JPH0683179A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To always compensate fixed image density by effectively detecting the deterioration of developer and preventing the image density from lowering according to the detected result. CONSTITUTION:A rotating sleeve 42a is installed on the outer periphery of a magnet 42b for forming a magnetic brush, and the developer is carried to a developing position opposed to the surface of a photosensitive drum 1 by the rotation of the sleeve 42a and restored to a stirring roller 41 by the rotation of the sleeve 42a after development. The developer is formed to the magnetic brush by the magnetic pole N1 of the magnet 42b at the developing position opposed to the drum 1 so as to develop an electrostatic latent image formed on the surface of the drum 1. A conductive plate 44 electrically coming in contact with the developer is installed before the developing position, and a current flowing to the plate 44 is detected by a current detection circuit 9. Based on the detected current quantity, a CPU 5 controls a main electrostatic charging control circuit 3 controlling the potential of the surface of the drum 1 through a main electrostatic charger 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus which discriminates a state of a developer and controls a charging potential in an electrophotographic process.

[0002]

2. Description of the Related Art In an electrophotographic apparatus such as a copying machine or a laser printer, mechanical stress such as polishing by a cleaning blade accumulates as copying and printing are repeated, resulting in film slippage and reduction in film thickness of a photosensitive layer. However, the surface potential tends to gradually decrease. When such a change in the surface potential occurs, the image quality of the formed image is greatly affected such as a decrease in density.

On the other hand, when the toner is consumed by the development, the developer is additionally mixed one after another and used for a long period of time. Therefore, a new initial developer and a deteriorated developer that has been used for a long period of time cannot be used. Even if the toner density of the developer is the same, the image density of the copied image obtained by development is different.

In order to deal with these problems, in the conventional electrophotographic apparatus, the optical sensor detects the optical density of the toner image on the photosensitive member to grasp the change in image quality, and the toner density of the developer is determined according to the detection result. Is controlled, or the surface potential of the photoconductor is controlled to correct the image quality.

The image quality correction by controlling the toner density means that when the optical sensor detects that the density of the reference toner image is lower than the reference, the developer is replenished with toner to increase the toner density of the developer. The image quality is corrected by increasing the image density.

The image quality correction by controlling the surface potential of the photoconductor is to increase the image density by increasing the surface potential of the photoconductor when the density of the reference toner image is detected to be lower than the reference, as described above. Then, the image quality is corrected.

[0007]

However, in the above-mentioned conventional configuration, when it is recognized that the image quality needs to be corrected, the image quality is corrected by controlling the toner concentration of the developer or the surface potential of the photoconductor. However, in order to detect the decrease in image density for that purpose, it is necessary to form an image of the reference density on the photoconductor, which makes the forming process and control of the reference image very troublesome and increases the cost. Tends to become.

Further, since an optical sensor is used as a sensor for detecting the density of the reference image, it may be erroneously detected due to dirt due to toner or the like. A circuit is needed.

The present invention has been made in view of the above problems, and directly detects a deterioration state due to a developer without forming a reference image on a photoconductor in order to correct the image quality density. By performing image correction, it is intended to obtain stable image quality without cost reduction.

[0010]

An electrophotographic apparatus of the present invention comprises a magnetic brush developing device, detects a current flowing through a conductive member brought into contact with a developer by the magnetic brush, and detects the current according to the detected current. It is characterized in that a means for controlling the image density formed on the photoconductor is provided.

Particularly as a means for controlling the image density, there is a means for controlling the surface potential of the photoconductor.

The means for controlling the image density is a means for controlling the toner density of the developer of the magnetic brush developing device.

Further, the means for controlling the image density is means for keeping the current flowing through the conductive portion constant.

[0014]

According to the above electrophotographic apparatus of the present invention, the electrostatic latent image formed on the photoconductor is developed by the magnetic brush developing apparatus. As the developing operation continues, the developer deteriorates, and the image density formed on the photoconductor decreases even if the toner density of the developer in the developing device is kept constant.

At this time, the developer comes into contact with the conductive member and the current is detected by the current detecting means, which gradually decreases as the developer deteriorates. The image density of the photoconductor is controlled according to the decrease in the current. That is, since the image density decreases due to the deterioration of the developer, the image density control unit controls the image density so as to obtain a predetermined image density.

