JP2007223298A - Electrooptical device and image printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrooptical device which can readily improve the quality of an electrostatic latent image formed on an image carrier by efficiently utilizing a flux of light from light emitting elements, appropriately reserving the distances between convex lenses and the image carrier, and reducing the influence caused by the eccentricity of the image carrier. <P>SOLUTION: The electrooptical device 10 has a light emitting panel 12 which has a plurality of light emitting elements and a micro-lens array 16 which keeps a plurality of convex lenses 18 respectively opposed to the light emitting elements for deflecting the light emitted from the corresponding light emitting elements disposed to integrate the convex lenses 18. The curvature radius R1 of the convex lens 18 in the light emitting panel 12 side is equal to or more than the curvature radius R2 of the convex lens 18 in the opposite side of the light emitting panel 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electro-optical device and an electrophotographic image printing apparatus having the same.

In order to write an electrostatic latent image on an image carrier (for example, a photosensitive drum or a photosensitive belt) of an electrophotographic image printing apparatus, light emission such as an electroluminescent element (hereinafter referred to as an “EL element”) is used. A technique using a light emitting panel in which elements are arranged has been developed. In such a technique, for example, as described in Patent Document 1, a converging lens array is disposed between a light emitting panel and an image carrier. An example of a converging lens array is SLA (Selfoc Lens Array) available from Nippon Sheet Glass Co., Ltd. (Selfoc \ SELFO).
C is a registered trademark of Nippon Sheet Glass Co., Ltd.). The converging lens array has a large number of gradient index lenses, and each gradient index lens can form an upright image on an image carrier with respect to an image obtained by a plurality of light emitting elements on a light emitting panel. Thus, the images obtained by the plurality of gradient index lenses constitute one continuous image. However, in the converging lens array, the light beam that travels from the light emitting panel and does not enter the gradient index lens is wasted.

Therefore, for example, as disclosed in Patent Document 2 and Patent Document 3, a large number of convex lenses are used to write an electrostatic latent image on an image carrier of an electrophotographic image printing apparatus. According to the technique of Patent Document 2, a large number of convex lenses are superimposed on a large number of light emitting array chips, and each convex lens refracts a light beam from the facing light emitting array chip. The refracted light reaches the image carrier and forms an electrostatic latent image here. Here, since one light emitting array chip has a plurality of light emitting sources, light from the plurality of light emitting sources enters one convex lens.

According to the technique of Patent Document 3, a large number of light-emitting elements and a large number of spherical convex lenses (ball lenses)
Are stacked, and each ball lens focuses the light flux from the opposing light emitting elements. The focused light reaches the image carrier and forms an electrostatic latent image there.

JP-A-10-55890 JP-A-8-166556 JP 2003-260811 A

The above-described refractive index distribution type lens of the converging lens array can project an erect image of the image on the light emitting panel onto the image carrier, but when using a convex lens as an electrostatic latent image writing device, Each convex lens projects an inverted image of the image on the light emitting panel onto the image carrier. Therefore, as in Patent Document 2, when light from a plurality of light sources is refracted by one convex lens, an inverted image of an image specified by the plurality of light sources is formed on the image carrier as an electrostatic latent image. . That is, it is difficult to obtain a desired electrostatic latent image on the image carrier. Further, for example, when a light emitting element having a wide emission angle of a light beam such as an EL element is used as a light source, an electrostatic latent image is obtained by refracting light beams of a plurality of light emitting elements having a wide emission angle by a convex lens. The electrostatic latent image is extremely disturbed.

According to the technique described in Patent Document 3, loss of light flux can be reduced by reducing the distance between the light source and the lens. In addition, since one ball lens is superimposed on one light emitting element, extreme image disturbance is suppressed. However, in the ball lens, the distance between the principal point (surface vertex) on the light emitting panel side and the principal point on the image carrier side in the lens is uniquely determined by the radius of curvature of the lens. It is difficult, and it is difficult to form a clear electrostatic latent image on the image carrier.

When a large number of convex lenses are used to write an electrostatic latent image on the image carrier, it is preferable to bring the lens and the light emitting element close to each other in order to efficiently use the light flux from the light emitting element. However, in the case of a conventional convex lens including a ball lens, if the distance between the lens and the light emitting element is reduced, the distance between the convex lens and the image carrier must be reduced. When the distance between the lens and the image carrier is very small, the floating toner peeled off from the image carrier may easily adhere to the convex lens, and the roll for rotating the photosensitive drum or the photosensitive belt is eccentric. In this case, the rate of change in the distance between the lens and the image carrier as the image carrier runs is extremely large.

Therefore, the present invention efficiently forms the light beam from the light emitting element, secures an appropriate distance between the convex lens and the image carrier, and reduces the influence of the eccentricity of the image carrier, thereby forming the image carrier. An electro-optical device that can easily improve the quality of an electrostatic latent image and an electrophotographic image printing apparatus having the same.

The electro-optical device according to the present invention includes a light-emitting panel in which a plurality of light-emitting elements are arranged, and a plurality of convex lenses that face the light-emitting elements and refract light that travels from the corresponding light-emitting elements. And an integrated microlens array. The radius of curvature of each convex lens on the light emitting panel side is equal to or larger than the radius of curvature of each convex lens on the side opposite to the light emitting panel.

According to the present invention, since the radius of curvature of each convex lens on the side of the light emitting panel is equal to or larger than the radius of curvature on the opposite side, the distance between the light emitting panel in which the light emitting elements having small areas are arranged and each convex lens can be reduced, While it is possible to efficiently use the light flux from the light emitting element, the distance between the convex lens and the light emitting panel and the distance between the convex lens and the light emitting panel is greater than the distance between the convex lens and the light emitting panel. Since it can be secured appropriately long, the possibility that floating toner adheres to the convex lens is reduced, and even when the photosensitive drum or the like is decentered, the distance between the lens and the image carrier as the image carrier travels The rate of change of is reduced. Further, since a microlens array is used instead of a ball lens, the thickness of the convex lens can be arbitrarily determined, and the electrostatic path formed on the image carrier can be determined by appropriately determining the path of the light beam passing through the convex lens. It is easy to improve the quality of the latent image.

Furthermore, the distance between the principal point of each convex lens on the light emitting panel side and the principal point on the opposite side of the light emitting panel of each convex lens is preferably 0.2 mm or more and 0.6 mm or less. If the distance between the principal points of each convex lens on the side opposite to the light emitting panel (that is, the maximum thickness of the convex lens) is smaller than 0.2 mm, the mechanical strength of the microlens array is lowered. On the other hand, the greater the distance between the principal points on the opposite side of the light emitting panel in each convex lens (that is, the maximum thickness of the convex lens), the lower the optical power of the light beam irradiated from the lens onto the image carrier. That is, paying attention to the distance between the principal point on the light emitting panel side of each convex lens and the principal point on the opposite side of the light emitting panel of each convex lens, and setting such conditions, while maintaining the mechanical strength of the convex lens, Compared with the case where a specific focusing lens is used, it is possible to obtain a power twice or more.

It is preferable that the light emitted from each light emitting element travels in a direction parallel to or diverging from the central axis of each convex lens inside each convex lens. In other words, except that the traveling path of the light emitted from each light emitting element inside each convex lens travels along the central axis of each convex lens itself, each convex lens becomes parallel to the central axis of each convex lens or farther from the light emitting panel. It is preferable to move away from the central axis of the. In such an aspect, compared with the case where light converges inside each convex lens, the light flux emitted from each convex lens is likely to gather in a narrow range, so that it is easy to increase the light collection efficiency. Further, in such an aspect, the quality of the electrostatic latent image is less uneven even when the distance between the lens and the image carrier is varied as compared with the case where the light converges inside each convex lens.

An image printing apparatus according to the present invention forms a latent image on a charged surface of an image carrier by light emitted from a light emitting element and transmitted through each convex lens, the image carrier, a charger for charging the image carrier. The electro-optical device includes a developer that forms a visible image on the image carrier by attaching toner to the latent image, and a transfer device that transfers the visible image from the image carrier to another object.

