JP2003228142A - Color image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow a light source turning-on control part 9 to prevent a driving current that exceeds forward current maximum rating from being supplied to a light source 16 even if thermal runaway, etc., occurs. <P>SOLUTION: A voltage converting part 14 converts the voltage of a value corresponding to a duty rate of a turning-on control signal outputted from the light source turning-on control part 9 and outputs the converted voltage, a G light source current switching part 12 selects either a resistance R2 or a resistance R3 according to whether the value of the converted voltage is larger than a reference voltage Vref and connects the selected resistance to a transistor TR2. In such a case, the reference voltage Vref is set so as to be the same value as a signal value outputted from the voltage converting part 14 when the duty rate becomes, for example, 33%, and when the duty rate is more than 33%, the resistance R2 is connected to the transistor so as to prevent a driving current that is not lower than the forward current maximum rating from being caused to flow to a G light source 16. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention performs color reading by alternately lighting three light sources of red, green and blue at a predetermined duty ratio, and one of the three light sources at a predetermined duty ratio. The present invention relates to a color image reading device that is turned on to perform monochrome reading, and relates to a color image reading device that prevents a current supplied to a particular light source from exceeding a maximum forward current rating.

[0002]

2. Description of the Related Art In a color image reading apparatus such as a color facsimile machine, a color image scanner, a color copying machine and a combination machine of these, red is used as a color light source.
Green and blue light sources are used to photoelectrically convert the reflected light from the document with a light receiving element to obtain image data.

At this time, the original is read by color-separating and reading the color original by alternately lighting the three light sources of red, green, and blue at one storage time interval in accordance with the line-sequential reading method. Hereinafter, the three light sources of red, green, and blue will be referred to as an R light source, a G light source, and a B light source.

When performing color reading by the line-sequential reading method as described above, the duty ratio of each light source is 3 at maximum.
Although it is 3% or less, when performing monochrome reading, since only the G light source is turned on for each line, the maximum duty ratio of the G light source may be 100%.

Generally, a light emitting diode (LED: Light Emitting D) is used as such a light source.
iode) is used, and the drive current thereof is not used below the maximum forward current rating, life deterioration or damage will occur.

Therefore, in monochrome reading, the driving current flowing through the G light source is set to a value smaller than that in color reading, and the maximum forward current rating is exceeded even if the duty ratio changes in the range of 33 to 100%. It is controlled not to.

[0007]

However, since the current control for such a light source is software control, if thermal runaway or the like occurs and normal control cannot be performed, the drive current exceeding the maximum forward current rating is exceeded. Is supplied to the light source, and there is a problem that the above-described life deterioration and damage occur.

Therefore, the present invention provides a color image reading apparatus with improved reliability by preventing the drive current exceeding the maximum forward current rating from being supplied to the light source even if thermal runaway or the like occurs. To aim.

[0009]

In order to solve the above problems, the invention according to claim 1 reads a color image by alternately lighting three light sources of red, green and blue at a predetermined duty ratio to read a color image. In a color image reading apparatus that performs monochrome reading by turning on one of the light sources at a predetermined duty ratio, a signal of the duty ratio is output as a lighting control signal so that each light source is turned on at a predetermined duty ratio. A light source lighting control unit and a light source current limiting unit that switches the driving current so that the driving current supplied to the light source in accordance with the duty ratio of the lighting control signal becomes equal to or less than the maximum forward current rating of the light source are provided. Even if a runaway or the like occurs, the drive current exceeding the maximum forward current rating is not supplied to the light source to improve reliability.

According to a second aspect of the present invention, the light source current limiting means outputs the switching signal with the signal level inverted when the duty ratio of the lighting control signal exceeds a preset duty ratio. A light source switch that switches the drive current supplied to the light source by selecting a control unit, a current limiting resistance unit that limits the drive current flowing in the light source, and a resistor having a different resistance value in the current limiting resistance unit according to the switching signal. And is provided.