For example, the surface potential control means of the photoconductor, which is an image density control means, controls to raise the surface potential of the photoconductor. Therefore, the surface potential of the photoconductor is increased in accordance with the decrease in image density due to the deterioration of the developer. In this case, the charger is controlled so that the charging potential of the photoconductor is increased in response to the deterioration of the developer. Alternatively, by reducing the amount of light that exposes the photoconductor, the potential on the surface of the photoconductor becomes higher than that at the initial stage. Therefore, it is possible to correct the decrease in the image density by increasing the toner adhesion amount and control the image density to be a normal determined value.

As the image density control means, the toner density of the developer is controlled. In this case, the toner concentration is set higher than the toner concentration of the initial developer, and the toner amount in the developer increases, so that the toner adhesion amount can be compensated and the normally determined image density can be compensated.

Further, in order to control the toner adhesion amount, the current changes due to the deterioration of the developer. Therefore, if the current is controlled to be kept constant, the toner adhesion amount can be kept constant.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

As shown in FIG. 1, a copying machine, which is an electrophotographic apparatus according to this embodiment, includes a cylindrical photosensitive drum 1 which is a photosensitive member. The photoconductor drum 1 is rotatably provided in the apparatus in the A direction, and an electrostatic latent image is formed by exposing a document image with light emitted from the B direction. There is.

Around the photosensitive drum 1, a main charger 2, a developing device 4, a transfer / separator 6 and the like are arranged so as to face each other. In addition, although not shown, a cleaning device for cleaning the toner remaining on the surface of the photosensitive drum 1 after the transfer is provided.

The main charger 2 is arranged near the uppermost end of the photosensitive drum 1. The main charger 2 is, for example, a scorotron type corona discharger, and has a high voltage power source (not shown) and a grid electrode for adjusting the main power output to the photosensitive drum 1. The main charging output is the photosensitive drum. The surface of No. 1 can be charged and the surface potential thereof can be controlled. A main charging control circuit 3 connected to a CPU 5 is connected to the main charger 2, and the main charging control circuit 3 controls the output of the high-voltage power supply and the voltage applied to the grid electrode according to a command from the CPU 5. The main charging output of the main charger 2 (voltage for charging the photosensitive drum 1) is changed stepwise to control the charging potential of the surface of the photosensitive drum 1. That is, the main charging control circuit 3 is one image density control means and constitutes a surface potential control means for controlling the surface potential of the photosensitive drum 1.

The main charging control circuit 3 changes the main charging output of the main charger 2 so that the CPU 5 corrects the image quality in response to the deterioration of the developer. As shown in FIG. 2, between the surface potential of the photosensitive drum 1 and the image density of the copied image copied by this copying machine,
Both the initial developer and the deteriorated developer have a characteristic that the image density increases up to a certain density as the surface potential increases. Here, the increase of the image density changes depending on the deterioration state of the developer, and in particular, in the case of the developer shown by the broken line which is being deteriorated, the image density becomes lower than the initial developer shown by the solid line. Utilizing this characteristic, the CPU 5 controls the main charging control circuit 3 to gradually increase the main charging output of the main charger 2 in accordance with the deterioration of the developer to increase the main charging output of the photosensitive drum 1. The surface potential is increased, the image density is increased, and the image quality is corrected.

The means for controlling the surface potential of the photosensitive drum 1 is not limited to the main charging control circuit 3 described above, but can also be controlled by controlling the light quantity at the time of image exposure. That is, by reducing the amount of light that exposes the surface of the photoconductor drum 1 to light, the potential of the surface of the photoconductor drum 1 becomes low as a whole. Further, since the discharge charge is reduced by increasing the light amount, the surface potential is increased and the toner adhesion is increased, so that the image density is increased. Therefore, the surface potential control means can be constituted by means for controlling the light quantity.

For example, when an image of a document (not shown) is exposed on the surface of the photosensitive drum 1 via the optical system at the position B, the exposure amount is controlled based on a command from the CPU 5. That is, the light amount of the exposure lamp that irradiates the original with light is controlled according to the deterioration of the developer. This allows
By reducing the exposure amount due to the decrease in the image density, the potential on the surface of the photosensitive drum 1 is substantially increased and the toner adhesion amount is increased, so that the decrease in the image density is corrected.

In the developing device 4, the stirring roller 41 and the magnet roller 42 are provided inside the developing tank for storing the developer.
Is equipped with. The agitating roller 41 is rotatably formed, and agitates the two-component developer to frictionally charge the toner and the carrier. Magnet roller 4
2 is a cylindrical non-magnetic sleeve 42a forming an outer peripheral portion
With a large number of magnetic poles N1, S1,
A magnet 42b obtained by magnetizing S2, N2 and S3 in this order.
Like the stirring roller 41, the sleeve 42a is rotatably formed. This magnet roller 42 has a sleeve 42a which is generated by the magnetic force of the magnet 42b.
A developer is attached to the top to form a magnetic brush, and the sleeve is rotated to supply the developer to the photosensitive drum 1. Although not shown, the developing device 4 has a toner hopper that stores toner.

