JPH04302260A - Image reader - Google Patents

Abstract

PURPOSE:To improve read efficiency and picture quality by making double the driving cycle of an image sensor and speed for conveying an original in the case of reading one side of the original at the reader to simultaneously read the front and back sides of the original in one scan line by a pair of image sensors. CONSTITUTION:When a control panel 12 instructs both side reading, a CCD drive control circuit 2 outputs synchronizing signals to image sensors 1a and 1b so that the both sides can be one scan line in a CCD driving cycle for normal picture, commands a normal feeding picture for both sides to a original feeding motor control/drive circuit 9 and command half turn-on to a fluorescent lamp control circuit 11 for original illumination. When the control panel 12 instructs one-side reading, the control circuit 2 validizes only one of the image sensors 1a and 1b, makes the cycle double as long as the CCD driving cycle for both sides and outputs the synchronizing signals so that only one side can be one scan line. Further, the original feeding motor control/drive circuit 9 makes feeding speed double, and the control circuit 11 makes double the quantity of light for a fluorescent lamp as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device for reading original images, and in particular to an image reading device that continuously transports a sheet-like original, and uses two image sensors installed above and below the transport path to scan both sides of the original image or The present invention relates to an image reading device that can read one side at high speed.

0002

2. Description of the Related Art In recent years, image information has been stored in file media such as optical disks or magneto-optical disks, and the stored image information can be searched and read out to reproduce the image information and print it or display it on a display. Various image information file systems have been proposed. As a fast and simple means of inputting image information on double-sided originals into such a file system, two image sensors (for example, CCD (
An image reading device is equipped with a charge-coupled device (solid-state imaging device such as a line sensor), and is configured to simultaneously read images of both the front and back sides of a double-sided document simultaneously within one scanning line, and perform subsequent image processing. It has been put into practical use.

0003

[Problems to be Solved by the Invention] However, in the conventional image reading device as described above, even if the document has valid image information on only one side, both sides of the document must be read. Also the image information of the side surface,
The information is stored in a file medium such as an optical disk or a magneto-optical disk, and as a result, the storage efficiency as a file device is significantly deteriorated. So, once on both sides,
A proposal to select either the front side (i.e., the first half of one scanning line) or the back side (i.e., the second half of one scanning line) as a valid image after reading it in one scanning line, and then store it in the file device. Although this proposal eliminates the above-mentioned drawbacks, it discards the single-sided information of the double-sided image information once read, so the efficiency in reading the original image is reduced. There was an issue that needed to be resolved, which was that the value had dropped by half.

SUMMARY OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to provide an image reading device capable of simultaneously reading both sides, which improves image reading efficiency and image quality when there is an effective image on only one side of a document. There is a particular thing.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention continuously transports a sheet-like original, and uses two image sensors consisting of solid-state image sensors installed above and below the transport path to An image reading device that is capable of reading both sides of an image of a document within one scanning line, and when reading a single-sided document in which the image on one side of the document is to be read, the side that reads the effective image of the single-sided document a first control means that selectively enables an image sensor to double the driving cycle of the image sensor when double-sided reading is performed; and a second control means that doubles the conveyance speed of the original document when double-sided reading is performed. and a third control means that performs correction control corresponding to the fact that the storage time of the image sensor is halved.

In a preferred embodiment of the present invention, the third control means performs control to double the amount of light from the document illumination light source during double-sided scanning.

[0007] In another preferred embodiment of the present invention, the third control means controls the slice level when binarizing the output signal of the image sensor to be half that of double-sided scanning. Features.

In another preferred embodiment of the present invention, the third control means performs control to double the amplification factor when amplifying the output signal of the image sensor when double-sided scanning is performed. shall be.

Further, in another preferred embodiment of the present invention, the third control means delays the sample hold timing of the analog-to-digital converter for digitizing the analog output of the image sensor by a predetermined period of time compared to when double-sided reading is performed. It is characterized by controlling.

Furthermore, in another aspect of the present invention, when reading a single-sided original in which an image on one side of the original is to be read, if the amount of light of the light source illuminating the original is lower than a predetermined value, the light source illuminates the original. By simply selectively enabling the image sensor on the side that reads the effective screen of the single-sided original until a predetermined value is reached, the conditions such as the drive cycle of the image sensor and the conveyance speed of the original are the same as for double-sided scanning. The present invention is characterized in that it includes a fourth control means for controlling.

