JP3093809B2 - Image reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading a document image, and more particularly, to a sheet-like document which is continuously conveyed by two image sensors provided above and below a conveyance path. The present invention relates to an image reading device capable of reading one side at high speed.

[0002]

2. Description of the Related Art In recent years, image information is stored in a file medium such as an optical disk or a magneto-optical disk, and the stored image information is searched as necessary, read out, reproduced, and printed or displayed on a display. Various image information file systems have been proposed. Two image sensors (for example, CCDs) are provided above and below a transport path for transporting a sheet-like document as a high-speed and simple means for inputting image information on a double-sided document to such a file system.
(Charge-coupled device) Solid-state image sensor such as line sensor)
An image reading apparatus has been put into practical use, in which images on both sides of a double-sided original are read simultaneously in one scanning line and image processing is performed thereafter.

[0003]

However, in the conventional image reading apparatus as described above, even if the original has effective image information on only one side of the original, both sides must be read. The image information of the side surface is also
The data is stored in a file medium such as an optical disk or a magneto-optical disk, and the storage efficiency as a file device is significantly deteriorated. So, once on both sides,
Proposal to select only one of the front side (ie, the front half of one scan line) or the back side (ie, the rear half of one scan line) as an effective image after reading within one scan line, and then store it in the file device However, although the above-mentioned disadvantage is solved by this proposal, the single-sided information of the double-sided image information once read is discarded, so that the efficiency at the reading speed of the document image is reduced. There was a problem to be solved that was reduced by half.

In view of the above, an object of the present invention is to provide an image reading apparatus capable of simultaneous reading on both sides, which improves image reading efficiency and image quality when an effective image is present on only one side of a document. It is in.

[0005]

In order to achieve the above object, according to the present invention, a sheet-shaped original is continuously conveyed, and the image is formed by two image sensors comprising solid-state image sensors provided above and below a conveying path. An image reading apparatus capable of reading both sides of an image of a document within one scanning line, wherein when reading a single-sided document whose image is to be read on one side of the document, a reading side of an effective image of the single-sided document is read. First control means for selectively enabling the image sensor and making the driving cycle of the image sensor twice as long as that for double-sided reading, and second control for making the conveyance speed of the document twice as long as that for double-sided reading Means, and a third control means for performing correction control corresponding to halving the accumulation time of the image sensor.

According to a preferred embodiment of the present invention, the third control means performs control for making the light amount of the original illumination light source twice as large as that for double-sided reading.

According to another preferred embodiment of the present invention, the third control means performs control to reduce a slice level at the time of binarization of the output signal of the image sensor to half that at the time of double-side reading. Features.

According to another preferred embodiment of the present invention, the third control means controls the amplification factor when amplifying the output signal of the image sensor to be twice as high as that for double-sided reading. And

In another preferred embodiment of the present invention, the third control means delays a sample hold timing of an analog-to-digital converter for digitizing an analog output of the image sensor by a predetermined time as compared with a double-side reading. The control is performed.

Further, another mode of the present invention is that, when reading a one-sided original whose image is to be read on one side of the original, if the light amount of a light source illuminating the original is lower than a predetermined value, the light source is turned off. Until the predetermined value is reached, only the image sensor on the side for reading the effective screen of the one-sided document is selectively enabled, and the conditions such as the driving cycle of the image sensor and the transport speed of the document are the same as those for the duplex reading. And a fourth control unit for performing the control.

[0011]

According to the present invention, in a double-sided image reading apparatus capable of reading the front and back surfaces of a document continuously and simultaneously in one scanning line by using a pair of image sensors, the driving cycle of the image sensor is set at the time of reading a single-sided document. By doubling the document speed, it is possible to double the document conveyance speed, and thereby to perform correction for halving the accumulation time of the image sensor. Therefore, in the present invention, optimal reading performance can be obtained for both double-sided and single-sided originals without lowering image quality and reading efficiency.

