JP2001103239A - Image reader and its lighting drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a read gravity center of each color from being shifted in a subscanning direction due to the difference of the afterglow characteristics of each color phosphor in the case of using a white fluorescent light or the like as the light source of an image reader. SOLUTION: The centers of dimmer control signals to control the light quantity of a fluorescent light or the like are controlled to be arranged not to the top of a Hsync period equivalent to one storage time of an image pickup element but to the center of the period. Thus, the gravity center shift is reduced to d1 compared to the gravity center shift d2 in the former case. Furthermore, the number of accumulated scan times with respect to each light source is measured and the control is conducted on the basis of the result so as to cope with changes in a dimmer control signal by the secular change of the light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading reflected light from an illuminated document or the like on an image sensor through an image forming optical system, and for reading the image. And an illumination driving method.

[0002]

2. Description of the Related Art Conventionally, a document surface to be read is illuminated, and its reflected light is transmitted to a line sensor (CCD) via an imaging optical system.
Various image reading apparatuses for reading a black-and-white or color image on the basis of an output signal obtained by forming an image on a solid-state imaging device and photoelectrically converting the line sensor have been put to practical use.

FIG. 9 shows a typical configuration of a reading optical system of such an image reading apparatus.

An original (not shown) placed on an original platen glass 100 is provided with a rod-shaped light source 10 extending in a direction perpendicular to the paper surface.
1 illuminates the lower surface (the surface to be read).
The rod-shaped light source 101 is provided with a reflection shade 102 in order to improve illumination efficiency. The illuminated reflected light from the original surface passes through a slit that also extends in a direction perpendicular to the paper surface, is guided to the imaging optical system 104 by mirrors 103a, 103b, and 103c, and also has a linear shape that also extends in a direction perpendicular to the paper surface. Is formed on the solid-state imaging device (line sensor) 105 of the first embodiment. The direction perpendicular to the paper is referred to as a main scanning direction.

[0005] Light source 101, slit and mirror 103a
Moves along the document surface in the sub-scanning direction indicated by the arrow A, for example, at a speed v.
And 103c also move at a speed v / 2 in the sub-scanning direction. As a result, the original surface is scanned line by line in the main scanning direction, which is the direction in which the line sensors 105 are arranged, and is also scanned in the sub-scanning direction perpendicular to the main scanning direction, thereby reading an image of the entire original surface.

The light focused on the line sensor 105 is converted into an electric signal there and read as electric image information. The read image information is, for example, after a predetermined process is performed in a subsequent signal processing circuit or image processing circuit,
It is output from a printer or stored in an appropriate storage device.

As a light source of such an image reading apparatus,
Conventionally, halogen lamps have been widely used. However, the halogen lamp has high brightness, but has a large temperature rise due to heat generation of the lamp, and 200 to 30 times.
There is a problem that the power consumption of the entire apparatus is increased because the power consumption of 0 W is required. Therefore, in order to solve such a problem, a fluorescent lamp or a xenon lamp having a high luminance has been developed and is being used as a light source of this type of image reading apparatus.

Many fluorescent lamps and xenon lamps have a rod-shaped hollow tube in which a small amount of mercury particles and several Torr of Ar, Kr, or Xe are sealed, and various phosphors are applied to the inner surface of the tube. Electrodes are arranged at both ends of the tube so that the tube is sealed. Then, ultraviolet rays emitted from mercury or various gases due to discharge from the electrodes excite the phosphor applied to the inner surface of the tube, and 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 apparatus, R
A light source in a wide wavelength range corresponding to GB or the like is required. In particular, when a high-luminance light source is required, a method of applying a mixture of phosphors of a plurality of colors is used.

When controlling the amount of light emitted from such a fluorescent lamp or a xenon lamp, as in the case of a halogen lamp,
Instead of controlling the lighting voltage, a pulse width modulation method for controlling the lighting time with a constant current value is generally adopted. This is because fluorescent lamps and xenon lamps have a characteristic of emitting light when a certain current value is exceeded, and the method of controlling the current value itself does not allow a large emission light amount control range.

In the image reading apparatus using such a fluorescent lamp or a xenon lamp, the above-described light amount control is omitted, and the output signal of the solid-state imaging device is electrically amplified in response to a decrease in light amount due to deterioration in durability. A method of obtaining an appropriate signal output by changing a gain setting of an amplifier or the like and changing the gain in accordance with a decrease in light amount has also been devised. However, in this method, a phenomenon that the S / N ratio of the read signal fluctuates depending on the gain value is considered to occur.

[0012]

A conventional image reading apparatus using a fluorescent lamp or a xenon lamp as described above has the following problems.

In an image reading apparatus using a light source using a phosphor as a light source, such as a fluorescent lamp or a xenon lamp,
As described above, a method of controlling the light emission amount by controlling the pulse width corresponding to the lighting time while keeping the current value flowing through the lamp constant is common.

FIG. 10 shows an example of a control waveform for controlling the amount of light emitted from the light source. In the drawing, the horizontal axis represents time, and the vertical axis represents a current value (corresponding to the light emission amount) for controlling the light emission amount of the fluorescent lamp.

