JPH10327298A - Original reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the quality of picture read by an image sensor from being lowered by preventing the luminance of LED array from being lowered by changes with the passage of time. SOLUTION: A ROM 22 is provided for storing the data table of control values for setting a current to be electrified to an LED array 15 corresponding to the cumulative ON time of LED array 15, and a CPU 21 reads any control value out of this ROM 22 corresponding to the cumulative ON time of LED array 15, outputs that value to a D/A converter 26 and controls a current to flow to the LED array 15 through an operational amplifier 27 and a transistor 28. Thus, the luminance reduction of LED array 15 caused by changes with the passage of time and therefore, the quality of picture read by an image sensor 17 is prevented from being lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading apparatus used for a facsimile apparatus, an image scanner, and the like, and more particularly to a technique for preventing a decrease in luminance of an LED array provided in an image sensor due to aging.

[0002]

2. Description of the Related Art Conventionally, a document reading apparatus for reading an image recorded on a document or the like is provided with an image sensor for photoelectrically converting an image on the document. In this image sensor, an image sensor from an LED array serving as a light source is provided. The image on the document reflected by the light is photoelectrically converted by the photoelectric conversion element. The brightness of this LED array decreases with aging. Therefore, in order to prevent a decrease in the accuracy of reading by the image sensor due to this, when the image sensor is a CCD, a white reference tape provided in the apparatus is read each time a reading operation is performed, and based on that, There is one in which reading quality is prevented from lowering by performing shading correction.

[0003]

However, according to the conventional document reading apparatus as described above, if the reading operation is repeated, the stains of the document adhere to the white reference tape and the white reference becomes unstable. In some cases, accurate correction cannot be performed. When the image sensor is a contact image sensor (CIS), the focus of the sensor is on the original reading surface of the sensor, and the depth of focus is very shallow.
The structure cannot read the white reference tape, and the correction cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and is intended to prevent a decrease in the brightness of an LED array due to aging, thereby preventing a decrease in output of image quality read by an image sensor. It is an object to provide a document reading device.

[0005]

According to a first aspect of the present invention, there is provided an original reading apparatus, comprising: an LED array serving as a light source; and an image reflected by light from the LED array. A document reading device having an image sensor comprising a photoelectric conversion element for converting, comprising:
Operating time counting means for counting the cumulative lighting time of the array; storage means for storing a table of the cumulative lighting time of the LED array and a control value for setting a current flowing through the LED array in accordance with the cumulative lighting time; Control means for reading a control value corresponding to the cumulative lighting time of the LED array counted by the operation time counting means from the storage means, and controlling a current flowing through the LED array based on the read control value. It is.

In the above configuration, the current supplied to the LED array is controlled based on the control value of the table stored in the storage means according to the cumulative lighting time. here,
L due to aging according to the cumulative lighting time of the LED array
Although the number of ED arrays is reduced, the control value corresponding to the accumulated lighting time of the LED array in the table stored in the storage means can cancel out the decrease in the brightness. Is kept constant. This prevents the image quality of the image sensor from deteriorating.

According to a second aspect of the present invention, there is provided the original reading apparatus according to the first aspect, wherein the control means corresponds to the cumulative lighting time of the LED array read from the storage means. A signal output means for outputting a signal about the control value; a D / A conversion means for converting a signal from the signal output means into an analog signal; and an LED array based on the analog signal from the D / A conversion means. Switching means for controlling the flowing current.

In the above configuration, the signal output means outputs L
A signal for a control value corresponding to the cumulative lighting time of the ED array is output, and this signal is converted into an analog signal by D / A conversion means, and a current flowing through the LED array is controlled by the switching means based on the analog signal. You. A CPU or the like can be used as the signal output means, and it is possible to compensate for a decrease in luminance of the LED array due to aging with a simple configuration.

According to a third aspect of the present invention, there is provided the original reading apparatus according to the first or second aspect, wherein the image sensor is a contact type image sensor.

In the above configuration, in the case of the contact type image sensor, it is not possible to adopt a configuration in which a white reference tape is read for shading correction. Can be prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an original reading apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG.
FIG. 3 is a cross-sectional view illustrating a document conveying path of a facsimile apparatus provided with a document reading device. A separation roller 3 for separating and conveying the document P from a plurality of document bundles set on the document table 2 and a sensor lever 4 as a detection unit of the ADF for automatically conveying the document P are provided on a document conveyance path of the facsimile machine 1.
A document sensor lever 5 for detecting the presence or absence of a document P on the document transport path; a contact type image sensor 10 for reading an image on the document P on the downstream side of the document sensor lever 5 for document transport; A transport roller 11 that is disposed to face and transports the document P is provided.

