JPH11295970A - Contact type electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily keep the electrifying performance of a contact constant by providing a means connected in parallel with the contact between the contact and a power source and varying voltage impressed on the contact. SOLUTION: The power source 2 is connected to a brush 1, and an image carrier 3 being a photoreceptor drum is uniformly electrified by static electricity by the brush 1. Then, an external variable resistance 12 is provided in parallel with the brush 1. It is good to attach the resistance 12 to the processing unit of the electrifying device or attach it to the image forming device main body side of the power source 2 other than the unit. When a current flowing to the image carrier 3 is largely fluctuated due to environmental change, the value of the current flowing to the image carrier 3 is easily restored to be an appropriate one when the resistance 12 is operated by a user. It is good to constitute the resistance 12 of plural fixed resistances and a switch properly switching and connecting the fixed resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus (copier, printer), an image carrier such as a photosensitive drum, and a transfer material such as paper (hereinafter, these are collectively referred to as an image forming medium). A) for charging.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic copying machine or printer, an image forming medium, that is, an image carrier such as a photosensitive drum or an insulating sheet, or a transfer material (for example, paper) for transferring a toner image is used. The corona charger is used as a device for charging the charge. However, this corona charger has a problem that it generates ozone and nitrogen oxides and pollutes the environment. In order to solve this problem, a contact-type charging device that brings a charge by applying a voltage by bringing a conductive roller, brush, blade, etc. into contact with the image carrier has been put to practical use and widely adopted. It has become. The use of this contact-type charging device hardly generates ozone or nitrogen oxides.

[0003]

However, the contacts, such as rollers and brushes, used in the contact-type charging device are made of conductive synthetic rubber or synthetic fiber, and the electrical resistance value is determined by the environmental (temperature, humidity). It fluctuates greatly due to changes. When the resistance value fluctuates, the current value flowing through the device fluctuates, and as a result, the charging performance of the contact changes greatly, which has a great influence on the charging position of the image carrier and the transferability of the toner image. As a result, problems may occur during image formation.

In order to eliminate this effect, as described in, for example, JP-A-4-219768, JP-B-7-14770, and JP-A-5-150612, the electric resistance is preferably controlled by temperature and humidity. Forming contacts with a material that is not easily affected, providing a plurality of brushes, switching these appropriately according to environmental changes, detecting the temperature of the contacts, and controlling the chargeability of the contacts based on the detected temperature Various solutions have been proposed, such as providing a so-called temperature control, and connecting a resistor having the same magnitude as the contact in series with the contact.

However, it cannot be said that these methods have sufficiently solved the problem of charging performance fluctuation due to environmental changes. In the power supply device for applying a voltage to the contact, a voltage and current adjustment mechanism is provided.
These are initialized when the device is installed. Therefore, once set, it is not easy to reset the current and voltage to desired values even if the electric resistance value largely fluctuates due to environmental fluctuations or the like.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. Therefore, even when the resistance of the contact fluctuates greatly according to an environmental change, the charging of the contact can be performed by a simple operation. It is an object of the present invention to provide a contact-type charging device whose performance can be easily kept constant.

[0007]

According to the present invention, there is provided a contact-type charging device for applying an electric charge by contacting an image forming medium of an electrophotographic image forming apparatus. A contact for contacting the forming medium, a power supply for applying a voltage to the contact, and means for connecting the contact and the power supply in parallel with the contact and varying a voltage applied to the contact; The contact type charging device is constructed. The image forming medium is an image carrier such as a photosensitive drum or an insulating sheet, or a transfer material such as paper.

[0008] The means for varying the voltage applied to the contact may be a combination of a variable resistor, a plurality of fixed resistors, and a switch means for selectively switching and connecting the fixed resistors, a variable resistor and a varistor. Or a series circuit of a variable resistor and a fixed resistor. With the above configuration, even if the resistance value of the contact changes due to environmental fluctuation or the like, it is possible to easily correct this and return to an appropriate value. Therefore, an excellent image can always be formed stably in the image forming apparatus.

