JPH03121653A - Picture reader - Google Patents

Abstract

PURPOSE:To decrease the dispersion of illuminance on an original face caused when an original read position is deviated by providing a condenser lens of a prescribed shape between a linear light source and the original read position not in symmetry with respect to an imaginary plane and lighting the original face via the condenser lens. CONSTITUTION:A condenser lens 2 is provided between a linear light source 1 and a reader of an original 3. The refracting face of the condenser lens 2 is in asymmetry with respect to an imaginary plane pi and formed with array of bars in the lengthwise direction of the linear light source 1 such as in a direction where plural light emitting elements are arranged. Then an original light section 10 is formed by the linear light source 1 and the condenser 2 and the original light section 10 lights the original 3 from the oblique and lower direction. Since the shape of the condenser lens 2 is formed properly with respect to the imaginary plane pi in this way, the dispersion in the illuminance on the original face caused when the read position of the original 3 is deviated is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image reading device, and particularly 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 one dimension). A condensing lens with a specific shape is used to illuminate the document surface from an oblique direction, and the reflected or transmitted light beam from the document is imaged on the image pickup device surface via an imaging lens system to produce an image on the surface. The present invention relates to an image reading device that sequentially reads information at a high M degree and is suitable for, for example, copying machines, facsimile machines, and image scanners.

(Prior Art) Conventionally, an image reading apparatus is known in which an LED array with a bar-shaped condensing lens is used as an illumination unit for illuminating the document surface to illuminate the document surface from an oblique direction.

Then, the light beam from the document surface is passed through an imaging lens system to a CO
Image information from the document surface is read by forming an image on the surface of an image sensor such as D.

When reading image information on the document surface using a COD shaded image sensor in such an image reading device, it is important to make the illuminance distribution (light m distribution) on the document surface as uniform as possible to improve reading accuracy. It is preferable to do so.

FIG. 9 is an explanatory diagram showing a schematic view of the main parts of the conventional image reading device and an illuminance distribution on the document surface.

In the figure, reference numeral 90 denotes an LED array (original illumination unit) with a condensing lens, which is composed of a linear light source (LED array light source) 91 and a rod-shaped condensing lens 92 for condensing light.
is illuminated diagonally from below.

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

Reference numeral 6 denotes a reflecting mirror, which bends the optical path by reflecting the reflected light beam from the original 3 toward an imaging means 4, which will be described later. Reference numeral 4 denotes an image forming means that forms an image of the reflected light beam from the original 3 on the surface of an image sensor (image sensor) 5.

The photographing element 5 is one-dimensional, for example, a CCD or the like. The conveyance roller 7 conveys the original 3 according to the reading direction.

In the figure, a light beam emitted from a linear light source 91 is condensed by a rod-shaped condensing lens 92, and the condensing lens 92 illuminates a predetermined area centered on the reading position A of the original 3 from diagonally below.

The reflected light flux from the illuminated original 3 is reflected by a reflection mirror 6.
An image is formed on the surface l- of the image sensor 5 by the imaging means 4 via the image forming means 4, thereby reading the image information on the surface 3 of the document.

FIG. 10 is an explanatory diagram showing the luminous energy emission distribution in space of the luminous flux emitted from the linear light source 91 at this time, and an explanatory diagram explaining the definition of the virtual plane π, which will be described later.

As shown in the figure, the direction in which the intensity of the luminous energy of the light beam emitted from the linear light source 91 peaks (maximum) is approximately perpendicularly above the substrate 91a of the linear light source 91.

The virtual plane formed by two directions, the direction Y in which the intensity value of the emitted light energy has the maximum value, and the longitudinal direction of the linear light source (for example, the direction in which chips are arranged in an LED array) X is hereinafter defined as a virtual surface plane. .

Note that the virtual plane π is given by a plane orthogonal to the substrate 91a of the linear light source 91 and including the linear light source 91.

Here, the cross-sectional shape of the rod-shaped condensing lens 92 constituting the conventional document illumination section 90 shown in FIG. It has a plane of symmetry.

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

■The optical path length from the linear light source (light emitting point) 91 to the reading position fffB on the document surface after passing through the condensing lens 92 is as follows: The illuminance at reading position B is higher than that at reading position C because the optical path length until reaching reading position raC is shorter.

