JP3450641B2 - Image reading device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device used in a copying machine or the like for reading an image of an original.

[0002]

2. Description of the Related Art FIG. 8 shows a sectional view of a fluorescent lamp of a light source for reading an original in a conventional copying machine, and FIG. 9 shows a side view thereof. In FIG. 9, a glass tube 801 is filled with mercury gas and a rare gas 901 by caps 902 at both ends of the glass tube 801. Furthermore, at both ends of the glass tube 801,
Electrode 90 of tungsten coil coated with electron emitting material
3 and the electrodes are supported by the stem 904. A conductive portion 905 for supplying an electric current to the base 902.
Is provided. Further, as shown in FIG. 8, a glass tube 801
A reflective film 804 that reflects the light generated inside the glass tube is applied to the inner side of the glass tube, and a fluorescent material 803 is applied to the inner side thereof.
Has been applied. The aperture 805 on the side surface of the glass tube 801 is not coated with the reflection film 804 or the phosphor 803, so that light is transmitted through the aperture 805.

When this fluorescent lamp is turned on, the electrode 903
The electrons emitted from collide with the mercury electrons, and the mercury electrons are excited to emit ultraviolet rays. This ultraviolet ray is converted into visible light having a wavelength peculiar to the phosphor by the phosphor 803 on the inner wall of the discharge tube. The light generated inside the glass tube 801 is reflected by the reflection film 804 and emitted from the aperture section 805. Due to the functions of the reflection film 804 and the aperture portion 805, strong light is output in the arrow direction of FIG.

An optical system of an image reading apparatus using this fluorescent lamp is shown in FIG. In FIG. 10, the light emitted from the aperture section 805 of the glass tube 801 is reflected by the condenser mirrors 1001 and 1002, and is irradiated near the reading line 1005 of the original 1004 on the platen glass 1003. The light emitted from the reading line 1005 of the original is reflected by the mirrors 1006, 1007, 1008, and the lens 1009, and the CCD image sensor 1010.
Be led to. A light blocking plate 1011 is provided so that the light emitted from the back surface of the glass tube 801 is not directly irradiated on the original 1004. Glass tube 801, condenser mirror 1001,
1002 and the shading plate 1011 move the document surface as one scanner unit 1012. In addition, the mirrors 1007 and 1008 are moved according to the movement of the scanner unit 1012.
Moves so that the optical path to the CCD image sensor 1010 is kept constant.

As described above, the light quantity of the light source of the image reading apparatus, that is, the fluorescent lamp, depends on the quantity of ultraviolet rays emitted from the excited mercury atoms in the tube. The light intensity of the fluorescent lamp is considered to be represented by the product of the electric power supplied to the fluorescent lamp and the luminous efficiency. Then, the luminous efficiency decreases as the number of atoms excited by collisions of electrons decreases when the mercury atom density decreases, and conversely decreases when the mercury atom density increases because the probability of photon reabsorption increases. To do.
Therefore, there is a mercury vapor pressure that maximizes the luminous efficiency. Further, the mercury vapor pressure depends on the temperature of the lowest temperature inside the tube (the temperature of the coldest part). That is, there is a coldest part temperature that maximizes the luminous efficiency.

The graph of FIG. 11 shows the relationship between the coldest temperature of the fluorescent lamp or the mercury vapor pressure and the luminous efficiency. The mercury vapor pressure that maximizes luminous efficiency depends on the inner diameter of the tube,
For example, when the tube inner diameter is 15 mm, the mercury vapor pressure that maximizes the luminous efficiency is about 1 Pascal, and the coldest part temperature is about 4 Pascal.
It is said to be about 4 ° C. When the fluorescent lamp for normal lighting is lit at the operating environment temperature of 25 ° C, the temperature of the coldest part (usually the temperature inside both ends of the tube) when it reaches a heat stable state due to its own heat generation and heat radiation is the optimum coldest temperature. It is designed to reach the part temperature.

