JPH06331930A - Line image forming element - Google Patents

Abstract

PURPOSE:To provide the line image forming element which does not require any special difficult know-how and is easily manufactured, small in chromatic aberration, and higher in performance. CONSTITUTION:The line image forming element is constituted by regarding two roof prisms 3 and 3 arranged symmetrically with their reflecting surfaces out and two convex lenses which are placed on those incidence and projection surfaces and equal in focal length as a constituent unit and arraying plural constituent units on a straight line so that the reflecting surfaces of the roof prisms contact each other; and piano-convex lenses 1 and 2 which each have a plane as one surface and a convex surface as the other surface are used as the convex lenses and arranged with their convex surfaces out, or biconvex lenses are arranged, thereby constituting the line image forming element. Further, two arrays of roof prisms which are arranged on a beltlike plate in the same direction at specific intervals perpendicularly to the reflecting surfaces are put one over the other so that the roof prisms of the opposite arrays are put in the specific intervals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line 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, etc., a line image forming element for projecting an object on a line onto a sensor or a photosensitive drum at an equal magnification is used.
As such a line imaging element, 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 formed with an array of spherical lenses Layered in many layers (for example, Japanese Patent Publication No. Sho 49-889)
No. 3, JP-A-57-104923, JP-A-57-66414, etc.), and an array of erecting equal-magnification optical systems formed by combining a roof prism and a lens (for example, JP-A-61). -21031
No. 9, JP-A-56-117201, JP-A-56-126801, JP-A-56-140301, JP-A-56-149002, JP-A-60-254018, JP-A-60-254019, JP-A-60-254020, JP-A-61-233714, JP-A-62-91902, JP-A-62-201417) and the like).

[0003]

In the above line imaging element, it is necessary to form and control the distribution of the refractive index in the cylindrical transparent body. Know-how is necessary and not easy.
In addition, since it is particularly difficult to make a rod lens having a particularly large diameter, there is a problem that when the distance between the lens and the subject is increased, the F value decreases and the optical system becomes dark.

Next, in the line imaging element, there is a problem that it is difficult to align the optical axes of the single lenses of the respective layers of the lens array with sufficient accuracy. Further, in the line image forming elements (1) and (2), since the integration of the refraction angles becomes large, there is a drawback that the chromatic aberration easily becomes large. On the other hand, in the line imaging element, since the roof prism (or roof mirror) is used to invert the image, the integration of the refraction angle is small and the chromatic aberration is small, but the axis alignment between the roof prism (or roof mirror) and the lens is performed. There is a problem in that it is difficult to realize

The present inventor has solved these problems, does not require particularly difficult know-how, is easy to manufacture, and
In order to provide a line imaging element with small chromatic aberration,
We have devised a line imaging element consisting of a combination of a Dove prism and a convex lens of 4-336834, but by further studying, a preferable form of such a line imaging element has been clarified, and it has higher performance. In addition, we have completed a lens array that is easy to make.

Therefore, the present invention solves the above-mentioned problems of the conventional line imaging element, does not require particularly difficult know-how, is easy to manufacture, has a small chromatic aberration, and has a higher performance. The purpose is to provide children.

[0007]

[Means for Solving the Problems] Two dove prisms, which are proposed as the above-mentioned Japanese Patent Application No. 4-336834, are placed symmetrically so that the reflecting surfaces are on the outside, and the two dove prisms are placed on the input / output surfaces. According to the first invention of the present application, in a line imaging element in which two convex lenses having the same focal length are used as constituent units and a plurality of the constituent units are linearly arranged so that the reflecting surfaces of the Dove prism face each other, As the convex lens, a plano-convex lens whose one surface is a flat surface and only one surface is a convex surface is used, and the line imaging element is configured by arranging it so that the convex surface is on the outside. Further, according to the second invention of the present application, , A biconvex lens is arranged to form a line imaging element.

