JPH0522523A - Document reader - Google Patents

Abstract

PURPOSE:To improve the uniformity of the S/N of a CCD image sensor and a signal waveform after shading correction when the relation of the mounting position between a shading correction board and a fluorescent light is fluctuated in the shading correction for the document reader. CONSTITUTION:The end of a shading correction board 8 is bent in the direction approaching the surface of the document gradually, and the upper end surface is formed so that an effective radiation width becomes almost constant all over the full length, and varied in the effective radiation width direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device such as a facsimile or an image scanner which illuminates a document surface with a tubular light source, and in particular, shading correction for uniforming the illuminance of the document surface by blocking a part of the irradiation light. It concerns the improvement of the plate.

[0002]

2. Description of the Related Art Generally, in a document reading apparatus, a document surface is illuminated by a tubular light source such as a fluorescent lamp, and reflected light is imaged by a lens on a light receiving surface of a light source conversion element such as a CCD image sensor. The information on the document surface is converted into an electric signal. FIG. 11 is a diagram showing a configuration of a photoelectric conversion unit of a conventional document reading apparatus of this type disclosed in, for example, Japanese Patent Laid-Open No. 58-96453. In the figure, 1 is a document to be read, 2 is a roller that gradually conveys the document 1 in the direction of arrow X in the figure, 3 is a fluorescent lamp as a tubular light source that illuminates the document surface of the document 1, and 4 is from the document surface. A reflecting mirror for reflecting the reflected light and a CCD for converting the light source of the image formed on the light receiving surface.
An image sensor, 6 is an imaging lens that collects the reflected light reflected by the reflection mirror 4 and forms an image on the light receiving surface of the CCD image sensor 5, and 7 shields a part of the illumination light of the original surface of the fluorescent lamp 3. This is a shading correction plate.

Next, the operation will be described. The original surface of the original 1 is illuminated by the fluorescent lamp 3, and the reflected light of the line P-P on the original surface is redirected by the reflection mirror 4 and then collected by the imaging lens 6 to be the light receiving surface of the CCD image sensor 5. An image is formed on the upper surface and converted into an electric signal for one scanning line. further,
The original 1 is conveyed by the roller 2 in the direction of arrow X in the drawing at a predetermined speed, and the sequential scanning operation is performed.

FIG. 12 is a waveform diagram showing a photoelectric conversion signal for one scanning line. The signal waveform when the shading correction plate 7 is not provided has a large signal level in the central portion near both ends as indicated by v1 in the figure. The signal level of becomes smaller. This is because the fluorescent lamp 3 has a finite length and the brightness distribution becomes dark near both ends of the fluorescent lamp 3. Therefore, as shown in FIG. 13, the central portion AA of the shading correction plate 7 is made higher than the end portion B-A so that the central portion in the length direction of the fluorescent lamp 3 is partially shaded, and the original 1 The illuminance on the surface is corrected so that the corrected signal is shown in Fig. 12.
The shape of the upper end surface is determined so as to be substantially uniform as indicated by v2.

[0005]

Since the conventional document reading apparatus is constructed as described above, the effect of shading correction is obtained when the relationship between the mounting positions of the fluorescent lamp 3 and the shading correction plate 7 varies. There is a problem that the uniformity of the corrected signal waveform is impaired.

