. 6, it can be seen that the spherical aberration is reduced regardless of the relative lens height position. As can be seen, by making the entrance surface 1a and the exit surface 1b aspherical, the spherical aberration is kept constant irrespective of the lens height position, as compared with the case where both the entrance surface and the exit surface are formed spherical. Thus, the imaging performance of each imaging element and the imaging element array can be improved.

FIG. 7 shows the aspherical shape X at this time.
Deviation Δ (H) of _ASP (H) with respect to spherical shape X _SPH (H)
Is shown. As described above, this deviation Δ (H) is, when the spherical shape X _SPH (H) is expressed as X _SPH (H) = H ² / [R + R {1− (H / R) ² }], (H) = X _ASP (H) −X _SPH (H)

As shown in FIG. 7, it can be seen that the deviation Δ (H) monotonously decreases as the lens height H increases. That is, the aspherical shape X _ASP (H) is set such that the deviation Δ (H) monotonously decreases as the lens height H increases. In this way, by making the entrance surface 1a and the exit surface 1b monotonous aspherical shapes, as shown in FIG. 12, the deviation of the entrance surface and the exit surface from the aspherical shape with respect to the spherical shape has an extreme value. Therefore, the workability and mass productivity of the imaging element array can be improved.

Next, optical data of another specific example will be described. Note that, as shown in FIG. 3, the incident surface 1 of the imaging element array 1 is shifted from the object point of the light emitting element surface of the light emitting element array 2.
L1 is the distance from the exit surface 1b of the imaging element array 1 to the image point of the scanned surface of the photoreceptor 3 on the optical axis from the incident surface 1a to the pair of total reflection surfaces 1c. Is D1, and the distance on the optical axis from the pair of total reflection surfaces 1c to the emission surface 1b is D2.

(Unit: mm) L1 = L2 = 6.0 D1 = D2 = 1.0 Refractive index = 1.525 Array pitch = 0.6 (Aspherical shape of entrance surface 1a) R = 3.148 K = 18.4257 A = -9.6487E-2 B = 0.0 C = 0.0 D = 0.0 (Aspherical shape of exit surface 1b) ) R = -3.148 K = 18.4257 A = 9.6487E-2 B = 0.0 C = 0.0 D = 0.0

Next, the beam spot diameter (1/1 /
shows data e ² diameter). As shown in FIG. 8, the lens height H is at two locations, H = 0.0 and H = 0.30, and H = 0.0 is on the optical axis of a certain imaging element 10. , H = 0.30 is the joint position between the imaging element 10 and the imaging element 11 adjacent to the imaging element 10.
As described above, a plurality of imaging elements of the imaging element array 1 are integrally arranged at a pitch of 0.6 mm in the arrangement direction. Reference numeral 6 denotes an aperture array having a wide shielding width. In addition, the light emitting element array 2
Assuming a LED array of dpi, a 20 μm × 20 μm planar perfect diffusion light source is used.

<Data of Beam Spot Diameter (1 / e ² Diameter)> (array direction) (array orthogonal direction) H = 0.0 H = 0.30 H = 0.0 H = 0.30 27 μm 27 μm 28 μm 29 μm

As shown in the above data, the beam spot diameter has substantially the same value in both the array arrangement direction and the direction orthogonal to the array arrangement direction.
The values are almost the same at the two lens heights.
In addition, the beam spot diameter also depends on the light emitting element pitch (42.3μ).
m). Therefore, the toner image on the image can be formed into an image close to the pitch of the light emitting elements, and a stable and small beam spot diameter can be obtained.

FIG. 9 shows the spherical aberration at this time. As shown in FIG. 9, it can be seen that the spherical aberration is reduced regardless of the relative lens height position. As can be seen, by making the entrance surface 1a and the exit surface 1b aspherical, the spherical aberration is kept constant irrespective of the lens height position, as compared with the case where both the entrance surface and the exit surface are formed spherical. Thus, the imaging performance of each imaging element and the imaging element array can be improved.

