Image reading device having a plurality of image sensors arranged in a main scanning direction and capable of producing continuous image data

An image reading device moves relative to a document in a lengthwise direction of the document so as to read a document image, and is provided with first and second image sensors arranged in line in a widthwise direction of the document, each image sensor including first to n-th photoelectric conversion elements arranged in line in the widthwise direction, each photoelectric conversion element receiving reflected light from the document and generating image data corresponding to the intensity of the received reflected light, and the first photoelectric conversion element of the second image sensor positioned following the n-th photoelectric conversion element of the first image sensor; a scanner for causing the lines of photoelectric conversion elements of the respective image sensors to scan in a specified direction at a specified speed; and a data processor for processing the image data from the n-th photoelectric conversion element of the first image sensor and the image data from the first photoelectric conversion element of the second image sensor so that these image data become continuous in the lengthwise direction. Accordingly, the image reproduced from the read image data is allowed to exhibit satisfactory reproducibility and appearance.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
This invention relates to an image reading device which includes a 
plurality of image sensors arranged in a widthwise direction of a document 
so as to scan sequentially from one lateral end to the other lateral end 
in the widthwise direction to read a document image, and outputs read data 
to such apparatus as image forming apparatus. 
Conventionally, in an image reading device for use in an image forming 
apparatus such as a facsimile machine, there is arranged in a widthwise 
direction of a document an image sensor including a photoelectric 
conversion element array in which photoelectric conversion elements such 
as photodiodes are arranged in line. The image reading device reads a 
document image by causing the image sensor to scan in the widthwise 
direction (hereinafter referred to as a main scanning) and by moving the 
image sensor or document relatively to scan in a lengthwise direction of 
the document (hereinafter referred to as a sub-scanning). Since there is a 
limit in the number of photoelectric conversion elements mounted on a 
single image sensor, the number of photosensors and the length of the 
image sensor become insufficient in the case where the document width is 
large. Thus, in this case, a plurality of image sensors are arranged side 
by side according to the document size so as to scan in the same direction 
and synchronously to read the document image. 
In this way, the array of photoelectric conversion elements sequentially 
scan so as to read the document image. Accordingly, there is a time 
difference between a reading timing of the first photoelectric conversion 
element and that of the last one. On the other hand, as described above, 
the image sensor and the document are moved relatively in the lengthwise 
direction of the document while the photoelectric conversion element array 
is being scanned. Consequently, an image data will have a discontinuity at 
a portion corresponding to a boundary between the juxtaposed image 
sensors. For example, in the case where a straight line S on a document G 
is read by image sensors 1 to 4 as shown in FIG. 10, the output data of 
the straight line S becomes discontinuous due to a difference in scanning 
time between two successively operated image sensors. Consequently, as 
shown in FIG. 10, an image reproduced is not accurately reproduced. Also, 
the appearance of the reproduced image is deteriorated. 
As a measure against this problem, there has been proposed an image reading 
device in which adjacent image sensors are arranged such that main 
scanning directions thereof are alternately opposite to each other so as 
to correspond the reading timings at boundaries between two successively 
operated image sensors, to thereby eliminate the aforementioned 
discontinuity in the output data from the image reading device (Japanese 
Unexamined Patent Publication No. 2-202265). 
However, since the main scanning directions of adjacent image sensors are 
alternately opposite to each other in the image reading device disclosed 
in the above publication, wires are connected to one end of the respective 
image sensors alternately at opposite positions, thereby complicating the 
wiring. Further, when the reading tracks of the respective image sensors 
are connected, the reproduced image is bent, thereby deteriorating the 
reproducibility and appearance. In order to solve this bending of the 
image, it is disclosed to arrange and incline the image sensors by the 
inclination of the reading tracks of the respective image sensors. 
However, this necessitates adjustment of the inclination of the respective 
image sensors, thus costing time and labor. Also, an adjusting operation 
requires skills since the inclination is adjusted by an extremely fine 
angle. 
