JPH0695258B2 - Development device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a wet developing device used in a transfer type electrophotographic apparatus such as an electrophotographic copying apparatus or a printer.

(Prior Art) In a transfer type electrophotographic apparatus such as an electrophotographic copying apparatus, a latent image potential on a photoconductor is detected and a suitable developing bias is developed in accordance with the detected level as a method for always obtaining a recorded material without background stain. There is a method of applying to the electrodes. In this method, the latent image potential can be detected by the detection electrode in the apparatus for wet development through the developing solution. However, in order to accurately detect the latent image potential, it is necessary to completely cover the detection electrode with the latent image. A conventional wet developing device uses a developing electrode plate having an extremely large area, and a potential induced on the developing electrode plate from a photoconductor through a developing solution is used as a developing bias potential.
For this reason, the latent image potential is accurately detected only after a considerable portion of the latent image on the photoconductor enters the developing area, so that a difference in developing bias occurs before and after the detection time and a difference in image density occurs. There are drawbacks. In order to eliminate this defect, a detection electrode having a small area is separately provided to detect the latent image potential,
It is necessary to apply a developing bias corresponding to the detection level to the developing electrode plate, which increases the cost.

In addition, toner adheres to the detection electrode and the development electrode, and if left as they are, a dielectric layer is formed on the surface and normal operation is hindered. Therefore, except during development, a bias having a polarity opposite to the development bias is applied to each electrode to electrostatically clean the electrode. However, this method is not preferable because a large amount of toner adheres to the photoconductor when the electrodes are electrostatically cleaned, which increases the load on the photoconductor cleaning device and deteriorates the toner.

(Aim) The present invention has an object to provide a developing device which is inexpensive and can reduce the burden on the photoconductor cleaning device and the toner deterioration.

(Structure) In order to achieve the above object, the present invention provides a developing device of a transfer type electrophotographic apparatus for developing a latent image formed on a photoconductor, which is rotationally driven while maintaining a minute gap from the photoconductor. A first developing solution supply roller for supplying a developing solution to the photoconductor to develop a latent image on the photoconductor, and a first developing solution provided in contact with the first developing solution supply roller. A first developing solution reservoir is formed between the first developing solution supplying roller and the first developing solution supplying roller so that the developing solution in the first developing solution reservoir is supplied to the photosensitive member by the first developing solution supplying roller. A cleaning member, a second developing solution supply roller that is driven to rotate while maintaining a minute gap from the photosensitive body, and supplies the developing solution flowing from the first developing solution supply roller to the photosensitive body; Is provided in contact with the developing solution supply roller of A second cleaning member for cleaning the liquid supply roller, a bias device for limiting the induced potential of the first developing roller to an intermediate value between a preset upper limit potential and a lower limit potential, and the first developing solution supply roller And a switch for electrically setting the second developing solution supply roller to an electrically floating state except during development.

FIG. 1 shows an embodiment of an electronic copying machine apparatus to which the present invention is applied.

During copying, the photoconductor drum 1 is rotationally driven in a direction indicated by an arrow at a constant speed by a driving device, and is uniformly charged by a charger 2 and then an original image is projected by an exposing device (not shown) to form a latent image. By 3, the area outside the image forming area is discharged. The latent image on the photoconductor drum 1 is developed by the wet developing device 4 and transferred by the transfer device 6 to the transfer paper fed from the paper feeding device (not shown) through the roller 5 as indicated by the broken line arrow. The transfer sheet is separated from the photosensitive drum 1 by the roller 7 and is conveyed by the conveying belt 8. The toner is fixed by the fixing device and discharged to the outside. After the transfer paper is separated from the photosensitive drum 1, the cleaning device 9 removes the residual toner, and the static eliminator 10 removes the residual potential to prepare for the next copying.

