JPH021467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document illumination device for illuminating a substantially linear portion of a document surface to be read, etc. in a document reading section of a facsimile machine.

Many facsimile machines, copying machines, etc. illuminate a striped portion of the document surface, and use a lens system to form an image of only the striped portion. Read or copy images.

In particular, for facsimile devices, in recent years it has become possible to realize high-speed, high-accuracy, and highly reliable reading devices by adopting a reading method using one-dimensional solid-state image sensors. When a reading method using a sensor is adopted, only the portion of the document surface along the scanning line needs to be stably and uniformly illuminated.

However, what should be taken into consideration for the reading optical system as a whole is the shedding phenomenon (reduction in peripheral light amount) in which the amount of image light at a position off the optical axis of the lens is attenuated during image formation. In other words, in an imaging system using a lens, the so-called "Lambert's
In addition to the "cos ⁴ φ law," the above-mentioned shading is caused by absorption and reflection of light by the lens itself, vignetting at the aperture, and differences in incidence efficiency depending on the angle of incidence on the image sensor. occurs.

To further conceptually explain the shading with reference to FIG. 1, a point 1 on the surface 1a of the original 1
A, 1B, etc. are fixed to point 3 on image plane 3 by lens 2.
When mapped to A, 3B, etc., the luminous flux 4 from the surroundings
Assuming that the angle between the point image 3B and the optical axis 5 is φ, the light intensity of the point image 3B includes an attenuation term of cos ⁴ φ compared to the point image 3A. Assuming that it is a perfectly diffusing surface,
It is generally said that the assumption of a perfect diffusion surface holds true for plain paper).

As an example, when a B4 original is imaged at a magnification of 0.112x using a lens with an angle of view of ±20.5°, cos ⁴ φ=cos ⁴ 20.5°≒0.77. However, due to the light transmission characteristics of the lens itself, there is an attenuation of about Tθ≒0.8 at θ=20.5°, so the overall shedding is 0.6 at the outermost periphery.
It will be about.

Such shedding causes a significant bias (distortion) in the intensity (hereinafter referred to as image intensity) distribution of an image formed during photoelectric conversion in a facsimile device or latent image formation in a copying machine, so it is difficult to obtain a good image. In order to obtain quality, it is important to correct the shading as much as possible to achieve a correct image intensity distribution.

Conventionally, the above-mentioned shading correction methods can be roughly divided into: (a) correction on the light source side;

(b) Correction in the imaging optical system.

(c) Electronic correction in the photoelectric conversion system.

There are three methods, but considering the signal-to-noise ratio of photoelectric conversion, correction using method (a) or (b) is first necessary, and method (c) is applied as a supplement to this. It is considered desirable to

Also, when comparing methods (a) and (b), we find that
In the method (b), when the shedding correction is performed using the light flux near the entrance pupil or exit pupil of the imaging lens, the correction effect can be obtained using a small-area optical filter or a light-shielding plate made of a metal plate, etc. It is excellent in that it can However, this requires greater precision in the mechanical design of the filter or light shielding plate. In this respect, in the method (a), it is sufficient to perform the shading correction along the document surface, and the accuracy in mechanical design is relaxed. This is particularly advantageous in terms of cost.

FIG. 2 shows an example of an optical system of a conventional facsimile apparatus that performs shading correction by the method (a). In the figure, a fluorescent tube 6 is placed on the document surface 1a.
are facing each other. The longitudinal direction of the fluorescent tube 6 is aligned with the main scanning direction (direction perpendicular to the paper surface). 2 is a lens, 8 is an image sensor,
A linear portion extending in the main scanning direction of the area of the document surface 1a illuminated by the fluorescent tube 6 is imaged on the image sensor 8 by the lens 2.

A light shielding plate 9 that does not transmit light is provided between the document surface 1 and the fluorescent tube 6. This blackout version 9
The upper edge 9a of the luminous flux emitted by the fluorescent tube 6 is
A predetermined arcuate curve is formed so that the amount of light of the component incident on the portion near the optical axis of the document surface 1a becomes small, and conversely, the amount of light of the component incident on the peripheral portion of the document surface 1a increases. .

Such conventional devices have a simple structure and seem to be able to achieve the general purpose, but the following two problems occur.
This point still remains as a drawback.

(a) Since the portion close to the shadow of the light-shielding plate 9 is read, if the document surface 1a moves somewhat in the optical axis direction for some reason, a significant change in the amount of light will occur.

(b) It is necessary to set the position of the light shielding plate 9 with considerable accuracy with respect to the set position of the document surface 1a and the fluorescent tube 6, and care must also be taken when replacing the fluorescent tube 6.

The present invention was made in view of the above circumstances, and does not require much precision in mechanical design.
It is an object of the present invention to provide a document illumination device that is highly economical and can provide a stable shading correction function.

The document illumination device according to the present invention includes a shading correction screen that is provided at an appropriate area ratio in each area, in which parts that transmit light with different degrees of diffusion are divided into appropriate areas, between the document surface and the light source. The shading correction is performed between the two.

