JPH06100778B2 - Automatic exposure control device for copiers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic exposure control apparatus for automatically controlling the exposure amount of a light source in a copying machine according to the lightness and darkness of a document.

<Prior Art> Generally, in a conventional copying machine, when a document such as a newspaper, a blueprint document, or a color document having a dark background is copied, the exposure amount is increased as compared with a normal white background document. , Was getting the best copy. Since these operations were performed by the operator operating the exposure adjustment dial provided on the operation panel in the related art, the operator sees the light and shade of the original or makes an exposure adjustment after trial copying. The position of the dial was set. For this reason, a few copy sheets were often wasted until the optimum copy was obtained.

<Object of the Invention> In order to eliminate these drawbacks, the present invention is designed to automatically obtain optimum copying for fluctuations in power supply voltage or various originals. Is to improve the operability of the copying machine, and the second purpose is to eliminate unnecessary copying.

<Embodiment> FIG. 1 is an explanatory diagram of a schematic operation of a copying machine according to the present invention. The document table 1 on which the document is placed is adapted to reciprocate in the direction of arrow 2 as necessary, and when the document table 1 moves forward, the document placed on it is illuminated by the exposure lamp 3. The reflected light is guided onto the photoconductor 5 via the converging light transmission body array (rod lens array) 4, and the image of the document is formed on the surface of the photoconductor 5. Further, in synchronization with the reciprocating movement of the document table, the photoconductor 5 is moved to the arrow
The image is rotated in the direction of, and the light and shade information of the original is formed as a latent image on the photoconductor 5 charged by the charger 7. The developing device 8
This latent image on the photoconductor 5 is visualized, and the visible image is transferred by the transfer device 10 onto the plain paper sent from the cassette 9 in synchronization with the rotation of the photoconductor 5. Further, the transferred plain paper is sent to the fixing device 11, where the visible image is fixed on the plain paper, and then output from the copying machine. Photoelectric conversion element used for automatic exposure control of the present invention for detecting light and shade of a document
A slit 12 is arranged parallel to the rod lens array 4 in order to receive a part of the reflected light from the original placed on the original table 1, and only the light passing through the slit 13 is converted into a photoelectric conversion element 12. To receive light.

FIG. 2 is a control block diagram of the exposure control apparatus according to the present invention. Although this is not shown, the exposure adjustment is performed by operating the exposure adjustment dial provided on the operation unit of the copying machine. To explain this operation, the exposure lamp 3 has
An AC power supply 14 and a bidirectional thyristor 15 are connected in series. Further, a voltage generation circuit 16 is connected to the AC power supply 14, and when the bidirectional thyristor 15 is turned on, a voltage corresponding to the voltage across the exposure lamp 3 is extracted and a voltage corresponding to the effective value voltage of the output voltage is extracted. Is being output. This output voltage and the reference voltage 17 generated by the variable resistor connected to the exposure adjustment dial are compared by the comparator 18, and if there is a voltage difference between the two voltages, it is determined according to the magnitude of the difference. Output a signal. The output signal of the comparator 18 is input to the trigger pulse generation circuit 19. The trigger pulse generation circuit 19 outputs a trigger pulse synchronized with the frequency of the AC power supply 14 and compares the generation phase of the trigger pulse with the comparator 18
It is controlled according to the output signal of. The controlled trigger pulse is supplied to the gate of the bidirectional thyristor 15. Therefore, by changing the variable resistor for setting the reference voltage, the light quantity of the exposure lamp 3 is increased or decreased, and the light quantity according to the original can be selected.

In view of the above, the automatic exposure control apparatus of the present invention has been devised so that the reference voltage can be automatically changed according to the type of document, and will be described in detail with reference to the drawings. FIG. 3 is a block diagram showing an example of an automatic exposure control device according to the present invention. Reference voltage in Fig. 2
17 is generated by a variable resistor, but in the present invention, the reference voltage is the collector voltage of the transistor 20,
Is controlled according to the intensity of the reflected light from the document surface. To explain this configuration and operation, the reflected light from the original document irradiated by the exposure lamp 3 is detected by the photodetector circuit 21, and the output voltage thereof is input to the difference integrator 22. On the other hand, the fixed voltage 23 is also input to the difference integrator 22, and the difference between the output voltage of the photodetection circuit 21 and the fixed voltage 23 is integrated by the difference integrator. Therefore, the output voltage of the difference integrator 22 increases or decreases depending on the magnitude of the output voltage of the photodetection circuit 21 and the fixed voltage. The output signal of the differential integrator 22 is input to the base of the transistor 20 and controls the collector voltage. In this operation, when there is no voltage difference between the output voltage of the photodetection circuit 21 and the fixed voltage 23, the output voltage of the difference integration circuit 22 is held. Therefore, the base voltage of the transistor 20 is constant, and the collector voltage input to the comparator is constant. Therefore, the light quantity of the exposure lamp is kept constant by the operation described in FIG.