In the wet developing device 4, the developing rollers 12, 13 and the squeeze roller 14 are arranged in the developing container 11, and the developing roller 1
2, 13 are held at a minute distance from the surface of the photosensitive drum 1. This distance is 0.1 mm. The developing rollers 12 and 13 are rotationally driven in a direction opposite to the photosensitive drum 1 at a peripheral speed higher than that of the photosensitive drum 1 by a driving device as shown by an arrow, and the developing container 11
The plate-like cleaning members 15 and 16 fixed to the developing roller 12 and
The toner on the developing rollers 12 and 13 is always cleaned by coming into contact with the toner. The developing solution supplied from the developing solution supply port 28 by the developing solution supply means flows down between the developing roller 12 and the cleaning member 15 to form a developing solution pool, and the developing roller 12 uniformly rotates the photosensitive drum. It is selected on the surface of No. 1 and further flows between the photoconductor drum 1 and the developing roller 13 to develop the latent image on the photoconductor drum 1. After that, it is collected from the developer discharge port 17 and reused. The squeeze roller 14 is driven to rotate in the same direction as the photoconductor drum 1 by a driving device to scrape off the excess developer on the photoconductor drum 1 to scrape the scraper 18 composed of a blade.
As a result, the developer on the surface is scraped off.

The developing device 4 has a sufficient developing ability, and the effective developing area is narrow in the rotating direction of the photoconductor drum 1, and the developing rollers 12 and 13 are set to the photoconductor drum when they are electrically floated. The latent image potential on 1 is faithfully induced, and this potential is used as a development bias potential to perform background-free development. It was found that the induced potential V _{E applied} to the developing rollers 12 and 13 can be expressed by the following formula (1) when expressed by an actual copy original.

Here, V ₁ is the image portion potential of the latent image, V ₂ is the non-image portion potential of the latent image, S ₁ is the image portion area in the developing region, and S ₂ is the non-image portion area in the developing region.

By the way, if the developing rollers 12 and 13 are left electrically floating, V _E becomes almost the same level as V ₂ when copying a document with a very small image area, and the effects of uneven exposure and uneven charging may occur. After receiving it, you get a dirty copy of the background. Further, when a document having a very large image area is copied, V _E becomes almost the same level as V _1, and the potential contrast necessary for development cannot be obtained, so that a copy having an extremely low image density can be obtained. This problem is solved,
In addition, even when copying a document such as a color document in which the potential of the non-image area is higher than that of a normal white background document, the bias device 19 is used to obtain a copy with high image density without any background stain. ing. The bias device 19 is composed of DC power supplies 20 and 21 and diodes 22 to 25 and is capable of supplying two kinds of potentials to the developing rollers 12 and 13 via the switches 26 and 27. That is, during development, the developing rollers 12, 13
Potential V _E is induced by the latent image potentials of the developing areas on the photoconductors 1 facing each other, and the induced potentials V _E of the developing rollers 12 and 13 on the photoconductor 1 facing the developing rollers 12 and 13, respectively. The potential V ₁ and area S ₁ of the image portion of each developing region and the potential V ₂ and area S ₂ of the non-image portion are potentials determined by the upper expression (1). In the case of copying an original having a very small image area, when the potential V _E of the developing rollers 12 and 13 is lower than the lower limit potential V _{B2 of the} DC power source 21, the diodes 22 and 23 become non-conductive and the diode 24 , 25 become conductive, developing roller 1
The lower limit potential V _B2 is supplied to the terminals 2 and 13 from the DC power supply 21. The developing rollers 12 and 13 are functionally identical to each other, and the developing roller 1
When 2 of the induced voltage V _E is lower than the lower limit voltage V _B2 is a lower limit voltage to the developing roller 12 from the DC power source 21 as shown in FIG. 5 V _B2
Is applied, the induced potential V _E of the developing roller 13 becomes lower limit voltage V _B2
When the voltage is lower, the lower limit voltage V _B2 is similarly applied to the developing roller 13 from the DC power source 21. The toner and the solvent constituting the developer are charged with different signs on the contact surface, and a negative charge of the toner appears. The image portion potential V _{1 on} the photosensitive drum 1, the non-image portion potential V ₂ on the photosensitive drum 1, and the induced potential V _E of the developing rollers 12 and 13 are V ₁ > V _E > V ₂ .

