JP2000050020A - Image reading apparatus and control method thereof - Google Patents

Abstract

(57) Abstract: In an image reading apparatus that reads a color image of a document using a photoelectric conversion element, a document image can be read without being affected by afterglow characteristics that differ for each color of a light source illuminating the document. In addition, circuit components with large rated power and large heat radiation members are not required. SOLUTION: A fluorescent lamp 5 is turned on by a secondary output of an inverter transformer 2 to illuminate a document. Then, the reflected light from the document is received by the solid-state imaging device, photoelectrically converted, subjected to predetermined signal processing, and transmitted to the printer unit. At that time, C
By controlling the PU1, the light amount control method is switched in accordance with the state of the fluorescent lamp 5, and when the fluorescent lamp 5 is in the initial state, current control using the series regulator 9 is performed. If it has decreased, PWM control is performed by turning on / off the switch circuit 4 to control the current of the fluorescent lamp 5.

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 forming an image of a document on a solid-state image sensor through an imaging lens and reading the image information, and a control method thereof.

[0002]

2. Description of the Related Art Hitherto, various image reading apparatuses for optically reading image information of a document using an image sensor as a solid-state image sensor have been proposed. FIG. 5 is a schematic view showing a main part of an optical system of a general color image reading apparatus.

In FIG. 5, reference numeral 100 denotes a platen glass on which a document (read image) is arranged; 101, a bar-shaped light source for illuminating the document; 102, a reflector for improving illumination efficiency; and 103a, 103b, 103c, mirrors. , 104 are imaging lenses, and 105 is a solid-state imaging device.

[0004] The reflected light from a document (not shown) illuminated by the rod-shaped light source 101 and the reflecting umbrella 102 passes through mirrors 103a, 103b, and 103c to form an image forming lens 10.
4, the image information of the document is imaged on the solid-state imaging device 105 by the imaging lens 104. At this time, the mirror 103a moves the image information of the document in the sub-scanning direction A at the scanning speed v and synchronizes with the mirror 103b, 103c.
Moves at a speed of v / 2, whereby the solid-state image sensor 105
The two-dimensional scanning in which the main scanning direction and the sub-scanning direction, which are the arrangement directions of the line sensors, are performed, and the image information of the original can be read.

[0005] The image information formed on the solid-state image sensor 105 is converted into an electric signal and subjected to signal processing. In some cases, the image information is sent to an output device (not shown) to output the image information as a printout, or the image information is sent to a storage device or the like to store the input image information. Is done.

As the light source 101 of the above-mentioned image reading apparatus, a halogen lamp, a fluorescent lamp, a xenon lamp or the like is used. On the other hand, the halogen lamp has a high brightness, but the temperature rise of the apparatus accompanying the temperature rise of the lamp is large.
Since the power consumption of up to 300 W is required, the power consumption required for the entire apparatus is increased. In recent years, in order to avoid such problems, fluorescent lamps and xenon lamps having high luminance have been developed and are being used as light sources for image reading apparatuses.

[0007] Fluorescent lamps and xenon lamps use a small amount of mercury particles and a few Torr of Ar or Kr, X in a hollow tube on a rod.
In many cases, various phosphors are applied to the inner wall of the tube, and electrodes are arranged at both ends of the tube to seal the tube. Then, discharge is performed from the electrodes, and the phosphor applied to the inside of the tube is excited by ultraviolet rays emitted from mercury and various gases. Thereby, visible light is emitted according to the emission characteristics of the phosphor.

Various phosphors are selected as the phosphor according to the spectral energy characteristics required as a light source.
In particular, in a color image reading device, a light source of a wide wavelength range corresponding to each color such as RGB is required. In particular, when a light source of light brightness is required, a plurality of phosphors of different colors are mixed and applied to the inner wall of the tube. A method such as coating is used.

When controlling the amount of emitted light, a fluorescent lamp or a xenon lamp emits light not by a method of controlling the lighting voltage like a halogen lamp but by a pulse width modulation method of controlling a lighting time at a constant current value. A method of controlling the amount of light and a method of controlling the amount of emitted light by controlling the current value using a series regulator with a low cost and a simple configuration are generally used.