This point will be described with reference to FIGS. 14, 15 and 16.
explain in detail. The line segment P-P on the document surface of the document 1 is illuminated by the light of the region M (hatched region in the drawing) of the illumination light of the fluorescent lamp 3, and a part of the light is shielded by the shading correction plate 7. Is shown to be done.
In FIG. 14, the central portion of the fluorescent lamp 3 is shielded by the AA portion of the shading correction plate 7 and is illuminated only by the light passing through the x1 portion, and both ends are shielded by the B portion of the shading correction plate 7 and x2. FIG. 15 shows a state where the shading correction plate 7 is moved in the Y direction from the state shown in FIG. 14 and the positional relationship with the fluorescent lamp 3 is changed. In the case of the state, the portion corresponding to AA of the shading correction plate 7 is illuminated with the light passing through x3, and the portion corresponding to B is illuminated with the light passing through x4. Therefore, it can be easily understood that the effect of shading correction at the central portion AA of the shading correction plate 7 and both ends B is substantially determined by the ratio of x1 to x2 and x3 to x4. However, the amount of change in the Y direction shown in FIG. 14 is the same for both the A-A part and the B part, so x2 / x1 <x4 / x3, and the shading correction amount is larger in the state of FIG. Become.

FIG. 16 is a diagram showing a photoelectric conversion signal that has been subjected to shading correction. Even if the photoelectric conversion signal is corrected almost uniformly as shown in v ₂ at the mounting position shown in FIG. 14, v ₃ at the mounting position shown in FIG. When the mounting position moves in the direction opposite to the Y direction shown in FIG.
As shown in v4, the correction is broken in a state opposite to v3.
Further, since the conventional document reading apparatus is configured as described above, the CC of the original illumination having a constant brightness and high sensitivity is used.
The signal output is saturated for the D image sensor, and conversely S for the low sensitivity CCD image sensor.
The / N ratio cannot be obtained, and particularly in a document reading device that photoelectrically converts a gradation image or a full-color image, it is necessary to adjust the document illumination to an optimum one according to the individual sensitivity of the CCD image sensor. As a method for adjusting the brightness of the original illumination, there is dimming by changing the current of the fluorescent lamp 3, but this method changes the spectral energy distribution of the fluorescent lamp 3, deterioration of life, and device cost for dimming. However, the method of adjusting the brightness of the original illumination by moving the shading correction plate 7 so that it is already extended has a problem that the uniformity of shading correction is impaired.

The present invention has been made in order to solve the above problems, and even if the position of the shading correction plate is displaced, the uniformity of shading correction is not impaired.
It is another object of the present invention to provide a document reading device capable of adjusting the brightness of document illumination.

[0009]

[Means for Solving the Problems] Claim 1 according to the present invention
In the document reading device, the end side of the shading correction plate is gradually bent toward the document surface, and the upper end surface is formed so that the effective irradiation width is substantially constant over the entire length. According to another aspect of the document reading apparatus of the present invention, the end portion side of the shading correction plate is gradually bent toward the document surface, and the upper end surface is formed so that the effective irradiation width is substantially constant over the entire length and the effective irradiation is performed. It is variable in the width direction.

According to a third aspect of the present invention, there is provided a document reading apparatus, wherein a portion for passing illumination light from a tubular light source is a shading correction plate having slits facing and parallel to the tubular light source, and an end of the shading correction plate. The document reading device according to claim 4, wherein the side of the document is gradually bent toward the document surface, and the width of the slit and the distance of the end of the shading correction plate that gradually approaches the document surface are adjustable. Is.

[0011]

The shading correction plate of the document reading apparatus according to the present invention can uniformly hold the shading correction even when the position of the shading correction plate is displaced, and can adjust the brightness of the document illumination.

[0012]

EXAMPLES Example 1. FIG. 1 is a diagram showing a configuration of a main part of a document reading device according to an embodiment of the present invention, and FIG. 2 is a diagram showing a shading correction plate constituting a main part of the document reading device in FIG. In the figure, the original 1 and the fluorescent lamp 3 are the same as those of the conventional apparatus. Reference numeral 8 denotes a shading correction plate, which is bent so that the end portion B side gradually approaches the document surface, and the upper end surface has an effective irradiation width which will be described later at any portion between B-A, between A-A and between A-C. Are formed to be substantially constant. That is, of the light of the area (hatched area in the drawing) indicated by M of the illumination light of the fluorescent lamp 3 in FIG. 1, the length of the portion not shielded by the AA portion and the BC portion, that is, The upper end faces (B to C) are formed so that the effective irradiation widths y1 and y2 are substantially equal.

