JPS6080834A - Automatic control device for exposing for copying machine - Google Patents

Abstract

PURPOSE:To make a copying machine easier to operate by constituting a titled device in such a way that optimum copying is automatically accomplished against fluctuation in source voltage or with various originals. CONSTITUTION:An AC power source 14 and a bidirectional thyristor 15 are connected in series to an exposing lamp 3. A voltage forming circuit 16 is connected to the power source 14 and outputs the voltage corresponding to the voltage at both terminals of the lamp 3 when the thyristor 15 is turned on. The output voltage thereof and a reference voltage 17 are compared by a comparator 18 and the signal corresponding to the magnitude of the difference is outputted if there is a voltage difference. The output signal of the comparator 18 is supplied via a trigger pulse generating circuit 19 to the gate of the thyristor 15. The quantity of the light corresponding to the original is therefore selected by varying the variable resistance which sets the reference voltage. The copying machine is thus made easier to operate.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an automatic exposure control device for a copying machine that automatically controls the exposure amount of a light source according to the density of a document.

<Prior art> In general, in conventional copying machines, when copying originals with a dark background, such as case studies and blueprinted one-color originals, the amount of exposure is higher than when copying originals with a normal white background. and obtained optimal copy. Conventionally, these operations were performed by the operator operating the exposure adjustment dial provided on the operation panel, so the operator adjusted the exposure by looking at the shading of the original or after making a trial copy. The position of the dial was set. As a result, two to three sheets of copy paper were often wasted until the optimum copy was obtained.

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

<Embodiment> FIG. 1 shows a schematic operation of a copying machine according to the present invention,
FIG. A document table 1 on which an original is placed is configured to reciprocate in the direction of an arrow 2 as necessary. When the document table 1 moves forward, the document placed on it is illuminated by an exposure lamp 3. The reflected light is guided onto a photoreceptor 5 via a convergent light transmission array (Selfoc lens) 4, so that an image of the document is formed on the surface of the photoreceptor 5. Also, in synchronization with the reciprocating movement of the document table, the photoreceptor 5
The developing unit 8 rotates in the direction of arrow 6 and forms the density information of the original as a latent image on the photoreceptor 5 charged by the charger 7.The developer 8 visualizes this latent image on the photoreceptor 5. , the visible image is transferred by a transfer device 10 onto plain paper fed from a cassette 9 in synchronization with the rotation of the photoreceptor 5. The plain paper onto which the image has been transferred is further sent to a fixing device 1, which fixes the visible image on the plain paper, and then outputs it from the copying machine. The photoelectric conversion element 12 for detecting the density of the original used in automatic exposure control of the present invention is equipped with a selfoc lens 4 to receive a part of the reflected light from the original placed on the original platen 1.
A slit 13 is arranged parallel to the slit 13, and only the light that passes through the slit 13 is received by the photoelectric conversion element 12.

FIG. 2 is a control block diagram of the exposure control device according to the present invention. Although this is not shown, exposure adjustment is performed by operating an exposure adjustment dial provided on the operation section of the copying machine. To explain this operation, the exposure lamp 8 is connected in series with an AC power source 4 and a bidirectional thyristor 15. In addition, a voltage generation circuit]6 is connected to the AC power supply +4, and when the bidirectional thyristor 150 is turned on, it extracts a voltage corresponding to the voltage across the exposure lamp 30, and generates a voltage corresponding to the effective value voltage of the output voltage. It is outputting.

Comparator 1 compares this output voltage with the reference voltage generated by the variable resistor connected to the exposure adjustment dial.
8, and if there is a voltage difference between the two voltages,
A signal is output according to the magnitude of the difference. This comparator 1
The output signal of 8 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 controls the generation phase of the trigger pulse in accordance with the output signal of the comparator 18. The controlled trigger, 2s, is supplied to the gate of bidirectional thyristor 15. Therefore, by varying the variable resistor that sets the reference voltage, the amount of light from the exposure lamp 3 can be increased or decreased, and the amount of light can be selected depending on the document.

