JPH1155474A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the image reader in which a reading speed of an image is increased by a linear image sensor with a plurality of light receiving sections. SOLUTION: In the image reader that reads a sheet original 7 with a linear image sensor such as a CCD, a plurality of light receiving sections 2, 3 read the same read line of the original 7, output charges of the light receiving sections 2, 3 are summed by an output section 5 and a delay circuit 4 corrects a deviation in the read lines 8 at the addition or presence of a delay by the delay circuit 4 is switched by a changeover circuit 9 to read the original 7 at a high speed.

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 sheet-shaped document at a high speed by a reading means comprising a linear image sensor such as a CCD.

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing a basic configuration of a conventional image reading apparatus. 6, the image reading unit 10 of the image reading apparatus includes a lens 6 and a linear image sensor 21 such as a CCD. The linear image sensor 21 includes a light receiving unit 22 and an output unit 23 of the image sensor 21. ing. The reading line 8 on the sheet-like original 7 is
This is a line read by the linear image sensor 21. Then, the image reading section 10 is provided with the original 7 or the image reading section 1.
0 itself moves in the sub-scanning direction to read the entire document 7. In this system of the image reading apparatus, it is assumed that the image reading section 10 is fixed and the document 7 is transported in the sub-scanning direction indicated by the white arrow.

FIG. 7 is a diagram showing the principle of operation of the linear image sensor 21 such as a CCD shown in FIG. FIG. 7 (a)
In the above, the light receiving section 22 is composed of a photodiode or the like, and the output section 23 is composed of a floating capacitor or the like that outputs to outside the linear image sensor.
The optical signal charges (shown by oblique lines) stored in the light receiving unit 22 are:
As shown in FIG. 2B, the optical signal charges (indicated by oblique lines) transferred to the CCD analog shift register 24 by the transfer pulse 13 and transferred to the CCD analog shift register 24 as shown in FIG. Is transferred to the output unit 23 by the drive clock pulse 14.

The time during which the optical signal charges are stored in the light receiving section 22 is called an accumulation time, and the cycle t of the transfer pulse 13 is the accumulation time. The output charge Q of the linear image sensor 21 depends on the accumulation time t and the sensitivity of the light receiving unit 22, and can be represented by Q = αt. The minimum storage time required to obtain an output signal level that can be sufficiently subjected to A / D conversion or the like after being output from the output unit 23 varies depending on the resolution of the linear image sensor 21 in the main scanning direction and the like. Further, the width L of the reading line 8 on the document 7 shown in FIG. 6 determines the resolution in the sub-scanning direction of the image reading apparatus, which depends on the transport speed v of the document 7 and the accumulation time t.

[0005]

However, in the above conventional example, the resolution in the sub-scanning direction indicated by the white arrow of the image reading apparatus using the linear image sensor 21 such as a CCD is
It depends on the transport speed v of the document 7. Linear image sensor 21
Assuming that the accumulation time is t and the width per one read line obtained from the target resolution in the sub-scanning direction is L, the transport speed is v = L / t. Here, when trying to double the transport speed, the accumulation time t cannot be changed, so that the width per read line is 2L, and the resolution in the sub-scanning direction is L / 2.

[0006] As the resolution in the main scanning direction increases, the resolution in the sub-scanning direction must be correspondingly increased. A higher resolution in the main scanning direction causes an increase in the accumulation time, and an increase in the accumulation time causes a decrease in the transport speed v of the document 7. That is, high resolution and high transport speed are contradictory elements, and it has been very difficult to achieve both.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a first object of the present invention is to provide a plurality of light receiving sections, add outputs of the respective light receiving sections, and shift a focal point of each light receiving section. Is to increase the reading speed of an image by a linear image sensor that corrects the image reading.

A second object of the present invention is to increase the reading speed of an image by providing a plurality of linear image sensors, adding the outputs of the respective linear image sensors, and correcting the deviation of the focal point of each linear image sensor. It is to speed up.