According to a third aspect of the present invention, there is provided an image sensor that photoelectrically converts reflected light from a document due to light from a light source to output image data, and a bright output detection unit that detects a bright output maximum value of the image data. Therefore, when setting the duty ratio of the light source, the light source lighting control unit sets the duty ratio of the light source to 10
It is characterized in that the bright output maximum value is set to fall within a predetermined range by being decreased by a predetermined amount from 0%.

According to a fourth aspect of the present invention, when the light source lighting control unit sets the duty ratio of the light source, the duty ratio of the light source set at the time of the previous reading is appropriately increased or decreased to obtain the maximum bright output value. Is set to fall within a predetermined range.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a color facsimile apparatus as an example of a color image reading apparatus according to the present invention, and FIG. 2 is a configuration diagram showing in detail a main part of a reading unit.

In such a color facsimile apparatus, a system control unit 1 for controlling the entire apparatus, a ROM 2 storing a control program for the system control unit 1, a RAM 3 storing various data regarding the operation of the apparatus, an operation state of the apparatus. Such as an operation display section 4 for displaying various information and various input operations by an operator, a reading section 7 for optically reading a document, a plotter section 8 for forming an image on a recording sheet, and a facsimile machine of the other party via a communication line. A communication control unit 6 for exchanging facsimile control signals with the communication control unit 6,
It has an encoding / combining unit 5 for encoding and decoding image data, and these are connected via a bus.

The reading unit 7 includes a light source lighting control unit 9, a lighting switch unit 10, a current limiting resistor unit 11, and a G light source current switching unit 1.
2, G light source current determination unit 13, light source 16, image sensor 17, A / D converter 18, image processing unit 19, bright output detection unit 20, power supply 22 and the like.

The light source 16 includes an R light source 16a and a G light source 16
It is composed of three light sources, b and B light sources 16c, and is used for irradiating the original with light of each color. The image sensor 17 is used for photoelectrically converting the reflected light from the original and outputting analog image data.

The light source lighting control unit 9 controls which color of the light source 16 is to be lit with which duty ratio.
The lighting control signal of the duty ratio is supplied to the lighting switch unit 10
Output to.

The lighting switch section 10 is a transistor TR which is turned on / off by inputting a lighting control signal to the base.
1 to TR3, the collector side of which is connected to each resistance of the current limiting resistance section 11.

The collector of the transistor TR2 corresponding to the G light source 16b is connected to each resistor of the current limiting resistor unit 11 via the G light source current switching unit 12.

The current limiting resistor section 11 controls the drive current flowing through each light source 16, and has a resistor R1 connected to the R light source 16a and resistors R2 and R connected to the G light source 16b.
3, a resistor R4 connected to the B light source 16c.

The G light source current switching unit 12 connects the collector of the transistor TR2 to either the resistor R2 or the resistor R3 in response to the switching signal from the G light source current determining unit 13.
When it is connected to the resistor R2, the G light source 16b has, for example, 40
When a driving current of mA flows and it is connected to the resistor R3, G
A drive current of, for example, 20 mA is allowed to flow in the light source 16b.

In the G light source current determination unit 13, the lighting control signal of the G light source 16b from the light source lighting control unit 9 receives the transistor T.
Since the R2 is a signal for turning ON / OFF at the duty ratio, the voltage conversion unit 14 that converts the voltage to a value corresponding to the duty ratio, and the signal value from the voltage conversion unit 14 is a preset reference voltage ( Vref) is larger than Vref), and the comparator 15 outputs a switching signal whose signal level is inverted according to the result.

The reference voltage is set to have the same value as the signal value output from the voltage converter 14 when the duty ratio of the G light source 16b becomes 33%, for example.

The A / D converter 18 is used to convert an analog image signal from the image sensor into a digital image signal, and the image processing section 19 applies an MTF (Modulation Transfer) to the digital image signal.
Function) correction, monochrome binarization or multi-value conversion, color separation, and the like.

