JPH05257352A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To effectively correct image quality and to provide a copy image with stable image quality. CONSTITUTION:A toner patch is formed on a photosensitive drum 1 and the amount of toner sticking to the photosensitive drum 1 is detected by an optical sensor 3. Based on the detection value, the concentration of the toner of developer is controlled by a toner concentration controller 4a to correct image density. When the correction of the toner concentration reaches its limit, the main electrification output of the main electrifier 2 is controlled by the main electrification controller 2a to carry out image quality correction by the surface potential of the photosensitive drum 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus capable of obtaining a stable formed image by controlling each part of the electrophotographic process based on the density of a reference toner image.

[0002]

2. Description of the Related Art In electrophotographic apparatuses such as copying machines and laser printers, mechanical stress such as polishing by a cleaning blade accumulates as copying and printing are repeated, and film thickness is reduced due to film slippage. 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 by 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 densities of the developers are the same, the image densities of the copied images obtained by development are different.

In order to deal with these problems, in the conventional electrophotographic apparatus, the optical density of the toner image on the photosensitive member is detected by the optical sensor to grasp the change in the 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 density of the reference toner image is detected to be lower than the reference by the optical sensor, 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 in the same manner 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 density of the developer or the surface potential of the photoconductor. Since the image quality is corrected only, the image quality becomes unstable despite the image quality correction.

In the case of image quality correction based on the toner concentration, the toner concentration of the developer is set in advance with an allowable range in order to avoid toner scattering due to excessive increase in toner concentration. For this reason, correction within the allowable range is unavoidable, the correction capability is limited, and sufficient correction cannot be performed.

Further, in the case of image quality correction by the surface potential of the photoconductor, if the charging potential is excessively increased regardless of the sensitivity of the photoconductor, there is a possibility that exposure change may occur. Therefore, similarly to the above, an allowable range is set for the surface potential of the photoconductor, and correction within this allowable range has a limited correction capability, and sufficient correction cannot be expected.

The present invention has been made in view of the above problems, and a stable image quality is obtained by switching and correcting both the image quality correction based on the toner density and the image quality correction based on the surface potential of the photoconductor. The purpose is to

[0011]

The electrophotographic apparatus of the present invention comprises a charging potential control means for controlling the charging potential of the photoconductor,
Toner density control means for controlling the toner density of the developer for visualizing the electrostatic latent image formed on the photoconductor as a toner image, and image density detection for detecting the toner amount of the reference toner image formed on the photoconductor Means and an image density control switching means for switching between the control by the charging potential control means and the control by the toner density control means on the basis of the output value of the image density detection means.

[0012]

In the above arrangement, the image density control switching means controls the charging potential control means on the basis of the output of the image density detecting means detecting the toner amount of the reference toner image.
The control by the toner density control means is switched. For example, first, the image quality correction is performed by the control of the toner density control unit, and when the image quality correction of the toner concentration control unit reaches a limit, the image quality correction is subsequently performed by the control of the charging potential control unit. ing.
Therefore, it is possible to perform more effective image quality correction and to always obtain a stable formed image, as compared with the conventional case where only one image quality correction is performed.

[0013]

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 photosensitive drum 1 is rotatably provided in the apparatus in the A direction, and an electrostatic latent image is formed by exposing the original 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, an optical sensor 3 and the like are arranged.

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 photoconductor drum 1. The main charge output is the photoconductor drum. The surface of 1 is charged. A main charging controller 2a connected to a CPU 5 is connected to the main charger 2, and the main charging controller 2a controls the output of the high voltage power source 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 is controlled (photosensitive drum 1
Is gradually changed to control the charging potential of the photosensitive drum 1. That is, the main charging controller 2a constitutes charging potential control means for controlling the charging potential of the photosensitive drum 1.