[0009]

According to a first aspect of the present invention, there is provided an image reading apparatus for reading a sheet-like document by a linear image sensor such as a CCD. A plurality of light receiving units inside the image sensor, a circuit for adding output charges of the plurality of light receiving units, a delay circuit for correcting a deviation of a read line at the time of addition, and a switching circuit for switching presence or absence of a delay by the delay circuit And reading the sheet-shaped document at a high speed.

According to a second aspect of the present invention, there is provided an image reading apparatus for reading a sheet-shaped original by a linear image sensor such as a CCD, wherein a plurality of linear image sensors and respective output voltages of the plurality of linear image sensors are added. And a switching circuit for switching the presence / absence of a delay by the delay circuit for reading the sheet-shaped document at a high speed.

[0011]

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

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

In FIG. 1, an image reading section of an image reading apparatus is a linear image sensor 1 having a plurality of light receiving elements.
And the lens 6, and the linear image sensor 1 is
A first light receiving section 2, a second light receiving section 3, a delay element 4 as a delay circuit, a switching circuit 9 for switching whether or not to apply a delay by the delay element 4, and an output section 5 of a linear image sensor. doing. Each of the light receiving units 2 and 3 is composed of a photodiode. The light receiving units 2 and 3 receive light reflected from the reading line 8 on the document 7 via the lens 6. The output of the first light receiving unit 2 is supplied to a switching circuit 9
Is input to the output unit 5 via the delay element 4 or directly. The switching circuit 9 outputs the delay element 4 to the output of the first light receiving unit 2.
Switches between applying and not applying a delay. on the other hand,
The output of the second light receiving unit 3 is directly input to the output unit 5.
The output unit 5 adds and outputs the respective optical signal charges input from the first light receiving unit 2 and the second light receiving unit 3.

The document 7 moves at a transport speed v 'with respect to the linear image sensor 1 in the sub-scanning direction indicated by a white arrow in the figure, and the linear image sensor 1 reads a reading line 8 on the document 7. The document 7 is conveyed in the direction of the arrow, so that the first light receiving unit 2 reads the reading line 8 before the second light receiving unit 3. Note that the width of the reading line 8 on the document 7 is L. Further, the deviation of the focal point between the first light receiving unit 2 and the second light receiving unit 3 via the lens 6 is defined as ΔL.

The operation of the circuit will be described below with reference to FIGS.

FIG. 2 is a diagram for explaining the operation principle of the image reading apparatus shown in FIG. FIG. 3 is a diagram illustrating an operation principle of the output unit 5 of the image reading apparatus illustrated in FIG.

As shown in FIGS. 2A and 2B, the optical signal charges (shown by oblique lines) stored in the first light receiving section 2 are transferred to the CCD analog shift register 11 by a transfer pulse 13, and The optical signal charges (shown by oblique lines) stored in the two light receiving sections 3 are transferred to the CCD analog shift register 12 by transfer pulses 13. The same transfer pulses 13 and 13 are provided to the first light receiving unit 2 and the second light receiving unit 3.
Is input, and each accumulation time is t ′. And FIG.
As shown in (c), the CCD analog shift register 11
Is transferred to the output unit 5 after being delayed by the delay element 4 for a predetermined time by the drive clock pulse 14. The optical signal charges transferred to the CCD analog shift register 12 are transferred to the output unit 5 by the drive clock pulse 14. CCD analog shift register 1
The same drive clock pulses 14 and 14 are also input to 1 and 12, and the delay element 4 is driven by the drive clock pulse 15.

As shown in FIG. 3, the output section 5 is provided with an optical signal charge Q 'transferred from the CCD analog shift register 11.
A floating capacitor 16 for storing the optical signal charge Q 'transferred from the CCD analog shift register 12, a floating capacitor 18 for adding the output charge Q' of the floating capacitor 16 and the output charge Q 'of the floating capacitor 17, And floating capacitors 16, 1
It comprises switching circuits 5A, 5B, 5C, etc., which switch between input and output of optical signal charges to 7, 18.