In the figure, the section of _{Hsync on} the horizontal axis indicates a time corresponding to one accumulation time of the solid-state image sensor, and this is where electric charge is stored in accordance with the amount of light incident on the light receiving portion of the solid-state image sensor. Time.

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 synchronized once per accumulation time. Output. As described above, the light amount control is performed while synchronizing with the signal corresponding to the trigger signal of one accumulation time, so that the pulse width control for controlling the light amount and the image signal due to the beat generated by the interference between the accumulation times are performed. Noise has been removed.

On the other hand, in the case of a fluorescent lamp or a xenon lamp using a phosphor as a light emitting source, especially when used as a light source of an image reading apparatus for reading color information, the 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.

However, when used as such a white light source, there has conventionally been a problem of color misregistration caused by the difference in the afterglow characteristic peculiar to each color phosphor. The afterglow phenomenon of a phosphor is a phenomenon in which light emission remains even when current for controlling light emission of a light source is instantaneously cut off. The afterglow characteristic is determined by the time during which the phosphor excited by the ultraviolet light stays at a high energy level, and generally decreases exponentially.

The afterglow characteristic can be expressed by the following equation depending on the characteristics of the phosphor material. T = exp [τ-1] Here, τ is a characteristic determined by the material of the phosphor.

The material used as the phosphor is generally 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. Blue: BaMg ₂ Al ₁₆ O ₂₇ center wavelength 452 nm, T = ₂ μsec Red: Y ₂ O ₃ : Eu ²⁺ center wavelength 611 nm, T = 1.1 msec Green: LaPO ₄ : Ce, Tb center wavelength 544 nm, T = 2. 6 msec Here, T indicates the decay time of each material, and is the time until the amount of emitted light reaches 1 / e due to each decay.

Since the afterglow characteristics of the respective colors are different (especially, the decay time of Blue is short), a phenomenon that the center of gravity of the reading position in the sub-scanning direction differs depending on the color has conventionally occurred.

This phenomenon will be described in more detail with reference to FIG.

In the dimming control of the fluorescent lamp, the solid-state image pickup device normally accumulates electric charge proportional to the amount of incident light during a period of _Hsync corresponding to one accumulation time of the solid-state image pickup device. In contrast,
The dimming section in the figure is the time during which the current for driving the fluorescent lamp is actually given, and the current in that section is conventionally mainly switched at a high frequency. After this dimming interval, the amount of emitted light attenuates. The attenuation characteristic at this time is determined by the following two factors. One is the attenuation characteristic of the emission line spectrum emitted from the fluorescent lamp, and the other is the attenuation characteristic of the phosphor described above. The light emission attenuation characteristic is determined by the sum of these two types of light emission amounts and the respective light emission attenuation characteristics. Normal,
One accumulation time corresponding to H _sync is several hundreds of microseconds, whereas the attenuation characteristic of the emission line spectrum is 1 μsec or less. Therefore, the attenuation characteristic of the emission line spectrum has little effect, but the attenuation characteristic of the phosphor is on the order of msec. The impact is significant.

In the drawing, the afterglow generated by the attenuation characteristics of each of the colors R, G, and B is modeled. In a dimming section, a fluorescent lamp lit with a substantially constant current by a substantially constant current, when the dimming section ends, first, the quantity of light corresponding to the emission line spectrum is instantaneously attenuated. That part is in the figure,
A portion corresponding to L _1. Then, in the figure, with respect to the amount of light corresponding to L _2, the remaining light is generated by decay characteristics of the phosphor.

The difference in the afterglow characteristics of each color at this time has caused the following problem in the image reading apparatus. That is,
One accumulation time of the solid-state imaging device serves as a time reference when reading image information, and also serves as a reference of a reading position for reading in the sub-scanning direction. The pixel density when reading image information, the main scanning direction is determined by the pixel size of the solid-state imaging device, the sub-scanning direction,
This corresponds to a moving distance at the time of scanning by a mirror scan or the like.
Therefore, the light emission amount in the H _sync section may be considered in the sub-scanning direction by replacing the horizontal axis of the graph in FIG. 7 with the position information. In this case, the fact that the afterglow characteristics differ depending on the color means that the barycenter of the reading position in the sub-scanning direction differs depending on the color. The phenomenon that the center of gravity of the reading position in the sub-scanning direction differs depending on the color is as follows.
Heretofore, this has caused a color shift during reading in the sub-scanning direction, and has been a factor of deteriorating the performance of the image reading apparatus.

The present invention has been made in view of such circumstances, and is intended for controlling light control of a fluorescent lamp or the like.
It is an object of the present invention to prevent a color shift in the sub-scanning direction caused by a difference in persistence characteristics of phosphors of each color.

[0027]

An image reading apparatus according to the present invention, which solves the above-described problems, captures reflected light from a document surface illuminated by a light source by a plurality of photoelectric conversion elements arranged in a line. An image reading device that forms an image on an element and reads an image on the original surface, wherein the original surface is line-sequentially scanned in a sub-scanning direction that is substantially perpendicular to an arrangement direction of the photoelectric conversion elements. In the image reading device that reads an image on the entire surface of the document, the light source includes:
A center of gravity that uses phosphors corresponding to a plurality of emission colors as light emission sources and reduces the shift of the center of gravity of the reading position of each color in the sub-scanning direction caused by the difference in the persistence characteristics of the phosphors of each color. The apparatus further includes a movement reducing unit, and the center-of-gravity movement reducing unit performs reduction control of the center-of-gravity movement based on the cumulative number of scans.