Further, according to the present invention, when it takes time for the light source for document illumination to reach a predetermined light amount such as a fluorescent lamp, the above control such as double-speed conveyance is performed until the light amount reaches the predetermined light amount. Before the operation, only the target image sensor is enabled at the time of single-sided reading, and thereafter the same drive control as at the time of double-sided reading is performed. Thereby, a high-quality image can be obtained by shortening the standby time.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a schematic circuit configuration of a main part of an image reading apparatus according to an embodiment of the present invention. CCD image sensor 1
Reference numerals a and 1b simultaneously read the front (front side) and the back side (back side) of the sheet-shaped document conveyed, respectively. The CCD drive control circuit 2 uses these two C
Drive control for operating the CD image sensors 1a and 1b is performed. The synthesizing circuit 3 is composed of analog switches, and synthesizes analog pixel data from the two CCD image sensors 1a and 1b to combine them into one signal. The image binarization circuit 4 converts the analog pixel data from the synthesizing circuit 3 into digital multi-valued pixel data by A / D (analog / digital) conversion, and further performs necessary digital image processing for improving image quality. Thereafter, binarization is performed by an internal digital comparator. The image data compression / expansion circuit 5 encodes and compresses an image signal when reading a document, and decodes and expands the image signal when reproducing and outputting.

A compressed image data file device 6, which is one of the external devices, inputs and stores and stores the image data encoded and compressed by the image data compression / decompression circuit 5. Further, the image display device 7 as another external device displays the read image as it is on the monitor at the time of reading, is searched from the compressed image data file device 6 at the time of reproduction output, and is decoded and expanded by the image data compression / decompression circuit 5. The reproduced image is displayed.

An original feed motor 8 is a drive source for continuously transporting a sheet original, and an original feed motor control / drive circuit 9 controls and drives the original feed motor 8. The fluorescent lamps 10a and 10b are light sources for irradiating the front and back surfaces of the original to be read. The original illumination fluorescent lamp control circuit 11 controls the light amount of each of the fluorescent lamps 10a and 10b.

The above-described CCD drive control circuit 2 switches the control operation mode in accordance with a selection signal indicating an effective reading screen. This selection signal is normally provided by a switch on the operation panel 12,
Alternatively, a double-sided / single-sided mode switching signal sent from a host device (not shown) such as a personal computer or the like to indicate which side is the effective reading side in the case of single-sided reading, for example, 11, 01, 10 Are represented by two bits.

When the selection signal indicates double-sided reading, the CCD drive control circuit 2 performs the same operation as in the prior art.
That is, at this time, the CCD drive control circuit 2 outputs a synchronizing signal to both the CCD image sensors 1a and 1b so that one scanning line is formed on both sides in the normal double-sided CCD drive cycle, and the document feed motor control / drive A normal double-sided feed image is instructed to the circuit 9, and a half-lighting (half of the illumination light amount at full lighting) is instructed to the document lighting fluorescent lamp control circuit 11.

On the other hand, when the selection signal indicates one-sided reading, the CCD drive control circuit 2 performs a specific operation as follows. That is, at this time, the CCD drive control circuit 2
Is the CCD image sensor 1a or 1b on the effective surface side designated by the selection signal among the CCD image sensors 1a and 1b.
Only a synchronization signal is output at a period twice as long as the above-described double-sided CCD driving period and one scanning line on one side in correspondence with double-speed conveyance of a document.

At the same time, the CCD drive control circuit 2 sends the double-sided feed speed to the document feed motor control / drive circuit 9 in order to obtain the same sub-scanning resolution as in double-sided reading and to improve the reading efficiency when reading only one side. Is commanded, and the original illumination fluorescent lamp control circuit 11 is instructed to turn on all lights which is double the amount of light during double-sided reading. This means that the CCD image sensor 1 responds to the doubling of the document feed speed.
In order to compensate for halving the charge accumulation time of a or 1b, the illumination light amount of the original is doubled. This prevents the storage efficiency of the compressed image data file device 6 from deteriorating, and at the same time, improves the reading efficiency of only one side without deteriorating the image quality.

In general, as a light source for irradiating a document of this type of image reading apparatus, a green fluorescent lamp which is generally compatible with the sensitivity characteristics of a CCD image sensor is used. After turning on the power, although the brightness of this fluorescent light stabilizes,
Although it depends on the ambient atmosphere temperature, it takes several tens seconds to several minutes, and the lower the atmosphere, the longer the time. This means that after the power is turned on, the device cannot be used simply because the light amount of the fluorescent lamp for illumination is insufficient, although all other functions are movable. On the other hand, in order to transport the document at double speed, the CCD image sensor on the reading side needs to be set at the time of double-side reading.
Since it is necessary to operate at twice the driving cycle (that is, the driving period is halved), the accumulation time of the CCD image sensor is halved as a result. Therefore, to obtain the same output value of the CCD image sensor as during double-sided reading Therefore, it is necessary to double the amount of illumination light for irradiating the original. Considering that the characteristic of the brightness stabilization curve of the fluorescent lamp shows an integral curve shape (for example, a curve indicating the voltage between both ends of C when the CR circuit is charged), the double-speed conveyance operation of the original is considered. Is a serious problem.