As shown in FIG. 3A, the switching circuit 5A is connected to the contact 5a and the switching circuit 5B is connected to the contact 5b.
When the switching circuit 5C is switched to the contact 5c 'side, the optical signal charge Q' transferred from the CCD analog shift register 11 is transferred to the floating capacitor 16 via the contact 5a of the switching circuit 5A. The optical signal charge Q 'transferred from the CCD analog shift register 12 is transferred to the floating capacitor 17 via the contact 5b of the switching circuit 5B and stored.

Next, as shown in FIG. 3B, when the switching circuits 5A and 5B are switched to the contacts 5a 'and 5b' and the switching circuit 5C is switched to the contacts 5c, the floating capacitors 16 and 17 accumulate. Each of the optical signal charges Q ', Q' is supplied to the floating capacitor 18 through the contacts 5a ', 5b' of the switching circuits 5A, 5B and the contact 5c of the switching circuit 5C.
Is forwarded to As a result, the optical signal charges Q ′ and Q ′ are added in the floating capacitor 18. That is, the optical signal charges Q ′ of the first light receiving unit 2 and the second light receiving unit 3
And Q ′ are added. Next, as shown in FIG. 3C, the switching circuits 5A and 5B are switched to the contacts 5a and 5b, and the switching circuit 5C is switched to the contact 5c '.
The CCD analog shift register 12 is transferred from the CCD analog shift register 11 to the floating capacitor 16.
Then, the next optical signal charge is transferred to the floating capacitor 17. Such an operation is repeatedly performed.

The conveying speed of the original 7 in the image reading device is v '= L / t, and the reading line 8 read by the first light receiving portion 2 is read by the second light receiving portion 3 by ΔL / L.
After v 'time has elapsed. Accordingly, if the output of the first light receiving unit 2, that is, the output of the CCD analog shift register 11 is delayed by ΔL / v ′ time by the delay element 4, the floating capacitors 16 and 17 input to the output unit 5
The analog outputs (optical signal charges) Q ′ and Q ′ are optical signal charges obtained by reading the same read line 8 by both the first light receiving unit 2 and the second light receiving unit 3. Thereby, the shift of the focal point between the first light receiving unit 2 and the second light receiving unit 3, that is, the shift of the reading line 8 is corrected.

By using the same delay element 4 as the CCD analog shift register 11 and independently inputting the driving clock pulse 15 input to the delay element 4, the delay time ΔL / v ′ is It can be set arbitrarily. The optical signal charges Q ′, Q ′ transferred from the CCD analog shift registers 11 and 12 and stored in the floating capacitors 16 and 17 are transferred to the floating capacitor 18 and added, and output to the outside of the linear image sensor 1. Is done.

When the first light receiving section 2 and the second light receiving section 3 have exactly the same performance including sensitivity and the like,
The electric charges stored in the floating capacitors 16 and 17 are respectively Q ′ = αt ′. These charges Q 'and Q' are added by the floating capacitor 18, so that the final output charge of the output unit 5 is 2Q '.

Therefore, if the subsequent circuit configuration connected to the linear image sensor 1 is exactly the same as the circuit configuration connected to the linear image sensor of the conventional image reading device, the output charge 2Q 'of the output unit 5 will be , 2Q ′ = Q, that is,
It is sufficient that Q '= Q / 2. Then, Q = αt, Q ′ =
Since αt ′, the accumulation time t ′ = t / 2, and the accumulation time can be reduced to half of the conventional accumulation time. Here, the conveying speed v ′ of the document 7 is v ′ = L / t ′ = 2L /
t = 2v, and the document 7 can be conveyed at twice the speed of the conventional image reading apparatus.