In one embodiment of the present invention, the center-of-gravity shift reducing means includes pulse width modulation for controlling the amount of light of the light source such that the shift of the center of gravity of each color within one accumulation time of the image sensor is reduced. Controls the phase of the signal.

According to one aspect of the present invention, there is provided a light amount control means for controlling the light amount of the light source by a pulse width modulation method,
The center-of-gravity shift reducing means causes the control pulse to grow within one accumulation time of the image sensor in a symmetric manner in the time axis direction about the reference position.

In one aspect of the present invention, the reference position is 1
This is the center position with respect to the time axis within the accumulation time.

In one embodiment of the present invention, the reference position is 1
This is the position of the tip with respect to the time axis within the accumulation time.

In the illumination driving method for an image reading apparatus according to the present invention, reflected light from a document surface illuminated by a light source having phosphors corresponding to a plurality of emission colors as light sources is arranged in a line. An image reading apparatus that forms an image on an image sensor composed of a plurality of photoelectric conversion elements and reads an image of the original surface, wherein the original surface is substantially perpendicular to an array direction of the photoelectric conversion elements. In the illumination driving method of the image reading device that reads an image of the entire original surface while scanning line-sequentially in the sub-scanning direction, a reading position of each color in the sub-scanning direction caused by a difference in persistence characteristics of the phosphor of each color. The driving of the light source is controlled based on the cumulative number of scans so as to reduce the movement of the center of gravity.

In one aspect of the present invention, when performing the control for reducing the shift of the center of gravity, the light amount of the light source is controlled so that the shift of the center of gravity of each color within one accumulation time of the image sensor is reduced. Controls the phase of the pulse width modulation signal.

According to one aspect of the present invention, there is provided a driving method for controlling the amount of light of the light source by a pulse width modulation method, wherein a method of growing a control pulse within one accumulation time of the image pickup element is centered on a reference position. To grow symmetrically in the time axis direction.

In one embodiment of the present invention, the reference position is 1
This is the center position with respect to the time axis within the accumulation time.

In one aspect of the present invention, the reference position is 1
This is the position of the tip with respect to the time axis within the accumulation time.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described according to preferred embodiments.

(First Embodiment) First, the principle of control according to the present invention will be described with reference to FIG.

FIG. 1 is a view similar to FIG. 10 described above. FIG. 1 (a) shows a fluorescent lamp lighting method according to the present invention, and FIG. 1 (b) shows a conventional lighting method. FIG. 1 (c)
Are Blue, Green, and Re in the lighting method of FIG.
1 (d) shows the movement of the center of gravity between Blue, Green and Red in the lighting method of FIG. 1 (b), respectively.

In the lighting method according to the present invention, FIG.
As in the conventional lighting method shown in FIG._{sy nc}Ward that forms section
In synchronization with the rise or fall of the signal during
Instead of starting the control of the dimming control signal, FIG.
As shown in the figure, the temporal center of the light control section is H_syncSection
Control is performed to match the center. In this case, dimming control
Even if the control request amount (duty) of the signal changes, the control signal
To prevent the position of the heart from changing, the rise of the control signal
The position changes according to the duty.

As shown in FIG. 1 (d), in the conventional lighting method, in particular, due to the difference in the afterglow characteristics of each phosphor, blue light
And A large center-of-gravity movement distance d ₂ between the Green and Red appears, as shown in FIG. 1 (c), the lighting system of the present invention, a very small amount of the center of gravity movement amount as d ₁ . Therefore, it is possible to reduce the performance of the image reading apparatus due to the color misregistration to a level having substantially no problem.

Next, a configuration for realizing the above-described control method of the present invention will be described.

In this type of image reading apparatus, the amount of light emitted from a fluorescent lamp or the like is usually detected by a light amount sensor, and based on the detection, the light amount is controlled by a light amount controller so that the amount of light from the fluorescent lamp or the like becomes constant. Do.

FIG. 2 shows the structure of a well-known fluorescent lamp.

Both ends of the fluorescent lamp 1 are supported by sockets 2a and 2b, and current is supplied from pins (not shown) provided in the sockets 2a and 2b. An aperture (optical opening) 3 is provided in a predetermined area of the fluorescent lamp 1, and strong light is emitted from the aperture 3 in the direction of arrow a, and is relatively weak from areas other than the aperture 3. Light is emitted. In addition, a light amount sensor 4 including a photodiode or the like is provided at an appropriate position of the fluorescent lamp 1.
A current corresponding to the amount of light emitted from the fluorescent lamp 1 is detected.

FIG. 3 shows a basic configuration of the light quantity control unit according to the first embodiment of the present invention.

The light quantity sensor 11 detects the light quantity of the fluorescent lamp 10 and outputs a light quantity signal corresponding to the light quantity. This light amount signal is converted into a voltage value by the amplifier 12 and amplified. The amplified voltage value is compared with a predetermined reference voltage by the comparator 13, and the comparison result is input to the light amount controller 14.

