JPH1138789A - Image forming method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an image change caused by the reduction of a toner density and maintain constant image quality by making a transfer with the transfer current having the value lower than the normal value after a toner end is detected. SOLUTION: When the toner in a toner replenishing bottle is exhausted and the reduction of the toner concentration TC from normal 3-5 wt.% to 3 wt. % or below, for example, is continuously detected, a current of A' microampere lower than the normal A microampere is fed as optimum transfer current value for realizing the best image quality based on the curve Cv2 of the image rank against the change of the transfer current corresponding to this concentration. The action to reduce the feed transfer current is compatible with the low-toner concentration condition. Even if the toner concentration TC is lowered, the occurrence of a void is eliminated, and the image quality of the allowed number of copies after the detection of a toner end can be maintained high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming apparatus applied to a copying apparatus, a printer, and the like, and more particularly to an image forming method and an image forming apparatus after toner end detection.

[0002]

2. Description of the Related Art Among copiers and printers, there is an apparatus having an image forming function in which a latent image formed optically and electrically is developed with toner and transferred to paper. Conventionally, a general configuration includes a developing unit using a two-component developer containing toner and a transfer unit for transferring toner to paper based on a transfer current.

In such a configuration, an appropriate amount of toner is supplied to a developing unit from a detachable toner supply bottle filled with toner to maintain a predetermined toner concentration. The transfer of toner to paper is performed based on a transfer current corresponding to a predetermined toner concentration.

Further, when the toner density is controlled to a normal density, for example, 3% by weight to 5% by weight, the toner density is supplied to a transfer unit in order to suppress the occurrence of white spots and wide area toner dust on paper. By setting the transfer current higher, the appropriate transfer current is obtained.

Further, a configuration is generally employed in which the toner supply bottle is emptied, that is, the toner end detecting means is provided, and a predetermined number of copies can be made after the toner end is detected.

[0006]

When a predetermined number of copies are made after the toner end detection as described above, the toner density in the developing unit decreases as the number of copies progresses. In the configuration of the related art, there is no means for responding to such a change in the image forming condition, and there is a disadvantage that the image quality is deteriorated due to the change in the image forming condition. That is, in the above-described conventional configuration, it is difficult to cope with a change in the image after the toner end is detected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and has as its object to provide an image forming method and an image forming apparatus capable of coping with a change in an image after toner end detection. And

[0008]

According to the present invention, there is provided an image forming method, comprising: a developing unit using a two-component developer containing at least a toner; a transfer unit to which a transfer current is supplied; Equipped with toner end detection means,
And a predetermined number of copies can be made after toner end detection,
An image forming method applied to a copying apparatus having an image forming apparatus, wherein a transfer with a transfer current having a value lower than a normal value is performed after the toner end detection.

According to the image forming method of the present invention having the above-described structure, the transfer current becomes a low value in response to the decrease in the toner density after the detection of the toner end, so that the image quality change due to the decrease in the toner density is suppressed. Thus, a constant image quality is maintained.

An image forming apparatus according to the present invention includes a developing unit using a two-component developer containing at least toner.
A copying apparatus including an image forming apparatus, including a transfer unit to which a transfer current is supplied, and a toner end detecting unit, and capable of copying a predetermined number of sheets after toner end detection.
After the toner end is detected, a transfer current having a value lower than a normal value is supplied to the transfer unit.

According to the image forming apparatus of the present invention having the above-described structure, the transfer current becomes a low value in response to the decrease in the toner density after the detection of the toner end, so that the image quality change due to the decrease in the toner density is suppressed. Thus, a constant image quality is maintained.

[0012]

Embodiments of the present invention will be described below. FIG. 1 is a diagram for explaining the principle in an embodiment of an image forming method according to the present invention. An image forming method according to the present invention includes a developing unit using a two-component developer containing a toner, a transfer unit to which a transfer current is supplied, and a toner end detecting unit, and detects a predetermined number of sheets after the toner end is detected. This is an image forming method applied to a copying apparatus having an image forming apparatus capable of copying.

As shown in FIG. 1, in a normal case where the toner is not at the toner end, the toner density is, for example, 3% by weight to 5% by weight, and the image rank (ie, image quality) with respect to the change in the transfer current corresponding to this density is , And a curve Cv1 in the figure. Thus, when the toner concentration is 3% by weight to 5% by weight, the appropriate transfer current value for realizing the best image quality is A microamperes. The best image quality is calculated comprehensively, including the absence of white spots and wide area toner dust on the image, and other image quality factors.

