JPH0764361A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To maintain stable high image quality by preventing deterioration of print quality, such as a toner fog increase in a non-image area or print blur due to an image density decrease, accompanied with the long term use of an electrophotographic device. CONSTITUTION:The amount of the operation of a developing device (developing means) is detected by a means B for detecting the amount of operation, and while the peripheral speed of a developing roller 13 is compared with the rotational-speed information of a memory means D according to the output of the means B, a drive means C is controlled by the rotation speed control means A and the rotation speed of the developing roller 13 is increased. Thus, because the toner carry performance of the developing roller 13 is improved according to the amount of the operation of the developing device, print blur and fog are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus for developing an electrostatic latent image formed on a photoconductor with toner (one-component non-magnetic developer).

[0002]

2. Description of the Related Art Conventionally, in this kind of electrophotographic apparatus,
As the operating amount (cumulative value of operating time) of the developing unit increases, the toner conveying performance of the developing roller decreases, or the triboelectric charge amount of the toner in the developing unit decreases. When the recording paper is printed without good development with the toner on the top, there is a problem that the printing quality is deteriorated or the toner fogging occurs on a portion without an image, which deteriorates the printing quality.

The reason why the toner conveying performance of the developing roller is deteriorated is, for example, that a developing blade is provided on the peripheral surface of the developing roller so as to be in sliding contact with the peripheral surface of the developing roller to form a toner layer having a predetermined thickness. However, when it is used for a long period of time, the developing blade wears due to friction with the developing roller and the contact surface with the developing roller, which was initially small, becomes large, resulting in a toner layer of a predetermined thickness on the peripheral surface of the developing roller. The formation of the toner particles is impaired, the resin particles of the toner collapse, and a part of the toner particles are melted and fixed in a thin film, so-called filming phenomenon occurs, and the amount of the toner attached to the surface of the developing roller is reduced. When the amount of residual toner decreases and the amount of toner becomes smaller than the rotation axis of the developing roller, the contact area between the developing roller and the residual toner layer decreases and the developing roller The toner supply toner transport performance may deteriorate due to causes such as reducing.
Further, it is considered that the reason why the triboelectric charge amount on the toner is decreased is that the filming phenomenon occurs on the surface of the developing roller, thereby hindering the normal electrification of the toner due to friction. As described above, each of the causes of the deterioration of the toner carrying performance and the decrease of the toner charge amount is related to the cumulative operating amount of the developing unit, that is, the cumulative operating time of the developing unit during actual printing.

It is to be noted that the number of rotations of the developing roller corresponding to each image density is set, and the toner supply amount to the photoconductor is adjusted by selecting the number of rotations of the developing roller according to the image density. However, this does not solve the above-described print fading and toner fog at the selected image density. When printing with the same image density, the above print fading and toner fog occur. It will be.

[0005]

FIG. 13 shows the relationship between the number of printed sheets in the conventional apparatus and the image density measured by a Macbeth densitometer at the leading and trailing edges of the sheet transferred during printing in solid black image printing. It is a graph showing. In this graph, the □ mark represents the leading edge density of the black solid image, and the Δ mark represents the trailing edge density (toner replenishment was performed every 2000 sheets). According to this, although there is some variation in the leading edge density even after printing up to 10,000 sheets, it does not change so much, but the trailing edge density recovers by replenishing the toner every 2000 sheets, but gradually decreases as the toner decreases. I understand. FIG. 14 is a graph showing the relationship between the number of printed sheets and the value of fog on the photoconductor measured by a color difference meter. When the number of printed sheets increases, the toner charge amount becomes insufficient, and the fog gradually increases. In particular, it can be seen that the fog further increases at the time of replenishing the toner every 2000 sheets.

The present invention solves the above problems and provides an electrophotographic apparatus which prevents the occurrence of print fading and toner fogging that occur when used for a long period of time.