FIG. 10 shows the deviation Δ of the aspherical shape X _ASP (H) from the spherical shape X _SPH (H) at this time.
(H) is shown. As described above, this deviation Δ (H) is, when the spherical shape X _SPH (H) is expressed as X _SPH (H) = H ² / [R + R {1− (H / R) ² }], (H) = X _ASP (H) −X _SPH (H)

As shown in FIG. 10, the deviation Δ (H) monotonously decreases as the lens height H increases. That is, the aspherical shape X _ASP (H)
The deviation Δ (H) is set to decrease monotonously as the lens height H increases. In this way, by making the entrance surface 1a and the exit surface 1b monotonous aspherical shapes, as shown in FIG. 12, the deviation of the entrance surface and the exit surface from the aspherical shape with respect to the spherical shape has an extreme value. hand,
The processability and mass productivity of the imaging element array can be improved.

As shown in FIG. 11, the imaging element array 1 has an incident optical axis of a light beam emitted from the light emitting elements of the light emitting element array 2 and an output light beam emitted to the surface to be scanned of the photosensitive member 3. The angle θ formed by the light emitting axis can be 90 degrees or more. Thus, the angle θ between the input optical axis and the output optical axis,
That is, by setting the optical path separation angle to 90 degrees or more,
The degree of freedom for optical path separation can be increased. In particular, when the image forming element array 1 is combined with the light emitting element array 2 to form an optical print head, and this is incorporated in an image output device, positional interference between the optical print head and the photosensitive body 3 and the periphery of the photosensitive body 3 Since it is possible to avoid positional interference with other units disposed in the device, the density of the device can be increased.

The imaging element array 1 can be used as an imaging element array of an optical print head. That is, it has the above-mentioned imaging element array 1 and the light-emitting element array 2, and the light flux from each light-emitting element constituting the light-emitting element array 2, among the respective imaging elements constituting the imaging element array 1,
An optical print head that forms a light spot on the scanned surface of the photoconductor 3 via at least two or more imaging elements can be provided. Therefore, a brighter optical system can be obtained as compared with an imaging element array including an inverted imaging system.

As described above, the imaging element array 1 is located between at least one of the area between the light emitting element array 2 and the imaging element array 1 and between the imaging element array 1 and the surface to be scanned of the photosensitive member 3. An opening means for removing flare light can be provided so as to correspond to the arrangement pitch. In the related art, flare light is removed by forming a cutout groove at a joint between imaging elements or by sandwiching a light blocking member at a joint between imaging elements. However, when a notch groove is formed at the joint of the imaging elements, the thickness of the portion where the notch groove is formed becomes extremely thin, so that the strength is weak and handling is difficult. Further, when an imaging element is manufactured by a molding method such as injection molding, it is difficult to process the resin because the resin is difficult to pass through. Further, it is very difficult to process the gold piece in the shape in which the notched groove is formed. On the other hand, when a light-blocking member is sandwiched between the image forming elements, it is possible to manufacture the image forming element array by connecting the individual image forming elements, but it is very difficult to manufacture the image forming element array by integral molding. Therefore, in order to obtain good beam shaping without deteriorating the workability of the imaging element, it is preferable to provide the aperture array as described above. In addition,
Each aperture of the aperture array is desirably formed large in a direction orthogonal to the arrangement direction in order to obtain a larger amount of light. Further, as the opening means, a non-transmissive member can be provided directly on the lens surface.

Further, in the above optical print head, the beam spot diameter can be made smaller than the light emitting element pitch. In the field of the writing optical system, the beam spot diameter has been reduced with the increase in the density of the apparatus, and a small and stable light spot has been required.
This is because a good image can be obtained by reducing the beam spot diameter. As you know,
In the electrophotographic process, a latent image is formed on a photoreceptor by a light spot (exposure), toner is attached (development), the toner image is transferred to a transfer paper, and fixed on the transfer paper by pressure or heat. The toner image is spread by performing the above-described development, transfer, and fixing steps, so that the toner image on the image is larger than the light spot on the photoconductor. Therefore, by making the beam spot diameter smaller than the light emitting element pitch, a toner image on an image can be formed into an image close to the light emitting element pitch.

