JPH0527555A - Electrifying device - Google Patents

Abstract

PURPOSE:To avert the out of focus of copied images occurring in ozone generation and to allow the inexpensive and stable electrification of a photosensitive body without generating defects in an electrifying member and the photosensitive body by executing an electric discharge in the part nearest the photosensitive body according to the voltage impression from power sources, thereby electrifying the photosensitive layer of the surface of the photosensitive body. CONSTITUTION:The electrifying device 20 has the electrifying members 21 which are fitted with spacing rollers at both ends and are disposed in proximity to the photosensitive drum 1 surface apart a specified spacing from the photosensitive layer 1b of this drum and the DC power source 22 and AC power source 23 for impressing the voltage above the discharge initiation voltage to the electrifying member 21. The electrifying member 1 is constituted to electrify the photosensitive layer 1b on the photosensitive drum 1 surface by discharging electricity to the part nearest the photosensitive drum 1 according to the impression of the oscillation voltages from the DC power source 22 and the AC power source 23. An excessively large electrifying current does not, therefore, flow from the electrifying member 21 to the photosensitive drum 1 even if there is the defect, such as pinhole, in the photosensitive drum 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging a photosensitive layer on the surface of a photosensitive member by applying a voltage to a charging member.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic apparatus such as a copying machine is generally provided with a photosensitive drum having a photosensitive layer formed on the surface thereof, and a toner image developed on the photosensitive drum corresponding to an image of an original document. Is transferred to a copy sheet so that the image of the original is copied onto the copy sheet.

Further, in the above-mentioned photoconductor drum, a toner image is developed by forming an electrostatic latent image on the photoconductor layer according to an image of an original, and the photoconductor layer of the photoconductor drum is developed. A corona discharger is used as a charging device for charging. However, in such a corona discharger, ozone is generated when the photosensitive layer of the photosensitive drum is charged, which causes corrosion of constituent members of the apparatus and deterioration of ozone on the surface of the photosensitive drum, resulting in copy image blurring. It is easy to occur.

Therefore, in recent years, as a charging device, one provided with a brush-shaped charging member disclosed in Japanese Patent Laid-Open No. 60-220587, and a blade-shaped charging disclosed in Japanese Patent Laid-Open No. 59-104349. Those provided with members, or JP-A-56-132356 and JP-A-6-
By providing a charging member to which a voltage has been applied in contact with the surface of the photosensitive drum, such as the one provided with a roller-shaped charging member disclosed in JP-A-3-149669, the photosensitive drum via the charging member. A charging device for charging the photosensitive layer has been proposed.

The above-mentioned charging device is designed to charge the photosensitive layer of the photosensitive drum by discharging in the gap near the contact point between the charging member and the photosensitive drum. The current is several tens of microamperes, but in order to reduce the influence of the voltage drop due to the charging member, a charging member having a resistance value of 10 ⁵ Ω or less is used.

[0006]

However, since the charging device provided with the charging member having a resistance value of 10 ⁵ Ω or less in contact with the surface of the photosensitive drum as in the above-mentioned conventional device does not generate ozone. Although it is possible to avoid the copy image blurring caused by the corrosion of the constituent members and the ozone deterioration of the surface of the photosensitive drum, if the resistance value of the charging member is too low, the photosensitive drum has a defect such as a pinhole. In this case, an excessive current flows from the charging member to the photosensitive drum, which causes further defects on the photosensitive drum and the charging member.

Further, in order to maintain a stable contact state between the charging member and the photosensitive drum and to avoid mechanical damage to the photosensitive layer of the photosensitive drum, the material of the charging member is elastic. Although required, it is difficult to improve dimensional accuracy and surface accuracy with a charging member having such elasticity, and as a result, the photosensitive layer of the photosensitive drum cannot be charged uniformly and uniformly. I have a problem.

[0008]

The charging device according to claim 1 of the present invention takes the following means in order to solve the above problems.

That is, the charging member is provided with a charging member which is in close proximity to the photosensitive layer on the surface of the photosensitive member at a constant distance, and a power source which applies a voltage of at least the discharge start voltage or higher to the charging member. As the voltage is applied from the power source, discharge is performed at the closest portion to the photoconductor to charge the photoconductive layer on the photoconductor surface.