[0007]

In order to solve the above problems, the present invention comprises a photoreceptor and at least a charging means, an exposing means, a developing means, and a transferring means, which are attached to the photoreceptor, and are provided with the charging means. An electrostatic latent image is formed on the charged photoconductor by the exposing means, the electrostatic latent image is converted into a visible image by a one-component non-magnetic developer by the developing means, and the visible image is transferred by the transfer means. In which the image is recorded by transferring the image onto a recording sheet by means of a driving means for rotating the developing roller provided in the developing means, an operating amount detecting means for detecting the operating amount of the developing means, and the operating amount. An electrophotographic apparatus is provided with: a rotation speed control means for controlling the driving means based on the detection output from the detection means to control the rotation speed of the developing roller.

[0008]

By configuring the electrophotographic apparatus as described above, it is possible to reduce the amount of toner according to the operating amount of the developing means, and to reduce the print quality due to the occurrence of fogging and fogging due to the scraping of the developing blade and the filming phenomenon. The decrease can be prevented by increasing the peripheral speed of the developing roller according to the operating amount to maintain a predetermined toner charge amount and a sufficient toner supply amount to the developing roller.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the relationship of control of driving means for rotating and driving a developing roller provided in the developing means according to the detection output of the operating quantity detecting means for detecting the operating quantity of the developing means used in the electrophotographic apparatus of the present invention will be described. A description will be given based on the control block diagram of No. 1. In FIG. 1, A is a rotation speed control unit including a CPU, and B is an operation amount detection unit for detecting an operation amount of a developing device 6 as a developing unit described later as a developing unit including various sensors. . Reference numeral C denotes a driving unit including a motor or the like, which is controlled by the control unit A and rotationally drives the developing roller 13 provided in the developing device 6 described later. D is a memory means,
The reference value of the rotation speed of the developing roller 13 to be compared with the output signal value from the operating amount detecting means B is stored. Then, when the apparatus 1 is used for a long period of time, the operation amount detection means B detects the operation amount of the developing device 6 and outputs an output signal value corresponding to the operation amount, and the control means A outputs this output signal value. The reference value stored in the memory means D is compared, the drive means C is controlled based on the reference value corresponding thereto, and the developing roller 13 is rotationally driven. That is, the control means A controls the rotation speed of the developing roller 13 according to the operating amount of the developing device 6.

Next, an embodiment of the electrophotographic apparatus according to the present invention will be described with reference to FIGS. Reference numeral 1 denotes a printer as an electrophotographic apparatus. As shown in FIG. 2, the printer 1 is provided with a photosensitive drum 2 as a photosensitive member that is rotatably supported, and a photosensitive drum 2 is provided around the photosensitive drum 2. A charging device 4 as a charging means for uniformly charging the surface of the photosensitive drum 2, an exposing device 5 as an exposing means for forming an electrostatic latent image on the surface of the uniformly charged photosensitive drum 2,
A developing device 6 as a developing means that contains toner, a drum cleaner 3 that sweeps off excess toner on the surface of the photosensitive drum 2, and a static eliminator 2 that uniformly removes static electricity on the surface of the photosensitive drum 2.
7. A transfer device 11 is provided as a transfer unit for removing the toner image on the surface of the photosensitive drum 2 onto the recording paper 7 by discharging. Further, a sheet feeding device 10 for feeding the recording sheets 7 stored in the tray 8 is provided on the upstream side in the conveying direction of the recording sheet 7 to the printer 1, and a toner image on the recording sheet 7 is provided on the downstream side in the conveying direction. Fixing device 1 as fixing means for fixing (printing)
2 is provided.

Next, the developing device 6 arranged to face the photosensitive drum 2 will be described. As shown in FIGS. 3 and 4, a cylindrical developing roller 13 is rotatably attached to an opening formed on one side surface of the housing 19 by a shaft 13a. The developing blade 17 and the supply roller 1 are brought into contact with the peripheral surface of the developing roller 13.
5. A recovery blade 21 is provided. A stirring roller 16 is rotatably provided behind the supply roller 15 so as to control the shaft. A toner hopper 25 is surrounded by a housing 19. The toner hopper 25 stores the toner 14 which is a one-component non-magnetic developer. The developing blade 17 has a structure capable of sliding in a groove formed by a blade guide 22 and a blade stay 26, and a spring 18 causes the developing roller 13 to move.
It is pressed against the contact surface with the specified pressure. As a result, a uniform toner layer is formed on the developing roller 13. As the toner 14 of the one-component non-magnetic developer, those having a styrene-based, acrylic-based, polyester-based, or epoxy-based resin as a matrix are generally known.

