JPH07281506A - Electrifier - Google Patents

Abstract

PURPOSE:To eliminate unsatisfactory electrification by reducing the drive torque of a photosensitive drum, and accurately maintaining a minute gap between a photosensitive drum surface and an electrifying surface over a long period of time. CONSTITUTION:A proximity electrifiying plate 25 is arranged so that its electrifying surface 25 is opposite the surface of the photosensitive drum 1, and its right and left ends each are held by hold members 26 (only one of the hold members 26 is illustrated). Each hold member 26 supports space rollers 27a, one upstream in the direction of the rotation of the photosensitive drum 1 and the other downstream, so that they freely rotate. The four space rollers 27a in all are made to abut on the surface of the photosensitive drum l by energizing the hold members 26 toward the photosensitive drum 1 by means of compression springs 28. Thus, the minute gap between the surface of the photosensitive drum 1 and the electrifying surface 25a is accurately obtained. When the photosensitive drum 1 is rotated and driven at the time of electrification, the space rollers 27a rotate following it, therefore friction is not caused between them.

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 uniformly charging a surface to be charged by applying an oscillating voltage to a charging member arranged close to the surface to be charged with a minute gap.

[0002]

2. Description of the Related Art Conventionally, a charging device mounted on an image forming apparatus such as an electrophotographic copying machine is in a non-contact state depending on whether the charging member is in non-contact or in contact with the surface (charged surface) of a body to be charged. They are roughly classified into a charging device and a contact charging device. The advantage of the latter contact charging device is that the charging voltage is lower than the corona charger that represents the former non-contact charging device.
It is mentioned that the amount of generated ozone is small, therefore a device for removing ozone is unnecessary and the configuration is simple, and maintenance-free is easy to realize.

In the above-mentioned contact charging device, in order to uniformly charge the surface to be charged, a superimposed voltage obtained by superimposing a DC voltage and an oscillating voltage (a voltage whose voltage value changes periodically with the passage of time). Is applied to a conductive charging member, and the charging member is brought into contact with a member to be charged to perform charging (for example, JP-A-63-149669).

FIG. 5 shows an example of such an image forming apparatus. This is a member to be charged such as a drum-shaped electrophotographic photosensitive member and an electrostatic recording dielectric (hereinafter referred to as "photosensitive drum 1").
This photosensitive drum 1 is rotationally driven in the direction of arrow R1 at a predetermined process speed (peripheral speed). The surface of the photosensitive drum 1 is uniformly charged by the contact charging device 2.

The contact charging device 2 has a charging roller (charging member) 20 composed of a cored bar 21 and a conductive roller body 22 surrounding the cored bar 21. Charging roller 20
Is abutted against the surface of the photosensitive drum 1 with a predetermined pressing force by an urging member (not shown) that urges both ends of the cored bar 21, and the rotation of the photosensitive drum 1 in the direction of arrow R1 causes the direction of arrow R20. Follow the rotation. The contact leaf spring 2 is attached to the core 21.
A power supply 23 is connected via 3a. Charging roller 2
0, the power supply 23, the vibration voltage V _AC and the DC voltage V _DC and is superimposed superimposed voltage having twice or more the peak voltage V _PP of the charge starting voltage of the photosensitive drum 1 (V _AC + V _DC) is applied As a result, the surface of the photosensitive drum 1 that is being rotationally driven is uniformly charged.

Thereafter, an electrostatic latent image is formed on the uniformly charged surface of the photosensitive drum 1 by the light irradiation of the exposing means 3, and the electrostatic latent image is developed as a toner image with toner adhered by the developing device 4. To be done. The toner image formed on the photosensitive drum 1 is transferred to the supplied transfer material P by the transfer device 5. Transfer material P after toner image transfer
The toner image on the surface is fixed by a transfer device (not shown). On the other hand, the surface of the photosensitive drum 1 after the toner image transfer is
The cleaning device 6 removes the transfer residual toner on the surface, and the toner is provided for the next image formation.

By the way, the following problems have been pointed out in the image forming apparatus having the above-mentioned contact charging device. As shown in FIG. 6, when a horizontal line pattern having a large number of horizontal lines in the direction intersecting the traveling direction (direction of arrow K) is output to the transfer material P, the interval of each horizontal line (solid line) Pa is charged. The problem is that interference fringes Pc are generated on the image surface when the unevenness (broken line) Pb of the drum surface potential determined by the frequency f of the voltage applied to the roller 20 is approached. The frequency f of the power source 23 varies from the value determined by the component accuracy within plus and minus 10%. Therefore, the interval of the horizontal line Pa approaches the spatial frequency of the cycle unevenness Pb due to the power source 23, resulting in severe level interference. Stripes Pc were sometimes generated.