The counter 19 is generally provided in a copying machine used for billing and the like. In this embodiment, it is assumed that the counter 19 is incremented by one for each scanning. The CPU 17 determines H based on the count value of the counter 19.
_It calculates how long the fluorescent lamp control signal is delayed with respect to the _sync section signal so that the center of the control signal coincides with the center of the H _sync section, and outputs the result to the delay adjustment circuit 18.

The synchronization signal (Sync) sent from the synchronization circuit (SYNC) 16 is input to the delay adjustment circuit 18,
In accordance with an instruction from the CPU 17, a synchronization signal (Sync) delayed by a predetermined amount is input to the light amount controller 14.
The light amount controller 14 synchronizes the phase with the predetermined synchronization signal (Sync) determined previously to perform pulse width modulation (Puls
e Width Modulation: Hereinafter referred to as “PWM”. ) Output a signal to perform duty control. That is, when the voltage value output from the amplifier 12 is larger than the reference value, the PWM signal is output so as to reduce the duty ratio. On the other hand, when the voltage value output from the amplifier 12 is smaller than the reference value, , And output a PWM signal such that the duty ratio is increased.

When the PWM signal input to the inverter 15 is at a high level, the inverter 15 outputs the PWM signal.
An alternating current having a frequency sufficiently higher than the signal (for example, a frequency that is 10 to 100 times the frequency of the PWM signal) is supplied to the fluorescent lamp 10 as a lamp current, and the fluorescent lamp 10 is turned on. On the other hand, when the PWM signal is at the low level, the lamp current is cut off and the fluorescent lamp 10 is turned off. Note that the frequency of the PWM signal is higher than the optical frequency of turning on and off the fluorescent lamp 10, and the turning on and off are repeated electrically according to the cycle of the PWM signal, but the lamp current is apparently averaged. Lights with a constant light amount corresponding to the current value.

FIG. 4 shows a main configuration of the image reading apparatus according to the present embodiment.

The apparatus includes a mirror table 21 for illuminating the document 20, an image processing unit 22 for reading an image of the document 20, performing predetermined image processing, and outputting the processed image to a printer (not shown), for example. An amplifier 24 for amplifying an output signal from the mirror base 21 and a comparator 2 for comparing the output signal from the amplifier 24 with a reference signal and outputting the comparison result
5, a light amount controller 26 composed of an ASIC or the like that controls the light amount based on the output of the comparator 25 and outputs a PWM signal phase-synchronized with a predetermined synchronization signal, and lights up based on a command from the light amount controller 26 Inverter 27 for controlling and CPU 2 for controlling the entire apparatus
8 and a backup memory 29 for storing the calculation results of the CPU 28 and the like. In the figure, 30 is A
A / D converter 31 is a driver, 45 is a self-running main scanning synchronization signal (SYNC), and a self-running SYNC generation and selector circuit 46 for selecting either the self-running main scanning synchronization signal BD or the printer main scanning synchronization signal BD. Is a self-propelled SYNC
A delay adjusting circuit that delays the generation and output of the selector circuit 45 for an arbitrary time based on a set value (duty value) from the CPU 28 (to make the light emitting area come to the center of the H _sync section as described above). It is. In addition, 47
SYNC 1, which is an output signal of the free-running SYNC generation and selector circuit 45, and SYNC 2, which is an output of the delay adjustment circuit 46.

The mirror base 21 includes a fluorescent lamp 32 and a heater 33 mounted on the fluorescent lamp 32. Further, a photodiode 35 attached to the heater 33 and detecting the temperature of the heater 33; There is provided a light amount sensor 37 including a preamplifier 36 for converting a minute current detected by the photodiode 35 into a voltage signal. The voltage signal output from the preamplifier 36 of the light amount sensor 37 and the voltage signal from the variable resistor 23 are input to the amplifier 24 described above, whereby the light amount signal is amplified by a predetermined amount.

For example, when the reflectance of the read image is particularly high and it is desired to reduce the light amount, the comparator 25 performs an initial operation of the switch 38 based on a command from the CPU 28, thereby obtaining the reference voltage. Switching is possible.

The light quantity controller 26 outputs a light quantity comparison signal from the comparator 25 in phase synchronization with the synchronization signal, and a flip-flop circuit (F / F) 39. Based on the light quantity comparison signal, the light quantity controller 26 synchronizes with the synchronization signal. Then, an up / down counter 40 for increasing / decreasing the counter, and an output value of the up / down counter 40 are loaded in phase synchronization with the synchronization signal and down-counted by a predetermined clock (as described later, the PWM signal ), And a preheating control unit 42 that controls preheating of the fluorescent lamp 32 before lighting. The output value of the up / down counter 40 is input to the CPU 28,
Can read the PWM value at an arbitrary timing.

The operation of the light amount controller 26 will be described. First, when the light amount is higher than a specified value, the output of the comparator 25, that is, the output of the F / F 39 becomes "0".
The count value of the up / down counter 40 decreases by a predetermined amount, the load value of the down counter 41 decreases, and as a result,
The PWM signal (pulse width) input to the inverter 27 is narrowed. Conversely, if the light intensity is lower than the specified value,
The output of the comparator 25, that is, the output of the F / F 39 becomes "1", the count value of the up / down counter 40 increases by a predetermined amount, the load value of the down counter 41 increases,
As a result, the PWM signal (pulse width) input to the inverter 27 is expanded. When the power is turned on, PW
The M value is equivalent to the full lighting of the fluorescent lamp, and is converged to a predetermined value.