By changing the main charging output of the main charger 2 by the main charging controller 2a, the CPU 5 corrects the image quality in response to the deterioration of the photosensitive drum 1 and the developer. Is becoming As shown in FIG. 2, between the surface potential of the photosensitive drum 1 and the image density of the copy image copied by the copying machine, the surface potential of the initial developer and the deteriorated developer increases as the surface potential increases. The image density is increased up to a certain density. Utilizing this characteristic,
The CPU 5 controls the main charging controller 2a to set the main charging output of the main charging device 2 to the limit value V according to the deterioration of the developer.
The surface potential of the photoconductor drum 1 is raised by gradually increasing to _MAX , the image density is raised, and the image quality is corrected. The limit value V _MAX is an upper limit value of the main charging output of the main charger 2 for charging the photosensitive drum 1 so as not to affect the sensitivity throughout the life.

The developing device 4 has a stirring roller 4a and a magnet roller 4b therein. Stirring roller 4a
Is rotatably formed so that the toner and the carrier are frictionally charged by stirring the two-component developer. The magnet roller 4b has a cylindrical non-magnetic sleeve forming an outer peripheral portion and a magnetic pole inside thereof, and is rotatably formed like the stirring roller 4a. The magnet roller 4a is adapted to adhere a developer to a sleeve by a magnetic force of a magnetic pole to form a magnetic brush and supply the developer to the photosensitive drum 1 by rotating the sleeve. Although not shown, the developing device 4 has a toner hopper that stores toner.

A toner concentration controller 4c, which is a toner concentration control means connected to the CPU 5, is attached to the developing device 4, and the toner concentration controller 4c controls the developer contained in the developing device. It has a toner concentration sensor (not shown) for detecting the toner concentration. In response to the command from the CPU 5, the toner concentration controller 4c gradually decreases the output of the toner concentration sensor from the reference voltage value V ₀ to the limit output value V ₁ as shown in FIG. 3, and the changed voltage ΔV The toner density is controlled by supplying the toner corresponding to the amount from the toner hopper. The limit output value V ₁ is an output upper limit value for adjusting the toner density to the maximum density that does not cause toner scattering.

As shown in FIG. 4, the toner density and the image density of the developer have a characteristic that the image density increases up to a certain density as the toner density of the developer increases. Utilizing this characteristic, the CPU 5 controls the toner density by the toner density controller 4c, thereby performing the image quality correction in response to the deterioration of the photosensitive drum 1 and the developer. There is.

The transfer / separator 6 is a charger 2 for the transfer paper.
By transferring the toner image of the photosensitive drum 1 to the transfer paper by applying corona discharge of the same polarity as the above, by applying AC corona discharge to the transfer paper on which the toner image is transferred,
The transfer force of the toner to the photosensitive drum 1 is relaxed, and the transfer paper is separated from the photosensitive drum 1.

In the image forming process after peeling, the transfer paper on which the toner image is transferred is conveyed to a fixing device (not shown), and the fixing device heats and pressurizes the transfer paper to melt and fix the toner image on the transfer paper. It has become so.

Although not shown, the optical sensor 3 is composed of a light emitting diode and a phototransistor, and is connected to the CPU 5. This optical sensor 3
The light emitted from the light-emitting diode is reflected by the toner patch, which is the reference toner image on the photoconductor drum 1, is reflected by the phototransistor, and as shown in FIG. The electric signal corresponding to the concentration is CP
It is designed to output to U5. The optical sensor 3 does not normally operate during the copying operation, and receives a command from the CPU 5 immediately after the power of the copying machine main body is turned on or when a specified number of copies are made. It is designed to work.

The CPU 5 detects the amount of toner adhering to the photosensitive drum 1 from the detection output of the optical sensor 3 that has read the toner patch, and based on this, first controls the toner density controller 4c. The image quality is corrected, and then the image quality is corrected by controlling the main charging controller 2a. That is, this CPU5
Is an image density control switching means.

In the copying machine having the above construction, when the developer is deteriorated or the photosensitive drum 1 is changed with time,
The CPU 5 corrects the toner density of the developer and then the surface potential of the photoconductor drum 1 to perform the image quality correction for stabilizing the image quality. Such image quality correction is shown in FIG.
It will be described based on the flowchart of FIG.