In order to eliminate this interference fringe Pc, a system has been proposed in which the frequency f of the power source 23 applied to the charging roller 20 is increased according to the process speed. However, as the process speed has increased in recent years with the increase in the speed of the image forming apparatus, the charging noise caused by the power supply frequency f at the time of charging becomes louder as the frequency f increases, which becomes a problem.

There is known a method of changing the charging member from a roller-shaped member to a blade-shaped member in order to eliminate the above-mentioned interference fringe Pc and charging noise. A blade-shaped charging member is brought into contact with the surface of the photosensitive drum 1, and the charging surface of this charging member is more exposed than the tangent line drawn from the contact position toward the downstream side in the rotation direction of the photosensitive drum 1 (direction of arrow R1). It is placed on the drum 1 side. With this configuration, the interference fringes and the charging sound can be suppressed to a level that does not pose a problem in practical use, and it has become possible to sufficiently cope with an increase in process speed.

The blade-shaped charging member described above does not necessarily have to contact the surface of the photosensitive drum 1. As long as the dischargeable area can be surely secured on the charged surface facing the surface of the photosensitive drum 1, it may be non-contact. However, in this case, it is necessary to bring the charging surface of the charging member close to the surface of the photosensitive drum 1 via a predetermined minute gap.
In order to satisfactorily charge the surface of the photosensitive drum 1 with this charging member (hereinafter, referred to as “proximity charging plate”) that is brought close to each other, the above-mentioned minute gap is set to 0 to 100 μm on the upstream side in the rotation direction of the photosensitive drum 1. It is necessary to hold it with high accuracy. This is ensured by bringing spacers into contact with the non-image forming areas at the left and right ends of the surface of the photosensitive drum 1.

[0011]

However, the contact charging device having the above-mentioned space has the following problems. As the photosensitive drum 1 rotates, the spacer is moved to the photosensitive drum 1
Since the surface is rubbed to generate contact resistance, the driving means for the photosensitive drum 1 must be torqued up. Since the spacer or the surface of the photosensitive drum 1 is abraded by the rubbing, a minute gap between the surface of the photosensitive drum 1 and the proximity charging plate changes. The rubbing causes noise.

Therefore, an object of the present invention is to provide a charging device capable of accurately maintaining a minute gap and performing good charging for a long period of time without increasing the torque of the driving means and generating noise. To do.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and applies an oscillating voltage to a charging member disposed in the vicinity of a movable surface to be charged to remove the surface to be charged. In a charging device that performs a charging process, a holding member that holds the charging member in a state where a charging surface of the charging member faces the surface to be charged, and a holding member for the moving direction of the surface to be charged by the holding member. A space roller rotatably supported on the upstream side and the downstream side of the charging surface, and a biasing member that biases the holding member toward the charged surface to bring the space roller into contact with the charged surface. The space roller has a minute gap between the charged surface and the charging surface by being brought into contact with the charged surface, and passes through the minute gap to a downstream side. The above obi than the drawn tangent Placing surface on the object to be charged surface,
It is characterized by

In this case, it is preferable that the charging member has an engaging portion for directly positioning and supporting the roller shaft of the space roller.

[0015]

According to the present invention, based on the above construction, the minute gap between the surface to be charged and the charging surface of the charging member is secured by bringing the space roller into contact with the surface to be charged. The gap can be maintained accurately. At this time, since the space roller is rotatably held, the space roller is driven to rotate as the surface to be charged moves. Therefore, the space roller and the surface to be charged are not worn by rubbing, and the precision of the minute gap is maintained for a long period of time.

When the charging member directly positions the shaft of the space roller by the engaging portion, the precision of the minute gap is further increased.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 shows a schematic configuration of a charging device 2 according to the present invention. The charging device 2 is mounted on an electrophotographic laser beam printer.

First, the outline of this printer will be described. The printer includes a rotating drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image bearing member (charged member). The photosensitive drum 1 is formed by forming an organic photoconductor (OPC) layer as a photosensitive layer 12 on the outer peripheral surface of a drum base 11 made of aluminum, and has an outer diameter of 30 mm. The photosensitive drum 1 is rotationally driven by a driving means (not shown) in the direction of arrow R1 at a predetermined process speed (peripheral speed) V _PS .