Further, according to the third invention of the present application, two dove prisms are arranged on the strip-shaped plate in the same direction at a predetermined interval in the direction perpendicular to the reflecting surface. Are overlapped with each other so that the other Dove prism is fitted into a predetermined space.

[0009]

[Function] According to the above-mentioned configuration, the entrance / exit of the dove prism array
By arranging a plano-convex lens with the convex surface on the exit surface, the MTF (Modulation T
It is possible to obtain a line imaging element having a uniform high ransfer function), and by disposing a biconvex lens, a line imaging element having a higher MTF can be obtained.

Further, when manufacturing the line imaging element according to the present invention, it is necessary to arrange a large number of Dove prisms on a straight line with high precision, but it is troublesome to make and arrange the individual Dove prisms separately, and the manufacturing cost is high. However, if the array of dove prisms is divided into two dove prism rows, and the dove prism rows can be integrally molded and superposed, the dove prisms can be manufactured. It is possible to save the trouble of arranging one by one.

[0011]

1 is a perspective view showing an example of a structural unit in a line imaging element according to the first invention of the present application, and FIG.
(A) is a plan view of the yz plane, and (b) is a plan view of the xz plane. In the figure, 1 and 2 are plano-convex lenses, 3 and 3 are Dove prisms, 3'and 3'are reflecting surfaces of Dove prisms 3 and 3, 4 is a light blocking member, 5 is a black adhesive, 6 is an object surface, and 7 is The image plane. The object plane 6 and the image plane 7 are located at positions away from the plano-convex lenses 1 and 2 on the respective sides by the focal length, and the intersections of the optical axes of the constituent units and the object plane 6 and the image plane 7 are origins O and O, respectively. , And the points x ₁ and ± y ₁ are distances x ₁ and ± y from the origin O on the x-axis and the y-axis, respectively.
₁ point.

FIG. 3 is an explanatory view for explaining the action of the Dove prism, in which light incident on the incident surface at an angle α with the optical axis is reflected by the reflective surface, and the light is incident at the same angle in the opposite direction from the outgoing surface. α
In addition, since the entrance / exit surface forms an acute angle with the reflecting surface, it efficiently acts on the light along the optical axis due to refraction. Due to such an action of the Dove prism, the present structural unit projects an inverted image in the y direction as shown in FIG. 2A, but does not project in the x direction as shown in FIG. 2B. The prism 3 serves to project an erect image.

Explain the operation of this structural unit in the xz plane.
For example, the point x on the object plane 6₁The light entering the plano-convex lens 1 from
First, due to the action of the lens 1, the optical axis (z axis) and the angle -tan^-1
(X₁/ F) is converted into parallel light. However, f is
The focal lengths of lenses 1 and 2 are represented. Then, the above
Due to the action of the prism, this light has an angle tan with the optical axis.
^-1(X₁/ F) is converted into parallel light, and the plano-convex lens 2
By the action, the coordinate x on the image plane 7₁Focus on the point. Sanawa
Then, (1) position-angle conversion by lens 1, (2) dub
Angle reversal by prism, (3) Angle by lens 2
By the position conversion, an erecting equal-magnification image in the x direction can be obtained.

FIG. 4 is a perspective view showing the construction of an embodiment of the line imaging element according to the first invention of the present application. This construction unit is linear so that the reflecting surfaces 3'of the Dove prism 3 face each other. A plurality of them are arranged on the top to form an array.
As described above, since the image of each structural unit is erect in the x direction, when arrayed as shown in the figure, the images of adjacent structural units are continuously connected, and the projection of the image on the line is realized. Will be done.