Further, the average distance between the convex lens and the image carrier when the image carrier travels is 0.03 smaller than the distance between the convex lens and the position where the area of the light beam emitted from the light emitting element and transmitted through each convex lens converges to the minimum. To 0.07 mm shorter. “0.03 to 0.07 mm shorter” means
It includes not only the value between 0.03 mm and 0.07 mm but also the case where it is just 0.03 mm shorter and just 0.07 mm shorter. The actually manufactured light emitting device has a certain area. For example, when the light emitting element is circular, the diameter is several tens of μm, which is approximately a fraction of the radius of curvature of the lens, and when the light emitting element is square, one piece is several tens of μm. Since the light source has a certain area in this way, the light refracted by the lens converges on a certain area range instead of a single point. As the distance between the lens and the image carrier changes, the area and power of the light beam that converges on the image carrier changes. For example, since the above-mentioned ball lens has a small depth of focus, the tolerance of the distance between the lens and the image carrier is small, and the image carrier and the lens are caused by the eccentricity of the photosensitive drum or the roll that rotates the photosensitive belt. Variation in the distance of the electrostatic latent image tends to cause unevenness in the quality of the electrostatic latent image. In contrast, if the average distance between the convex lens and the image carrier is 0.03 to 0.07 mm shorter than the distance between the convex lens and the position where the area of the light beam emitted from the light emitting element and transmitted through the convex lens converges to the minimum. Even if the distance between the lens and the image carrier deviates from a certain reference distance, the change in the effective size of the electrostatic latent image and the change in the power of the electrostatic latent image are small. Therefore, the tolerance of the distance between the lens and the image carrier is large, and even if the distance between the lens and the image carrier due to the eccentricity of the photosensitive drum or the like varies, the unevenness of the quality of the electrostatic latent image is small.

The thickness of the transparent member that covers the side of the light emitting panel that emits light of the light emitting element is t (mm),
When the refractive index of the transparent member is n, the distance between the light emitting element and the convex lens is 0.3 mm−t / n.
The following is preferable. Furthermore, the distance between the light emitting element and the convex lens is preferably 0.2 mm-t / n or less. As in the present invention, in an optical system that refracts light from one light emitting element with one convex lens, the proportion of the light incident on the convex lens becomes smaller in the light from the light source as the position of the convex lens is further away from the light source. Become. Therefore, the distance between the light emitting element and the convex lens is 0.3 mm−t /
It is preferably n or less, and more preferably 0.2 mm-t / n or less.

Hereinafter, various embodiments according to the present invention will be described with reference to the accompanying drawings. In the drawings, the ratio of dimensions of each part is appropriately different from the actual one.
<First Embodiment>
FIG. 1 is a cross-sectional view showing an electro-optical device according to an embodiment of the present invention, and FIG. 2 is a plan view of the electro-optical device. More specifically, FIG. 1 is a cross-sectional view taken along the line II in FIG. 2, and FIG. 2 is a view taken along the line II-II in FIG.

An electro-optical device 10 illustrated in the figure is a line type exposure head for writing a latent image on an image carrier (for example, a photosensitive drum 110 rotating around an axis 20) in an image printing apparatus using an electrophotographic system. Used as The electro-optical device 10 includes a light emitting panel 12 in which a plurality of light emitting elements 14 having the same shape and size are arranged on the same plane, and a microlens array 16 superimposed on the light emitting panel 12.

In this embodiment, the light emitting element 14 is an organic light emitting diode (Organic Light Emitting).
Diode (hereinafter abbreviated as “OLED”) element or inorganic light-emitting diode element, and each light-emitting element 14 emits light according to a flowing current. The light emitting panel 12 includes a flat substrate, and the light emitting element 14 is formed on the substrate. The sealing body which protects the light emitting element 14 from external air is joined to the board | substrate. The light emitted from the light emitting element 14 may be emitted through the substrate or may be emitted through the sealing body on the opposite side of the substrate.

As shown in FIG. 2, the light emitting elements 14 are arranged in two rows and a staggered pattern. The arrangement pattern of the light emitting elements 14 is not limited to the illustrated form, and may be a single row or three or more rows, or may be arranged in another appropriate pattern.

The microlens array 16 is a transparent body and has a plurality of isomorphisms arranged on the same plane.
It has a convex lens 18 of the same size. These convex lenses 18 are joined by a flat plate portion 17 of the microlens array 16. More precisely, the microlens array 16 having the flat plate portion 17 and the convex lens 18 is integrally formed. Each of the illustrated convex lenses 18 includes a flat plate portion 17.
A portion protruding from one side to the other side and a portion protruding to the other side are asymmetric biconvex lenses across the flat plate portion 17. Specifically, the surfaces 18a and 18b of the portion protruding from the flat plate portion 17 are substantially part of a sphere, and the curvature radius R1 of the lens surface 18a on the light emitting panel 12 side of each convex lens 18 is.
Is the lens surface 18 of each convex lens 18 on the side opposite to the light emitting panel 12 (photosensitive drum 110 side).
It is more than the curvature radius R2 of b. However, it may not be a biconvex lens, and a planoconvex lens in which the radius of curvature R1 of the lens surface 18a on the light emitting panel 12 side is infinite may be used.

As shown in FIG. 2, each of these convex lenses 18 concentrically overlaps each of the light emitting elements 14. Accordingly, each convex lens 18 refracts and converges the light beam from the facing light emitting element 14 and forms an image on the photosensitive drum 110.

The light emitting panel 12 and the microlens array 16 are supported substantially parallel to the shaft 20 of the photosensitive drum 110. An interval L1 between each convex lens 18 and the light emitting panel 12 is equal to or less than an interval L2 between each convex lens 18 and the photosensitive drum 110. This is because the curvature radius R1 of the lens surface 18a on the light emitting panel 12 side of the convex lens 18 is greater than or equal to the curvature radius R2 of the lens surface 18b on the photosensitive drum 110 side. A light beam emitted from the light emitting element 14 of the light emitting panel 12 travels in the air between the light emitting panel 12 and the convex lens 18, is incident on the convex lens 18 at the lens surface 18 a, and is refracted inward. Then, the light is emitted from the convex lens 18 into the air through the lens surface 18 b and refracted inward, and reaches the photosensitive drum 110. By setting R1 ≧ R2, the light flux can be appropriately converged on the photosensitive drum 110 even if L1 ≦ L2.

The microlens array 16 is made of, for example, a transparent resin, and the refractive index is preferably 1.4 or more and 1.7 or less. If the refractive index of the microlens array 16 is smaller than 1.4, the difference from the refractive index of air (about 1) is small, so the refraction angle of the light beam at the interface between the air and the convex lens (lens surfaces 18a, 18b) Small and wasteful of luminous flux increases. When the refractive index of the microlens array 16 is larger than 1.7, the refraction angle of the light beam emitted from the lens surface 18b becomes remarkably large, and condensing is difficult.

FIG. 3 is a graph showing a change in light flux power with respect to a change in distance from a light source (light emitting element) assuming that the light emitting element is a circular OLED element having a diameter of 40 μm. This graph was obtained by simulation. In the simulation, the light emitting element is assumed to be a circular OLED element. However, the present invention is not intended to be limited to a circular light emitting element, and the light emitting element may have other shapes. The unit of power is w (watts), but the vertical axis of the graph is normalized with the power when the distance from the light source is 0 as 1.

As shown in FIG. 3, when the distance from the light source is 0, the power of the light beam from the light emitting element is maximum, but the power gradually decreases as the distance from the light source becomes longer due to the emission of the light beam. That is, in the optical system that refracts light from one light emitting element with one convex lens as in this embodiment, the more the convex lens is moved away from the light source, the smaller the substantial aperture angle of the convex lens (light source The ratio of the light incident on the convex lens out of the light from is small). For example, if the distance from the light source is only 0.5 mm, only 10% of the power at the light source is incident on the convex lens. As described at the beginning of this specification, an optical system using a convex lens as in this embodiment originally solves the power loss problem of the focusing lens array. If only 10% is incident on the lens, only the use efficiency equal to or lower than that of the converging lens array can be obtained, and the meaning of using the microlens array is diminished. In an optical system using a convex lens as in this embodiment, it is desirable that the distance between the light source and the convex lens be 0.3 mm or less. In this case, a light beam having a power 1.3 times that of the converging lens array enters the lens. Furthermore, it is desirable that the distance between the light source and the convex lens be 0.2 mm or less. In this case, 40% of the power at the light source is incident on each convex lens.
That is, when the light emitting element is a circular OLED element having a diameter of 40 μm, each convex lens 1
The distance L1 (see FIG. 1) between 8 and the light-emitting panel 12 is preferably 0.3 mm or less,
More preferably, it is 0.2 mm or less. Strictly speaking, L1 ≦ 0.3 mm−t / n is desirable, and L1 ≦ 0.2 mm−t / n is desirable. Here, t represents the light emitting panel 1 that covers the side of the light emitting element 14 that emits light, and is between the light emitting element 14 and the lens 18.
2 is the thickness (mm) of the transparent member (transparent substrate or transparent sealing body), and n is the refractive index of the transparent member.