As described above, when the PWM signal input to the inverter 27 is at a high level, the inverter 27 operates at a frequency sufficiently higher than the PWM signal (for example, 10 to 100 times the frequency of the PWM signal). (Frequency) is supplied to the fluorescent lamp 32 as a lamp current, and the fluorescent lamp 32 is turned on. On the other hand, when the PWM signal is at the low level, the lamp current is cut off and the fluorescent lamp 32 is turned off. The frequency of the PWM signal is higher than the optical frequency of turning on and off the fluorescent lamp 32, and is electrically turned on and off in accordance with the cycle of the PWM signal. Lights at a constant light amount corresponding to the value.

The image processing section 22 receives the reflected light from the document 20 and converts it into an electric signal.
An analog processor 43 that performs predetermined signal processing on an electric signal output from the CD 58 and an A / D converter 44 that converts an analog signal output from the analog processor 43 into a digital signal are provided. CCD 58
Accumulates charges read during one scanning period which is one cycle of the synchronization signal. Therefore, the output from the CCD 58 has a magnitude obtained by integrating the light amount during one scanning period, and the blinking of the fluorescent lamp 32 and the scanning by the CCD 58 are synchronized in the same cycle, so that a constant output can be obtained.

FIG. 5 shows an example of the configuration of the delay adjustment circuit 46.

This circuit is reset by a main scanning synchronizing signal (SYNC1) 47 of the image processing section 22 and the like, and an up counter 48 which counts up by a clock signal;
Synchronization signal SYNC2 which is a signal for raising the WM signal
(54) two comparators 49 and 50 for respectively determining the fall timing and the rise timing,
Two registers 51 and 52 in which a fall control value P ₁ and a rise control value P ₂ described later are set by the CPU 28.
And a JK flip-flop (JK-F / F) 53.

Here, for example, when one scanning period corresponds to the A clock (a signal of one pixel is output from the CCD 58 for one clock), the synchronizing signal SYNC2 set in the register 51 rises. The falling control value P ₁ (at what clock from the start of each main scanning period the synchronization signal S
P ₁ = A / 2− (duty value (%) / 200) × A (a) On the other hand, the rising control value P ₂ of SYNC ₂ is P ₂ = [A / 2− (duty value (%) / 200) × A] +1 (b) In the examples shown in Expressions (a) and (b), the pulse width of SYNC2 is one clock. However, the pulse width is not limited to one clock, and may be shorter than one main scanning period. It is possible to replace +1 with a value equal to or less than + (A-2).

FIG. 6 shows a configuration example of the down counter 41.

This circuit comprises a down counter 57 and a JK-
F / F55. The JK-F / F 55 outputs a PWM signal 56 by inputting SYNC2 to its J input and the RC output of the down counter 57 to its K input. The reset is released after desired initial settings are made.

Next, each of the above-mentioned output signals will be described with reference to FIG.

Output signals include a SYNC signal and a PWM signal.
The signal, control current waveform (tube current), and light amount will be described. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the magnitude of each output signal. FIG. 7A shows that the duty value is about 25%.
(B) shows the output signal at about 60%.

In the figure, Sync1 is a Sy output from the synchronizing circuit (Sync generator) 16 described with reference to FIG.
Sync 2 is a Sync signal delayed by the delay adjustment circuit 18 in accordance with an instruction from the CPU 17 based on the duty value from the light amount controller 14.
Represents a signal.

Based on the falling time t _{1 of} Sync ₁ as a reference, the delay time until the falling time t _{2 of} Sync ₂ is A ₁
It is represented by This delay time A ₁ is determined by the light amount controller 1
Using the duty value from 4, the CPU 17 can calculate by the following equation. T = S × (100−duty) / 2 (1) In the equation (1), T is a delay time, S is a time of an H _sync section corresponding to one accumulation time, and duty is expressed in%.
Each shows the duty value. PWM signal output from the light quantity controller 14, a signal output based on the falling edge t ₂ of Sync2 delayed, continues to output the high level signal only sections of a predetermined duty value. This PW
Based on the M signal, the inverter 15 supplies a current to the fluorescent lamp 10 at a frequency sufficiently higher than the PWM signal. The tube current in FIG. 7 indicates the signal. With this tube current, the fluorescent lamp 10 is turned on with a constant light amount corresponding to a current value obtained by averaging the tube current. In this, PWM signal when the fluorescent lamp lighting, tube current, and, C line which is the center of all the signals of the light amount is the Sync1 interval signal representative of the H _sync interval corresponding to one charge accumulation period of the solid-state imaging device Coincides with the center of the fall.

Similarly, in FIG. 7B, the PWM
The center C of each signal of the signal, the tube current, and the light amount is Syn.
It coincides with the center of the section signal of c1. In this (B), the duty value is about 60%, and again, from the falling t _{3 of} Sync 1, Sy is calculated according to the above equation (1).
delay time B ₁ to the falling t ₄ of nc2 is calculated. Due to the increase in duty value, delay time B
₁ indicates that the delay time in the case of (A) is shorter than A ₁ .