On the other hand, in an image reading apparatus using a fluorescent lamp or a xenon lamp, the above-described light amount control is omitted,
The gain setting of an amplifier or the like that electrically amplifies the output signal of the solid-state imaging device with respect to deterioration of the light amount due to durability is variable,
There is also proposed a method of changing the gain in accordance with the light quantity deterioration to obtain an appropriate signal output. In such a method, a phenomenon that the S / N of the read signal varies depending on the gain value may occur.

Here, the above-mentioned two light amount control methods will be described. First, a method of controlling the amount of emitted light by controlling the pulse width corresponding to the time during which the lamp is turned on while keeping the current value flowing through the lamp constant will be described.

FIG. 6 is a diagram showing a light amount control system by PWM control for controlling a pulse width corresponding to a lamp lighting time. Switching transistor Q from CPU1
An on / off signal S1 for turning on / off (ON / OFF) the signal 1 at a predetermined frequency is output. Inverter transformer 2
Is supplied with a predetermined input voltage from a power supply (not shown). C
Reference numeral 1 denotes a resonance capacitor that stably oscillates the inverter transformer 2 in accordance with the frequency of the on / off signal S1 output from the CPU 1. Reference numeral 3 denotes a current adjusting inductor for adjusting the impedance on the secondary side of the inverter transformer 2. A switch circuit 4 turns on / off a voltage applied to the fluorescent lamp 5 by a PWM signal S2 output from the CPU 1. Reference numeral 6 denotes a light amount sensor, 7 denotes an amplifier, 8 denotes an A / D converter, and inputs a light amount signal S3 to the CPU 1.

FIG. 4 shows a current flowing through the fluorescent lamp 5. FIG.
(A) shows the on / off signal S1, and when "H" (high level), the switching transistor Q1 is turned on. FIG.
(B) shows the PWM signal S2, and is "L" (low level)
, The switch circuit 4 is turned on, and the voltage between both terminals of the fluorescent lamp 5 becomes 0 V during the “L” period, and the fluorescent lamp 5 is turned off. The rising of the PWM signal S2 is synchronized with Hsync corresponding to one accumulation time of the solid-state imaging device. FIG. 4C shows the tube current of the fluorescent lamp 5, and indicates that no current flows through the fluorescent lamp 5 while the PWM signal S2 is "L".

Normally, the frequency of the on / off signal S1 is sufficiently higher than the frequency of the PWM signal S2 (for example, 10 to 100 times the frequency of the PWM signal S2). The frequency of the PWM signal S2 is higher than the optical frequency for turning on and off the fluorescent lamp 5, and is electrically
Lighting and extinguishing are repeated in accordance with the cycle of the WM signal S2, but apparently the light is turned on with a constant light amount corresponding to a current value obtained by averaging the lamp current.

The fluorescent lamp 5 is provided with a light amount sensor 6 comprising a photodiode or the like, and outputs a photocurrent corresponding to the amount of light emitted from the fluorescent lamp 5. This photocurrent is converted into a voltage value by the amplifier 7 and amplified, and then the A / A
The signal is converted into a digital signal by the D converter 8 and input to the CPU 1 as a light amount signal S3.

The CPU 1 compares the light amount signal S3 with a predetermined value, and when the light amount of the fluorescent lamp 5 is smaller than the predetermined value, the "H" period of the PWM signal S2 is extended to reduce the light amount of the fluorescent lamp 5. When the light amount of the fluorescent lamp 5 is larger than a predetermined value, the light amount of the fluorescent lamp 5 is reduced by shortening the "H" period of the PWM signal S2. That is, the light amount of the fluorescent lamp 5 is adjusted by the duty (Duty) of the PWM signal S2 in the 1Hsync period.