On the other hand, in order to reduce the possibility that the floating toner peeled off from the photosensitive drum 110 adheres to the convex lens 18, it is desirable that the distance between the convex lens 18 and the photosensitive drum 110 is large. Also,
In order to reduce the rate of change in the distance between the convex lens 18 and the photosensitive drum 110 as the photosensitive drum 110 travels (rotates) even if the photosensitive drum 110 is decentered, the distance between the convex lens 18 and the photosensitive drum 110 is The larger one is still desirable. This is because the change in the distance accompanying the running of the photoconductor drum 110 leads to a change in the size of the electrostatic latent image on the photoconductor drum 110 and a change in the light energy applied to the photoconductor drum 110. For these reasons, the photosensitive drum 1
The average distance between the convex lens 18 and the photosensitive drum 110 when the 10 travels is preferably 0.4 mm or more.

In this embodiment, since the distance L1 between the convex lens 18 and the light emitting panel 12 can be reduced, the light flux from the light emitting element 14 can be used efficiently, while the light emitting panel 12 is sandwiched between the convex lenses 18. L between the photosensitive drum 110 and the convex lens 18 on the opposite side
2 can be secured appropriately long so as to be equal to or greater than L1, so that the floating toner is less likely to adhere to the convex lens 18 and the photosensitive drum 1 is decentered even when the photosensitive drum 110 is eccentric.
The rate of change in the distance between the convex lens 18 and the photosensitive drum 110 associated with the travel of 10 is reduced. Further, since the microlens array 16 is used instead of the ball lens, the thickness of the convex lens 18 can be arbitrarily determined. Therefore, the path of the light beam passing through the convex lens 18 is appropriately determined,
It is easy to improve the quality of the electrostatic latent image formed on the photosensitive drum 110.

For this embodiment, the size of the electrostatic latent image (image spot diameter) that will be formed on the surface of the photoconductive drum 110 and the spot diameter of the light beam that will reach the surface of the photoconductive drum 110. A simulation was performed to calculate the power inside. The parameters in the simulation were set as follows. The light emitting element was assumed to be a circular OLED element having a diameter of 40 μm. The distance L1 between the lens surface 18b of each convex lens 18 and the light emitting panel 12 is 0.2 mm, the distance L2 between each convex lens 18 and the photosensitive drum 110 is 0.4 mm, and the light emitting panel 1 of each convex lens 18 is.
The curvature radius R1 of the lens surface 18a on the second side is 0.25 mm, and the light emitting panel 12 of each convex lens 18 is used.
The radius of curvature R2 of the lens surface 18b on the opposite side (photosensitive drum 110 side) is 0.19 mm, and the distance d between the principal point on the light emitting panel 12 side and the principal point on the photosensitive drum 110 side in each convex lens 18 is 0.5 mm. The refractive index of the lens material was set to 1.62.

For comparison, a converging lens array having specific properties will reach the spot diameter of the image that will be formed on the surface of the photoconductive drum 110 and the surface of the photoconductive drum 110. A simulation was performed to calculate the power within the spot diameter of the luminous flux.
In the simulation, it is assumed that the light-emitting element is a circular OLED element having a diameter of 40 μm, and the distance between the converging lens array and the light-emitting element and the distance between the converging lens array and the photosensitive drum depend on the conditions set from the characteristics of the converging lens array. Calculated. The “focusing lens array” described for the following simulation is a focusing lens array having the same characteristics.

In this simulation, a region where a light beam having a light power of 13.5% or more of the maximum light power among the light beams reaching the photosensitive drum 110 is regarded as a spot, and the diameter of the region is estimated. The diameter of this region is called the spot diameter of the image spot diameter image.

As a result, in this embodiment, the spot diameter of the image formed on the surface of the photosensitive drum 110 is 60.5 μm, which is about 0.9 times that in the case where the converging lens array is used. It was. Since the spot diameter of the image can be reduced in this way, the resolution is improved.
In this embodiment, the total power within the spot diameter of the light beam reaching the surface of the photosensitive drum 110 is 1.98 μW, which is about 2 as compared with the case where a converging lens array is used.
. It became 51 times. Therefore, the waste of the light beam can be reduced. From another viewpoint, since the surface of the photosensitive drum 110 is irradiated with the light beam having the same power, the luminance of the light emitting element 14 can be reduced to about 40%. Since it is known that the luminance of the EL element is proportional to the drive current, the drive current can be saved to about 40%, and as a result, the life of the light-emitting element 14 can be greatly extended (see above). The spot diameter and power are only the result of simulation, and there is a slight deviation from the actual situation).

Next, the convex lens 18 and the photosensitive drum 110 in the electro-optical device 10 of this embodiment.
A change in characteristics due to a minute change in the interval L2 was investigated by simulation. When the size of the electrostatic latent image and the optical power change abruptly due to the minute change of the distance L2, the tolerance of the distance between the lens and the image carrier is small, and the eccentricity of the photosensitive drum or the roll for rotating the photosensitive belt Unevenness in the quality of the electrostatic latent image is likely to occur due to a change in the distance between the image carrier and the lens due to the eccentricity of the image.
Therefore, even if the distance L2 between each convex lens 18 and the photosensitive drum 110 changes, the photosensitive drum 1
It is desirable that the change in the spot diameter of the image formed on the surface 10 and the power of the light beam reaching the surface of the photosensitive drum 110 be as small as possible. The simulation conditions or parameters are the same as the simulation parameters described above except that the interval L2 changes. The simulation results are shown in FIGS.

4 to 8 are graphs showing the change in the spot diameter of the image formed on the surface of the photosensitive drum 110 with respect to the change in the distance L2 between each convex lens 18 and the photosensitive drum 110 in this embodiment. In FIG. 4, the vertical axis of the graph is normalized with the spot diameter being 1 when the interval L2 = 0.36 mm. Similarly, L2 = 0.38 mm in FIG. 5 and L2 = 0 in FIG.
. The vertical axis of the graph is normalized assuming that the spot diameter is 40 mm, L2 = 0.42 mm in FIG. 7, and L2 = 0.44 mm in FIG. FIG. 4 shows the interval L2 = 0.36 ± 0.
. FIG. 5 shows the change in the spot diameter of the image in the range of 08 mm, and FIG. 5 shows L2 = 0.38 ± 0.08 m.
m, FIG. 6 is L2 = 0.40 ± 0.08 mm, FIG. 7 is L2 = 0.42 ± 0.08 mm, FIG.
Indicates a change in the spot diameter of the image in the range of L2 = 0.44 mm ± 0.08.

The method of calculating the spot diameter differs depending on the graphs of FIGS. Specifically, regarding FIG. 4, when the interval L2 = 0.36 mm, the maximum optical power of the light beams reaching the photosensitive drum 110 is calculated, and then the interval L2 = 0.36 mm. 1 of the maximum optical power
The diameter of the region where the light flux of 3.5% or more will reach is the distance L2 = 0.36 ± 0.08 m.
The spot diameter was calculated in the range of m. With respect to FIG. 5, when the distance L2 = 0.38 mm, the maximum light power of the light beams reaching the photosensitive drum 110 is calculated, and then the maximum light power at the distance L2 = 0.38 mm. The diameter of the region where 13.5% or more of the light flux would reach was calculated as the spot diameter in the range of the interval L2 = 0.38 ± 0.08 mm. That is, when the lens and the photosensitive drum are separated by a reference distance that is a numerical value at the center of the horizontal axis in each graph, the maximum optical power of the light beams reaching the photosensitive drum 110 is obtained, and the optical power is calculated. As a reference, the diameter of a region where a light flux of 13.5% or more would reach was calculated as the spot diameter. Since the power distribution of the light beam reaching the photosensitive drum 110 varies depending on the interval L2, the diameter of the region where the light beam of 13.5% or more of the maximum power at the reference distance will reach varies depending on the reference distance. . Therefore, for example, as shown in FIG. 6, the reference distance is 0.4 m.
In the case of m, the spot diameter does not change in the range of L2 = 0.4 to 0.48 mm. However, as shown in FIG. 7, when the reference distance is 0.42 mm, L2 = 0.4 to 0. The spot diameter varies in the range of .48 mm.

As shown in FIG. 4, the maximum change rate of the spot diameter is 22.5% in the range of the distance L2 = 0.36 ± 0.08 mm. This is because the spot diameter at the distance L2 = 0.28 mm is the largest (specifically, 73 μm), and this is the spot diameter at the distance L2 = 0.36 mm (64
. 2 .mu.m) and the spot diameter at the interval L2 = 0.42 or 0.44 mm is the smallest (59.6 .mu.m), which is 0 of the spot diameter at the interval L2 = 0.36 mm.
. Because it is 928 times.

As shown in FIG. 5, the maximum change rate of the spot diameter is 20.8% in the range of the distance L2 = 0.38 ± 0.08 mm. This is because the spot diameter at the distance L2 = 0.30 mm is the maximum (specifically 72 μm), and this is the spot diameter at the distance L2 = 0.38 mm (63
. The spot diameter at the interval L2 = 0.42 to 0.46 mm is the smallest (59.6 μm), which is 0.9 of the spot diameter at the interval L2 = 0.38 mm.
Because it is 43 times.

