JPH0450695Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a digital image processing device.

[Background of the idea]

Conventionally, image processing devices use a method of reading image information such as characters on a document in an analog manner using an illumination light source such as an incandescent light bulb, and temporarily recording this information on a photoreceptor such as selenium. However, in this method, the configuration of the equipment is relatively simple, and if the illuminance is high as a light source for illumination, the optical ripple (a fluctuation in the amount of light, the amount of light fluctuation is expressed as the average value of the light output) The permissible range (divided) is relatively large, and for practical purposes, it is considered sufficient if it is within ±15%.

However, in this method, the image information can only be used once, so the image information cannot be edited for other purposes, and an expensive lens system is required when enlarging or reducing the image. , there is also a problem of poor image accuracy.

Due to these circumstances, recently, image information such as characters on a document is digitally encoded and read by an image sensor made of a charge-coupled device, etc. using an illumination light source such as an incandescent light bulb, and this is stored in a memory element. A so-called digital image processing device that employs a storage method is attracting attention. This method uses an image sensor, so
The device can be configured compactly, and by storing the signals read by the image sensor in a storage element, it is possible to accurately enlarge or reduce image information, and it is also possible to edit it freely. There are advantages.

Image sensors used in digital image processing devices typically integrate a group of pixels with photoelectric conversion and charge accumulation functions and a scanning circuit that sequentially reads out pixel signals accumulated in each pixel on the same substrate. Since the photocurrent obtained through photoelectric conversion is proportional to the light intensity, a light source for illumination with high light intensity is required, and a light source for illumination with high light intensity is also required from the perspective of increasing the light response speed. Furthermore, in order to accurately digitally encode and read image information, an illumination light source with particularly small optical ripple is required. That is, when the light ripple of the illumination light source is large, the image sensor makes a mistake in reading and erroneous information is digitally encoded, making it impossible to obtain accurate image information.
In fact, the reading speed of an image sensor is usually 0.1 to 1 msec per line in the short side direction of A4 size paper.
In addition, recently, image sensors have been developed in which the variation in photocurrent for each pixel is less than 2%, so the optical ripple within the reading time per line is at least within ±3%. This is required.

[Problem that the invention attempts to solve]

One way to reduce the light ripple of an incandescent light bulb for illuminating a document is to turn on an incandescent light bulb with direct current. However, when lighting an incandescent light bulb with direct current, stepped or serrated overheated areas are created on the surface of the filament coil, which accelerates the evaporation of tungsten in the overheated areas and shortens the life of the lamp (notching phenomenon). ) occurs. This notching phenomenon occurs because polarity occurs when an incandescent lamp is lit with direct current, so not only the electrons in tungsten are transported, but also some tungsten metal ions are transported, and the surface condition of the filament is caused by the transport of the tundaste metal ions. In addition, tungsten metal ions are transported due to the large temperature gradient at the filament boundary, and as a result, steps and serrations occur on the surface of the filament, causing damage to the area. This is thought to be due to overheating. In fact, in some cases, when an incandescent light bulb for document illumination is lit with direct current, the lifespan of the incandescent light bulb is one-third that of when lit with alternating current.

On the other hand, when an incandescent light bulb is turned on with alternating current at a commercial frequency, there is a problem in that the light ripple is large and the reading error by the image sensor is large. In other words, when lighting an incandescent light bulb with alternating current, there is a known technology that stabilizes the lighting voltage by controlling the phase of the commercial frequency.
Hz: 8.3msec), the non-lighting time is usually 1~
There is about 2 msec, so 1 in the short side direction of A4 size
There is a problem in that the optical ripple is large within the time of approximately 0.1 to 1 msec during which a line is read, resulting in reading errors.

On the other hand, it is possible to use discharge lamps such as fluorescent lamps instead of incandescent lamps, but although discharge lamps are relatively superior in terms of light distribution characteristics and light ripple, on the other hand, the lighting circuit is complicated. Moreover, it is difficult to increase the light intensity, and it is not practical as a light source for illumination of a digital image processing device.

[Purpose of invention]

The present invention was developed based on the above-mentioned circumstances, and its purpose is to suppress light ripple to a small level without shortening the service life of incandescent light bulbs for illuminating documents, and to provide high-speed and accurate reading. The object of the present invention is to provide a digital image processing device capable of processing images.

[Means for solving problems]

The present invention provides a digital image processing device that includes an incandescent light bulb for illuminating a document, a lighting circuit that lights the incandescent light bulb, and an image sensor that reads image information of the document illuminated by the incandescent light bulb. The circuit is inserted into the power line leading to the incandescent light bulb, and lights up the incandescent light bulb at 0.3k.
comprising a switching element that performs on/off control at a frequency of Hz or more, and a control circuit that detects the lighting voltage of the incandescent lamp and controls the pulse width of the switching element to constantize the lighting voltage of the incandescent lamp,
The control circuit includes a voltage detection resistor connected to both ends of the incandescent light bulb to detect the lighting voltage of the incandescent light bulb, and a pseudo-effective value conversion circuit that converts the voltage detected by the voltage detection resistor into a pseudo-effective value. , a comparator that compares the pseudo effective value from the pseudo effective value conversion circuit with a reference voltage and generates an output that cancels out the difference; and a pulse width modulation circuit that changes the pulse width of the switching element based on the output from the comparator. The pseudo-effective value conversion circuit includes a first rectifying diode that receives a detected voltage from a voltage detecting resistor, and a first rectifying diode connected to the first rectifying diode via a current limiting resistor. a second rectifying diode, a smoothing circuit including a resistor and a capacitor connected to the output end of the second rectifying diode, and feeding back the output of the smoothing circuit to the second rectifying diode. It is characterized by having a feedback resistor.