In addition, the above image reading device including a plurality of image 
sensors adopts a fabricating method of connecting manually the respective 
image sensors to one another and fixing the connected image sensors on a 
long rectangular substrate with adhesive or the like. Thus, there have 
been cases where the image sensors are fixed while being slightly 
displaced in the lengthwise direction of the document at the points of 
connection. 
The displacement between the image sensors turns out to be a displacement 
of the image at the connections between the image sensors in the case 
where image data are output from the image sensors. 
SUMMARY OF THE INVENTION 
In view of the problems residing in the prior art, it is an object of the 
invention to provide an image reading device capable of reproducing a 
document image in a satisfactory appearance. 
Accordingly, the invention is directed to an image reading device which 
moves relative to a document in a lengthwise direction of the document so 
as to read a document image. The image reading device comprises first and 
second image sensors arranged in line in a widthwise direction of the 
document, each image sensor including first to n-th photoelectric 
conversion elements arranged in line in the widthwise direction, each 
photoelectric conversion element receiving reflected light from the 
document and generating image data corresponding to the intensity of the 
received reflected light and the first photoelectric conversion element of 
the second image sensor positioned following the n-th photoelectric 
conversion element of the first image sensor; scan means for causing the 
lines of photoelectric conversion elements of the respective image sensors 
to scan in a specified direction at a specified speed; and data processing 
means for processing the image data of the first and the second image 
sensors so that the image data from the n-th photoelectric conversion 
element of the first image sensor and the image data from the first 
photoelectric conversion element of the second image sensor become 
continuous in the widthwise direction. 
With the image reading device thus constructed, the image data read by the 
first and second image sensors exhibits discontinuity at a boundary 
between the first and second image sensors by an amount corresponding to a 
scanning time required for the scanning of the photoelectric conversion 
elements to make one run. This discontinuity is eliminated by the data 
processing means. 
The scan means may include scan control means for causing the lines of 
photoelectric conversion elements of the respective image sensors to scan 
in a scanning direction from the first to the n-th photoelectric 
conversion elements cyclically and synchronously. The data processing 
means may include memory means consisting essentially of first, second, 
third, and fourth memory blocks; write means for writing the image data 
read by the respective image sensors in the memory means in the scanning 
direction, the write means writing the image data read by the first image 
sensor during a first scanning in the first memory block writing the image 
data read by the second image sensor during the first scanning in the 
second memory block, writing the image data read by the first image sensor 
during a second scanning in the third memory block, and writing the image 
data read by the second image sensor during the second scanning in the 
fourth memory block; and read means for reading the image data stored in 
these memory blocks, the read means first reading the image data stored in 
the in second memory block in the writing order, second reading the in 
image data stored in the first and fourth memory blocks synchronously in 
the writing order, and third reading the image data stored in the third 
memory block in the writing order. 
With this arrangement, the image data read by the first and second image 
sensors in the first scanning is stored in the first and second memory 
blocks, and the image data read thereby in the second scanning is stored 
in the third and fourth memory blocks. These image data exhibit the 
discontinuity by a scanning time required for the scanning of the line of 
photoelectric conversion elements to make one run between the n-th 
photoelectric conversion element of the first image sensor and the first 
photoelectric conversion element of the second image sensor. This 
discontinuity is eliminated at least by reading the image data stored in 
the first and fourth memory blocks synchronously. 
Further, the scan means may advantageously include first scan means for 
causing the line of first to n-th photoelectric conversion elements of the 
first image sensor to scan at the specified speed, and second scan means 
for causing the line of first to n-th photoelectric conversion elements of 
the second image sensor to scan at the specified speed. The data 
processing means may advantageously include output means for sending 
scanning start signals to the first and second scan means so as to cause 
the first and second scan means to start the scanning, and scan control 
means for controlling the first and second scan means so that the scanning 
by the second scan means is started following completion of the scanning 
by the first scan means. 