FIG. 7 is a diagram showing the light quantity control signal and the afterglow characteristic, and shows a control waveform for controlling the light emission quantity of the light source. The horizontal axis in the figure indicates time, and the vertical axis indicates a current value for controlling the amount of light emitted from the light source. The section of Hsync on the horizontal axis indicates a time corresponding to one accumulation time of the solid-state imaging device, and corresponds to a time in which electric charges are accumulated according to the amount of light incident on the light receiving unit of the solid-state imaging device as usually used. Equivalent to. In the case of performing the normal pulse width control, the control signal is synchronized with the rising or falling position of the trigger signal indicating the beginning of the accumulation time, and the control signal is output once in synchronization with one accumulation time. It has such a configuration.

As described above, by performing light quantity control while synchronizing with a signal corresponding to a trigger signal for one accumulation time, beat generated by interference between pulse width control for controlling light quantity and accumulation time is performed. To remove noise from the image signal.

On the other hand, in the case of a fluorescent lamp or a xenon lamp using a phosphor as a light emitting source, when used as a light source for an image reading apparatus for reading color information, a phosphor of each color is mixed and applied to obtain a visible light. In many cases, the white light source has light emission characteristics in a wide wavelength range over the entire region. When such a white light source is used, a problem arises due to the difference in the afterglow characteristics unique to the phosphors of each color. The afterglow characteristic is a characteristic that is determined by a time during which a phosphor excited by ultraviolet light stays at a high energy level, and generally decreases exponentially. This phenomenon indicates that the light emission remains even when the current for controlling the light emission of the light source is instantaneously cut off, and can be expressed by the following equation depending on the characteristics of the material of the phosphor.

T = e (τ-1) In the above equation, τ is a characteristic value determined by the material of the phosphor, and is obtained by mixing phosphors corresponding to RGB, such as a white light source used in a color image reading apparatus. When used,
There is a problem caused by the difference in afterglow characteristics of each color. In general, the material used for the phosphor is determined from the viewpoints of emission wavelength characteristics, luminous efficiency, and life in each wavelength range of the material, but the following materials are often used.

B (Blue): BaMg2Al16O27 Central wavelength 452 nm T = 2 μsec R (Red): Y2O3: Eu2 + Central wavelength 611 nm T = 1.1 msec G (Green): LaPO4: Ce, Tb Central wavelength 544 nm T = 2.6 msec Represents the decay time of each material, and is the time required for the amount of emitted light to reach 1 / e due to each decay. Thus, the afterglow characteristics of each color are different (particularly, B
(ie, the decay time of “le” is short), and the phenomenon occurs that the center of gravity of the reading position in the sub-scanning direction differs depending on the color.

This phenomenon will be described with reference to FIG. 7. Normally, the dimming control of the fluorescent lamp is in a section of Hsync corresponding to one accumulation time of the solid-state imaging device, and the solid-state imaging device in this section has a charge proportional to the amount of incident light. To accumulate. On the other hand, the dimming section in the figure corresponds to the time during which the current for driving the fluorescent lamp is continuously provided in an amount proportional to the dimming duty, and the method of switching the current in that section to a high frequency is mainly used. Is coming. And after the time corresponding to the dimming section has passed,
The amount of emitted light attenuates. Its attenuation characteristics are determined by the following two factors. One is the attenuation characteristic of the emission line spectrum emitted by the fluorescent lamp, and the other is the attenuation characteristic of the phosphor described above.

Normally, one accumulation time corresponding to Hsync is several hundred μsec, whereas the attenuation characteristic of the emission line spectrum is 1 μsec or less, so that there is almost no effect, but the attenuation characteristic of the phosphor is on the order of msec. The effect is large. Therefore, the attenuation characteristic of the light emission amount is determined by the sum of the two types of light emission amounts and the attenuation characteristic of each light emission.

FIG. 7 shows a model of afterglow generated by the attenuation characteristics of R, G, and B colors. In a fluorescent lamp that is lit with a substantially constant light amount by a substantially constant current in a light control section, the light amount corresponding to the emission line spectrum is instantaneously attenuated when the light control section ends. That portion is a portion corresponding to L1 in the figure, and further, afterglow occurs due to the attenuation characteristic of the fluorescent lamp with respect to the light amount corresponding to L2 in the figure.