In the developing device 6 thus constructed,
The toner 14 stored in the toner hopper 25 is agitated by the agitating roller 16 and is agitated by the supply roller 15
Are supplied to the supply roller 15 and the developing roller 13
First, the peripheral surface of the developing blade 17 is conveyed to the contact surface with the developing blade 17. At this contact surface, since a toner layer is formed on the peripheral surface of the developing roller 13 with a uniform thickness, the excess toner 14 is scraped off, and the toner having a uniform toner layer is transferred to the developing blade 17 and the toner. Due to the friction with the developing roller 13, the toner is negatively charged by friction. The toner layer thus uniformly formed on the developing roller 13 is attached to the electrostatic latent image on the photosensitive drum 2 by electrostatic force at a position facing the photosensitive drum 2, and the electrostatic latent image is formed. Is developed, that is, visualized as a toner image. Normally, a bias voltage applying means for achieving a predetermined image density by applying a bias voltage of about -180 V to the developing roller 13 and preventing the occurrence of image fog in the background portion, thereby improving the contrast, is provided. Has been done. The toner layer on the developing roller 13 left as a result of the development without adhering to the photosensitive drum 2 then passes through the recovery blade 21, is collected inside the developing device 6, and is awaited for the next development.

The developing roller 13 of the developing device 6 is made of urethane, ethylene-propylene-diene rubber (EPDM),
Nitrile rubber (NBR), a rubber roller made of silicon or the like is used as a base material, and urethane conductive conductive paint is applied as a coating material on the surface of the material. Both ends of the material have good compression set as a toner sealing material. The sponge-like toner seal 20 is fixed to the housing 19 and arranged in pressure contact with the developing roller 13 to prevent toner leakage from both ends of the rotating developing roller 13. As the developing blade 17, a rubber blade such as silicon rubber or urethane rubber is used. Further, a urethane foam material or a porous cylindrical sponge roller is used as the supply roller 15, and this roller is brought into contact with the developing roller 13 at a nip of 2 to 3 mm. The recovery blade 21 is provided with a member that can collect the toner 14 without scraping it off, and a member having a negatively charged polarity member attached to the surface of a sponge sheet and fixed to the surface of the developing roller 13 so as to be lightly pressed. .

When an image is printed by the printer 1 having the above-mentioned structure, the photosensitive drum is synchronized with the movement of the recording paper 7 fed from the tray 8 by the paper feeding device 10. 2, the charger 4, the exposure device 5, the developing device 6, the drum cleaner 3, and the static eliminator 27 operate. Here, the peripheral surface of the photosensitive drum 2 charged to about -500V by the corona discharge of the charger 4 is selectively discharged to about -70V by the optical scanning of the exposure unit 5 according to the recorded image. An electrostatic latent image is formed. This electrostatic latent image is developed by the negatively charged toner supplied to the developing roller 13 to which a voltage of about -180 V of the developing device 6 is applied, and is visualized as a toner image. Printer 1
The toner image visualized by the toner 14 on the surface of the photosensitive drum 2 with respect to the surface of the recording paper 7 conveyed inside is transferred by the transfer device 11 at a voltage of about +5 kV. After that, the transferred image on the recording paper 7 is pressed and heated by the fixing device 12 to be fixed and then discharged to the outside of the printer 1 to complete the printing of the image. The transfer residual toner image on the photosensitive drum 2 is transferred to the drum cleaner 3
The electrostatic latent image disturbance is uniformly removed by the drum static eliminator 27, and the image is prepared for the next image formation, that is, the charging of the photosensitive drum 2 by the drum charger 4.