[Function and effect of the idea]

According to the present invention, the lighting of an incandescent light bulb for document illumination is controlled on and off at a frequency of 0.3kHz or higher by a switching element driven by a control circuit, so the on/off control characteristics follow the thermal inertia of the filament. As a result, within the time of approximately 0.1 to 1 msec for reading one line in the direction of the short side of an A4 sheet, the optical output becomes virtually constant, and the optical ripple is significantly reduced. In fact, it is possible to reduce the optical ripple to within 1%.

Moreover, since the lighting of the incandescent light bulb is controlled on and off at a frequency of 0.3 kHz or higher, no notching phenomenon occurs in the filament of the incandescent light bulb, and therefore the service life of the incandescent light bulb is prevented from being shortened.

In the control circuit, we have installed a pseudo-effective value conversion circuit that converts the voltage detected by the voltage detection resistor connected to both ends of the incandescent bulb into a pseudo-effective value, so it corresponds strictly to the light output state of the incandescent bulb. Based on the voltage detected by the voltage detection resistor, the pulse width of the switching element is changed to control on/off so that the light output of the incandescent bulb is kept constant with high precision within the reading time of about 0.1 to 1 msec. This allows good feedback control.

In addition, the pseudo-rms value conversion circuit includes a diode,
Since it is constructed by combining a resistor and a capacitor, it can be made inexpensive and simple.

As a result, according to the present invention, it is possible to suppress light ripple to a small value without shortening the service life of an incandescent light bulb for illuminating a document, and to obtain a digital image processing device that can read images accurately at high speed.

[Specific structure of the idea]

The configuration of the present invention will be specifically explained below.

In this invention, an incandescent light bulb for illuminating the manuscript,
A digital image processing device is configured using a lighting circuit that lights the incandescent bulb and an image sensor that reads image information of a document illuminated by the incandescent bulb.

An example of a lighting circuit is shown in FIG. In the figure, 10 is an incandescent light bulb, 30 is a switching element,
40 is a control circuit.

The switching element 30 is inserted into the power supply line leading to the incandescent light bulb 10, and controls the lighting of the incandescent light bulb 10 on and off at a frequency of 0.3 kHz or higher, and is, for example, a field effect transistor (FET).
etc. can be used.

The control circuit 40 detects the lighting voltage of the incandescent light bulb 10 and controls the pulse width of the switching element 30.
The voltage detection resistors 41 and 45 are connected to both ends of the incandescent light bulb 10 in order to detect the lighting voltage of the incandescent light bulb 10, and the voltage detection resistor 41 is used to stabilize the lighting voltage of the incandescent light bulb 10. and a comparator 43 that compares the pseudo effective value from the pseudo effective value conversion circuit 42 with a reference voltage and generates an output that cancels out the difference.
and a pulse width modulation circuit 44 that changes the pulse width of the switching element 30 based on the output from the comparator 43.

The pseudo effective value conversion circuit 42 includes a voltage detection resistor 4
1 and 45; a second rectifying diode 53 connected to the first rectifying diode 51 via a current limiting resistor 52; A smoothing circuit including a resistor 55 and capacitors 56 and 57 is connected to the output end 54 of the second rectifying diode 53, and a feedback resistor 59 feeds back the output of this smoothing circuit to the second rectifying diode 53. It will be done. 60 is a variable resistor for taking out a pseudo effective value, 61 is a balance resistor, and 63 is a photocoupler.

Although this pseudo-effective value conversion circuit 42 has an inexpensive and simple configuration consisting of a resistor, a diode, and a capacitor, it is particularly provided with a feedback resistor 59, so that the voltage detection resistors 41 and 4
The pulsed detection voltage from 5 is converted into a voltage value corresponding to the effective value with high accuracy at the variable resistor 60 for extracting the pseudo effective value, and there is no time delay problem, so the response is extremely good. be.

In fact, as shown in FIG. 2, according to the pseudo effective value conversion circuit 42, the actual measured value (indicated by the broken line A)
It has been confirmed that the value matches the theoretical value of the effective value (indicated by the solid line B) extremely well. In addition,
The solid line C is the average value of the detected voltage. On the other hand, when the feedback resistor 59 is omitted, the actual measured value (indicated by the broken line D) deviates significantly from the theoretical effective value.

