JPH06208282A - Electrostatic charger - Google Patents

Abstract

PURPOSE:To impart a stable electrostatic charge potential to a photoreceptor regardless of humidify with the electrostatic charger for which a contact electrostatic charge method is used. CONSTITUTION:This electrostatic charger electrostatically charges the photoreceptor 1 by applying a voltage to an electrostatic charging roller 5 and bringing this electrostatic charging roller 5 into contact with the photoreceptor 1 to be carried with toner images. The electrostatic charger has a detection circuit 30 which detects the resistance value of a conductive base fabric 5a of the electrostatic charging roller, a conversion circuit 31 which converts the resistance value detected by this detection circuit 31 to voltage value information and a voltage value selection circuit 32 which selects the voltage value to be applied from a power source 34 from plural set voltages in accordance with the voltage value information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine, a printer, and other charging devices mounted on an image forming apparatus for charging an electrophotographic photosensitive member.

[0002]

2. Description of the Related Art In an apparatus for forming an image by using a so-called electrophotographic method (Carlson process), corona charging using a corona discharge phenomenon is used to charge a photoreceptor as an image carrier to a desired potential. Devices have been commonly used. However, in this method, due to the high voltage required to cause a discharge phenomenon, electrical noise to various peripheral devices or a large amount of ozone generated during discharge causes an uncomfortable feeling to surrounding people. It was

Therefore, as an alternative to this corona charging device, as shown in FIG. 6, a conductive elastic resin roller 65 is brought into contact with the photoconductor 1 which is an image bearing member as a contact member, and the photoconductor 1 and the photoconductor 1. A contact charging method has been proposed in which a voltage is applied between the two to charge the photoreceptor 1.

Further, instead of the conductive resin roller, as shown in FIG. 7, there is also proposed a charging device in which conductive fibers 75a are planted as a contact member on a substrate 75b.

[0005]

However, in the case of the contact charging method as described above, it is easily affected by the environment, and the charging potential of the photoconductor at high temperature and high humidity is increased as compared with that at normal temperature and normal humidity. However, there is a problem that stable charging characteristics cannot be obtained. This principle will be described below. Here, the charging principle of a method of charging the photoconductor by applying a voltage between the conductive fiber or the aggregate thereof, which is the contact member, and the photoconductor, which is the image carrier, will be described. FIG. 8 shows a schematic diagram for explaining the manner of contact charging between the conductive fiber and the photoconductor. As shown in FIG. 8, when an arbitrary point A on the photoconductor 1 faces the tip of the conductive fiber 85d to which a voltage is applied across a gap of a certain size, the applied voltage is different from that of the photoconductor 1. When it is larger than the discharge start voltage (Vth) determined by the air gap,
Discharge is excited from the conductive fibers 85d and the photoconductor 1 starts to be charged (region C). Charge potential (Vsp) rises and applied voltage
The discharge is stopped when the difference between (Vap) and (Vsp) becomes equal to (Vth). That is, (Vsp) = (Vap)-(Vth) holds when the dark decay of the charged potential of the photoconductor 1 can be ignored. After that, the point A moves out to the position (position B) where the point A comes out of the region C that allows the discharge and contacts the conductive fiber 85d while maintaining the charged potential. Needless to say, the potential difference between the conductive fiber 85d at the position B and the point A of the photoconductor 1 is Vth as described above. The charge moves to the point A, and the charging potential at the point A is further increased. That is, it is considered that the charging potential is given by the discharge phenomenon and the charge injection phenomenon. The charge injection amount by the above-mentioned contact is determined by the contact resistance at the position B, and this contact resistance is determined by the condition of the contact surface. For example, when moisture adheres to the contact surface in high humidity, the contact resistance is greatly reduced and the charge injection amount is increased.
As a result, it is considered that the charging potential rises.
This is considered to be the main cause of the unstable environmental characteristics of the charging potential in this charging method.

As a means for solving this problem, for example, Japanese Patent Application Laid-Open No. 56-132356 proposes to use a constant current power source as an applied power source for the contact member, but this is because a current always flows through the contact member. However, there arises a problem of charge up.

The present invention provides a method of solving the problems relating to the stability of the charging potential in a charging device using the contact charging method.