Since the amount of passing light per unit area in the effective irradiation width y1 and the amount of passing light per unit area in the effective irradiation width y2 are different, even if the effective irradiation widths y1 and y2 are the same. The shading correction is performed, and the brightness of the original irradiation is adjusted to be substantially uniform over the entire length. In addition, the length Z of the bent portion that determines the effective irradiation width y2
Is long when the shading correction amount is large, and is short when the shading correction amount is small. These lengths are determined based on experiments so that the corrected signal waveform is most uniform.

In FIG. 3, bending points D and E of the shading correction plate 9 are added to further improve the correction accuracy. As described above, the shape of the correction plate becomes complicated, but the correction shape can be arbitrarily changed by further adding a bending point or forming a curved shape. In short, in the shading correction plates 8 and 9 of the present invention, the boundary line (upper end surface) that blocks the illumination light is defined by the length direction of the fluorescent lamp 3.
It is formed so that the fluorescent lamp 3 is changed in the direction of the original surface and the effective irradiation width is almost the same in any part of the shading correction plates 8 and 9 in the length direction.

Example 2. 4 is a diagram showing a configuration of a main part of a document reading device according to a second embodiment of the present invention, and FIG. 5 is a diagram showing a shading correction plate constituting a main part of the document reading device in FIG. In the figure, the original 1 and the fluorescent lamp 3 are the same as those in the first embodiment of the present invention.
Reference numeral 10 denotes a shading correction plate, which includes a fixed frame 10a and a movable frame 10b.
The fixed frame 10a and the movable frame 10b are fixed by screws through the elongated holes 10c formed on the fixed frame 10a side. The upper end surface of the movable frame 10b is processed into the same shape as the upper end surface of the shading correction plate 8 in the first embodiment shown in FIG.

According to the shading correction plate 10 thus constructed, the movable frame 10b is fixed along the elongated hole 10c.
Since the upper end surface can be adjusted in the direction of the arrow Y in the figure by sliding on a, it is possible to adjust the brightness of the document illumination without impairing the uniformity of shading correction. It is possible to adjust the document illumination according to the sensitivity of.

Embodiment 3. 6 is a diagram showing a configuration of a main part of a document reading apparatus according to a third embodiment of the present invention, and FIG.
FIG. 8 is a diagram showing a shading correction plate which constitutes a main part of the document reading apparatus in FIG. 8, and FIG. 8 is an operation explanatory diagram of shading correction in the third embodiment. In the figure, 1 and 3
Is the same as that described in the first embodiment. A shading correction plate 11 is provided with parallel slits 12 facing the fluorescent lamp 3. Shading correction plate 11
Ends B and C are gradually bent so as to approach the original surface, and the shading on the irradiation line P-P on the original surface is performed on the basis of the principle described below regarding the decrease in the irradiation light amount at both ends of the fluorescent lamp 3. Get uniformity of correction.

In FIG. 8, the illuminance E (Lux) of the irradiation line P-P on the original surface is X, where X is the distance between the fluorescent lamp 3 and the irradiation line P-P.
The distance between the shading correction plate 11 and the irradiation line PP is x,
If the width of the slit 12 is d, the light emitting surface of the fluorescent lamp 3 is approximated to a perfect diffusing surface, its surface luminance is L (cd / m ² ), and the proportional constant is k.

E = (kL / X) (d / x) holds as an approximate expression.