With this arrangement, the n-th photoelectric conversion element of the 
first image sensor and the first photoelectric conversion element of the 
second image sensor scan continuously. Thus, the image data does not 
exhibit discontinuity. 
The invention is also directed to an image reading device which moves 
relative to a document in a lengthwise direction of the document so as to 
read a document image, the apparatus comprising first and second image 
sensors arranged in line in a widthwise direction of the document, each 
image sensor including first to n-th photoelectric conversion elements 
arranged in line in the widthwise direction, each photoelectric element 
receiving reflected light from the document and generating image data 
corresponding to the intensity of the received reflected light; first scan 
means for causing the line of photoelectric conversion elements of the 
first image sensor to scan in a specified direction at a specified speed: 
second scan means for causing the line of photoelectric conversion 
elements of the second image,sensor to scan in another specified direction 
at the same speed as the first scan means: and scan control means for 
controlling the first and second scan means so as to offset a displacement 
of the second image sensor relative to the first image sensor in the 
lengthwise direction of the document. 
The image reading device thus constructed offsets the displacement of the 
image due to the displacement between the first and second image sensors 
in the lengthwise direction of the document. 
The scan control means may include output means for sending scanning start 
signals simultaneously to the first and second scan means so as to cause 
the first and second scan means to start the scanning; measurement means 
for measuring a time required to move relatively a displaced amount of the 
second image sensor relative to the first image sensor in the lengthwise 
direction of the document; and delay means for sending the scanning start 
signal to the second scan means at a timing delayed by the measured time 
from the one at which the scanning start signal is sent to the first scan 
means. 
With this arrangement, there is measured the time required to move 
relatively the displaced amount of the second image sensor relative to the 
first image sensor in the lengthwise direction of the document. The 
scanning by the second image sensor is delayed relative to the scanning by 
the first image sensor by the measured time, thereby offsetting the 
displacement of the image due to the displacement between the respective 
image sensors. 
Further, there may be provided three or more image sensors arranged in the 
widthwise direction of the document, each image sensor including first to 
n-th photoelectric conversion elements arranged in line in the widthwise 
direction of the document. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a reading of the following detailed 
description and accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
There will be first described a schematic construction of an image forming 
apparatus incorporating an image reading device according to the invention 
with reference to FIG. 1. 
An image forming apparatus 71 is provided with an image reading unit 73 and 
an image forming unit 74. In FIG. 1, the image reading unit 73 and the 
image forming unit 74 are separated so as to facilitate the understanding 
of their construction. 
The image reading unit 73 includes an exposure lamp 75 for exposing a 
document, an optical system having a line magnification forming element 76 
such as a rod lens array for focusing a reflected light from the document 
on an image sensor array to be described later, and the like, and an image 
reading device having the image sensor array 77 for reading the image 
formed by the reflected light as image data. 
The image forming unit 74 includes a photosensitive member 81, a charger 
82, an LED array 83, a developing device 84, a transfer device 85, a 
cleaner 86, etc. 
An image forming operation will be described summarily next. A document G 
is fed by a feed roller 78. The document G reflects light from the 
exposure lamp 75 while being transported by a pair of transport rollers 79 
and a transport roller 80. This reflected light converged and focused on 
the image sensor array 77 by the line magnification focusing element 76. 
On the other hand, the surface of the photosensitive member 81 is exposed 
to an image light emitted from the LED array 83 based on the image data 
read by the image sensor array 77 after being charged uniformly by the 
charger 82, and thereby an electrostatic latent image is formed thereon. 
Charged toner is supplied to the photosensitive member 81 from the 
developing device 84 to deposit on the electrostatic latent image to 
thereby form a toner image. 
On the other hand, a sheet is fed to the image forming unit 74 by 
unillustrated feed means from a cassette 87, and the toner image is 
transferred to the sheet by the transfer device 85. The sheet is separated 
from the photosensitive member 81, and is discharged onto a discharge tray 
88 from the image forming unit 74 after having the toner image fixed 
thereto. The cleaner 86 cleans the toner residual on the surface of the 
photosensitive member 81 after the image forming operation. 