As shown in FIG. 6, the maximum change rate of the spot diameter is 14.8% in the range of the distance L2 = 0.40 ± 0.08 mm. This is because the spot diameter at the distance L2 = 0.32 mm is the largest, which is 1.148 times the spot diameter at the distance L2 = 0.40 mm, and the spot at the distance L2 = 0.40-0.48 mm. The diameter is the smallest, which is the distance L2 = 0.40
This is because it is 1 time the spot diameter in mm.

As shown in FIG. 7, the maximum change rate of the spot diameter is 15.4% in the range of the distance L2 = 0.42 ± 0.08 mm. This is because the spot diameter at the interval L2 = 0.34 mm is the maximum (specifically 69.9 μm), and this is the interval L2 = 0.42 mm (62.2 μm).
The spot diameter at the interval L2 = 0.44 or 0.46 mm is the smallest (60.6 μm), and this is 0 of the spot diameter at the interval L2 = 0.42 mm. Because it is 974 times.

As shown in FIG. 8, the maximum change rate of the spot diameter is 16% in the range of the distance L2 = 0.44 ± 0.08 mm. This is because the spot diameter at the distance L2 = 0.52 mm is the maximum, which is 1.16 times the spot diameter at the distance L2 = 0.44 mm, and the distance L2 =
This is because the spot diameter at 0.44 mm is the smallest, and naturally this is one time the spot diameter at the interval L2 = 0.44 mm. Therefore, from the viewpoint of the rate of change of the spot diameter accompanying the minute change of L2, the reference distance between each convex lens 18 and the photosensitive drum 110 is L2 = 0.36 to
In the range of 0.44 mm, it was found that the longer one is preferable.

For example, as shown in FIG. 6, the maximum change rate of the spot diameter when L2 changes by ± 0.08 mm is 14.8% in the range of the interval L2 = 0.40 ± 0.08 mm. The maximum rate of change of this level is not much different from that of a conventional converging lens array. However, as will be described below, there is a marked difference in the rate of change of the power of the light beam reaching the surface of the photosensitive drum 110. It was.

FIGS. 9 to 18 are graphs showing the change in the total power within the spot diameter of the light beam reaching the surface of the photosensitive drum 110 with respect to the change in the distance L2 between each convex lens 18 and the photosensitive drum 110 in this embodiment. It is. The unit of power is w (watts), but the vertical axis of the graphs of FIGS. 9 to 13 assumes that the light-emitting element is a circular OLED element having a diameter of 40 μm in the same manner as described above. The total power within the spot diameter of the light beam reaching the surface of the photosensitive drum 110 calculated according to the conditions set from the property of the converging lens array is normalized as 1. In FIG. 14, the vertical axis of the graph is normalized with the total power in the case of the interval L2 = 0.36 mm being 1. Similarly, in FIG. 15, L2 = 0.38 mm.
16, L2 = 0.40 mm, FIG. 17 L2 = 0.42 mm, and FIG. 18 L2 = 0.
. The vertical axis of the graph is normalized with the total power in the case of 44 mm being 1. 9 and 14 show changes in the total power in the range of the distance L2 = 0.36 ± 0.08 mm.
0 and FIG. 15 are L2 = 0.38 ± 0.08 mm, and FIGS. 11 and 16 are L2 = 0.40 ± 0.0 mm.
8 mm, L2 = 0.42 ± 0.08 mm in FIGS. 12 and 17, and L2 = 0.0.0 mm in FIGS.
The change in the total power in the range of 44 ± 0.08 mm is shown.

In the graphs of FIGS. 9 to 18, the power calculation method is different. Specifically, as in FIG. 4, with respect to FIGS. 9 and 14, the maximum optical power of 13.5 at the interval L2 = 0.36 mm is obtained.
The diameter of the region where more than% light flux would reach was calculated as the spot diameter within the interval L2 = 0.36 ± 0.08 mm, and the power within the spot diameter was calculated. Similar to FIG. 5, with respect to FIGS. 10 and 15, the diameter of the region where the light flux of 13.5% or more of the maximum optical power at the interval L2 = 0.38 mm will reach is expressed as the interval L2 = 0.38. In the range of ± 0.08mm,
The spot diameter was calculated and the power within the spot diameter was calculated. That is, when the lens and the photosensitive drum are separated by a reference distance that is a numerical value at the center of the horizontal axis in each graph, the maximum optical power of the light beams reaching the photosensitive drum 110 is obtained, and the optical power is calculated. As a reference, 13.
The diameter of the region where a light flux of 5% or more would reach was calculated as the spot diameter, and the optical power within the spot diameter was calculated.

As shown in FIGS. 9 to 13, the reference distance (the numerical value at the center of the horizontal axis) is 0.36 mm to 0.00.
In the case of 44 mm, even when the distance L2 changed by ± 0.08 mm, a power of 2.2 times or more was always obtained as compared with the case where the converging lens array was used. In particular, as shown in FIGS. 9 to 13, when the reference distance (the numerical value at the center of the horizontal axis) is 0.36 mm to 0.42 mm, the converging lens array is changed even if the interval L2 changes by ± 0.08 mm. Compared with the case of using, 2.26 times or more of power was always obtained.

As shown in FIGS. 9 and 14, the maximum change rate of the optical power within the spot diameter is 8.8% in the range of the distance L2 = 0.36 ± 0.08 mm. Because the interval L2 = 0.28mm
This is 0.941 times the optical power at the interval L2 = 0.36 mm, and the optical power at the interval L2 = 0.44 mm is the maximum, which is the interval L2 = 0. 3
This is because it is 1.024 times the optical power at 6 mm.

As shown in FIGS. 10 and 15, the maximum change rate of the optical power is 6.9% in the range of the distance L2 = 0.38 ± 0.08 mm. This is because the optical power at the interval L2 = 0.30 mm is minimum, which is 0.951 times the optical power at the interval L2 = 0.38 mm, and the optical power at the interval L2 = 0.42 mm is the maximum. This is because this is 1.017 times the optical power at the interval L2 = 0.38 mm.

As shown in FIGS. 11 and 16, the maximum change rate of the optical power is 7.4% in the range of the distance L2 = 0.40 ± 0.08 mm. This is because the optical power at the interval L2 = 0.48 mm is minimum, which is 0.934 times the optical power at the interval L2 = 0.40 mm, and the optical power at the interval L2 = 0.42 mm is the maximum. This is because this is 1.003 times the optical power at the interval L2 = 0.40 mm.

As shown in FIGS. 12 and 17, the maximum change rate of the optical power is 11.2% in the range of the distance L2 = 0.42 ± 0.08 mm. This is because the optical power at the interval L2 = 0.50 mm is minimum, which is 0.899 times the optical power at the interval L2 = 0.42 mm,
The optical power at the interval L2 = 0.42 mm is the maximum, and naturally this is the interval L2 = 0.4.
This is because the optical power at 2 mm is one time.

As shown in FIGS. 13 and 18, the maximum change rate of the optical power is 14.8% in the range of the distance L2 = 0.44 ± 0.08 mm. This is because the optical power at the interval L2 = 0.52 mm is minimum, which is 0.881 times the optical power at the interval L2 = 0.44 mm,
This is because the optical power at the interval L2 = 0.42 mm is the minimum, which is 1.011 times the optical power at the interval L2 = 0.44 mm.

Therefore, from the viewpoint of the change rate of the optical power accompanying the minute change in the distance L2, the reference distance between each convex lens 18 and the photosensitive drum 110 is 0. 0 in the range of L2 = 0.36 to 0.44 mm. It turned out that it is preferable that it is 36-0.42 mm. 4 to 8 and the simulation results of FIGS. 9 to 18 are considered together, the reference distance of the distance L2 between the convex lens 18 and the photosensitive drum 110 is 0.38 to 0.42 mm (0).
. Not only between 38 mm and 0.42 mm, but also including 0.38 mm and 0.42 mm), and 0.4 to 0.42 mm (including 0.40 mm and 0.42 mm at both ends) is more preferable. I found out. Considering the eccentricity of the photosensitive drum 110 or the eccentricity of the roll supporting the photosensitive belt, each convex lens 1 resulting from the eccentricity when such an image carrier travels.
8 and the image carrier can be regarded as a minute change in L2, the average distance between each convex lens 18 and the image carrier can be regarded as the reference distance. Accordingly, the average distance between each convex lens 18 and the image carrier when the image carrier travels is preferably 0.38 to 0.42 mm, and is preferably 0.4 to 0.
. It can be said that 42 mm is more preferable.