Next, the relationship between the peripheral speed of the developing roller 13 and the developer carrying amount is shown in FIG.
Peripheral speed is twice as high as the peripheral speed of the photosensitive drum 2,
The amount of developer conveyed increases as the number of times increases. This can be said to be the same as the tendency even if the developing roller 13 accumulates the operating amount from the initial state, although the absolute amount is different. Further, as the peripheral speed of the developing roller 13 is increased, the charge amount due to friction of the toner 14 on the contact surface between the developing roller 13 and the developing blade 17 is also increased, and as a result, there is no image blurring or toner fogging. Uniform and excellent development can be performed. Therefore, the peripheral speed ratio of the developing roller 13 to the photosensitive drum 2 is doubled as the number of printed sheets increases, for example, in the initial state of 1 to 1000 sheets, 200
2.25 times from 0 to 3000 sheets, 5000 to 6000 sheets
It may be set to gradually increase by a developing process such as 2.5 times for a sheet and 3 times for 8000 sheets or more. This condition may be set according to the condition of the device.

Next, an embodiment of the operating amount detecting means will be described. As means for detecting the operating amount, detection of the amount of wear of the developing blade 17, detection of the cumulative value of the number of rotations of the developing roller 13, detection of the residual amount of toner 14, and development roller 1
3. A method for directly detecting the operating amount of the developing device 6 such as detection of the degree of progress of the filming phenomenon, and the use of recording paper (or printed paper) having a substantially proportional correlation with the operating amount of the developing device 6. There are methods such as detection of the total number of sheets and detection of the total number of rotations of the photosensitive drum 2. Therefore, as a first embodiment, an operating amount detecting means in the case of detecting the cumulative number of used recording sheets 7 will be described with reference to FIG.

In FIG. 6, reference numeral 23 is a paper feed sensor for detecting the recording paper 7 supplied each time printing is performed, and reference numeral 23a is a counter for counting the number of papers supplied by the paper feed sensor 23. And constitute the operating amount detecting means. Then, the counter 23a counts the signal from the paper feed sensor 23 output each time the paper is fed, and the rotation speed control means A correlates the accumulated count value with the operating amount of the developing means stored in the memory in advance. The roller rotation speed information, that is, a predetermined number of sheets to be fed is compared, and when a predetermined value is reached, the driving means C is controlled to increase the peripheral speed of the developing roller 13 of the developing device 6. As a result, the toner transport performance of the developing roller 13 can be improved, and it is possible to prevent fading and fogging in printing. The operating amount can be detected in the same manner by detecting the number of recording sheets printed by the sheet feeding sensor 23 instead of detecting the number of fed sheets and counting the number.

When the peripheral speed of the developing roller 13 is increased and controlled in accordance with the count value of the number of supplied recording sheets as the operating amount of the developing device 6, the number of sheets supplied, that is, the number of printed sheets and the leading edge of the sheet in black solid image printing. FIG. 7 shows the relationship between the image density at the trailing edge of the paper and the value measured by a Macbeth densitometer. In this graph, □ indicates the density of the leading edge of black solid paper, and Δ indicates the density of the trailing edge (toner replenishment was performed every 2000 sheets).
According to this graph, the density of the leading edge of the paper does not change so much even when printed up to 10,000 sheets, but the density of the trailing edge of the sheet is almost the same as the density of the leading edge of the sheet up to 10,000 sheets. It can be seen that the density deterioration is remarkably improved. It is considered that this is because the toner transport performance is maintained uniform. Further, FIG. 8 shows the relationship between the number of printed sheets and the value of the fog on the photoconductor measured by a color difference meter in the same control. As is clear from the comparison between the graph of FIG. 8 and the graph of FIG. 14 showing the conventional case, even if the number of printed sheets is increased, the fogging is small up to 10,000 sheets, and the print quality is deteriorated. I confirmed that it is not.

