JPH07231376A - Light source control circuit and picture reader - Google Patents

Abstract

PURPOSE:To provide a picture reader capable of maintaining the light emitting amount of a light source constant over a long period and thus performing high picture quality read over the long period. CONSTITUTION:In this picture reader for reading pictures formed in an original 2 by irradiating the original 2 with light emitted from an LED array 3 and photoelectrically converting reflected light from the original 2 at the time by a CCD line sensor 6, the LED array 3 is provided with a circuit composed of plural resistors and plural switches for changing the light emitting amount of the LED. Also, a rear surface plate 7 is provided opposite to the CCD line sensor 6 holding the original 2 there between. Then, a light emitting amount detection circuit 10 detects the light emitting amount of the LED array 3 based on signals obtained by photoelectrically converting the reflected light from the rear surface plate 7 by the CCD line sensor 6. A light emitting amount control circuit 11 controls the switches emitting amount approach a prescribed light emitting amount set beforehand.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source control circuit for controlling the amount of light emitted from a light source for illuminating a document in a facsimile device or an image scanner device, and a document formed in a facsimile device or an image scanner device. The present invention relates to an image reading device that reads an image.

[0002]

2. Description of the Related Art Generally, an image reading apparatus uses a light source such as an LED array to illuminate a document and reflects light reflected from the document by C
An image signal is obtained by converting into an electric signal using a photoelectric conversion element such as a CD.

In such an image reading apparatus, when the amount of light emitted from the light source changes, the amount of reflected light incident on the photoelectric conversion element, and thus the level of the image signal, also changes, so that the voltage and current values applied to the light source are kept constant. The amount of light emitted from the light source does not change.

However, the light source is generally inevitably aged, and the light emission amount gradually decreases in the long term even if the supplied voltage and current values are specified values. For this reason, the level of the obtained image signal also gradually changes over a long period of time, eventually affecting the image quality and the like.

[0005]

As described above, the prior art is as follows.
Since the light source is always driven by supplying a constant voltage and current, there is a problem that the amount of light emission changes when the characteristics of the light source change due to deterioration over time.

The present invention has been made in consideration of such circumstances, and the first object thereof is to control a light source capable of maintaining the light emission amount of the light source constant over a long period of time. To provide a circuit.

Secondly, it is possible to provide an image reading apparatus capable of keeping the light emission amount of the light source constant over a long period of time, and thereby capable of performing high-quality reading over a long period of time. Especially.

[0008]

In order to achieve the above first object, a first aspect of the present invention provides a light emission amount varying means for changing the light emission amount of a light source to be controlled, and a light emission amount of the light source. A light emission amount detection means for detecting and a light emission amount control means are provided, and the light emission amount control means emits light so that the light emission amount detected by the light emission amount detection means approaches a predetermined light emission amount set in advance. The quantity varying means is controlled.

In order to achieve the above second object, a second
According to another aspect of the present invention, there is provided an image reading apparatus for irradiating an original with light emitted from a light source and photoelectrically converting reflected light from the original at this time by photoelectric conversion means to read an image formed on the original. A light emitting amount changing means for changing the light emitting amount of the light source; a back member arranged to face the photoelectric conversion means with the document interposed therebetween; and the document including the photoelectric conversion means and the back member. Provided is a light emission amount detection unit that detects the light emission amount of the light source based on a signal obtained by photoelectrically converting the reflected light from the back surface member by the photoelectric conversion unit in a state where it is not provided, and a light emission amount control unit. ,
The luminescence amount control means controls the luminescence amount varying means so that the luminescence amount detected by the luminescence amount detecting means approaches a preset predetermined luminescence amount.

[0010]

By taking such means, according to the first aspect of the present invention, the light emission amount of the light source to be controlled is detected by the light emission amount detecting means, and the detected light emission amount is set to a predetermined value. The light emission amount of the light source is adjusted by the light emission amount varying means under the control of the light emission amount control means so that the light emission amount approaches the light emission amount.