[0008]

SUMMARY OF THE INVENTION The present invention provides a charging device for charging a contact member by applying a voltage to the contact member to bring it into contact with an image carrier for carrying a toner image. A detection means for detecting the resistance value of the contact member; and a voltage control means for controlling the voltage value applied to the contact member based on the resistance value detected by the detection means. Is.

More specifically, the voltage control means converts the resistance value detected by the detection means into voltage value information, and the voltage value applied to the contact member based on the voltage value information. It is characterized by comprising a voltage value selecting means for selecting from among a plurality of set voltages.

[0010]

In the contact charging method, as the humidity is higher as described above, the contact resistance between the contact member and the image carrier becomes lower, so that the amount of charges injected into the image carrier increases and the charging potential rises.

According to the present invention, the resistance value of the contact member, which fluctuates depending on the humidity, is detected, and the voltage value applied to the contact member is controlled based on the detected resistance value, so that the image carrier does not cause the problem of charge-up. It is possible to stabilize the charging potential of.

More specifically, the control of the voltage value applied to the contact member is performed by converting the detected resistance value into voltage value information and a plurality of voltage values applied to the contact member based on the voltage value information. The voltage control means is composed of a voltage value selection means for selecting from among the set voltages of

[0013]

First, an example of an image forming apparatus using the charging device of the present invention will be described with reference to FIG. As the charging member, the one having the structure shown in the conventional example (FIGS. 6 and 7) can be used, but conductive fibers are flocked in a roller shape from the viewpoints that uneven charging is less likely to occur, long life, and the like. Use one. Data relating to image formation from a host computer (not shown) is processed by the controller 16. Then, an image formation start signal is sent to the engine controller 17. From this, the operation proceeds according to a predetermined process.

The transfer materials stored in the transfer material cassette 7 are drawn out one by one by the paper feed roller 8 and conveyed to the front of the registration roller 11 by the conveyance rollers 9 and 10.

The photosensitive member 1 is rotated at a constant speed by a rotating mechanism (not shown). The charging roller 5 similarly rotates at a constant speed. The photoconductor 1 is charged by applying a voltage while bringing the charging roller 5 which is the charging device into contact with the photoconductor 1 which is the image carrier. As shown in FIG. 2, for the charging roller 5 used here, for example, an assembly of conductive fibers, which is a contactor, having a resistance value adjusted to a desired value by adjusting the dispersion amount of carbon in rayon is implanted. The conductive base cloth 5a formed into a strip shape with a width of 20 mm is wound around a conductive core metal 5c having a diameter of 6 mm as a base. Here, the resistance of the charging roller is 10
The diameter of the single fiber of the conductive fiber was 20 μm, and the planting density was 80000 fibers / inch ² .

On the other hand, in the developing device 2, the magnet roller 2 is used.
The toner tank 2 so that the toner on the surface d has a predetermined density.
From e, it is appropriately fed to the developing tank 2f by the supply roller 2b and agitated by the mixer roller 2c. At this time, the toner is
It is charged to the same polarity as the photoconductor charging potential. Here, when a value close to the charging potential of the photoconductor 1 is applied to the magnet roller, the toner adheres to the portion irradiated by the exposure writing head 6 and is developed.

The transfer material is conveyed by the registration roller 11 at a timing corresponding to the image position on the photosensitive member 1. The transfer material is nipped and conveyed by the photoconductor 1 and the transfer roller 3. At this time, a voltage having a polarity opposite to that of the toner is applied to the transfer roller 3. Therefore, the toner on the photoconductor 1 is transferred onto the transfer material.

The toner on the transfer material is internally heated by the heater 12.
c heat roller 12a and pressure roller 12
The toner is nipped and conveyed at b, during which the toner is fused and fixed on the transfer material.

The transfer material is sent to the stack guide 15 by the transport roller 13 and the paper discharge roller 14.

On the other hand, the untransferred toner on the photoreceptor 1 is cleaned by the cleaning blade 4 of the cleaning unit 4.
The toner is scraped off from the photosensitive member 1 by a and sent to a toner disposal container (not shown) by the toner screw 4b.

With the above, a series of image forming steps is completed.

FIG. 3 is a schematic view of the structure of a charging device used in the above-mentioned image forming apparatus.

