JPH0793670B2 - Image reader - Google Patents

Description

The present invention relates to an image reading device, and in particular to a linear light source (such as a fluorescent lamp, a halogen lamp, or an LED array light source in which a plurality of light emitting elements are arranged in a one-dimensional direction). An image on the surface of the original is formed by illuminating the surface of the original from a diagonal direction using a condenser lens of a specific shape, and forming an image of the reflected light beam or the transmitted light beam from the original document on the image pickup element surface via the imaging lens system. The present invention relates to an image reading apparatus suitable for, for example, a copying machine, a facsimile, an image scanner or the like, which sequentially reads information with high accuracy.

(Prior Art) It has been known that an image reading apparatus illuminates a document surface from an oblique direction by using an LED array with a rod-shaped condenser lens as an illumination unit for illuminating the document surface.

Then, the light flux from the document surface is passed through the imaging lens system to the CCD.
The image information is read from the original surface by forming an image on the surface of the image pickup device such as.

In such an image reading apparatus, when the image information on the document surface is read by using an image pickup device such as a CCD, the illuminance distribution (light amount distribution) on the document surface should be as uniform as possible to improve the reading accuracy. Is preferred.

FIG. 9 is a schematic view of a main part of a conventional image reading apparatus of this type and an explanatory view showing an illuminance distribution on a document surface.

In the figure, 90 is an LED array with a condensing lens (document illuminating section), which is composed of a linear light source (LED array light source) 91 and a rod-shaped condensing lens 92 for condensing the document 3 in an oblique downward direction. Lighting from.

Reference numeral 3 is an original (for example, a reflective original or a transparent original), which is moved in the sub-scanning direction as indicated by an arrow D by a conveyance roller 7 described later.

Reference numeral 6 denotes a reflecting mirror, which bends the optical path by reflecting the light flux reflected from the original 3 toward the image forming means 4 described later. An image forming unit 4 forms an image of the reflected light flux from the original 3 on the surface of an image sensor (image sensor) 5.
The image pickup device 5 is composed of a one-dimensional CCD, for example. The conveyance roller 7 conveys the document 3 according to the reading direction.

In the figure, the light flux emitted from the linear light source 91 is condensed by a rod-shaped condenser lens 92, and the condenser lens 92 illuminates a predetermined area from the reading position A of the original 3 obliquely from below.

The reflected light flux from the illuminated original 3 is reflected by the reflection mirror 6.
An image is formed on the surface of the image sensor 5 by the image forming means 4 via
As a result, the image information on the third surface of the document is read.

FIG. 10 is an explanatory view showing the emission energy emission distribution to the space of the luminous flux emitted from the linear light source 91 at this time and an explanatory view for explaining the definition of a virtual plane π described later.

As shown in the figure, the direction in which the intensity value of the luminous energy of the luminous flux emitted from the normal linear light source 91 reaches a peak (maximum) is substantially vertically above the substrate 91a of the linear light source 91.

An imaginary plane formed by two directions, that is, the direction Y in which the value of the intensity of the emission energy has the maximum value and the longitudinal direction of the linear light source (for example, the chip array direction of the LED array) X is defined as a virtual plane π.

The virtual plane π is the linear light source 9 with respect to the substrate 91a of the linear light source 91.
Given in an orthogonal plane containing 1.

Here, the cross-sectional shape orthogonal to the original plane 3 and the virtual plane π of the rod-shaped condenser lens 92 constituting the conventional original illumination unit 90 shown in FIG. 9 is generally a plane of symmetry with the virtual plane π as a boundary. It is symmetrical to the plane.

(Problems to be Solved by the Invention) However, when a document is illuminated obliquely from below by using such a rod-shaped condenser lens, the following problems occur.

The optical path length from the linear light source (light emitting point) 91 to the reading position B on the document surface after passing through the condenser lens 92 is the linear light source.
Scanning position C on the 3rd side of the original from 91 through the condenser lens 92
Since it is shorter than the optical path length to reach the reading position B
Has higher illuminance than the reading position C.

A phenomenon in which the image forming position where the focal point of the light flux passing through the center of the condenser lens 92 and the focal point of the light flux passing through the peripheral portion are displaced, and in particular the light flux passing through the peripheral portion is strongly bent and goes around inward,
So-called negative spherical aberration occurs.

Therefore, as shown in the illuminance distribution on the document surface of FIG. 9, ripples occur in the illuminance of the document surface at each of the reading positions B and C.