According to the second aspect of the invention, the photoelectric conversion means is arranged such that the original is not between the photoelectric conversion means and a back member arranged opposite to the photoelectric conversion means with the original interposed therebetween. The light emission amount of the light source is detected based on the signal obtained by photoelectrically converting the reflected light from the back member, and the light emission of the light source is set so that the detected light emission amount approaches a preset predetermined light emission amount. The amount is adjusted by the light emission amount varying means under the control of the light emission amount control means.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a main configuration of an image reading apparatus according to this embodiment. In the figure, reference numeral 1 denotes a document table made of a transparent glass plate, on which a document 2 is placed. The original 2 is placed on the original table 1 as needed by a transport system (not shown).
Be transported over.

Reference numeral 3 denotes an LED array as a light source, which irradiates the original 2 with light from the lower side of the original table 1. This L
The ED array 3 has a circuit for changing the light emission amount.

FIG. 2 is a circuit diagram specifically showing the structure of the LED array 3. In the figure, 20 (20-1 to 20-10, 20-11 to
20-20, 20-21 to 20-30, 20-31 to 20-40) are LEDs, 21 (21-1 to 21-n), 22 (22-1 to 22-n), 2 respectively.
3 (23-1 to 23-n) and 24 (24-1 to 25-n) are resistors, 25 (25-1 to 25-n), 26 (26-1 to 26-n) and 27, respectively.
(27-1 to 27-n) and 28 (28-1 to 28-n) are switches.

The LED 20 includes LEDs 20-1 to 20-10, LE
D20-11 ~ 20-20, LED20-21 ~ 20-30, LED20-3
Each of 1 to 20-40 constitutes one group, and ten LEDs 20 of each group are connected in series. In the mounted state, all 40 LEDs 20 are linearly arranged on the substrate.

The resistors 21-1 to 21-n have different resistance values, and each of them is connected in series to the LEDs 20-1 to 20-10.
And they are connected in parallel with each other. Resistor 22
-1 to 22-n have different resistance values, and each has LE
D20-11 to 20-20 are connected in series and in parallel with each other. The resistors 23-1 to 23-n have different resistance values, and are connected to the LEDs 20-21 to 20-30 in series and in parallel with each other. The resistors 24-1 to 24-n have different resistance values,
Each of them is connected to the LEDs 20-31 to 20-40 in series and in parallel with each other.

The switches 25-1 to 25-n are respectively connected to the resistor 21.
-1 to 21-n are connected in series. Switches 26-1 to 26-n
Are respectively connected in series to the resistors 22-1 to 22-n. Switches 27-1 to 27-n are resistors 23-1 to 23-n, respectively.
Are connected in series. The switches 28-1 to 28-n are connected in series to the resistors 24-1 to 24-n, respectively.

The LED 20-1 and the switches 25-1 to 25-n
Between LED 20-11 and switches 26-1 to 26-n,
Between ED20-21 and switches 27-1 to 27-n and LED20
+ 24V between -31 and switches 28-1 to 28-n
Is being applied.

Thus, the current supplied to the LEDs 20-1 to 20-10 changes depending on which of the switches 25-1 to 25-n is ON, and the light emission amount of the LEDs 20-1 to 20-10 is changed. Will change. That is, the resistors 21-1 to 21-n and the switches 25-1 to 25-n form a circuit that makes the light emission amounts of the LEDs 20-1 to 20-10 variable. Similarly, resistors 22-1 to 22-n and switches 26-1 to 26-n are connected to resistors 23-1 to 23-n and switches that change the amount of light emitted from LEDs 20-11 to 20-20. 27-1 to 27-n is a circuit that allows the amount of light emitted from LEDs 20-21 to 20-30 to be variable, using resistors 24-1 to 24-n and switches 28-1 to 28.
-n is a circuit that makes the amount of light emitted from LEDs 20-31 to 20-40 variable.

Reflected light from the predetermined reading position P1 of the original 2 is imaged on the CCD line sensor 6 by the reflection mirror 4 and the lens 5, and is converted into an electric signal (image signal) by the CCD line sensor 6.

Above the reading position P1, there is provided a back plate 7 whose lower surface is coated in a uniform white color. When the original 2 is not placed on the original table 1, the reading position P1 is set.
The light reflected from the rear plate 7 at a position P2 above the CCD line sensor 6 is reflected by the reflection mirror 4 and the lens 5.
Is imaged.

