JP2878308B2 - Document reading device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a document reading apparatus.

2. Description of the Related Art Conventionally, as shown in FIG. 4, a light source (straight tube fluorescent lamp) 3 for illuminating a document 2 on a document table 1 is provided movably in the sub-scanning direction relative to the document table 1. There is a document reading apparatus in which an image of the document 2 is formed on the image sensor 5 by the optical system 4. As shown in FIG. 5, the light source 3 has an opening 6 in which the irradiation angle with respect to the document table 1 is determined.

When the original 2 is illuminated by the light source 3, there are a case where there is a dark portion such as a black image near a reading point on the original 2 and a case where there is a bright portion such as white. There is a phenomenon that the brightness of the reading point differs due to this difference. This is because the reflected light of the document 2 is incident on the opening 6 of the light source 3 and
The illumination distribution 7 on the reading line 8 spreads as shown in FIG. This phenomenon becomes a serious problem in guaranteeing the gradation accuracy as the read gradation increases. When the original white document is certified and the original document having a white area surrounded by the black area is illuminated, the white reading level is lower in the latter. For example, as shown in FIG. 6, when reading the reading line 8 in the main scanning direction, if the black image 9 exists on both sides in the sub-scanning direction in the range between a and b in the main scanning direction, the white reading level becomes the seventh level. As shown in the figure, if the portion other than between the abs is 100%, the ab
It becomes 0%. However, the light source 3 is a case where a 15 mm diameter FL tube having an opening angle of 70 ° is used. Due to such a phenomenon, the read gradation cannot be guaranteed more than 5 gradations. On the other hand, 32 to 256 gray levels are required today.

For this reason, as described in Japanese Utility Model Laid-Open Publication No. 63-113144, a plurality of partition plates parallel to the sub-scanning direction are provided at predetermined intervals between a light source elongated in the main scanning direction and the document. By arranging them in the main scanning direction, there is a device designed to compensate for the above-mentioned drawbacks. However, illumination unevenness occurs between a portion with and without a partition plate. In other words, the illumination distribution in the area between the partition plates is a Kamaboko-shaped illumination distribution in which the center is bright and the vicinity of the partition plate is dark. As a result, when a read image is copied, a plurality of bands along the sub-scanning direction appear as density unevenness.

Means for Solving the Problems A document table on which a document is placed and an opening which defines an irradiation angle with respect to the document table are extended in the main scanning direction, and the document table is extended in the sub-scanning direction. A light source that moves relatively to the original, an optical system arranged in an optical path from the document to the image sensor, and extends from both sides of the opening toward the reading line of the document in parallel with the main scanning direction. And a light-shielding plate located at the center of the opening and extending toward the reading line of the document in parallel with the main scanning direction.

The illumination range in the sub-scanning direction can be narrowed by blocking unnecessary illumination light to the document with a light shielding plate.
Since the light shielding plate is also located at the center of the opening, the directivity of the illumination light is increased, and the influence of the brightness of the reading line can be reduced.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 4 to 6 are denoted by the same reference numerals, and description thereof is omitted. As shown in FIG. 1, two light sources 3 are provided by straight tube fluorescent lamps facing each other with a vertical line passing through a reading line 8 interposed therebetween. A light-shielding plate 10 extending toward the reading line 8 and a light-shielding plate 11 extending from the center of the opening 6 toward the reading line 8 are arranged in the main scanning direction. As shown in FIG. 2, both ends of these light-shielding plates 10 and 11 are formed continuously and integrally as one part.

In such a configuration, the light from the light source 3 is
The image of the original 2 is formed on the image sensor 5 by the optical system 4 shown in FIG. At this time, unnecessary illumination light for the document 2 is
By shielding the light at 10 and 11, the illumination range in the sub-scanning direction can be narrowed as shown in the illumination distribution 7 in FIG. 1, and light can be prevented from entering the opening 6 from the document 2. Accordingly, the influence of the brightness around the reading line 8 can be reduced. Therefore, as described above, the influence of the black image 9 when reading the white portion between the abs of the reading lines 8 of the original 2 shown in FIG. 6 can be reduced. As a result, as shown in FIG. 3, the white read level in the read line 8 is 98
The difference can be almost eliminated by about%. Thereby, the image of the document 2 can be read faithfully.

In addition, since the light-shielding plate 11 is provided at the center of the opening 6 of the light source 3 toward the reading line 8, it is possible to further limit the illumination light emitted to portions other than the reading line 8. Shade plate 10
By making the inner surface of the light-shielding plate 11 and both surfaces of the light-shielding plate 11 substantially non-reflective surfaces such as black, it is possible to further limit the illumination light emitted to portions other than the reading line 8. Even if the surfaces of the light shielding plates 10 and 11 are reflection surfaces, the illumination distribution 7 can be narrowed as long as the surfaces are non-diffuse reflection surfaces. Therefore, the object can be achieved even with a regular reflection surface (mirror surface). In this case, the illumination light amount on the reading line 8 can be increased as compared with the non-reflection surface.

Advantageous Effects of the Invention As described above, the present invention provides a platen on which a document is placed,
A light source extending in the main scanning direction with an opening having an irradiation angle with respect to the platen and moving relatively in the sub-scanning direction with respect to the platen; An optical system arranged in an optical path leading to the reading line of the original in parallel with the main scanning direction from both sides of the opening and positioned at the center of the opening and parallel to the main scanning direction. Since the light-shielding plate extends toward the reading line of the document, the illumination range in the sub-scanning direction can be reduced by blocking unnecessary illumination light on the document with the light-shielding plate. Because the light-shielding plate is also located, the directivity of the illumination light is increased, and the influence of the brightness of the reading line can be reduced. In addition, the guaranteed range of the reading gradation without being affected by the brightness of the original document Greatly improve DOO has the effect of such possible.

[Brief description of the drawings]

1 to 3 show an embodiment of the present invention.
FIG. 1 is a vertical sectional side view showing the relationship between a platen and a light source.
FIG. 3 is a perspective view showing a light source and a light shielding plate, FIG. 3 is a graph showing a change in a white reading level on one reading line, FIGS. 4 to 7 show a conventional example, and FIG. FIG. 5 is a principle view showing the internal structure of the document reading apparatus, FIG. 5 is a vertical sectional side view showing the relationship between the document table and the light source, FIG. 6 is a plan view showing an image pattern on the document, and FIG. 7 is a graph showing a change in a white reading level of the image. DESCRIPTION OF SYMBOLS 1 ... Original platen, 2 ... Original, 3 ... Light source, 4 ... Optical system, 5 ... Image sensor, 6 ... Opening, 8 ... Read line, 10, 11 ...
Shade plate

Claims (1)

(57) [Claims] 1. An original plate on which an original is placed, and an opening which defines an irradiation angle with respect to the original plate, extends in the main scanning direction, and extends in the sub-scanning direction with respect to the original plate. A light source that moves relatively to the original, an optical system arranged in an optical path from the original to the image sensor, and extending from both sides of the opening toward the reading line of the original in parallel with the main scanning direction. A document reading device, comprising: a light-shielding plate located at the center of the opening and extending toward a reading line of the document in parallel with a main scanning direction.