JPH0358112B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an image forming apparatus that forms an electrostatic latent image on a photoreceptor and develops it, and in particular, it relates to an image forming apparatus that forms a test pattern on the surface of the photoreceptor and develops the image. The present invention relates to an image forming apparatus that detects an image density-related value of a copy image corresponding to a , or a pattern thereof, and controls image processing parameters that affect the image density based on the detected value.

[Conventional technology]

In this type of image forming apparatus, an electrostatic latent image formed on a photoreceptor is developed by supplying colored fine particles called toner from a developing device. The toner is
Usually, development is performed by being charged with a polarity opposite to that of the electrostatic latent image and being electrostatically attracted to the electrostatic latent image.

As a method for charging a toner with a polarity opposite to that of an electrostatic latent image, a method is known in which a developer is composed of a toner and a carrier, and the two are mixed and stirred to mutually triboelectrically charge each other. Such a developer is generally called a two-component developer. Although the developing method using a two-component developer can sufficiently charge the toner, only the toner is consumed during development, so a means is required to keep the toner concentration in the developer constant. Become. For this purpose, it is essential to measure the toner concentration of the developer.

As one method of measuring the toner concentration of a developer, a method described in Japanese Patent Publication No. 16199/1983 is known. This method forms a standard electrostatic latent image pattern on a photoreceptor, develops it, and then measures the density of the developed image photoelectrically.This is an indirect method of measuring developer toner density. . Direct developer toner concentration measurement methods are also known, such as measuring the weight of the developer or measuring the magnetic permeability. In addition, a proposal was made to control the toner density by detecting the surface potential of the toner image on the photoconductor surface (Japanese Patent Application Laid-Open No.
92138), a proposal to control the developing bias voltage according to the difference between the light reflectance of the reference density plate and the light reflectance of the original (Japanese Unexamined Patent Publication No. 103736/1983), and the image density adjustment during the copying process of the reference original. (Japanese Unexamined Patent Publication No. 141645/1983) proposed to control the development characteristics by detecting the original image density, latent image potential, and toner image density after development. There are proposals to control the voltage and/or the amount of exposure light (US Pat. No. 2,956,487).

[Problem to be solved by the invention]

However, the surface of the photoreceptor is thinly laminated on the conductive layer and is easily scratched when removing the jam paper, cleaning or repairing, and the surface of the photoreceptor may peel off or become uneven. Also, discharge between the charger wire and the conductive layer of a charger or static eliminator,
A so-called lightning strike destroys the insulating layer of the photoreceptor layer even if there is no scratch on the surface of the photoreceptor, resulting in areas that are not charged. Toner tends to adhere to scratches on the photoreceptor surface, causing black streaks on recorded images. Toner does not adhere to areas where the photoreceptor is peeled off or struck by lightning, resulting in white spots on the recorded image. Further, toner filming, in which a thin toner film is formed over the entire photoreceptor even though the photoreceptor is not charged, or deterioration of the photoreceptor, etc., occur. If the above-mentioned density control is performed in the event of an abnormality in the photoreceptor, the recording density will be adjusted to a high level due to oversupply of toner, etc., resulting in collapse of the recorded image and staining of the recording paper, impairing the image quality.

SUMMARY OF THE INVENTION An object of the present invention is to prevent disturbances in recording density control due to abnormalities on the surface of a photoreceptor.

[Means to solve the problem]

The present invention provides a means for forming a reference potential pattern area of a predetermined potential on the surface of a photoreceptor, a means for detecting an image density related value of the reference potential pattern area, and an image density related value corresponding to the detection result of the image density related value. An image forming apparatus comprising: means for controlling recording density by changing density parameters; means for detecting maximum and minimum values of image density-related values obtained from the reference potential pattern area;
means for comparing the difference between the maximum value and the minimum value of the image density related values; and a result of the comparison by the comparison means;
means for outputting an abnormal signal when the difference between the maximum value and the minimum value of the image density related values becomes larger than a predetermined value; and a means for outputting the abnormal signal continuously or cumulatively for a predetermined number of times or more. and a means for issuing an alarm when a warning occurs.