For example, for the preferred case where the reference distance of L2 is 0.4 mm, the results of FIGS. 6, 11 and 16 are considered again. The maximum rate of change of optical power is only 7.4%. The maximum change rate of the spot diameter is 14.8% (the spot diameter at the interval L2 = 0.32 mm is the interval L2).
= 1.148 times the spot diameter at 0.40 mm). In the case of L2 = 0.4 mm, the spot diameter of the image formed on the surface of the photosensitive drum 110 is about 0.9 times as described above, compared with the case where the converging lens array is used. Even if the spot diameter is increased by 14.8% by changing L2 to 0.32 mm, the maximum spot diameter is 1.033 times that of the spot diameter obtained by the converging lens array. (= 1.148 × 0.
9) which is almost the same as the spot diameter obtained with the converging lens array. Therefore,
In general, since the spot diameter of the image can be made smaller than the spot diameter obtained by the converging lens array, the resolution is improved. The allowable error and allowable change range of L2 can be considered as ± 0.08 mm.

FIG. 19 shows that this embodiment is similar to the above in that L1 = 0.2 mm and R1 = 0.2.
Calculates the trajectory where the light beam emitted from a point light source travels through a single convex lens 18 when 5 mm, R2 = 0.19 mm, d = 0.5 mm, and the refractive index of the lens material are set to 1.62. The simulation result obtained in is shown. As shown in FIG. 19, the light emitted from the point light source travels in a diverging direction inside the convex lens 18. That is, the traveling locus of light inside the convex lens 18, that is, the traveling path, except for the light traveling along the central axis of the convex lens 18 itself,
It can be understood that the farther from the point light source, the farther from the central axis of the convex lens 18. This phenomenon is caused by the refractive index of air between the light source and the convex lens 18 (about 1), the refractive index of the lens material, R1 and L1. The circular OLED element having a diameter of 40 μm described above is used as the light emitting element 14.
, The light emitting element 14 has a very small area and can be regarded as a point light source.
In this case, the light emitted from the light emitting element 14 travels in a diverging direction inside the convex lens 18 as in FIG.

As shown in FIG. 19, the position where the area of the light beam transmitted through the convex lens 18 converges to the minimum, that is, the focal point is not a position 0.4 mm away from the lens surface 18b from which the light exits the convex lens 18, but 0.44-0. .46 mm, specifically 0.45 mm away. That is, the focal length is 0.45 mm. However, as described above, the convex lens 18 and the photosensitive drum 110 are used.
The reference distance of the interval L2 is preferably 0.38 to 0.42 mm shorter than the focal length,
0.4 to 0.42 mm is more preferable. That is, the average distance between each convex lens 18 and the image carrier when the image carrier travels is based on the distance between the position where the area of the light beam emitted from the light emitting element 14 and transmitted through each convex lens 18 converges to the minimum and the distance between each convex lens 18. Is preferably 0.03 to 0.07 mm (including 0.03 mm and 0.07 mm at both ends), and more preferably 0.03 to 0.05 mm. The reason for this phenomenon is not clear, but this phenomenon can be confirmed from the simulation results described above with reference to FIGS.

In the above simulation, the distance d between the principal point on the light emitting panel 12 side and the principal point on the photosensitive drum 110 side in each convex lens 18 is 0.5 mm, but the distance d is 0.2 mm or more and 0.
. It is preferable that it is 6 mm or less. The distance d (that is, the maximum thickness of the convex lens 18) is 0.2 mm.
If it is smaller, the thickness of the flat plate portion 17 is even smaller, so that the mechanical strength of the microlens array 16 is lowered. On the other hand, the greater the distance d (the maximum thickness of the convex lens 18), the lower the optical power of the light beam irradiated from the lens 18 onto the photosensitive drum 110. This will be described below.

FIG. 20 is a graph showing the change in the power of the light beam reaching the surface of the photosensitive drum 110 with respect to the change in the maximum thickness d of the convex lens 18 in this embodiment. In the simulation for obtaining this graph, L1 = 0.2 mm, L2 = 0.4 mm, R, as described above.
1 = 0.25 mm, and the refractive index of the lens material was set to 1.62. However, R2 was adjusted so that the convex lens 18 was focused on the photosensitive drum 110 with the change of d. In the graph of FIG. 20, the vertical axis represents the light-emitting element having a diameter of 4 with respect to the converging lens array.
Assuming a 0 μm circular OLED element, the power of the light beam reaching the surface of the photosensitive drum 110 calculated according to the conditions set from the properties of the converging lens array is normalized as 1. As shown in FIG. 20, when d = 0.2 mm, the power of the light beam from the light emitting element is maximum, but the power gradually decreases as the maximum thickness d of the convex lens 18 increases. In order to obtain twice or more power of the converging lens array, the maximum thickness d is preferably 0.6 mm or less.

FIG. 21 is a graph showing the change in the spot diameter of the image formed on the surface of the photosensitive drum 110 with respect to the change in the maximum thickness d of the convex lens 18 in this embodiment. As the maximum thickness d of the convex lens 18 increases, the spot diameter gradually decreases. For the purpose of reducing the spot diameter, the maximum thickness d is preferably as large as possible. Therefore, d = 0.5 mm is a preferred example.

<Comparative example>
As a comparative example, a microlens array in which many convex lenses 18A shown in FIG. 22 are arranged is assumed. FIG. 22 shows a simulation result obtained by calculating a locus in which a light beam emitted from a point light source travels through one convex lens 18A of a microlens array as a comparative example.
In the comparative example, L1 = 0.2 mm, R1 = 0.15 mm, R2 = 0.25 mm, d = 0.5
mm, and the refractive index of the lens material was set to 1.62.

As shown in FIG. 22, the light emitted from the point light source travels in a converging direction inside the convex lens 18A. That is, it can be understood that the light traveling locus, that is, the traveling path inside the convex lens 18A is closer to the central axis of the convex lens 18 as it is farther from the point light source, except for the light traveling along the central axis of the convex lens 18 itself. This phenomenon is caused by the refractive index of air between the light source and the convex lens 18 (about 1), the refractive index of the lens material, R1 and L1. When the above-described circular OLED element having a diameter of 40 μm is used as the light-emitting element 14, the light-emitting element 14 can be regarded as a point light source because the light-emitting element 14 has a small area, and the light emitted from the light-emitting element 14 in that case is shown in FIG. As in the case of No. 22, the lens advances in the direction of convergence inside the convex lens 18A.

For this comparative example, the size of the electrostatic latent image (image spot diameter) that would be formed on the surface of the photoconductive drum 110 and the spot diameter of the light beam that would reach the surface of the photoconductive drum 110. A simulation to calculate the power of was performed. In this simulation,
The refractive indexes of L1, R1, R2, d, and the lens material were set in the same manner as described above, and the light emitting element was assumed to be a circular OLED element having a diameter of 40 μm, and L2 = 0.4 mm.

In this comparative example, the photosensitive drum 110 is compared with the case where a converging lens array is used.
The power within the spot diameter of the luminous flux reaching on the surface of the film improved by about 5.2 times. However, the spot diameter of the image formed on the surface of the photosensitive drum 110 is about 1.28 times that in the case where the converging lens array is used. Thus, the spot diameter of the image has increased. In order to make the spot diameter of the image the same as that of the first embodiment, the size of the light-emitting element 14 may be reduced. However, since the power also decreases with this, the substantial power improvement effect is the first.
This is no different from the embodiment.

Further, similarly to the first embodiment, the convex lens 18A and the photosensitive drum 1 in the comparative example are used.
A change in characteristics due to a minute change of 10 intervals L2 was investigated by simulation.

FIG. 23 shows a distance L2 between the convex lens 18A and the photosensitive drum 110 in the comparative example of FIG.
6 is a graph showing a change in the spot diameter of an image formed on the surface of the photosensitive drum 110 with respect to a change in the angle. In FIG. 23, the vertical axis of the graph is normalized by setting the spot diameter to 1 when the interval L2 = 0.40 mm. When the distance L2 = 0.40 mm, the photosensitive drum 110 is used.
Is calculated, and then the diameter of the region where the luminous flux of 13.5% or more of the maximum optical power at the interval L2 = 0.40 mm will reach is calculated as follows: Interval L2 =
The spot diameter was calculated in the range of 0.40 ± 0.08 mm.

FIG. 24 shows the distance L2 between the convex lens 18A and the photosensitive drum 110 in the comparative example of FIG.
6 is a graph showing a change in total power within a spot diameter of a light beam reaching the surface of the photosensitive drum 110 with respect to a change in. In FIG. 24, the vertical axis of the graph is normalized with the total power when the interval L2 = 0.40 mm being 1. FIG. 24 shows the change in the total power within the spot diameter in the range of L2 = 0.40 ± 0.08 mm. For the power, the total power within the spot diameter obtained by the same method as in the simulation of FIG. 23 was obtained.