FIG. 12 is a block diagram of a light quantity control circuit of the fluorescent lamp, and FIG. 13 is a peripheral view of the fluorescent lamp. In FIG. 13, a fluorescent lamp 1206 is supported by a socket 1301 and electric current is supplied from a pin on the socket 1301. The fluorescent lamp 1206 is provided with an aperture portion 805 (optical opening) in the necessary direction,
In FIG. 13, strong light is output in the arrow direction, and relatively weak light is output in the opposite direction.

A fluorescent lamp light quantity sensor 1201 is provided to measure the light quantity of the fluorescent lamp 1206.
A photodiode or the like is used as the light quantity sensor 1201 and outputs a current proportional to the light quantity of the fluorescent lamp. The fluorescent lamp 1206 is controlled so that the light amount measurement value obtained by the fluorescent lamp light amount sensor 1201 is fed back to make the light amount constant.

FIGS. 7A, 7B and 7C are timing charts for explaining the operation of the light quantity control circuit of FIG. 7A shows the case where the light amount is appropriate, FIG. 7B shows the case where the current value is large because the light amount is small, and FIG. 7C shows the time when the current value is small because the light amount is large.

In FIG. 12, the light amount signal output from the light amount sensor 1201 is converted into a voltage value by the amplifier 1202 and amplified. The comparator 1203 compares the voltage corresponding to the observed light amount with the desired light amount value and outputs the result. The light quantity controller 1204 uses pulse width modulation (PW
M) Output the signal. As shown in FIG. 7, the pulse width modulation signal is phase-synchronized with the synchronization (SYNC) signal, and the duty becomes small when the observed light amount is larger than the desired light amount, and the observed light amount is smaller than the desired light amount. When it is small, the duty is controlled to be large.

The inverter 1205 supplies an alternating current to the fluorescent lamp at a frequency (generally about 10 to 100 times) sufficiently higher than the pulse width modulated signal when the input pulse width modulated signal is at "H" level. The lamp current is supplied to turn on the lamp, and when the level is "L", the lamp current is cut off and turned off. This lighting / extinction is repeated according to the cycle of the pulse width modulation signal. The frequency of the pulse width modulation signal is higher than the optical response frequency of turning on and off the fluorescent lamp. In other words, electrically, lighting and extinguishing are repeated according to the cycle of the pulse width modulation signal, but apparently it seems that lighting is performed with a constant light amount corresponding to the average current value. As described above, the fluorescent lamp 1206 is controlled so that the light amount is constant by controlling the duty of the lighting and extinguishing cycles.

The light quantity of the fluorescent lamp is the ON-OF of the tube current.
It changes with F as shown in FIG. In the period in which no current flows, the amount of light becomes small, although some amount of light is emitted due to the afterglow property of the phosphor. However, depending on the fluorescent lamp, the fluctuation range of the light amount is small and there may be no problem in image reading.

On the other hand, an image reading device such as a CCD accumulates the read image information as electric charge during one cycle of the SYNC signal, that is, during one main scanning period. That is, the output of the CCD is an output value having a magnitude obtained by integrating the light amount in one main scanning period.

Therefore, if the blinking of the fluorescent lamp and the scanning of the CCD are not synchronized, the output value fluctuation of the frequency difference occurs, but if the blinking of the fluorescent lamp and the scanning of the CCD are synchronized in the same cycle, A constant CCD output value is obtained.

FIG. 6 shows aged deterioration characteristics of the fluorescent lamp.
The luminous efficiency of the fluorescent lamp decreases as the cumulative lighting time increases due to deterioration of the phosphor. As indicated by the horizontal axis of FIG. 6, the light amount deteriorates in accordance with the cumulative value of the product of the electric power at the time of lighting and the lighting time. Since the light quantity required for the image reading device is constant, the light quantity control means using the above-described light quantity sensor controls so that the light quantity remains constant even after deterioration. For example, if the amount of light actually used is set to half of the amount of light of the initial lamp, it can be used until the amount of light at full lighting deteriorates to half, and the lamp must be replaced there. Since the amount of light is approximately compared with the current value, the current value during the initial lamp is about half the current value during lamp replacement in the case of FIG.