Here, when the toner in the toner supply bottle runs out and the toner concentration TC is continuously detected to decrease from, for example, 3% by weight to 5% by weight or less to 3% by weight or less, the toner concentration TC corresponds to this concentration. Based on the curve Cv2 of the image rank with respect to the change of the transfer current, A ′ microamperes, which is lower than A microampere in the normal state, is supplied to the transfer unit as an appropriate transfer current value for realizing the best image quality.

As described above, when the toner density is reduced due to the toner end, the optimum transfer current value for suppressing the occurrence of white spots and wide area toner dust under such low toner density conditions also changes. In the method (1), the supply transfer current is shifted to a lower level as described above, so that it is possible to meet the low toner density condition. As a result, even if the toner concentration TC decreases, it is possible to eliminate the occurrence of white spots and wide area toner dust, and thus it is possible to maintain a high image quality for the allowable number of copies after toner end detection.

FIG. 2 is a schematic sectional view of an embodiment of the image forming apparatus according to the present invention. FIG. 3 is a schematic sectional view of a main part of the developing unit shown in FIG. The image forming apparatus 1 shown in FIG. 2 includes a copying machine, a printer, a facsimile machine or a multifunction peripheral thereof (not shown).
Image forming apparatus).

The image forming apparatus 1 has a unit case 2 and various image forming elements described later incorporated therein. The unit case 2 shown as an example in FIG. And a developing case cover 5 constituting an upper wall of a developing unit, which will be described later. The case cover 4 and the developing case cover 5 are snap-fit (so-called ) For detachable locking.

In the unit case 2, a drum-shaped photosensitive member 7 as an example of an image carrier on which an electrostatic latent image is formed and a charging roller 8 as an example of a charging device are rotatably provided inside. Assembled, the charging roller 8 extends parallel to the photoconductor 7.

During the image forming operation, the photosensitive member 7 is driven to rotate clockwise in FIG. 1 by a driving device (not shown), and at this time, static elimination light from a static elimination device (not shown) supported by the main body of the image forming apparatus. L1 is the case cover 4
The light enters the unit case 2 through an opening 34 formed in the photoconductor 7 and irradiates the surface of the photoconductor 7. As a result, the surface potential of the photoconductor 7 is averaged to a reference potential of, for example, 0 to -150V. On the other hand, the charging roller 8 is pressed against the surface of the photoconductor 7 and is driven to rotate by the rotation of the photoconductor 7, thereby causing the photoconductor 7 to have a surface potential of −1100
It is uniformly charged to be around V. At this time, a predetermined voltage is applied to the charging roller 8 by a power supply (not shown).

The surface portion of the photoreceptor 7 charged to a predetermined polarity as described above is irradiated with an optically modulated laser beam L2 in the exposure section 9. The laser light L2 is emitted from an exposure optical system (not shown) supported by the image forming apparatus main body, and enters the unit case 2 through an opening 35 formed in the case cover 4. With such exposure,
A predetermined electrostatic latent image is formed on the photoconductor 7. For example, the surface potential of the photoconductor portion (image portion) irradiated with the laser beam L2 is 0 to -290 V, and the surface potential of the photoconductor portion (background portion) not irradiated with the laser beam L2 is as described above. Maintain around -1100V. It is also possible to form an electrostatic latent image by illuminating a document (not shown) and forming a reflected light image on the photoreceptor 7.

On the other hand, a developing sleeve 11 of a developing unit 10 is rotatably supported on the unit case 2, and this sleeve 11 is rotated in a counterclockwise direction in FIG. 1 during an image forming operation. The developing case 1 of the developing unit 10 is formed by a part of the case main body 3 in the unit case 2 and the developing case cover 5 that covers the upper part thereof.
2 and a developer chamber 90 is defined therein. A powdery two-component developer 101 having a toner and a carrier is accommodated in a developer chamber 90 of the developing case 12.
Are immovably arranged.

As the developing sleeve 11 rotates as described above, the developer 101 in the developing case 12 is conveyed while being carried on the developing sleeve 11 by the magnetic force of the magnet 13, and a developer regulating member comprising a doctor blade 14. Regulates the amount of developer conveyed. The regulated developer is conveyed to a developing area between the developing sleeve 11 and the photoconductor 7, and at this time, the developing sleeve 11 is supplied with, for example, -80.
Since the developing bias voltage of about 0 V is applied, the toner in the developer conveyed to the developing area is electrostatically transferred to and adheres to the image area on the photoconductor 7 and is fixed on the photoconductor 7 by a predetermined amount. Is formed. The electrostatic latent image formed on the photoconductor 7 is visualized as a toner image.