The means for varying the voltage applied to the contact is provided in the process unit or the image forming apparatus main body that houses the contact and the image forming medium. Therefore, the installation location can be selected in consideration of maintainability and user convenience.

[0010]

FIG. 1 is a schematic structural view of an electrophotographic image forming apparatus to which a contact-type charging device of the present invention can be applied. In the drawing, reference numeral 1 denotes a brush constituting a contact in a contact-type charging device, which is formed of conductive fibers. A power source 2 is connected to the brush 1 to supply a voltage to the brush 1. The image carrier 3, for example, a photosensitive drum, is uniformly charged electrostatically by the brush 1. Reference numeral 4 denotes a laser beam for forming a latent image on the image carrier 3, and 5 denotes a developing device, which attaches toner or the like to the latent image on the image carrier 3 formed by the laser beam 4. Develop the image.

Reference numeral 6 denotes a transfer roller, which constitutes a contact type transfer device. This transfer roller is also one embodiment of the contact of the charging device. Reference numeral 7 denotes a power supply for applying a voltage to the transfer roller 6, which charges a transfer material 8 such as paper by applying a predetermined voltage to the roller 6, for example, a toner formed on the image carrier 3. The image is transferred to this transfer material 8
Transfer to the top. Reference numeral 9 denotes a cleaner for cleaning the image carrier 3. The toner image transferred onto the transfer material 8 is fixed on the transfer material 8 by, for example, a fixing device including a fixing roller 10.

In this embodiment, the brush 1, the image carrier 3, the developing unit 5, and the cleaner 9 are housed in a process unit 11. Generally, the brush 1 of the contact charging device is connected to a power source 2 as shown in FIG. In this case, when the electric resistance of the brush 1 fluctuates due to environmental fluctuation or the like, the current flowing to the image carrier 3 fluctuates. If the current fluctuates, the surface potential formed on the image carrier 3 fluctuates, which adversely affects the quality of the image formed. In order to suppress the fluctuation of the current, it is necessary to reduce the fluctuation of the electric resistance of the brush 1 or to devise the power supply 2 so that the current flowing to the image carrier 3 does not fluctuate even if the electric resistance of the brush 1 fluctuates. It is.

However, if the current flowing to the image carrier 3 fluctuates greatly due to environmental conditions, the brush 1 and the power source 2
It is difficult to keep the fluctuations small enough no matter how much effort is made. Therefore, in the present invention, when the current flowing to the image carrier 3 fluctuates greatly, by providing a mechanism that can easily adjust the fluctuation, the surface potential of the image carrier 3 is not affected by environmental fluctuations. It is always constant.

FIG. 3 is a schematic configuration diagram showing a first embodiment of the present invention. This embodiment is characterized in that an external variable resistor 12 is provided in parallel with the brush 1.
The variable resistor 12 may be specifically attached to the process unit 11 of the charging device, or may be attached to the main body of the image forming apparatus such as the power supply 2 other than this unit.
It is only necessary to decide where to install in consideration of maintainability and user-friendliness.

Therefore, in this apparatus, when the current flowing through the image carrier 3 fluctuates greatly due to an environmental change, the value of the current flowing through the image carrier 3 can be easily and appropriately adjusted by the user operating the variable resistor 12. You can go back. Note that the variable resistor 12 may be configured by a plurality of fixed resistors and a switch that switches and connects these fixed resistors as appropriate.

FIG. 4 is a schematic configuration diagram showing a second embodiment of the present invention. This embodiment is characterized in that a series circuit of a variable resistor 12 and a fixed resistor 13 is provided in parallel with the brush 1. FIG. 5 is a schematic configuration diagram showing a third embodiment of the present invention.
It is characterized in that a series circuit of a variable resistor 12 and a varistor 14 is provided.