Next, a method of controlling the amount of emitted light by controlling the current value using a series regulator will be described.

FIG. 8 is a diagram showing a light quantity control system for adjusting the light quantity of the fluorescent lamp 5 using a series regulator 9 composed of Darlington-connected transistors. CPU1
The analog control signal S4 of the series regulator 9
And an on / off signal S1 for turning on / off the switching transistor Q1 at a predetermined frequency. The series regulator 9 current-amplifies the analog control signal S4 output from the CPU 1 and supplies the inverter transformer 2 with a voltage reduced by two transistors by the analog control signal S4. For example, when the analog control signal S4 output from the CPU 1 is 3V, the voltage supplied to the inverter transformer 2 is 3−0.6−0.6 = 1.
8V.

C1 is a capacitor for resonance, and
The inverter transformer 2 oscillates stably in accordance with the frequency of the on / off signal S1 output from the inverter 1. Reference numeral 3 denotes a current adjusting inductor for adjusting the impedance on the secondary side of the inverter transformer 2.

The fluorescent lamp 5 is provided with a light amount sensor 6 composed of a photodiode or the like, and outputs a photocurrent corresponding to the amount of light emitted from the fluorescent lamp 5. This photocurrent is converted into a voltage value by the amplifier 7 and amplified, and then the A / A
The signal is converted into a digital signal by the D converter 8 and input to the CPU 1 as a light amount signal S3.

The CPU 1 compares the light amount signal S3 with a predetermined value. When the light amount of the fluorescent lamp 5 is smaller than the predetermined value, the CPU 1 increases the analog control signal S4 to thereby increase the fluorescent lamp 5 signal.
When the light amount of the fluorescent lamp 5 is larger than a predetermined value, the analog control signal S4 is decreased to reduce the light amount of the fluorescent lamp 5.

When this method is used, the fluorescent lamp 5
Can be turned on at a constant cycle, and by selecting the frequency of the on / off signal S1 to an appropriate value, it becomes possible to adjust the amount of light without being affected by the afterglow characteristic for each color.

[0031]

However, the conventional image reading apparatus as described above has the following problems due to differences in the light amount control method.

That is, in the light amount control by the PWM control using the circuit shown in FIG. 6, one accumulation time of the solid-state image pickup device serves as a time reference when reading pixel information and also in the sub-scanning direction. For reading, it serves as a reference for the reading position. The pixel density for reading image information is determined by the pixel size of the solid-state imaging device in the main scanning direction, and the sub-scanning direction corresponds to a moving distance at the time of reading an image scanned by a mirror scan or the like.

Therefore, the phenomenon that the position of the center of gravity of the light emission amount of each color with respect to the time of Hsync differs depending on the afterglow characteristic may be considered by replacing the horizontal axis of the graph of FIG. 7 with position information. This indicates that the center of gravity of the reading position in the sub-scanning direction differs depending on the color.

The fact that the center of gravity of the reading position in the sub-scanning direction differs depending on the color causes a color shift at the time of reading in the sub-scanning direction. In particular, the fluorescent lamp and the xenon lamp are in the initial state (undegraded state). In this case, a desired amount of light can be obtained even if the ratio of turning on the lamp during the 1Hsync period is small, so that the center of gravity of the reading position for each color is shifted between the color having a long afterglow time and the color having a short afterglow time. However, there is a problem that the size becomes significantly large.

In the light amount control by voltage control using the circuit of FIG. 8, in order to adjust the light amount of the lamp in a wide range, the voltage supplied to the inverter transformer may be varied in a wide range. Required. For that purpose, it is necessary to increase the power supply voltage supplied to the collector C of the series regulator.

In this case, in the initial state of the fluorescent lamp (a state in which a sufficient amount of light can be output even with a small current), by setting the voltage supplied to the inverter transformer low, the power consumption of the series regulator becomes extremely large, In addition to the efficiency degradation, there is a problem that a component having a large rated power must be used for the series regulator and a large heat radiating member must be attached to the series regulator.