(Second Embodiment) When the linear image sensor 1 of the first embodiment is used, the deviation ΔL of the focal point of the lens 6 of the first light receiving unit 2 and the second light receiving unit 3 is Although the width L of the reading line 8 is constant depending on the configuration of the image reading apparatus, the width L of the reading line 8 increases or decreases depending on the conveying speed v 'of the document 7, that is, the resolution in the sub-scanning direction. Two light receiving units 2, 3
In the case of the linear image sensor 1 having the following expression, if 2ΔL ≦ L, it can be considered that the first light receiving unit 2 and the second light receiving unit 3 are reading the same read line 8 at the same time. Therefore, the resolution in the sub-scanning direction is reduced,
Of the lens 6 of the first light receiving unit 2 and the second light receiving unit 3
Is less than ΔL ≦ L / 2
In this case, the delay by the delay element 4 becomes unnecessary. Therefore, whether to delay according to the transport speed v 'of the document 7 or
By providing the switching circuit 9 for switching whether or not to apply in the linear image sensor 1, it is possible to prevent a shift of the read line 8 to be added or the like beforehand.

(Third Embodiment) FIG. 4 is a diagram showing a basic configuration of an image reading apparatus according to a third embodiment of the present invention. In FIG. 4, a first linear image sensor 19 such as a CCD includes a light receiving unit 2, a delay element 4, a switching circuit 9 for switching whether or not to apply a delay by the delay element 4, and an output unit of the linear image sensor 19. The output unit 5 is connected to the inverting input terminal of the adder 20 via the resistor R1.

The second linear image sensor 1 'such as a CCD is equivalent to the conventional linear image sensor such as a CCD shown in FIG. 6, and includes a light receiving section and an output section (both not shown). The output is connected to the inverting input terminal of the adder 20 via the resistor R2. The output terminal of the adder circuit 20 is connected to the inverting input terminal via the resistor R3, and the non-inverting input terminal is grounded. Manuscript 7
Moves in the sub-scanning direction indicated by a white arrow in the drawing at a transport speed v ′ with respect to the first linear image sensor 19 and the second linear image sensor 1 ′, and the reading line 8 is moved by these linear image sensors 19 ′. , 1 '.
The deviation of the focal point between the light receiving section 2 of the first linear image sensor 19 and the light receiving section (not shown) of the second linear image sensor 1 'via the lens 6 is ΔL.

The second linear image sensor 1 'is similar to the one shown in FIG.
The first linear image sensor 19 has a built-in delay element 4 and a switching circuit 9 as shown in FIG. Each output unit of the first and second linear image sensors 19 and 1 ′ converts the optical signal charge into a voltage and outputs the voltage. Delay element 4
The output voltage of the first linear image sensor 19 and the output voltage of the second linear image sensor 1 ′ delayed by ΔL / v ′ are added by the adding circuit 20. As a result, the same output signal level as that of the related art can be obtained in half the accumulation time as in the first embodiment, and the transport speed v ′ of the document 7 can be improved.

(Fourth Embodiment) FIG. 5 is a diagram showing a basic configuration of an image reading apparatus according to a fourth embodiment of the present invention. In FIG. 5, first and second linear image sensors 1 ′ and 1 ′ such as CCDs are arranged in a conventional C
It is equivalent to a linear image sensor such as a CD, and has a light receiving unit and an output unit (neither is shown). One of the first
The output part of the linear image sensor 1 ′ is a delay element 4,
A switching circuit 9 for switching whether or not to apply a delay by the delay element 4 is connected to an inverting input terminal of an adding circuit 20 via a resistor R1, and the output of the other second linear image sensor 1 'is connected to a resistor. It is connected to the inverting input terminal of the adding circuit 20 via R2. The output terminal of the adder circuit 20 is connected to the inverting input terminal via the resistor R3, and the non-inverting input terminal is grounded. The original 7 is moved in the sub-scanning direction as indicated by a white arrow in the figure,
The reading line 8 is moved at a transport speed v 'with respect to the second linear image sensor 1' and the reading line 8 is read by these linear image sensors 1 'and 1'. The deviation of the focal point via the lens 6 of each light receiving unit of the first linear image sensor 1 'and the second linear image sensor 1' is ΔL.