As described above, the developing unit 10 converts the electrostatic latent image formed on the image carrier composed of the photoreceptor 7 into a visible image as a toner image using the two-component developer 101 having toner and carrier. The developing sleeve 11 is
An example of a developer carrying member that carries and conveys the two-component developer 101 used for development is configured.

On the other hand, as shown in FIG. 1, a transfer roller 15 which is an example of a transfer unit is rotatably supported on the main body of the image forming apparatus so as to face the photoconductor 7. Further, a paper feeding device (not shown) is provided on the image forming apparatus main body side, and a transfer paper 10 which is an example of a transfer material is provided from the paper feeding device.
0 indicates the photosensitive member 7 and the transfer roller 1 as indicated by an arrow B in FIG.
5 is conveyed toward the transfer unit 22. The transfer paper 100 is transferred from the photosensitive member 7 to the transfer roller 1 in a state where the leading end of the transfer paper 100 matches the leading end of the toner image formed on the photosensitive member 7.
5 pass through the transfer section 22. At this time, the transfer roller 15 rotates counterclockwise in FIG. 1 while abutting on the photoconductor 7 via the transfer paper 100, and since a transfer bias voltage is applied to the transfer roller 15,
The toner image on the photoconductor 7 is transferred to the transfer paper 100.

The transfer paper 100 leaving the photoreceptor 7 is conveyed to a fixing device (not shown) as shown by an arrow B1 in FIG. 1, where the toner image is transferred by the action of heat and pressure. 100 and fused. The static elimination needle 16 supported by the image forming apparatus main body is disposed downstream of the transfer unit 22 in the transfer direction of the transfer paper 100. The static elimination needle 16 is made of a thin metal plate extending in parallel with the photoreceptor 7, the portion of the static elimination needle 16 facing the photoreceptor 7 is formed in a sawtooth shape, and the tip of each tooth is sharply sharp. . A voltage is applied to the static elimination needle 16 from a power source (not shown), thereby eliminating the charge of the transfer paper 100 and facilitating separation of the transfer paper 100 from the photoconductor 7.

An intermediate transfer member is used as a transfer material, and a toner image on a photoreceptor is primarily transferred to the intermediate transfer member, and then the toner image is secondarily transferred to a transfer paper as a final transfer material. You can also.

The residual toner adhering to the photoconductor 7 after the transfer of the toner image is scraped off the surface of the photoconductor 7 by the cleaning blade 18 of the cleaning device 17 shown in FIG. Thus, the surface of the photoreceptor 7 is cleaned, and the process proceeds to the next image forming operation again. Cleaning device 1
7 has a cleaning case 19 constituted by a part of the case main body 3 in the unit case 2, and the toner scraped off by the cleaning blade 18 is
The toner is discharged out of the cleaning device 17 by the rotation of the toner conveying member 20 disposed in the cleaning case 19, and is reused in the developing unit 10. The toner conveying member 20 is configured in an appropriate form such as a toner conveying screw or a toner conveying coil. The cleaning blade 18 is an example of a cleaning member that removes toner remaining on the surface of the photoreceptor 7 from the surface and cleans the surface, and is fixed and held on the case main body 3.

As described above, the image forming apparatus includes the photosensitive member 7
The image forming apparatus is configured to transfer the toner image formed on the image carrier to the transfer paper 100 conveyed toward the image carrier to obtain a recorded image, and to be detachable from the image forming apparatus main body. The mounted image forming unit is one in which at least one of the image forming elements including the above-described image carrier is assembled to a unit case. In the illustrated example, the photosensitive member 7, the charging roller 8, the developing unit 10, and The components of the cleaning device 17 are assembled to the unit case 2 to form the image forming device 1.

Next, the developing unit 10 will be described. The developing case 12 contains, for example, a two-component developer 101 having a carrier formed of a small iron ball and a toner, and the developer 101 is supplied to the developing case 12 by first and second agent stirring members 44 and 45. The developer is stirred while being circulated in the developer chamber 90 and supplied to the developing sleeve 11. As described above, the layer thickness of the developer supplied to the developing sleeve 11 is regulated by the doctor blade 14 provided around the developing sleeve 11. A portion of the peripheral surface of the developing sleeve 11 facing the photoconductor 7 is exposed from the developing case 12 to the outside.