FIG. 5 is a plan view showing a comparative example in which the plano-convex lenses 1 and 2 are arranged so that their convex surfaces face inward, and shows an example in the above-mentioned Japanese Patent Application No. 4-336834. In the figure, the same components as those in FIGS. 1 and 2 are designated by the same reference numerals, and the description thereof will be omitted. By thus directing the convex surface inward, as shown in FIG.
Since the lens surface can be closer to the entrance / exit surface of the Dove prism than the one directed to the outside as in the present structural unit shown in, the utilization factor of light rays is high, and
There is a merit that it is easy to handle because the outside is a flat surface,
Subsequent studies revealed that this form is disadvantageous in terms of MTF, and found that it can be improved by orienting the convex surface to the outside or employing a biconvex lens.

FIG. 6 is a plan view showing a structural unit in the line imaging element according to the second invention of the present application, and this structural unit is the line imaging element according to the first invention of the present application shown in FIGS. 1 and 2. The plano-convex lenses 1 and 2 of the structural unit in 2 are replaced with biconvex lenses 1'and 2 '. The operation of this structural unit is similar to the case of FIGS. 1 and 2 described above, but has an improved MTF and can realize high-resolution image projection.

FIG. 7 is an exploded perspective view showing the structure of an embodiment of a line imaging element according to the third invention of the present application. In this embodiment, the structural units shown in FIGS. 1 and 2 are arrayed. A line imaging element is shown that is optically equivalent to the line imaging element but has a different configuration. The line image forming element of the present embodiment has, as shown in the drawing, a row of Dove prisms in the line image forming element according to the first aspect of the present application.
It is constructed by focusing on the fact that it can be decomposed into two identical Dove prism arrays 8.

That is, as shown in the figure, the dove prisms 3-1, 3-1, ... On the strip-shaped plate 8'-1.
In a direction perpendicular to those reflecting surfaces at a predetermined distance, that is, approximately the thickness of the Dove prism (FIG. 1 or FIG. 3b).
The dove prism row members 8-1 are formed by arranging them at equal intervals and arranging them in the same direction. Similarly, the dove prisms 3-2, 3-2, ... Are arranged on the strip-shaped plate 8'-2 to form the dove prism row member 8-2. Then, both dove prism row members 8-1 and 8-2 are turned upside down and leftward and rightward so that the respective dove prisms 3-1 and 3-2 are superposed so that their reflecting surfaces are in contact with each other. hand,
Form a dove prism row. Convex lens row members 9-1 and 9-2 in which plano-convex lenses 1 and 2 are arranged are arranged on the entrance and exit surfaces of the Dove prism row thus formed. Thus, as a result, the line imaging element including the array of the constituent units shown in FIGS. 1 and 2 is formed.

In the line imaging element according to the third aspect of the present invention having such a configuration, the dove prism row members (prism arrays) 8-1 and 8-2 and the convex lens row members (convex lens sheet) 9-1 and 9 are provided. 2 can be integrally molded with a transparent material such as plastics. By forming these as an integrally molded product, it is possible to save the labor of arranging the Dove prisms when manufacturing the line imaging element, and it is possible to reduce the cost. Further, this makes it possible to always keep the array accuracy of the Dove prisms constant, and it is possible to suppress the occurrence rate of defective products to be low.

In consideration of a concrete example, θ
= 45 °, a = 11.8 mm, b = 2.8 mm, prism height c = 6 mm and material BK7 Dove prism and square polymethylmethacrylate plano-convex lens with radius of curvature 8 mm and 6 mm x 6 mm Then, when the MTF of the 4 lp / mm grating of the structural unit in FIG. 5 was measured, it was about 50% near the origin O of the image plane, whereas from O to x
It was clarified that the distance between the lenses is 3 mm, which is as low as less than 10%, and the MTF is significantly reduced at the portions corresponding to the lenses. On the other hand, when MTF was measured using the same plano-convex lens as the structural unit shown in FIG. 1, 50% or more was recorded at any measurement point, and the arrayed one as shown in FIG. It showed an MTF of 40% or more.