[Effect]

When there is an abnormality on the photoreceptor surface that causes black streaks or white streaks on the recorded image and this is in the reference potential pattern area, the difference between the maximum and minimum image density related values is greater than a predetermined value. also becomes larger. At this time, the means for outputting an abnormal signal outputs the signal, and if this output is output continuously or more than a predetermined number of times, an alarm is issued. The user can recognize an abnormality in the photoreceptor, and can be prompted to take measures such as replacing the photoreceptor.

〔Example〕

FIG. 1 shows a mechanical section of an embodiment of the present invention. To explain this mechanism, an image of an original 3 placed on a contact glass plate 1 and pressed against the contact glass plate 1 by a presser plate 2 is illuminated by an illumination lamp 4, and is illuminated by a first mirror 5 and a second mirror 6. , lens 8 , third mirror 9 , fourth mirror 10 , magnification setting lens 25 , and slit 7 . Irradiation light 4, first mirror 5
And the second mirror 6 is an arrow of the photoreceptor drum 11.
In synchronization with the rotation in the AR1 direction, the contact glass plate 1 is scanned and driven in the directions of arrows AR2 and AR3. As a result, the entire image of the document 3 is projected onto the surface of the photoreceptor drum 11, and a latent image corresponding to the image is formed. This latent image is
2, and the developed toner is transferred onto the recording paper fed from the registration rollers 14 directly below the transfer charger 13. The toner image on the recording paper is fixed by the fixing roller 15, and the recording paper after fixing is transferred to the paper output tray 1 by the conveyance roller 16.
7. 18 is an electrostatic charger, 19
20 is a static elimination charger, 20 is a cleaning roller,
21 is a cleaning blade. The recording apparatus shown in FIG. 1 is of a two-stage paper feeding type in which two cassettes 22 ₁ and 22 ₂ can be attached and detached. By selectively driving one of the paper feed rollers 23 ₁ and 23 ₂ , the recording paper in the cassette 22 ₁ or 22 ₂ is fed to the registration roller 14 . The magnification of the recorded image is determined by the position of the lens 25 for magnification setting, and the lens 25 moves according to the specified magnification.
It is driven and positioned in the AR4 direction. an emission diode ₃₀₁ that projects light onto the photoreceptor surface between the transfer charger 13 and the cleaning roller 20;
A phototransistor ₃₀₂ is arranged to detect light reflected from the photoreceptor surface.

FIG. 2 shows the configuration of a recording density control device that performs abnormality detection and recording density control together with a light emitting diode 30 ₁ and a phototransistor 30 ₂ . In FIG. 2, a phototransistor 30
₂ generates a voltage at its emitter end according to the amount of light received,
The transistor Tra amplifies this, and the emitter voltage Va of Tra becomes a voltage approximately proportional to the amount of received light.
This light amount detection voltage Va is applied to the minimum value hold circuit 32 ₁ and the maximum value hold circuit 32 ₂ via the analog gate 31. The hold voltage of the minimum value hold circuit ₃₂₁ is sent to the differential amplifier 33,
Further, the hold voltage of the maximum value hold circuit 32 ₂ is applied to the differential amplifier 33 and the comparator 34 ₁ , and the output of the differential amplifier 33 is applied to the comparator 34 ₂ .
Note that since the recording density and the detection voltage Va are in an inversely proportional relationship, the holding voltage of the minimum value hold circuit 32 ₁ indicates the maximum density value, and the holding voltage of the maximum value holding circuit 32 ₂ indicates the minimum density value.

The outputs of the comparators 34 ₁ and 34 ₂ are applied to an AND gate 35 together with the timing signals c and f, and the output of the AND gate 35 is applied to the trigger input of a mono-multi vibrator 37 which determines the toner supply time. vibrator 37
is applied to the base of clutch energizing transistor 38. A toner supply clutch 39 is connected to transistor 38 . Hold circuit 3
A timing control circuit 36 controls the application of the detection voltage Va to 2 ₁ and 32 ₂ , resetting their hold values, and turning on the gate of the AND gate 35 .