The present invention has been made in view of the above problems, and can read an original image without being affected by the afterglow characteristic which differs for each color of the light source.
An object of the present invention is to provide an image reading apparatus which does not require a circuit component having a large rated power or a large heat radiation member, and a control method thereof.

[0038]

According to the present invention, there is provided an image reading apparatus comprising: a light source for irradiating an original; an image sensor for receiving reflected light from the original and converting the reflected light into an image signal; And a light amount control unit that switches a light amount control method between a control method performed by phase control of a pulse width modulation signal and a control method performed by voltage control according to a state of a light source. It is.

In the above-mentioned apparatus, a white fluorescent lamp having phosphors having different afterglow characteristics of each color is used as a light source.

A control method for an image reading apparatus according to the present invention comprises a light source for irradiating a document, an image pickup device for receiving reflected light from the document and converting it into an image signal, and a light amount control for controlling the light amount of the light source. And controlling the light amount control method between a control method performed by phase control of a pulse width modulation signal and a control method performed by voltage control in accordance with the state of the light source. It was made.

Further, in the above method, the original is illuminated by using a white fluorescent lamp having a phosphor having different afterglow characteristics of each color as a light source.

[0042]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention. The same reference numerals as those in FIGS. 6 and 8 denote the same components.

In FIG. 1, reference numeral 1 denotes a CPU for controlling the entire lighting circuit of a white phosphor (light source) 5 having phosphors having different afterglow characteristics of each color, and a light amount control means for controlling the light amount of the fluorescent lamp 5. And switches the light amount control method between the two methods according to the state of the fluorescent lamp 5. One method is PWM in one accumulation time of a line sensor which is a solid-state imaging device.
(Pulse width modulation) A method of controlling the phase of a signal, and another method is a method of controlling a voltage.

Reference numeral 2 denotes an inverter transformer, and on the primary side, a switching transistor Q1 and a resonance capacitor C1.
Is connected. 3 is a current adjusting inductor for adjusting the impedance of the secondary side of the inverter transformer 2;
4 is a switch circuit for turning on / off the voltage applied to the fluorescent lamp 5, 6 is a light amount sensor for detecting the light amount of the fluorescent lamp 5, 7 is an amplifier for amplifying the detection signal of the light amount sensor 6, 8
Is an A / D converter for converting the amplified analog signal into a digital signal.

Reference numeral 9 denotes a series regulator composed of Darlington-connected transistors, which is connected to a DC power supply (not shown). Reference numeral 10 denotes a switch circuit, one of which is connected to a DC power supply (not shown), and the other of which is connected to the primary side of the inverter transformer 2 via a diode D1. The output side of the series regulator 9 is also connected to the primary side of the inverter transformer 2 via the diode D2.

S1 to S5 are input / output signals of the CPU 1, S1 is an on / off signal to the switching transistor Q1, S2 is a PWM signal to the switch circuit 4, S3 is a light signal from the light sensor 6, and S4 is a light signal. An analog control signal to the series regulator 9, S5 is a switch circuit 10
Is a switching signal.

FIG. 2 is a block diagram showing a configuration of an image processing unit 12 which takes in reflected light from the original 11 irradiated by the fluorescent lamp 5 and performs signal processing. In FIG. 1, reference numeral 13 denotes a CCD which is the above-mentioned solid-state image sensor which receives reflected light from the original 11 through an imaging lens and converts the received light into an image signal (electric signal). The output signal of the image processing unit 12 is sent to a printer (not shown), printed out, or stored in a memory.

In the image reading apparatus configured as described above, the switch circuit 10 changes the voltage supplied to the inverter transformer 2 to the emitter output of the series regulator 9 and the +24 V output by the switching signal S5 output from the CPU 1. Switch to. That is, the light amount control method by voltage control using the series regulator 9 and the light amount control method by phase control of the PWM signal are switched.