Therefore, in this embodiment, before such a fluorescent lamp is stabilized, a CCD on the reading side is used as described later.
A third drive mode is provided in which the line sensor 1a or 1b is operated at the same drive cycle as that for double-sided reading, so that even when reading one-sided originals, the apparatus can be operated with the same short waiting time as when reading double-sided originals. It was possible to do. Further, the CCD drive control circuit 2 detects that the light amount of the fluorescent lamp 10a or 10b, which is the light source, has reached the light amount required for the double-speed conveyance operation of the document by a sensor output (not shown) after a lapse of time after the power is turned on. Double speed operation is performed. Therefore, in this embodiment, a one-sided document immediately after power-on can be read very reasonably.

FIG. 2 shows a detailed structure of the reading unit of the apparatus according to the embodiment of the present invention. Two pairs of transport rollers 20a, 20b, 2
The transport guides 22a, 22d are rotated by the rotation of
The double-sided (or single-sided) original 25 conveyed along the space 2b is read by a reading unit physically provided at substantially the same position. The reflected light of the image of the surface of the document 25 illuminated by the fluorescent lamp 10a is projected and formed on the CCD image sensor 1a for surface reading through an optical path passing through the reading glass 21a, the total reflection mirror plate 23a and the imaging lens 24a. On the other hand, the reflected light of the image on the back side of the original 25 illuminated by the fluorescent lamp 10b is projected onto the back side reading CCD image sensor 1b via an optical path passing through the reading glass 21b, the total reflection mirror plate 23b and the imaging lens 24b. , Is imaged.

FIGS. 3 to 5 show the drive timing of each operation mode of the CCD image sensor according to the embodiment of the present invention. A diagram showing the correspondence between the composite image and the actual image is added to the position of F on the lower side of each drawing.

In FIG. 3 at the time of double-side reading, reference numeral SH1 is a synchronizing signal for starting output of a pixel row to the front-surface reading CCD image sensor 1a.
The output of the pixel array from the image sensor 1a is started, and an effective pixel signal is output during the interval t1 (A and C in FIG.
reference). On the other hand, back side reading CCD image sensor 1
b is output immediately after the end of the section t1, the output of the pixel array from the back side reading CCD image sensor 1b starts from the rising edge e2 of the signal SH2, and the effective pixel signal is output during the section t2. (See B and D in the figure). Section t3 is the surface reading C
In the vicinity of the conversion point P1 between the effective pixel section t1 of the CD image sensor 1a and the effective section t2 of the backside reading CCD image sensor 1b, both effective signals are switched by the synthesizing circuit (analog switch) 3 in FIG. A synthesized image output section synthesized as a signal is shown (see E in the figure). By combining the front and back signals using the analog switch 3, it is possible to use only one image processing system thereafter.

When the above-described timing control is performed during normal double-sided image reading, the CCD drive control circuit 2 shown in FIG.
This is a control content for the D image sensors 1a and 1b. At this time, a normal speed command is sent from the CCD drive control circuit 2 to the document feed motor control / drive circuit 9 as described above, A half-lighting instruction is sent to the irradiation fluorescent lamp control circuit 11.

Next, the driving timing of the CCD image sensor when reading a one-sided image having an effective image only on the front side of the document will be described. Referring to FIG. 4, the case of double speed driving will be described first. In this case, the surface reading C
After the end of the effective output section t1 of the CD image sensor 1a,
The synchronization signal SH2 for the back-surface reading CCD image sensor 1b is not output (see B in the same figure), and the synchronization signal SH1 for the front-surface reading CCD image sensor 1a is continuously output instead (see A in the same figure). . Therefore, the pixel array from the front-surface reading CCD image sensor 1a is output also in the section t2 'following the section t1 (see C and D in the same figure). By outputting the continuous pixel output from the surface reading CCD image sensor 1a as a composite image output as it is, the surface image is output for two scanning sections in the composite image output section t3 '(E in FIG. 4). reference). Here, by doubling the speed on the sub-scanning side, the same sub-scanning resolution as in double-sided reading can be obtained. Therefore, in this case, the CCD drive control circuit 2 shown in FIG. 1 performs the above-described timing control operation, and as described above, the document feed motor control / drive circuit 9
Double speed command is sent.
Since the storage time for photoelectric conversion for the D image sensor is reduced by half, the original illumination fluorescent lamp control circuit 1
1 is sent a full lighting command.