The developing device 4 is provided with a toner concentration control circuit 7 which is a toner concentration control means connected to the CPU 5, and the toner concentration control circuit 7 is provided for the developer contained in the developing device. The toner density is controlled to a predetermined density according to the detection signal from the toner density sensor 8 which detects the toner density. The toner concentration sensor 8 inputs its output to the CPU 5 to form a replenishing roller for replenishing the toner in the developing device with toner from a toner hopper (not shown) via the toner concentration control circuit 7. It is used for drive control. Thereby, the toner concentration of the developer stored in the developing device is kept constant. By controlling this toner density, the toner adhesion amount of the electrostatic latent image formed on the photosensitive drum 1 can be controlled. That is, the higher the toner density, the darker the image density. Therefore, while the image density decreases due to the deterioration of the developer,
Control is performed via the toner concentration control circuit 7 so as to increase the toner concentration. The toner density control circuit 7 constitutes another image density control means.

The developing device 4 includes a magnet roller 42.
In particular, in order to regulate the amount of developer adhering to the sleeve 42a, the doctor 43 is arranged at a predetermined distance d from the sleeve 42a. The doctor 43 regulates the amount of developer attached to the sleeve 42a of the magnet roller 42 to a predetermined amount, and keeps the amount of developer constant at the developing position facing the photoconductor drum 1.

A conductive plate 44, which is a conductive member for detecting the deterioration state of the developer according to the present invention as a current amount, is provided further downstream of the doctor 43 and in front of the developing position facing the photosensitive drum 1. It is arranged. This conductive plate 44
Are arranged in contact with the developer adsorbed on the sleeve 42a.

The magnet roller 42 is supplied with a predetermined voltage from a power source 45 which acts as a bias voltage on the photosensitive drum 1. The power supply 45 is generally close to the surface potential of the non-image area in order to prevent the toner from adhering to the non-image area when the electrostatic latent image formed on the surface of the photosensitive drum 1 is developed. The voltage values are set to the same level. The power supply 45 is normally supplied to the sleeve 42a. Therefore, by grounding the conductive plate 44, an electric circuit is formed between the conductive plate 44 and the sleeve 42a via the developer, and the current flowing therethrough changes particularly in accordance with the deterioration state of the developer. To do.

In order to detect the current flowing through the conductive plate 44, a current detection circuit 9 connected to the conductive plate 44 is provided. The current detection circuit 9 has a conversion circuit or the like for converting a voltage corresponding to the current to detect the current flowing through the conductive plate 44. The current detection circuit 9
The detected current is supplied to the CPU 5 described above as information (digital information) according to the amount of the current. Based on the information according to the amount of current supplied from the current detection circuit 9, the CPU
Reference numeral 5 particularly sends information for controlling the surface potential of the photosensitive drum 1 to the main charging control circuit 3 and the toner concentration control circuit 7 to determine the surface potential and the toner concentration of the photosensitive drum 1. In this case, the CPU 5 also outputs a similar control signal to a light amount control circuit (not shown) which controls the light amount of the exposure lamp.

3 and 4 show the characteristics of the developer according to the present invention due to deterioration. Deterioration of the developer gradually increases as the number of times of image formation by the electrophotographic apparatus increases. At this time, as shown in FIG.
The current flowing through the device gradually decreases. This is due to the characteristics shown in FIG. That is, by changing the distance (gap) d between the doctor 43 and the sleeve 42a that regulates the amount of the developer adsorbed on the sleeve 42a of the magnet roller 42, the amount of the developer adsorbed on the sleeve 42a changes. However, the amount of the developer increases as the gap d increases, which increases the current flowing through the conductive plate 44.

Therefore, although the gap d of the doctor 43 with respect to the sleeve 42a is always kept constant,
Due to the deterioration of the developer, the amount of the developer passing through the doctor 43 is reduced as compared with the initial amount of the developer. This is because when the developer deteriorates, the fluidity of the developer decreases, so that the amount of the developer passing through the doctor 43 decreases. Therefore, the decrease in the amount of developer passing is as shown in FIG.
As can be understood from the characteristic diagram of FIG. 5, the doctor gap d is apparently narrowed, and the current flowing through the conductive plate 44 is also reduced. The deterioration state of the developer can be determined by detecting the current at this time.