That is, since the distance X between the fluorescent lamp 3 and the irradiation line P-P and the surface brightness L are fixed depending on the structure of the apparatus, the illuminance E of the irradiation line P-P is proportional to the width of the slit 12 and is shaded. It is inversely proportional to the distance x between the correction plate 11 and the irradiation line PP. Therefore, by bending the ends B and C of the shading correction plate 11 so as to approach the document surface, the distance x between the shading correction plate 11 and the irradiation line PP at that portion is bent.
Becomes smaller, the illuminance E to the irradiation line PP becomes larger, and the decrease in the amount of irradiation light at both ends of the fluorescent lamp 3 can be corrected. Also,
Since the width d of the slit 12 of the shading correction plate 11 is fixed, even if the shading correction plate 11 moves in the Y direction of FIG. 6, the illuminance E of the irradiation line PP of the document surface becomes constant.

Example 4. 9 is a plan view showing the configuration of a shading correction plate that freely adjusts the amount of light to the irradiation line P-P, and FIG. 10 is a front view of the main parts of FIG. In the figure,
1, 5 and 12 are the same as those described in the second embodiment. Reference numerals 13 and 14 denote a pair of shading correction plates,
The slit 12 is formed by combining both. 1
5 is a movable frame that supports the shading correction plate 13, 16
Is a fixed frame that supports the shading correction plate 14. The shading correction plates 13 and 14 are made of elastic thin plates, and central portions (F to G in the figure) are fixed to the movable frame 15 and the fixed frame 16, respectively, but both ends in the longitudinal direction are not fixed. Shading correction plates 13, 1
Bent portions 13a and 14a in the directions of the movable frame 15 and the fixed frame 16 are provided at both ends in the longitudinal direction of 4. The movable frame 15 and the fixed frame 16 are provided with screw holes 15a and 16a at positions facing the bent portions 13a and 14a.
An adjusting screw 17 is attached to each of a and 16a, and a tip of the adjusting screw 17 abuts on a concave portion of the bent portions 13a and 14a.

Reference numeral 18 denotes sleeves provided at both ends of the movable frame 15, and threaded holes 18a are provided in the width direction of the slit 12. Numeral 19 is a collar provided at both ends of the fixed frame 16, and has a through hole 19a facing the through screw hole 18a. Reference numeral 20 denotes a slit width adjusting screw, which connects the through-screw hole 18a and the through hole 19a to connect the movable frame 15 and the fixed frame 16. One end of the slit width adjusting screw 20 is inserted into the through hole 19a with an appropriate degree of fusion and is rotatably fixed by a stop ring 21. Slit width adjustment screw 20
A screw is provided on the other end side of and is fitted into the threaded hole 18a. Reference numeral 22 is a pressing spring that biases the sleeve 18 and the collar 19 in the separating direction to prevent the slit width adjusting screw 20 from moving under the influence of vibration or the like.

In the shading correction plate of the document reading apparatus constructed as described above, the slit width adjusting screw 2
By rotating the slit width d by 0, the irradiation amount of the irradiation line P of the document 1 can be easily adjusted to the irradiation amount that optimizes the S / N ratio of the CCD image sensor 5. Further, in a region where the dose of irradiation is weak at both ends of the fluorescent lamp 3, the tip of the adjusting screw 17 can bring each end of the shading correction plates 13 and 14 closer to the original 1 by an arbitrary distance, so that the irradiation line P is irradiated. The uniformity of the amount can be easily adjusted, and the illumination of the original document can be adjusted according to the individual sensitivity of the CCD image sensor 5.

Although each of the above embodiments has been described with respect to a document feeding type document reading device, the same effect can be obtained even when applied to a reading unit moving type device such as that used in a digital copying machine. It goes without saying that the CCD image sensor 5 may be a contact image sensor.

[0025]

As described above, the claims 1 and 2 of the present invention are as follows.
According to the method, the end side of the shading correction plate is gradually bent toward the original surface, and the upper end surface is formed so that the effective irradiation width is almost constant over the entire length. However, the uniformity of shading correction will not be impaired, and the end of the shading correction plate will be gradually bent toward the original surface, and the effective irradiation width will be almost constant over the entire length. Since the end faces are formed and made variable in the effective irradiation width direction, it is possible to provide the respective document reading devices capable of adjusting the brightness of the document illumination without impairing the uniformity of shading correction.