When the induced potential V _E of the developing rollers 12 and 13 is lower than the lower limit voltage V _B2 , the potential of the developing rollers 12 and 13 is forcibly set by applying the lower limit voltage V _B2 from the bias device 19 as described above. The lower limit voltage is set to V _B2, and V ₁ > V _B2 > V ₂ so that the lines of electric force from the image portion on the photosensitive drum 1 to the developing rollers 12 and 13 and the developing rollers 12 and 13 to the photosensitive drum 1 are set. And the lines of electric force toward the non-image part of are generated. The toner in the developing solution migrates to the image portion on the photosensitive drum 1 by the electric force line at the portion where the electric force line goes from the image portion on the photosensitive drum 1 to the developing rollers 12 and 13. In a portion where the lines of electric force are attached to the upper image portion and the lines of electric force are directed from the developing rollers 12, 13 to the non-image portion on the photosensitive drum 1, the lines of electric force migrate to the developing rollers 12, 13. For this reason, the latent image is developed on the photosensitive drum 1 because the toner adheres to the image area and the toner does not adhere to the non-image area. in this case,
The potentials of the developing rollers 12 and 13 are the lower limit voltage V _B2 , and even if the potential V ₂ of the non-image portion on the photoconductor drum 1 fluctuates due to uneven exposure or uneven charging, V _B2 > V ₂ always holds. Lower limit voltage V _B2
By setting, you can obtain a copy with no background stains.

Further, when copying a normal document (a document excluding a document having a very small image area or a document having a very large image area), the potential V _E of the developing rollers 12 and 13 is set to the lower limit voltage V _E.
If it is between the upper limit voltage (V _B1 + V _B2 ) that is the sum of the voltages V _B1 and V _B2 of _B2 and DC power supplies 20 and 21, diode 22 to
25 becomes non-conductive, and the voltages of the developing rollers 12 and 13 remain the induced voltage. In this case, as shown in FIG.
12 is disconnected from the DC power supplies 20 and 21 by the diodes 22 and 24, and similarly, the developing roller 13 is disconnected from the DC power supplies 20 and 21 by the diodes 23 and 25. The induced potentials V _E of the developing rollers 12 and 13 are V ₁ > V _E > V ₂ , and the lines of electric force from the image portion on the photosensitive drum 1 toward the image rollers 12 and 13 and the developing rollers 12 and 13
Electric lines of force from 13 toward the non-image portion on the photosensitive drum 1 are generated. The toner in the developing solution migrates to both images on the photoconductor drum 1 by the lines of electric force at the portion where the lines of electric force go from the image portion on the photoconductor drum 1 to the developing rollers 12 and 13. In the portion where the lines of electric force are attached to the upper image portion and the lines of electric force are directed from the developing rollers 12, 13 to the non-image portion on the photosensitive drum 1, the lines of electric force cause the developing rollers 12, 13 to move.
Migrate to. For this reason, the latent image is developed on the photosensitive drum 1 because the toner adheres to the image area and the toner does not adhere to the non-image area. Further, in the case of copying a document having an extremely large number of image parts, and when the voltage V _E of the developing rollers 12 and 13 is higher than the upper limit voltage, the diodes 22 and 23 become conductive and the diodes 24 and 25 become non-conductive, The upper limit voltage is applied to the developing rollers 12 and 13, and the upper limit voltage is limited. In this case, the upper limit voltage (V _B1 + V _B2 ) is applied to the developing roller 12 from the DC power supplies 20 and 21 as shown in FIG.
The potential of 12 is forcibly limited to the upper limit voltage (V _B1 + V _B2 ),
Similarly, the upper limit voltage (V _B1
By applying + V _B2 ), the potential of the developing roller 13 is forcibly limited to the upper limit voltage (V _B1 + V _B2 ). The potential (V _B1 + V _B2 ) of the developing rollers 12 and 13 is V ₁ > (V _B1 + V _B2 )> V
₂ from the image portion on the photosensitive drum 1 to the developing roller 12,
A line of electric force directed to 13 and a line of electric force directed from the developing rollers 12, 13 to the non-image portion on the photosensitive drum 1 are generated. The toner in the developing solution migrates to the image portion on the photosensitive drum 1 by the electric force line at the portion where the electric force line goes from the image portion on the photosensitive drum 1 to the developing rollers 12 and 13. The lines of electric force attached to the upper image area and the lines of electric force are the development roller.
In the portion from 12, 13 toward the non-image portion on the photosensitive drum 1, the lines of electric force migrate to the developing rollers 12, 13. For this reason, the latent image is developed on the photosensitive drum 1 because the toner adheres to the image area and the toner does not adhere to the non-image area. Therefore, the potential contrast necessary for development can be obtained, and a copy having a sufficiently high image density can be obtained. These states are shown in FIG.

As described above, a normal original with a white background can be copied well even if the original has a very small image area or the original has a large image area.

