JP2848477B2 - Optical reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reader for irradiating a character or image on a document with light and receiving the reflected light by a light receiving element.

[0002]

2. Description of the Related Art FIG. 4 is a view showing the configuration of a conventional optical reading apparatus, wherein 1 is a light receiving element, 2 is a convex lens located below the light receiving element 1 and arranged on the optical axis to the light receiving element 1. The light is condensed by the convex lens 2 to form an image on the light receiving element 1. Reference numeral 3 denotes a document to be read on which characters and images are written, and reference numerals 4a and 4b denote light receiving elements 1 through a convex lens 2.
An optical axis extending, in the lamp as a light emitting element for irradiating the intersection of the original 3 located away light receiving element 1 and the predetermined distance L _1, includes a plurality of lamps in order to increase the illuminance of the reading surface of the original 3 The light axis of the lamp 4a is
The lamps 4a and 4b are connected to the light receiving element 1 such that the optical axis of the document 3 intersects with the intersection of the original 3 and the optical axis of the lamp 4b intersects the intersection of the optical axis of the light receiving element 1 with the optical axis of the original 3 and the lamp 4a. Are arranged symmetrically with respect to the optical axis.

[0003] As a result, the light emitted from the lamp 4a is reflected by the original 3 and is condensed by the convex lens 2 so that the light receiving element 1
At the same time, the light emitted from the lamp 4b is reflected on the original 1, condensed by the convex lens 2 and reaches the light receiving element 1, and the characters and images on the original 3 form images on the light receiving element 1.
FIG. 5 is an explanatory diagram showing an example of the directional characteristics of the lamps 4a and 4b, and shows the relationship between the illuminance and the angle at a certain distance from the lamps 4a and 4b. The lamps 4a and 4b have a built-in lens to increase the illuminance on the reading surface of the document 3, and condensed light to sharpen the directivity. Light emitted by the lamps 4a and 4b is, as shown in FIG. Light is collected in a small area.

FIG. 6 shows a conventional light receiving element 1 to an original 3
FIG. 5 is an explanatory diagram showing a relationship between the distance L to the output and the output V of the light receiving element 1, wherein a two-dot chain line indicates an output when the document 3 is irradiated by one of the lamps 4 a and 4 b;
The solid line indicates the output when the document 3 is irradiated by both the lamps 4a and 4b. 4, the distance L ₁ shown in FIG. 6, the lamp 4
When the light emitted from a and 4b is reflected by the original 3 and condensed by the convex lens 2 and reaches the light receiving element 1, the focus is adjusted, and the characters and images on the original 3 are converted into images on the light receiving element 1. a distance required for connecting, when the document 3 is located a distance L ₁ away from the light receiving element 1 is output V of the light receiving element 1 becomes large,
The output V of the light receiving elements shifted position of the original 3 from the distance L ₁ in perspective respectively is to decrease rapidly.

[0005]

However, in the conventional optical reading apparatus, bending of the original, change in thickness,
Since the reading surface of the original by the flapping or the like when to convey the document is moved in the vertical direction, FIG. 4 the distance between the original and the light receiving element can not be maintained at a predetermined distance L ₁ shown in FIG.

[0006] As described in FIG. 6, the distance between the document and the light receiving element even if changes in the direction or away direction who approaching from L ₁ decreases the output of the light receiving element, the output of the light receiving element decreases document There is a problem that the difference in shading between the above character and image portions and the other portions is small, and accurate recognition cannot be performed. The present invention has been made to eliminate the above-described problem that the illuminance at the reading position changes due to the vertical movement of the reading surface of the document.

That is, even when the original reading surface moves up and down due to the original bending, the change in the thickness, or the fluttering during the transportation of the original, the variation in the illuminance can be reduced, and the reading accuracy of characters and images can be improved. It is an object to provide a possible optical reader.

[0008]

In order to achieve this object, the present invention illuminates a reading surface of a document with a plurality of light emitting elements, collects the reflected light with a lens, forms an image on a light receiving element, In an optical reader that reads characters and images, when the original moves along the optical axis that passes through the lens to the light-receiving element, the characters and images read by the light-receiving element must be within the depth of field where they can be recognized. The irradiation positions of the plurality of light emitting elements are shifted vertically along the optical axis of the light receiving element so that the illuminance on the optical axis of the light receiving element is substantially constant over the range of the depth of field. is there.

[0009]

According to the present invention having the above-described structure, when a plurality of light emitting elements illuminate the reading surface of an original, the reflected light is condensed by a lens to form an image by a light receiving element, and characters and images on the original are recognized. Is done. Here, the characters read by the light receiving element,
Within the range of the depth of field where the image can be recognized, and the irradiation position by the plurality of light emitting elements such that the illuminance on the optical axis of the light receiving element is substantially constant over the range of the depth of field. By shifting the light source up and down along the optical axis of the light receiving element, an image is formed on the light receiving element so that the illuminance does not fluctuate even if the original moves up and down and does not affect the recognition of characters and images. It is.

[0010]

An embodiment will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an optical reader according to one embodiment of the present invention. In the figure, 1 is a light receiving element, 2 is a convex lens located below the light receiving element 1 and arranged on the optical axis to the light receiving element 1, and the light is condensed by the convex lens 2 to form an image on the light receiving element 1. .

Reference numeral 3 denotes an original to be read on which characters and images are written. Reference numeral 5a denotes a first lamp. The optical axis of the first lamp 5a passes through the convex lens 2 and the light receiving element 1a.
A predetermined distance (L ₁ −a ₁ ) from the optical axis to the light receiving element 1
The mounting position or mounting angle of the first lamp 5a is set so as to intersect at a distant position.

Reference numeral 5b denotes a second lamp such that the optical axis of the second lamp 5b intersects the optical axis of the light receiving element 1 at a predetermined distance (L ₁ + a ₂ ) from the light receiving element 1. The mounting position or mounting angle of the second lamp 5b is set. Here, the distance L ₁ is the light receiving element 1
The original 3 is placed at a distance L ₁ from the original 3 when this
By irradiating the intersection of the light and the optical axis of the light receiving element 1, the characters and the image of the original 3 located on the intersection are focused, and the image of the character and the image of the original 3 is formed on the light receiving element 1. Is the distance at which characters and images can be recognized.

[0013] However, the focus that fit not only when the original 3 is placed at a distance L ₁ from the light receiving element 1, there is a range that looks like is in focus before and after. This range is called the depth of field, and is obtained by the following equation.

[0014]

(Equation 1) H: hyperfocal distance (distance at which the far end of the depth of field becomes infinity) f: focal length B: object distance (distance from document to light receiving element) T1: near point T2: far point C: minimum Circle of confusion 1 ": 0.03 mm, 2/3": 0.02 mm, 1 /
2 ″: 0.015 mm F: f / D D: lens aperture The range from T1 to T2 shown in the above formulas (2) and (3) is the depth of field, that is, the range in focus, and the distance (a ₁ + A ₂ ) falls within the depth of field, and the distance (a ₁ + a ₂ ) is obtained by the following equation (4).

[0015]

## EQU2 ## Depth of field = T2−T1 ≒ a ₁ + a ₂ (4) As described above, the optical axis of the first lamp 5a is set to the optical axis of the light receiving element 1 and the light receiving element 1 A predetermined distance (L ₁ −
a ₁ ) The two lamps 5b intersect at a distance from each other, and the optical axis of the second lamp 5b is set at a predetermined distance (L ₁
+ A ₂ ) when crossing at a distance, the distance (L ₁ +
range of the distance (L ₁ -a ₁₎ from a _2), i.e., a character on the document 3 to focus over a range of depth of field is an image is recognizable, the optical axis extending the convex lens 2 as the light receiving element 1 The lamps 5a and 5b are set so that the illuminance is constant.
Directional characteristics, mounting position or mounting angle are set.

FIG. 2 is an explanatory diagram showing the relationship between the distance L from the light receiving element 1 to the document 3 and the output V of the light receiving element 1 in this embodiment. The two-dot chain line shows the output when the original 3 is irradiated with either one of the lamps 5a and 5b, and the solid line shows the combined output when the original 3 is irradiated with both the lamps 5a and 5b.

[0017] As shown in FIG. 2 by the solid line, across the distance L ₁ from the distance (L ₁ + a ₂₎ the distance when the document 3 is located in the range of (L ₁ -a _1), the light receiving element 1 The output is almost constant. FIG. 3 is a diagram for explaining the operation of the present embodiment.
As shown in FIG. 2A, when the document 3 approaches the light receiving element 1 and the document 3 is located at a distance (L ₁ −a ₁ ) from the light receiving element 1, the first lamp is mainly used as shown in FIG. The required illuminance is ensured by 5a. FIG. 3 (b)
When the document 3 is separated from the light receiving element 1 and the document 3 is located at a distance (L ₁ + a ₂ ) from the light receiving element 1 as shown in FIG.
The illuminance required mainly by the second lamp 5b is secured. Further, when the document 3 is located within the range of the distance (L ₁ −a ₁ ) to the distance (L ₁ + a ₂ ), the illuminance required by the sum of the light amounts of the first lamp 5 a and the second lamp 5 b Secured. As described above, the fluctuation of the illuminance due to the vertical movement of the document 3 can be suppressed low.

In the above-described embodiment, a pair of lamps is arranged with the optical axis to the light receiving element 1 interposed therebetween. However, if the number of lamps is further increased, the variation in illuminance due to the vertical movement of the document 3 is reduced. It can be kept lower. Further, in the above-described embodiment, a plurality of first lamps 5a and second lamps 5b are respectively arranged in a line, and the light receiving element 1 is arranged in a line corresponding to the line.
A configuration may be adopted in which a certain width of the document can be read at the same time. In this case, the convex lens 2 can be replaced with a rod lens array that forms an image at the same magnification over the entire area in the line direction.

[0019]

As described above, according to the present invention, a plurality of light-emitting elements illuminate the reading surface of a document, the reflected light is condensed by a lens and focused on a light-receiving element to read characters and images. In an optical reading device, when a document moves along an optical axis extending from a lens to a light receiving element, characters and images read by the light receiving element are within a depth of field at which the characters and images can be recognized, and The irradiation positions of the plurality of light emitting elements are shifted up and down along the optical axis of the light receiving element so that the illuminance on the optical axis of the light receiving element is substantially constant over the range of the depth of field.

Therefore, even if the reading surface of the document moves up and down due to the bending and change in the thickness of the document and the fluttering during document transport, the illuminance does not fluctuate much, and at this time, the recognition of characters and images may be affected. Since an image is formed on the light receiving element so as not to cause the problem, there is an effect that the accuracy of reading and recognizing characters and images can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an optical reading device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a distance from a light receiving element to a document and an output of the light receiving element in the embodiment.

FIG. 3 is an operation explanatory diagram of the present embodiment.

FIG. 4 is a configuration diagram showing a conventional optical reading device.

FIG. 5 is an explanatory diagram showing an example of a directional characteristic of a lamp.

FIG. 6 is an explanatory diagram showing a relationship between a distance from a light receiving element to a document and an output of the light receiving element in the related art.

[Description of Signs] 1 light receiving element 2 convex lens 3 document 5a first lamp 5b second lamp

Claims (1)

(57) [Claims] 1. An optical reading apparatus for irradiating a reading surface of a document with a plurality of light emitting elements, condensing reflected light by a lens, forming an image on a light receiving element, and reading a character or an image, comprising the steps of: When the original moves along the optical axis of the light receiving element, the characters and images read by the light receiving element can be recognized within the depth of field and within the depth of field. An optical reading device, wherein irradiation positions of a plurality of light emitting elements are shifted up and down along an optical axis of a light receiving element so that illuminance on the optical axis is substantially constant.