A voltage is applied to the charging roller 5 from a power source 34, and the charging roller 5 is brought into contact with the photosensitive member 1 to charge the photosensitive member 1 to a predetermined potential. The voltage applied to the charging roller here was a DC voltage superimposed with an AC voltage. This is because the photoconductor 1 can be charged more uniformly than when only the DC voltage is applied.

The conductive base cloth 5a, which is a contact member, is connected to a detection circuit 30 for detecting this resistance value. Based on the resistance value detected here, the voltage control circuit controls the voltage applied from the power supply 34. Have control. The voltage control circuit includes a conversion circuit 31 and a voltage value selection circuit 32. The conversion circuit 31 converts the resistance value detected by the detection circuit 30 into voltage value information, and based on the voltage value information, the voltage value information is converted into voltage value information. The value selection circuit 32 selects the voltage value to be applied to the contact member from a plurality of set voltages, and the voltage is applied from the power supply 34.

Here, the voltage applied to the charging device is controlled on the basis of FIG. 5 so that the photosensitive member 1 is at -600V.

FIG. 5 is a diagram for explaining the humidity dependence of the relationship between the DC voltage value superposed on the charging roller 5 with an AC voltage of 900 V and an AC voltage of 200 Hz in this embodiment and the surface potential of the photosensitive member 1. According to this, in order to charge the photoconductor 1 to -600V, it is -6 at normal humidity.
00V, -700V at low humidity, -50 at high humidity
It can be understood that a DC voltage of 0V may be superposed.

The control of the above charging device will be described in more detail with reference to FIG.

When the image is not formed, the charging roller 5 is set to -1000.
Only the DC voltage of V is applied and the resistance value ΔR of the conductive base cloth 5a which varies depending on the humidity is detected by the detection circuit 30 (S1). This is because the photosensitive member 1 is charged to -600 V when the above voltage is applied, and is suitable as a reference.

The detected resistance value ΔR is converted into voltage value information ΔV of 0V to 5V by the conversion circuit 31 according to its magnitude (S2).

On the other hand, in the voltage value selection circuit 32, a plurality of DC voltage values to be superimposed on the AC voltage applied to the charging roller 5 at the time of image formation are set, and depending on the magnitude of the voltage value information ΔV from the conversion circuit 31. Then, the applied voltage value is selected from the set voltages (S3). For example, -500V when ΔV is 2V or less, -600V when ΔV is 2V to 4V.
When V and ΔV are 4V or more, −700V is selected.

The applied voltage selected by the voltage value selection circuit 32 is output from the power supply 34 (S4).

As described above, the resistance value of the charging roller 5 is detected in advance during non-image formation, and the voltage value applied to the charging roller 5 during image formation is determined each time. It is possible to prevent variation in the amount of charges injected into the battery, and stabilize the charging potential.

[0033]

According to the present invention, it is possible to provide a charging device using the contact charging method, in which the fluctuation of the charging potential of the photosensitive member with respect to the humidity change is suppressed.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus including a charging device according to an embodiment of the present invention.

FIG. 2 is a schematic view of a charging device showing an embodiment of the present invention.

FIG. 3 is a schematic view of a charging device showing an embodiment of the present invention.

FIG. 4 is a diagram for explaining a control method of the charging device according to the embodiment of the present invention.

FIG. 5 is a diagram for explaining the humidity dependence of the relationship between the DC voltage value applied to the charging roller and the surface potential of the photoconductor according to the embodiment of the present invention.

FIG. 6 is a schematic view of a charging device showing a conventional example.

FIG. 7 is a schematic view of a charging device showing a conventional example.

FIG. 8 is a diagram for explaining a charging method of a charging device using conductive fibers.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 5 Charging roller 5a Conductive substrate 30 Detection circuit 31 Conversion circuit 32 Voltage value selection circuit 34 Power supply

Claims (2)

[Claims] 1. A charging device for applying a voltage to a contact member to bring the contact member into contact with an image carrier for carrying a toner image to charge the image carrier, wherein a resistance value of the contact member is detected. And a voltage control means for controlling the voltage value applied to the contact member based on the resistance value detected by the detection means. 2. The voltage control means converts the resistance value detected by the detection means into voltage value information, and a plurality of voltage values applied to the contact member based on the voltage value information. A charging device comprising a voltage value selecting means for selecting from a set voltage.