There will be described a first image reading device according to the 
invention next with reference to FIGS. 2 to 4. 
The image reading device is, as shown in FIG. 2, provided with the image 
sensor array 77 including scanning type image sensors 1 to 4, a memory 
controller 5, a memory 6, a main scanning signal generator 7, etc. The 
image reading device is adapted for reading an image of the document while 
scanning the document being transported in a lengthwise direction. Since 
the document is scanned relatively in the sub-scanning, it may be 
appropriate to fix the document while moving the optical system and image 
sensor array. 
The image sensor array 77 includes four image sensors 1 to 4 arranged side 
by side in a main scanning direction. Each of the image sensors 1 to 4 
includes n photosensors such as phototransistors arranged side by side in 
the main scanning direction which receive the reflected light from the 
document and read the document image every photosensor. For example, an 
image of a document of A0 size can be read by the image sensor array 77. 
Each of the photosensors provided in the image sensors 1 to 4 outputs light 
reception data (analog data) according to a light reception level to the 
memory controller 5. The photosensors: of the image sensor 1 are scanned 
sequentially from the first one to the n-th one each time in accordance 
with a main signal R from the main scanning signal generator 7, and the 
light reception data of the respective photosensors is output to the 
memory controller 5. The photosensors of the other image sensors 2 to 4 
are scanned in the same way. 
The main scanning signal generator 7 outputs the main scanning signals R 
synchronously to the respective image sensors 1 to 4 so that the 
photosensors of the image sensors 1 to 4 are scanned. Upon receipt of 
these main scanning signals, the light reception data are output 
synchronously from the respective photosensors of the image sensors 1 to 4 
to the memory controller 5. The memory controller 5 reads the light 
reception data sequentially from the image sensors 1 to 4; converts the 
same into digital data (image data); and stores the image data in 
correspondence with respective blocks of the memory 6 as described later. 
The memory 6 includes a plurality of memory blocks 611 to 644. Each of the 
memory blocks 611 to 644 has the same number of memory elements (n memory 
elements) for storing image data from the corresponding photosensors of 
each image sensor. 
The memory blocks 611 to 614 are adapted for storing image data read by 
four consecutive main scannings of the image sensors 1 to 4. Specifically, 
the image data read by the four consecutive main scannings of the image 
sensor 1 is stored in the memory blocks 611 to 614. Likewise, the image 
data read by the four consecutive main scannings of the image sensors 2 to 
4 are stored respectively in the memory blocks 621 to 624, 631 to 634, and 
641 to 644. 
The memory controller 5 reads the respective image data stored in the 
memory blocks 611 to 644 synchronously in a specified order to be 
described later, and outputs the same as output data to the image forming 
unit 74. 
The memory blocks 611 to 644 from which previous image data have been read 
are sequentially written with newly read image data. For example, when the 
image data obtained in the first main scanning is read from the memory 
block 611, the image obtained in the fifth main scanning is written in the 
memory block 611. 
Further, more specifically, there will be described exemplary operations of 
the image reading device next with reference to FIGS. 4A to 4I. The 
following description will be made with reference to a case where a white 
document G having a black straight line S in parallel with the main 
scanning direction is read as shown in FIG. 4A. Also, it is assumed that 
reading of the straight line S is started in the i-th main scanning and 
completed in the (i+2)th main scanning. 
First, there will be described operations of obtaining image data 
represented by one bit, i.e., white and black data, and reproducing a 
monotone image. The memory controller 5 diigitalizes the output from each 
photosensor to image data in the form of one bit. Each of the memory 
blocks 611 to 644 has the 1-th to n-th memory elements. Each memory 
element is written with one-bit image data. 
When the i-th main scanning is carried out upon receipt of the main 
scanning signal R from the memory controller 5, the reading of the 
straight line S on the document G by the image sensors 1 to 4 is started. 
The memory controller 5 causes the lead image data to be written in the 
memory blocks 611, 621, 631, and 641. 