(Fluctuation of Duty Value) In the pulse driving method (PWM) of the fluorescent lamp used in the present embodiment, the fluorescent lamp and the light amount detection circuit are the same, and the same pulse width is applied. However, the light amounts are not the same. Since the luminous efficiency of a fluorescent lamp changes due to a relatively long-term change with time, the amount of light when a pulse width is applied with the same duty value decreases. That is, the duty value required to generate the same light amount increases with the aging of the fluorescent lamp.

Therefore, if the degree of change of the fluorescent lamp with time is measured, the duty value at that time is directly calculated according to the degree.
It is possible to know without referring to the ty value, and it is possible to set a delay amount accordingly. As a result, an increase in the load on the CPU that occurs when directly referencing the duty value that changes at high speed can be prevented, and cost reduction can be expected by reducing the circuit scale.

Duty value required for lighting with a constant amount of light
Is proportional to the number of scans made with the fluorescent light.
And is represented by the following relational expression. duty value (%) = α x 100 x C_n/ C_l ... (c) In this equation (c), α is a proportional constant, C_nAt that time
Number of scans at a point, C _lIs the warranty scan for the fluorescent light.
The number of times (life of the fluorescent lamp) is shown.

A copy machine is generally provided with various counters for copying in order to know the billing and the replacement time of parts. Of these, if the value of the counter for counting the number of scans is used, there is no cost increase factor, and from the above-described equations (a), (b), and (c), the synchronization signal at a certain number of scans is obtained. The delay amount can be calculated.

(Setting Timing) The setting of the delay amount of the synchronization signal is not synchronized with the synchronization signal, and is performed by the CPU asynchronously. Therefore, when the setting is performed, the synchronization signal becomes indefinite for one cycle or indefinite in the delay position. Therefore, for one cycle, the driving pulse of the fluorescent lamp is not in a normal state, and the light amount is instantaneously uncertain.

Accordingly, if the delay setting is performed during the image reading, the image may be abnormal. Therefore, the delay setting cannot be changed at such timing.

The CC driven based on the synchronization signal
Regarding D, if the synchronization signal is shorter than a predetermined period, even if it is not during image reading, if the time until the start of image reading is short (several 100 msec or less),
This may affect the image at the time of reading.

Therefore, at the timing when the image is not read, that is, when the optical system of the reading device finishes moving in the sub-scanning direction and returns to the reading start position for the next reading scan (hereinafter, " It is conceivable that the delay amount is set during “back scan”.) If the delay amount is set immediately after the start of the back scan, even if the CCD drive signal is changed at that timing, a time period of several hundred milliseconds before normal reading can be sufficiently performed.

In order to eliminate the influence on the read image in principle, a scanner start synchronizing signal (RTOP) which is a trigger signal for activating the scanner motor is used. At the same time, control to mask the synchronization signal for one cycle during the period is conceivable. This prevents a synchronization signal shorter than a predetermined period from being output.

Next, the mask processing of the synchronization signal by the RTOP will be described in detail.

(Timing Chart) FIG. 11 shows a timing chart of the contents described above.

The scanner start synchronizing signal RTOP is different from the reference synchronizing signal SYNC, as shown in FIG.
It is output for the period. Synchronized signal MSYNC after mask
Is a signal resulting from masking SYNC by RTOP.

The delay amount setting is set to a value of T ₁ before an RTOP occurs. After the RTOP is processed by an interrupt, the value is changed to T ₂ after the RTOP.

(Hardware Configuration) FIG. 12 shows a hardware configuration for the above processing.

In the figure, reference numeral 1021 denotes a CPU for controlling the whole, 1022 denotes a gate circuit for masking, and 1023 denotes a delay means.

A scanner start synchronization signal RTOP and a reference synchronization signal SYNC are input to a gate circuit 1022 as a masking means, respectively.
Generates a masked MSYNC signal. CPU10
Reference numeral 21 denotes an MSYNC signal which is input to an interrupt terminal, and performs a register setting to a delay unit as an interrupt process. The delay means 1023 delays the input MSYNC signal by an amount set by the CPU 1021 and outputs a signal D
This is a circuit for generating SYNC.

(Delay Setting) Next, referring to the flowcharts of FIGS. 13 and 14, the CPU 17 shown in FIG.
Are the registers 51 and 52 of the delay adjustment circuit 18 (FIG. 5).
A series of control operations for setting the delay amount will be described.

When the image reading operation is started, the CPU
17 first reads the count value of the counter 19, and calculates the amount of delay of the synchronization signal from the above-described formulas (a), (b) and (c) based on the count value. Is set in the registers 51 and 52 to turn on the fluorescent lamp which has been turned off (steps S1 to S3 in FIG. 13).

During the continuous scanning operation, the CPU 17
The counter 19 is counted up for each can.
Of the registers 51 and 52 based on the count value of
P₁, P _TwoIs recalculated and held (step in FIG. 13).
Steps S4 to S6).

When the RTOP signal is given during the continuous scanning operation, the CPU 17 sets the values P ₁ and P ₂ held at that time in the registers 51 and 52 to reset the delay amount. I do. The RTOP signal is provided for each scan operation, and in the present embodiment, the interval is about 4.5 seconds.

As described above, in the present embodiment, even when the duty value changes, the center position of the lighting control signal does not change with time, and is always positioned at the center of the _Hsync section signal. Even when the afterglow characteristic of the phosphor is different for each color, the position of the center of gravity of the light quantity is always located near the center of the section signal of _Hsync , and the light quantity in the non-lighting section due to the afterglow is 1 By averaging before and after the lighting period within the accumulation time, it is possible to make the change in the position of the center of gravity small.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

The hardware configuration of the image reading apparatus according to the second embodiment is the same as that of the above-described first embodiment, and a description thereof will be omitted.

In FIG. 8, the SYNC signal, the PWM signal, the control current waveform (tube current), and the light amount are described as output signals as in the first embodiment. This FIG.
In the graph, the horizontal axis represents time, and the vertical axis represents the magnitude of each output signal. FIG. 8A shows an output signal when the duty value is about 25%, and FIG. 8B shows an output signal when the duty value is about 60%.

In the second embodiment, the PW at the time of dimming
The central value of the M signal changes symmetrically around the falling position of Sync1. Here, Syn
c1 is the synchronization circuit (Sync generator) 1 described with reference to FIG.
6 represents the Sync signal output from
2 is C based on the duty value from the light amount controller 14.
A Sync signal delayed by the delay adjustment circuit 18 according to an instruction from the PU 17 is shown.

[0094] Taking reference to the falling edge t ₅ of Sync1, delay time to the falling t ₆ of Sync2 is A ₂
It is represented by The delay time A ₂ is determined by the light amount controller 1
Using the duty value from 4, the CPU 17 can calculate by the following equation. T = S × (100−duty) / 2 (2) In the equation (2), T is a delay time, S is a time of an H _sync section corresponding to one accumulation time, and duty is expressed in%.
Each shows the duty value. PWM signal output from the light quantity controller 14, a signal output based on the falling t ₆ of Sync2 delayed, continues to output the high level signal only sections of a predetermined duty value. This PW
Based on the M signal, the inverter 15 supplies a current to the fluorescent lamp 10 at a frequency sufficiently higher than the PWM signal. The tube current in FIG. 8 indicates the signal. With this tube current, the fluorescent lamp 10 is turned on with a constant light amount corresponding to a current value obtained by averaging the tube current. At this time, the center of all the signals of the PWM signal, the tube current, and the light amount when the fluorescent lamp is turned on is at the falling position t ₅ of the section signal of Sync1 representing the H _sync section corresponding to one accumulation time of the solid-state imaging device. Matches.

Similarly, in FIG. 8B, the PWM
The center of each signal of the signal, the tube current, and the light amount is Sync.
Coincides with the trailing edge point t ₇ of one of the interval signal. In this case (B), the duty value is about 60%.
Delay time B ₂ from ₇ to the fall t _{8 of} Sync2
Is calculated. Due to the increase in the duty value, the delay time B ₂ is shorter than the delay time A _{2 in} the case of (A).

Also in the second embodiment, even when the duty value changes, the position of the center of the lighting control signal does not change with time and is always located at the center of the section signal of _Hsync . Even when the afterglow characteristics of the phosphors are different for each color, the position of the center of gravity of the light quantity is always located near the center of the section signal of _Hsync , and the light quantity in the non-lighting section due to the afterglow is accumulated by one. By averaging before and after the lighting section within the time, the change in the position of the center of gravity can be made a very small amount.

[0097]

As described above, according to the present invention, when a white light source having a phosphor having different afterglow characteristics for each of a plurality of reading colors corresponding to the line sensor is used. By having a means for reducing or correcting the shift of the center of gravity of the reading position of each color in the sub-scanning direction, which is generated depending on the afterglow characteristic of the light source, depending on the lighting method or the reading method of the fluorescent lamp, By using a pulse width modulation method, the control pulse is grown symmetrically in the time axis direction around the reference position, so that the amount of light can be increased even if the afterglow characteristics of the phosphor differ for each color. of located near the center of always H _sync interval signal the position of the center of gravity, and, the amount of light in the non-lighting period according to afterglow, by averaging before and after the lighting section within one accumulating time, the center of gravity The change of location may be a small amount.

Further, the provision of the means for performing the correction in units of one scan makes it possible to perform an optimum control which is not influenced by the duty fluctuation of the fluorescent lamp due to the continuous lighting.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a principle of an illumination driving method according to the present invention.

FIG. 2 is a schematic perspective view of a fluorescent lamp.

FIG. 3 is a block diagram illustrating a configuration of a light amount control unit of the image reading device according to the first embodiment of the present invention.

FIG. 4 is a block diagram illustrating a main configuration of the image reading apparatus according to the first embodiment of the present invention.

FIG. 5 is a block diagram illustrating a configuration of a delay adjustment circuit of the image reading device according to the first embodiment of the present invention.

FIG. 6 is a block diagram illustrating a configuration of a down counter of the image reading device according to the first embodiment of the present invention.

FIG. 7 is a timing chart of a light amount control signal according to the first embodiment of the present invention.

