JPH06250117A - Image forming element - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an imaging element that realizes performance and cost equal to or higher than that of a rod lens array and does not require special know-how. [Structure] Columnar transparent members 3 and 4 each having two parallel cylindrical lens surfaces on both sides are arranged in two rows so that the cylindrical lens surfaces on one side face each other so as to be plane-symmetrical, and face to both outer sides. The cylindrical lenses 1 and 2 parallel to the arrangement direction and the generatrix are respectively installed so as to face the cylindrical lens surface on the other side, and the two parallel cylindrical lens surfaces of the respective transparent members have the same shape, respectively, and Two cylindrical lens surfaces arranged in parallel are paired with each other, and both cylindrical lens surfaces of each pair are arranged so as to be separated by the focal length of the cylindrical lens surface located inside.

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 used in facsimiles, electronic copying machines, LED printers and the like.

[0002]

2. Description of the Related Art In facsimiles, electronic copying machines, LED printers and the like, an image forming element for projecting an object on a line onto a sensor or a photosensitive drum at an equal magnification is used. An example of such an imaging element is a so-called rod lens array, which is an array of cylindrical transparent bodies whose refractive index continuously changes in the radial direction from the center, and a plate on which an array of convex lenses is formed is stacked in three layers. Tamono (for example, Japanese Patent Publication Sho 49-88)
No. 93, JP-A-57-104923, JP-A-57-66414, etc.), and an array of thick convex lenses in two layers (for example, JP-A-54-54).
No. 81571), an erecting equal-magnification optical system formed by combining a roof prism and a lens is arranged in an array (for example, Japanese Patent Laid-Open No. 61-210319 and Japanese Patent Laid-Open No. 5-10319).
6-117201, JP-A-56-126801, JP-A-56-140301, JP-A-56-
149002, JP-A-60-254018, JP-A-60-254019, and JP-A-60-2.
54020, JP-A 61-233714,
JP-A-62-91902, JP-A-62-2014
17).

[0003]

In particular, the rod lens array of the above-mentioned system is most widely used at present, and the commercialized product leads the other systems greatly in terms of quality and price. In the rod lens array, the technical point is to form the refractive index distribution in a cylindrical transparent body and to control it precisely, but this requires special know-how. It is not easy for a third party who doesn't have to produce. Further, since it is particularly difficult to make a rod lens having a particularly large diameter, there is a problem that the F value increases when a large distance between the lens and the subject is desired, resulting in a dark optical system.

Therefore, an image forming element which does not use a rod lens and which is easy to manufacture is desired. However, in the already known method, the distance between the single lenses of the lens array of the integrally molded layers is different from the molding condition or the molding condition. If the layers differ due to material variations, it is difficult to align the optical axes with sufficient accuracy, and the work of providing light-shielding means between adjacent lenses is troublesome, and it is somewhat difficult to make a particularly long array. Difficult and costly.

Further, in the method, since each single lens is made independently and formed into an array, the accuracy of the axial alignment is not determined at the time of molding as in the method, and the prismatic lens shape and the lens are two. Since it becomes a layer, it becomes easy to form an array, and it has an advantage over the method, but there is a problem that the cost rises because it becomes impossible to integrally mold each layer. In order to make a lens array of a practical length for use in facsimiles and copying machines, it is usually necessary to have several hundreds of single lenses, and it is necessary to keep the manufacturing cost of single lenses extremely low. It is difficult to realize a cost that can compete with the rod lens array of the method not only by polishing but also by injection molding.

Further, this is also common to the rod lens, but if the F-number is lowered by increasing the aperture of the lens or shortening the working distance in order to increase the brightness of the image, in particular, The integration of the refraction angles of the light passing through the peripheral portion of the lens becomes large, and the chromatic aberration becomes large, which is not preferable. Therefore, in the methods 1 to 3, it is difficult to form a bright optical system except in a special case where monochromatic light is used as the light source.