The constituent unit of FIG. 6 in which the convex lens is replaced by the biconvex lens 1 ', 2'having a focal length of 18 mm is about 85% near the origin O and 65% at a point 3 mm away from the origin O in the x direction. , And even when arrayed, 60% overall
The MTF is improved as described above. Since a biconvex lens is more expensive than a plano-convex lens, it should be used when a particularly high resolution is required, and a line imaging element using a plano-convex lens should be used when a relatively low resolution is required. By properly using both, it is possible to support a wide range of applications.

Further, the above-mentioned Dove prism (θ = 45 °,
a = 11.8 mm, b = 2.8 mm, c = 6 mm) are arranged on a 12 mm wide plate with a period of 6 mm to form a prototype of the prism arrays 8-1 and 8-2 of FIG. Was molded with a silicone resin, and a transparent polyurethane resin was poured into the silicone mold in a vacuum to form a dove prism array member, and portions other than the entrance / exit surface and the reflection surface were painted black. Further, plano-convex lens sheets 9-1 and 9-2 having the same arrangement as the plano-convex lens are prepared and a line image forming element equivalent to that shown in FIG. 4 is assembled to obtain continuous projection images. It was confirmed.

If injection molding is used for forming the prism array 8, the prism array can be manufactured with higher accuracy than in this example, and a higher performance line imaging element can be obtained.

[0024]

As described above, according to the line image forming element of the present invention, in the line image forming element in which the structural unit in which the Dove prism and the convex lens are combined is arranged, the plano-convex lens is used as the convex lens, and the convex surface thereof is used. It has become possible to uniformly show a high MTF value by arranging the lens toward the outside, and it has become possible to realize a higher MTF by using a biconvex lens.

Further, by assembling the line imaging element by using the prism array integrally molded so that the Dove prisms are arranged on the line, the assembly is greatly simplified.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a structural unit in a line imaging element according to a first invention of the present application.

FIG. 2 is a plan view showing an example of a structural unit in the line imaging element according to the first invention of the present application.

FIG. 3 is an explanatory diagram for explaining the action of the Dove prism.

FIG. 4 is a perspective view showing a configuration of an embodiment of a line imaging element according to the first invention of the present application.

FIG. 5 is a plan view showing a configuration of a comparative example.

FIG. 6 is a plan view showing a structural unit in a line imaging element according to a second invention of the present application.

FIG. 7 is an exploded perspective view showing a configuration of an embodiment of a line imaging element according to the third invention of the present application.

[Explanation of symbols]

1, 2 ... Plano-convex lens 1 ', 2' ... Bi-convex lens 3, 3-1, 3-2 ... Dove prism 4 ... Light blocking member 5 ... Black adhesive 6 ... Object surface 7 ... Image surface 8-1, 8-2 ... Dove prism array member (prism array) 9-1, 9-2 ... Plano-convex lens array member (plano-convex lens sheet)

Claims (3)

[Claims] 1. Two dove prisms symmetrically placed with their reflecting surfaces on the outside, and two focal lengths placed on their entrance / exit surfaces with their convex parts on the outside. A line imaging element having a plurality of equal plano-convex lenses as constitutional units, and a plurality of the constitutional units arranged in a straight line so that the reflecting surfaces of the Dove prism face each other. 2. A structural unit comprising two dove prisms symmetrically placed with their reflecting surfaces facing outward and two biconvex lenses having equal focal lengths placed on these entrance and exit surfaces, respectively. A line imaging element in which a plurality of the structural units are linearly arranged so that the reflecting surfaces of the Dove prism face each other. 3. Two dove prism row members having dove prisms arranged in the same direction at a predetermined interval in a direction perpendicular to the reflecting surface on a strip-shaped plate, and the dove prism row members are reversed vertically and horizontally. , A dove prism row formed by superposing so that the dove prisms of each dove prism row member are alternately arranged, and arranged to face each of the input and output surfaces of the dove prism row,
The line imaging element according to claim 1 or 2, further comprising: a band-shaped lens sheet having convex lenses arranged on a straight line at the same intervals as the dove prism row.