As a result of the appearance of such a phenomenon, the variation ΔE of the illuminance at the deviation of the document reading position (between the reading positions B and C) due to the mechanical precision of the apparatus becomes large and the unevenness of the illuminance distribution on the document surface is caused. come.

For this reason, in the conventional image reading apparatus, it is difficult to set a margin for signal output in designing the apparatus, and strict mechanical precision requirements and adjustment items increase, which causes a cost increase of the apparatus.

In order to solve the above-mentioned problems of the conventional image reading apparatus, the present invention appropriately forms the shape of the condenser lens with respect to the virtual plane π or decenters the position of the condenser lens to read a document. The variation in illuminance on the document surface that occurs when the position is misaligned can be suppressed to a small value, the mechanical precision is relaxed while achieving high-accuracy reading, and the assembly can be easily assembled without increasing the adjustment items. An object is to provide an image reading device.

(Means for Solving Problems) An image reading apparatus of the present invention illuminates a reading surface on a document surface with a light beam from a linear light source obliquely with respect to the reading surface,
In an image reading device for reading the image information on the document surface by forming an image of the light flux from the reading surface on the image pickup element surface by an image forming means, a condenser lens is provided between the linear light source and the document surface. The condensing lens is provided with a refraction of a non-symmetrical shape with respect to a plane π formed by two directions of a direction in which the emission energy intensity of the linear light source has a maximum value and a longitudinal direction of the linear light source. Ra> Rb, where Ra is the radius of curvature of a refracting surface closer to the original surface than the plane π and Ra is Rb, and Rb is the radius of refraction surface farther away from the original surface than the plane π. In this way, the illuminance distribution on the document surface is made uniform.

(Embodiment) FIG. 1 is a schematic view of a main part of an image reading apparatus according to an embodiment of the present invention.

In the figure, the same elements as those shown in FIG. 9 are designated by the same reference numerals.

Reference numeral 1 denotes a linear light source, which includes, for example, an LED array light source in which a plurality of light emitting elements are arranged in a one-dimensional direction, a halogen lamp, a fluorescent lamp, and the like, and is arranged obliquely with respect to the original 3.

Reference numeral 2 denotes a condenser lens according to the present invention, which is provided between the reading device for the original 3 and the linear light source 1. The condensing lens 2 has a refraction surface that is asymmetric with respect to the virtual plane π described above, and is formed in a rod shape in the longitudinal direction of the linear light source 1, for example, the direction in which a plurality of light emitting elements are arranged. There is.

In the present embodiment, each element of the linear light source 1 and the condenser lens 2 constitutes a document illuminating section 10, and the document illuminating section 10 illuminates the document 3 obliquely from below.

In this embodiment, the original 3 illuminated by the original illuminating unit 10 is moved by the conveying roller 7 in the sub-scanning direction as indicated by arrow D in FIG. An image is formed on the surface of the image sensor 5 by the image means 4 and the image information on the surface of the original 3 is read sequentially.

Next, the shape and optical action of the condenser lens 2 according to the present invention will be described with reference to FIG.

FIG. 2 is an enlarged cross-sectional explanatory view of a part of the linear light source 1 and the condenser lens 2 shown in FIG.

In the figure, the condenser lens 2 has a surface shape that is asymmetrical (non-plane symmetric) with respect to the virtual plane π.

Specifically, when the distance d ₀ from the intersection a between the incident surface of the condenser lens 2 and the optical axis to the substrate 1a is set as d ₀ = 1, the exit surface of the condenser lens 2 and the optical axis from the intersection a. interval d ₁ to an intersection b of the
Is d ₁ = 11, the radius of curvature R2 of the lens surface 2a on the incident surface side is R2 =
5. Radius of curvature R of one surface 2b1 of the exit surface side lens surface 2b
1 is R1 = 6, and the width dimension D of the condenser lens 2 is set to a ratio of D = 8 to set the dimensions of each part of the condenser lens 2.

The surface 2b2 (the portion near the original surface 3 in FIG. 1) on the left side of the drawing on the exit surface side of the condenser lens 2 which is an asymmetric portion, for example, exceeds 30 ° from the virtual plane π when viewed from the center of curvature O. No power (refractive power) is attached to the portion 2b2.
That is, the non-power portion 2b2 is formed from a flat surface and the other portion 2
The b1 (power part) is formed in a cylindrical shape. This forms a left-right asymmetry with respect to the virtual plane π.

The light beam from the linear light source 1 that has passed through the non-power portion 2b2 of the condenser lens 2 having such a shape is not condensed at the reading position of the original 3. For this reason, the illuminance for illuminating the original 3 is reduced, but in the vicinity of the reading position B, the phenomenon of the light flux wrapping around due to spherical aberration does not occur.