A detection instruction signal instructing abnormality detection and a timing pulse synchronized with the rotation of the photoreceptor drum 11 are applied to the timing control circuit 36 from a central control device (not shown) of the copying machine. The timing control circuit 36 is uniformly charged with a charger,
The pattern of the black development level formed by exposing the black pattern or not lighting the exposure lamp is detected by the photo sensor 30.
High level "1" immediately after reaching the bottom of _{1,30 2}
A detection instruction signal and a timing pulse synchronized with the rotation of the drum 11 are applied. In this way, when the detection instruction signal becomes "1" and a timing pulse arrives, the AND gate 36a of the timing control circuit 36 converts the timing pulse b to the counter 36b.
to be applied. Further, until the counter 36b counts ²⁷ timing pulses, the output g of the AND gate 36c becomes "1", turning on the analog gate 31 and applying the detection voltage Va to the hold circuits 32 ₁ and 32 ₂ . counter 36b
When the count value reaches ²⁷ , the output g of the AND gate 36c becomes a low level "0" and the analog gate 31 is closed. The timing signals c and f to the AND gate 35 are "1" from when the count value of the counter 36b reaches 2 ⁷ +2 ² until it reaches 2 ⁷ +2 ³ , and during this period, the comparator 34 ₁
and 34 ₂ are both "1", the output h of the AND gate 35 becomes "1", the mono multivibrator 37 is triggered, and the transistor 3
8 becomes conductive and energizes the toner supply solenoid 39 for a predetermined period of time. The count value of counter 36b is 2 ⁷ +
When 2 ³ is reached, AND gate 35 closes (gate off)
Instead, the output i of the AND gate 36d becomes "1", and the hold circuits 32 ₁ and 32 ₂
The reset analog switch closes and the hold capacitor is discharged (reset).
Furthermore, when the count value of the counter 36b reaches 2 ⁷ +2 ⁴ , the output j of the AND gate 36e becomes "1" and the central control unit of the copying machine is notified of the end of detection. When the central control device receives this detection end signal, it changes the detection instruction signal "1" to "0". When this becomes "0", the counter 36b is cleared.

The operation timing explained above is shown in FIG. 2b. As explained above, while the developed surface of the black development level pattern is directly under the sensors 30 ₁ and 30 ₂ (counts 0 to 2 ⁷ ), the hold circuits 32 ₁ and 32 ₂ are connected to the maximum density value and the minimum density value, respectively. is retained. Also, as a result, when the difference between the highest density value and the lowest density value (output of 33) is greater than a predetermined value (when abnormalities on the photoreceptor surface such as black streaks and white streaks are held), the output of the comparator ₃₄₂ is "0'' and the AND gate 35 is restricted to OFF (gate closed), and when the value is less than a predetermined value (when the value of the abnormal part is not held), the output of the comparator ₃₄₂ is ``1'' and the AND gate 35 is restricted to OFF (gate closed). The gate 35 is turned on (gate open). Therefore, when the value of the abnormal portion on the photoreceptor surface is held, the energizing signal to the mono-multivibrator 37 is cut off. On the other hand, hold circuit 3
When the output of 2 ₂ is above a predetermined value (when the minimum density value is below a predetermined value), the output of comparator 34 ₁ becomes "1" which instructs toner supply, and the hold circuit 32
When the hold value of _{No. 2} is less than the predetermined value (when the minimum density value exceeds the predetermined value), the output of the comparator 34 ₁ becomes "0" indicating that toner supply is not necessary. Therefore,
The output of the AND gate 35 is such that the output of the comparator 34 ₂ is "1" (no abnormality on the photoconductor surface) and the output of the comparator 34 ₁ is "1" at a predetermined determination timing.
It becomes "1" only when (toner supply is required), and at this time, the mono-multivibrator 37 is triggered and the toner supply clutch 39 is energized for a predetermined period of time.