In addition, when a document such as a color document in which the potential of the non-image part is higher than that of a normal white background document, but the potential of the non-image part is lower than the lower limit potential V _B2 , the copy is generally performed. The potential of the non-image portion is lower than the lower limit potential V _B2 , and the potentials of the developing rollers 12 and 13 are higher than the potential of the non-image portion. Therefore, as in the case of copying an original having a white background, the lines of electric force from the image portion on the photosensitive drum 1 to the developing rollers 12 and 13 and the developing rollers 12 and 13 to the photosensitive drum 1 are the same.
An electric line of force toward the upper non-image portion is generated. The toner in the developing solution migrates to the image portion on the photosensitive drum 1 by the electric force line at the portion where the electric force line goes from the image portion on the photosensitive drum 1 to the developing rollers 12 and 13. The lines of electric force that adhere to the upper image area and the lines of electric force are the developing rollers 12, 13
At the portion from the photoconductor drum 1 toward the non-image portion, the line of electric force swims to the developing rollers 12 and 13. For this reason, the latent image is developed on the photosensitive drum 1 by the toner adhering to the image portion and not adhering to the non-image portion, so that a copy having a high image density without a background stain is always obtained.

Further, when copying a document such as a color document in which the potential of the non-image portion is higher than that of a normal white background document and the potential of the non-image portion is higher than the lower limit potential V _B2 , the developing roller 12 is used. , 13 potential V _E is V _1> V _E> V ₂ becomes a potential determined by the equation (1). Therefore, similarly to the above, in the photosensitive drum 1, toner adheres to the image portion where the potential V ₁ is higher than the potential V _{E of} the developing rollers 12 and 13 and the potential V _{E of the} developing rollers 12 and 13 is attached.
The toner does not adhere to the non-image area where the potential V ₂ is lower, the latent image is developed, and the background stain does not occur. It should be noted that the upper limit voltage and the lower limit voltage are appropriately determined according to the photosensitive drum 1 to be used, and by combining with an exposure light amount adjusting unit (not shown) and varying, a better effect is exhibited.

The switches 26 and 27 are closed by the sequence controller of this copying machine only during development and opened except during development.
The potential difference between 12, 13 and the photoconductor drum 1 is minimized to prevent electrostatic adhesion of the toner to the photoconductor drum 1 and prevent the toner from deteriorating and the burden on the cleaning device 9 from increasing.

Although the number of developing rollers is two in the above embodiment, the number of developing rollers is appropriately determined depending on the copy speed. Further, although the developing rollers have independent circuit configurations, the same effect can be obtained with a common circuit configuration. Further, the squeeze roller 14 may be electrically connected to the developing roller 13. Further, the present invention can be similarly applied to a wet developing device in a transfer type electrophotographic apparatus such as a printer.

FIG. 3 shows another embodiment of the electrophotographic copying apparatus to which the present invention is applied. When the developing rollers 12 and 13 are electrically floated, the potentials of the developing rollers 12 and 13 are faithful to the latent image potential if plural density or color information are mixed in the width direction of the same document. Because of the change, some information may be lost without being developed. That is, the developing roller 12, 1
3 has a developing area for developing the latent image on the photoconductor drum 1 that is narrow in the rotational direction of the photoconductor drum 1 and wide in the width direction (axial direction of the photoconductor drum 1). If a plurality of pieces of density or color information are mixed in the width direction and the latent images for the plurality of pieces of density or color information face the developing roller 12 or the developing roller 13 at the same time, the developing roller 1
The induced potentials V _{E of} 2 and 13 are potentials determined by the equation (1).
When this potential is between the upper limit voltage (V _B1 + V _B2 ) and the lower limit potential V _B2 , the potential of the latent image with respect to a part of a plurality of density or color information is the developing roller 12 , 13 is lower than the induced potential V _E , and the lines of electric force are not directed from the image portion on the photosensitive drum 1 to the developing rollers 12, 13 from the developing rollers 12, 13 at the latent image for some information. The toner does not adhere to the image portion on the photoconductor drum 1, and some of the information disappears without developing the latent image. In order to solve this problem, in this embodiment, the switches 29 and 30 are replaced by the diodes 24 and 25 in the above embodiment.
It is connected in parallel with. The switches 29 and 30 are normally open, and are closed by the operator operating a switch (not shown) on the operation panel. When the switches 29 and 30 are open, the operation is similar to that of the above-described embodiment, and a copy with high image density can be obtained without background stain. When the switches 29 and 30 are closed, the diodes 24 and 25 are short-circuited, and the developing rollers 12 and 13 are constantly supplied with a constant developing bias voltage V _B2 from the DC power source 21, as shown in FIG. As a result, when various densities are mixed in the width direction within the same document, the developing bias potential is kept constant by operating the switches on the operation panel to close the switches 29 and 30, and the potential difference between the latent images. Is faithfully and faithfully developed. That is, even if the induced potential V _E of the developing rollers 12 and 13 is higher than the lower limit potential V _B2 , the lower limit voltage V _B2 is applied from the DC power supply 21 to the developing rollers 12 and 13, so that the potentials of the developing rollers 12 and 13 are forced. _Is limited to the lower limit potential V _B2 . Therefore, information of various densities (or various colors) is mixed in the width direction within the same document, and latent images corresponding to the information of these various densities (or various colors) are simultaneously opposed to the developing rollers 12 and 13. At that time, the potential V _B2 of the developing rollers 12 and 13 becomes lower than the potential of the latent image for the information of various densities (or various colors), and the lines of electric force are information of the various densities (or various colors). At the position of the latent image to the developing roller 12, 13 from the image portion on the photosensitive drum 1, toner is attached to the latent image corresponding to information of various densities (or various colors) to be developed. Further, the latent image on the photosensitive drum 1 with respect to a portion other than the information of the various densities (or various colors) of the original document is developed in the same manner as in the above embodiment. Therefore, a copy with good gradation can be obtained.