At the start of lighting of the fluorescent lamp 5, a voltage control method is selected as the light amount control method, and the switch circuit 10 is controlled so that the emitter output of the series regulator 9 is supplied to the inverter transformer 2. At this time, C
PU1 outputs an analog control signal S4 to the series regulator 9 and an on / off signal S1 for turning on / off the switching transistor Q1 at a predetermined frequency.

Then, in the series regulator 9, the CP
The analog control signal S4 output from U1 is current-amplified, and a voltage reduced by two transistors is supplied to the inverter transformer 2 by the analog control signal S4. Also,
The resonance capacitor C1 allows the inverter transformer 2 to stably oscillate according to the frequency of the on / off signal S1 output from the CPU 1, and the current adjustment inductor 3 controls the impedance of the secondary side of the inverter transformer 2. Do.

FIG. 3 is a perspective view showing the outer shape of a general fluorescent lamp 5. Both ends of the fluorescent lamp 5 are supported by sockets 21a and 21b, and current is supplied from pins (not shown) of the sockets 21a and 21b. An aperture (optical opening) 22 is provided in a predetermined area of the fluorescent lamp 5, and strong light is emitted in the direction of arrow a, and relatively weak light is emitted from an area other than the aperture 22. You.

A light amount sensor 6 composed of a photodiode or the like is provided at an appropriate position near the fluorescent lamp 5 and outputs a current corresponding to the amount of light emitted from the fluorescent lamp 5. This photocurrent is converted into a voltage value by the amplifier 7 and amplified. Thereafter, the amplified voltage value is converted into a digital signal by the A / D converter 8, and is converted into a light amount signal S3 by the CP.
It is input to U1.

The CPU 1 outputs an analog control signal S4 of a predetermined minimum voltage level to the release regulator 9 at the start of lighting of the fluorescent lamp 5, and compares the light amount signal S3 at that time with a predetermined value. When the light amount is smaller than the predetermined value, the light amount of the fluorescent lamp 5 is increased by increasing the analog control signal S4.

Here, if the desired amount of light cannot be obtained even when the analog control signal S4 reaches a predetermined maximum voltage, the voltage supplied to the inverter transformer 2 is switched to +24 V by the switching signal S5. The light amount is adjusted by PWM control.

At this time, the switch circuit 4 turns on / off the voltage applied to the fluorescent lamp 5 by the PWM signal S2 output from the CPU 1. The switch circuit 4 is always fixed to the off state while the current control method using the series regulator 9 is employed, and the secondary output voltage of the inverter transformer 2 is always applied to the fluorescent lamp 5 during this time.

FIG. 4 is a timing chart showing a current flowing through the fluorescent lamp 5 during the PWM control. FIG. 4 (a)
Indicates an on / off signal S1. When "H", the switching transistor Q1 is turned on. FIG. 4B shows the PWM signal S2, and when "L", the switch circuit 4 is turned on and "L".
During the period, the voltage between both terminals of the fluorescent lamp 5 becomes 0 V, and the fluorescent lamp 5 is turned off. Further, the rising of the PWM signal S2 is Hs corresponding to one accumulation time of the solid-state imaging device (CCD 13).
Synchronized with sync. FIG. 4C shows the tube current of the fluorescent lamp 5, and indicates that no current flows through the fluorescent lamp 5 while the PWM signal S2 is "L".

Normally, the frequency of the on / off signal S1 is sufficiently higher than the frequency of the PWM signal S2 (for example, 10 to 100 times the frequency of the PWM signal). The frequency of the PWM signal S2 is higher than the optical frequency of turning on and off the fluorescent lamp 5, and is electrically
Lighting and extinguishing are repeated according to the cycle of the M signal S2, but apparently the light is turned on at a constant light amount corresponding to a current value obtained by averaging the lamp current.

Next, the CPU 1 compares the light amount signal S3 with a predetermined value, and when the light amount of the fluorescent lamp 5 is smaller than the predetermined value, the "H" period of the PWM signal S2 is extended to thereby increase the fluorescent lamp 5 signal. When the light amount of the fluorescent lamp 5 is larger than a predetermined value, the “H” level of the PWM signal S2 is increased.
The light amount of the fluorescent lamp 5 is reduced by shortening the period. That is, the PWM signal S in the 1Hsync period
The light quantity of the fluorescent lamp 5 is adjusted by the duty of 2.