[0011]

[Operation] In the present invention, in a double-sided image reading device that is capable of reading both the front and back sides of a document simultaneously within one scanning line using a pair of image sensors, the driving cycle of the image sensor is changed when reading a single-sided document. By doubling the speed, it is possible to double the document conveyance speed, and furthermore, it is possible to compensate for the fact that the storage time of the image sensor is halved. Therefore, in the present invention, optimal reading performance can be obtained for both double-sided and single-sided originals without deteriorating image quality or reading efficiency.

Furthermore, in the present invention, when the light source for document illumination takes time to reach a predetermined light intensity, such as a fluorescent lamp, the above-mentioned control such as double-speed transport is carried out until the predetermined light intensity is reached. Before doing so, all you have to do is enable the target image sensor for single-sided reading, and then perform the same drive control as for double-sided reading. This makes it possible to shorten standby time and obtain high-quality images.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail below 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 1a
, 1b simultaneously read each of the front and back sides of the sheet-like document being conveyed. The CCD drive control circuit 2 controls these two CCs.
Drive control for operating the D image sensors 1a and 1b is performed. Synthesis circuit 3 is composed of analog switches,
Analog pixel data from two CCD image sensors 1a and 1b are combined into one signal. The image binarization circuit 4 converts the analog pixel data from the synthesis circuit 3 into A/
After D (analog/digital) conversion and conversion into digital multi-value pixel data, and necessary digital image processing to improve image quality, binarization is performed using 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 it into an image signal when outputting a reproduced image.

The compressed image data file device 6, which is one of the external devices, inputs, stores and accumulates the image data encoded and compressed by the image data compression/expansion circuit 5. In addition, the image display device 7, which is another external device, displays the read image as it is on the monitor during reading, and when reproducing and outputting it, it is retrieved from the compressed image data file device 6, and is decoded and expanded by the image data compression/expansion circuit 5. Display the playback image.

The document feed motor 8 is a drive source for continuously conveying a sheet of document, and the document feed motor control/drive circuit 9 controls and drives the document feed motor 8. Further, the fluorescent lamps 10a and 10b are light sources that respectively illuminate the front and back sides of the document to be read. A document illumination fluorescent lamp control circuit 11 controls the light amount of each fluorescent lamp 10a, 10b.

The above CCD drive control circuit 2 switches the control operation mode in response to a selection signal instructing an effective reading screen. This selection signal is normally transmitted by a switch on the operation panel 12,
Alternatively, it is a duplex/single-sided mode switching signal sent from a host device (not shown) such as a personal computer, and indicates which side is the valid scanning side when double-sided scanning is single-sided scanning, such as 11, 01, 10. It is represented by two bits.

When the selection signal instructs double-sided reading, the CCD drive control circuit 2 performs the same operation as the conventional one. That is, at this time, the CCD drive control circuit 2 outputs synchronization signals to both CCD image sensors 1a and 1b so that one scanning line is formed on both sides at the normal CCD drive cycle for both sides, and also controls/drives the document feed motor. The circuit 9 is instructed to send an image for normal double-sided printing, and the document illumination fluorescent lamp control circuit 11 is instructed to be half-lit (half the amount of illumination light when fully lit).

On the other hand, when the selection signal instructs single-sided reading, the CCD drive control circuit 2 performs the following specific operation. That is, at this time, the CCD drive control circuit 2
is the CCD image sensor 1a or 1b on the effective side indicated by the selection signal among the CCD image sensors 1a and 1b.
In addition, in response to double-speed conveyance of the document, a synchronizing signal is output at a cycle twice as long as the CCD drive cycle for both sides, and one scanning line on one side.

At the same time, the CCD drive control circuit 2 controls the document feed motor control/drive circuit 9 to control the feed speed for both sides in order to obtain the same sub-scanning resolution as in double-sided reading and to improve the reading efficiency in reading only one side. It also instructs the document illumination fluorescent lamp control circuit 11 to turn on all lights, which will produce twice the amount of light during double-sided scanning. This is because the CCD image sensor 1a corresponds to doubling the document feeding speed.
Alternatively, in order to compensate for the charge accumulation time of 1b being halved, the amount of original illumination light is doubled. This results in
Deterioration of the storage efficiency of the compressed image data file device 6 is prevented, and at the same time, the efficiency of reading only one side can be improved without deteriorating the image quality.