As is clear from comparison between the graph (FIGS. 6 and 16) regarding the preferred case in the embodiment (the reference distance of L2 is 0.4 mm) and FIGS. 22 and 23, in this comparative example, L2
The change in spot diameter and power is remarkable with respect to the change in. As shown in FIG. 22, in the comparative example, in the range of the interval L2 = 0.40 ± 0.08 mm, the spot diameter varies by −0.5% to + 20% with respect to the spot diameter at L2 = 0.40 mm. To do. That is, the maximum change rate of the spot diameter in this range is about 20.5%. This is 1.37 times the result of FIG. 6 regarding the embodiment. As shown in FIG. 23, in the comparative example, the interval L2 = 0.40 ± 0.0.
In the range of 8 mm, the optical power is -12% with respect to the optical power at L2 = 0.40 mm.
~ + 5% variation. That is, the maximum change rate of the optical power in this range is about 17%. This is 2.3 times the result of FIG. 16 regarding the embodiment. In this comparative example, in order to make the change rate of the optical power as small as that of the embodiment, the distance L2 = 0.40 ± 0.02 mm. Therefore, it can be considered that the allowable error and the allowable change range of L2 are only ± 0.02 mm.

With reference to FIG. 19 and FIG. 22, the light traveling paths in the embodiment and the comparative example are compared.
Due to the refractive index of air between the light source and the convex lens, the refractive index of the lens material, R1 and L1,
In the embodiment (FIG. 19), the light beam travels in a diverging direction inside the convex lens 18.
The luminous flux emitted from the convex lens 18 is a refractive index of the lens material, a refractive index of air, and R
2 converges, and the light is condensed in a fairly narrow range when the distance from the lens is 0.4 ± 0.08 mm.

On the other hand, in the comparative example (FIG. 22), the light beam travels in the direction of convergence inside the convex lens 18A. Of the luminous flux emitted from the convex lens 18A, the light passing through the outside of the lens converges to a position close to the lens, and the light passing through the inside of the lens is already spread at a position where it converges. Therefore, when the spot diameter of the obtained image becomes large and L2 changes,
Both the spot diameter of the image and the optical power change significantly. Since the light beam converges inside the convex lens 18A, the light once incident on the convex lens 18A does not escape to the outside of the lens (for example, the adjacent lens), so that the power at the spot diameter is higher than in the embodiment. However, a significant problem is that the characteristics of the latent image change significantly due to changes in L2.

Even when the exit side lens radius of curvature R2 was changed among the parameters of the comparative example, good light convergence was not obtained. On the other hand, similar to the above-described embodiment, in other forms that proceed in the direction in which the light beam diverges inside the convex lens, good light convergence is obtained, and even if L2 changes,
The change in the spot diameter of the image and the optical power, that is, the unevenness of the quality of the electrostatic latent image was small. Also, in other forms in which the light beam travels parallel to the central axis of the convex lens inside the convex lens, good light convergence can be obtained, and even if L2 changes, the spot diameter of the image and the optical power change, i.e., static. The unevenness of the quality of the electrostatic latent image was small. Some of such forms are described below.

<Second Embodiment>
In the electro-optical device 10 according to the above-described embodiment, L1 = 0.2 mm and L2 = 0.4.
mm, R1 = 0.25 mm, R2 = 0.18 mm, d = 0.3 mm, and the refractive index of the lens material was set to 1.62. Assuming that the light-emitting element 14 is a circular OLED element having a diameter of 40 μm,
A simulation was performed to calculate the spot diameter of the image formed on the surface of the photoconductive drum 110 and the power of the light beam reaching the surface of the photoconductive drum 110.

For the converging lens array, the light emitting element has a diameter of 40 μm as described above.
And the spot diameter of the image formed on the surface of the photosensitive drum 110 and the photosensitive drum 1 calculated according to the conditions set from the properties of the converging lens array.
The power of the luminous flux reaching the surface of 10 was compared with the simulation result of the second embodiment.

In this embodiment, the photosensitive drum 1 is compared with the case where a converging lens array is used.
The power of the luminous flux reaching the surface of 10 was increased about 3.9 times. On the other hand, in this embodiment, the spot diameter of the image formed on the surface of the photosensitive drum 110 is about 8% larger than when the converging lens array is used. However, the diameter of the light emitting element 14 is about 8 mm.
By reducing the percentage by%, the spot diameter of the image is the same as that obtained by the converging lens array. As the diameter of the light-emitting element 14 is reduced by about 8%, the power of the light beam is reduced. However, the light beam reaching the surface of the photosensitive drum 110 is still less than when the converging lens array is used. The power has increased about 3.3 times.

In this embodiment, since the refractive indexes of L1, R1 and the lens material are the same as those in the first embodiment, the light beam travels in a diverging direction in each convex lens. The change in the power and the size of the electrostatic latent image with respect to the change in L2 is similar to that in the first embodiment, and the allowable error and the allowable change range of L2 can be obtained in the same manner as in the first embodiment.

<Third Embodiment>
In the electro-optical device 10 according to the above-described embodiment, L1 = 0.2 mm and L2 = 0.4.
mm, R1 = 0.25 mm, R2 = 0.16 mm, d = 0.5 mm, and the refractive index of the lens material was set to 1.51. Assuming that the light-emitting element 14 is a circular OLED element having a diameter of 40 μm,
A simulation was performed to calculate the spot diameter of the image formed on the surface of the photoconductive drum 110 and the power of the light beam reaching the surface of the photoconductive drum 110. Then, similar to the above-described embodiment, the simulation result related to the converging lens array was compared with this simulation result.

In this embodiment, the photosensitive drum 1 is compared with the case where a converging lens array is used.
The spot diameter of the image formed on the surface of 10 was reduced by about 14%. Since the spot diameter of the image can be reduced in this way, the resolution is improved. In this embodiment,
Compared with the case where the converging lens array is used, the power of the light beam reaching the surface of the photosensitive drum 110 is about 2.3 times. The effect of improving power is the same as in the first embodiment and the second embodiment.
However, since the spot diameter can be reduced, the power density is substantially equal to that of the first embodiment and the second embodiment, and the exposure head of the image printing apparatus is actually used. As a result, sufficient performance was obtained.

Also in this embodiment, the light beam travels in a diverging direction in each convex lens. The change in the power and the size of the electrostatic latent image with respect to the change in L2 is similar to that in the first and second embodiments.
The allowable error and the allowable change range can be obtained in the same manner as in the first and second embodiments.

<Fourth embodiment>
In the electro-optical device 10 according to the above-described embodiment, L1 = 0.2 mm and L2 = 0.4.
mm, R1 = 0.25 mm, R2 = 0.14 mm, d = 0.5 mm, and the refractive index of the lens material was set to 1.43. Assuming that the light-emitting element 14 is a circular OLED element having a diameter of 40 μm,
A simulation was performed to calculate the spot diameter of the image formed on the surface of the photoconductive drum 110 and the power of the light beam reaching the surface of the photoconductive drum 110. Then, similar to the above-described embodiment, the simulation result related to the converging lens array was compared with this simulation result.

In this embodiment, the spot diameter of the image formed on the surface of the photosensitive drum 110 is smaller than in any of the previous embodiments. Since the spot diameter of the image can be reduced in this way, the resolution is improved. Further, in this embodiment, the power of the light beam reaching the surface of the photosensitive drum 110 is about twice that in the case where the converging lens array is used. Although the effect of improving the power is small compared to the first to third embodiments, the spot diameter can be reduced, so that the power density is substantially the same as that of the first to third embodiments, and actually In addition, sufficient performance for use as an exposure head of an image printing apparatus was obtained.

Also in this embodiment, the light beam travels in a diverging direction in each convex lens. The change in the power and the size of the electrostatic latent image with respect to the change in L2 is similar to that in the first and second embodiments.
The allowable error and the allowable change range can be obtained in the same manner as in the first and second embodiments.

<Fifth embodiment>
In the electro-optical device 10 according to the above-described embodiment, L1 = 0.15 mm, L2 = 0.
4 mm, R1 = 0.2 mm, R2 = 0.15 mm, d = 0.3 mm, and the refractive index of the lens material were set to 1.62. Assuming that the light-emitting element 14 is a circular OLED element having a diameter of 40 μm,
A simulation was performed to calculate the spot diameter of the image formed on the surface of the photoconductive drum 110 and the power of the light beam reaching the surface of the photoconductive drum 110. Then, similar to the above-described embodiment, the simulation result related to the converging lens array was compared with this simulation result.