Here, the developing sleeve 11 is made of a non-magnetic cylindrical body made of aluminum having an outer diameter of, for example, 16 to 20 mm, and its peripheral surface is formed smoothly or in order to improve the transportability of the developer. On the outer peripheral surface of the developing sleeve 11, irregularities such as a v-groove are formed. A shaft 46 passes through the inside of the developing sleeve 11, and the magnet 13 is fixed to the shaft 46. The front end of the shaft 46 is
The unit case 2 is fixedly supported on the case body 3, and the rear end is rotatably fitted via a bearing to a sleeve end member fitted and fixed to the rear end of the developing sleeve 11. I have. The front end of the developing sleeve 11 is rotatably supported by a shaft 46 via a bearing.

As described above, the shaft 46 is fixedly supported on the unit case 2 together with the magnet 13, and the shaft 4
6, a developing sleeve 11 is rotatably supported. When the sleeve end member is driven to rotate, the developing sleeve 11 is driven to rotate counterclockwise in FIG. A bias voltage to the developing sleeve 11 is applied from the image forming apparatus main body side via the above-described coupling.

FIG. 10 is an explanatory view showing the relationship between the developing sleeve 11, the magnet 13 which is non-rotatably disposed inside the developing sleeve 11, and the photosensitive member 7. As shown here, the individual magnets of the magnet 13, that is, the first to fifth magnets 13a to 13a
Reference numerals 3 e are arranged in the circumferential direction of the developing sleeve 11, are fixed to the shafts 46, respectively, and extend in the longitudinal direction of the sleeve 11. Then, these magnets 13a to 13
By e, magnetic force distributions P1 to P6 in the normal direction are formed in the circumferential direction of the developing sleeve.

As described above, when the sleeve end member is rotationally driven by the driving device on the image forming apparatus main body side, the developing sleeve 11 is rotated, and the rotation of the sleeve end member is driven by the first and the other via drive gears. The second stirring member 44,
45, and these members are each driven to rotate in a predetermined direction. As a result, the developer contained in the developer chamber 90 in the developing case 12 is conveyed while being stirred, and the developer circulates through the passages at both ends thereof while being guided by the partition wall 71. As a result, the toner and the carrier of the developer are frictionally charged to different polarities.
The developer is supplied to the developing sleeve 11, and the developer from the developing sleeve 11 is returned to the stirring member.
Since each of the elliptical plates 65 and 66 has a shape in which a part of an ellipse is cut out, the stirring effect of the developer is enhanced by contacting the edge of the notch with the developer.

In the developing case 12, a sensor for detecting the toner concentration of the developer 101, in this embodiment, a magnetic permeability measuring sensor 7
2 are provided. Further, a toner supply bottle 73 is detachably attached to the image forming apparatus main body.

When the sensor 72 detects that the toner concentration TC of the developer 101 contained in the developer chamber 90 in the developing case 12 has become lower than the reference value, the toner is replenished based on the detection signal. Toner supply bottle 7 by signal
3, the toner is supplied from a supply port 73a of the toner supply bottle 73 to a toner supply section (not shown) formed by the case body 3.

Toner supply bottle 7 containing supply toner
3 has a spiral projection formed on its inner wall surface, and its rotation causes the toner inside to be sequentially sent from the back side to the front side supply port 73a to be supplied to the toner supply section. A drive shaft (not shown) that rotates the toner supply bottle 73 is provided with an electromagnetic clutch (not shown). When a toner supply signal is output, the electromagnetic clutch is turned on,
The drive shaft for the toner supply bottle rotates.

As described above, when the first stirring member 44 rotates, the toner in the toner replenishing section is fed into the developer chamber 90 in which the stirring member 44 is provided.

As described above, the toner from the toner replenishing bottle 73 is temporarily stored in the toner replenishing unit and is sent out to the developer chamber 90 little by little. The toner is replenished to the developer chamber 90 by a constant amount. Developer chamber 90
The replenished toner is stirred by the stirring members 44 and 45.
The mixture is stirred and mixed with the two-component developer present here.

If the sensor 72 continues to detect a decrease in the toner concentration TC even after performing the above-described toner supply operation,
Assuming that the toner in the toner supply bottle 73 has run out, the display unit indicates that the toner end is near, and notifies the user to that effect. If the toner supply bottle is not replaced despite such a display, when the image forming operation is performed on, for example, 50 sheets of A4 size transfer paper after the display, the operation of the image forming apparatus is performed. To stop.

