JP2990849B2 - Charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device having a charging member for charging (including static elimination) a charged object by contacting the charged object.

[0002]

2. Description of the Related Art Conventionally, a corona discharger provided with a wire electrode facing a photoreceptor and a shield electrode surrounding the wire electrode as a device for charging a photoreceptor as an object to be charged in an image forming apparatus such as an electrophotographic copying machine. It is known to use

However, when such a corona discharger is used, (1) the voltage applied to the wire electrode becomes a high voltage of 4 kV to 8 kV, and (2) most current flows from the wire electrode to the shield electrode. There are problems that the charging efficiency is low, ozone is generated by corona discharge, and (3) discharge unevenness occurs due to contamination of the discharge wire electrode.

In order to solve such a problem, there is known a contact charging device for charging a member to be charged by bringing a charging member into contact with the member to be charged.

FIG. 7 is a schematic configuration diagram of an electrophotographic apparatus using such a contact charging device 6. The drum-type photoreceptor 5 as a member to be charged rotates in the direction of an arrow, and a charging roller 30 as a charging member has both ends of a core metal (shaft core, rotating shaft) 31 supported by bearings 35, respectively. Bearing 35
Are biased in the direction of the photoconductor 5 by a spring 36 to form a contact portion (nip portion) n between the charging roller 30 and the photoconductor 5, and pressurize and contact the photoconductor 5. A contact 37, a spring 36, a bearing 35, a metal core 31 from a power source 38
By applying a bias voltage to the charging roller 30 through the charging roller 30, the peripheral surface of the rotary photoconductor 5 is charged, and an exposure L on the charged surface forms an electrostatic latent image. The formed electrostatic latent image on the photoconductor 5 is visualized as a toner powder image Ta by the developing device 7, and the toner powder image is transferred Tb to the transfer paper P by the transfer unit 16. The transfer paper P to which the image has been transferred is heated by a fixing device (not shown) so that the toner powder image is permanently fixed. The toner powder remaining on the photoconductor 5 after the transfer is cleaned by the cleaning device 8, and the photoconductor 5 is repeatedly used for image formation.

The bearings 35 for bearing and supporting both ends of the cored bar 31 of the charging roller 30 are made of a plastic material. Of the two bearings, the bearing for supplying power to the charging roller 30 is made of a plastic material at the time of molding. The resistance value is about 1 by dispersing carbon fiber inside.
The conductivity is set to be in the range of 0 ³ to 10 ⁴ Ω · cm. Therefore, from the power source 38, the contact 37, the spring 36, the bearing 35, and the core 3
1, a bias voltage is applied to the charging roller 30.

[0007]

However, in the above-described charging device, the dispersion state of the carbon fibers in the plastic material varies, the resistance value increases, and the conductive bearing 35 becomes insulated depending on the molding conditions. Had to be. For this reason, the photosensitive member as the member to be charged cannot be charged to a predetermined potential due to poor conduction, and an image defect may occur.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent the occurrence of defective charging of a member to be charged due to the above-described poor conduction of a power supply path from a power supply to a charging member.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a charging device for contacting a member to be charged and supplying power to a rotating shaft of a rotatable charging member , wherein the conductive bearing supports the rotating shaft end face and the rotating shaft.
A charging device, which is supplied with power from the charging device.

[0010]

In other words, the power supply to the rotating shaft of the charging member is
Power supply path from the shaft end face and conductive bearing that supports the rotating shaft
Power supply path from the power supply path
If the power supply path from the conductive bearing
Resistance increases due to conductive bearing molding conditions
Even if it becomes difficult to supply power to the rotating shaft of the charging member,
Another feeding path, the feeding path from the end face of the rotating shaft
More power is supplied to the rotating shaft of the charging member,
The charged body can be charged without any trouble. Conversely, the rotation axis
In the power supply path from the end face,
An insulating oxide film is generated between the
If the power supply from this power supply path becomes defective due to
One feed path, the feed path from the conductive bearing.
Power supply to the rotating shaft of the charging member
The electric body can be charged without any trouble. Thus, the non-conductivity factor in the power supply path from the power supply to the charging member is reduced and the conductivity is improved, and the occurrence of charging process failure of the charged body due to the poor conduction in the power supply path from the power supply to the charging member is prevented. be able to. Therefore, in an image forming apparatus using the charging device, the occurrence of an image defect due to the above-described charging process defect of the photosensitive member as a member to be charged is prevented.

[0011]

FIG. 1 is a schematic structural view of an image forming apparatus using a charging device according to the present invention. The image forming apparatus of this embodiment is a laser beam printer that uses a detachable process unit (process cartridge) and uses an electrophotographic process. FIG.
FIG. 3 is an enlarged cross-sectional view of a process unit.