In this time, the document G is moved in the sub-scanning direction. As 
shown in FIG. 4B, consequently, the reading area of each image sensor 
becomes inclined with respect to the straight line S. The read image data 
is digitalized in the binary basis by the memory controller 5. Thereafter, 
the image data (hereinafter referred to as "white data") corresponding to 
the white portion are written in the 1-th to j-th memory elements of the 
memory block 611 and the image data (hereinafter referred to as "black 
data") corresponding to the straight line S in the (j+1)th to n-th memory 
elements of the memory block 611. The white data is represented by the 
digit "0" while the black data is represented by the digit "1". In other 
words, each memory element is written with binary code. The image data 
obtained by the other image sensors 2 to 4 are digitalized and written in 
the same way. Accordingly, the memory blocks 611, 621, 631, 641 have the 
white data in their respective 1-th to j-th memory elements and the black 
data in their respective (j+1)th to n-th memory elements. 
Next, when the (i+1)th main scanning is carried out, the black data of the 
straight line S are written in the memory blocks 612, 622, 632, and 642 
respectively. 
In the (i+2)th main scanning is carried out, similarly to the writing in 
the i-th main scanning, the black data are written in the 1-th to j-th 
memory elements of each of the memory blocks 613, 623, 633, and 643 while 
the white data are written in the (j+1)th to n-th memory elements thereof. 
The reading of the straight line S is completed. 
In the (i+3)th main scanning, in the memory blocks 614, 624, 634, 641 are 
entirely written the white data from the image sensors 1 to 4. 
In the (i+4)th main scanning the image data from the image sensors 1 to 4 
are written in the memory blocks 611, 621, 631, and 641. Subsequently, the 
above-mentioned operations follow. In this way, the memory 6 has the image 
data in FIG. 4C. in each memory in FIG. 4C block of the memory 6 as shown 
in the memory 6 
Next, reading in the memory 6 of the image data written will be described 
with reference to FIG. 4D. It should be noted that in FIG. 4D, memory 
blocks which are read in the same timing are arranged in the same line. 
Immediately after completion of the image data writing operation in the 
i-th main scanning, the reading of the written i-th image data from the 
memory 6 is started. During this i-th image data reading operation, the 
image data are read from the memory blocks 612, 623, 634, and 641. The 
memory blocks 612, 623, 634 respectively have the white data obtained in 
the (i-3), (i-2), and (i-1)th main scannings. 
Subsequently, immediately after completion of the (i+1)th image data 
writing operation, the (i+1)th image data reading operation is carried out 
to read the image data from the memory blocks 613, 624, 631, and 642. The 
memory blocks 613 and 624 respectively have the white data obtained in the 
(i-2) and (i-1)th main scannings. 
Subsequently, immediately after completion of the (i+2)th image data 
writing operation, the (i+2)th image data reading operation is carried out 
to read the image data from the memory blocks 614, 621, 632, and 643. The 
memory block 614 has the white data obtained in the (i-1)th main scanning. 
Further, after completion of the (i+3)th image data writing operation, the 
(i+3)th image data reading operation is carried out to read the image data 
from the memory blocks 611, 622, 633, and 644. Subsequently, after 
completion of the (i+4)th image data writing operation, the (1+4)th image 
data reading operation is carried out to read the image data from the 
memory blocks 612, 623, 634, and 641. After completion of the (i+5)th 
image data writing operation, the (1+5) th image data reading operation is 
carried out to read the image data from the memory blocks 613, 624, 631, 
and 642. 
As shown in FIG. 4E, consequently, an image having no discontinuity is 
reproduced. 
Second, there will be described operations of obtaining image data 
represented by multi-bit, and reproducing a halftone image. In this 
embodiment, the memory controller 5 digitalizes the output from each 
photosensor to image data in the form of eight bits. Each of the memory 
blocks 611 to 644 is written with eight-bit image data. This eight-bit 
reading operation is basically the same as the one-bit reading operation 
except for the memory block capable of storing eight-bit data. 