Next, with reference to FIG. 5, a description will be given of the case of driving at normal speed in reading a one-sided image. In this case, only the synchronizing signal SH1 for the front-surface reading CCD image sensor 1a is output at the same cycle as in the simultaneous reading of both images, and the back-surface reading CCD image sensor 1b is output.
Is not output (see A and B in FIG. 3). Therefore, in this case, if the pixel output from the surface reading CCD image sensor 1a (see C in the figure) is output as it is as a composite image, the surface image is output in the first half in section 3 "and no image signal is output in the second half. (Refer to E in the same figure) In this case, C shown in FIG.
The CD drive control circuit 2 simultaneously sends a normal speed command to the document feed motor control / drive circuit 9 and a half-lighting command to the document irradiation fluorescent lamp control circuit 11.

As described above, by configuring the image reading apparatus having three types of operation modes in accordance with the change of the CCD driving method, the optimum image reading is always performed for both the double-sided original and the single-sided original. It is possible to do.

FIGS. 6 to 8 each show a schematic circuit configuration of a main part of another embodiment of the present invention, which will be described step by step.

In the first embodiment of the present invention shown in FIG. 1, as a countermeasure against halving the accumulation time for the photoelectric conversion of the CCD with the doubling of the document conveyance speed,
In contrast to the case where the irradiation light amount of the document is doubled, the following three embodiments all deal with the change of the parameters in the electric circuit. Therefore, the following three embodiments are very effective when there is a margin in the characteristics such as the sensitivity of the CCD. It is to be noted that these four embodiments including the embodiment of FIG. 1 may of course be implemented independently, but it is a matter of course that the measures taken in a plurality of embodiments may be implemented in combination. Next, each of the embodiments will be described.

FIG. 6 shows a schematic circuit configuration of a main part of an image reading apparatus according to a second embodiment of the present invention.

In the single-sided reading mode of this embodiment,
As a countermeasure against the doubling of the document transport speed, the CCD drive control circuit 1
By giving a slice level switching signal to the image binarization circuit 4 from 02, the slice level (threshold) for binarization is set to a half of the normal value (during double-sided reading). As a result, the same density output as in the case of both sides can be obtained.

FIG. 7 shows a schematic circuit configuration of a main part of an image reading apparatus according to a third embodiment of the present invention. In the single-sided reading mode of the present embodiment, the CC speed is increased due to the doubling of the document conveyance speed.
As a countermeasure to reduce the accumulation time of D by half, CC
By providing a gain switching signal from the D drive control circuit 202 to each of the amplifiers 12a and 12b for amplifying the output of the image sensor which is present in other embodiments but is not shown in the drawing, The gain of the amplifier is doubled as compared with normal (during double-sided reading). As a result, the output voltage after amplification for the same density original is the same on both sides.

FIG. 8 shows a schematic circuit configuration of a main part of an image reading apparatus according to a fourth embodiment of the present invention. In the single-sided reading mode of the present embodiment, the CC speed is increased due to the doubling of the document conveyance speed.
As a countermeasure to reduce the accumulation time of D by half, CC
In the other embodiment, the D drive control circuit 302 delays the sample and hold timing of the pixel signal with respect to the A / D converter 13 for digitization, which is included in the image binarization circuit 4 (not shown).

FIG. 9 shows a CCD according to a fourth embodiment of the present invention.
The change state of the pixel signal output during one clock period is shown. As shown in (D) of the figure, in the case of single-sided reading (that is, when the accumulation time is 1 / 2t), the change in the pixel signal output voltage is larger than in the case of double-sided reading (that is, when the accumulation time is 1t). Since the amount is reduced by half, the sample hold timing is changed to be delayed by a predetermined time from the time of double-sided reading as shown in the figure.
As a result, the output voltage is almost the same as in the case of double-sided reading.