In order to solve the above-mentioned problems, the charging device according to the second aspect of the invention has the following means in the charging device according to the first aspect.

That is, the charging member is made of a rod-shaped conductor extending along the longitudinal direction of the photoconductor, and the outer peripheral surfaces of the annular space members fitted to both ends of the charge member are in the non-photosensitive region of the photoconductor. By being provided in contact with each other, a certain distance is maintained between the photosensitive layer and the photosensitive layer on the surface of the photosensitive body.

[0012]

According to the structure of the above-mentioned claim 1, the voltage of at least the discharge start voltage is applied to the charging member which is close to the photosensitive layer on the surface of the photosensitive member at a constant interval, whereby the charging member Discharge is performed at the portion closest to the photoreceptor to charge the photosensitive layer on the surface of the photoreceptor. Thus, when the photosensitive layer is charged, ozone is not generated, and a gap is provided between the charging member and the photosensitive member, so that an abnormal current flow to the photosensitive member can be avoided.

According to the second aspect of the invention, annular space members are fitted and provided at both ends of the charging member made of a rod-shaped conductor extending along the longitudinal direction of the photoconductor. By providing each outer peripheral surface of the space member in contact with the non-photosensitive region of the photoconductor, a constant distance can be always maintained between the charging member and the photosensitive layer on the surface of the photoconductor.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. In this embodiment, the charging device is applied to a copying machine.

As shown in FIG. 3, the copying machine according to this embodiment has a cylindrical photosensitive drum 1 as a photosensitive member. This photosensitive drum 1 is provided rotatably in the direction A in the apparatus, and as shown in FIGS. 1 and 2, a photosensitive layer 1b having a film thickness T of 20 μm is formed on the outer peripheral surface of the drum substrate 1a. Is configured. In addition, an LED (Light Emittimg Diode) head 2, a developing unit 3, a sheet feeding / conveying path 4, a transfer roller 5, and a cleaning unit 6 are arranged around the photosensitive drum 1.

The LED head 2 emits light R corresponding to an image of an original document (not shown) to an exposure point B on the photosensitive drum 1.
By exposing to the above, an electrostatic latent image corresponding to the image of the original is formed on the photosensitive layer 1b of the photosensitive drum 1 charged by the charging device 20 described later.

The developing unit 3 includes a toner tank 3a.
And an agitator roller 3b, a supply roller 3c, and a developing tank 3f equipped with a mixer roller 3d and a magnet roller 3e. Then, the developing unit 3
Means that the toner (not shown) stored in the toner tank 3a does not remain in the toner tank 3a due to the rotation of the agitator roller 3b and the supply roller 3c, and the developing tank 3f does not.
And then the toner in the developing tank 3f is mixed and stirred with a carrier (not shown) by the mixer roller 3d, and then transferred and adhered to the electrostatic latent image on the photosensitive drum 1 by the magnet roller 3e to be developed as a toner image. It is supposed to do.

The development of the toner image on the photosensitive drum 1 by the magnet roller 3e is performed by the magnet roller 3e.
For e, a desired voltage having the same polarity as the surface potential of the photosensitive drum 1 and close to the charging potential of the photosensitive drum 1 is applied.

One end of the paper feeding / conveying path 4 is arranged in the vicinity of a pressure contact portion between the photosensitive drum 1 and a transfer roller 5 described later, while the other end thereof is arranged in the vicinity of a copying paper cassette 7. In the middle, a plurality of paper feed rollers 4a ... Are arranged. Then, the paper feed transport path 4 is provided with a paper feed roller 4a.
.. is rotated to convey a copy sheet (not shown) in the copy sheet cassette 7 to a pressure contact portion between the photosensitive drum 1 and the transfer roller 5.

The transfer roller 5 is provided in pressure contact with the photosensitive drum 1. Then, the transfer roller 5
Sandwiches the copy sheet conveyed from the above-mentioned sheet feeding and conveying path 4 with the photosensitive drum 1 on which the toner image is formed, and in this state, a predetermined voltage having a polarity opposite to that of the toner is applied. When applied, the toner image on the photosensitive drum 1 is transferred to the copy sheet.

The cleaning unit 6 includes a cleaning blade 6a which is in contact with the photosensitive drum 1,
This cleaning blade 6a is the A of the photosensitive drum 1.
The residual toner is peeled off from the photosensitive drum 1 with the rotation of the direction, so that the surface of the photosensitive drum 1 is cleaned.