FIG. 2 shows a contact type image sensor (CIS) 1.
FIG. 2 is a cross-sectional view showing an internal structure of a No. 0. Facsimile machine 1
Is not an image sensor using an IC technology such as a CCD or a MOS image sensor, but a contact image sensor 10 using a thin film technology.
Has been adopted. A transparent glass 1 is placed on the original reading position A of the chassis 12 of the contact type image sensor 10.
3 are provided. Below this transmission glass 13,
An LED array 15 having an LED (Light Emitting Diode) 15a as a light source for irradiating an original placed on the transmission glass 13, a selfoc lens 16 as a light guide system for condensing reflected light of the original, and A sensor (photoelectric conversion element) 17 for photoelectrically converting the read image is provided. As the sensor 17, amorphous chalcogenite (for example, CdS or the like) is used. These LEDs
Array 15, Selfoc lens 16 and sensor 17
Has a length equivalent to the width dimension orthogonal to the transport direction of the read original. The LED array 15 is set at an angle at which the reflected light of the document is reflected to the position of the selfoc lens 16. The sensor 17 is provided on a circuit board (PCB) 18 and is connected to a CPU (described later) that functions as a control unit and the like.

An operation of reading a document by the document reading apparatus having the above-described configuration will be described below. The document P set on the document table 2 is separated and conveyed by the separation roller 3, and is conveyed between the conveyance roller 11 and the contact image sensor 10. The document is pressed against the transparent glass 13 at the document reading position A of the contact type image sensor 10 by the transport roller 11, and the LED array 1 is read at the document reading position A.
Irradiation with light from 5 The light from the LED array 15 passes through the transmission glass 13 and is reflected by the document P, and the light reflected by the document P is condensed by the selfoc lens 16, focused on the surface of the sensor 17, and received by the sensor 17. The light is converted into an electric signal and output to the CPU. The document after the image is read by the contact type image sensor 10 is conveyed to a document discharge port (not shown).

FIG. 3 shows an electric block of the document reading apparatus. CPU that controls the operation of the entire facsimile machine 1
(Signal output means, control means) 21 include a ROM (storage means) 22 in which an operation program is stored, a RAM 23 for temporarily storing image data from the sensor 17, and the like.
And a counter (operating time counting means) 24 for counting the cumulative lighting time of the LED array 15. The ROM 22 stores the cumulative lighting time of the LED array 15 as shown in FIG.
A data table with control values for setting a current flowing through the D array 15 is stored. This control value is
Since the luminance decreases due to aging due to the cumulative lighting time of the array 15, the LE required to cancel the luminance decrease is used.
This is for setting the current supplied to the D array 15.

The CPU 21 reads out a D / A output value (hereinafter, referred to as a control value) corresponding to the accumulated lighting time of the LED array 15 counted by the counter 24 from the ROM 22 and outputs it to the I / O gate array 25. Also, CPU2
1 is connected to the CPU 21 via the I / O gate array 25.
A D / A converter (D / A conversion means) 26 for converting a digital signal of a control value output from the D / A converter into an analog signal is connected to the D / A converter 26.
An operational amplifier 27 for controlling a current flowing through the D array 15 and a transistor 28 as switching means are connected. The LED array 15 is formed by connecting a series circuit of a plurality of LEDs in parallel.
8 between the power supply Vcc and the ground.
By these operational amplifier 27 and transistor 28, C
D / A converter 26 of control value output from PU 21
, The current flowing through the LED array 15 is controlled.

Next, control of the current supplied to the LED array 15 will be described with reference to FIG. FIG. 5 is a flowchart showing the flow of the process at the time of this control. When the document reading operation starts, the LED array 15 is turned on (S
1). At this time, the CPU 21 stores the previous control value stored in the RAM 23 through the I / O gate array 25 as D
The operational amplifier 27 controls the transistor 28 based on the control value to control the energization of the LED array 15. Next, the cumulative lighting time of the LED array 15 counted by the counter 24 is confirmed (S2). Then, the control value corresponding to the accumulated lighting time is read from the data table in the ROM 22, and is compared with the current control value (S3).