The present invention will be explained in more detail below based on embodiments shown in the drawings.

FIG. 4 shows an embodiment of the present invention.
A fluorescent tube 6 is arranged below the document surface 1a in the main scanning direction. A shading correction screen 10 is installed between the document surface 1a and the fluorescent tube 6.

2 is a lens, and 8 is a one-dimensional image sensor.
The image is now focused upwards. Further, the linear portion is irradiated with a beam of light emitted from the fluorescent tube 6 and transmitted through the screen 10. Note that arrow a indicates the direction in which the document is fed, that is, the width scanning direction.

The screen 10 includes a diffuse transmission medium section 11
(the hatched part in the figure) and the specular transmission medium part 12 (the part shown in white in the figure) are combined in a mosaic shape. The diffuse transmission medium part 11 is a part that diffuses and transmits the light flux, such as frosted glass or frosted glass, and is designed to uniformly diffuse the parallel incident light flux component within a certain angle range (for example, ±20° to 30°). It's summery. Further, the specular transmission medium section 12 is configured to specularly transmit a luminous flux with uniform transmittance.

To explain in more detail, the screen 10
have a width p (for example, about 5 mm) in the main scanning direction.
It is composed of an appropriate number of areas, and each of these areas has one of the combination patterns of the diffuse transmission medium part 11 and the specular transmission medium part 12 shown in () to () shown in FIG. It consists of

Here, the above () is a pattern consisting only of the regular transmission medium section 12, () is a pattern consisting of only the diffuse transmission medium section 11, and () to () are appropriate patterns consisting of the diffuse transmission medium section 11 and the regular transmission medium section 12. It is a pattern that is combined with an area ratio of () to ().
The area ratio of the diffusion-transmitting medium section 11 gradually increases in this order. As clearly shown in FIG. 5, a predetermined number of areas each consisting of patterns () to () are provided in this order from the peripheral side of the screen 10 toward the optical axis side.

Note that, as described above, the diffuse transmission medium section 11 has the property of diffusing the luminous flux within the range of ±20° to 30° with respect to the parallel incident luminous flux component, so in this embodiment, the above-mentioned pattern () is used. In the area consisting only of the diffuse transmitting medium section 11, when the incident light amount is 1, the light amount in the linear portion on the document surface 1a is attenuated to 0.6 (selecting the material and processing method of the diffuse transmitting medium section 11) (Needless to say, it is possible to select the diffusion angle distribution of the luminous flux and, by extension, the optical attenuation characteristics). Furthermore, in areas formed by other patterns as well, the amount of light is attenuated according to the area ratio of the diffuse transmission medium section 11 and the specular transmission medium section 12.

Since the screen 10 has the above structure,
The light emitted from the fluorescent tube 6 and passing through the screen 10 is attenuated more greatly near the optical axis, and is hardly attenuated near the periphery. Therefore, shading correction can be performed.

According to actual measurements, the light amount distribution of the image corresponding to the white original before the shading correction was as shown by the curve M in FIG. 5, but the light amount distribution of the image plane after the shading correction according to this embodiment , as shown by curve N in the figure, and the fluctuation in light amount with respect to the average image intensity level was less than ±10%. (In FIG. 5, the X axis indicates the main scanning direction). It goes without saying that the shading correction accuracy can be further improved by further increasing the types of combination patterns of the diffuse transmission medium section 11 and the specular transmission medium section 12 constituting each area.

In this document illumination device, even if an appropriate amount of light is attenuated (approximately 1/2), a noticeable shadow does not occur as in the case where the light shielding plate or the like is used. Therefore, when the screen 10 is installed between the document surface 1a and the fluorescent tube 6, the installation position does not require strict precision.

FIG. 7 shows another embodiment of the pattern constituting each area of the shading correction screen according to the present invention. In this embodiment, each area is composed of one of six types of patterns (A) to (F). Each of the patterns is formed by arranging a total of 25 element regions 13 with dimensions a x b, 5 in each direction, and each of the 25 element regions 13 is divided into a predetermined number by the diffusive transmission medium section 11 and the rest. is used as the specular transmission medium section 12.

Specifically, the number of element regions 13 made up of the diffused transmission medium portions 11 in each of the patterns (A) to (F) is 7, 10, 13, 16, 20, and 25, respectively.

In this embodiment, not only the main scanning direction but also
Since the diffuse transmission medium section 11 and the specular transmission medium section 12 are also distributed in a direction perpendicular to this, it is possible to further reduce illumination unevenness compared to the embodiments shown in FIGS. 4 to 6.

In addition, (1) to () and (A) to (F) of each of the above examples
A pattern such as this can be easily realized on a glass plate, a plastic sheet material, etc. by various methods including printing, and thus can be manufactured at low cost.

Further, the specular transmission medium section 12 in the pattern in each of the above embodiments may be formed of a normal transparent glass body, sheet film, etc.; however, the screen 10
The specular transmission medium section 12 may be configured by an opening provided in the material that constitutes the specular transmission medium section 12 . Furthermore, instead of the specular transmission medium section 12, another diffuse transmission medium section having less diffusivity than the diffuse transmission medium section 11 may be provided.