In this embodiment, the photosensitive drum 1 is compared with the case where a converging lens array is used.
The power of the luminous flux reaching the surface of 10 was increased about 4.5 times. On the other hand, in this embodiment, the spot diameter of the image formed on the surface of the photosensitive drum 110 is larger than when the converging lens array is used. However, as in the second embodiment, by reducing the diameter of the light-emitting element 14, the spot diameter of the image can be the same as that obtained by the converging lens array. As the diameter of the light-emitting element 14 is reduced, the power of the light beam is reduced. However, the power of the light beam reaching the surface of the photosensitive drum 110 is still larger than when the converging lens array is used. became.

Also in this embodiment, the light beam travels in a diverging direction in each convex lens. The change in the power and the size of the electrostatic latent image with respect to the change in L2 is similar to that in the first and second embodiments.
The allowable error and the allowable change range can be obtained in the same manner as in the first and second embodiments.

<Sixth Embodiment>
In the electro-optical device 10 according to the above-described embodiment, L1 = 0.1 mm and L2 = 0.4.
mm, R1 = 0.2 mm, R2 = 0.14 mm, d = 0.3 mm, and the refractive index of the lens material was set to 1.62. Assuming that the light emitting element 14 is a circular OLED element having a diameter of 40 μm, a simulation is performed to calculate the spot diameter of an image formed on the surface of the photosensitive drum 110 and the power of the light beam reaching the surface of the photosensitive drum 110. went. Then, similar to the above-described embodiment, the simulation result related to the converging lens array was compared with this simulation result.

In this embodiment, the photosensitive drum 1 is compared with the case where a converging lens array is used.
The power of the luminous flux reaching the surface of 10 was increased by about 5.7 times. On the other hand, in this embodiment, the spot diameter of the image formed on the surface of the photosensitive drum 110 is larger than when the converging lens array is used. However, as in the second embodiment, by reducing the diameter of the light-emitting element 14, the spot diameter of the image can be the same as that obtained by the converging lens array. As the diameter of the light-emitting element 14 is reduced, the power of the light beam is reduced. However, the power of the light beam reaching the surface of the photosensitive drum 110 is still larger than when the converging lens array is used. became. Further, when high resolution is not required, it is not necessary to reduce the diameter of the light emitting element 14.

Also in this embodiment, the light beam travels in a diverging direction in each convex lens. The change in the power and the size of the electrostatic latent image with respect to the change in L2 is similar to that in the first and second embodiments.
The allowable error and the allowable change range can be obtained in the same manner as in the first and second embodiments.

<Seventh embodiment>
In the electro-optical device 10 according to the above-described embodiment, L1 = 0.2 mm, L2 = 0.5
mm, R1 = 0.25 mm, R2 = 0.2 mm, d = 0.5 mm, and the refractive index of the lens material was set to 1.62. Assuming that the light emitting element 14 is a circular OLED element having a diameter of 40 μm, a simulation is performed to calculate the spot diameter of an image formed on the surface of the photosensitive drum 110 and the power of the light beam reaching the surface of the photosensitive drum 110. went. Then, similar to the above-described embodiment, the simulation result related to the converging lens array was compared with this simulation result.

In this embodiment, the photosensitive drum 1 is compared with the case where a converging lens array is used.
The spot diameters of the images formed on the surface of 10 were almost the same. In this embodiment, the power of the light beam reaching the surface of the photosensitive drum 110 is about 2.6 times that in the case where the converging lens array is used, and the exposure of the image printing apparatus is actually performed. Performance sufficient for use as a head was obtained.

Also in this embodiment, the light beam travels in a diverging direction in each convex lens. The change in power with respect to the change in L2 is similar to that in the first embodiment, and the change in the size of the electrostatic latent image with respect to the change in L2 can be made smaller than that in the first embodiment. Therefore, the allowable error and allowable change range of L2 can be obtained in the same manner as in the first embodiment.

In the above description, the simulation results are described in which a converging lens array having a specific property is compared. However, when a microlens is used, compared to the case where a converging lens array is used. Thus, it is estimated that the power extraction setting can be easily performed.

<Image printing device>
As described above, the electro-optical device 10 according to the embodiment can be used as a line-type exposure head for writing a latent image on an image carrier in an image printing apparatus using an electrophotographic system. Examples of the image printing apparatus include a printer, a printing part of a copying machine, and a printing part of a facsimile.

FIG. 25 is a longitudinal sectional view showing an example of an image printing apparatus using the electro-optical device 10 as a line type exposure head. This image printing apparatus is a tandem type full-color image printing apparatus using a belt intermediate transfer body system.

In this image printing apparatus, four organic EL array exposure heads 10K, 10C having the same configuration are used.
, 10M, 10Y are four photosensitive drums (image carriers) 110K, 11 having the same configuration.
Arranged at the exposure positions of 0C, 110M, and 110Y, respectively. The organic EL array exposure heads 10K, 10C, 10M, and 10Y are the electro-optical device 10 described above.

As shown in FIG. 25, this image printing apparatus is provided with a driving roller 121 and a driven roller 122, and an endless intermediate transfer belt 120 is wound around these rollers 121 and 122, as indicated by arrows. Thus, the periphery of the rollers 121 and 122 is rotated. Although not shown, tension applying means such as a tension roller that applies tension to the intermediate transfer belt 120 may be provided.

Around the intermediate transfer belt 120, photosensitive drums 110K, 110C, 110M, and 110Y having photosensitive layers on four outer peripheral surfaces are arranged at predetermined intervals. Subscript K
, C, M, and Y mean that they are used to form visible images of black, cyan, magenta, and yellow, respectively. The same applies to other members. Photosensitive drums 110K and 11
0C, 110M, and 110Y are rotationally driven in synchronization with the driving of the intermediate transfer belt 120.

Around each photosensitive drum 110 (K, C, M, Y), a corona charger 111 (K, C,
M, Y), organic EL array exposure head 10 (K, C, M, Y), and developing device 114 (K, Y).
C, M, Y) are arranged. The corona charger 111 (K, C, M, Y) uniformly charges the outer peripheral surface of the corresponding photosensitive drum 110 (K, C, M, Y). The organic EL array exposure head 10 (K, C, M, Y) writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum. Each organic EL array exposure head 10 (K, C, M, Y) includes a plurality of OLED elements 1.
4 are arranged so that the arrangement direction of 4 is along the bus (main scanning direction) of the photosensitive drum 110 (K, C, M, Y). The electrostatic latent image is written by irradiating the photosensitive drum with light from the plurality of OLED elements 14. The developing device 114 (K, C, M, Y) forms a visible image, ie, a visible image, on the photosensitive drum by attaching toner as a developer to the electrostatic latent image.

Black, cyan, magenta, and black formed by such a four-color monochromatic image forming station
The yellow visible images are sequentially primary-transferred onto the intermediate transfer belt 120 to be superimposed on the intermediate transfer belt 120, and as a result, a full-color visible image is obtained. Inside the intermediate transfer belt 120, four primary transfer corotrons (transfer units) 112 (K, C, M, Y) are provided.
Is arranged. The primary transfer corotron 112 (K, C, M, Y) is connected to the photosensitive drum 11.
0 (K, C, M, Y) are arranged in the vicinity of the photosensitive drum 110 (K, C,
The visible image is electrostatically attracted from (M, Y) to transfer the visible image to the intermediate transfer belt 120 passing between the photosensitive drum and the primary transfer corotron.

A sheet 102 as an object on which an image is finally formed is fed one by one from the sheet feeding cassette 101 by the pickup roller 103, and between the intermediate transfer belt 120 and the secondary transfer roller 126 in contact with the driving roller 121. Sent to the nip. The full-color visible image on the intermediate transfer belt 120 is secondarily transferred to one side of the sheet 102 by the secondary transfer roller 126 and fixed on the sheet 102 by passing through a fixing roller pair 127 as a fixing unit. . Thereafter, the sheet 102 is discharged onto a paper discharge cassette formed on the upper part of the apparatus by a paper discharge roller pair 128.

Next, another embodiment of the image printing apparatus according to the present invention will be described.
FIG. 26 is a longitudinal sectional view of another image printing apparatus using the electro-optical device 10 as a line type optical head. This image printing apparatus is a rotary development type full-color image printing apparatus using a belt intermediate transfer body system. In the image printing apparatus shown in FIG. 26, a corona charger 168, a rotary developing unit 161, an organic EL array exposure head 167, and an intermediate transfer belt 169 are provided around a photosensitive drum (image carrier) 165. Yes.