In this embodiment, this optical action is used to prevent ripples from occurring in the illuminance distribution between the reading positions B-A on the document surface.

On the other hand, the portion 2b on the right side in the drawing of the exit surface with respect to the virtual plane π
The shape of 1 is the same as the shape (cylindrical shape) of the conventional condenser lens 92 shown in FIG.
The illumination illuminance decreases more toward the reading position C, but the illumination illuminance rises again due to the rounding phenomenon due to spherical aberration, and eventually the illuminance variation ΔE from the reading position B to the reading position C as shown in FIG. It is possible to obtain a broad (wide) original surface illuminance distribution that is kept small.

In particular, compared with the conventional illuminance distribution between the document reading positions B-A shown by the dotted line in FIG. 3, the variation in illuminance becomes ΔE as shown by the solid line in FIG. Is getting Thereby, the illuminance between the document reading positions B and C is made uniform.

As described above, in the present embodiment, the refracting surface shape of the condenser lens 2 is formed so as to be asymmetric with respect to the virtual plane π as described above, and the light flux emitted from the linear light source 1 is generated by the condenser lens 2. The original surface is efficiently irradiated to make the illuminance distribution on the original surface uniform, and accurate reading is performed.

In this embodiment, the cross-sectional shape of the condenser lens 2 orthogonal to the original surface and the virtual plane π is formed by the cylindrical shape and the flat surface to make the illuminance distribution uniform on the original surface. Any shape may be used as long as it is non-asymmetrical. For example, even if the cross-sectional shape of the condenser lens 2 is formed by using an aspherical shape, the present invention is similar to the above-mentioned illumination on the document surface. The distribution can be made uniform.

As shown in FIG. 4, the radii of curvature R1 and R2 of the two refracting surfaces may be different on the left and right in the drawing with the virtual plane π as a boundary, for example, R1 (left)> R2 (right). Even if the condensing lens 2 is formed by using the same, the variation ΔE in the illuminance distribution on the document surface can be suppressed to a small level as in the above-described embodiment.

FIG. 5 and FIG. 6 are explanatory views relating to a document surface of a condensing lens of another embodiment of the present invention and a sectional direction orthogonal to the virtual plane π, and an explanatory view of illuminance distribution on the document surface.

The condenser lens 2 of the above-mentioned embodiment collects the luminous flux emitted from the linear light source 1 by forming the shape itself of the condenser lens 2 so as to have an asymmetric shape with respect to the virtual plane π. The case where the light is condensed by the optical lens 2 and the original 3 is illuminated from the obliquely downward direction by the condensing lens 2 is shown. In each of the embodiments shown in FIGS. 5 and 6, the shape of the condensing lens 2 is The condensing lens 2 itself has a shape symmetrical to the optical axis.
The symmetry plane of is eccentric with respect to the virtual plane π, and the original 3 is illuminated obliquely from below.

That is, the condensing lens 2 is decentered so that the shape of the condensing lens 2 is asymmetric with respect to the virtual plane π.

Condensing lens 2 in each of the embodiments shown in FIGS.
Has a semi-cylindrical shape which is symmetrical with respect to the optical axis.

In FIG. 5, the condenser lens 2 is configured so as to be decentered parallel to the virtual plane π by a distance l so as to be asymmetric about the virtual plane π.

At this time, left-right asymmetrical coma aberration occurs due to decentering, and as shown in the figure, the light beam is refracted in the area between the reading positions A to C of the document because the angle of incidence on the curved surface of the condenser lens 2 is large. The amount is large and it is strongly bent and tends to become dense.

On the other hand, in the area between the reading positions A and B, on the contrary, since the angle of incidence on the curved surface of the condenser lens 2 is small, the amount of refraction of the light beam is small and the light beam is weakly bent and tends to be sparse.

As a result, the variation ΔE in illuminance on the document surface can be suppressed to a small level as shown in FIG.

As described above, in the present embodiment, the reading position B that accompanies when the document is illuminated obliquely from below using the decentering coma aberration generated when the condenser lens 2 is decentered in parallel with the virtual plane π.
The phenomenon that the illuminance on the side (shorter optical path length) increases is mitigated. As a result, the variation ΔE of the illuminance is suppressed to be small, and the illuminance on the document surface is made uniform.

In FIG. 6, the condenser lens 2 is tilted and decentered with respect to the substrate 1a by an angle θ so as to be asymmetric with respect to the virtual plane π.