The reading area of each image sensor becomes inclined with respect to the 
straight line S, similarly to the above-mentioned one-bit reading. The 
respective photosensors' outputs of each image sensor are digitalized into 
8-bit image data each of which are in turn written in memory elements of 
each memory block. Specifically, as shown in FIG. 4F, in the case of 
writing the image data obtained in the i-th scanning in the memory block 
611, the respective image data are written in the 1-th to n-th memory 
element in the form of binary codes "00H" to "FFH". The binary code "00H" 
represents "white". The binary code "FFH" represents "black". The binary 
codes between "00H" and "FFH" represent half tone. 
As shown in FIG. 4G, the image data obtained in the i-th to (i+3)th main 
scannings are written in the corresponding memory blocks of the memory 6 
in the same way as the one-bit reading. The written image data are read in 
the order shown in FIG. 4H. FIG. 4I shows an image reproduced based on the 
8-bit data. 
Accordingly, although being read by the image sensors 1 to 4, the straight 
line S is reproduced into an image having no discontinuity as shown in 
FIG. 4I. Thus, an image having the satisfactory reproducibility and 
appearance can be formed. 
The reproduced image is oblique relative to the main scanning direction as 
shown in FIG. 4I. However, the length in the sub-scanning direction of the 
photosensors of the image sensor is so much smaller than the length in the 
main scanning direction of the image sensor that the inclination is 
neglectably small and thus will not stand as a hindrance to a practical 
use. 
Further, it may be appropriate to arrange a memory sectioned for the 
respective image sensors 1 to 4. The image data stored in the sectioned 
memory are output to the image forming unit 74 in a parallel manner while 
carrying out the image data reading operation similar to the above. 
The number of memory blocks provided in the memory 6 is not limited to the 
above. It will be sufficient to provide memory blocks equal to or more 
than squared by the number of image sensors, that is, n.times.n blocks. 
FIG. 2A shows another embodiment similar to the embodiments of FIGS. 2-4 
and which operates like the embodiment of FIGS. 2-4, except that two image 
sensors 1A and 2A are used in FIG. 2A, rather than the four image sensors 
shown in FIG. 2. 
There will be described a second image reading device according to the 
invention next with reference to FIGS. 5 to 9. 
As shown in FIG. 5, this image reading device is provided with an image 
sensor array 77 including scanning type image sensors 11 to 14, a main 
scanning start signal generator 15, delay circuits 16a, 16b, 16c, 16d, a 
clock generator 17, a controller 18, first and second memories 19, 61, a 
memory controller 51, etc. This image sensor array 77 is adapted for 
reading a document image by scanning a document relatively into a 
sub-scanning direction. 
The image sensor array 77 includes four image sensors 11 to 14 arranged 
side by side in a main scanning direction. Each of the image sensors 11 to 
14 includes n photosensors such as phototransistors arranged side by side 
in the main scanning direction which receive the reflected light from the 
document and read the document image by the photosensor. For instance, an 
image of a document of A0 size can be read by the image sensor array 77. 
These image sensors 11 to 14 are fixed on a substrate in the form of, e.g. 
along rectangle, using adhesive after connected to one another. 
Each of the photosensors provided in the image sensors 11 to 14 outputs a 
light reception data SG to the memory controller 51. The respective image 
sensors 11 to 14 output the light reception data SG from the first 
photosensor put to the memory controller 51 in synchronism with a 
synchronization signal CK2 each time delayed main scanning start signals 
R1a to R1d to be described later are received. 
The main scanning start signal generator 15 sends main scanning start 
signals R0 to the delay circuits 16a to 16d in a specified order so as to 
cause the image sensors 11 to 14 to start the main scanning. The delay 
circuits 16a to 16d are provided between the image sensors 11 to 14 and 
the main scanning start signal generator 15 respectively, and adapted for 
sending the delayed main scanning start signals R1a to R1d delayed by a 
predetermined period from the main scanning start signals R0 to the 
corresponding image sensors 11 to 14. Accordingly, the main scanning start 
timings of the respective image sensors 11 to 14 are delayed by the 
predetermined period. The clock generator 17 sends a clock signal CK1 and 
the synchronization signal CK2 respectively to the delay circuits 16a to 
16d and the memory controller 51. 