Further, a discharge / conveyance path 8 and a heat roller 9 and a pressure roller 10 which are arranged in pressure contact with each other are provided in the conveying direction of the copy sheet from the photosensitive drum 1. Then, as described above, the copy sheet on which the toner image is transferred by the transfer roller 5 passes through the discharge / conveyance path 8 and is sandwiched between the heat roller 9 and the pressure roller 10 to be conveyed. The toner image is fixed by being heated and pressed.

Further, in the copying machine of this embodiment, a charging device 20 is arranged on the outer circumference of the photosensitive drum 1 between the LED head 2 and the cleaning unit 6. As shown in FIG. 1, the charging device 20 includes three charging members 21 having a round bar shape, three DC power sources 22 serving as a power source, and an AC power source 23.

The charging member 21 is made of sulfur composite free-cutting steel which is an electric conductor that can be easily machined and has high dimensional accuracy, and, as shown in FIG. 2, has annular space rollers at both ends as space members. 21a and 21a are fitted and provided. These space rollers 21a ・ 21a
Consists of an electrically insulating polyacetal,
Since the outer peripheral surface is provided in contact with the non-photosensitive regions at both ends of the photoconductor drum 1, the outer peripheral surface is driven to rotate with the rotation of the photoconductor drum 1 in the direction A, and the charging member 21 moves the photosensitive member 1 to the photosensitive layer 1.
It is designed to be held at a constant interval W of 80 μm from b.

Each of the DC power sources 22 ... Is connected to the charging member 21 on the negative electrode side, and is connected to the other end of the AC power source 23 whose one end is grounded. Then, the DC power supply 22 and the AC power supply 23 are configured to apply an oscillating voltage having a cycle that does not affect an image by superposing the respective voltages to the charging member 21. The drum base 1a of the photosensitive drum 1 is grounded.

The charging device 20 includes a DC power source 2
2 and an oscillating voltage from the AC power supply 23 are applied to the charging member 21, discharge is caused from the closest portion of the charging member 21 to the photosensitive drum 1 toward the photosensitive layer 1b on the surface of the photosensitive drum 1, and the photosensitive member The photosensitive layer 1b of the drum 1 is charged.

By the way, in the discharge between the air gaps, generally, as shown in the discharge characteristic diagram of Paschen in FIG. 4, a specific relationship is established between the air gap width and the breakdown voltage of the air gap, that is, the discharge start voltage. is doing. Therefore, the voltage applied to the charging member 21 from the DC power supply 22 and the AC power supply 23 is at least the charging member 21 and the photosensitive layer 1 on the surface of the photosensitive drum 1.
A voltage equal to or higher than the discharge start voltage corresponding to the gap width W with respect to b is applied. In this embodiment, discharge from the charging member 21 to the photosensitive layer 1b started at a peak voltage of around 1000V, and a desired surface potential of the photosensitive drum 1 could be obtained at a peak voltage of 2000V.

A controller 11 and an engine controller 12 are provided on the lower side of the copying machine. The controller 11 receives an image signal and a printer engine control signal from a host computer (not shown). Is generated, and the engine controller 12 receives the printer engine control signal and performs engine control, thereby controlling the operation of the various components described above.

As described above, the main charging device 20 includes the charging members 21 which are fitted with the space rollers 21a and 21a at both ends thereof and are brought close to the photosensitive layer 1b on the surface of the photosensitive drum 1 at a constant distance W. The charging member 21 is provided with a DC power supply 22 and an AC power supply 23 that apply a voltage of at least the discharge start voltage or more, and the charging member 21 is exposed to light by the DC power supply 22 and the AC power supply 23. Discharge is performed at the portion closest to the body drum 1 to charge the photosensitive layer 1b on the surface of the photosensitive drum 1.