The optical print head forms a latent image by irradiating a light spot from the optical print head onto a photosensitive member (exposure), and forms a toner image by adhering toner to the latent image. It can be used as an exposure unit in an image forming apparatus that forms an image by an electrophotographic process of (developing), transferring the toner image to transfer paper (transfer), and fixing the image on the transfer paper by pressure or heat (fixing).

[0055]

According to the first aspect of the present invention, there is provided an imaging element array in which a plurality of equivalent imaging elements are integrally arranged, wherein each of the imaging elements is an incident surface located on an incident side. And an exit surface located on the exit side, and a pair of two total reflection surfaces for guiding a light beam from the entrance surface to the exit side, wherein the entrance surface and the exit surface are aspherical. Since the arrangement pitch of the image elements is 1 mm or less, the following effects can be obtained. In other words, since a plurality of equivalent imaging elements are integrally arranged, it is possible to suppress the deviation of the optical axis of each lens and the variation of the focal point. Further, since the entrance surface and the exit surface are formed in an aspherical shape, the imaging performance of the imaging element array and the imaging element can be improved, and a stable beam spot diameter can be obtained. Further, since the arrangement pitch of each imaging element is set to 1 mm or less, it is possible to suppress the density unevenness that is hardly noticeable to human eyes and to reduce the diameter of the beam spot.

According to the second aspect, in the first aspect, the lens height is H, the paraxial radius of curvature is R, the conic constant is K, and the constants are A, B, C, and D. When
The aspherical shape X _ASP (H) is given by X _ASP (H) = H ² / [R +
R√ {1- (1 + K) (H / R) 2}] + AH 4 + BH 6
+ CH ⁸ + DH ¹⁰ +...
_SPH (H) _{is, X SPH (H) = H} 2 / [R + R√ {1-
(H / R) ² }], and the aspherical shape X _ASP (H)
Of the spherical shape X _SPH (H) to Δ
When (H) = X _ASP (H) −X _SPH (H), the aspherical shape X _ASP (H) is set such that the deviation Δ (H) monotonously decreases as the lens height H increases. Therefore, the workability and mass productivity of the imaging element array can be improved as compared with the case where the deviation between the aspheric surface and the spherical surface between the entrance surface and the exit surface has an extreme value.

According to a third aspect of the present invention, in the second aspect of the present invention, the entrance surface and the exit surface have the same aspherical shape, and each imaging element is an erecting equal-magnification system in the arrangement direction. Therefore, the distortion can be reduced to zero,
Light transmission efficiency can be increased, and a brighter imaging system can be obtained.

According to the fourth aspect of the present invention, in the third aspect of the present invention, the angle between the incident optical axis and the outgoing optical axis is 90 degrees or more, so that the degree of freedom for optical path separation can be increased. it can.

According to the fifth aspect of the present invention,
5. An imaging element array according to 2, 3, or 4, and a light-emitting element array, and a light flux from each light-emitting element constituting the light-emitting element array is transmitted to each imaging element constituting the imaging element array. Since a light spot is formed on the surface to be scanned through at least two or more imaging elements, a brighter optical system can be obtained as compared with an imaging element array including an inverted imaging system. .

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, at least one of between the light emitting element array and the imaging element array or between the imaging element array and the surface to be scanned. Since the aperture means is provided so as to correspond to the arrangement pitch of the imaging element array, good beam shaping can be obtained without deteriorating the workability of the imaging element.

According to the invention of claim 7, in the invention of claim 6, since the beam spot diameter is smaller than the light emitting element pitch, a toner image on an image is formed into an image close to the light emitting element pitch. be able to.

According to an eighth aspect of the present invention, in an image forming apparatus for forming an image, the optical print head according to the fifth, sixth or seventh aspect is used as an exposure unit, so that the imaging performance is improved. And transmission efficiency can be improved, so that good images can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment according to the present invention.