The method (1) uses a roof prism (or roof mirror) for reversing the image, which is advantageous in terms of aberration, but it requires a reflecting means for changing the optical path other than the lens and the prism. In order to secure a curved optical path, the distance between the lens and the object or image needs to be several times the lens aperture or more, and there is a problem that it is difficult to obtain brightness because the F value cannot be made too small. Further, there is a problem that the reflection surface of the prism and the reflection coating (generally metal plating) on the reflection means increase the manufacturing cost.

After all, it is understood that it is difficult for the conventional method to realize the performance and cost equal to or higher than those of the rod lens array, without requiring a special technique of controlling the refractive index distribution. The problem to be solved by the present invention is to provide an imaging element that can realize performance and cost equal to or higher than those of a rod lens array and does not require special know-how.

[0009]

In the image forming element according to the present invention, columnar transparent members each having two parallel cylindrical lens surfaces on both sides are made plane-symmetric with the cylindrical lens surface on one side facing each other. As shown in the figure, the two cylindrical lens surfaces of the transparent members are arranged in parallel. Have the same shape, and each pair forms a pair with two cylindrical lens surfaces arranged in parallel on the opposite side, and both cylindrical lens surfaces of each pair are separated by the focal length of the cylindrical lens surface located inside.

It should be noted that the cylindrical lens and the cylindrical lens surface referred to here do not indicate only so-called a part of a cylinder or a cylinder surface, but the shape of the bottom surface is formed by a quadratic curve or other curves with less aberration as a lens. It also includes a lens having a cylindrical surface represented and a cylindrical surface.

[0011]

In the image forming device using the lens array, it is necessary for each constituent unit to form an erecting equal-magnification image in order to obtain a continuous image. However, since the continuity of the image is maintained if this erecting condition is satisfied only in the arrangement direction of the lens array, an inverted image in the direction perpendicular to this may be used.

In the image forming element of the present invention, an erecting equal-magnification image is formed by four cylindrical lens surfaces along the optical axis of two rows of transparent members in the arrangement direction of the lens array, and two outer lenses are formed in the vertical direction. By forming an inverted image with the cylindrical lens of
The action of the four cylindrical lens surfaces acting in the longitudinal direction is a plan view of the action of the above method.

As described above, since the action of the array is limited to one direction, the need for axial alignment is limited to only the longitudinal direction, which makes the array easier than the method, and each transparent member has a columnar shape. Therefore, a long rod of a predetermined cross-sectional shape is molded at a time, a method of polishing and then cutting to a length to be used, particularly in the case of a thin cylindrical lens, extrusion molding of a fiber of the same cross-sectional shape, A cost-effective mass production method such as continuous polishing and cutting can be used if necessary, and the cost disadvantages of the method can be overcome. Furthermore, since the width of the array parallel to the generatrix of the cylindrical lens array can be set arbitrarily, the brightness of the image can be easily obtained by widening the width.

Further, according to the present invention, the eight cylindrical lens surfaces constituting the two optical units acting in the longitudinal direction are combined into two transparent members to reduce the number of parts and facilitate the manufacture. Has become.

[0015]

1 is a perspective view of a part of an embodiment of an imaging element according to the present invention, and FIG. 2 is a plan view of the same part. An object plane 5 and an image plane 6 on which an erecting equal-magnification image can be obtained by an array of two rows of transparent members 3 and 4 are located at positions separated by focal lengths from the cylindrical lenses 1 and 2, respectively. As shown in (a), an inverted image is obtained by the cylindrical lenses 1 and 2, and an erect image is obtained in the x direction by the array of transparent members 3 and 4 as shown in FIG. 2 (b).

The functions of the transparent members 3 and 4 in the xz plane are the same as the functions of the two-layer lens array of the above-described method described in JP-A-54-81571, as described above. . This will be described with reference to FIG. In the figure, the cylindrical lens surface _{r 11, r 21, r 31} , r 41 and the cylindrical lens surface _{r 12, r 22, r 32} , r 42 is a lens system having the same functions become respectively set. Explaining the lens system of one of the cylindrical lens surfaces r ₁₁ , r ₂₁ , r ₃₁ , r ₄₁ , as shown in the figure, the reduced inverted image P ₁ of the subject P ₀ on the object plane 5 becomes the cylindrical lens surface r ₁₁ . By the action of r _21, the cylindrical lens surfaces r ₂₁ and r ₃₁
The inverted image is magnified and projected by the action of the cylindrical lens surfaces r ₃₁ and r ₄₁ , and an erect image P ₂ having the original size is obtained on the image plane 6.