■The imaging position that focuses the light beam that has passed through the center of the condenser lens 92 and the light beam that has passed through the periphery may be shifted.In particular, the light beam that has passed through the periphery is strongly bent and wraps around inward, a so-called phenomenon. Negative spherical aberration occurs.

Therefore, as shown in the illuminance distribution on the document surface in FIG. 9, the reading position i1 of the valley! Ripples occur in the illuminance of the document surface of B and C.

As a result of this phenomenon, the variation ΔE in illuminance due to the deviation of the document reading position (between reading positions raB and C) due to the mechanical precision of the device becomes large, causing unevenness in the illuminance distribution on the document surface. come.

For this reason, in conventional image reading devices, it is extremely difficult to set margins for signal output in the device design, and strict mechanical accuracy requirements and an increase in the number of adjustment items become a factor that increases the cost of the device.

In order to solve the problems of the conventional image reading device described above, the present invention is capable of reading a document by appropriately forming the shape of the condensing lens with respect to the virtual plane π, or by decentering the position of the condensing lens. An inexpensive configuration that can suppress variations in illuminance on the document surface that occur when the document is misaligned, reduce mechanical precision while achieving high-precision reading, and can be easily assembled without increasing the number of adjustment items. The purpose is to provide an image reading device.

(Means for Solving the Problems) The image reading device of the present invention illuminates a reading surface on a document surface with a light beam from a linear light source from a diagonal direction with respect to the reading surface,
In an image reading device that forms an image of a light beam from the reading surface on an image sensor surface by an imaging means and reads image information on the document surface, the linear light source is provided between the linear light source and the document surface. characterized by providing a condenser lens having a refractive surface asymmetrical with respect to a plane π formed by two directions: the direction in which the luminous energy intensity of the linear light source reaches its maximum value, and the longitudinal direction of the linear light source. There is.

(Embodiment) FIG. 1 is a schematic diagram of main parts of an image reading device according to an embodiment of the present invention.

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

A linear light source 1 is composed of, for example, an LED array light source in which a plurality of light emitting elements are arranged in one dimension, a herogen lamp, a fluorescent lamp, etc., and is arranged diagonally with respect to the document 3.

Reference numeral 2 denotes a condensing lens according to the present invention, which is provided between the document reading device 3 and the linear light source 1. The condensing lens 2 has a refractive surface that is asymmetrical with respect to the virtual plane π described above, and is formed into a rod-like shape with respect to the longitudinal direction of the linear light source l, for example, the direction in which a plurality of light emitting elements are lined up. There is.

In this embodiment, a linear light source 1 and a condensing lens 2 constitute a document illumination section 10, and the document 3 is illuminated from diagonally downward by the document illumination section 10.

In this embodiment, the original 3 illuminated by the original illumination unit 10
While moving the document 3 in the sub-scanning direction as shown by the arrow shown in the figure by the conveyance roller 7, the reflected light beam from the document 3 is sequentially imaged on the surface of the image pickup device 5 by the imaging means 4 via the reflection mirror 6. Image information on three sides of the original is being read.

Next, the shape and optical function of the condensing lens 2 according to the present invention will be explained using FIG. 2.

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

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

Specifically, when the distance d0 between the intersection a of the entrance surface of the condenser lens 2 and the optical axis and the substrate 1a is set to d0=1, the distance between the exit surface of the condenser lens 2 and the optical axis from the intersection a is The distance d between the points of intersection is d,=t 1. The radius of curvature R2 of the lens surface 2a on the entrance surface side is R2=5, the radius of curvature R1 of the surface 2bl on one side of the lens surface 2b on the exit surface side is R1=6, and the width dimension of the condenser lens 2 is D=8. The dimensions of each part of the condenser lens 2 are set according to the ratio of .

Also, the surface 2b2 on the left side of the drawing on the exit surface side of the condensing lens 2, which is an asymmetrical part (the part close to the document surface 3 in FIG. 1), for example, is 30 degrees from the virtual surface π when viewed from the center of curvature O.
The portion 2b2 beyond 2b2 has no power (refracting power), that is, the non-power portion 2b2 is formed from a flat surface, and the other portion 2b1 (power portion) is formed from a cylindrical shape. As a result, the shape is asymmetrical with respect to the virtual plane π.

The light flux from the linear light source l that passes through the non-power portion 2b2 of the condensing lens 2 having such a shape is not focused on the reading position of the original 3, and therefore the illumination intensity for illuminating the original 3 is reduced. In the vicinity of the reading position B, the phenomenon of light flux convergence due to spherical aberration does not occur.