Reference numeral 8 denotes an A / D conversion circuit, which converts an image signal in an analog state output from the CCD line sensor 6 into a digital state. The image signal digitized by the A / D conversion circuit 8 is applied to the image processing circuit 9 and the light emission amount detection circuit 10.

The image processing circuit 9 performs predetermined image processing such as shading correction processing and outputs it as image data of a predetermined form. The light emission amount detection circuit 10 has, for example, a microcomputer as a main control circuit, detects the light emission amount of the LED array 3 based on the image signal digitized by the A / D conversion circuit 8, and notifies the light emission amount control circuit 11 of it. To do.

The light emission amount control circuit 11 includes a light emission amount detection circuit 1
The switches 25-1 to 25-n of the LED array 3 are set so that the light emission amount of the LED array 3 notified from 0 becomes a predetermined design value.
Controls 26-1 to 26-n, 27-1 to 27-n, 28-1 to 28-n.

Next, the operation of the image reading apparatus configured as described above will be described. The operation of reading an image is similar to that of a conventional general image reading apparatus, and therefore the description thereof is omitted. Here, the operation of controlling the light emission amount of the LED array 3 will be described.

First, the accuracy of each LED 20 is high,
When the amount of light emission is uniform between the two 20s, if the rear plate 7 is read without setting the original 2 on the original table 1, an image signal of a uniform level is output as shown in FIG. However,
The level of the image signal should originally be the designed value b, but in the example of FIG. 3, it is lowered as shown by the measured value a due to deterioration of the LED 20.

Now, after the image signal as shown in FIG. 3 is digitized by the A / D conversion circuit 8, the light emission amount detection circuit 1
When it is set to 0, the light emission amount detection circuit 10 detects the signal level at an arbitrary position in the image signal as the actual measurement value a, and supplies this actual measurement value a to the light emission amount control circuit 11.

The light emission amount control circuit 11 includes a light emission amount detection circuit 1
When the measured value a is received from 0, the light emission amount of the LED array 3 is controlled by the processing as shown in FIG. That is, the light emission amount control circuit 11 first obtains the difference X between the measured value a and the design value b (step ST41), and determines whether X is within the predetermined range c (step ST42). Here, the predetermined range c is set with a slight margin around "0", and is preferably set according to the control resolution of the light emission amount (variable step amount of the light emission amount) in this device. Thus, in step ST42, the light emission amount control circuit 11 determines whether or not X is a value near "0", that is, whether or not the difference between the measured value a and the design value b is very small. .

When X is outside the predetermined range c,
Since it can be seen that the current light emission amount of the LED 20 deviates from the design value b, the light emission amount control circuit 11 switches the LED array 3 switches 25-1 to 25- so that the measured value a approaches the design value b.
Controls 25-n, 26-1 to 26-n, 27-1 to 27-n, 28-1 to 28-n. That is, it is determined whether or not X is larger than the upper limit of the predetermined range c, and if it is larger, it can be seen that the light emission amount of the LED 20 is higher than the design value b, and therefore the light emission amount is reduced (step ST44). ), Otherwise LED20
Since it can be seen that the light emission amount of is lower than the design value b, the light emission amount is increased (step ST45).

Specifically, only one of the switches 25-1 to 25-n is turned on, and a resistor 21 connected in series to the turned-on switch 25 is used. Current is flowing to LEDs 20-1 to 20-10. Therefore,
In order to reduce the light emission amount of the LEDs 20-1 to 20-10, the resistor 21 having a larger resistance value than the resistor 21 currently used.
The switch 25 connected in series with is turned on. As a result, the current flowing through the LEDs 20-1 to 20-10 decreases, and
The light emission amount of ED20-1 to 20-10 decreases. Also LED20-1
To increase the amount of light emitted from ~ 20-10, the switch 25 connected in series to the resistor 21 having a smaller resistance value than the resistor 21 currently used is turned on. This gives L
The current flowing through ED20-1 to 20-10 rises and LED20-1 to
The amount of light emitted from 20-10 increases. Each of the switch 26, the switch 27, and the switch 28 also includes the switch 2
It is controlled in the same way as 5 LED20-11 to 20-20, LED20
-21 to 20-30 and LEDs 20-31 to 20-40 each have their light emission amounts increased or decreased as in the case of LEDs 20-1 to 20-10.