The controller 18 includes CPU or the like, and controls the main scanning 
start signal generator 15, the memory controller 51, etc. The first memory 
19 includes a ROM or the like, and stores a control program. The second 
memory 61 includes a RAM or the like, and stores the image data and 
various other data. The memory controller 51 converts the light reception 
data SG sent in time series from the respect image sensors 11 to 14 in 
synchronism with the synchronization signal CK2 as shown in FIG. 6 to a 
digital image data according to a method similar to the one described with 
respect to the memory controller 5 in the first embodiment. Then, the 
memory controller 51 causes the second memory 61 to store the converted 
image data temporarily or outputs the same to the image forming unit 74. 
The main scanning start signal R0 synchronizes with the clock signal CK1. 
Subsequently, examples of the delay circuits 16a to 16d will be described 
with reference to FIG. 7 which is a circuit diagram of the delay circuit 
16d. 
Each of the delay circuits 16a to 16d includes a D flip-flop 60, a counter 
61, a comparator 62, a delay setting unit 63, and monostable 
multivibrators 64, 65. 
Each D flip-flop 60 inverts a clear signal CL to the counter 61 from low to 
high upon receipt of the main scanning start signal R0 from the main 
scanning start signal generator 15 (see FIG. 9) so as to cause the counter 
61 to start a counting operation. The counter 61 counts the clock signal 
CK1 from the clock generator 17 when the clear signal CL is high, and 
sends a count value (binary value) to the comparator 62. 
The comparator 62 compares the count value from the counter 61 with a delay 
amount (binary value) set in advance by the delay setting unit 63. When 
the count value coincides with the delay amount, the comparator 62 sends a 
high signal to the monostable multivibrator 64. The delay setting unit 63 
includes switches SW1 to SW4 consisting of four bits. The delay amount is 
set by on or off states of these switches SW1 to SW4. More specifically, 
the switches SW1 to SW4 input "0" to the comparator 62 as a set value for 
the four bit delay amount when they are on while inputting "1" when they 
are off. For example, when the switches SW1, SW3 are set on and the 
switches SW2, SW4 are set off, a binary value "1010" is input to the 
comparator 62 as a set value. 
There will be described an example of setting in the delay setting unit 63 
with reference to FIG. 8. The image sensors 11 to 14 are displaced more 
toward a downstream side of the sub-scanning direction in the order of the 
image sensors 11, 13, 14, and 12. The displaced amount is calculated in 
the following manner, for example. A test pattern including a straight 
line S written in parallel with the main scanning direction is read by the 
image sensors 11 to 14, and the image sensor which has carried out the 
first image reading operation is selected (in this example, the image 
sensor 11). Then, there are calculated displaced amounts of the other 
image sensors (in this example, the image sensors 12 to 14) relative to 
the selected image sensor. More specifically, in FIG. 8, the image sensor 
12 reads the straight line image S completely after a period T1 (for 
example, a period corresponding to 10 cycles of the clock signal CK1) 
following the reading operation of the image sensor 11. The image sensor 
13 reads the straight line image S completely after a period T2 (for 
example, a period corresponding to 2 cycles of the clock signal CK1) 
following the reading operation of the image sensor 11. The image sensor 
14 reads the straight line image S completely after a period T3 (for 
example, a period corresponding to 5 cycles of the clock signal CK1) 
following the reading operation of the image sensor 11. 
Thereafter, the set value of the comparator 62 of the delay circuit 16a is 
set at "0000" by setting the states of the switches SW1 to SW4 of the 
delay circuit 16a for sending the delayed main scanning start signal R1a 
to the image sensor 11. Since the delay amount of the delay circuit 16a is 
zero in this case, the delay circuit 16a sends the main scanning start 
signal R0 to the image sensor 11 as the delayed main scanning start signal 
R1a without any delay. 