Here, the cylindrical lens surface r_{twenty one}And r
₃₁Acts as a field lens, allowing light from the object plane 5 to
Communicate efficiently. That is, the cylindrical lens
Surface r ₁₁, R₄₁Is the cylindrical lens surface
r_{twenty one}, R₃₁From those lens surfaces r _{twenty one}, R₃₁Is the focal length of
These lens surfaces r are separated from each other._{twenty one}, R₃₁Lens of
Cylindrical lens surface r due to action₁₁The same size image of
Cylindrical lens surface r₄₁Overlaid and projected, Siri
Fundamental lens surface r₁₁To cylindrical lens surface r
_{twenty one}The light that reaches to the lens surface r without loss₄₁To
Be guided.

Side surfaces s ₁₁ , s ₁₂ , s ₂₁ , s of the transparent member
₂₂ is preferably a surface that does not reflect light by applying a black paint after roughening. By doing so, it is possible to absorb the light that reaches the side surfaces s ₁₁ and s ₁₂ among the other light rays that have entered the cylindrical lens surface r ₁₁ , and prevent the generation of stray light. The light incident from the cylindrical lens surface r ₁₁ on the cylindrical lens surface r ₂₂ is to try to make the same magnification image r ₁₁ 'by the lens effect of the cylindrical lens surface r _22, r _32, is blocked by the side surface s ₂₂ All the components other than the light rays that are absorbed and eventually form the equal-magnification image P _{2 along} the route of the cylindrical lens surfaces r _{11 to} r _{21 to} r _{31 to} r ₄₁ are cut.

As can be easily understood from the above description,
Put together three or more optical system cylindrical lenses.
Is the same size image r₁₁Cylindrical lens surface r at position '
₄₃Means that there is a cylindrical lens surface
r₁₁~ R_{twenty two}~ R₃₂~ R₄₃By the route of₂Statue that does not overlap
Is not preferred. Transparent members 3 and 4 have different shapes and materials
It is possible to make with quality, but by doing so
Not found, but conversely manufactured by increasing the type of parts
It is not preferable because it increases the cost. Therefore,
For the bright members 3 and 4, it is preferable to use transparent members of the same shape in plane symmetry.
good. Therefore, L₁= L₂My neighbor cylindrical lens
Surface r_iRadius of curvature (r_i) For (r₁₁) =
(R₁₂) = (R₄₁) = (R₄₂), (R _{twenty one}) = (R_{twenty two}) =
(R₃₁) = (R₃₂). In addition, is the necessity of equal magnification?
Focal length D₁= D₂Becomes

The radius of curvature of the cylindrical lens surface
(R₁₁), (R₁₂), (R₄₁), (R₄₂) And focal length
Distance D₁, D₂Is the subject P₀, Projected image P₂Intermediate compared to
Image P ₁Is determined so that the projection width S₁, S₂
Is larger than the lens pitch. Na
The cylindrical lens surface r₁₁, R₁₂, R₄₁, R₄₂To
A parabolic column surface or other cylindrical surface with less aberration should be used.
And significantly improve the image resolution compared to the case of a cylindrical surface.
You can

If the gap G between the transparent members 3 and 4 is large, as shown in FIG. 4, more stray light enters the adjacent cylindrical lens, which is not preferable. As shown in FIG. 5, the generation of the stray light is reduced by providing a light shielding portion 8 between the cylindrical lens surfaces of the transparent members and by interposing a light shielding member 7 between the transparent members. Further, as shown in FIG. 6, by dividing the pair of transparent members by the light-shielding member 7 for the purpose of axial alignment, almost all of them can be eliminated. Further, as shown in FIG. 7, it is also effective to dispose a light shielding means 9 acting as a diaphragm between the adjacent cylindrical lens surfaces. However, even if stray light is cut by these methods, a decrease in efficiency cannot be avoided, so the gap G is preferably set to be about the lens width d or less. From the point of efficiency, as shown in FIG. 8, it is best to set the gap G = 0, but in this case, the cylindrical lens surfaces r ₂₁ , r ₂₂ , r ₃₁ , r ₃₂ have scratches or dust attached. If this is the case, the image will be projected onto the image plane 6 in a superposed manner, so that sufficient care must be taken.

