JPH0448377B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure control device for a copying machine that controls the amount of exposure in an electronic copying machine that uses a fluorescent lamp as an exposure light source, for example.

Conventionally, in an electronic copying machine that uses a fluorescent lamp as the light source for exposure, when changing the exposure amount, the amount of light from the fluorescent lamp is constant, and by changing the aperture amount of the aperture mechanism provided in the projection lens system, The surface illuminance of the photoreceptor drum was changed. However, in such a conventional method, the mechanism for connecting the exposure dial provided on the operation panel and the aperture mechanism is extremely complicated, and since it is performed mechanically, it lacks reliability and operability. Furthermore, there was a problem in that the amount of light from the fluorescent lamp changed due to fluctuations in the power supply voltage, resulting in changes in the amount of exposure.

The present invention has been made in view of the above circumstances, and its purpose is to improve reliability and operability by controlling the light amount of a fluorescent lamp by electronic phase angle control, and to improve the reliability and operability of the fluorescent lamp. It is an object of the present invention to provide an exposure control device for a copying machine that has little variation in the amount of light from a fluorescent lamp even when the voltage changes and can always provide a stable amount of exposure.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 schematically shows an electronic copying machine according to the present invention, in which a document table 1 on which a document is placed is configured to reciprocate in the direction of arrow a as necessary. When the document table 1 moves forward, the document placed thereon is irradiated by the fluorescent lamps 2, 2, and the reflected light is transmitted to the mirror 4 supported by the optical system block 3, the lens mechanism 5, and the document placed thereon. The document is guided to a photosensitive drum 7 via a mirror 6, and an image of the document is formed on the surface of the photosensitive drum 7.
The photosensitive drum 7 rotates in the direction of arrow b, is first charged by a charger 8, and then the image of the document is exposed to light to form an electrostatic latent image on the surface of the photosensitive drum 7. This electrostatic latent image is made visible by applying toner by a developing device 9. On the other hand, the transfer paper in the cassette 10 is sent out by a paper feed roller 11 that operates according to the rotation of the photoreceptor drum 7, and transferred to a conveyance roller 12.
transported by The transferred transfer paper comes into close contact with the surface of the photoreceptor drum 7 at the transfer charger 13, and the toner image on the photoreceptor drum 7 is transferred by the charger 13. The transfer paper after transfer is transferred to the photosensitive drum 7 by a peeling charger 14.
The transferred image is fixed by being peeled off from the surface and sent to a fixing device 16 by a conveyance roller 15. After fixing, the transfer paper is transferred to a paper ejection roller 17.
The paper is discharged onto a tray 18 by the following means. On the other hand, the photosensitive drum 7 after the transfer is transferred to the static eliminator 1.
9, and the fluorescent lamp 20
The electrostatic latent image is erased by the cleaner 21, and finally cleaned by the cleaner 21.
It is starting to return to its initial state.

A photodetecting element, for example, a photodiode 22 is provided in the optical path between the lens mechanism 5 and the mirror 6 in the optical system block 3, and this diode 22 is connected to the optical system by a mounting member 23. Fixed to block 3. The photodiode 22 detects a part of the light reflected from the document by the fluorescent lamp 2 and converts it into an electrical signal, and is used in the photodetection circuit (see 36 in FIGS. 2 and 3) to be described later. It constitutes a photodetector.

FIG. 2 schematically shows an exposure control device according to the present invention, in which a ballast circuit 33 is connected to a commercial AC power source 31 via a bidirectional thyristor 32.
The fluorescent lamp 2 is connected to this ballast circuit 33. Further, a power supply circuit 34 is connected to the power supply 31, and a voltage generation circuit 34 is connected to the power supply circuit 34.
5. Power supply voltage is supplied to the photodetection circuit 36 and the trigger pulse generation circuit 37, respectively. The voltage generating circuit 35 is linked to an exposure dial on an operation panel (not shown), and outputs a voltage signal according to the set value of the exposure dial.
Further, the light detection circuit 36 detects reflected light from the original and outputs a voltage signal corresponding to the detected amount of light. The output voltage of the voltage generation circuit 35 is supplied to the trigger pulse generation circuit 37 through the b side of the selection switch 38, and the output voltage of the photodetection circuit 36 is supplied to the a side of the selection switch 38, respectively. The trigger pulse generation circuit 37 is connected to the power supply 3
A switch 3 that outputs a trigger pulse synchronized with the frequency of 1 and selects the generation phase of the trigger pulse.
The controlled trigger pulse is supplied to the trigger circuit 39. This trigger circuit 39 widens the width of the trigger pulse supplied to the thyristor 3.
By applying voltage to the gate of thyristor 3,
2.