Next, the original 11 is illuminated by the fluorescent lamp 5 whose light amount is controlled as described above, the reflected light is received by the CCD 13, and the image information of the original 11 is converted into an analog electric signal. 14 is output. The analog processing circuit 14 amplifies the analog electric signal output from the CCD 13, converts the signal into a digital signal, and outputs the digital signal to the digital processing circuit 15. In the digital processing circuit 15,
It performs known shading correction and masking correction, and outputs an image signal to the printer unit.

As described above, in this embodiment, a desired light amount can be obtained with a small lighting current in the initial state of the light source such as the fluorescent lamp 5 and the xenon lamp.
When the fluorescent lamp 5 or the xenon lamp is deteriorated and a large amount of current is required to obtain a desired amount of light, that is, in the current control method using the series regulator 9, heat is generated from the element. When the power becomes large and the power efficiency is remarkably deteriorated, the light amount of the fluorescent lamp 5 and the xenon lamp is adjusted using the PWM method. By employing this method, it is possible to reduce the shift of the center of gravity of the reading position in the sub-scanning direction, which occurs depending on the afterglow characteristic of the light source, and is not affected by the afterglow characteristic that differs for each color of the phosphor. The original image can be read.

[0061]

As described above, according to the present invention,
The original image can be read without being affected by the afterglow characteristic that differs for each color of the light source, and the effect that a circuit component having a large rated power and a large heat radiating member are not required is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an image processing unit according to the embodiment.

FIG. 3 is a perspective view showing an outer shape of a fluorescent lamp.

FIG. 4 is an explanatory diagram showing tube current of a fluorescent lamp by PWM control.

FIG. 5 is a schematic diagram showing an optical system of a general image reading apparatus.

FIG. 6 is a circuit diagram showing a method of controlling the amount of light of a fluorescent lamp by PWM control.

FIG. 7 is an explanatory diagram showing a light amount control signal and an afterglow characteristic;

FIG. 8 is a circuit diagram showing a fluorescent lamp light amount control method using a switching regulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU (light amount control means) 2 Inverter transformer 3 Inductor 4 Switch circuit 5 Fluorescent lamp (light source) 6 Light amount sensor 7 Amplifier 8 A / D converter 9 Series regulator 10 Switch circuit 11 Document 12 Image processing unit 13 CCD (Solid-state image sensor) 14 Analog processing circuit 15 Digital processing circuit 21a Socket 21b Socket 22 Aperture Q1 Switching transistor C1 Capacitor D1 Diode D2 Diode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Sugiura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Koji Arai 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon In-house F term (reference) 5B047 AB04 BB02 BC05 BC09 BC11 CA19 CB04 CB18 DA06 DC06 5C072 AA01 BA17 CA02 CA04 CA07 CA14 CA17 CA18 DA02 DA04 EA05 UA20

Claims (4)

[Claims] A light source for irradiating a document, an image sensor for receiving reflected light from the document and converting the reflected light into an image signal, and a light amount control unit for controlling a light amount of the light source; An image reading apparatus according to claim 1, wherein a light amount control method is switched between a control method based on phase control of a pulse width modulation signal and a control method based on voltage control according to a state of a light source. 2. A white fluorescent lamp having a phosphor having different afterglow characteristics of each color as a light source.
An image reading device according to claim 1. 3. A control of an image reading apparatus having a light source for irradiating a document, an image sensor for receiving reflected light from the document and converting it into an image signal, and a light amount control unit for controlling a light amount of the light source. The image reading apparatus according to claim 1, wherein the light amount control means switches between a control method performed by phase control of a pulse width modulation signal and a control method performed by voltage control in accordance with a state of a light source. Control method. 4. The control method for an image reading apparatus according to claim 3, wherein the original is illuminated using a white fluorescent lamp having phosphors having different afterglow characteristics of each color as a light source.