Further, the maximum value detecting section 20 determines the bright output maximum value (Vma) from the read digital image data of one line.
x) is detected and stored in the RAM 3.

With such a configuration, color reading and monochrome reading are performed according to the timing charts shown in FIGS. In addition, in the case of color reading, FIG.
FIG. 4 shows respective timing charts in the case of monochrome reading.

For color reading, the R light sources 16a, G
Since the three light sources 16 of the light source 16b and the B light source 16c are sequentially switched on and switched on at one line intervals, the duty ratio of each color is limited to 33% at maximum even when all the lights are turned on in one accumulation time.

However, the G light source 1 is used for monochrome reading.
Since only 6b lights up, the maximum duty ratio is 100
May be%.

FIG. 5 is a diagram showing the relationship between the duty ratio of each LED and the maximum forward current rating. The solid line indicates G during color reading.
The forward current maximum ratings of the light source 16b and the B light source 16c are shown.
The alternate long and short dash line indicates the maximum forward current rating of the R light source 16a during color reading. The dotted line indicates the maximum forward current rating of the G light source 16b during monochrome reading.

When the drive current of the G light source 16b is set to 40 mA, the duty ratio of each light source 16 does not exceed the 33% duty ratio during color reading. Therefore, even if a thermal runaway occurs, the drive current will be normal. The maximum current rating will not be exceeded.

However, at the time of monochrome reading, the G light source 16
Since the duty ratio of b changes up to 100%, 40%
If the above conditions are exceeded, the maximum forward current rating will be exceeded, leading to deterioration in service life and damage.

Therefore, the G light source current switching unit 12 and the G light source 1
6b, two resistors R2 and R3 are provided, and the resistor R2 is selected so that the driving current to the G light source 16b is 40 mA during color reading, and the G light source 16 is selected during monochrome reading.
The resistor R3 is selected and connected to the transistor TR2 so that the drive current to b is 20 mA.

At this time, for example, as shown in FIG. 6, when the control signal for the purpose of switching control of the G light source current switching unit 12 is output from the light source lighting control unit 9, when a thermal runaway or the like occurs. Since a normal control signal will not be output, a drive current of 40 mA may continue to flow to the G light source 16b.

However, in the configuration according to the present invention, even when the lighting control signal output from the light source lighting control unit 9 becomes an inappropriate signal due to thermal runaway or the like, the G light source current switching is performed based on the duty ratio. Since the section 12 is operated, the drive current exceeding the maximum forward current rating is not supplied to the G light source 16b.

Since each light source 16 has a variation in light quantity and the image sensor 17 has a variation in sensitivity, preprocessing such as setting the duty ratio of the light source 16 is necessary to read an image in an optimum state. become.

The procedure at this time will be described with reference to the flowchart shown in FIG. Although FIG. 7 refers to the procedure of monochrome reading using the G light source 16b, in the case of color reading, the same processing is repeated for the R light source 16a, the G light source 16b, and the B light source 16c, and the respective light sources are repeated. It suffices to set the duty ratio of.

To set the duty ratio of the G light source 16b, first, the duty ratio of the G light source 16b is set to 100% (steps S1 and S2).

At this time, since the duty ratio is 100%,
A signal having a value higher than the reference voltage of the comparator 15 is output from the voltage conversion unit 14, and the comparator 15 outputs “L”.
A level switching signal is output to the G light source current switching unit 12.

As a result, the G light source current switching section 12 is
The resistor R3 is connected to the transistor TR2 to connect the G light source 16
A drive current of 20 mA is allowed to flow in b.

In this state, the white reference plate is read and 1 at that time is read.
The bright output maximum value (Vmax) of the line is measured (step S3).