The operation of FIG. 2 in such a configuration will be explained. First, let's talk about the case where the selection switch 38 is set to side a. In this case, the fluorescent lamp 2
The light from the document is reflected by the original and enters the photodetection circuit 36, so the photodetection circuit 36 outputs a voltage corresponding to the amount of incident light, and this output voltage is sent to the trigger pulse generation circuit 37 via the selection switch 38. supplied to Assuming that the output voltage of the photodetection circuit 36 is low when the amount of incident light is small, in the case of an original with a dark background, there is little reflected light from the original, and therefore the output voltage of the photodetection circuit 36 is low. As a result, the trigger pulse generating circuit 37 and the trigger circuit 39 control the thyristor 32 so that its conduction angle increases, and the amount of light from the fluorescent lamp 2 increases.
On the other hand, in the case of a document with a thin background, the amount of light reflected from the document increases, and therefore the output voltage of the photodetection circuit 36 is high. As a result, the trigger pulse generating circuit 37 and the trigger circuit 39 control the thyristor 32 so that its conduction angle becomes small, and therefore the amount of light from the fluorescent lamp 2 decreases. In this way, control is performed so that the amount of light reflected from the original is always constant as a whole, so that the optimum amount of exposure can always be obtained regardless of the density of the original. Furthermore, since the reflected light from the original is detected, control can be performed to compensate for fluctuations in the power supply voltage.

Next, we will discuss the case where the selection switch 38 is set to the b side. In this case, the voltage generation circuit 3
As mentioned above, the reference numeral 5 is connected to an exposure dial (not shown), and outputs a voltage signal according to the setting value thereof. Therefore, the output voltage is supplied to the trigger pulse generation circuit 37 via the selection switch 38. Thereby, the trigger pulse generation circuit 37 and the trigger circuit 39 control the conduction angle of the thyristor 32 according to the output voltage of the voltage generation circuit 35, and change the light amount of the fluorescent lamp 2. in this way,
The amount of light from the fluorescent lamp 2 can be electronically controlled simply by operating an exposure dial, thereby improving reliability and operability. Further, detailed explanation will be given later, but the trigger pulse generation circuit 37
The trigger pulse generation phase is variably controlled in accordance with fluctuations in the power supply voltage. for example,
As the power supply voltage increases, the timing of trigger pulse generation becomes delayed, the conduction angle of the thyristor 32 becomes smaller, and the amount of light from the fluorescent lamp 2 decreases.
On the other hand, when the power supply voltage decreases, the trigger pulse generation timing becomes faster, the conduction angle of the thyristor 32 becomes larger, and the amount of light from the fluorescent lamp 2 increases. In this way, by detecting fluctuations in the power supply voltage and controlling the amount of light from the fluorescent lamp, a stable exposure amount can always be obtained even with fluctuations in the power supply voltage.

FIG. 3 specifically shows each circuit in FIG. 2. The primary coil of a transformer 41 is connected to the power source 31, and one end of the secondary coil of this transformer 41 is connected to the first anode of the thyristor 32. be done. The other end of the secondary coil of the transformer 41 is connected to the gate of the thyristor 32 via a bidirectional trigger thyristor 42 and a resistor 43 in series.
Here, the transformer 41, thyristor 42, resistor 43, etc. constitute a trigger circuit 39. Further, a full-wave rectifier 44 is connected to the power source 31. And the DC output terminal P of this rectifier 44,
A smoothing capacitor 45 and a resistor 46 are connected between N.
and Zener diodes 47 and 48 are connected in series. Here, the rectifier 44, capacitor 45, resistor 46 and diode 47,
48 constitutes the power supply circuit 34.

In addition, the output terminal P and the diodes 47, 48
Resistors 49, ₅₀ and a Zener diode 51 are connected in series between the connection point O1 and the connection point _O2 between the resistor 50 and the diode 51, and the anode of the diode 52. The cathode of the diode 52 is connected to a programmable union transistor (hereinafter simply PUT).
) 53, and is also connected to the connection point _O1 via a capacitor 54. The cathode of the PUT 53 is connected to the connection point via the primary coil of the pulse transformer 55.
The _secondary coil of the pulse transformer 55 is connected between the gate of the thyristor 42 constituting the trigger circuit 39 and the first anode. Further, the connection point _O3 between the resistors 49 and 50 is
It is connected to the gate of PUT 53 through a level shift diode 56 and a resistor 57 in series, and this connection point is connected to the connection point _O1 through resistors 58 and 59 in series. However, the resistor 58
The connection point O ₄ between and 59 is connected to the output terminal of the selection switch 38 . Here, the above diode 5
1, 52, 56, PUT 53, capacitor 54, pulse transformer 55, etc. constitute a trigger pulse generation circuit 37.

On the other hand, the cathode of the photodiode 22 is connected to the connection point O ₁ in the power supply circuit 34 and also to the non-inverting input terminal of the operational amplifier 60 . The anode of the diode 22 is connected to the inverting input terminal of the operational amplifier 60, and is also connected to the output terminal of the operational amplifier 60 via a feedback resistor 61 and a capacitor 62 in parallel. The output terminal of the operational amplifier 60 is
It is connected to the inverting input terminal of another operational amplifier 64 through a resistor 63, and this connection point is connected to the output terminal of the operational amplifier 64 through a feedback resistor 65 and a capacitor 66 in parallel. Further, the non-inverting input terminal of the operational amplifier 64 is connected to the output terminal N in the power supply circuit 34 via a resistor 67, and is also connected to the connection point _O1 in the power supply circuit 34 via a resistor 68. . The output terminal of the operational amplifier 64 is connected to the a side of the selection switch 38 via a resistor 69. Here, the photodiode 22, operational amplifiers 60, 64, etc. constitute a photodetection circuit 36.

Further, a series circuit of a resistor 70, a variable resistor 71, and a resistor 72 is connected between a connection point _O5 and a connection point _O1 between the resistor 46 and the diode 47 in the power supply circuit 34. The slider of the variable resistor 71 is connected to the b side of the selection switch 38. The variable resistor 71 is adapted to be linked to an exposure dial on an operation panel (not shown).
Here, the resistors 70, 72 and the variable resistor 7
1 constitutes a voltage generation circuit 35.

The operation of FIG. 3 in such a configuration will be explained. First, the case where the selection switch 38 is set to the a side will be described. In this case, voltage generation circuit 3
5 becomes irrelevant to the exposure control described below.
Now, when the power supply 31 is turned on, the power supply circuit 34 operates, and power supply voltage is supplied to each circuit. Then, trapezoidal wave voltages are generated at the connection points O ₂ and O ₃ , respectively.
The voltage generated at the connection point O ₃ above is the voltage generated at the diode 5
6 and resistors 57 to 59,
Applied to the gate of PUT53. When the power supply voltage rises from the zero cross point, the voltage at the connection point _O2 also rises, and this causes the diode 5 to
2, the capacitor 54 is charged through PUT5
The anode voltage of 3 increases. And PUT5
When the anode voltage of 3 becomes higher than the gate voltage
PUT 53 is turned on, and a pulse current flows through the primary coil of pulse transformer 55. Therefore,
A pulse is generated in the secondary coil of the pulse transformer 55, which becomes a trigger pulse and activates the thyristor 42.
is applied to the gate of As a result, thyristor 4
2 is turned on and current flows through the secondary coil of the transformer 41, a gate current of the thyristor 32 flows through the resistor 43, so the thyristor 32 is turned on and supplies current to the ballast circuit 33, causing the fluorescent light to emit light. Turn on lamp 2.

On the other hand, the light from the fluorescent lamp 2 is reflected by the original and guided to the photosensitive drum 7, but a part of the reflected light is incident on the photodiode 22. A detection current of the photodiode 22 caused by the incident light is converted into a voltage by an operational amplifier 60 and a resistor 61. At this time, the larger the amount of incident light, the larger the detection current, and the output voltage of the operational amplifier 60 becomes a large negative voltage. The output voltage of this operational amplifier 60 is supplied to an operational amplifier 64, and is inverted and amplified by the operational amplifier 64 at a ratio of resistors 63 and 65. The output voltage of this operational amplifier 64 is
9 and the selection switch 38 to the connection point O ₄ of the trigger pulse generation circuit 37 . When the background of the original is dark, the amount of reflected light is small and the detection current of the photodiode 22 is also small, so the operational amplifier 6
An output voltage of 0 becomes a small negative voltage. For this reason,
The output voltage of the operational amplifier 64 becomes a low voltage, and therefore the voltage applied to the connection point _O4 also becomes low, so that the conduction angle of the fluorescent lamp 2 becomes large and the amount of light increases. That is, when the voltage applied to the connection point _O4 is lowered, the gate voltage of the PUT 53 is also lowered, and the timing at which the PUT 53 is turned on becomes faster. This speeds up the trigger pulse generation timing, increases the conduction angle of the thyristor 32, and thus increases the amount of light from the fluorescent lamp 2. Note that when the background of the document is thin, the operation is opposite to the above case, and the amount of light from the fluorescent lamp 2 is reduced. In this way, the amount of light from the fluorescent lamp 2 is controlled according to the density of the document, and thereby the optimum amount of exposure can always be automatically obtained for various documents.

Next, the case where the selection switch 38 is set to the b side will be described. In this case, the photodetection circuit 36 becomes irrelevant to the exposure control described below. Since the variable resistor 71 is linked to the exposure dial, its resistance value changes depending on the setting position of the exposure dial, and therefore, a voltage corresponding to the resistance value is applied to the trigger pulse generation circuit 37 via the selection switch 38. Applied to connection point O ₄ . That is, variable resistor 71
As the slider is moved in the direction of arrow A, the voltage applied to the connection point _O4 becomes higher, and therefore, as described above, the trigger pulse generation timing is delayed, the conduction angle of the thyristor 32 is reduced, and the fluorescence is emitted. The light intensity of lamp 2 decreases. On the other hand, the more the slider of the variable resistor 71 is moved in the direction of arrow B, the more
The voltage applied to O ₄ becomes lower, and therefore, as mentioned above, the timing of trigger pulse generation becomes faster.
The conduction angle of the thyristor 32 increases and the fluorescent lamp 2
The amount of light increases. In this way, the amount of light from the fluorescent lamp 2 is controlled in accordance with the setting operation of the exposure dial on the operation panel, and a desired amount of exposure can be obtained arbitrarily.

Further, when the power supply voltage fluctuates, the exposure amount is controlled according to the voltage fluctuation. That is, a divided power supply voltage is applied to the gate of the PUT 53 in the trigger pulse generation circuit 37, and therefore, the gate voltage of the PUT 53 changes in accordance with fluctuations in the power supply voltage. Therefore, for example, when the power supply voltage increases, the gate voltage of the PUT 53 increases, and as a result, the conduction angle of the thyristor 32 decreases through the above-described operation, and the amount of light from the fluorescent lamp 2 decreases. On the other hand, when the power supply voltage decreases, the gate voltage of PUT53 decreases, and therefore, through the above-mentioned operation, the thyristor 3
The conduction angle of the fluorescent lamp 2 increases, and the amount of light from the fluorescent lamp 2 increases. In this way, by detecting the power supply voltage and controlling the amount of light from the fluorescent lamp 2 in accordance with its fluctuations, a stable exposure amount can always be obtained even with fluctuations in the power supply voltage.

Note that the term "copying machine" as used in the present invention includes not only electronic copying machines but also facsimile machines, image information storage and retrieval devices, etc. that have an equivalent exposure mechanism.

As described in detail above, according to the present invention, by controlling the light intensity of a fluorescent lamp as an exposure light source by electronic phase angle control, reliability and operability are significantly improved, and the power supply voltage is reduced. It is possible to provide an exposure control device for a copying machine that can obtain various effects such as little variation in the amount of light from a fluorescent lamp and a stable amount of exposure at all times.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention, in which FIG. 1 is a side view showing the schematic structure of an electronic copying machine, and FIG. 2 is a block diagram showing the overall schematic structure of an exposure control device. 3 are block diagrams specifically showing each circuit in FIG. 2. 1... Original table, 2... Fluorescent lamp, 7... Photoconductor drum (photoconductor), 22... Photodiode (light detection element), 31... AC power supply, 32... Thyristor, 33... Stability 35... Voltage generation circuit, 36... Photo detection circuit, 37... Trigger pulse generation circuit, 38... Selection switch, 39... Trigger circuit.

Claims (1)

[Scope of Claims] 1. A copying machine configured to expose an image by irradiating a document with a fluorescent lamp and guiding light from the document resulting from the irradiation to a photoreceptor, comprising: A thyristor connected between an AC power source that supplies an AC voltage, a light detection circuit that detects light from the document and converts it into a voltage signal, and a voltage generation circuit that can arbitrarily vary the voltage signal. , a selection means for selecting either the output signal of the voltage generation circuit or the output signal of the photodetection circuit; a power supply circuit for outputting a voltage signal according to voltage fluctuations in the voltage of the AC power supply; Trigger means for triggering the thyristor with a trigger pulse obtained by controlling pulses generated in synchronization with the voltage cycle of the AC power supply according to the output signal and the output signal selected by the selection means. An exposure control device for a copying machine characterized by the following.