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

On the other hand, the right part 2 of the exit surface in the drawing with respect to the virtual plane π
The shape of bl is the conventional condenser lens 92 shown in FIG.
(cylindrical shape), the illumination illuminance decreases as it moves from the reading position iQA toward the reading position rftC, but due to the wrap-around phenomenon caused by spherical aberration, the illumination illuminance rises again and eventually moves from the reading position 19B to the reading position rIIC.
Until now, as shown in Figure 3, we have created a broad document surface illuminance distribution with the illuminance variation reduced by ΔE ().
can be done.

In particular, the conventional document reading position 13- indicated by the dotted line in FIG.
Compared to the illuminance distribution between A and A, in this embodiment, the illuminance variation is ΔE as shown by the solid line in the figure, and the illuminance distribution is kept extremely small (1).
-C is aimed at making the illuminance uniform.

In this way, in this embodiment, the shape of the refractive surface of the condenser lens 2 is formed to be asymmetric with respect to the virtual plane π as described above, and the light beam emitted from the linear light source 1 is directed by the condenser lens 2. The illuminance is efficiently irradiated onto the document surface, and the illuminance distribution on the document surface is made uniform to achieve highly accurate reading.

In this embodiment, the cross-sectional shape of the condenser lens 2 perpendicular to the document surface and the virtual plane π is formed by a cylindrical shape and a plane to make the illuminance distribution on the document surface uniform. For example, even if the cross-sectional shape of the condenser lens 2 is formed using an aspherical shape, the present invention can reduce the illuminance on the document surface as described above. It is possible to make the distribution uniform.

Further, as shown in FIG. 4, the curvatures of the two refractive surfaces are set to diameters 1i11.
R2 may be set to a different value on the left and right sides of the drawing with the virtual flat streetcar as the border. For example, even if the condenser lens 2 is formed so that R1 (left)>R2 (right), the same result as in the above embodiment can be achieved. The variation ΔE in the illuminance distribution on the document surface can be kept small.

FIGS. 5 and 6 are explanatory diagrams of a cross-sectional direction perpendicular to the document surface and the virtual plane π of a condensing lens according to another embodiment of the present invention, and an explanatory diagram of the illuminance distribution on the document surface, respectively.

The condensing lens 2 of the above-mentioned embodiment is formed so that the shape of the condensing lens 2 itself is asymmetrical with respect to the virtual tram, so that the light beam emitted from the linear light source l is condensed. Note: Although the case where the light is focused by the light lens 2 and the document 3 is illuminated from diagonally downward by the light condensing lens 2 is shown, in each of the embodiments shown in FIGS. 5 and 6, the shape of the light condensing lens 2, The condensing lens 2 has a shape that is symmetrical with respect to the optical axis.
The plane of symmetry of is eccentric to the virtual plane π, and the original 3 is illuminated obliquely from below.

That is, it is characterized in that the condenser lens 2 is decentered so that the shape of the condenser lens 2 is asymmetric with respect to the virtual γ and π.

Condenser lens 2 in each embodiment of FIGS. 5 and 6
has a semicylindrical shape that is symmetrical with respect to the optical axis.

In FIG. 5, the condensing lens 2 is parallel and decentered by a distance @It in parallel to the virtual plane π, so that it is asymmetrical with respect to the virtual tram.

At this time, asymmetrical comatic aberration occurs due to eccentricity, and as shown in the figure, in the region between reading positions A and C of the document, the angle of incidence on the curved surface of the condenser lens 2 is large, so the light beam is refracted. It shows a tendency for the view to be greatly curved and become denser.

Moreover, in the area between the reading positions Δ and B, on the contrary, since the angle of incidence on the curved surface of the condenser lens 2 is small, the refraction of the light beam is small and weakly bent, and the light beams tend to be sparse.

As a result, the variation ΔE in illuminance on the document surface can be kept small as shown in the figure.

In this way, in this embodiment, the reading position B that accompanies when illuminating the original from diagonally below is utilized by using the eccentric coma aberration that occurs when the condensing lens 2 is decentered in the direction of the virtual plane π. This alleviates the phenomenon of increased illuminance (on the short optical path length side). As a result, variations in illuminance 8E are suppressed to a small level, and the illuminance on the document surface is made uniform.