Then, the light emission amount control circuit 11 executes step S
After changing the light emission amount of each LED 20 in T44 or step ST45, the processes from step ST41 are repeated until the actual measurement value a falls within the predetermined range c. Then, if the measured value a falls within the predetermined range c, the processing is terminated, and the switches 25, 26, 27, and 28 are fixed as they are, and each L is fixed.
The amount of light emitted from the ED 20 is kept constant.

By the way, in general, there is a variation in characteristics between the LEDs 20, and even if the same current is supplied, the light emission amount varies. Therefore, if the rear plate 7 is read without setting the original 2 on the original table 1, for example, an image signal as shown in FIG. 5 is obtained.

In such a case, the light emission amount control processing by the light emission amount control circuit 11 may be changed as follows. That is, as shown in FIG.
First, the ratio Y between the measured value a and the design value b is obtained (step ST61), and it is determined whether Y is within the predetermined range d (step ST62). Here, the predetermined range d is
It is set with a slight margin around "1", and is preferably set according to the control resolution of the light emission amount (variable step amount of the light emission amount) in this device. Thus, in step ST62, the light emission amount control circuit 11
Whether Y is a value near “1”, that is, the measured value a
And the design value b are substantially the same.

If Y is outside the predetermined range d,
Since it can be seen that the current light emission amount of the LED 20 deviates from the design value b, the light emission amount control circuit 11 switches the LED array 3 switches 25-1 to 25- so that the measured value a approaches the design value b.
Controls 25-n, 26-1 to 26-n, 27-1 to 27-n, 28-1 to 28-n. That is, it is determined whether or not Y is larger than the upper limit of the predetermined range d. If Y is larger, it can be seen that the light emission amount of the LED 20 is higher than the design value b, and therefore the light emission amount is reduced (step ST64). ), Otherwise LED 20
Since it can be seen that the light emission amount of is lower than the design value b, the light emission amount is increased (step ST65).

Subsequently, the light emission amount control circuit 11 performs step S
The processing after T61 is repeated until the measured value a falls within the predetermined range d. Then, if the measured value a falls within the predetermined range d, the process is terminated, and the switches 25, 26, 27, and 28 are fixed as they are, and the light emission amount of each LED 20 is maintained constant.

By the way, when there is a large variation in the amount of light emission between the LEDs 20, the actual measurement value a greatly differs depending on the position of the image signal at which the actual measurement value a is set.
Therefore, it is desirable to use the most effective one of the maximum value a _max , the average value a _av, and the minimum value a _min as the actual measurement value a in consideration of various conditions related to image reading. Specifically, when the minimum light amount of the illumination light of the document 2 is important when reading the image, the minimum light amount can be secured above a certain value by using the minimum value a _min as the measured value a.

As described above, according to the present embodiment, the LED based on the image signal output from the CCD line sensor 6 is used.
The actual light emission amount (actual measurement value a) of each LED 20 of the array 3 is detected, and each LE is set so that this light emission amount approaches the design value b.
The light emission amount of D20 is controlled. Therefore, the light emission amount of each LED 20 is always maintained near the design value b.

As a result, when the original 2 is read, the original 2 can always be illuminated with the optimum amount of light, and the image formed on the original 2 can be read well.
Further, in the above-described embodiment, since the CCD line sensor 6 provided for reading the image is diverted to detect the light emission amount of the LED array 3, a new sensor for detecting the light emission amount of the LED array 3 is newly added. It does not need to be provided in the above and can be realized with a simple configuration.

The present invention is not limited to the above embodiment. For example, it is realized as a light source control circuit which is externally attached to the image reading device and controls the light source of the image reading device,
Alternatively, it can be realized as a light source control circuit in which a light source other than the light source of the image reading device is controlled.