Next, when the output voltage of the light detection circuit 21 rises due to the reflected light of the original, a positive voltage is generated between the output voltage of the fixed voltage 23 and the output voltage of the integration circuit when the difference integrator 22 integrates the voltage difference. Will increase. Then, the base voltage of the transistor 20 increases, the internal resistance of the transistor 20 decreases, and the collector voltage decreases. Since the collector voltage is the input voltage of the comparator 18, the trigger pulse generating circuit 19 is controlled by the output voltage of the comparator 18 and the voltage (effective value) of the exposure lamp 3 decreases as described with reference to FIG. Therefore, the photodetector circuit 21
Output voltage decreases, and the voltage difference from the fixed voltage 23 decreases. By repeating these operations, the voltage difference between the output voltage of the photodetection circuit and the fixed voltage 23 becomes stable in a state of zero.

When the output voltage of the photodetector circuit 21 falls below the fixed voltage 23, a negative voltage difference occurs, so that the base voltage of the transistor 20 decreases and the collector voltage increases. Therefore, as described with reference to FIG. 2, the input voltage of the exposure lamp 3 increases and the output voltage of the photodetector circuit 21 also increases. Also in this case, the output voltage of the light detection circuit 21 and the fixed voltage 23 are stable in the state where there is no voltage difference.

It operates as described above. Actually, the response speed of the exposure lamp 3 is much slower than the response of the electric circuit, so that a delay occurs between these feedback loops and the exposure lamp pulsates. Explaining this pulsation further, the automatic exposure control circuit 24 outputs a control signal to match the reflected light from the exposure lamp 3 with the fixed voltage 23. However, the exposure lamp 3 exceeds the input voltage corresponding to the fixed voltage 23. To shoot.
Therefore, the automatic exposure control circuit 24 sends the reverse control signal again. However, it is considered that the exposure lamp pulsates due to repeated overshooting. If the circuit constants are appropriately selected, these are pulsations of about 40 Hz and their amplitude is 5 to 10% of the detection component of the reflected light from the original.
It was about. According to the experiment, the effect was hardly seen in the copying of the black and white binary document, but the pulsation was clearly confirmed in the document including the halftone.

In order to solve this, the automatic exposure control circuit 24 may be configured not to accurately respond to the minute pulsating component caused by the feedback loop.

FIG. 4 is a circuit diagram showing an embodiment of the present invention for removing the pulsation generated as described above in the automatic exposure apparatus of the present invention. The present invention is characterized in that a minute modulation signal is superimposed on the output voltage of the photodetector circuit.

In the circuit diagram of FIG. 4, the reflected light from the original is received by the photoelectric conversion element 25, and the output voltage current-voltage converted by the resistor 26 is composed of resistors 27, 28, 29, a capacitor 30, and an operational amplifier 31. An output voltage of a multivibrator circuit that constitutes an oscillation circuit that outputs a modulation signal of a predetermined amplitude and frequency is connected via a capacitor 32 and a resistor 33. The oscillation frequency of the multivibrator circuit is determined by the constants of the resistor 27 and the capacitor 30, and is set to about 400 Hz, for example. The ratio of the output voltage of the photoelectric conversion element 25 and the output voltage of the multivibrator circuit corresponds to the ratio of the resistors 34 and 33, so that the output voltage of the multivibrator circuit becomes equal to or greater than the pulsation amplitude,
Resistors 33 and 34 are set. The superimposed output voltage is designed so that an amplifier including an operational amplifier 35 and a variable resistor 36 can correct element variations on the circuit. The voltage difference between the output voltage of the amplifier and the output voltage determined by the resistance ratio of the resistors 37 and 38 is calculated by the operational amplifier 39, the capacitor 40, and the resistance.
Input to the differential integrator composed of 41. The output voltage of the differential integrator limits the base current of transistor 20 with resistor 42 and controls transistor 20. The collector voltage of the transistor 20 passes through the switch 43 and the comparator described in FIG.
Sent to 18. The switch 43 switches between the operation by the automatic exposure control and the operation by the exposure adjustment dial.