The voltage value converted into a pseudo effective value as described above is input to the comparator 43. This comparator 43 is composed of, for example, a variable shunt regulator with a built-in reference voltage source, and when the input voltage exceeds the voltage level set by the reference voltage source, the anode A of the variable shunt regulator and the cathode K, which activates the photocoupler 63 and transmits a high-level signal to the comparator 73 of the pulse width modulation circuit 44. The operation of the pulse width modulation circuit 44 that receives this high level signal causes the oscillation operation of the switching element 30 to be stopped. Note that the input voltage to the variable shunt regulator can be easily variably adjusted by changing the resistance value of the pseudo effective value extracting variable resistor 60. Also,
In this example, the voltage detection system and the control system are separated by the photocoupler 63, so
It is possible to effectively prevent signals from going around.

In the pulse width modulation circuit 44, the voltage value converted into the pseudo effective value and a sawtooth reference voltage having a frequency of 0.3 kHz or more formed by the reference voltage source 72, the oscillator 71, the resistor, and the capacitor are connected to a comparator. 73, and a pulse-like output is generated that cancels out the difference between the two. The pulse width of the switching element 30 is controlled by this pulsed output. Therefore, the incandescent light bulb 10 is controlled on and off with the pulse width controlled in this way, and as a result, the lighting voltage (effective value) of the incandescent light bulb 10 is made constant.

In this way, in the incandescent light bulb 10, 0.3kHz
In addition to on-off control and pulse lighting at a frequency above, the pulse width is controlled and the pulse lighting voltage (effective value) is kept constant, so the on-off control characteristics no longer follow due to the thermal inertia of the filament. As a result, within the time period of approximately 0.1 to 1 msec during which the image sensor reads one line in the direction of the short side of an A4 sheet, the light output becomes virtually constant, and the light ripple is significantly reduced. In fact, it is possible to reduce the optical ripple to within 1%.

Since the lighting of the incandescent light bulb 10 is controlled on and off at a frequency of 0.3 kHz or higher and is lit in pulses, the notching phenomenon does not occur in the filament of the incandescent light bulb 10, and therefore the service life of the incandescent light bulb 10 is prevented from being shortened. The desired performance can be stably obtained over a long period of time.

In the control circuit 40, voltage detection resistors 41 and 45 that detect the lighting voltage of the incandescent light bulb 10 are connected to both ends of the incandescent light bulb 10, and the voltage detected by the voltage detection resistors 41 and 45 is converted into a pseudo effective value. Since the pseudo effective value conversion circuit 42 is provided,
The voltage detected by the voltage detection resistors 41 and 45 strictly corresponds to the light output state of the incandescent bulb, and based on this detection voltage, the light output of the incandescent bulb 10 is high within the reading time of about 0.1 to 1 msec. On/off control can be performed by changing the pulse width of the switching element 30 so as to keep it constant with precision, and feedback control can be performed satisfactorily.

Since the pseudo-effective value conversion circuit 42 has a simple configuration combining a diode, a resistor, and a capacitor, it can be manufactured at extremely low cost.

In the end, according to the device having the above configuration, it is possible to suppress the light ripple to a small value without shortening the service life of the incandescent light bulb 10 for illuminating the document, and to obtain a digital image processing device that can read accurately at high speed. I can do it.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a lighting circuit, and FIG. 2 is a curve diagram comparing actual measured values and theoretical values of the pseudo-effective value conversion circuit. 10... Incandescent light bulb, 30... Switching element, 40... Control circuit, 41, 45... Voltage detection resistor, 42... Pseudo-effective value conversion circuit, 43...
Comparator, 44...Pulse width modulation circuit, 52
... Current limiting resistor, 51, 53... Rectifying diode, 55... Resistor, 56, 57... Capacitor, 59... Feedback resistor, 60... Variable resistor for taking out pseudo effective value, 61... Balance resistor. , 63...
Photocoupler, 71...Oscillator, 72...
Reference voltage source, 73... comparator.

Claims (1)

[Scope of Claim for Utility Model Registration] A digital image processing device comprising an incandescent light bulb for illuminating the original, a lighting circuit for lighting the incandescent light bulb, and an image sensor for reading image information of the original illuminated by the incandescent light bulb. In the lighting circuit, the lighting circuit includes a switching element that is inserted in a power line leading to the incandescent light bulb and controls the lighting of the incandescent light bulb on and off at a frequency of 0.3 kHz or more, and a switching element that detects the lighting voltage of the incandescent light bulb. a control circuit that controls the pulse width of the switching element to constantize the lighting voltage of the incandescent lamp, the control circuit controlling a voltage that detects the lighting voltage of the incandescent lamp connected to both ends of the incandescent lamp. A detection resistor, a pseudo-effective value conversion circuit that converts the voltage detected by this voltage detection resistor into a pseudo-effective value, and an output that compares the pseudo-effective value from this pseudo-effective value conversion circuit with a reference voltage and cancels out the difference. and a pulse width modulation circuit that changes the pulse width of the switching element based on the output from the comparator, and the pseudo effective value conversion circuit converts the detected voltage from the voltage detection resistor into a first rectifying diode connected to the first rectifying diode through a current limiting resistor; and a second rectifying diode connected to the output end of the second rectifying diode. A digital image processing device comprising: a smoothing circuit including a resistor and a capacitor; and a feedback resistor for feeding back the output of the smoothing circuit to the second rectifying diode.