As described above, in the projection of an erect image forming an intermediate image, the aberrations of the individual lenses are added up to form the total aberration, and it is a problem to suppress this aberration to a small value. In fact, can be considerably smaller aberrations than chromatic aberration by optimizing the shape of the cylindrical lens surface r _11, r _41, it is unrealistic in terms of cost to use an achromatic lens in the cylindrical lens surface r _11, r ₄₁ Therefore, it is not easy to suppress chromatic aberration. In this respect, the smaller the widths of the cylindrical lens surfaces r ₁₁ and r ₄₁ , the more advantageous.

On the other hand, since the projection of an inverted image does not form an intermediate image in the y direction, the problem of aberration including chromatic aberration is not as severe as in the x direction. Therefore, the cylindrical lens 1,
The width w of 2 can be made wider than the width d of the cylindrical lens surface, whereby the brightness can be obtained. FIG. 3 is a perspective view showing a usage example of the embodiment of the imaging element according to the present invention. Inverted in the y direction, a continuous image is obtained in the x direction. Inverting the image in the y direction does not cause any inconvenience in applications such as linear image sensors, liquid crystal printers, and LED printers. On the other hand, although the inverted image is inconvenient for the purpose of the copying machine, it can be used for the copying machine by reversing it by using a mirror and erecting the image.

[0024]

As described above, the imaging element according to the present invention obtains a continuous image on a line by using an array of transparent members in two rows and two cylindrical lenses. The child does not require special know-how such as control of the refractive index distribution of the rod lens, and is manufactured more than the conventional lens array described in JP-A-54-81571. It is easy and it is possible to obtain a brighter image.

[Brief description of drawings]

1 is a partial perspective view of an embodiment of an imaging element according to the present invention. FIG.

FIG. 2 is a plan view of a part of an embodiment of an imaging element according to the present invention.

FIG. 3 is a perspective view showing a usage example of an embodiment of the imaging element according to the present invention.

FIG. 4 is an explanatory diagram for explaining the operation of the imaging element of the present invention.

FIG. 5 is an explanatory diagram for explaining the operation of the modified example of the imaging element of the present invention.

FIG. 6 is an explanatory diagram for explaining the operation of the modified example of the imaging element of the present invention.

FIG. 7 is an explanatory diagram for explaining the operation of the modified example of the imaging element of the present invention.

FIG. 8 is an explanatory diagram for explaining the operation of the imaging element of the present invention.

FIG. 9 is an explanatory diagram for explaining in detail the operation of a pair of transparent members arranged in two rows in the imaging element of the present invention.

[Explanation of symbols]

1 ... cylindrical lens 2 ... cylindrical lens 3 ... transparent member 4 ... transparent member 5 ... object plane 6 ... image surface 7 ... light blocking member 8 ... shielding portion 9 ... shielding means _{r 11 ~r 41, r 12 ~r} 42 ... cylindrical lens surface

Claims (1)

[Claims] 1. A columnar transparent member having two parallel cylindrical lens surfaces on both sides thereof is arranged in two rows so that the cylindrical lens surface on one side faces each other and is in plane symmetry, and is directed to both outer sides. An imaging element comprising a cylindrical lens having a generatrix parallel to the array direction, the cylindrical element facing each other on the other side, and the two parallel cylindrical lens surfaces of the transparent member have the same shape. , An imaging element characterized by forming two pairs of parallel cylindrical lens surfaces on the opposite side, and the two cylindrical lens surfaces of each pair being separated by the focal length of the cylindrical lens surface located inside.