Therefore, even if the photoconductor drum 1 has a defect such as a pinhole, there is no fear that an excessive current will flow from the charging member 21 to the photoconductor drum 1. Further, as a material of the charging member 21, In addition, since it is not necessary to particularly limit the elastic member to the elastic member, the dimensional accuracy of the charging member 21 can be increased, and the photosensitive layer 1b of the photosensitive drum 1 can be uniformly and uniformly charged. . Further, at both ends of the charging member 21, there are provided space rollers 21a, 21a whose outer peripheral surfaces are in contact with the non-photosensitive regions of the photoconductor drum 1, so that the photoconductor drum 1 rotates in the A direction. As the space rollers 21a and 21a are driven to rotate, the charging member 21 is always kept at a constant distance W from the photosensitive layer 1b of the photosensitive drum 1.

The above embodiment is not intended to limit the present invention, and various modifications can be made within the scope of the present invention.
For example, in the present embodiment, as the power supply for applying the voltage to the charging member 21, the one in which the DC power supply 22 and the AC power supply 23 are superposed is used, but the invention is not particularly limited to this. As described above, the charging of the photosensitive drum 1 is performed by the gap width W between the photosensitive layer 1b of the photosensitive drum 1 and the charging member 21.
Since this is determined by the voltage applied to this gap, more stable charging is performed when discharge is performed at a low void breakdown voltage because there are many opportunities for discharge. Therefore, the voltage applied to the charging member 21 may be a pulsating flow or a pulse.

Further, as in this embodiment, a plurality of charging members 2 are provided.
1 and the like, different voltage may be applied to each charging member 21. In such a case, the charging members are moved toward the downstream side with respect to the rotation of the photosensitive drum 1 in the A direction. By increasing the voltage applied to 21 ..., a more stable and higher surface potential of the photosensitive drum 1 can be obtained.

[0033]

As described above, the charging device according to the first aspect of the present invention has at least a charging member which is placed in close proximity to the photosensitive layer on the surface of the photosensitive member at a constant distance, and at least discharges the charging member. And a power supply for applying a voltage higher than the start voltage,
The charging member has a structure in which a photosensitive layer on the surface of the photoconductor is charged by discharging at a portion closest to the photoconductor in response to application of a voltage from a power source.

As a result, unlike the charging using the corona discharger as in the conventional example, ozone is not generated, so that the copy image blur caused by the ozone generation can be avoided. Further, by providing a gap between the charging member and the photoconductor, even if there is a defect such as a pinhole on the surface of the photoconductor, there is no possibility that an abnormal current will flow to the photoconductor. In addition, the charging member does not have to be further defective, and the material of the charging member does not have to be particularly elastic. Therefore, the range of selection of the material of the charging member is widened and the dimensional accuracy of the charging member is improved. Therefore, it is possible to inexpensively and stably charge the photoconductor.

A charging device according to a second aspect is the charging device according to the first aspect, wherein the charging member is made of a rod-shaped conductor extending along the longitudinal direction of the photoconductor.
The outer peripheral surface of the annular space member fitted to both ends thereof,
By being provided in contact with the non-photosensitive region of the photoconductor, a certain distance is maintained between the photoconductor layer and the photosensitive layer.

Thus, the charging member and the photosensitive layer on the surface of the photosensitive member can be held with a simple structure and reliably at a constant interval, and the photosensitive layer on the surface of the photosensitive member can be made uniform and uniform. The effect of being able to be electrically charged is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a charging device according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing a charging member that constitutes the charging device.

FIG. 3 is a vertical sectional view showing a copying machine to which the charging device is applied.

FIG. 4 is a graph showing the discharge characteristics of Paschen.

[Explanation of symbols]

1 photoconductor drum (photoconductor) 1b Photosensitive layer 20 Charging device 21 Charging member 21a Space roller (space member) 22 DC power supply (power supply) 23 AC power supply (power supply)

Claims (2)

[Claims] 1. A charging member, which is placed in close proximity to a photosensitive layer on the surface of a photosensitive member at a constant interval, and a power source for applying a voltage of at least a discharge start voltage or higher to the charging member. A charging device characterized in that, when a voltage is applied from a power source, discharge is performed at a portion closest to the photoconductor to charge a photoconductive layer on the surface of the photoconductor. 2. The charging member is made of a rod-shaped conductor extending along the longitudinal direction of the photoconductor, and the outer peripheral surfaces of annular space members fitted to both ends of the charge member are in the non-photosensitive region of the photoconductor. The charging device according to claim 1, wherein the charging device is provided so as to be in contact with each other so that a constant space is maintained between the photosensitive layer and the photosensitive layer.