In this way, when a minute modulation signal is superimposed on the output voltage of the photoelectric conversion element 25, the output voltage of the photoelectric conversion element whose amplitude is less than or equal to the modulation signal is substantially not a control target. According to the experiment, the amplitude of this modulation signal is equal to or more than the pulsation amplitude described in FIG. 3, the frequency is about 5 times or more the pulsation frequency, and the exposure lamp is driven at a frequency corresponding to it. Since it becomes a pulsation with a very short cycle,
The influence of the image due to the pulsation became negligible.
This is because the blinking cycle of the exposure lamp corresponds to the cycle of the modulation signal, so that flicker can be ignored and the light quantity is substantially stabilized. In this embodiment, the frequency of the modulated signal is 400 Hz and the amplitude is 20 mV.

Further, in the present embodiment, a fixed voltage is set and controlled so that a photoelectric conversion output corresponding to the fixed voltage is obtained. However, the voltage corresponding to the output voltage of the difference integrator is superimposed on the fixed voltage to obtain the difference integrator. It is also possible to control by giving a hysteresis characteristic to.

Although the present embodiment describes the copying machine using the rod lens array, the same applies to a through lens type copying machine.

<Advantages of the Invention> According to the exposure control device of the copying machine of the present invention, a copy image can be formed with an optimum exposure amount according to the lightness and darkness of the original. At this time, since the drive of the exposure lamp can be controlled according to the reflected light from the original document to such an extent that the influence of the pulsation due to the delay of the response speed of the exposure lamp can be ignored, it is not limited to the black and white original document, and it can be applied to an image including a halftone. It is possible to irradiate light with a practically stable light amount, and it is possible to form a clear copy image.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing the internal structure of a copying machine according to the present invention, FIG. 2 is a control block diagram of an exposure lamp of the copying machine according to the present invention, and FIG. 3 is an automatic exposure control according to the present invention. FIG. 4 is a block diagram showing an example of the apparatus, and FIG. 4 is a circuit diagram showing an example in which the pulsation due to the exposure lamp of the present invention is removed. 1 ... original table, 3 ... exposure lamp, 4 ... rod lens array, 5 ... photoconductor, 12 ... photoelectric conversion element, 13 ... slit, 15 ... bidirectional thyristor, 21 ... photodetection Circuit, 22 ... Differential integrator, 23 ... Fixed voltage.

Front page continuation (72) Inventor Takao Tagawa 22-22 Nagaikecho, Abeno-ku, Osaka, Osaka Prefecture (56) References JP-A-57-22268 (JP, A) JP-A-57-124373 (JP, A) JP-A-50-49576 (JP, A) JP-A-48-59286 (JP, A)

Claims (1)

[Claims] 1. A copying machine configured to form an image by irradiating an original with an exposure lamp and guiding the irradiation light to a photoconductor, thereby generating a voltage corresponding to a voltage applied to the exposure lamp. A voltage generation circuit, a photodetection circuit for detecting reflected light from the original, an oscillation circuit for oscillating a modulation signal having a frequency higher than the pulsation frequency of the detection signal of the photodetection circuit, the detection signal of the photodetection circuit and the An adder circuit that adds the modulation signal of the oscillation circuit so that the amplitude of the modulation signal is larger than the amplitude of the detection signal, and outputs a signal according to the potential difference between the addition signal of the addition circuit and a predetermined fixed voltage. An automatic exposure control circuit configured by a differential integrator circuit that outputs a reference voltage according to a signal of the differential integrator circuit, an output voltage of the voltage generation circuit, and the automatic exposure control circuit A comparison circuit that compares a reference voltage and outputs a signal according to the comparison result, and a voltage supplied to the exposure lamp is controlled according to an output signal of the comparison circuit to control the light amount of the exposure lamp. An automatic exposure control device for a copying machine, comprising: a light amount control circuit;