The embodiment shown in FIGS. 4 and 5 is suitable for the case where the power supply 2 is provided with a means for stabilizing the current value fluctuation in order to correct the electric resistance fluctuation due to the environmental fluctuation of the brush 1 to some extent. It is a form. If a certain adjustment device for adjusting the current flowing into the image carrier 3 is provided in advance, the current adjustment width by the variable resistor 12 for completely adjusting the environmental fluctuation can be small, A fixed resistor 13 or a varistor 14 is connected in series to limit the voltage applied to the variable resistor 12 to a small value.

In the second and third embodiments, the variable resistor 12 may be installed on either the process unit 11 or the image forming apparatus main body. The first and second
Each of the third and third embodiments is an example in which the present invention is applied to a contact device for charging the image carrier 3, that is, a contact-type charging device including the brush 1 and the power supply 2. The invention is of course not limited to this example.

FIG. 6 is a block diagram showing a fourth embodiment of the present invention. In this example, a transfer roller 6 and a power supply 7 constitute a contact transfer device. Reference numeral 15 denotes a variable resistor connected in parallel to the transfer roller 6, and the charging performance of the transfer roller 6 is properly maintained by changing the resistance value of the variable resistor 15, as in the above embodiments. .
As in the above embodiments, it is needless to say that a fixed resistor or a varistor is provided in series with the variable resistor 15 so that the current adjustment width by the variable resistor 15 can be reduced.

In each of the above embodiments, only the resistance change of the contact due to the environmental change has been described.
The contacts of the brushes, blades and the like have variations in the individual resistance values at the manufacturing stage, and it is a matter of course that these variations can be corrected by the configuration of the present invention.

[0021]

As described above with reference to each embodiment, in the contact-type charging device according to the present invention, variations in the electrical resistance of the contacts such as brushes and the like due to environmental fluctuations caused during the manufacturing process of the charging contact device. It is possible to easily adjust and compensate for the change in the resistance value caused even after the start of use without depending on the voltage adjusting device in the power supply device. Therefore, it is possible to minimize the occurrence of image defects and the like due to environmental fluctuations in the image forming apparatus, and it is possible to always stably form excellent images. In addition, the means for this can be installed in a process unit of the charging contact device or on a side of the image forming apparatus main body that can be easily operated by the user, so that the user can easily perform adjustment in the field. Become.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus employing an electrophotographic method to which the present invention can be applied.

FIG. 2 is a schematic diagram showing a configuration of a part of the device shown in FIG.

FIG. 3 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a third embodiment of the present invention.

FIG. 6 is a schematic configuration diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Brush 2 ... Power supply 3 ... Image carrier 5 ... Developing device 6 ... Transfer roller 11 ... Housing 12 ... Variable resistance 13 ... Fixed resistance 14 ... Varistor 15 ... Variable resistance

Claims (9)

[Claims] 1. A contact-type charging device for applying an electric charge by contacting an image forming medium of an electrophotographic image forming apparatus,
A contact that comes into contact with the image forming medium, a power supply for applying a voltage to the contact, and a voltage that is connected between the contact and the power supply in parallel to the contact and applied to the contact is variable A contact-type charging device, comprising: 2. The contact type charging device according to claim 1, wherein said image forming medium is an image carrier including one of a photosensitive drum and an insulating sheet. 3. The contact-type charging device according to claim 1, wherein the image forming medium is a transfer material. 4. The contact-type charging device according to claim 1, wherein the means for varying the voltage applied to the contact is a variable resistor. 5. The device according to claim 1, wherein the means for varying the voltage applied to the contact comprises a plurality of fixed resistors and switch means for selectively switching and connecting the fixed resistors. Or a contact-type charging device according to 3. 6. The contact-type charging device according to claim 1, wherein the means for varying the voltage applied to the contact comprises a series circuit of a variable resistor and a varistor. 7. The contact-type charging device according to claim 1, wherein the means for varying the voltage applied to the contact comprises a series circuit of a fixed resistor and a variable resistor. 8. The contact-type charging device according to claim 1, wherein the means for varying a voltage applied to the contact is provided in a process unit that accommodates the contact and the image forming medium. apparatus. 9. The contact-type charging device according to claim 1, wherein the means for varying the voltage applied to the contact is provided on the image forming apparatus main body side.