The control value read from the data table in the ROM 22 and the current control value are the same, and the D / A
When it is not necessary to update the control value output to converter 26, the processing of S2 and S3 is repeated (N in S4
O). The control value read from the data table in the ROM 22 differs from the current control value, and the D / A converter 26
When it is necessary to update the control value to be output to the D / A converter 26 (YES in S4), the new control value read from the data table in the ROM 22 is output to the D / A converter 26 (S4).
5) The current supplied to the LED array 15 is controlled based on the new control value.

As described above, according to the document reading apparatus of the present embodiment, the current flowing through the LED array 15 according to the cumulative lighting time of the LED array 15 counted by the counter 24 is based on the control value stored in the table. Control, the brightness of the LED array 15 can be kept constant regardless of the cumulative lighting time. Therefore, the image quality read by the close contact type image sensor 10, for example, the thin gradation of the white portion is prevented from being reduced, and the image can always be read stably. In particular, when the image sensor is a CCD, the shading correction can be performed by reading a white reference tape, whereas when the image sensor is a contact type image sensor, the correction by such reading is performed. However, by controlling the current supplied to the LED array 15 as in the present embodiment, it is possible to compensate for the decrease in luminance without reading the white reference tape.

The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. For example, in the above-described embodiment, the A / D output value (control value) for the lighting time stored in the data table in the ROM is data relating to voltage. The data may be data relating to a value, and in that case, the CPU 21 may use a circuit configuration that detects the current flowing through the LED array 15 and controls the conduction.

[0020]

As described above, according to the document reading apparatus according to the first aspect of the present invention, the current corresponding to the cumulative lighting time of the LED array is controlled so as to flow through the LED array. The brightness of the LED array is kept constant irrespective of the effect, so that the effect of maintaining the fine gradation of the white part forever can be obtained, and the image sensor always reads a stable image regardless of aging. It can be performed. In addition, in a case where the image sensor output is corrected by shading using a white reference tape to compensate for a decrease in the brightness of the LED array due to aging, there is a problem that the LED array is weak to dirt. Brightness reduction can be compensated without being affected by contamination of the device.

Further, according to the document reading apparatus of the present invention, the current value flowing through the LED array is controlled by the signal output means, the D / A conversion means and the switching means. With a simple configuration using a CPU or the like, it is possible to correct a decrease in the brightness of the LED array due to aging, and to prevent deterioration of the image quality read by the image sensor.

According to the document reading apparatus of the third aspect of the present invention, in addition to the above effects, when a contact type image sensor is used, a white reference tape is used for shading correction due to its structure. Although they cannot be read, shading correction can be performed without the need for such reading.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a document conveyance path of a facsimile apparatus including a document reading device.

FIG. 2 is a cross-sectional view illustrating an internal structure of a contact image sensor.

FIG. 3 is a block diagram illustrating an electrical configuration of the document reading apparatus.

FIG. 4 is a diagram showing a data table of an accumulated lighting time of an LED array and a control value for setting a current flowing through the LED array according to the accumulated lighting time.

FIG. 5 is a flowchart illustrating a flow of a process of controlling a current flowing through the LED array.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Contact image sensor 15 LED array 17 Sensor (photoelectric conversion element) 21 CPU (signal output means, control means) 22 ROM (storage means) 24 Counter (operating time count means) 26 D / A converter (D / A conversion means) , Control means) 28 transistor (switching means, control means)

Claims (3)

[Claims] 1. An LED array serving as a light source, and the LED
In a document reading apparatus having an image sensor comprising a photoelectric conversion element for photoelectrically converting an image reflected by light from an array, an operation time counting means for counting an accumulated lighting time of the LED array, and an accumulated lighting time of the LED array Storage means for storing a table of control values for setting a current flowing through the LED array in accordance with the cumulative lighting time; and the L counted by the operation time counting means.
A reading means for reading the control value corresponding to the cumulative lighting time of the ED array from the storage means, and controlling a current flowing through the LED array based on the read control value; apparatus. 2. The signal processing device according to claim 1, wherein the control unit outputs a signal about the control value corresponding to the cumulative lighting time of the LED array read from the storage unit, and outputs a signal from the signal output unit to an analog signal. Convert to D /
2. The image processing apparatus according to claim 1, further comprising: A conversion means; and switching means for controlling a current flowing through the LED array based on an analog signal from the D / A conversion means.
The document reading device according to 1. 3. The document reading apparatus according to claim 1, wherein the image sensor is a contact image sensor.