When the bright output maximum value Vmax exceeds 100% of the dynamic range in the A / D converter 18, the duty ratio of the lighting control signal corresponding to the G light source 16b is 10% (can be arbitrarily set). The maximum bright output value Vmax is 80 in the dynamic range.
It is set so as to fall within the range of 100% (step S4).
-Step S6).

When the bright output maximum value Vmax is in the range of 80% to 100% of the dynamic range, the setting of the duty ratio is normally completed, and dark output data sampling, shading data sampling, and document reading are performed (steps S8 to step). S10).

However, when the bright output maximum value Vmax is not within the range of 80% to 100% of the dynamic range, a light source setting error occurs, and the reading process is forcibly terminated (step S7).

When the duty ratio is set so that the bright output maximum value Vmax is in the range of 80% to 100% of the dynamic range, the duty ratio of the lighting control signal corresponding to the G light source 16b is 30% or less. If so, the switching signal from the comparator 15 becomes the “H” level, so the G light source current switching unit 12 causes the resistor R2 to be connected to the transistor TR2. As a result, a driving current of 40 mA flows through the G light source 16b.

Therefore, the driving current of the G light source 16b is switched between 20 mA and 40 mA at a duty ratio of 30% as shown in FIG. 8, and the relative light amount changes at the duty ratio of 30%. The relative light amount is 100 for the G light source 16b.
When the duty ratio is 40 mA, the light quantity is 10
It is a relative light amount when 0% is set.

As described above, the G light source current switching unit 1
Since the switching of 2 is performed based on the duty ratio of the lighting control signal output from the light source lighting control unit 9, even if the light source lighting control unit 9 causes thermal runaway or the like, the G light source 16b has a forward current maximum rating or more. The driving current does not flow, and it is possible to prevent the deterioration of the life of the G light source 16b and the damage thereof, and the reliability is improved.

Next, a second embodiment of the present invention will be described with reference to the drawings. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted as appropriate.

In the first embodiment, when setting the duty ratio, first, the duty ratio of the G light source 16b is set to 100%, and the bright output maximum value Vmax for one line is set.
Was set by changing the duty ratio so that the value of the duty ratio was within the range of 80% to 100%.

On the other hand, in the present embodiment, first, the duty ratio of the G light source 16b is set to the previous value so that the maximum bright output value Vmax of one line is within the range of 80% to 100%. In addition, the duty ratio is changed and set.

This setting procedure will be described with reference to FIG.
When the setting of the duty ratio of the light source 16 is completed, the light source lighting control unit 9 stores the value in the RAM 3 or the like to prepare for the next reading.

Therefore, when the reading process is newly started,
The previous duty ratio stored in the RAM 3 is read, and the G light source 16b is turned on at this duty ratio (steps S11 and S12).

Then, the bright output maximum value Vmax of one line in this state is measured, and the bright output maximum value Vmax is A.
100% of the dynamic range in the D / D converter 18
It is determined whether or not the following (step S14).

When the dynamic range is not less than 100%, the duty ratio of the G light source 16b is set to, for example, 15%.
As described above, the predetermined amount is decreased (step S15), and the procedure returns to step S13 to repeat the procedure for measuring the bright output maximum value Vmax.

When the bright output maximum value Vmax becomes 100% or less of the dynamic range in the A / D converter 18 by repeating such processing, it is determined whether it is 80% or more of the dynamic range this time.

When the dynamic range is not 80% or more, the duty ratio of the G light source 16b at that time is 10%.
It is determined whether it is 0% (step S17).

In the case of 100%, the predetermined light amount cannot be obtained even if the G light source 16b is continuously turned on.
The reading process ends as a light source setting error (step S
19).

On the other hand, the duty ratio of the G light source 16b is 10
If it is not 0%, the duty ratio is set to 10%, for example.
As described above, the predetermined amount is increased (step S18), and the process returns to step S13 to repeat the procedure for measuring the bright output maximum value Vmax.