In view of the above, the automatic exposure control device of the present invention has been devised to be able to automatically change the reference voltage depending on 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. The reference voltage 17 in FIG. 2 is generated by a variable resistor, but in the present invention, the reference voltage is the collector voltage of a transistor 20, and the transistor 20 is controlled according to the intensity of light reflected from the surface of the original. To explain the configuration and operation of this device, the light reflected from the document irradiated by the exposure lamp 3 is detected by the photodetector circuit 21, and the output voltage thereof is input to the differential integrator 22. On the other hand, a fixed voltage 23 is also input to a differential integrator 22, and the voltage difference between the output voltage of the photodetection circuit 21 and the fixed voltage 23 is integrated by the differential integrator. Therefore, the difference integrator 2
The output voltage of 2 increases or decreases depending on the magnitude of the output voltage of the photodetector circuit 21 and the fixed voltage. The output signal of the differential integrator 22 is input to the base of the transistor 20 to control the collector voltage. In this operation, when there is no voltage difference between the output voltage of the photodetector circuit 21 and the fixed voltage 23, the output voltage of the differential 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, so the amount of light from the exposure lamp is kept constant by the operation described in FIG. 2.

Next, when the output voltage of the photodetector circuit 21 increases in response to the reflected light from the original, a positive voltage difference is generated between it and the fixed voltage 23, and when the voltage difference is integrated by the differential integrator 22, the output of the integrating circuit is The voltage increases. Then, the base voltage of the transistor 200 increases and the internal resistance of the transistor 20 decreases, so that the collector voltage becomes low. Collector voltage is comparator I8
As described in FIG. 2, the output voltage of the comparator 18 controls the tripper pulse generating circuit 19, and the voltage (effective value) of the exposure lamp 3 decreases. Therefore, the output voltage of the photodetector circuit 21 is lower than the fixed voltage 2.
The voltage difference with 3 becomes small.

By repeating these operations, the voltage difference between the output voltage of the photodetection circuit and the fixed voltage 23 becomes stable at zero.

When the output voltage of the photodetector circuit 21 falls below the fixed voltage 23, a negative voltage difference occurs, so the base voltage of the transistor 20 decreases and the collector voltage increases. Therefore, as explained in FIG. 2, the input voltage of the exposure lamp 3 increases, and the output voltage of the photodetector circuit 21 also increases. In this case as well, the voltage is stabilized with no voltage difference between the output voltage of the photodetector circuit 21 and the fixed voltage 23.

It works as described above. In reality, the response speed of the exposure lamp 3 is much slower than the response of the electric circuit, so a delay occurs between these feedback loops, causing the exposure lamp to pulsate. To further explain this pulsation, the automatic exposure control circuit 24 outputs a control signal to make the reflected light from the exposure lamp 3 match the fixed voltage 23, but the exposure lamp 3 does not exceed the input voltage corresponding to the fixed voltage 23. Shoot.

Therefore, the automatic exposure control circuit 24 sends a reverse control signal again. However, the exposure lamp is thought to cause pulsation due to repeated overshooting. If the circuit constants are selected appropriately, these pulses have a frequency of about 40 Hz, and the amplitude is 5 to 1 liters of the detected component of the reflected light from the original.
It was about 0%.

According to experiments, this effect was hardly seen when copying black and white binary originals, but pulsation was clearly visible on originals containing halftones.

In order to solve this problem, it is preferable to configure the automatic exposure control circuit 24 so that it does not respond accurately to minute pulsating components caused by the feedback loop.

FIG. 4 shows a second embodiment of the present invention in which this pulsation is removed, in which a minute modulation signal is superimposed on the output voltage of the photodetector circuit.