Although the image sensor using a CCD has been exemplified in the above embodiment, the present invention can be applied to an image sensor using another type of solid-state image sensor. Also, a fluorescent lamp has been exemplified as a light source for document illumination,
The present invention is not limited to this, and can be applied to, for example, a xenon lamp. Further, it is apparent that the present invention can be applied not only to a copying apparatus or a facsimile apparatus in which an image reading section and a recording section are integrated, but also to an input terminal apparatus such as a computer.

[0038]

As described above, according to the present invention,
In a double-sided image reading apparatus capable of reading the front and back of a document continuously and simultaneously in one scanning line using a pair of image sensors, the driving cycle of the image sensor is doubled when reading a single-sided document. Set the document transport speed to 2
A correction means is provided for reducing the accumulation time of the image sensor by half, thereby reducing the image quality and reading efficiency for both double-sided and single-sided originals. An image reading apparatus that can obtain optimum reading performance can be configured.

Further, according to the present invention, when it takes time for the light source for document illumination to reach a predetermined light amount such as a fluorescent lamp, only the target image sensor is used during one-side reading until the light amount reaches the predetermined light amount. By simply performing the same drive control as in duplex reading, it is possible to shorten the standby time and obtain a high-quality image.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view illustrating details of a configuration of an image reading unit according to the embodiment of the present invention.

FIG. 3 is a timing chart showing the drive timing of the CCD image sensor during double-sided reading according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating a single-sided CCD according to an embodiment of the present invention and double-speed reading.
6 is a timing chart showing driving timing of an image sensor.

FIG. 5 is a diagram illustrating a CCD during initial reading in single-sided reading according to the embodiment of the present invention.
6 is a timing chart showing driving timing of an image sensor.

FIG. 6 is a block diagram illustrating a schematic circuit configuration of an image reading apparatus according to a second embodiment of the present invention.

FIG. 7 is a block diagram illustrating a schematic circuit configuration of an image reading apparatus according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a schematic circuit configuration of an image reading apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a waveform diagram illustrating a change state of a pixel signal output of the image reading apparatus according to the fourth embodiment of the present invention.

[Explanation of symbols]

 1a CCD image sensor for reading the front surface 1b CCD image sensor for reading the back surface 2, 102, 202, 302 CCD drive control circuit 3 Synthesis circuit (analog switch) 4, 304 Image binarization circuit 8 Document feed motor 9 Document feed motor control / Drive circuit 10a Fluorescent lamp for front surface 10b Fluorescent lamp for back surface 11 Fluorescent lamp control circuit for illuminating original 12a Amplifier for front CCD 12b Amplifier for back CCD 13 A / D converter 20a to 20d Transport rollers 22a, 22b Transport guides 24a, 24b Image lens 25 original

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/04 H04N 1/203 H04N 1/21

Claims (6)

(57) [Claims] 1. A sheet-shaped document is transported continuously, and both sides of an image of the document can be read within one scanning line by two image sensors comprising solid-state image sensors provided above and below a transport path. An image reading apparatus for reading an effective image of a single-sided original when reading a single-sided original whose image is a single-sided image, and selectively driving the image sensor. A first control means for making the period twice as long as that for double-sided reading, a second control means for making the document conveyance speed twice as long as that for double-sided reading, and an accumulation time of the image sensor being halved. An image reading apparatus, comprising: third control means for performing corresponding correction control. 2. The image reading apparatus according to claim 1, wherein the third control unit performs control to make the amount of light of a document illumination light source twice as large as that during double-sided reading. 3. The image according to claim 1, wherein the third control unit performs control to reduce a slice level in binarizing an output signal of the image sensor to half that in a double-sided reading. Reader. 4. The image reading apparatus according to claim 1, wherein said third control means controls the amplification factor when amplifying the output signal of said image sensor to be twice that of the double-sided reading. apparatus. 5. The apparatus according to claim 1, wherein said third control means performs control for delaying a sample and hold timing of an analog-to-digital converter for digitizing an analog output of said image sensor by a predetermined time as compared with a time of double-side reading. 2. The image reading device according to 1. 6. When reading a one-sided original with an image on one side of the original as an object to be read, if the light amount of a light source for illuminating the original is lower than a predetermined value, the one-sided original is used until the light source reaches the predetermined value. A fourth control unit is provided which makes only the image sensor on the side that reads the effective screen of the original selectively effective, and sets the conditions such as the drive cycle of the image sensor and the conveyance speed of the original to be the same as those for the duplex reading. The image reading device according to claim 1, wherein the image reading device is configured to: