JPH0731429B2 - Control device for electrophotographic copying machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting the image density of a toner image formed on a photoconductor of an electrophotographic copying machine and controlling the copying machine using the detected value.

[0002]

2. Description of the Related Art Conventionally, in this type of copying machine, a device for automatically controlling the amount of toner supply and a developing bias voltage are used as a device for maintaining a constant image quality of the obtained copy, especially the density of the copied image. A device for controlling the device is used. These devices improve the stability of image quality by detecting changes in the amount of transmitted light, electric resistance, magnetic resistance, etc. of the developer and automatically maintaining the toner content in the developer at a constant level. .

[0003]

However, in these devices, since the toner content is controlled to be constant even when the developer, the exposure lamp, etc. are deteriorated or the humidity is increased, a copy obtained in the opposite way can be obtained. Image quality deteriorates. In particular, a copying machine using a magnetic brush developing device has a drawback that it is susceptible to these effects. Therefore, the present applicant has previously proposed that a toner supply device, a developing bias voltage, a charger, an exposure system, and the like are comprehensively controlled, especially in the vicinity of a document table, in order to improve the drawbacks of the conventional control device. A toner image of the arranged reference target is formed on the photoconductor, and the image density detected from this toner image is compared and judged with a preset reference value, and the toner supply amount to the developing device is controlled according to the judgment result. Of an electronic copying machine in which at least one of image forming conditions such as a bias voltage applied to a developing electrode of the developing device or a charging current of a charging device is controlled by a predetermined control mode output from a central control circuit. I applied for a control method. According to this control method, it is possible to always obtain more stable image quality.

Here, in order to detect the image density of the toner image, it is general to detect the reflected light from the toner image by a detector. Since such a detector has a structure in which a light emitting element and a light receiving element are arranged so as to face a toner image formed on the surface of the photoconductor, the detection output is naturally generated when the light receiving element or the light emitting element is contaminated by adhesion of toner or the like. As a result, the toner density of the toner image cannot be correctly detected. Therefore, in the previously applied control method, a gain adjustment circuit is provided in the detection device, and reflected light from the surface of the photoconductor on which a toner image is not formed (hereinafter referred to as a reference surface) is provided prior to the actual toner density detection operation. The gain of the amplification circuit provided on the output side of the detector is set based on the detection result.

With this configuration, the detector output is increased according to the degree of contamination of the detector, and even if the detector is somewhat contaminated, the toner density of the toner image is not affected by the contamination of the detector. Can be correctly detected and the above-mentioned drawbacks can be solved. However, there is a limit to the method of avoiding the influence of the detector contamination due to the toner and the like by adjusting the gain of the amplification circuit, and when the degree of the contamination is remarkable, the detection operation cannot be performed sufficiently. The control of the image forming condition is not properly performed according to the toner density of the toner image, and the image quality is poor.

This means that when an operator makes a copy with poor image quality, it is impossible to judge whether the cause is malfunction of the control system or contamination of the detector, and the maintainability is lowered. The present invention has been made in view of the above circumstances, and an object of the present invention is to allow an operator to display a detector for detecting a toner density of a toner image formed on a photoconductor so as to display a stain on the detector. It is an object of the present invention to provide an image density detecting device for an electrophotographic copying machine, which facilitates cleaning.

[0007]

Means and Actions for Solving the Problems A latent image of a reference target is formed on a photoconductor, the latent image of the reference target is developed to form a toner image of the reference target, and the reflection image includes a light emitting element and a light receiving element. The toner density of the toner image of this reference target is detected by the detector consisting of the type sensor,
The control apparatus for an electrophotographic copying machine to control the copying condition based on the toner image of the detected reference target, the
A preamplifier that amplifies the output from the opposite sensor and this
It has a main amplifier connected to the output side of the reamp,
By detecting the photoconductor before the latent image of the reference target is formed on the photoconductor by the detector,
A circuit for controlling the gain of the main amplifier to obtain a constant final amplification output; and the constant final amplification before the latent image of the reference target is formed on the photoconductor. So that you can get the output
A change in the sensor output is compensated by providing a means for determining whether the final output of the circuit is within a certain level and displaying when the output is below a certain level .
Display operation near the limit where
It

[0008]

EXAMPLE FIG. 1 shows an electronic copying machine in which a control device according to the present invention is adopted, and a document table 2 for placing a document (not shown) is provided on an upper part of a copying machine main body 1. Below the document table 2 and the reference target 3. As shown in FIG. 1, the exposure lamp 4 is provided to move along the document table, this exposure lamp 4 is original and reference target 3 to be able to exposure ing. The reflected light from the document or the reference target 3 reaches the photoconductor 6 in the copying machine main body 1 through the optical system 5 and forms an electrostatic latent image on the peripheral surface of the photoconductor 6 charged by the charger 25. The electrostatic latent image on the photoconductor 6 is developed into a toner image by the next developing device 7. The developing device 7 has a developing electrode 8 to which a high voltage is applied along the peripheral surface of the photoconductor 6, and by a developer containing toner supplied from a toner supply device 9,
The electrostatic latent image on the photoconductor 6 is developed. Above the developing device, the reference target 3 formed on the photoconductor 6 is formed.
A detector 10 is provided to detect the density of the toner image.

As shown in FIG. 2, the detector 10 is a reflection type sensor comprising a light emitting element 10a such as a light emitting diode and a light receiving element 10b such as a phototransistor, and is formed outside the effective copy surface on the photoconductor 6. Is provided at a position corresponding to the toner image B of the reference target 3,
From this toner image, the density of the toner image and the density of the background portion can be detected. That is, the detection signal detected by the light receiving element 10b of the detector 10 is amplified to a signal of an appropriate level by the amplification circuit 12 shown in FIG. 3, and then sample-held by the sample-hold circuit 15. The amplification circuit 12 includes a detector 10 and a drift compensation circuit (ALC) 13 for compensating for a drift amount generated in the amplification circuit 12, and a level generated when the detector 10 is contaminated by toner. Gain adjustment circuit (AGC) 14 for maintaining a constant output even when the output voltage drops.
The drift compensation circuit 13 among these circuits 13 and 14 is composed of a differential amplifier 33 and a hold circuit 34 as shown in FIG. 4, for example, and operates as follows. That is, the differential amplifier 33 and the hold circuit 34 are provided for a specified time, for example, a few tens of msec, during a few hundred msec immediately after the start switch (not shown) of the main body of the copier 1 is pressed and the main body 1 of the copier 1 starts to operate. The analog switch 31 provided between the two is turned on, and the drift potential generated in the detector 10 and the amplification circuit 12 is charged and stored in the capacitor 32. At this time, the detector 1
The 0 light emitting element 10a is turned off.

Next, this value is fed back to one input side of the differential amplifier 33 through the hold circuit 34, and when the detector 10 detects the toner image of the reference target 3,
Since the drift component included in the signal is canceled, only the true detection signal detected from the toner image is amplified and output to the output side of the differential amplifier 33, and its value is output. (V ₀ ) is as follows. V ₀ = (R ₁ + R ₂ ) R ₄ V _IN / (R ₃ + R ₄ ) R ₁
-R ₂ V _H / R _{1 If} R ₁ = R ₃ and R ₂ = R _4, then V ₀ = R ₂ (V _IN −V _H ) / R ₁ . Here, if the formula is rewritten as V _IN = (V _s + V _b ), V _b = V _H, V _{s is the} true signal V _{b is the} drift potential V _{H is the} hold potential. _{V 0 = R 2 {(V} s + V b) -V b} / R 1 = R 2 V s
/ R ₁ , and the output voltage V ₀ is amplified and output only for the true signal.