In this image reading apparatus, each linear image sensor 1 'is equivalent to a conventional linear image sensor such as a CCD shown in FIG. 6, and a first linear image sensor 1'.
Is provided with a delay element 4 and a switching circuit 9 outside. ΔL /
The delay of v ′ is multiplied by the output voltage of the first linear image sensor 1 ′, and is added by the adding circuit 20. When this image reading apparatus is used, the same effect as in the third embodiment can be obtained without using a special linear image sensor.

(Fifth Embodiment) In the third and fourth embodiments, as in the case of the second embodiment, the focal point of each linear image sensor 1 ', 1' is set. The deviation ΔL is constant depending on the configuration of the image reading apparatus, but the width L of the reading line 8 is different from the conveying speed v ′ of the document 7.
That is, it increases or decreases depending on the resolution in the sub-scanning direction. When two linear image sensors 19 and 1 ′ are used, 2Δ
If L ≦ L, the first linear image sensor 19 and the second linear image sensor 1 ′
Can be regarded as being read. Accordingly, the resolution in the sub-scanning direction is reduced, and the relationship between the width L of the reading line 8 and the shift of the focal point via the lens 6 of the first linear image sensor 19 and the first linear image sensor 1 ′ is ΔL ≦ L. In the case of / 2, the delay by the delay element 4 becomes unnecessary.

If a switching circuit 9 for switching whether or not to apply a delay in accordance with the transport speed v 'is provided inside or outside the linear image sensor 19, the displacement of the read line 8 to be added can be reduced. It can be prevented beforehand. In particular, when the delay element 4 is provided outside, the same effect can be obtained by a single linear image sensor by using the linear image sensor 1 'itself for color.

[0033]

As described above, according to the image reading apparatus of the present invention, a linear image sensor having a plurality of light receiving sections or a plurality of linear image sensors is used, and the output charge or output voltage is added. Accordingly, high-speed reading can be performed without lowering the resolution in the sub-scanning direction of the image reading device. In addition, by providing a switching circuit for switching whether or not to apply a delay by the delay circuit, the resolution in the sub-scanning direction is reduced, and even if the transport speed of the document is increased, the displacement of the read line added is eliminated. Can be.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating the operation principle of the image reading apparatus shown in FIG.

FIG. 3 is a diagram showing an operation principle of an output unit of the image reading apparatus shown in FIG.

FIG. 4 is a diagram showing a basic configuration of an image reading device according to a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a basic configuration of an image reading device according to a fourth embodiment of the present invention.

FIG. 6 is a diagram illustrating a basic configuration of a conventional image reading apparatus.

FIG. 7 is a diagram showing the operation principle of the linear image sensor such as the CCD shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1 'Linear image sensor 2 First light receiving part of linear image sensor 3 Second light receiving part of linear image sensor 4 Delay element 5 Output part of linear image sensor 6 Lens 7 Original 8 Reading line on original 9 Switching circuit DESCRIPTION OF SYMBOLS 10 Image reading part 11, 12, 24 CCD analog shift register 13 Transfer pulse 14, 15 Drive clock pulse 16, 17, 18 Floating capacitor 19, 21 Linear image sensor 20 Addition circuit 22 Light receiving part of linear image sensor 23 Linear image sensor Output section

Claims (2)

[Claims] 1. An image reading apparatus for reading a sheet-shaped document by a linear image sensor such as a CCD, wherein a plurality of light receiving sections are provided inside the linear image sensor, and a circuit for adding respective output charges of the plurality of light receiving sections; An image reading apparatus comprising: a delay circuit that corrects a shift of a read line at the time of addition; and a switching circuit that switches whether or not there is a delay by the delay circuit, and reads the sheet-shaped document at a high speed. 2. An image reading apparatus for reading a sheet-like document by a linear image sensor such as a CCD, a plurality of linear image sensors, a circuit for adding output voltages of the plurality of linear image sensors, and reading at the time of addition An image reading apparatus, comprising: a delay circuit that corrects a line deviation; and a switching circuit that switches whether or not there is a delay caused by the delay circuit, and reads the sheet-shaped document at a high speed.