At this time, by using the decentering coma aberration generated when the condenser lens 2 is decentered, the reading position B (the side where the optical path length is short is accompanied by the illumination of the document from the obliquely downward direction as in the embodiment of FIG. ), The phenomenon that the illuminance rises is alleviated, and the illuminance on the document surface is made uniform.

In this way, the condenser lens 2 shown in each of the embodiments of FIGS. 5 and 6 is decentered so as to be asymmetric with respect to the virtual plane π by using a kamaboko type lens, and at this time, By utilizing the generated coma aberration, the variation ΔE of the illuminance on the document surface is suppressed to be small.

It should be noted that there is an optimum solution for the shape of the condenser lens 2 at this time even if both surfaces are formed with convex portions.

Further, as described above, a condensing lens having a shape that is asymmetrical with respect to the virtual plane π may be further arranged in parallel decentering or tilt decentering with respect to the virtual plane π.

In each of the embodiments described above, the original surface of the condenser lens and the virtual plane π
Although it has been shown only in the cross-sectional direction orthogonal to, the condensing lens 2 having a partially strong convex shape as shown in FIGS. 7 and 8 having power in the longitudinal direction of the linear light source,
Alternatively, even in the condenser lens 2 having a shape in which convex portions are arranged stepwise, the same effect as that of the above-described embodiment can be obtained as long as the shape is asymmetric with respect to the virtual plane π.

Further, in each of the embodiments, the document illuminating unit of the image reading apparatus is configured to illuminate the document obliquely from below and read the image information of the document, but it is also possible to illuminate the document obliquely from above and use the transmitted light flux. The present invention can obtain the same effects as those of the above-mentioned embodiment.

Further, as the original scanning, in each embodiment, the original is moved in the sub-scanning direction by using the conveying roller to sequentially read the image information of the original, but the original is fixed and the optical system is moved to use the mirror lens for scanning. The present invention can be similarly applied to an apparatus using a mirror scanning method and an apparatus using an original scanning method in which an image forming unit and an optical member such as an image sensor are integrally formed to scan an original.

(Effect of the Invention) According to the present invention, a condenser lens having a predetermined shape is provided between the linear light source and the document reading position so as not to be asymmetric with respect to the virtual plane π, and the condenser lens is provided. By illuminating the original surface via the light source, even if the original surface is illuminated from an oblique direction, it is possible to suppress the variation in the illuminance on the original surface caused by the deviation of the original reading position. It is possible to reduce the mechanical precision of the image reading apparatus and to achieve an inexpensive image reading apparatus with a high reading accuracy that facilitates the assembly process.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an image reading apparatus according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of a part of the linear light source and the condenser lens shown in FIG. 1, and FIG. FIG. 4 is an explanatory view of the illuminance distribution on the document surface, FIG. 4 is a cross-sectional view of a condenser lens having a shape in which the left and right curvatures are different, and FIGS. 5 and 6 are the condensers of another embodiment of the present invention. FIG. 7 is a perspective view of a condenser lens of another embodiment of the present invention, and FIG. 9 is a conventional image reading method. FIG. 10 is a schematic view of a main part of the apparatus and an explanatory view of illuminance distribution on a document surface, and FIG. 10 is an explanatory view for explaining the definition of the virtual plane π and an explanatory view of emission energy distribution. In the figure, 1 and 91 are linear light sources, 2 and 92 are condenser lenses, 3 are originals, 4 is image forming means, 5 is an image pickup element, 6 is a reflection mirror, and 7
Is a transport roller, 1a is a substrate, 10 and 90 are original document illumination parts, and π is an imaginary plane determined by two directions, the direction in which the emission intensity of the linear light source has a maximum value and the longitudinal direction of the linear light source.

Claims (1)

[Claims] 1. A reading surface on a document surface is illuminated with a light beam from a linear light source obliquely to the reading surface, and the light beam from the reading surface is imaged on an image pickup element surface by an image forming means. In an image reading device for reading image information on the document surface,
A condenser lens is provided between the linear light source and the document surface,
The condensing lens has a refracting surface that is asymmetric with respect to a plane π formed by two directions of a direction in which the emission energy intensity of the linear light source has a maximum value and a longitudinal direction of the linear light source. When the radius of curvature of the refracting surface closer to the original surface than the plane π is Ra and the radius of curvature of the refractive surface farther from the plane π to the original surface is Rb, Ra> Rb. The image reading apparatus is characterized in that the illuminance distribution on the surface of the original is made uniform.