[0016]

When the fluorescent lamp deteriorates and reaches the end of its life, the rise in the amount of light at the start of lighting is delayed. It becomes remarkable especially when the environmental temperature is low. A slow rise of the light quantity adversely affects the processing speed of the image reading apparatus. Therefore, immediately after the start of lighting, the tube current value should be controlled so as to reach the desired light quantity in a short time.
On the other hand, after the desired light amount is reached, if the light amount fluctuates, the image reading quality deteriorates, so stable control should be performed so as not to be affected by some disturbance.

Therefore, the present invention has been made in order to solve the above problems, and provides an image reading apparatus capable of performing a light amount startup in a short time and performing stable light amount control after the startup. It is an object.

[0018]

An image reading apparatus of the present invention comprises a light source means for irradiating a document with light, a lighting means for turning on the light source means, and a reading of light from the document.
A reading unit that outputs an image signal, a light amount detection unit that detects the light amount of the light source unit, and a light amount control value that is supplied to the lighting unit when the light source unit is turned on at a predetermined light amount in the previous lighting. After the lighting of the light source means by the memory means and the lighting means is started, the light source means is fully turned on until the light quantity of the light source means detected by the light quantity detection means reaches the predetermined light quantity. When the light quantity reaches the predetermined light quantity, the light quantity control value held in the memory means is supplied to the lighting means as an initial value, and then the light quantity is maintained so that the light source means continues to light at the predetermined light quantity. The light amount control value increased or decreased from the initial value according to the detection output of the detection means is supplied to the lighting means.

Another feature of the present invention is that after the light source means starts lighting the light source means by the lighting means, the light quantity of the light source means detected by the light quantity detecting means reaches the predetermined light quantity, and then the light source Further comprising timer means for counting a predetermined time for the lighting state of the means to stabilize,
The control unit increases or decreases the light amount control value at every predetermined timing according to the detection output of the light amount detection unit, and after the predetermined time is counted by the timer unit, the light amount control value at each predetermined timing is changed. It is characterized by reducing the number of changes.

Another feature of the present invention is that the reading means reads the light from the document by line scanning, and the predetermined timing is a timing synchronized with the line scanning. .

Another feature of the present invention is that the comparing means compares the light quantity of the light source means detected by the light quantity detecting means with the predetermined light quantity, and the count value according to the output of the comparing means. It further comprises counter means for outputting and pulse width modulation means for outputting a pulse width modulation signal having a pulse width for controlling the light quantity of the light source means according to the count value, and the light quantity control value is the count value. Is characterized in that.

[0022]

1 shows an embodiment of an image reading apparatus according to the present invention. In FIG. 1, the mirror stand 20
The amount of light of the fluorescent lamp 201 on the light source No. 5 is detected by the photodiode 202 on the light amount sensor substrate 204 arranged near the fluorescent lamp. The light amount signal is converted from a minute current signal into a voltage signal by the preamplifier 203 and input to the amplifier 206. The amplifier 206 adjusts the light amount signal to an appropriate voltage by the accompanying variable resistor 218, and the comparator 20
Send to 7 comparison inputs.

The CPU 208 has reference power sources 219 and 220 for obtaining a designated value of the light amount reference signal of the comparator 207.
Is switched by the switch 221 and sent to the other comparison input of the comparator 207. This switching is, for example, a means for switching when the light amount is specifically reduced when the reflectance of the read image is particularly high, and this switching is not necessary if the read light amount is a constant value. The comparator 207 compares the light amount reference signal with the light amount signal from the amplifier 206, and outputs the comparison result to the flip-flop 209.