By the way, in general, a greenish fluorescent lamp, which is compatible with the sensitivity characteristics of a CCD image sensor, is generally used as a light source for illuminating a document in this type of image reading apparatus. After the power is turned on, it takes several tens of seconds to several minutes for the brightness of this fluorescent lamp to stabilize, depending on the ambient temperature, and the lower the atmosphere, the longer it takes. do. This means that after power-on, the device cannot be used simply because the amount of light from the fluorescent lamp for illumination is insufficient, even though all other functions are movable. On the other hand, in order to transport the document at double speed, it is necessary to operate the CCD image sensor on the reading side at twice the driving cycle (that is, the driving period is half) as for double-sided scanning, so as a result, the accumulation of the CCD image sensor is reduced. Since the time is halved, the same C as for double-sided scanning is required.
In order to obtain the output value of the CD image sensor, it is necessary to double the amount of illumination light that illuminates the original. This means that the characteristic of the brightness stabilization curve of fluorescent lamps is an integral curve (for example, C
Considering that a curve showing the voltage across C when the R circuit is charged, etc., this becomes a serious problem when a document is transported at double speed.

Therefore, in this embodiment, before such a fluorescent lamp is stabilized, the CCD on the reading side is
A third drive mode is provided in which the line sensor 1a or 1b is operated at the same drive cycle as when reading double-sided documents, so that even when reading single-sided originals, the device can operate with the same short waiting time as when reading double-sided originals. It was possible to do this. Further, the CCD drive control circuit 2 automatically detects, through a sensor output (not shown), when the light intensity of the fluorescent lamp 10a or 10b, which is a light source, has reached the light intensity necessary for double-speed document transport operation after the power is turned on. to perform double-speed operation. Therefore, in this embodiment, a single-sided original immediately after power is turned on can be read very efficiently.

FIG. 2 shows the detailed structure of the reading section of the apparatus according to the embodiment of the present invention. Two pairs of transport rollers 20a, 20b, 2
The conveyance guides 22a and 2 are rotated by rotations of 0c and 20d, respectively.
The double-sided (or single-sided) original 25 that is conveyed along between the two sides is read by a reading section that is physically provided at approximately the same position. The reflected light of the image on the surface of the document 25 illuminated by the fluorescent lamp 10a passes through the reading glass 21a, the total reflection mirror plate 23a, and the imaging lens 24a, and is projected and imaged onto the CCD image sensor 1a for surface reading. On the other hand, the reflected light of the image of the back side of the document 25 illuminated by the fluorescent lamp 10b is projected onto the CCD image sensor 1b for reading the back side through 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 drive timings for 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 at position F at the bottom of each drawing.

In FIG. 3 during double-sided reading, reference numeral SH1 is a synchronizing signal for starting output of a pixel array to the front-side reading CCD image sensor 1a, and from the rising edge e1 of this signal, the front-side reading CCD image sensor
Output of a pixel row from the image sensor 1a is started, and effective pixel signals are output during section t1 (A, C in the same figure).
reference). On the other hand, the CCD image sensor 1 for reading the back side
The synchronizing signal SH2 for b is output immediately after the end of the interval t1, and the output of the pixel row from the back side reading CCD image sensor 1b starts from the rising edge e2 of this signal SH2, and during the interval t2, an effective pixel signal is output. (See B and D in the same figure). Section t3 is C for surface reading
Both effective signals are switched by the synthesizing circuit (analog switch) 3 of FIG. 1 near the conversion point P1 between the effective pixel section t1 of the CD image sensor 1a and the effective section t2 of the back side reading CCD image sensor 1b, and one composite image is produced. A composite image output section synthesized as a signal is shown (see E in the same figure). By combining the front and rear signals using this analog switch 3, it becomes possible to use only one system for the subsequent image processing system.