FIG. 4 shows that the current gradually decreases due to the deterioration of the developer as an image is formed by the electrophotographic apparatus as described above. In FIG. 4, the point P due to the developer in the initial state in which the number of image formed sheets is small is shown.
1 and the image characteristics at the point P2 due to the developer in which the number of image formations is increased are shown in FIG. 2 described above.

It can be seen that the image characteristics at P2 when the developer is deteriorated are lower than the image density at the initial P1 time of the developer. Therefore, the initial potential V of the surface of the photosensitive drum 1
If the setting control is performed by the main charging control circuit 3 with the value of 1 being maintained, the deteriorated developer P is compared with the image density obtained with the initial developer.
The image density at 2 becomes low. Therefore, at the time P2 due to the deterioration of the developer, the surface potential of the photosensitive drum 1 is set to Δ in order to obtain the same density as the image density of the initial developer.
The surface potential V2 of the photosensitive drum 1 is raised by V.

Therefore, the means for controlling the image density according to the present invention uses the current flowing in the conductive plate 44 as the current detection circuit 9.
By detecting the voltage via the developer, the surface potential V2 of the photosensitive drum 1 is calculated so that the image density by the initial developer is obtained as shown in FIG. 2, and the main charging control is performed to raise the ΔV surface potential. The voltage supplied to the main charger 2 by the circuit 3 is controlled. That is, as the developer gradually deteriorates, the detected current decreases, so that the voltage supplied to the main charger 2 by the main charging control circuit 3 is controlled to be gradually increased. This allows
It is possible to always obtain a stable image density without causing a decrease in image density due to deterioration of the developer. The image density control means, in short, controls the potential on the surface of the photosensitive drum 1.

In this case, in order to control the surface potential of the photosensitive drum 1, the image density can be corrected by controlling the light quantity of the exposure lamp. That is, by controlling the amount of light from the exposure lamp according to the amount of current flowing through the conductive plate 44, the same effect as when the surface potential is controlled by the main charger 2 can be obtained. This is because the amount of current is reduced based on the deterioration of the developer so that the amount of light of the exposure lamp is reduced. As a result, the potential of the electrostatic latent image on the surface of the photoconductor drum 1 becomes higher, and the same effect as when the surface potential of the photoconductor drum 1 is actually raised by the main charger 2 can be obtained. Further, the image density control means is not limited to the one that controls the surface potential of the photosensitive drum 1 as described above, and the same image density control can be performed even if the image density is controlled according to the current detection. . For example, the toner density control circuit 7 may control the toner density to be higher than the initial toner density. That is, the toner concentration control circuit 7
Controls the toner replenishment in order to maintain the toner concentration determined by the initial developer, but sets the toner concentration higher than the initial toner concentration according to the deterioration of the developer, Toner replenishment control is performed so that As a result, the amount of toner in the developer becomes larger than that in the initial state, so that a large amount of toner adheres to the electrostatic latent image on the photosensitive drum 1. Therefore, the image density tends to decrease due to the decrease of the toner adhesion due to the deterioration of the developer, but the image density is compensated by the increase of the toner.

Further, as the means for controlling the image density, not only controlling the toner density as described above,
It can also be realized by controlling the bias voltage supplied to the developing roller 42 of the magnetic brush developing device 4. That is, the bias voltage power source 45 is applied to the developing roller, especially the sleeve 42a.
By controlling the value of the current flowing through the developer in order to control the voltage supplied to, the amount of toner adhering to the surface of the photosensitive drum 1 can be controlled and the image density can be controlled.

Therefore, in the embodiment shown in FIG. 5, as the image density control means, the variable resistor 46 is connected between the bias power supply 45 and the grounding portion, and the CPU 5 is operated based on the current value from the current detection circuit 9. However, the resistance value of the variable resistor 45 is changed. Thereby, the value of the current flowing through the developer can be freely controlled. Particularly, by controlling the resistance value of the developer and the resistance by the variable resistor 46 to be constant, the current flowing through the conductive plate 44 is made constant, and the resistance change due to the deterioration due to the developer is apparently changed. The image density can be made constant by the correction by the device 46.