(Effect) As described above, according to the present invention, the induced potential of the developing roller is limited to the middle of the upper limit potential and the lower limit potential by the bias device, so that development with high image density can be performed without background stain. Further, since the developing roller is electrically floated by a switch except when developing and the developing roller is cleaned by a cleaning member instead of an electrostatic cleaning means, it is possible to reduce toner deterioration and burden on the photoconductor cleaning device. It can be measured. Further, since it is not necessary to provide a detection electrode other than the developing roller, the cost is reduced. Further, a developer pool is formed by the first developer supply roller and the first cleaning member that is in contact with the first developer supply roller, and the developer in the developer pool is supplied to the photoconductor by the first developer supply roller. The developer flowing from the first developer supply roller is supplied to the photoconductor by the second developer supply roller and the second developer supply roller is cleaned by the second cleaning member. While uniformly supplying to the body, the first cleaning member and the second cleaning member can always efficiently and effectively clean the first developing solution supply roller and the second developing solution supply roller. .

[Brief description of drawings]

FIG. 1 is a diagram showing a cross section and a circuit configuration of an embodiment of an electrophotographic copying apparatus to which the present invention is applied, and FIG. 2 is a characteristic diagram showing a relationship between a latent image potential and a developing bias potential of the embodiment, FIG. 3 is a diagram showing a cross section and a circuit configuration of another embodiment of an electrophotographic copying apparatus to which the present invention is applied, FIG. 4 is a characteristic diagram showing characteristics of the same embodiment in a fixed bias state, and FIGS. The figure is a circuit diagram showing an equivalent circuit in each state of the above embodiment. 12,13 …… Developing roller, 15,16 …… Cleaning member, 19 …… Bias device, 26,27 …… Switch.

Claims (2)

[Claims] 1. A developing device of a transfer type electrophotographic apparatus for developing a latent image formed on a photoconductor, which is rotationally driven while maintaining a minute gap from the photoconductor to supply a developing solution to the photoconductor. A first developing solution supply roller for developing the latent image on the photoconductor, and a first developing solution supply roller provided in contact with the first developing solution supply roller for cleaning the first developing solution supply roller. A first cleaning member that forms a developer pool with the liquid supply roller and supplies the developer in the developer pool to the photoconductor by the first developer supply roller; And a second developing solution supply roller that is driven to rotate and that flows from the first developing solution supply roller to the photoconductor, and a second developing solution supply roller that is in contact with the second developing solution supply roller. To remove the second developer supply roller to clean the second developer supply roller. A member, a bias device for limiting the induced potential of the first developing roller to an intermediate value between a preset upper limit potential and a lower limit potential, and developing the first developing solution supply roller and the second developing solution supply roller. A developing device comprising: a switch that electrically floats when not in use. 2. The developing device according to claim 1, wherein a fixed potential is applied to the developing roller by selection of a fixed bias mode by a bias mode selection switch.