FIG. 3a shows another embodiment of the invention,
The operation timing is shown in FIG. 3b. In this case, another set of white portion maximum value hold circuits 32
Accordingly, _three sets of analog gates 31 ₁ to 31 ₃ are added, and differential amplifiers 33 ₂ and 33 ₃ and comparators 34 ₃ and 34 ₄ are further added. In this embodiment, the central control unit of the copying machine sets the detection instruction signal to "1" immediately after starting the white pattern image scan, and after starting the subsequent black pattern image scan, the timing control circuit 36 outputs the detection end signal "1". In response to "1", the detection instruction signal is set to "0". Note that the scanning width of the white pattern is narrower than the equivalent of ²⁷ timing pulses.
The scanning width of the black pattern is wider than the equivalent of ²⁷ timing pulses.

The central control unit of the copying machine energizes the main charger to uniformly charge the photoreceptor, and the surface of the photoreceptor on which a white pattern is projected is connected to the photo sensor 30 ₁ , 3 .
2 Immediately after entering directly below ₂ , a detection instruction signal "1" and a timing pulse are given to the timing control circuit 36. The timing control circuit 36 turns on the analog gate 31 1 while the detection instruction signal is "1", and turns on the analog gate 31 ₁ after the detection instruction signal becomes "1" until the count value of the counter 36b reaches 2 ⁷ . Turn on ₃ and the count value changes from 2 ⁷ to 2 ⁷
The analog gate 31 ₂ is turned on during +2 ⁷ .
As a result, the hold circuit 32 ₁ holds the minimum value of Va of the black pattern, the hold circuit 32 ₂ holds the maximum value of Va of the black pattern, and the hold circuit 32 ₃ holds the maximum value of Va of the white pattern. Ru.

When the count value of the counter 36b reaches 2 ⁷ +2 ⁶ +2 ⁵ +2 ⁴ +2 ³ +2 ² , the timing control circuit 36 sends the status acquisition signal D= to the flip-flops 37 ₁ to 37 ₄ .
Apply "1" (corresponding to a clock pulse, E is "0"). Flip-flops 37 ₁ to 37 ₄ are set when the J input terminal is "1" at this time. J
If the input terminal is "0", the reset state remains. After that, the circuit 36 outputs E with D=“1”.
= "1" and reset the flip-flops ₃₇₁ to ₃₇₄ . At E=“0” and D=“1”,
When the output of the comparator ₃₄₂ is "1" (the difference between the highest density and the lowest density of the black pattern is more than a predetermined value: there is an abnormality such as white spots or black streaks on the photoreceptor surface), the J input terminal of the flip-flop ₃₇₁ is Since it is "1", the flip-flop ₃₇₁ is set and its Q output = A = "1" indicates an abnormality, and when the output of the comparator ₃₄₁ is "1" (the highest density of the black pattern and the lowest density of the white pattern). The difference in density is less than the specified value: Toner shortage)
In this case, the J input terminal of flip-flop ₃₇₂ is "1".
Therefore, the flipflop ₃₇₂ is set and its Q output = "1" indicates a lack of toner (insufficient recording density).
When the output of the comparator ₃₄₃ is "1" (the difference between the minimum density of the black pattern and the minimum density of the white pattern is less than a predetermined value: abnormality with white spots or black streaks), the output of the flip-flop ₃₇₃ is Since the J input terminal is "1", the flip-flop ₃₇₃ is set and its Q output = B = "1" indicates an abnormality, and when the output of the comparator ₃₄₄ is "1" (the lowest density of the white pattern is above a predetermined value: toner filming error), the J input terminal of the flip-flop ₃₇₄ is set to ``1'', so the flip-flop <sub>374</sub> is set and its Q output = C = ``1'' indicates an error (toner filming). represent.

