JP2000050030A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the non-uniformity of concentration even when the reflection efficiency of a reflecting board is low. SOLUTION: Concerning this reader, first and second white reference plates 2 and 3 are read, respective read values in the case of making constant a reference voltage Vref of an A/D converter 16 are stored in a memory 17, average values (a) and (b) at the central parts of the first and second white reference plates 2 and 3 in main scanning direction are calculated and using the number of pulses of an SP motor as an address in sub scanning direction, the table of correction values of a primary expression obtd. by connecting the average values (a) and (b) is prepared. When an original is read, the correction values of the table are read out based on the number of pulses of the SP motor and applied to the A/D converter 16 as the reference voltage Vref. In place of the reference voltage Vref of the A/D converter 16, the gain of a gain control amplifier can be controlled as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus for reading reflected light of a document by reflecting it on a mirror.

[0002]

2. Description of the Related Art Generally, in an image reading apparatus such as a copying machine, a bar-shaped halogen lamp is arranged in the main scanning direction as a light source for illuminating a document, and a mirror-like reflector is used to improve the illumination efficiency. ing. This reflector is composed of two front and rear plates in order to eliminate the shadow of the bonded original, and is designed so that the light amount distribution is mountain-like in the sub-scanning direction and the reading position is superimposed on the mountain.

The document scanning means of the image reading apparatus comprises a first carriage having a first mirror disposed at an angle of 45 degrees with respect to the document and bending the reflected light path of the document by 90 degrees, and a first mirror. It has a second carriage on which a second mirror and a third mirror called a roof mirror are mounted to bend the reflected light path of the original bent by 90 degrees and guide the reflected light path to the image forming means. The second carriage moves in the sub-scanning direction at half the speed of the first carriage, so that the optical path length from the document to the image forming means is always constant.

As a conventional example of this kind, for example,
JP-A-58-222663, JP-A-2-135607
JP-A-2-224456, JP-A-2-28533
8, many inventions are known, including the inventions described in each gazette such as JP-A-8-287529.

[0005]

However, since the angles (dach angles) of the second and third mirrors, which are called roof mirrors of the second carriage, are not exactly 90 degrees in practice, the originals at the front and rear ends of the originals , The reading angle of the document is different, and this appears as an error in the reading position of the document. Even if the top of the document is at the top of the mountain-shaped light distribution in the sub-scanning direction, it is not at the top of the document at the rear end. As a method for solving this problem, when designing a reflector, the peak of the mountain-shaped light quantity distribution is made flat in the sub-scanning direction so that even if an error occurs in the reading position, the peak does not deviate from the peak. It is designed to.

[0006] However, in recent years, the reading speed has become faster, and the accumulation time of the CCD has also become shorter, so that the illuminance on the document surface is required to be higher in accuracy than ever. On the other hand, it is difficult to increase the lamp power due to power distribution and heat generation in the entire machine. Therefore, it is required to increase the reflection efficiency of the reflection plate. However, if the reflection efficiency is increased, the peak of the mountain-shaped light amount distribution cannot be flattened.

Further, a reading sensor of a recent color copying machine uses a three-line CCD. This 3 lines C
The CD has a configuration in which an RGB filter is provided for each of three reading sensors arranged in the sub-scanning direction. Since the reading width is wider than that of a one-line CCD, the peak light amount distribution of the reflection plate is provided. Is desired to be wider and flatter. However, high illuminance of the document surface is required due to attenuation of the light amount by the RGB filters and high-speed reading. Therefore, for the same reason, the peak of the mountain-like light amount distribution is flattened, and the reflection efficiency cannot be increased.

A phenomenon caused by this is uneven density of the read original image. When the illuminance at the rear end of the original is lower than that at the front end of the original, "background dirt" occurs at the rear end of the copy image. In the opposite case, a “jump” occurs at the rear end of the copy image.

The present invention has been made in consideration of the above-described problems of the related art, and has as its object to provide an image reading apparatus that can prevent density unevenness even when the reflection efficiency of a reflector is low.