In FIG. 6, the condenser lens 2 is placed at an angle θ with respect to the substrate 1a.
By making the inclination and eccentricity by 1, it is configured to be asymmetrical with respect to the virtual plane π.

At this time, using decentering coma aberration that occurs when the condensing lens 2 is decentered, the reading position ra8 (1111 with a short optical path length) that accompanies when illuminating the original from diagonally downward as in the embodiment shown in FIG. ) to reduce the phenomenon in which the illuminance increases and to make the illuminance uniform on the document surface.

In this way, the condensing lens 2 shown in each of the embodiments of FIGS. 5 and 6 uses a semicylindrical lens and is decentered so as to be asymmetric with respect to the virtual plane π. The generated coma aberration is used to suppress the variation ΔE in illuminance on the document surface.

Note that an optimal solution exists even if the shape of the condenser lens 2 at this time is formed with convex portions on both sides.

Further, as described above, the condenser lens having a shape asymmetrical with respect to the virtual plane π may be further arranged with N-row eccentricity or tilt eccentricity with respect to the virtual plane π.

Each of the embodiments constructed above is based on the original surface of the condensing lens and the virtual plane π.
Although only the cross-sectional direction perpendicular to the linear light source has been shown, for example, as shown in FIGS. 7 and 8, the condenser lens 2 has a strong convex shape, and has power in the longitudinal direction of the linear light source.
Alternatively, even if the condenser lens 2 has a shape in which convex portions are arranged in stages, the same effect as in the above embodiment can be obtained if the condenser lens 2 has a shape that is imaginary asymmetric with respect to the plane π.

Furthermore, in each of the embodiments, the document illumination section of the image reading device is configured to illuminate the document from diagonally below to read the image information of the document, but it is also possible to illuminate the document from diagonally above and use transmitted light flux. The present invention can obtain the same effects as the above-described embodiments.

Furthermore, in each of the embodiments, the original is scanned in the sub-scanning direction using a conveyance roller, and the image information of the original is sequentially read. 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 optical member such as an image forming means and an imaging element are integrally configured to scan an original.

(Effects of the Invention) According to the present invention, a condensing lens of a predetermined shape is provided between a linear light source and a document reading position so as to be asymmetrical with respect to the virtual plane π, and the condensing lens is By illuminating the document surface through the scanner, it is possible to suppress variations in illumination on the document surface that occur when the document reading position shifts, even if the document surface is illuminated from an oblique direction. In addition, it is possible to achieve an inexpensive image reading device with high reading accuracy and easy assembly process.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main parts of an image reading device according to the -χ embodiment of the present invention, FIG. 2 is an enlarged sectional view of a portion of the linear light source and condensing lens shown in FIG. 1, and FIG. An explanatory diagram of the illuminance distribution on the document surface in Figure 1, and Figure 4 shows the shape with different left and right curvatures as fY.
FIGS. 5 and 6 are cross-sectional views of a condensing lens according to another embodiment of the present invention, and explanatory diagrams of the illuminance distribution on the document surface with respect to the direction thereof, FIGS. 7 and 6, respectively. 8 is a perspective view of a condensing lens according to another embodiment of the present invention, FIG. 9 is a schematic diagram of the main parts of a conventional image reading device and an explanatory diagram of the illuminance distribution on the document surface, and FIG. 10 is a virtual plane. FIG. 2 is an explanatory diagram for explaining the definition of π and an explanatory diagram of the emission energy distribution. In the figure, l, 91 is a linear light source, 2.92 is a condenser lens, 3
is the document, 4 is the image forming means, 5 is the image pickup device, 6 is the reflection mirror, 7 is the transport roller, la is the substrate, 10.90 is the document illumination section, π is the direction in which the emission intensity of the linear light source takes the maximum value This is a virtual plane determined from two directions: and the longitudinal direction of the linear light source.

Claims (1)

[Claims] (1) A reading surface on the document surface is illuminated with a light beam from a linear light source from a diagonal direction with respect to the reading surface, and the light beam from the reading surface is imaged on the image sensor surface by an imaging means, In an image reading device that reads image information on a surface, there are two directions between the linear light source and the document surface: the direction in which the emitted energy intensity of the linear light source is at its maximum value, and the longitudinal direction of the linear light source. What is claimed is: 1. An image reading device comprising: a condenser lens having a refractive surface asymmetrical with respect to a plane π formed by the condenser lens.