Above the photosensitive drum 1, a proximity charging plate 25 is provided.
A charging device 2 having a power source (not shown)
A charging voltage is applied by. This charging voltage is, for example, a bias voltage (V _DC + V _AC ) in which an alternating current having a frequency f is superimposed on a direct current. By applying the above-mentioned bias voltage to the proximity charging plate 25 and rotating the photosensitive drum 1 in the direction of arrow R1, the image forming area on the surface of the photosensitive drum 1 is uniformly charged. The charging device 2 will be described later in detail.

The exposure means 3 is image-modulated with a constant print density D _dpi in response to a time-series electric digital pixel signal of a target image input from a host device such as a computer, a word processor, and an image reading device (not shown). It oscillates laser light. An electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1 that has been subjected to the above-described charging process by main scanning exposure in the generatrix direction with laser light controlled by the controller.

Next, the electrostatic latent image is developed as a toner image with toner (developer) attached by the developing sleeve of the developing device 4. The toner image thus formed on the photosensitive drum 1 is transferred onto the transfer material P supplied from a paper feeding unit (not shown) to the transfer unit between the photosensitive drum 1 and the transfer roller 5 at an appropriate timing. The transfer material P after the toner image transfer is separated from the photosensitive drum 1 and conveyed to a fixing device (not shown), where the toner image is fixed. After the transfer of the toner image, the transfer residual toner on the surface of the photosensitive drum 1 is removed by the cleaning blade of the cleaning device 6, and the photosensitive drum 1 is used for the next image formation.

Next, the charging device 2 described above will be described. The charging device 2 includes a proximity charging member 25 and a holding member 26.
And space rollers 27a and 27b, and a biasing member 28. The proximity charging plate 25 is, for example, a metal plate, an electrode plate formed of a conductive plastic, or a conductive rubber in a substantially rectangular shape, and has a long side in the generatrix direction of the photosensitive drum 1 (hereinafter referred to as “left-right direction”). It is placed facing. On the lower surface of the proximity charging plate 25, a charging surface 25a that is gently curved along the rotation direction of the photosensitive drum 1 (direction of arrow R1) is formed. The length of the charging surface 25a in the left-right direction is set to be longer than the image forming area on the surface of the photosensitive drum 1. Contact charging plate 25
As shown in FIG. 2, the left and right ends of the holding member 26 are
(However, in FIG. 2, only the holding member 26 on the right side is shown).

The holding members 26 are arranged at the left and right ends of the photosensitive drum 1. As shown in FIG. 1, the space rollers 27a, 2 are provided at the lower portions of the upstream side and the downstream side of each holding member 26 (referred to the rotating direction of the photosensitive drum 1. The same applies hereinafter).
7b is rotatably supported. Each space roller 2
7a and 27b are rotatably supported by a roller shaft 27c in the left-right direction supported by a holding member 26, and a part of the lower end side A of the outer peripheral surface is close to the proximity charging plate 25.
From the charged surface of the photosensitive drum 1 toward the surface of the photosensitive drum 1. This ensures a minute gap as described later. Further, the holding member 26 is the body frame 1
0 (cartridge container 10 when the photosensitive drum 1 and the charging device 2 are incorporated in the process cartridge)
It is supported so that it can move up and down. Further, a compression spring (biasing member) 28 is interposed between the main body frame 10 and the holding member 26. The holding member 26 is urged toward the surface of the photosensitive drum 1 by the compression spring 28, which causes the space rollers 27a, 2 and 2 described above.
7b, the lower end side A is in contact with the surface of the photosensitive drum 1 on the upstream side and the downstream side, respectively. The contact positions of the space rollers 27a and 27b are set in the non-image forming areas at the left and right ends of the surface of the photosensitive drum 1.

A total of four space rollers 27a and 27b are arranged on the upstream and downstream sides of the left and right ends of the surface of the photosensitive drum 1, respectively, and these four space rollers 27a and 27b are exposed to light. By being brought into contact with the surface of the drum 1, the charging surface 25a of the proximity charging plate 25 is arranged at a predetermined position with respect to the surface of the photosensitive drum 1. That is, the gap between the surface of the photosensitive drum 1 and the charging surface 25a is formed such that the minute gap G is 0 to 100 μm on the upstream side. A portion of the charging surface 25a on the downstream side of the minute gap G is arranged closer to the photosensitive drum 1 than a tangent line drawn from the minute gap G to the downstream side.
As a result, the width of the gap between the surface of the photosensitive drum 1 and the charging surface 25a becomes the smallest in the minute gap G, and gradually increases toward the downstream side.