The AND gate 35 that triggers the mono multivibrator 37 includes flip-flops 37 ₁ , 3
Since the outputs of flip-flops ₇₃ and ₃₇₄ are applied, and the Q output of flip-flop ₃₇₂ is applied, there is no abnormality (A, B, C = "0") and there is no toner shortage (Q output of flip-flop ₃₇₂ = "1"). ”), the output of the AND gate 35 becomes “1” and the mono multivibrator 37 is triggered to supply toner. When there is an abnormality even though there is a lack of toner (A,
When either B or C is "1"), the AND gate 35 is closed and toner is not supplied. In addition, the abnormal signal is given to the central control device,
The central control device reads these at the timing of D=1, and issues an alarm when an abnormality has occurred consecutively a predetermined number N or more, and when the cumulative abnormality value is a predetermined number M or more.

Next, other embodiments and modifications of the present invention will be described. In the above embodiment, only the black pattern and the white and black patterns (charged patterns) are obtained by exposure scanning of optical marks attached to the edge of the contact glass plate 1, but this is due to the charger. Charging, non-charging control, exposure lamp ON,
It may be formed by OFF control, ON/OFF control of the erase lamp, or development bias control of the developing roller. Furthermore, in the above embodiment, the image density-related value is obtained by detecting the density of the developed toner image of the charged pattern (white, black pattern) with a photo sensor, but this value is obtained by detecting the surface potential of the charged pattern before development. It may be obtained by detecting the surface potential of the charged pattern toner image after development, or by detecting the density of the transferred toner image on recording paper. Furthermore, in the above embodiment, the recorded image density is made constant by toner replenishment to the developing section, but this is a ratio of image density related values, and is determined by charge control, exposure light amount control, and development bias voltage. control, toner supply control to the developer, toner supply amount control to the developing section, and/or transfer potential control, or a combination of two or more thereof.

〔Effect of the invention〕

As described above, according to the present invention, an alarm is issued when there is an abnormality on the surface of the photoreceptor that causes a recorded image, such as white or black streaks. The user can recognize an abnormality in the photoreceptor, and can be prompted to take measures such as replacing the photoreceptor.

[Brief explanation of drawings]

FIG. 1 is a side view showing a mechanical part of an embodiment of the present invention, FIG. 2a is a circuit diagram showing an electric circuit for detecting an abnormality on the surface of a photoreceptor in the embodiment, and FIG. 2b is a circuit diagram showing an electric circuit shown in FIG. 2a. This is a time chart showing the electrical signals of each part of the circuit. FIG. 3a is a circuit diagram showing another electric circuit for detecting an abnormality on the surface of the photoreceptor, and FIG. 3b is a time chart showing electrical signals of various parts of the electric circuit shown in FIG. 3a. 1: contact glass plate, 2: presser plate, 3: original, 4: illumination light, 5: first mirror, 6: second mirror, 7: slit, 8, 25: lens, 9: third
Mirror, 10: Fourth mirror, 11: Photosensitive drum, 12: Developing device, 13: Transfer charger, 1
4: Registration roller, 15: Fixing roller, 16:
Conveyance roller, 17: Paper discharge tray, 18: Electrostatic charger, 19: Discharge charger, 20: Cleaning roller, 21: Cleaning plate, 22
₁ , 22 ₂ : Cassette, 23 ₁ , 23 ₂ : Paper feed roller,
24: Operation board, 33, 33 ₁ to 33 ₃ : Differential amplifier, 34 ₁ to 34 ₄ : Comparator, 39: Toner supply solenoid.

Claims (1)

[Scope of Claims] 1. Means for forming a reference potential pattern area of a predetermined potential on the surface of a photoreceptor, means for detecting an image density related value of the reference potential pattern area, and a means for detecting a detection result of the image density related value. An image forming apparatus comprising: means for controlling recording density by changing an image density parameter accordingly; means for detecting a maximum value and a minimum value of image density related values obtained from the reference potential pattern area;
means for comparing the difference between the maximum value and the minimum value of the image density related values; and a result of the comparison by the comparison means;
means for outputting an abnormal signal when the difference between the maximum value and the minimum value of the image density related values becomes larger than a predetermined value; 1. An image forming apparatus comprising: means for issuing an alarm when an image forming apparatus is activated.