In the circuit diagram of FIG. 4, reflected light from the original is received by a photoelectric conversion element 25, and an output voltage obtained by converting current to voltage by a resistor 26 is converted to an output voltage by resistors 27, 28, 29, and a capacitor 30. The output voltage of a multivibrator circuit composed of an operational amplifier 31 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 capacitor 30, and is approximately 400 Hz, for example.
It is set to . 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 resistor 34 and the resistor 33, and the resistors 33 and 34 were set so that the output voltage of the multivibrator circuit exceeds the pulsation amplitude. . The superimposed output voltage is applied to the operational amplifier 35. The amplifier composed of the variable resistor 36 is designed to correct variations in elements 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 measured by the operational amplifier 39. Capacitor 40. It is input to a differential integrator composed of a resistor 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 transistor 20 is sent through switch 43 to comparator I8 described in FIG. The switch 43 is used to switch between automatic exposure control and exposure adjustment dial operation.

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 the amplitude of the modulation signal is not substantially controlled.

According to experiments, the amplitude of this modulation signal was greater than the pulsation amplitude explained in FIG. 3, and its frequency was about five times the pulsation frequency or more, so that the pulsation of the exposure lamp was almost negligible.

In this example, the modulation signal has a frequency of 400 Hz and an amplitude of 20 mV.

Further, in this embodiment, the capacitor 40 constitutes the differential integrator, but there is no problem in operation even if the capacitor 40 is omitted and the differential integrator is operated as a comparator in order to operate in conjunction. In this case, transistor 20 is controlled by the effective value of the output voltage of the comparator.

In addition, in this example, a fixed voltage was set and control was performed so that a photoelectric conversion output corresponding to the fixed voltage was obtained, but by superimposing a voltage corresponding to the output voltage of the differential integrator on the fixed voltage, It is also possible to control by providing a special hysteresis.

In this embodiment, a copying machine using a SELFOC lens has been described, but the same applies to a copying machine using a through-lens type.

<Effects of the Invention> As detailed above, according to the present invention, the light/darkness information of the original is detected and controlled by the light detection circuit, so that the optimum exposure amount can be automatically obtained for various originals. Therefore, optimal copying can always be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing the internal configuration 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 a first embodiment of the present invention. FIG. 4 is a block diagram showing an example, and is a circuit diagram showing a second embodiment in which pulsation of the exposure lamp of the present invention is eliminated. l...Original table, 3...Exposure lamp, 4...Selfoc lens, 5...Photoconductor, 12...Photoelectric conversion element, 13...S, lit, I5...Bidirectionality Cyrisk, 21...], Optical inspection circuit, 22... Differential integrator, 23... Fixed voltage.

Claims (1)

[Scope of Claims] (1) A copying machine configured to form an image by irradiating an original with an exposure lamp and guiding the reflected light to a photoreceptor, which corresponds to the voltage applied to the exposure lamp. an automatic exposure control circuit that generates a reference voltage according to the density of the document; and a signal that compares the output voltage of the voltage generation circuit with the reference voltage and that corresponds to the comparison result. An automatic exposure control device for a copying machine, comprising a comparator that outputs a signal, and a control circuit that controls the amount of light from the exposure lamp according to the output signal of the comparator. 2. The automatic exposure control circuit includes a photodetection circuit that detects reflected light from the document, and a differential integration circuit that outputs a signal according to the voltage difference between the output voltage of the photodetection circuit and a preset fixed voltage. 2. The automatic exposure control device for a copying machine according to claim 1, wherein the automatic exposure control device includes: and a circuit that outputs a reference voltage according to the signal of the differential integration circuit. 3. The automatic exposure control circuit includes the photodetection circuit, an addition circuit that adds a modulated voltage of a predetermined frequency or higher to the output voltage of the photodetection circuit, and an output voltage of the addition circuit and a predetermined fixed voltage. A copying machine according to claim 1, characterized in that the copying machine is comprised of a differential integration circuit that outputs a signal according to the voltage difference between the two and a differential integration circuit, and a circuit that outputs a reference voltage according to the signal of the integration circuit. automatic exposure control device.