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

Next, the driving timing of the CCD image sensor when reading a single-sided image with an effective image only on the front side of the document will be explained. Referring to FIG. 4, first, the case of double speed driving will be described. In this case, C for surface reading
After the effective output section t1 of the CD image sensor 1a ends,
The synchronizing signal SH2 for the back-side reading CCD image sensor 1b is not output (see B in the same figure), and instead, the synchronizing signal SH1 for the front-side reading CCD image sensor 1a is continuously output (see A in the same figure). . Therefore, the pixel array from the front surface reading CCD image sensor 1a is output for the section t2' following the section t1 (see C and D in the figure). By outputting the continuous pixel output from the CCD image sensor 1a for surface reading as it is as a composite image output, the surface image for two scanning sections is output in the composite image output section t3' (E in the same figure). reference). 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. CCD compared to time
Since the storage time for photoelectric conversion for the image sensor is halved, the fluorescent lamp control circuit 11 for illuminating the original is
Sends an all-lighting command to.

Next, referring to FIG. 5, a description will be given of normal speed driving in reading a single-sided image. In this case, only the synchronization signal SH1 for the front side reading CCD image sensor 1a is output at the same cycle as when both images are read simultaneously, and the synchronization signal SH2 for the back side reading CCD image sensor 1b is not output (as shown in the figure). (See A, B). Therefore, in this case, if the pixel output from the surface reading CCD image sensor 1a (see C in the same figure) is output as a composite image, the front surface image will be output in the first half of section 3'', and the second half will be invalid where no image signal is output. (See E in the same figure).In this case, the CC shown in Figure 1
At the same time, the D drive control circuit 2 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 an image reading device that has three types of operation modes in accordance with changes in the CCD drive system, it is possible to always perform optimal image reading for both double-sided and single-sided originals. It becomes possible to do so.

FIGS. 6 to 8 show schematic circuit configurations of main parts of other embodiments of the present invention, which will be explained in order below.

In the first embodiment of the present invention shown in FIG. 1, as a countermeasure to the problem that the storage time for photoelectric conversion of the CCD is halved as the document transport speed is doubled,
In contrast to the problem solved by doubling the amount of light irradiated on the original, the following three embodiments deal with this problem by changing parameters in the electric circuit. Therefore, the following three embodiments are very effective when there is a margin in characteristics such as sensitivity of the CCD. It should be noted that each of these four embodiments including the embodiment of FIG. 1 may of course be implemented independently, but it is of course possible to implement the countermeasures in a plurality of embodiments in combination. Next, each embodiment will be individually explained.

FIG. 6 shows a schematic circuit configuration of the main parts 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 to the fact that the CCD storage time is halved due to the doubling of the document transport speed, the CCD drive control circuit 1
By applying a slice level switching signal from 02 to the image binarization circuit 4, the slice level (threshold value) for binarization is set to half the value compared to normal (during double-sided reading). As a result, the same density output as in double-sided printing can be obtained.

FIG. 7 shows a schematic circuit configuration of the main parts of an image reading apparatus according to a third embodiment of the present invention. In the single-sided scanning mode of this embodiment, the CC
As a countermeasure to the fact that the accumulation time of D is halved, CC
By applying 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 exists in other embodiments but is not shown in the drawing, The gain of the amplifier is doubled compared to normal (during double-sided scanning). As a result, the output voltage after amplification is the same for one side and both sides of an original with the same density.

FIG. 8 shows a schematic circuit configuration of the main parts of an image reading apparatus according to a fourth embodiment of the present invention. In the single-sided scanning mode of this embodiment, the CC
As a countermeasure to the fact that the accumulation time of D is halved, CC
In other embodiments, the sample and hold timing of the pixel signal from the D drive control circuit 302 is delayed with respect to the A/D converter 13 for digitization (not shown), which is included in the image binarization circuit 4.

FIG. 9 shows a CCD according to a fourth embodiment of the present invention.
It shows the state of change of pixel signal output during one clock period. As shown in (D) of the same figure, in the case of single-sided reading (i.e., when the accumulation time is 1/2t), the change in the pixel signal output voltage is greater than in the case of double-sided scanning (i.e., when the accumulation time is 1t). Since the amount will be halved, change the sample hold timing to be delayed by a predetermined time compared to when scanning both sides, as shown in the figure.
This keeps the output voltage almost the same as in double-sided scanning.