The dimming logic circuit 217 is composed of a gate array or the like, and the flip-flop 209 therein is a SYN.
The light amount comparison signal from the comparator 207 is output in synchronization with the C signal. This SYNC signal is a signal for performing line scanning by a CCD line sensor described later.
The up / down counter 210 increases the value of the counter by a predetermined value when the light quantity is less than the light quantity reference signal, and decreases the counter value by a predetermined value when the light quantity is equal to or larger than the light quantity reference signal according to the result of the light quantity comparison signal. Here, the predetermined value to be increased or decreased is normally ± 1 and is set to ± 16 at the beginning of lighting.

The down counter 211 loads the value of the up / down counter 210 in synchronization with the SYNC signal,
Count down with a predetermined clock. The output PWM signal is at the high level during the period from the loading to the carry output, and is at the low level during the other periods. Also, C
The PU 208 can read the value of the up / down counter 210 at any time.

The dimming logic circuit 217 also includes a preheat control circuit 222 which produces a control signal for preheating the fluorescent lamp electrodes before lighting. The inverter 212 preheats the electrodes of the fluorescent lamp 201 according to a preheat control signal before the fluorescent lamp is turned on, and then P
It lights up according to the WM signal. The fluorescent lamp 201 is turned on only when the PWM signal is at a high level, and is turned off when the PWM signal is at a low level.

The fluorescent lamp 201 may be equipped with a heater 213 for keeping the temperature before lighting at a predetermined value. The heater 213 is further equipped with a thermistor 214 for temperature detection, and the comparator 215 and the driver 2 are arranged so that the temperature detected by the thermistor 214 reaches a predetermined value.
16 works to preheat the heater 213. The temperature control value may be constant, but the temperature control value may be instructed by the CPU 208 to the reference power supply 223. As described with reference to FIG. 10, the light output from the fluorescent lamp 201 is reflected by the surface of the original 224, input to the CCD line sensor 225, level-corrected by the analog processor (analog processor circuit) 226, and the AD converter 227. It is converted and output to the printer. The original 224 may be a transparent original instead of a reflective original.

Next, the dimming logic circuit 217 is shown in FIG.
Will be explained in more detail. A time chart of the operation of FIG. 2 is shown in FIG. FIG. 4 shows a time chart in which a part of FIG. 3, particularly a PWM signal generation part is enlarged and shown in detail. In FIG. 2, the comparator 207 and the flip-flop 2
09, up-down counter 210, down-counter 2
Reference numeral 11 corresponds to the same numbered portion in FIG. Comparator 2
Reference numeral 07 denotes a desired light amount generation circuit 102 (219 to 221 in FIG. 1).
(Including) and the desired light amount signal value generated by (1) are compared with the fluorescent light amount value, and the result is output. The flip-flop 209 is S
In synchronization with the YNC1 signal, the light amount comparison signal, which is the output of the comparator 207, is input and output. SYNC
The signal generation circuit 110 inputs the SYNC signal for performing the line scanning by the CCD line sensor 225, and FIG.
, The phase is shifted one clock at a time
Output as C1, 2, 3, and 4.

As shown in FIG. 5A, the lower limit value limiter 104 forcibly outputs "1" when all the high-order bits of the bits held in the up / down counter 109 are "0". It is supposed to be. This is a circuit that prevents the value held by the counter 109, that is, the width of the PWM signal, from becoming smaller than a predetermined lower limit value.
The up / down counter 210 is composed of two up / down counters 106 and 109. As shown in FIG. 5B, the upper limit value limiter 105 is configured to forcibly set the output to “0” when all the high-order bits of the bits held in the counter 109 are “1”. There is.
This is a circuit that prevents the value held by the counter 109, that is, the width of the PWM signal, from exceeding a predetermined upper limit value.

The output of the upper limit value limiter 105 is input to the up / down input terminals of the counters 106 and 109.
When this signal is at a high level, that is, when the sensor light amount is insufficient for the desired light amount, the counter is incremented. On the contrary, when the signal is low level, that is, when the sensor light amount is larger than the desired light amount, the counter is down. In the case of an ordinary counter, the carry-out output CO of the lower counter 106 is unchanged, and the carry-in C of the upper counter 109 is used.
Although connected to the I input, in the case of the present invention, an OR gate 108 is inserted between the two counters 106 and 109.

Immediately after the fluorescent lamp is turned on, the output of the timer 107 becomes high level, and the counter 106 is forcibly loaded with "0" by the inverter 101 and remains stopped. On the other hand, the counter 109 is in the operating state because the carry-in CI is forcibly set to "1". The counter 109 synchronizes with SYNC, and SYNC1
Since the SYNC2 signal whose phase is delayed by one clock from the signal is supplied as the enable EN, the SYNC1
The high-order bit counter 109 is incremented or decremented by "1" each time. Assuming that the lower bit counter 106 has 4 bits, the counter 106 and the counter 1
09 is regarded as one counter 210, one SY
The light amount is compared once for each NC, and the count value is increased or decreased by 16.

In a stable state after lighting the fluorescent lamp,
The output of the timer 107 becomes low level, and the counter 10
The load of 6 is released and the counter 106 is in the operating state. On the other hand, the counter 109 is in a state in which the carry-in CI is forcibly input and the carry signal CO of the counter 106 is normally input. Since the SYNC2 signal is supplied to the counters 106 and 109 as the enable EN, the lower bit counter 10 is supplied every time SYNC is performed.
6 goes up or down by "1". Counter 1
If 06 and the counter 109 are regarded as one counter 210, the light amount is compared once for each SYNC, and the count value is increased or decreased by one.

As shown in FIG. 4, the SYNC signal generating circuit 110 synchronizes the SYNC signal with the system clock CLK, and the SYNC1, 2, ...
Make 3 or 4 signals. Down counter 211 is SYNC3
The held values of the counters 106 and 109 are loaded at the timing of. The down counter 211 counts down with the system clock CLK immediately after the completion of loading, and outputs a carry-out CO when the count is completed. The flip-flop 113 is set by SYNC4 and reset by the carry-out CO of the down counter 211. That is, while the down counter 211 is counting, the output of the flip flip 113 is at high level.

On the other hand, as shown in FIG. 3, the other timer 114 first turns on the electrode part preheating signal for a predetermined time when a lighting ON signal is input. Next, when the preheating time ends, a lighting signal is output. This lighting signal is ON
It stays high until the signal ends. Full lighting circuit 1
The full lighting signal output from 15 rises in accordance with the lighting signal from the timer 114 and rises to the comparator 207.
When the output of is first low level, that is, when it is detected that the amount of light reaches the desired amount of light, it falls to low level. OR gate 11 while the full lighting signal is at high level
6. Since the PWM signal output through the AND gate 117 becomes high level, the fluorescent lamp becomes full output during this period.

The preset circuit 111 is a comparator 20.
When the output of 7 falls, it falls at the timing of the next SYNC1. At the timing of SYNC2 before the preset circuit 111 starts up, the counter 109 has already loaded the initial value (predetermined value). When the preset circuit 111 goes low, the up / down count of the counter 109 is started.

As the initial value (predetermined value) preset in the counter 109, the CPU 208 reads the counter holding value (width of the PWM signal) at the previous lighting, and the value is shown after the power is turned off. If the CPU 208 presets the value in the first backup memory 228 as the initial value (predetermined value) when the power is turned on, it is effective in stabilizing the light amount in a short time.

The timer 107 counts a predetermined time a after the full lighting signal falls, and the output level during that time becomes high level. Then, during the period a, the counter 106
Is stopped, and only the counter 109 is set to 1 for each SYNC.
Count up or down times. That is, in the period a, for example, 16 up and down counts thereafter are performed.
Up / down counting is performed at double speed, and the value is converged to a desired value in a short time. In the period b after the end of period a, the up / down speeds of the counters 106 and 109 are, for example, 1/16 of those before. Therefore, during this period, a stable dimming light amount that keeps up with a slow change in the light amount but is not affected by an instantaneous disturbance is maintained.

[0038]

As described above, according to the present invention,
After lighting, it is controlled to fully turn on until it reaches a predetermined light amount, and after reaching the predetermined light amount, a more appropriate light amount control value is immediately supplied, so the light amount reaches the predetermined light amount in a short time immediately after lighting, and once the predetermined light amount is reached. After that, stable lighting is achieved with little change in light amount, the image reading processing speed is increased, and at the same time, the image reading quality is improved.

[0039]

[0040]

[0041]

[0042]

[0043]

[Brief description of drawings]

FIG. 1 is a block diagram showing an image reading device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the dimming logic circuit of FIG. 1 in detail.

FIG. 3 is a time chart illustrating the operation of FIG.

FIG. 4 is a time chart for explaining the operation of FIG. 2 by enlarging a part of FIG.

5 is a circuit diagram of a lower limit value limiter and an upper limit value limiter of FIG.

FIG. 6 is a graph showing the change over time in the amount of light for explaining the function of the light amount control circuit.

FIG. 7 is a timing diagram illustrating the operation of the light amount control circuit.

FIG. 8 is a cross-sectional view of a fluorescent lamp for an image reading device.

FIG. 9 is a side view of a fluorescent lamp for an image reading device.

FIG. 10 is a configuration diagram of an optical system of the image reading apparatus.

FIG. 11 is a graph showing a relationship between mercury vapor pressure and luminous efficiency of a fluorescent lamp.

FIG. 12 is a block diagram of a fluorescent lamp light amount control circuit.

FIG. 13 is a configuration diagram around a fluorescent lamp.

[Explanation of symbols]

101 Inverter 102 desired light amount generation circuit 106,109 Up-down counter 107 timer 108 OR gate 110 SYNC signal generator 111 preset circuit 113 flip-flops 114 timer 115 Full lighting circuit 116 OR gate 117 AND gate 201 fluorescent light 204 Light intensity sensor 207 Comparator 208 CPU 209 flip-flops 210 Up Down Down 211 down counter 212 inverter 217 Dimming logic circuit 224 manuscript 225 CCD line sensor 228 Backup memory

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-8-307609 (JP, A) JP-A-59-72866 (JP, A) JP-A-5-176122 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04N 1/04 101

Claims (4)

(57) [Claims] 1. A light source unit for irradiating a document with light, a lighting unit for lighting the light source unit, a reading unit for reading light from the document and outputting an image signal, and a light amount of the light source unit. A light quantity detection means, a memory means for holding the light quantity control value supplied to the lighting means when the light source means is lighted by a predetermined light quantity in the previous lighting, and after the lighting means starts the lighting of the light source means, Until the light quantity of the light source means detected by the light quantity detecting means reaches the predetermined light quantity, the light source means is fully turned on,
When the light quantity of the light source means reaches the predetermined light quantity, the light quantity control value held in the memory means is supplied to the lighting means as an initial value, and then the light source means continues to light at the predetermined light quantity. An image reading apparatus comprising: a control unit that supplies the light amount control value increased or decreased from the initial value to the lighting unit according to the detection output of the light amount detection unit. 2. The lighting state of the light source means is stabilized after the light quantity of the light source means detected by the light quantity detecting means reaches the predetermined light quantity after the lighting means starts the lighting of the light source means. Further comprising a timer means for counting a predetermined time, the control means increases or decreases the light quantity control value at every predetermined timing according to the detection output of the light quantity detecting means, and after the predetermined time is counted by the timer means The image reading apparatus according to claim 1, wherein the number of increase / decrease of the light amount control value at each of the predetermined timings is reduced. 3. The image reading apparatus according to claim 2, wherein the reading unit reads the light from the original document by line scanning, and the predetermined timing is a timing synchronized with the line scanning. 4. Comparing means for comparing the light quantity of the light source means detected by the light quantity detecting means with the predetermined light quantity, counter means for outputting a count value according to the output of the comparing means, and the count value. Further comprising pulse width modulation means for outputting a pulse width modulation signal having a pulse width for controlling the light quantity of the light source means, wherein the light quantity control value is the count value. The image reading device according to any one of 1 to 3.