Subsequently, the set value of the comparator of the delay circuit 16b is 
set at "1010" which corresponds to the period T1 by setting the states of 
the switches SW1 to SW4. Further, the set value of the comparator 62 of 
the delay circuit 16c is set at "0010" which corresponds to the period T2 
by setting the states of the switches SW1 to SW4. Consequently, the set 
value of the comparator 62 of the delay circuit 16d is set at "0101" which 
corresponds to the period T3 by setting the states of the switches SW1 to 
SW4. 
In this way, the document image, e.g. the straight line image S, can be 
read by the respective image sensors 11 to 14 at the same timing. 
The delay circuit corresponding to the image sensor which has first read 
the straight line image S (the image sensor 11 in FIG. 8) is not required 
to delay the main scanning start signal R0. In view of this, it may be 
appropriate to change the wiring such that the main scanning start signal 
R0 is sent from the main scanning start signal generator 15 directly to 
the image sensor 11 without passing through the delay circuit 16a. In this 
case, since the delay circuit 16a can be omitted from the construction, 
the number of elements can be reduced. Further, it may be also appropriate 
to give a reference delay amount to the main scanning start signal R0 
applied to the image sensor 11 and to add the reference delay amount to 
the delay amounts of the other delay circuits 16b to 16d. 
Upon receipt of the high signal from the comparator 62, the monostable 
multivibrator 64 sends pulses of a specified pulse duration (delayed main 
scanning start signals R1a to R1d) to the image sensors 11 to 14 and the 
monostable multivibrator 65. Upon receipt of the signals R1a to R1d from 
the monostable multivibrator 64, the monostable multivibrator 65 sends a 
pulse of a specified pulse duration (reset signal RE) to the D flip-flop 
60. Upon receipt of the reset signal RE, the D flip-flop 60 inverts the 
clear signal CL to applied to the counter 61 from high to low so as to 
reset the counter 61. 
There will be described an exemplary operation of the image reading device 
next with reference to a timing chart shown in FIG. 9. This operation is 
described taking the delay circuit 16b corresponding to the image sensor 
12 as an example, and it is assumed that the switches SW1 to SW4 are set 
to output a set value "1010". 
When the sub-scanning of the document is started, the main scanning start 
signal generator 15 sends the main scanning start signals R0 to the 
respective delay circuits 16a to 16d, for example, at time t1. When the 
main scanning start signal R0 is applied to the D flip-flop 60 of the 
delay circuit 16b, the clear signal CL applied from the D flip-flop 60 to 
the counter 61 is inverted from low to high, causing the counter 61 to 
start the counting operation. The count value of the counter 62 is output 
to the comparator 62, which in turn compares the count value with the set 
value "1010". 
If the count value coincides with the set value "1010" the high signal is 
sent from the comparator 62 to the monostable multivibrator 64. Then, the 
delayed main scanning start signal R1b is sent from the monostable 
multivibrator 64 to the image sensor 12, and the light reception data SG 
of the image sensor 12 are sent to the memory controller 51 sequentially 
from the first photosensor. 
On the other hand, the signal R1b is also sent to the monostable 
multivibrator 65, which in turn sends the reset signal RE to the D 
flip-flop 60. Upon receipt of the reset signal RE, the D flip-flop 60 
inverts the clear signal CL to be applied to the counter 61 to low level. 
Thus, the counter 61 is reset. The above operations are repeated each time 
the main scanning start signal R0 is output from the main scanning start 
signal generator 15 in the specified cycle. 
In this way, the main scanning start signals R0 are delayed according to 
the displaced amounts between the image sensors 11 to 14 by the delay 
circuits 16a to 16d. Thus, a satisfactory image can be formed even when 
the light reception data from the image sensors 11 to 14 are converted 
into the image almost without exhibiting displacement. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be understood that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, 1Artless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.