Next, the operating amount detecting means in the case of detecting the residual toner amount in the toner hopper will be described. Figure 1
As can be seen from the change in print density in the conventional example of No. 3, the print density tends to gradually decrease with the repetition of printing after the toner is replenished. Therefore, the working amount detecting means B is used by detecting the lowering of the upper surface of the toner residual layer in the toner hopper 25 due to the toner consumption accompanying the printing. As shown in FIGS. 9 and 10, here, a toner sensor 28 as an operating amount detecting means B is constituted by a photo interrupter or the like in the toner hopper 25, and the toner sensor 28 is provided in accordance with the height of several steps. The upper surface of the toner is detected to detect the residual toner amount. Then, the detection output signal of the residual toner amount as the operating amount detecting means B is input to the rotation speed control means A, and the image density lowering or the fogging on the photoconductor increases corresponding to the residual toner amount in the toner hopper 25. The peripheral speed of the developing roller 13 is controlled with reference to the memory means D that stores the degree of increase in the peripheral speed of the developing roller 13 which compensates for this. As shown in FIG. 10, the photosensitive drum 2 of the developing roller 13
The peripheral speed ratio to the following is according to the amount of residual toner in the toner hopper, for example, the residual toner amount is 100%, doubled, the residual toner amount is 50%, 2.25 times, and the residual toner amount is 2.5%.
2 times, the residual toner amount is 10%, and the toner residual amount is tripled.

Next, the operation amount detecting means in the case of detecting the abrasion amount of the developing blade will be described with reference to FIGS. 4 and 9. As the operating amount detecting means B of the developing device 6, the developing blade 17 is worn by friction with the developing roller 13 due to long-term use. Therefore, the operating amount detecting means B is detected by detecting the abrasion amount. As shown in FIG. 4, a developing blade upper end position sensor 29 (not shown in FIG. 4) as an operation amount detecting means B is formed on the inner walls of the blade guide 22 and the blade stay 26 by a photo interrupter or the like, and this is installed in several stages. It is provided over the entire length to detect the upper end position of the developing blade to detect the amount of wear of the developing blade. Then, a detection output signal of the abrasion amount of the developing blade as the operation amount detecting means B is inputted to the rotation speed control means A, and the characteristic of the image density decrease and the increase of the fog on the photoconductor corresponding to the abrasion amount of the developing blade 17 are inputted. Thus, the peripheral speed of the developing roller 13 is controlled in light of the memory means D which stores the degree of increase in the peripheral speed of the developing roller 13 which compensates for this. As shown in FIG. 12, the peripheral speed ratio of the developing roller 13 to the photosensitive drum 2 is, for example, 2 times in the initial state according to the wear amount of the developing blade, 2.25 times when the wear amount is 0.5 mm, and 2. 1 times when the wear amount is 1 mm. 5 times wear amount is 1.
It will be gradually increased, such as 3 times at 5 mm.

Next, the operating amount detecting means for detecting the progress of the filming phenomenon will be described. As the operating amount detecting means B of the developing device 6, since the developing roller 13 causes a filming phenomenon on its surface due to long-term use and intervening toner adheres in a thin film form, the operating amount is detected by detecting the adhered amount. The detection means B is used. Operation amount detecting means B facing the developing roller 13
The filming sensor 30 as described above is configured by a photo sensor or the like to detect a change in the light reflectance on the surface of the developing roller to detect the degree of filming. Then, a detection output signal of the filming degree as the operation amount detecting means B is inputted to the rotational speed control means A, and the development is made up to compensate for it by the characteristic of the image density decrease and the increase of the fog on the photoreceptor corresponding to the filming degree. The peripheral speed of the developing roller 13 is controlled with reference to the memory means D that stores the degree of increase in the peripheral speed of the roller 13.

Next, the operation amount detecting means in the case of detecting the cumulative rotation number of the developing roller will be described. As the operating amount detecting means B of the developing device 6, the toner conveying performance is deteriorated as the developing device 6 is used due to the above-mentioned cause. Therefore, the operating amount detecting means B is detected by detecting the cumulative rotation number of the developing roller. It is a thing. The developing roller 13
A well-known counter (not shown) as the operation amount detecting means B for counting the rotation of the developing roller 6 is provided to detect the cumulative number of rotations of the developing roller to detect the deterioration of the developing device 6. Then, the detection output signal of the deterioration of the developing device 6 as the operation amount detecting device B is input to the rotation speed control device A, and the characteristics of the decrease of the image density and the increase of the fog on the photoconductor corresponding to the deterioration of the developing device 6 are inputted. The peripheral speed of the developing roller 13 is controlled with reference to the memory means D that stores the degree of increase in the peripheral speed of the developing roller 13 which compensates for this. The same applies when the cumulative rotation speed of the photosensitive drum 2 is detected instead of the cumulative rotation speed of the developing roller 13. Further, although the above description has been made on the case where each operating amount detecting means is individually used, it is also possible to use these in combination.