[0010]

In order to achieve the above object, the first means comprises first and second white plates having the same density provided at the leading and trailing ends of the original, respectively, and the first and second white plates. Second
Storage means for storing the read value of the white plate, and a correction value for the density unevenness in the sub-scanning direction of the document is calculated based on the read values of the first and second white plates stored in the storage means, A correction unit configured to correct a read value of the document in the sub-scanning direction based on the correction value.

A second means is that, in the first means, the correction means controls a reference voltage of an A / D converter for converting an analog image signal of the document into a digital image signal so that the original is scanned in the sub-scanning direction. Is characterized by correcting the read value of.

A third means is the first means, wherein the correction means controls a gain of a gain control amplifier for amplifying an analog image signal of the document, thereby correcting a read value of the document in the sub-scanning direction. It is characterized by.

The fourth means is characterized in that in the first to third means, the second white plate is a white area of a bar code for managing a machine number.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an image reading apparatus according to the present invention. FIG. 2 is an explanatory view showing a shift of a roof angle when the image reading apparatus shown in FIG. 4 is a block diagram showing the image reading apparatus of FIG. 1, and FIGS. 4 and 5 are explanatory diagrams showing the roof angle correction processing of the image reading apparatus of FIG.

In FIG. 1, first and second white reference plates 2 and 3 having the same density are arranged on a contact glass 1 on which a document (not shown) is placed. The first white reference plate 2 is disposed on the leading end side of the document, and the second white reference plate 3 is disposed on the trailing end side of the document. The first carriage 8 includes a bar-shaped light source 4 extending in the main scanning direction for illuminating the original and the first and second white reference plates 2 and 3, a main reflector 5, an auxiliary reflector 6, and a first mirror 7. The first mirror 7 reflects the reflected light path of the original and the first and second white reference plates 2 and 3 at an angle of 90 degrees to the left in the drawing. Second and third mirrors 9 and 10 are mounted on the second carriage 11, and the second mirror 9 reflects the optical path reflected by the first mirror 7 at an angle of 90 degrees in the downward direction in the figure. Mirror 10 reflects the optical path reflected by the second mirror 9 rightward in the figure at an angle of 90 degrees and guides it to the imaging lens 12 and the CCD 13.

FIG. 2 shows that the roof angles of the second and third mirrors 9 and 10 are not exactly 90 degrees and the reading position is shifted from the flat portion of the peak of the light amount distribution. For more information,
FIG. 2A shows the first to third mirrors 7, 9, 10 and their reflection optical paths when reading the leading edge of the original, and FIG.
Are first to third mirrors 7 'for reading the rear end of the original,
9 'and 10' and their reflected light paths are shown. The ideal reading position for the light quantity distribution is indicated by a solid line, and the actual reading position is indicated by a broken line. FIG. 2 (A)
In (B), the reading levels of the white reference plates 2 and 3 are respectively set to a and b.

When the leading edge of the original is read as shown in FIG. 2A, the deviation of the reading position from the ideal value due to the deviation of the roof angle is slight, but as shown in FIG. When the edge is read, the deviation from the ideal value is larger than the leading edge of the document, deviates from the flat portion at the top of the mountain-shaped light amount distribution, and density unevenness occurs as it is.

In FIG. 3, an analog image signal photoelectrically converted by the CCD 13 is amplified by a gain control amplifier in a signal processing circuit 15 and then converted into a digital image signal by an A / D converter (ADC) 16. . Then, the digital image signals obtained when the first and second white reference plates 2 and 3 are read are stored in the memory 17, and the arithmetic unit 18 determines the A / D converter 1 based on these values.
6 and calculates the reference voltage Vref of the D / A converter (DA
C) The deviation of the roof angle is corrected by applying the voltage via 19.

More specifically, the correction is performed as follows.

(1) When the power is turned on, the first and second white reference plates 2 and 3 are read by controlling the SP motor that drives the first carriage 8 and the second carriage 11 in the sub-scanning direction.
Each read value when the reference voltage Vref of the A / D converter 16 is kept constant is stored in the memory 17.

(2) After reading the first and second white reference plates 2 and 3, the average of the center of the first and second white reference plates 2 and 3 in the main scanning direction stored in the memory 17. The values a and b are calculated as shown in FIG.