The replacement operation of the toner supply bottle 73 is determined based on the opening / closing time of the front door (not shown) of the image forming apparatus main body. After the replacement of the toner supply bottle 73, the toner supply operation is performed for a predetermined time. After confirming that the detected voltage has reached a certain value, the operation prohibition of the image forming apparatus is released.

Next, the transfer unit will be described. FIG.
The transfer roller 15 shown in (1) is formed by winding a conductive resin around a metal core, and is pressed against the photoreceptor along with the re-bearing by a compression spring (not shown). A transfer current is supplied to the transfer roller 15 from a controller 50, and based on the transfer current, the transfer roller 15
The upper toner is transferred to the transfer paper 100.

In a normal case where the toner end is not detected, the toner concentration is, for example, 3% by weight to 5% by weight.
A higher transfer current is supplied to the transfer roller 15 from the controller 50 as an appropriate transfer current. The reason why the appropriate transfer current is set higher is to eliminate the occurrence of white spots and wide area toner dust on the transferred image.

Here, the sensor 72 in the developing unit 10
Continues to detect a decrease in the toner concentration TC, it is determined that the toner in the toner supply bottle 73 has run out, and a toner end detection signal is sent to the controller 50 of the transfer unit. In response to this signal, the controller 50 supplies a predetermined lower transfer current to the transfer roller 15 than the normal transfer current as the appropriate transfer current.

As described above, depending on the toner end, the toner concentration becomes, for example, from 3% by weight to 5% by weight to 1% by weight or less.
When the content is reduced to 3% by weight, the optimum transfer current value for suppressing the occurrence of white spots and wide-area toner dust under such a low toner density condition also changes. However, in the configuration of the present invention, the supply current is controlled as described above. By responding by shifting the transfer current to a lower level, it becomes possible to meet the low toner density condition. As a result, even if the toner concentration TC is reduced, it is possible to eliminate the occurrence of white spots and wide-area toner dust, thereby maintaining a high image quality for the allowable number of copies after the toner end detection.

[0045]

As described in detail above, claim 1 of the present invention
The image forming method according to the above includes a developing unit using a two-component developer containing at least a toner, a transfer unit to which a transfer current is supplied, a toner end detecting unit, and a predetermined number of copies after the toner end is detected. Is an image forming method applied to a copying apparatus having an image forming apparatus, wherein a transfer is performed with a transfer current having a value lower than a normal value after the toner end is detected. By setting the transfer current to a low value corresponding to the decrease in the toner density, it is possible to suppress a change in the image quality due to the decrease in the toner density, and to maintain a constant image quality.

An image forming apparatus according to a second aspect of the present invention includes a developing unit using a two-component developer containing at least a toner, a transfer unit to which a transfer current is supplied, and toner end detecting means, A copying apparatus having an image forming apparatus capable of copying a predetermined number of sheets after toner end detection, wherein a transfer current having a value lower than a normal value is supplied to a transfer unit after toner end detection. Therefore, by setting the transfer current to a low value in response to a decrease in the toner density after the detection of the toner end, it is possible to suppress a change in image quality due to the decrease in the toner density, and to maintain a constant image quality.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a principle in an embodiment of an image forming method according to the present invention.

FIG. 2 is a schematic sectional view of an embodiment of an image forming apparatus according to the present invention.

FIG. 3 is a schematic sectional view of a main part of the developing unit shown in FIG.

[Explanation of symbols]

 Cv1 Transfer current curve when toner density is high Cv2 Transfer current curve when toner density is low I Transfer current R Image rank TC Toner density

Claims (2)

[Claims] 1. A developing unit using a two-component developer containing at least toner, a transfer unit to which a transfer current is supplied, and a toner end detecting means, and a predetermined number of copies can be made after the toner end is detected. An image forming method applied to a copying apparatus having an image forming apparatus, wherein a transfer is performed by a transfer current having a value lower than a normal value after the toner end is detected. . 2. A developing unit using a two-component developer containing at least a toner, a transfer unit to which a transfer current is supplied, and a toner end detecting means, and a predetermined number of copies can be made after the toner end is detected. A copying apparatus having an image forming apparatus, wherein a transfer current having a value lower than a normal value is supplied to the transfer unit after the toner end is detected.