FIG. 8 is a timing chart of a light amount control signal according to a second embodiment of the present invention.

FIG. 9 is a schematic diagram illustrating a configuration of an optical system of an image reading unit of the image reading device.

FIG. 10 is a characteristic diagram showing a conventional light amount control signal and afterglow characteristics.

FIG. 11 is a timing chart for setting a delay amount according to the first embodiment of the present invention.

FIG. 12 is a block diagram showing a hardware configuration for realizing a delay amount setting according to the first embodiment of the present invention.

FIG. 13 is a flowchart of control for setting a delay amount from a duty value according to the first embodiment of the present invention.

FIG. 14 is a flowchart of control for setting a delay amount from a duty value according to the first embodiment of the present invention.

[Explanation of symbols]

 1: Fluorescent light 2a, 2b: Socket 3: Aperture 4: Light intensity sensor 10: Fluorescent light 11: Light intensity sensor 12: Amplifier 13: Comparator 14: Light intensity controller 15: Inverter 16: Synchronous circuit (SYNC) 17: CPU 18: Delay adjustment circuit 19: Counter 20: Document 21: Mirror base 22: Image processing unit 23: Variable resistor 24: Amplifier 25: Comparator 26: Light intensity controller 27: Inverter 28: CPU 29: Backup memory 30: A / D converter 31 : Driver 32: Fluorescent lamp 33: Heater 34: Thermistor 35: Photodiode 36: Preamplifier 37: Light intensity sensor 38: Switch 39: Flip-flop circuit (F / F) 40: Up / down counter 41: Down counter 42: Preheating control unit 43: Analog processor 44: A / D converter 45: Free-running SYNC generation and selector circuit 46: Delay adjustment circuit 47: Main scanning synchronization signal 48: Up counter 49, 50: Comparator 51, 52: Register 53: JK flip-flop circuit (JK -F / F) 54: SYNC2 55: JK flip-flop circuit (JK-F / F) 56: PWM signal 57: Down counter 58: CCD 100: platen glass 101: Bar light source 102: Reflector shade 103a, 103b, 103c : Mirror 104: imaging optical system 105: solid-state imaging device 1021: CPU 1022: gate circuit 1023: delay circuit

Claims (10)

[Claims] An image reading apparatus for forming an image of reflected light from a document surface illuminated by a light source on an image pickup device comprising a plurality of photoelectric conversion elements arranged in a line and reading an image on the document surface. An image reading apparatus that reads an image of the entire original surface while scanning the original surface line-sequentially in a sub-scanning direction that is substantially perpendicular to the arrangement direction of the photoelectric conversion elements, The use of a light emitting source of a phosphor corresponding to each of a plurality of emission colors, and reducing the shift of the center of gravity of the reading position of each color in the sub-scanning direction caused by the difference in the persistence characteristics of the phosphor of each color. An image reading apparatus comprising: a center-of-gravity shift reducing unit, wherein the center-of-gravity shift reducing unit performs control for reducing the center-of-gravity shift based on the cumulative number of scans. 2. The method according to claim 1, wherein the center-of-gravity shift reducing unit controls a phase of a pulse width modulation signal for controlling a light amount of the light source such that a shift of a center of gravity of each color within one accumulation time of the image sensor is reduced. The image reading device according to claim 1, wherein: 3. A light quantity control means for controlling a light quantity of the light source by a pulse width modulation method, wherein the center-of-gravity shift reducing means sets a control pulse growth method within one accumulation time of the image pickup element as a reference. 2. The image reading apparatus according to claim 1, wherein the image is grown symmetrically in the time axis direction about the position. 4. The image reading apparatus according to claim 3, wherein the reference position is a center position with respect to a time axis within one accumulation time. 5. The image reading apparatus according to claim 3, wherein the reference position is a position of a leading end with respect to a time axis within one accumulation time. 6. A reflected light from a document surface illuminated by a light source having phosphors respectively corresponding to a plurality of emission colors as a light source is transferred onto an image pickup device comprising a plurality of photoelectric conversion elements arranged in a line. An image reading device that forms an image and reads an image on the original surface, wherein the original surface is scanned line-sequentially in a sub-scanning direction that is substantially perpendicular to an array direction of the photoelectric conversion elements. An illumination driving method for an image reading apparatus that reads an image on the entire surface of a document, wherein the driving of the light source is performed so as to reduce a shift in the center of gravity of the reading position of each color in the sub-scanning direction caused by a difference in the persistence characteristics of the phosphor of each color. Is controlled based on the cumulative number of scans. 7. When performing the movement reduction control of the center of gravity,
The phase of a pulse width modulation signal for controlling the light amount of the light source is controlled so that the movement of the center of gravity of each color within one accumulation time of the image sensor is reduced. Method. 8. A driving method for controlling the amount of light of said light source by a pulse width modulation method, wherein a method of growing a control pulse within one accumulation time of said image sensor is performed in a time axis direction around a reference position. 7. The method according to claim 6, wherein the growth is symmetrical. 9. The method according to claim 8, wherein the reference position is a center position with respect to a time axis within one accumulation time. 10. The method according to claim 8, wherein the reference position is a position of a tip with respect to a time axis within one accumulation time.