With the above-described structure, the position of the charging surface 25a of the proximity charging plate 25 can be held accurately with respect to the surface of the photosensitive drum 1. Therefore, the bias voltage (V _DC When + V _AC ) is applied, the surface of the photosensitive drum 1 can be charged well. Further, since the space rollers 27a and 27b are driven to rotate in association with the rotation of the photosensitive drum 1 in the direction of arrow R1 during charging, the contact resistance that tries to prevent the rotation of the photosensitive drum 1 is small, and the rotation of the photosensitive drum 1 is small. The torque can be kept low.

Further, the photosensitive drum 1 and the space roller 2
Unlike the case where they rub against each other, there is almost no wear between 7a and 27b.
It is possible to accurately hold the position of 5a. <Embodiment 2> In FIGS. 3 and 4, the space rollers 27a, 2
7b (however, in these figures, only one space roller 27a is shown), the roller shaft 27c is directly supported by the proximity charging plate 25.

The proximity charging plate 25 has engaging portions 25c, 25 for directly positioning and supporting the roller shaft 17c on the upstream side and the downstream side of the charging surface 25a which actually contributes to charging.
have d. These engaging portions 25c and 25d are provided when the proximity charging plate 25 is manufactured by, for example, a drawing process.
It is formed so as to penetrate in the longitudinal direction. By forming in this way, it is possible to effectively prevent the formation positions of these engaging portions 25c and 25d from varying at the left and right ends of the proximity charging plate 25. Therefore, when the roller shaft 27c is held by the engaging portions 27c and 27d, the accuracy of the space rollers 27a and 27b as a single item can be secured without being affected by the forming accuracy of the holding member 26. The minute gap G between the photosensitive drum 1 and the charging surface 25b described above can be formed more accurately than in the first embodiment.

[0028]

As described above, according to the present invention,
To secure a minute gap between the surface to be charged (the photosensitive drum 1 in the above-described embodiment) and the charging surface of the proximity charging member, the space to be charged is secured through a rotatable space roller, and the surface to be charged and the space roller are secured. Since the contact resistance acting between and can be reduced, the drive torque of the drive unit for moving on the surface to be charged can be suppressed low.

Further, since the wear due to the contact between the surface to be charged and the space roller is small, the precision of the minute gap can be kept good for a long period of time, and the charging failure can be prevented. Furthermore, the surface to be charged and the space roller are prevented. It is also possible to reduce the noise generated between and.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a configuration of a charging device according to a first exemplary embodiment and the vicinity thereof.

FIG. 2 is a diagram of the charging device according to the first exemplary embodiment viewed from the cleaning device side.

FIG. 3 is a diagram of the charging device according to the second exemplary embodiment viewed from the cleaning device side.

FIG. 4 is a perspective view showing a configuration of an end surface of a proximity charging plate according to a second embodiment.

FIG. 5 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 6 is a diagram showing how interference fringes are generated on a transfer material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charged object (image bearing member, photosensitive drum) 2 Charging device 3 Exposure means 4 Developing device 5 Transfer device 6 Cleaning device 20 Charging member (charging roller) 23 Power supply 25 Charging member (proximity charging plate) 25a Charging surface 25c, 25d Engagement part 26 Holding members 27a, 27b Space roller 27c Roller shaft 28 Energizing member (compression spring) G Small gap P Transfer material

Claims (2)

[Claims] 1. A charging device for charging a charged surface by applying an oscillating voltage to a charged member arranged in the vicinity of a movable charged surface, wherein the charging member is a charging surface of the charging member. A holding member that holds the surface to be charged and a space roller rotatably supported by the holding member on the upstream side and the downstream side of the charging surface in the moving direction of the charging surface; An urging member for urging the holding member toward the charged surface to bring the space roller into contact with the charged surface, wherein the space roller is in contact with the charged surface. With this, a minute gap is secured between the charged surface and the charged surface, and the charged surface is arranged on the charged surface side with respect to a tangent line drawn to the downstream side through the minute gap. Characteristic charging device 2. The charging device according to claim 1, wherein the charging member has an engaging portion that directly positions and supports the roller shaft of the space roller.