1 is a lower housing of the printer, and 2 is an upper housing of the printer. The upper housing 2 is freely openable and closable about the hinge shaft 3 with respect to the lower housing 1 between a closed state shown by a solid line and an opened state shown by a two-dot chain line.

Reference numeral 4 denotes a process unit. In this embodiment, a drum type photoreceptor 5, a charging device 6, a developing device 7, and a cleaning device 8 are assembled on a frame 9 to form a frame with respect to a printer body. It is a detachable unit. The process unit 4 opens the upper housing 2 of the printer from the lower housing 1 and raises the unit mounting portion 10 inside the upper housing 2.
And the upper housing 2 is closed in the lower housing 1 so that the upper housing 2 is properly mounted inside the printer.

11 is a laser scanner unit, 12 is a sheet cassette, 13 is a feed roller, 14 is a pair of registration rollers, 15 is a transfer guide, 16 is a transfer charger, 17
Is a conveying member, and 18 is a fixing device. These are devices provided on the lower housing 1 side of the printer. 11a is a laser beam reflection mirror, 19 is a paper discharge roller, 20 is a paper discharge tray, and these are devices provided on the upper housing 2 side of the printer.

On the basis of the print start signal, the photosensitive member 5 is driven to rotate at a predetermined peripheral speed (process speed) in the clockwise direction indicated by the arrow, and the peripheral surface of the rotating photosensitive member 5 comes into contact with the photosensitive member 5. The charging process is performed by the charging roller (charging member) 30 of the charging device 6 to which the bias voltage is applied.

A laser beam L modulated in accordance with a time-series electric digital pixel signal of target image information is output from a laser scanner unit 11 and reflected by a mirror 11a to expose a frame 9 of the process unit 4. Light enters the unit 4 through the window 9a (FIG. 2) and is
, And the surface of the rotating photoconductor 5 is irradiated with the laser light L
Is exposed by scanning. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the photoconductor 5. The formed latent image is formed on a developing sleeve 7a of a developing device 7 by a developing blade 7b.
Developed with the applied toner powder with the layer thickness regulated.

On the other hand, the transfer material P is fed one by one from the sheet cassette 12 by the paper feed roller 13, and the photosensitive member 5 and the transfer charge are transferred through the transfer guide 15 at the same time as the laser is emitted by the registration roller pair 14. The timing is fed to a transfer position between the transfer unit 16 and the transfer unit 16. As a result, the formed toner powder image on the photoconductor 5 side is sequentially transferred to the transfer material P surface.

The transfer material P to which the toner powder image has been transferred is separated from the surface of the photoreceptor 5 and is conveyed to a fixing device 18 by a conveying member 17 to pass through a nip portion between a fixing roller 18a and a pressure roller 18b. After receiving the image fixing process, the discharge roller 1
9 discharges the paper to the paper discharge tray 20. The photoreceptor 5 after the transfer receives the residual toner removed by the blade 8a of the cleaning device 8, and is repeatedly subjected to image formation.

In FIG. 2, reference numeral 9c denotes a process unit 4
Opening and closing cover for the photosensitive member surface exposure opening 9b,
When the process unit 4 is removed from the printer or when the upper housing 2 is opened, the unit moves to the closed position to cover and protect the exposed surface of the photoconductor.

FIG. 3 shows a preferred example of the configuration of the charging roller 30 as a charging member. FIG. 3 is a schematic diagram of the layer structure of the charging roller 30. A conductive elastic layer 32 on a cored bar 31
There is an elastic layer 33 having a high resistance thereon and a protective film 34 on the surface. The conductive elastic layer 32 is made of a material obtained by dispersing carbon in EPDM, and functions to guide a bias voltage supplied to the metal core 31. The high-resistance elastic layer 33 is made of urethane rubber or the like, and includes a small amount of conductive fine powder (for example, carbon) as an example.
Even when the charging roller 30 is opposed to a highly conductive portion such as a pinhole of the photoconductor 5, it functions to limit the leak current to the photoconductor 5 and prevent a sharp drop in the bias voltage. The protective film 34 on the surface is made of N-methylmethoxylated nylon, and the composition of the conductive elastic layer 32 and the high-resistance elastic layer 33 does not touch the photoconductor 5 and deteriorate the surface of the photoconductor 1. As such, it has a protective effect.

FIG . 5 shows the configuration of a power supply section for the charging roller 30. Although not shown, the photosensitive member 5 is rotatably supported at both ends between side plates of the process unit frame (9). G is a drum gear provided concentrically on one end of the photoconductor 5. When the process unit 4 is mounted on the printer main body in a predetermined manner, the gear G is engaged with a driving gear (not shown) on the printer main body side, and the rotational force of the driving gear is applied to the photosensitive member 5 via the gear G. The rotation of the photoconductor 5 is performed by the transmission.