The corona charger 168 uniformly charges the outer peripheral surface of the photosensitive drum 165. The organic EL array exposure head 167 writes an electrostatic latent image on the charged outer peripheral surface of the photosensitive drum 165. The organic EL array exposure head 167 is the electro-optical device 10 described above, and includes a plurality of O
The LED elements 14 are arranged so that the arrangement direction thereof is along the bus (main scanning direction) of the photosensitive drum 165. The electrostatic latent image is written by irradiating the photosensitive drum with light from the plurality of OLED elements 14.

The developing unit 161 includes four developing units 163Y, 163C, 163M, and 163K.
The drums are arranged at an angular interval of ° and can be rotated counterclockwise about the shaft 161a. The developing units 163Y, 163C, 163M, and 163K supply yellow, cyan, magenta, and black toners to the photosensitive drum 165, respectively, and attach the toner as a developer to the electrostatic latent image, thereby the photosensitive drum 165. A visible image, that is, a visible image is formed.

The endless intermediate transfer belt 169 is wound around a driving roller 170a, a driven roller 170b, a primary transfer roller 166, and a tension roller, and is rotated around these rollers in a direction indicated by an arrow. The primary transfer roller 166 transfers the visible image to the intermediate transfer belt 169 that passes between the photosensitive drum and the primary transfer roller 166 by electrostatically attracting the visible image from the photosensitive drum 165.

Specifically, in the first rotation of the photosensitive drum 165, an electrostatic latent image for a yellow (Y) image is written by the exposure head 167, and a developed image of the same color is formed by the developing unit 163Y.
Further, the image is transferred to the intermediate transfer belt 169. Further, in the next rotation, an electrostatic latent image for a cyan (C) image is written by the exposure head 167 and a developed image of the same color is formed by the developing device 163C, and an intermediate transfer is performed so as to overlap the yellow developed image. Transferred to the belt 169. Then, during the four rotations of the photosensitive drum 9, the yellow, cyan, magenta, and black visible images are sequentially superimposed on the intermediate transfer belt 169. As a result, a full-color visible image is formed on the transfer belt 169. It is formed. When images are finally formed on both sides of a sheet as an object on which an image is to be formed, the same color visible images of the front and back surfaces are transferred to the intermediate transfer belt 169, and then the front and back surfaces are transferred to the intermediate transfer belt 169. A full-color visible image is obtained on the intermediate transfer belt 169 by transferring the next-color visible image.

The image printing apparatus is provided with a sheet conveyance path 174 through which a sheet is passed. The sheets are picked up one by one from the paper feed cassette 178 by the pick-up roller 179, advanced through the sheet transport path 174 by the transport roller, and between the intermediate transfer belt 169 and the secondary transfer roller 171 in contact with the drive roller 170a. Pass through the nip. The secondary transfer roller 171 transfers the developed image to one side of the sheet by electrostatically attracting a full-color developed image from the intermediate transfer belt 169 collectively. The secondary transfer roller 171 can be moved closer to and away from the intermediate transfer belt 169 by a clutch (not shown). And
The secondary transfer roller 171 moves the intermediate transfer belt 169 when transferring a full-color visible image onto the sheet.
And is separated from the secondary transfer roller 171 while the visible image is superimposed on the intermediate transfer belt 169.

The sheet on which the image has been transferred as described above is conveyed to the fixing device 172 and is passed between the heating roller 172a and the pressure roller 172b of the fixing device 172, whereby the visible image on the sheet is fixed. The sheet after the fixing process is drawn into the discharge roller pair 176 and proceeds in the direction of arrow F. In the case of double-sided printing, after most of the sheet passes through the paper discharge roller pair 176, the paper discharge roller pair 176 is rotated in the reverse direction.
75. Then, the visible image is transferred to the other surface of the sheet by the secondary transfer roller 171, the fixing process is performed again by the fixing device 172, and then the sheet is discharged by the discharge roller pair 176.

The image printing apparatus to which the electro-optical device 10 can be applied has been described above, but the electro-optical device 10 can also be applied to other electrophotographic image printing apparatuses. Within the scope of the invention. For example, the electro-optical device 10 can be applied to an image printing apparatus that directly transfers a visible image from a photosensitive drum to a sheet without using an intermediate transfer belt, and an image printing apparatus that forms a monochrome image. It is.

1 is a cross-sectional view illustrating an electro-optical device according to an embodiment of the invention. FIG. 2 is a plan view of the electro-optical device in FIG. 1. It is a graph which shows the change of the light beam power with respect to the change of the distance from a light source (light emitting element) on the assumption that a light emitting element is a circular OLED element with a diameter of 40 micrometers. 6 is a graph showing a change in spot diameter of an image formed on the surface of a photosensitive drum with respect to a change in a distance L2 between each convex lens and the photosensitive drum in the first embodiment. 10 is another graph showing a change in spot diameter of an image formed on the surface of the photosensitive drum with respect to a change in a distance L2 between each convex lens and the photosensitive drum in the first embodiment. 10 is another graph showing a change in spot diameter of an image formed on the surface of the photosensitive drum with respect to a change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 10 is another graph showing a change in spot diameter of an image formed on the surface of the photosensitive drum with respect to a change in a distance L2 between each convex lens and the photosensitive drum in the first embodiment. 10 is another graph showing a change in spot diameter of an image formed on the surface of the photosensitive drum with respect to a change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 7 is a graph showing a change in power of a light beam within a spot diameter of an image formed on the surface of the photosensitive drum with respect to a change in a distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. 6 is another graph showing the change in the power of the light beam within the spot diameter of the image formed on the surface of the photosensitive drum with respect to the change in the distance L2 between each convex lens and the photosensitive drum in the first embodiment. It is a figure which shows the simulation result which calculated the locus | trajectory which the light beam emitted from the point light source permeate | transmits a single convex lens, and advances about 1st Embodiment. 6 is a graph showing a change in the power of a light beam reaching the surface of the photosensitive drum with respect to a change in the maximum thickness d of the convex lens in the first embodiment. 6 is a graph showing a change in the spot diameter formed on the surface of the photosensitive drum with respect to a change in the maximum thickness d of the convex lens in the first embodiment. It is a figure which shows the simulation result which calculated the locus | trajectory which the light beam emitted from the point light source permeate | transmits and propagates through a single convex lens about a comparative example. FIG. 23 is a graph showing a change in spot diameter of an image formed on the surface of the photosensitive drum with respect to a change in a distance L2 between the convex lens and the photosensitive drum in the comparative example of FIG. FIG. 23 is a graph showing a change in power of a light beam within a spot diameter of a light beam reaching the surface of the photosensitive drum with respect to a change in a distance L2 between the convex lens and the photosensitive drum in the comparative example of FIG. It is a longitudinal cross-sectional view which shows an example of the image printing apparatus using the electro-optical apparatus in any one of the 1st to 5th embodiment. It is a longitudinal cross-sectional view which shows the other example of the image printing apparatus using the electro-optical apparatus in any one of 1st to 5th embodiment.

Explanation of symbols

10 electro-optical device, 110 photosensitive drum (image carrier), 12 light emitting panel, 14
Light emitting element, 16 micro lens array, 18 convex lens, 18a, 18b lens surface.

Claims (6)

A light-emitting panel in which a plurality of light-emitting elements are arranged;
A plurality of convex lenses facing each of the light emitting elements and refracting light traveling from the corresponding light emitting elements, and a microlens array in which these convex lenses are integrated, and
An electro-optical device, wherein a radius of curvature of each convex lens on the light emitting panel side is equal to or larger than a radius of curvature of each convex lens on the side opposite to the light emitting panel. The distance between the principal point on the light emitting panel side of each convex lens and the principal point on the opposite side of the light emitting panel of each convex lens is 0.2 mm or more and 0.6 mm or less. The electro-optical device described. The light emitted from each light emitting element travels in a direction parallel to or diverging from the central axis of each convex lens inside each convex lens. Electro-optic device. An image carrier;
A charger for charging the image carrier;
The electro-optical device according to any one of claims 1 to 3, wherein a latent image is formed on a charged surface of the image carrier by light emitted from the light emitting element and transmitted through the convex lenses.
A developing unit that forms a visible image on the image carrier by attaching toner to the latent image; and
An image printing apparatus comprising: a transfer unit that transfers the visible image from the image carrier to another object. The average distance between the convex lens and the image carrier when the image carrier travels is larger than the distance between the convex lens and the position where the area of the light beam emitted from the light emitting element and transmitted through the convex lens converges to the minimum. The image printing apparatus according to claim 4, wherein the image printing apparatus is 0.03 to 0.07 mm shorter. The thickness of the transparent member that covers the side of the light emitting panel that emits light of the light emitting element is t (mm),
When the refractive index of the transparent member is n, the distance between the light emitting element and the convex lens is 0.3 mm.
The image printing apparatus according to claim 4, wherein the image printing apparatus is −t / n or less.

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