In the above-described embodiment, the method of detecting the operating amount of the developing device is the method of measuring the number of printed sheets, the residual toner amount, or the abrasion amount of the developing blade, but the invention is not limited to this. It is sufficient that the deterioration in performance and the increase in fog on the photoconductor can be known directly or indirectly, or a combination thereof. In that case, the correction characteristics of the operating amount of the developing device detected and the amount of increase in the peripheral speed of the developing roller according to the degree of the decrease in the developer transport performance and the increase in the fog on the photoconductor were adjusted to each method. It must be stored in the memory means D as an entity.

[0024]

Since the present invention is configured as described above, the peripheral speed of the developing roller is detected by detecting the operating amount of the electrophotographic apparatus and comparing the detected output with the characteristics of image density decrease and toner fog increase. By increasing the value, the toner conveying performance can be maintained and the toner fogging can be prevented from increasing, and the printing quality of the electrophotographic apparatus can be maintained at a stable high image quality for a long period of time.

[Brief description of drawings]

FIG. 1 is a control block diagram for controlling a rotation speed of a developing roller according to an embodiment of the present invention.

FIG. 2 is a side view showing an arrangement of main components of the printer according to the embodiment of the invention.

FIG. 3 is a perspective view of a developing device according to an embodiment of the present invention.

FIG. 4 is a sectional view of a developing device according to an embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a developing roller peripheral speed ratio and a developer transport amount in the present invention.

FIG. 6 is a block diagram of the developing roller peripheral speed control of the first embodiment of the operating amount detecting means used in the present invention.

FIG. 7 is a diagram showing the relationship between the number of printed sheets and the image density when the first embodiment is used.

FIG. 8 is a diagram showing the relationship between the number of printed sheets and fog on the photosensitive member when the first embodiment is used.

FIG. 9 is a block diagram showing a second embodiment of the operating amount detecting means used in the present invention.

FIG. 10 is a diagram showing a residual toner amount and a correction amount of a peripheral speed ratio of a developing roller to a photosensitive drum in the second embodiment.

FIG. 11 is a block diagram showing a third embodiment of the operating amount detecting means used in the present invention.

FIG. 12 is a diagram showing the amount of wear of the developing blade and the amount of correction of the peripheral speed ratio of the developing roller to the photosensitive drum of the third embodiment.

FIG. 13 is a diagram showing the relationship between the number of printed sheets and the image density in the conventional example.

FIG. 14 is a diagram showing a relationship between the number of printed sheets and fogging on a photoconductor in a conventional example.

[Explanation of symbols]

1 Printer 2 Photosensitive Drum (Photosensitive Member) 4 Charging Device (Charging Means) 6 Developing Device 13 Developing Roller 14 Toner 17 Developing Blade 25 toner hopper

Claims (1)

[Claims] 1. A photosensitive member, and at least a charging unit, an exposing unit, a developing unit, and a transferring unit attached to the photosensitive member, the electrostatic latent image on the photosensitive member charged by the charging unit by the exposing unit. And the electrostatic latent image is formed into a visible image by a one-component non-magnetic developer by the developing means, and the visible image is transferred onto a recording sheet by the transfer means to perform image recording. A driving unit that rotationally drives a developing roller provided in the developing unit, an operating amount detecting unit that detects an operating amount of the developing unit, and the driving unit that controls the driving unit based on a detection output from the operating amount detecting unit. An electrophotographic apparatus, comprising: a rotation speed control unit that controls a rotation speed of a developing roller.