The charging roller 30 serving as a charging member includes a core 3
1 are respectively supported on bearings 35, and the both bearings 35 are connected to the bearings and a process unit frame (not shown) (9).
The charging roller 30 is pressed against the photoconductor 5 in a predetermined pressure by being biased in the direction of the photoconductor 5 by a spring 36 contracted therebetween. The charging roller 30 rotates following the rotation of the photoconductor 5.

Reference numeral 40 denotes a power supply end of the core metal 31 of the charging roller 30.
The electrode disposed on the base side, the base side (root part) 4
0b is extended to the upper end side of the spring 36 and extended.
Pressurized and fixed to the unit frame (9) and bend the electrode
The upper end of the spring 36 is brought into contact with the extension portion 40b to be received.
It is. The tip side 40a is the gap of the core metal 31 of the charging roller 30.
The end face 31a in the last direction is
They are in contact with a constant pressure. Spring 36 and bearing
The shield 35 is conductive. When the process unit 4 is mounted in the printer main body in a predetermined manner, the power receiving terminal 41a of the process unit 4 and the power supply terminal 41b of the printer main body come into contact, and the power supply 38 and the electrode 40 of the printer main body communicate with each other.

[0024]

[0025]

[0026]

According to this configuration, the power supply path from the power supply 38 to the charging roller 30 includes a path through the base 40 b of the electrode 40 → the conductive spring 36 → the conductive bearing 35, and a path from the tip 40 a of the electrode 40 to the charging roller 30. There are two routes for supplying power directly to the end surface 31a in the thrust direction of the metal core 31.

For this reason, even if the resistance value increases due to the molding conditions of the conductive bearing 35 and it becomes difficult to supply power to the charging roller 30, the photosensitive member 5 can be supplied through the latter power supply path.
And the charging performance and reliability were further improved and stabilized. Conversely, even if an insulating oxide film is generated between the tip end portion 40a of the electrode 40 and the shaft end surface 31a of the metal core 31 of the charging roller 30 due to long-term storage, etc., and the power supply from the latter path becomes defective, Good charging performance can be ensured by supplying power from the former conductive bearing 35 path. In addition, since the electrode 40 is fixed at the base 40b, the length of the tip 40a can be reduced. Therefore, it is also possible to prevent the generation of noise due to the vibration of the electrode 40.

FIG. 6 shows still another configuration of the power supply unit. This example in the configuration of the feeding portion of FIG. 5, divided into two tip portions 40a of the thrust end face 31a electrode 40 for pressure contact with the metal core 31 of the charging roller 30 in the longitudinal slit 40c 40a ₁ · 40a ₂ And the divided electrodes 40a ₁ and 40a ₂ are both connected to the core metal 3 of the charging roller 30.
1 is brought into pressure contact with the end surface 31a in the thrust direction. By this way, the electrode divided form, also one of the divided electrodes 40a ₁ or 40a ₂ is turned to the core metal end face 31a and the non-contact by the influence of such vibration, continuity if other is in contact As a result, the charging failure of the photoconductor 5 was prevented, and the reliability of the charging performance of the photoconductor 5 was improved and stabilized.

FIG . 4 is a reference example. In this example, the power supply 38
The power supply path from the charging roller 30 to the
40a to the end in the thrust direction of the core metal 31 of the charging roller 30
There is only one path that feeds directly to surface 31a.

As described above, according to the present invention, in a charging device which contacts a member to be charged and supplies power to a rotating shaft of a rotatable charging member , a conductive shaft supporting an end surface of the rotating shaft and the rotating shaft.
Since the power is supplied from the receiver, it is possible to prevent the occurrence of a charging process failure of the charged body due to a conduction failure of the power supply path from the power supply to the charging member. Therefore, in an image forming apparatus using the charging device, the occurrence of an image defect due to the above-described charging process defect of the photosensitive member as a member to be charged is prevented.

[Brief description of the drawings]

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

FIG. 2 is an enlarged cross-sectional view of a process unit.

FIG. 3 is a schematic diagram of a layer configuration of a charging roller.

FIG. 4 is a configuration diagram of a power supply unit according to a reference example;

Figure 5 is a configuration diagram of a power supply unit of Example

FIG. 6 is a configuration diagram of a power supply unit according to another embodiment .

FIG. 7 is a schematic configuration diagram of an example of an electrophotographic apparatus using a contact charging device.

[Explanation of symbols]

5 Rotary Drum Type Photoreceptor as Charged Object 30 Charging Roller as Charging Member 31 Roller Core (Rotary Shaft) 31a Core End Face 35 Conductive Bearing 40 Electrode 38 Power Supply

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Hishita 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-1-310377 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/02

Claims (1)

(57) [Claims] 1. A of contact with the member to be charged rotatable charging member
In the charging device for supplying power to the rotating shaft, the rotating shaft end face and the times
A charging device, wherein power is supplied from a conductive bearing that supports a turning shaft .