According to a third aspect of the present invention, a shading correction plate having a slit in which a passage of illumination light from the tubular light source faces the tubular light source and is parallel, and an end portion of the shading correction plate. By bending the side gradually toward the document surface, it is possible to provide a document reading device in which the uniformity of shading correction is not impaired even if the position of the shading correction plate shifts.

Further, according to the third aspect of the present invention, the width of the slit and the distance gradually approaching the original surface of the end portion side of the shading correction plate are adjustable so that the end portion side of the shading correction plate is gradually adjusted. The document reading device according to claim 4 is bent in a direction approaching the document surface. It is possible to provide a document reading device in which the uniformity of shading correction is not impaired and the brightness of document illumination can be adjusted.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of a document reading apparatus showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a shading correction plate according to the first embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the shading correction plate of the first embodiment.

FIG. 4 is a diagram showing a main configuration of a document reading apparatus according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a shading correction plate according to a second embodiment.

FIG. 6 is a diagram showing a main configuration of a document reading apparatus according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a shading correction plate according to a third embodiment.

FIG. 8 is a diagram illustrating an operation of shading correction according to the third exemplary embodiment.

FIG. 9 is a plan view showing the configuration of shading correction according to the fourth embodiment of the present invention.

FIG. 10 is a front view of a main part of the shading correction plate of FIG.

FIG. 11 is a diagram showing a configuration of a photoelectric conversion unit of a conventional document reading apparatus.

FIG. 12 is a waveform diagram showing a photoelectric conversion signal for one scanning line.

FIG. 13 is a diagram showing a relationship between a conventional shading correction plate and a fluorescent lamp.

FIG. 14 is a diagram showing a state of light shielding depending on a positional relationship between a shading correction plate and a fluorescent lamp.

FIG. 15 is a diagram showing a light shielding state due to a positional relationship between a shading correction plate and a fluorescent lamp different from that in FIG.

16 is a waveform diagram showing a shading-corrected photoelectric conversion signal in the states of FIGS. 14 and 15. FIG.

[Explanation of symbols]

1 manuscript 3 Fluorescent lamp as a tubular light source 5 CCD image sensor 7 Shading correction plate 8 Shading correction plate 9 Shading correction plate 10 Shading correction plate 10a Fixed frame 10b movable frame 11 Shading correction plate 12 slits 13 Shading correction plate 14 Shading correction plate 15 movable frame 16 fixed frame 17 Adjustment screw 18 sleeves 20 Slit width adjustment screw

Claims (4)

[Claims] 1. A reading portion of the document surface, wherein illumination light from a tubular light source is shaded by a shading correction plate so that the central portion of the light is shielded from the end portion so that the illuminance of the document surface is uniform over the entire length. In a document reading device in which the reflected light from the lens is condensed by a lens to form an image on the light receiving surface of the one-dimensional image sensor and photoelectrically converted, the end side of the shading correction plate is gradually approached to the document surface. An original reading device characterized in that the upper end face is formed so that the effective irradiation width is substantially constant over the entire length while being bent. 2. The document reading apparatus according to claim 1, wherein the shading correction plate is variable in the effective irradiation width direction. 3. The shading correction plate adjusts the shading amount of the illumination light from the tubular light source, and the light reflected from the reading portion of the document surface is condensed by a lens to form an image on the light receiving surface of the one-dimensional image sensor. In a document reading device configured to perform photoelectric conversion by means of a shading correction plate, the passage portion of the illumination light faces the tubular light source and is composed of parallel slits,
An original reading apparatus characterized in that an end portion side of the shading correction plate is gradually bent in a direction approaching the original surface. 4. The document reading apparatus according to claim 3, wherein the width of the slit and the distance gradually approaching the document surface on the end side of the shading correction plate are adjustable.