The gain adjusting circuit 14 is shown in FIG.
It is configured as shown in (a) and operates as follows. That is, the gain adjustment circuit 14 controls so that the detection voltage is always constant even if the value of the reflected light on the surface of the photoconductor 6 that has not been exposed and developed changes due to dirt on the detector 10. Works like. When a start switch (not shown) of the copying machine main body 1 is pressed, the drift compensating circuit 13 operates to compensate the drift amount of the detector 10 and the amplification circuit 12. After that, prior to the density detection of the toner image, the detector 10 and the amplification circuit 12 are operated for several tens of msec, and the detector 10 detects the reflected light on the surface (reference surface) of the photoreceptor 6 which has not been exposed and developed. . That is, when the reflected light is input to the phototransistor 20 serving as the light receiving element 10b, the phototransistor 20 outputs a detection signal proportional to the amount of light. Then, this signal is amplified by the operational amplifier 21 of the preamplifier 12a. . Then, this output is input to an operational amplifier (error amplifier) 35 which functions as a main amplifier 12b for setting the gain of the gain adjusting circuit 14, and the output of the differential amplifier 3
The output from 8 is input to the attenuator 42 including a field effect transistor or the like connected to one input side of the error amplifier 35 when the analog switch 41 provided on the output side is turned on, and the gate voltage (VGS). And the value is stored in the capacitor 43.

That is, if the output V _{0 of the} error amplifier 35 is high (when the detector 10 is not dirty), the error amplifier 3 is
5 operates so that the input V _IN becomes small, and conversely, if it is low, the attenuator 42 is controlled so that the input V _IN becomes large so that the output V ₀ is constantly increased regardless of dirt on the detector 10. It is output to the width circuit 12 to control the gain of the widening circuit 12, and the output of the widening circuit 12 is output to the processor 37.
The sample and hold unit 15 holds the sample signal according to the sequence signal output from the sample and hold unit 15.

According to the present invention, in the control device of the electrophotographic copying machine as described above, the reflected light from the toner image is received,
A means for detecting and displaying the dirt of the detector to be detected is prepared. As such a display means,
There is a reference example based on FIG. 3 in which the main circuit is shown in FIG. 5A and an embodiment in FIG. 5B in which the main circuit is shown in FIG. 6, and the reference example is the gist of the present invention. And not. First, in the reference example of the present invention, the output of the preamplifier 21 is input to the level shift circuit 16, and the latch circuit 1
It is connected to the display circuit 18 via 7. The level shift circuit 18 is configured to output a display signal only when the output of the preamplifier 21 drops below a predetermined level, and the predetermined level is the operation limit of the gain adjusting circuit 14 and the fluctuation of the detection signal. It is decided considering the amount.

The display circuit 16 operates as follows. That is, when the operation of the copying machine main body 1 is started, the reset signal R ₁ is input to the flip-flop 24, which serves as the latch circuit 17, to be reset, and the output of the preamplifier 21 is input to the operational amplifier 35. When it is closed, it is also input to the level shift circuit 16. This level shift circuit 16 has an analog switch 22 on the circuit diagram.
It is a Zener diode immediately after, and the display operation is controlled by its set voltage value. Here, the opening / closing timing of the analog switch 22 is outside the period in which a latent image is formed on the photoconductor, and the non-image area or the cleaned image area of the photosensitive material of the photoconductor is below the sensor. For example, an appropriate period within the period in which the preamplifier output is obtained is selected. That is, the determination timing can be freely determined by a command from the central control circuit 42 such as turning on / off the analog switches 22 and 31 of the determination circuit according to a command from the central control circuit 42. Note that this timing control is performed by a method similar to that in which the processor 37 controls timing for drift compensation, AGC, sample hold, etc. in FIG. 3, but such timing control by the processor is well known. Since this is a technology, its details are omitted.

Then, the light reflected from the reference surface deteriorates because the detector 10 becomes dirty due to the adhesion of toner or the like, and the preamplifier 2
When the output of 1 becomes equal to or less than the predetermined value, the output of the flip-flop 24 becomes H (High) and outputs the display signal. Since this display signal is input to the base of the display circuit switching transistor 25 and turned on, the light emitting diode 26 is turned on. This allows the operator to use the detector 10
Can be detected as being highly contaminated.