The variable resistor 46 is variably controlled by the CPU 5 according to the amount of current detected by the current detection circuit 9 for the current flowing into the conductive plate 44. At this time, the decrease in the current flowing through the developer is controlled by decreasing the resistance value of the variable resistor 46 because the resistance is increased due to the deterioration of the developer. As a result, the current value flowing into the conductive plate 44 is kept constant according to the added resistance value of the developer and the variable resistor 46. Therefore, the image density due to the deterioration of the developer, particularly the amount of toner adhering to the photosensitive drum 1, can be made constant, and thus the decrease in the image density due to the deterioration of the developer can be corrected.

The variable resistor 46 is not of the volume type shown in the figure, but a plurality of resistors are connected in parallel or in series, and each resistor is controlled to have a predetermined resistance value under the control of the CPU 5. The switch means may be controlled so as to connect or disconnect (including short circuit).

Further, in the CPU 5, when a new developer is exchanged in advance, the current value at that time is read and compared with the current value from the current detection circuit 9 by using this as a reference value to compare the resistance of the variable resistor 46. Control the value. For example,
At the time when the developing device is filled with a new developer, the resistance value of the variable resistor 46 is set to the maximum value, and a normal density image is obtained at a predetermined voltage value of the bias power supply 45. The value of the current flowing at that time is stored. By gradually decreasing the resistance value as the developer deteriorates, the image density can be kept constant and the developer can be used for a long period of time.

Here, not the variable resistor 46 but the power source 46
The image density can also be controlled by controlling the voltage itself. That is, the power supply 46 that is the bias voltage is made variable,
The CPU 5 may be configured to control the voltage based on the current detection value of the current detection circuit 9.

The conductive plate 44 shown in FIG. 1 is provided so as to face the magnetic pole S3 forming a magnetic brush separately from the developing pole N1 of the magnet 42b. This forms a magnetic pole brush of the developer at the magnetic pole S3. Therefore, in this portion, the developer is vertical so as to be substantially along the magnetic lines of force, and the conductive plate 44 and the developer are electrically and surely brought into contact with each other, so that the current detection is stabilized.

[0045]

In the electrophotographic apparatus of the present invention, the deterioration of the developer is carried out by detecting the current flowing through the conductive plate brought into contact with the developer by the magnetic brush, so that erroneous detection due to contamination by the optical sensor or the like is eliminated. The image density can always be controlled to a constant state by a simple means without requiring any special means such as forming a reference image on the surface of the photoconductor.

In particular, since the surface potential of the photosensitive member is controlled, the toner density is controlled, or the toner adhesion amount is controlled in accordance with the detection of the current, the image density control can be performed by using the conventional means. You can do it.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main part of an electrophotographic process section of an electrophotographic apparatus according to an embodiment of the present invention and a block circuit relating to image density control by the process section.

FIG. 2 is a characteristic diagram in image density control according to the present invention, which shows the relationship between the surface potential of a photosensitive drum and the image density.

FIG. 3 is a characteristic diagram showing the relationship between the amount of developer and the current flowing through a conductive plate in contact with the developer.

FIG. 4 is a characteristic diagram showing a relationship between a deterioration state of a developer depending on the number of images formed and a current amount at that time.

FIG. 5 is a schematic diagram relating to image density control showing another embodiment according to the present invention.

[Explanation of symbols]

 1 Photoreceptor Drum (Photoreceptor) 2 Main Charger 3 Main Charge Controller (Surface Potential Control Means) 4 Magnetic Brush Developing Device 5 CPU 7 Toner Density Control Circuit 8 Toner Density Sensor 9 Current Detection Circuit 44 Conductive Plate 45 Power Supply (Bias) Voltage) 46 variable resistor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03G 15/09 Z

Claims (4)

[Claims] 1. A charging unit for charging a photosensitive member, an exposing unit for exposing the charged surface of the photosensitive member to an image, and a developer for developing an electrostatic latent image formed on the photosensitive member as a toner image. A magnetic brush developing device formed with a magnetic brush; a conductive member arranged to come into contact with a developer before developing the electrostatic latent image formed on the photoconductor by the magnetic brush developing device; An electrophotographic apparatus comprising: a current detection unit that detects a current flowing through a conductive member; and an image density control unit that controls the image density formed on the photoconductor according to the current detected by the current detection unit. apparatus. 2. The electrophotographic apparatus according to claim 1, wherein the image density control means is a charge control means or an exposure amount control means for controlling the surface potential of the photoconductor. 3. The electrophotographic apparatus according to claim 1, wherein the image density control means is a control means for controlling the toner density of the magnetic brush developing device. 4. The electrophotographic apparatus according to claim 1, wherein the image density control means is means for keeping a current flowing through the conductive member constant.