FIG. 8 shows yet another embodiment of the invention.
14 and 15 are paper feed rollers, 16 and 17 are guide plates facing the rollers 14 and 15, and the document 1
is conveyed between roller 14 and guide plate 16 and between roller 15 and guide plate 17 by the rotation of paper feed rollers 14 and 15. Reference numeral 18 denotes an aperture type fluorescent tube, and an aperture 19 of this fluorescent tube 18 faces diagonally to the document surface 1a. A cylindrical lens 20 is installed between the document surface 1 a and the aperture 19 by being attached to a guide plate 17 .

On the plane part of the cylindrical lens 20, there is a shedding correction screen 10, which is provided with a diffuse transmission medium part 11 and a specular transmission medium part 12 in an appropriate area ratio for each area, similar to the case in each of the above embodiments.
are in close proximity or close contact. Further, a portion of the guide plate 16 is bent obliquely with respect to the traveling direction of the original 1 (arrow R direction), and forms a reflective surface 21 . This reflective surface 21 receives the incident light beam that is emitted from the aperture 19 of the fluorescent tube 18, passes through the screen 10 and the cylindrical lens 20, is reflected on the original surface 1a, and the incident light beam that is emitted from the aperture 19 and passes through the screen 10 and the cylindrical lens 20. After passing through the lens 20, the light flux that is directly incident without passing through the original surface 1a is reflected onto the original surface 1a.

In this embodiment as well, the light beam emitted from the aperture 19 of the fluorescent tube 18 passes through the screen 10, and then is condensed by the cylindrical lens 20 and irradiates the document surface 1a. Shading correction can be performed.

In this embodiment, the aperture 19
Since the light beam emitted from the aperture 19 is effectively focused on the document surface 1a by the cylindrical lens 20 and reflected by the reflective surface 21, the light beam emitted from the aperture 19 can be efficiently utilized.

In addition, by forming the diffuse transmission medium part 11 directly on the surface of the cylindrical lens 20 by a processing method such as chemical treatment or sandblasting used in the production of ordinary frosted glass or cloud glass,
The screen 10 is placed directly on the surface of the cylindrical lens 20.
may be formed.

FIG. 9 shows yet another embodiment of the invention.
22 is a glass plate, and the original 1 is placed on this glass plate 2.
2. Reference numeral 18 denotes an aperture type fluorescent tube having an aperture 19, and the aperture 19 faces the document surface 1a with a glass plate 22 in between.

A shading correction screen 10 similar to those in the embodiments described above is attached to or close to the aperture 19 by being attached to the fluorescent tube 18 directly or via a spacer.

Also in this embodiment, the light emitted from the aperture 19 passes through the screen 10 and the glass plate 22 and illuminates the document surface 1a, thereby making it possible to perform the shading correction.

Incidentally, the screen 10 may be formed directly on the wall surface of the aperture 19 in the same manner as in the embodiment shown in FIG.

As described above, according to the present invention, (a) unlike the case of using a conventional light-shielding plate, no noticeable shadow is generated, so when installing the screen between the document surface and the light source, a strict mechanical Does not require design precision. Also, for the same reason,
A stable shading correction effect can be achieved not only when the document is stationary, but also when the document surface is slightly curved or displaced in the optical axis direction while the document is running.

(b) Since the original is illuminated by diffused light, even if dust or dirt adheres to the tube wall of a light source such as a fluorescent tube, uneven illuminance is less likely to occur on the original surface.

(c) Screens can be manufactured easily and at low cost.

You can obtain excellent effects such as

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the shading phenomenon in a general imaging optical system, FIG. 2 is a schematic configuration diagram showing a conventional document illumination device, and FIG. 3 is a front view showing a screen in the conventional document illumination device. , 4A and 4B are a side view and a front view of a document illumination device according to an embodiment of the present invention, and FIG. 5 is a characteristic showing the light intensity correction characteristics of the document illumination device in correspondence with the cross-sectional structure of the screen. 6 is a front view of six types of combination patterns of diffuse transmission medium portions and specular transmission medium portions constituting each area on the screen of the original illumination device, and FIG. FIG. 8 is a sectional view of a document illumination device according to still another embodiment of the present invention, and FIG. 9 is a front view of six types of patterns constituting each area on the screen, and FIG. 9 is a document illumination device according to still another embodiment of the present invention. FIG. 2 is a cross-sectional view of the device. 1...Original, 1a...Document surface, 2...Lens,
6... Fluorescent tube, 10... Shading correction screen, 11... Diffuse transmission medium section, 12... Specular transmission medium section, 18... Aperture type fluorescent tube, 19...
...Aperture, 20...Cylindrical lens.

Claims (1)

[Claims] 1. It has a diffuse transmission medium part and a specular transmission medium part which transmit light with different degrees of diffusion,
and a shading correction screen is provided between the document surface and the light source, and the shading correction screen is configured such that the area ratio of the diffuse transmission medium portion becomes gradually larger than that of the transmission medium portion from the peripheral side of the light source toward the optical axis side. lighting equipment.