In the above reference example, the level shift circuit 16,
Since the display means including the latch circuit 17 and the display circuit 18 is operated by the output of the preamplifier 12a, the sensor output is input to the dirt display circuit immediately after the preamplifier 12a, so that the change in the sensor output can be directly detected in real time. Therefore, there is an effect that the limit of dirt can be detected earlier. On the other hand, in the embodiment of the present invention shown in FIG. 6, the display means utilizes the output of the differential amplifier 38 of the output of the error amplifier 35 of the value derived from the detection value of the light receiving element. It is operated, and becomes an operating state when the analog switch 22 is closed. The timing of opening and closing the analog switch 22 in this embodiment is the first.
Similar to the embodiment, it is based on the control of the processor 37, but such timing may be any time during the AGC operation in the embodiment. In the embodiment having such a configuration, the sensor output is input to the dirt display circuit through the AGC, so that the display operation is performed near the limit where the change in the sensor output cannot be compensated. Therefore, the limit (contamination limit) that supports the control of the various control circuits 4 can be detected, and malfunctions can be reduced.

As described above, in the present invention, the determination timing may be any time after the power is turned on and before the development.
Then, the output of the amplification circuit 12 is held by the sample hold circuit 15 as shown in FIG. 7, and compared with the reference density signal input from the reference circuit 41 by the comparison circuit 40 at the next stage, and the result is in the center. It is input to the control circuit 42. The central control circuit 42 selects a control mode according to the density determination result input from the comparison circuit 40, and sends a control signal to various control circuits 44 via the output circuit 43. The control circuit 44 includes a developing bias control circuit 44a, an exposure lamp control circuit 44b, a toner supply amount control circuit 40c, a charging current control circuit 44d and the like.

According to the control method described above, the image density detected from the toner image of the reference target 3 is compared with a preset reference density, and the determination is made, and the developing bias voltage, the light amount of the exposure lamp 4 and the developing unit 7 are determined according to the stability result. Since the image forming conditions such as the amount of toner supplied to the toner and the charging current of the charger 25 are controlled, the density of the copied image is maintained constant even when the developer, the exposure lamp, etc. are deteriorated or the humidity is increased. As a result, more stable image quality can be obtained at all times. The present invention is as described above, and the operator can detect that the detector is dirty, and the operator can be prompted to clean the detector, which facilitates maintenance.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an entire copying machine.

FIG. 2 is an explanatory diagram of a detector.

FIG. 3 is a block diagram of a reference example of the present invention.

FIG. 4 is a drift compensation circuit diagram.

FIG. 5A is a circuit diagram of a main part of a reference example. (B) is a block diagram of an embodiment of the present invention.

FIG. 6 is a circuit diagram of a main part of the embodiment.

FIG. 7 is a block diagram of a control circuit.

[Explanation of symbols]

2 ... Original platen, 3 ... Reference target, 6 ... Photoconductor, 10 ...
Detector.

Claims (1)

[Claims] 1. A detector including a latent image of a reference target formed on a photoconductor, developing the latent image of the reference target to form a toner image of the reference target, and comprising a reflective sensor including a light emitting element and a light receiving element. In the controller of the electrophotographic copying machine, which detects the toner density of the toner image of the reference target by means of this, and controls the copying conditions based on the detected toner image of the reference target, the output from the opposite type sensor is detected.
Connect the preamplifier that amplifies the force and the output side of this preamplifier.
And a connection has been the main amplifier, by detecting the photoreceptor before the latent image of the reference target is formed on the photosensitive member by said detector, controls the gain of the main amplifier of the control circuit, a constant And a constant final amplification before the latent image of the reference target is formed on the photoconductor.
Electrophotographic copying, characterized in that it comprises means for judging whether or not the final output of the circuit enabling the output to be obtained is within a certain level, and displaying when the output is below a certain level. Machine control device.