When the toner patch is formed on the photosensitive drum 1 (S1), the image density of the toner patch is read by the optical sensor 3 according to a command from the CPU 5, and the image density is detected (S2). .. At this time, if the image density is equal to or higher than the reference, no treatment is required, so no processing is performed. However, if the image density is below the reference, the CPU 5 issues a toner density control command to the toner density controller 4c. In response to this command, the toner concentration controller 4c determines whether or not the output value of the toner concentration sensor has already dropped to the limit value V ₁ (S
3), if not yet reached V _1, the output value by a predetermined amount down to replenish toner (S4). The toner concentration control by the toner concentration controller 4c is repeatedly performed until the output value of the toner concentration sensor reaches the limit value V ₁ (S1, 2, 3, 4).

When the image quality correction by the toner concentration controller 4c reaches the limit (when the output of the toner concentration sensor becomes V ₁ or less), the CPU 5 then proceeds to the main charging controller 2a.
Then, a command is issued to control the surface potential of the photosensitive drum 1. Thus, the main charging controller 2a determines whether or not the main charging output of the main charger 2 has reached the limit voltage V _MAX (S5). If not, the main charging output is increased by a certain amount. (S6).

Then, a toner patch is formed again (S
7) The image density is read (S8), and if the image density is higher than the reference, the process is terminated. However,
If the image density is below the reference, the above-described steps S5 to S8 are repeated until the main charging output reaches the limit voltage V _MAX to correct the image density. If the main charging output reaches the limit voltage V _MAX while continuing the correction, it is determined that the correction is impossible due to a trouble, a trouble display is displayed, and the main body is stopped (S9).

As described above, in the copying machine of this embodiment, first, the image quality correction by the toner density controller 4c is performed, and when the image quality correction by the toner density controller 5 is no longer possible, the main operation continues. The image quality is corrected by the charge controller 2a. Therefore, the effect of image quality correction is improved more than in the past, and a stable copied image can be obtained.

Further, since the correctable range is expanded as compared with the case where the image quality is corrected by only one of them as in the conventional copying machine, the conventional image quality correction is not enough to deal with the problem. Even if a deteriorated developer or a deteriorated photoreceptor is used,
It is possible to obtain a constant image. As a result, it is possible to reduce the number of replacements of the consumable developer and the photosensitive drum 1, and it is possible to improve the maintainability.

In this embodiment, the toner concentration controller 4c is first used for correction, and then the main charge controller 2a is used for correction. This is due to the high voltage of the photosensitive drum 1. This is for avoiding stress and is not limited to this. First, the main charge controller 2a
May be performed, and then the toner concentration controller 4c may be used.

[0032]

As described above, the electrophotographic apparatus of the present invention comprises the charging potential control means for controlling the charging potential of the photoconductor,
Toner density control means for controlling the toner density of the developer for visualizing the electrostatic latent image formed on the photoconductor as a toner image, and image density detection for detecting the toner amount of the reference toner image formed on the photoconductor Means and image density control switching means for switching between the control by the charging potential control means and the control by the toner density control means based on the output value of the image density detection means.

Therefore, the image quality can be corrected more effectively than the conventional image quality correction using only one, and a stable formed image can be obtained at all times.

[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.

FIG. 2 is a graph showing the relationship between the surface potential of the photosensitive drum and the image density.

FIG. 3 is a graph showing the relationship between the toner concentration of the developer and the output of the toner concentration sensor.

FIG. 4 is a graph showing the relationship between the toner density of the developer and the image density.

FIG. 5 is a graph showing the relationship between the image density on the photoconductor and the output of the optical sensor.

FIG. 6 is a flowchart illustrating image quality correction in the electrophotographic apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum (photoconductor) 2 Charging device 2a Main charging controller (charging potential control means) 3 Optical sensor (image density detection means) 4c Toner density controller (toner density control means) 5 CPU (Image density control switching means) )

Claims (1)

[Claims] 1. A charging potential control means for controlling a charging potential of a photoconductor, and a toner concentration control means for controlling a toner concentration of a developer for visualizing an electrostatic latent image formed on the photoconductor as a toner image. Image density detecting means for detecting the toner amount of the reference toner image formed on the photoconductor, and switching between control by the charging potential control means and control by the toner density control means based on the output value of the image density detecting means. And an image density control switching means for performing the above.