(3) Then, using the number of pulses of the SP motor as an address in the sub-scanning direction, a table of a linear correction value connecting the average values a and b is created as shown by a broken line in FIG.

(4) When reading a document, a correction value in a table is read out based on the number of pulses of the SP motor, and applied to the A / D converter 16 as a reference voltage Vref.

By this correction, the reading illuminance of the original is
Although slightly deviated from the ideal value as shown in FIG. 5, it is improved as compared with the values a and b shown in FIG.

FIG. 6 shows a second embodiment. In this embodiment, the reference voltage Vref of the A / D converter 16
The arithmetic unit 18a is configured to control the gain of the gain control amplifier in the signal processing circuit 15 for amplifying the analog image signal photoelectrically converted by the CCD 13 instead of correcting the shift of the roof angle by controlling ing. Here, since the gain input of the gain control amplifier is digital, the D / A converter 19 can be omitted.

In the correction according to the second embodiment, after the processes (1) and (2) are performed, (3) ′ the average value a is calculated by using the number of pulses of the SP motor as an address in the sub-scanning direction. , B, a table of correction values approximated by the reciprocal of the difference between them is created.

(4) ′ When reading a document, a correction value in a table is read based on the number of pulses of the SP motor,
It is applied to the gain input terminal GCAW of the gain control amplifier.

Here, the first white reference plate 2 provided at the leading end of the document is provided for shading correction in a general copying machine or the like, and does not need to be provided separately. Also, a second white reference plate 3 provided at the rear end of the document
In general copiers and the like, a bar code is provided for managing the machine number, so that the bar code need not be separately provided by using the read value of the white area of the bar code.

[0029]

As described above, according to the first aspect of the present invention, the original is read out based on the read values of the first and second white plates having the same density provided at the leading end and the trailing end of the original. Since density unevenness in the sub-scanning direction is corrected,
Even if the reflection efficiency of the reflector is low, it is possible to prevent density unevenness.

According to the second aspect of the invention, the reference value of the A / D converter for converting the analog image signal of the original into a digital image signal is controlled to correct the read value of the original in the sub-scanning direction. In addition, even if the reflection efficiency of the reflection plate is low, it is possible to prevent density unevenness.

According to the third aspect of the present invention, the read value of the document in the sub-scanning direction is corrected by controlling the gain of the gain control amplifier that amplifies the analog image signal of the document. Even if the density is low, the density unevenness can be prevented.

According to the fourth aspect of the present invention, density unevenness can be prevented without separately providing a white plate.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a shift of a roof angle when the image reading apparatus of FIG. 1 reads a leading edge and a trailing edge of a document.

FIG. 3 is a block diagram illustrating the image reading device of FIG. 1;

FIG. 4 is an explanatory diagram illustrating a roof angle correction process of the image reading apparatus of FIG. 1;

FIG. 5 is an explanatory diagram showing a roof angle correction process of the image reading apparatus of FIG. 1;

FIG. 6 is a block diagram illustrating an image reading device according to a second embodiment.

[Explanation of symbols]

 2 First white reference plate 3 Second white reference plate 15 Signal processing circuit (gain control amplifier) 16 A / D converter (ADC) 17 Memory 18 Operation unit 19 D / A converter (DAC)

Claims (4)

[Claims] 1. An image reading apparatus for optically scanning a document to read an image, the first and second white plates having equal densities respectively provided at a leading edge and a trailing edge of the document; Storage means for storing a read value of the second white plate; and a correction value for density unevenness in the sub-scanning direction of the document based on the read values of the first and second white plates stored in the storage means. An image reading apparatus comprising: a correction unit that calculates and corrects a read value of a document in the sub-scanning direction based on the correction value. 2. The apparatus according to claim 1, wherein the correction unit controls a reference voltage of an A / D converter that converts an analog image signal of the document into a digital image signal, thereby correcting a read value of the document in the sub-scanning direction. The image reading device according to claim 1. 3. The apparatus according to claim 1, wherein the correction unit corrects a read value of the document in the sub-scanning direction by controlling a gain of a gain control amplifier that amplifies an analog image signal of the document. Image reading device. 4. The image reading apparatus according to claim 1, wherein the second white plate is a white area of a barcode for managing a machine number.