When the above processing is completed, the bright output maximum value Vmax of one line falls within the range of 80% to 100% of the dynamic range in the A / D converter 18, and the duty ratio of the G light source 16b at that time is set. It is stored in the RAM 3 and dark output data collection, shading data collection, and document reading are performed (steps S20 to S2).
2).

As described above, when setting the duty ratio of the G light source 16b, the setting process is started from the previous duty ratio, so that the time required for the setting can be shortened.

In particular, when there is no change in the light quantity variation of each light source 16 or the sensitivity variation of the image sensor 17, dark output data collection, shading data collection,
The original can be read and the time can be greatly reduced.

[0061]

As described above, according to the present invention,
A light source lighting control unit that outputs a signal of the duty ratio as a lighting control signal so that each light source lights at a predetermined duty ratio, and a driving current supplied to the light source according to the duty ratio of the lighting control signal is the light source. Since it has a light source current limiting means that switches the drive current so that it is below the maximum forward current rating, the drive current exceeding the maximum forward current rating will not be supplied to the light source even if thermal runaway etc. occurs. The property is improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a facsimile apparatus as a color image reading apparatus applied to the description of each embodiment of the present invention.

FIG. 2 is a diagram illustrating a detailed configuration of a reading unit.

FIG. 3 is a timing chart of three light sources when performing color reading.

FIG. 4 is a timing chart of three light sources when performing monochrome reading.

FIG. 5 is a diagram showing a forward current as a duty ratio of a light source.

FIG. 6 is a diagram applied to description of an effect.

FIG. 7 is a diagram showing a procedure for performing monochrome reading by setting a duty ratio of a G light source and the like.

FIG. 8 is a diagram showing a relative light amount with respect to a duty ratio.

9 is a diagram showing a procedure for performing monochrome reading by setting a duty ratio of a G light source instead of the configuration shown in FIG. 7.

[Explanation of symbols]

1 System control unit 2 ROM 3 RAM 7 Reader 9 Light source lighting control unit 10 Lighting switch part 11 Current limiting resistor 12 G light source current switching unit 13 G light source current determination unit 14 Voltage converter 15 Comparator 16 (16a-16c) light source 17 Image sensor 18 A / D converter 19 Image processing section 20 Maximum value detector 20 Bright output detector 22 power

Claims (4)

[Claims] 1. Color reading is performed by alternately lighting three light sources of red, green, and blue at a predetermined duty ratio, and the above-mentioned 3
In a color image reading apparatus that performs monochrome reading by turning on one of the light sources at a predetermined duty ratio, a signal of the duty ratio is output as a lighting control signal so that each of the light sources is turned on at a predetermined duty ratio. And a light source current limiting unit that switches the drive current so that the drive current supplied to the light source according to the duty ratio of the lighting control signal is equal to or less than the maximum forward current rating of the light source. A color image reading device characterized by the above. 2. The light source current limiting means outputs a switching signal with a signal level inverted when the duty ratio of the lighting control signal exceeds a preset duty ratio, and a light source switch controller. A current limiting resistor section that limits the drive current flowing through the light source, and a light source switch that switches the drive current supplied to the light source by selecting resistors having different resistance values in the current limiting resistor section corresponding to the switching signal. The color image reading apparatus according to claim 1, further comprising: 3. An image sensor for photoelectrically converting light reflected from an original by the light of the light source to output image data, and a bright output detection unit for detecting a bright output maximum value of the image data. When setting the duty ratio of the light source,
The light source lighting control unit sets the duty ratio of the light source to 100.
3. The color image reading apparatus according to claim 1, wherein the bright output maximum value is set so as to fall within a predetermined range by decreasing the value by a predetermined amount from%. 4. When the light source lighting control unit sets the duty ratio of the light source, the duty ratio of the light source set at the time of the previous reading is appropriately increased or decreased to set the bright output maximum value to a predetermined value. 3. The color image reading device according to claim 1, wherein the color image reading device is set to fall within the range.