[0037]Although the above-described embodiment uses a CCD as an image sensor, the present invention can also be applied to image sensors using other types of solid-state image sensors. In addition, although a fluorescent lamp is illustrated as a light source for document illumination,
The invention is not limited to this, and can also be applied to, for example, a xenon lamp. It is clear that the present invention can be applied not only to copying machines or facsimile machines in which an image reading section and a recording section are integrated, but also to input terminal devices such as computers.

[0038]

[Effects of the Invention] As explained above, according to the present invention,
In a double-sided image reading device that can read both the front and back sides of a document simultaneously within one scanning line using a pair of image sensors, by doubling the drive cycle of the image sensor when reading a single-sided document, Change the document transport speed to 2
Furthermore, we have provided a means to compensate for the fact that the image sensor's storage time is halved, so there is no reduction in image quality or reading efficiency for both double-sided and single-sided originals. It is possible to configure an image reading device that provides optimal reading performance.

Furthermore, in the present invention, when the light source for document illumination takes time to reach a predetermined amount of light, such as a fluorescent lamp, only the target image sensor is turned on during single-sided reading until the predetermined amount of light is reached. By simply enabling this and performing the same drive control as during double-sided scanning, it is possible to shorten standby time and obtain high-quality images.

[Brief explanation of the drawing]

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

FIG. 2 is a sectional view showing details of the configuration of an image reading section according to an embodiment of the present invention.

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

[Figure 4] CCD at double speed reading with single-sided reading according to the embodiment of the present invention
5 is a timing chart showing drive timing of an image sensor.

[Figure 5] CCD during initial reading with single-sided reading according to the embodiment of the present invention
5 is a timing chart showing drive timing of an image sensor.

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

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

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

FIG. 9 is a waveform diagram illustrating changes in pixel signal output of an image reading device according to a fourth embodiment of the present invention.

[Explanation of symbols]

1a CCD image sensor for surface reading 1b
CCD image sensor 2, 102, 20 for back side reading
2,302 CCD drive control circuit 3 Synthesizing circuit (analog switch) 4,304 Image binarization circuit 8 Original feed motor 9 Original feed motor control/drive circuit 10a Front side fluorescent lamp 10b Back side fluorescent lamp 11 Fluorescent lamp for illuminating the original Control circuit 12a Front side CCD amplifier 12b Backside CCD amplifier 13 A/D converters 20a to 20d Conveyance rollers 22a, 22b Conveyance guides 24a, 24b Imaging lens 25 Original

Claims (6)

[Claims] [Claim 1] Continuously transporting a sheet-like original,
An image reading device capable of reading both sides of the image of the document within one scanning line using two image sensors consisting of solid-state image sensors installed above and below the conveyance path, and the image of one side of the document is to be read. a first control means that selectively enables an image sensor on a side that reads an effective image of the single-sided original when reading a single-sided original, and doubles the driving cycle of the image sensor when reading a double-sided original; , a second control means for doubling the conveyance speed of the original document during double-sided scanning; and a third control means for performing correction control corresponding to the fact that the storage time of the image sensor is halved. An image reading device characterized by: 2. The image reading apparatus according to claim 1, wherein the third control means controls the light amount of the document illumination light source to be twice as large as that for double-sided scanning. 3. The third control means controls the slice level when binarizing the output signal of the image sensor to be half that of double-sided scanning.
The image reading device described in . 4. The third control means sets the amplification factor when amplifying the output signal of the image sensor to 2 when double-sided reading is performed.
The image reading device according to claim 1, wherein the image reading device performs doubling control. 5. The third control means controls the sample hold timing of an analog-to-digital converter that digitizes the analog output of the image sensor to be delayed by a predetermined period of time compared to when double-sided reading is performed. 1. The image reading device according to 1. 6. When reading a single-sided original in which an image on one side of the original is to be read, if the light intensity of the light source that illuminates the original is lower than a predetermined value, the image on one side of the original is scanned until the light source reaches the predetermined value. A fourth control means is provided for making conditions such as the driving cycle of the image sensor and the conveyance speed of the document the same as in the case of double-sided scanning by simply selectively enabling the image sensor on the side that reads the effective screen of the document. The image reading device according to any one of claims 1 to 5, characterized in that: