JPH0337077Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a reflective reading type optical reading device used in facsimile machines, copying machines, and the like.

1 and 2 show conventional examples of such reflective reading type optical reading devices. As shown in FIGS. 1 and 2, the optical reading device has a convergent light transmitting array 1. As shown in FIGS.

The transmitter array 1 is constructed by arranging a large number of refractive index gradient lenses 2 made of a transparent material such as glass or plastic in a cylindrical shape in, for example, two rows in a close-packed state, and filling the gaps between them with opaque resin. It is an optical element that can transmit an image with a two-dimensional spread at once by sequentially overlapping the erect equal-magnification real images formed by the individual lenses 2.

In addition, the refractive index of the gradient index lens 2 is maximum at the axial center position and decreases in the radial direction in approximately proportion to the square of the distance, so even if the light input and output end surfaces are flat, the lens still functions. It is a lens in which light travels in a meandering manner around its axis.

The transmitter array 1 is arranged so that one end surface 1a faces a transparent document table 8, and the band-shaped portion of the document 3 placed on the document table 8 and facing the end surface 1a is The light is irradiated from below by a light source 4 such as an LED array. In addition, so as to face the other end surface 1b of the transmitter array 1,
An image sensor 5 such as a CCD array is provided.

In the configuration described above, light emitted from the power source 4 and reflected by the original 3 enters the transmitter array 1 from the end surface 1a. The light traveling through the transmitter array 1 and emitted from the end face 1b is sensed by the image sensor 5.

Since such light transmission and sensing are performed simultaneously in the width direction of the original 3, the original 3 can be gradually moved in the direction of arrow A, or vice versa.
If the transmitter array 1, light source 4, image sensor 5, etc. are gradually moved in the direction of arrow B while keeping the original 3 stationary, the entire surface of the original 3 can be read. In other words, in this case, the document 3 is the object to be read.

By the way, since the transmitter array 1 using the gradient index lens 2 ideally forms an erect, equal-magnification real image, the image sensor 5 detects the portion of the document 3 corresponding to the image sensor 5, that is, the portion to be read. Only the reflected light from the transmitter array 1 should enter the transmitter array 1.

However, in reality, there is an aberration from the ideal refractive index distribution near the outer periphery of the lens 2, and due to this aberration, reflections from parts of the original 3 that do not correspond to the image sensor 5, that is, parts that should not be read. Light also passes through the transmitter array 1 to the image sensor 5.
This poses a problem in that the resolving power of the reading mechanism is reduced.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide an optical reading device that has a high resolution despite having an extremely simple configuration.

Hereinafter, an embodiment of the optical reading device according to the present invention will be described with reference to FIG.

As is clear from FIG. 3, in this embodiment, the anti-reflection mask 6 is brought into contact with the lower surface of the document table 8, and one slit 7 formed in the mask 6 is used for reading the document 3. The structure may be substantially the same as that of the conventional example shown in FIGS. 1 and 2, except that the portions are disposed opposite each other.

The mask 6 is made by attaching a matte black coating to a metal plate, a glass plate, etc. to prevent reflection of light, and when the transmitter array 1 is moved, this mask 6 is also attached to the transmitter array 1. They are designed to work as one.

In the embodiment shown in FIG. 3, of the light from the light source 4, the light received by the end surface 1a of the transmitter array 1 is the reflected light from the slit 7, that is, from the part of the document 3 to be read. Only reflected light.
Therefore, the reading head has a high resolving power because the light from the light source 4 is not reflected from other parts and the reflected light is not sensed by the image sensor 5 via the transmitter array 1. will have the following.

In the conventional example shown in FIGS. 1 and 2, the width of the band-shaped portion of the document 3 irradiated by the light source 4 is 5 to 10 mm, and the width is 5 to 10 mm. The width of the band-shaped image is approximately 4 mm, but since the width of the image sensor 5 is approximately 0.1 mm, an image with a width slightly larger than this is sufficient; any other light will cause a decrease in resolution. . However, if the width _W1 of the slit 7 is too small, the image formed on the image sensor 5 will become smaller than necessary, and the resolution will decrease due to the decrease in the amount of light.

Therefore, the width W ₁ of the slit 7 is approximately 0.05 to 1 mm (that is, approximately 1/2 to 10 times the width of the image sensor 5).
is preferable, and more preferably about 0.1 to 0.6 mm (that is, about one to several times the width of the image sensor 5). Further, the width W ₂ of the mask 6 may be at least equal to or larger than the field of view width of the transmitter array 1 .

FIG. 4 shows a method of measuring the resolving power of an optical reader, and FIG. 4A shows a method of measuring the resolving power of a conventional read head without an antireflection mask.

As shown in FIG. 4A, a test pattern 11 in which pairs of black lines and white lines having the same width are lined up is printed on the original 3, and the reflected light from this test pattern 11 is transmitted. The body array 1 receives light and forms an image 12.

Figure 4B shows straight lines X ₁ and X ₂ in Figure 4A.
The upper light intensity level is shown. That is, I _nax =100,
A rectangular wave having a light intensity level having a value of I _nio =0 is converted by the transmitter array 1 into a slightly sloping waveform having values of i _nax and i _nio .

This state can be expressed as MTF expressed by the following formula.
The resolving power expressed by (Modulation Transfer Function) was measured.

MTF=i _nax −i _nio /I _nax +I _nio ×100 (%) In Figure 4A, test pattern 11 is
In the case of 4LP/mm (Line Pair/mm; the number of pairs of black lines and white lines per mm), the maximum value of MTF measured for a large number of pairs of black lines and white lines = 68.6%, minimum value = 63.7% , the average value was 66.1%.

FIG. 4C shows a method for measuring the resolving power of the optical reader of this embodiment with an anti-reflection mask. The mask 6 used had a slit 7 with a width of 0.5 mm. In this case, the MTF measured for a large number of pairs of black and white lines is
Maximum value = 82.6%, minimum value = 75.0%, average value = 79.2
%, and it was confirmed that the optical reading device of this example had higher resolution than the conventional example.

The present invention has been explained above based on one embodiment.
The present invention is not limited to this embodiment.
Various changes are possible. For example, in this embodiment, the original 3 is placed on the upper surface of the transparent original platen 8, and the mask 6 is brought into contact with the lower surface of the original platen 8, so that the original 3 is irradiated from below. If the light is irradiated from above, there is no need to use the transparent document table 8, and therefore the mask 6 can be brought into contact with or close to the document 3.

As described above, in the present invention, an anti-reflection mask having a slit is disposed facing the object to be read, and the reflected light from the portion of the object to be read facing the slit is directed to a convergent light transmitter. Since the light is received in an array, it is possible to provide a reading head having a high resolution despite having an extremely simple structure.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway schematic perspective view showing a conventional example, Fig. 2 is a schematic side view of the conventional example shown in Fig. 1, and Fig. 3 is a schematic diagram showing an embodiment of the present invention. 4 shows a method for measuring resolution, A is a schematic perspective view showing the conventional measuring method shown in FIG. 1, B is a schematic graph showing the measurement results, C is a schematic perspective view showing the measuring method of the embodiment shown in FIG. 3; In addition, in the symbols used in the drawings, 1...
. . . convergent light transmitting body array, 3 . . . original, 4 . . . light source, 6 . . . antireflection mask, 7 .

Claims (1)

[Claims for Utility Model Registration] A light source for irradiating an object to be read, and a columnar shape that receives light from the light source reflected by the object to be read at one end surface and receives the light from the light source reflected by the object to be read, and the other end face receives light from the light source that is reflected by the object to be read. A plurality of the convergent light transmitters are arranged in parallel to each other so that the end faces of the one and the other end faces of the convergent light transmitters are emitted from the end faces and form an image on the object to be read. a convergent light transmitting body array, a light sensor disposed on an imaging plane of the convergent light transmitting body array, and between the object to be read, the light source, and the convergent light transmitting body array; and has a slit extending along a surface of the convergent optical transmitter array facing the object to be read, and a field of view of the convergent optical transmitter array in the direction facing the object to be read. and an anti-reflection mask each having a size equal to or greater than the above, the light source, the convergent light transmitter array, the optical sensor, and the anti-reflection mask are directed toward the object to be read in the width direction of the slit. An optical reader that is moved relative to the