FIG. 2A is an equivalent optical system diagram viewed from a direction orthogonal to the array arrangement,
(B) is an equivalent optical system diagram viewed from the array arrangement direction.

FIG. 3 is a side view showing the embodiment.

FIG. 4 is a front view showing an aperture array applicable to the present invention.

FIG. 5 is an optical layout diagram showing the imaging element array of the embodiment.

FIG. 6 is a diagram of spherical aberration in the embodiment.

FIG. 7 is an aspherical surface shape X in the above embodiment.
Deviation Δ (H) of _ASP (H) with respect to spherical shape X _SPH (H)
FIG.

FIG. 8 is an optical layout diagram showing an imaging element array according to another embodiment.

FIG. 9 is a diagram of spherical aberration in the embodiment.

FIG. 10 shows an aspherical shape X in the above embodiment.
Deviation Δ (H) of _ASP (H) with respect to spherical shape X _SPH (H)
FIG.

FIG. 11 is an optical layout diagram showing an embodiment of an optical print head applicable to the present invention.

FIG. 12 is a graph showing a shift Δ (H) of a conventional aspherical shape X _ASP (H) with respect to a spherical shape X _SPH (H).

FIG. 13: Spherical shape X of aspherical shape X _ASP (H)
FIG. 9 is a graph showing a shift Δ (H) with respect to _SPH (H).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Imaging element array 1a Incident surface 1b Emission surface 1c Two pair of total reflection surfaces 1d Rib portion 2 Light emitting element array 3 Photoconductor 5 Opening array 6 Opening array

Claims (8)

[Claims] 1. An imaging element array in which a plurality of equivalent imaging elements are integrally arranged, wherein each of said imaging elements has an incident surface located on an incident side and an exit surface located on an exit side. And a pair of two total reflection surfaces for guiding a light beam from the entrance surface to the exit side. The entrance surface and the exit surface are aspherical, and the arrangement pitch of each imaging element is 1 mm or less. An imaging element array, characterized in that: 2. When the lens height is H, the paraxial radius of curvature is R, the conic constant is K, and the constants are A, B, C, and D, the aspherical shape X _ASP (H) is X _ASP (H ) = H ² / [R + R√ ｛1- (1 + K) (H /
R) ² ｝] + AH ⁴ + BH ⁶ + CH ⁸ + DH ¹⁰ +..., And the spherical shape X _SPH (H) is as follows: X _SPH (H) = H ² / [R + R√ ｛1− (H / R) ² ｝], and the deviation Δ (H) of the aspherical shape X _ASP (H) from the spherical shape X _SPH (H) is defined as Δ (H) = X _ASP (H) −X _SPH (H). 2. The imaging element array according to claim 1, wherein the aspherical shape X _ASP (H) is set such that the deviation Δ (H) monotonously decreases as the lens height H increases. 3. The imaging element array according to claim 2, wherein said entrance surface and said exit surface have the same aspherical shape, and each imaging element is an erecting unit-size system in the arrangement direction. . 4. The angle formed between the input optical axis and the output optical axis is 9
The imaging element array according to claim 3, wherein the angle is 0 ° or more. 5. A light-emitting element array comprising: the imaging element array according to claim 1; and a light-emitting element array. Of the imaging elements constituting the imaging element array,
An optical print head, wherein a light spot is formed on a surface to be scanned via at least two or more imaging elements. 6. A method according to claim 1, wherein the light emitting element array and the imaging element array are
6. The optical print according to claim 5, wherein an opening means is provided between at least one of the imaging element array and the surface to be scanned so as to correspond to an arrangement pitch of the imaging element array. head. 7. The optical print head according to claim 6, wherein the beam spot diameter is smaller than the light emitting element pitch. 8. An image forming apparatus for forming an image, wherein the optical print head according to claim 5, 6 or 7 is used as an exposure unit.