In the above embodiment, the light emission amount is detected by using the CCD line sensor 6 provided for reading the image, but the light sensor for detecting the light emission amount (not limited to the CCD line sensor). May be separately provided.

Further, in the above embodiment, the LED array is illustrated as the light source, but the present invention can be applied to other types such as a fluorescent lamp. In addition, various modifications can be made without departing from the scope of the present invention.

[0042]

According to the first aspect of the present invention, the light emission amount varying means for changing the light emission amount of the light source to be controlled, the light emission amount detecting means for detecting the light emission amount of the light source, and the light emission amount. Since the light emission amount control means controls the light emission amount varying means so that the light emission amount detected by the light emission amount detection means approaches a predetermined light emission amount set in advance, the light source The light source control circuit is capable of maintaining a constant light emission amount of the light source over a long period of time.

In order to achieve the above second object, the second
According to another aspect of the present invention, there is provided an image reading apparatus for irradiating an original with light emitted from a light source and photoelectrically converting reflected light from the original at this time by photoelectric conversion means to read an image formed on the original. A light emission amount varying means for changing the light emission amount of the light source; a back member arranged to face the photoelectric conversion means with the document interposed therebetween; and the document including the photoelectric conversion means and the back member. Provided is a light emission amount detection unit that detects the light emission amount of the light source based on a signal obtained by photoelectrically converting the reflected light from the back surface member by the photoelectric conversion unit in a state where it is not provided, and a light emission amount control unit. ,
Since the light emission amount control means controls the light emission amount varying means so that the light emission amount detected by the light emission amount detection means approaches a preset predetermined light emission amount, the light emission amount of the light source is kept for a long period of time. Can be kept constant over
As a result, the image reading device becomes capable of performing high-quality reading over a long period of time.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram specifically showing a configuration of an LED array 3 in FIG.

FIG. 3 is a diagram showing an example of an image signal obtained when the back plate 7 is read by the CCD line sensor 6 when the light emission amount is uniform between the LEDs 20.

FIG. 4 is a flowchart showing a processing procedure of a light emission amount control circuit 11 relating to light emission amount control of the LED array 3.

FIG. 5 is a diagram showing an example of an image signal obtained when the back plate 7 is read by the CCD line sensor 6 when there is a variation in the amount of emitted light between the LEDs 20.

FIG. 6 is a flowchart showing a modification of the processing procedure of the light emission amount control circuit 11 relating to the light emission amount control of the LED array 3.

[Explanation of symbols]

1 ... Original platen 2 ... Original 3 ... LED array 20-1 to 20-40 ... LED 21-1 to 21-n, 22-1 to 22-n, 23-1 to 23-n, 24-1 to 24-- n ... Resistor 25-1 to 25-n, 26-1 to 26-n, 27-1 to 27-n, 28-1 to 28-n ... Switch 4 ... Reflecting mirror 5 ... Lens 6 ... CCD line sensor 7 Back plate 8 A / D conversion circuit 9 Image processing circuit 10 Light emission amount detection circuit 11 Light emission amount control circuit

Claims (2)

[Claims] 1. A light emission amount varying means for changing the light emission amount of a light source to be controlled, a light emission amount detecting means for detecting the light emission amount of the light source, and light emission detected by the light emission amount detecting means. A light source control circuit comprising: a light emission amount control means for controlling the light emission amount varying means so that the light amount approaches a predetermined light emission amount set in advance. 2. An image reading apparatus for irradiating a document with light emitted from a light source, and photoelectrically converting reflected light from the document at this time by photoelectric conversion means to read an image formed on the document. In the above, the light emission amount varying means for changing the light emission amount of the light source, a back surface member arranged to face the photoelectric conversion means with the original document sandwiched therebetween, the original document including the photoelectric conversion means and the rear surface member. And a light emission amount detection means for detecting the light emission amount of the light source based on a signal obtained by photoelectrically converting the reflected light from the back surface member by the photoelectric conversion means in a state not present between the light emission amount detection means. An image reading apparatus, comprising: a light emission amount control means for controlling the light emission amount varying means so that the detected light emission amount approaches a preset predetermined light emission amount.