JPH07114246A - Image forming device - Google Patents

Abstract

PURPOSE:To perform satisfactory electrification free of an electri-fication noise and an interference fringe by accurately positioning an electrifying member close to the surface of an image carrier. CONSTITUTION:The proximity electrifying plate (electrifying member) 2 held by a holder 21 is energized and pressed toward a photosensitive drum l by means of a compression spring 22. At this time, a sheet member 23 is interposed between the upstream side 2d of the proximity electrifying member 2 and the surface of the photo sensitive drum 1. A minute space S between both is accurately made by the thickness of the sheet member 23, and even when a current in which an alternating current and a direct current are superimposed is applied via a power source 5, satisfactory electrification free of an electrification noise is performed. Further, because the direct contact of the proximity electrifying plate 2 with the photosensitive drum 1 can be prevented, even in the case of the electrifying plate 2 made of metal, this plate does not damage the surface of 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 an image forming apparatus which charges a surface of an image carrier by applying an oscillating voltage to a charging member which is arranged close to the image carrier.

[0002]

2. Description of the Related Art A contact charging device and a contact charging device are known as devices for charging an object to be charged. The former contact charging device is one in which a charging member to which a voltage is applied is brought into contact with or close to a member to be charged to directly transfer the charge to the member to be charged, and the surface to be charged is charged to a predetermined potential. . The contact charging device, for example, has a lower applied voltage required to charge the surface to be charged to a predetermined voltage than a corona discharge device which has been widely used as a contact type charging device. The amount of ozone generated during the charging process is very small, and therefore a special device for removing ozone (for example, an ozone removal filter)
It is not necessary to install, and therefore the exhaust system configuration of the device can be simplified, maintenance-free,
It has advantages such as

Due to these advantages, the contact charging device is used as an image carrier such as a photoconductor or a dielectric in an image forming apparatus such as an electrophotographic device (copier, laser beam printer) or electrostatic recording device. As a charging processing means for the charged body, the following attention has been focused on as a substitute for a contact charging device such as a corona discharge device, and has been put into practical use.

In the above-mentioned contact charging device, in order to realize uniform charging of the body to be charged, a voltage in which a DC voltage and an oscillating voltage are superimposed is applied to the conductive member (contact charging member), and this conductive member is applied. A method has been proposed in which a charging member is brought into contact with or brought close to a member to be charged (Japanese Patent Laid-Open No. 63-149669).
Issue).

FIG. 6 shows an outline of one embodiment thereof. Examples of the member to be charged include a drum-type electrophotographic photosensitive member that is rotationally driven at a predetermined peripheral speed (process speed) in the direction of arrow R1 and an electrostatic recording dielectric (hereinafter referred to as "photosensitive drum 1").
Say. ) And the like are provided. A charging roller 2 as a contact charging member is in contact with the surface of the photosensitive drum 1. The charging roller 2 includes a cored bar 2a made of metal or the like, and a conductive roller body 2b made of conductive rubber or the like on the outer periphery thereof. The charging roller 2 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force by pressing springs (not shown) arranged at both ends of the cored bar 2a in the axial direction. Is rotated by the rotation of the arrow.

A contact leaf spring 3 is in contact with the core bar 2a of the charging roller 2 described above, and a power source 5 is connected to the contact leaf spring 3. The charging roller 2 has this power source 5
As a result, a voltage (Vac + Vdc) obtained by superposing the oscillating voltage Vac having the peak-to-peak voltage Vpp that is at least twice the charging start voltage of the photosensitive drum 1 and the DC voltage Vdc is applied via the contact leaf spring 3 and the core bar 2a. As a result, the surface of the photosensitive drum 1 which is rotationally driven is uniformly charged.

By the way, the image forming apparatus using the voltage applying type contact charging device as the charging means of the photosensitive drum 1 has the following problems.

That is, as shown in the example of FIG. 7, when the horizontal line pattern image Ga is output on the transfer material P, the horizontal line pattern interval is determined by the frequency of the power source 5 for applying the voltage to the charging roller 2 and the drum surface potential. That is, when it comes close to the so-called cycle unevenness Gb (dotted line), interference fringes Gc are generated in the horizontal line pattern Ga.

The frequency f of the power source 5 has a variation of about plus or minus 10% from the predetermined frequency based on the machining accuracy and the assembly accuracy of the parts. Depending on the power source 5, the frequency f becomes the spatial frequency of the horizontal line pattern Ga. In this case, the interference fringes Gc may be generated to a lesser degree.

As a measure for preventing the interference fringe Gc, a method of increasing the frequency f of the voltage applied to the charging roller 2 according to the process speed has been proposed. However, according to this, when the process speed is increased as in recent years with the increase in the speed of the image forming apparatus, the charging sound caused by the frequency f of the charging power source 5 is also increased as the frequency is increased. , Has become a problem.

As one of the measures to eliminate the above-mentioned interference fringes and charging noise, the position of the charging surface of the charging member should be located closer to the photosensitive drum than the tangent line drawn from the contact position between the photosensitive drum and the charging member. There is something to place. By doing so, it became possible to suppress the interference fringes and the charging noise to a level at which practically no problems occur.

Further, the charging member does not necessarily have to contact the charging surface with the photosensitive drum, and may be in non-contact as long as a region capable of discharging is surely secured between the surface of the photosensitive drum and the charging surface. . That is, the charged surface may be brought close to the surface of the photosensitive drum via a predetermined gap in a non-contact state. When such a charging member is referred to as a proximity charging plate, the upstream side of the proximity charging plate in the rotation direction of the photosensitive drum 2 is brought close to the surface of the photosensitive drum, and at this time, the charging member is placed between the surface and the surface of the photosensitive drum 2. If a minute gap of 0 to 100 μm is maintained, almost good discharge can be performed. Note that, on the downstream side of the minute gap, the distance between the surface of the photosensitive drum 2 and the proximity charging plate is gradually increased.

[0013]

However, there is the following problem in maintaining the minute gap when the proximity charging plate is brought close to the photosensitive drum as in the above-mentioned conventional technique. Since the upstream clearance of the proximity charging plate is as small as 0 to 100 μm, in order to structurally maintain this clearance, it is necessary to maintain a high accuracy of all of the constituent parts. If the precision of the parts is reduced, it must be assembled with the adjustment mechanism. Assuming that the proximity charging plate and the photosensitive drum may contact each other on the upstream side, the material of the proximity charging plate becomes expensive in order to prevent damage to the photosensitive drum. In addition, it is necessary to have rigidity that does not cause warpage in the longitudinal direction. A material of the proximity charging plate that is rigid and inexpensive is a metal plate material (or a plate-shaped material), but when it comes into contact with the photosensitive drum, it damages the photosensitive drum.

Therefore, an object of the present invention is to provide an image forming apparatus which solves the above problems.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, in which a charging member of a charging device is brought close to an image carrier and at least an oscillating voltage is applied to the charging member. In the image forming apparatus in which the image carrier is charged, the charging member has a charging surface facing the surface of the image carrier through a minute gap, and the charging surface is in the minute gap. The charging device is disposed closer to the surface of the image carrier than the tangent line drawn to the surface of the image carrier, and the charging device is interposed between the surface of the image carrier and the charging surface so that the minute gap is formed. It has a sheet member to secure.

The intermediate portion of the sheet member is sandwiched between the surface of the image carrier and the charging surface, and
At least one end may be fixed to a support member that supports the charging member or a support member that supports the image carrier.

Further, the sheet member may be fixedly arranged on the charging member.

[0018]

According to the above construction, a sheet member is sandwiched between the image carrier and the charging surface of the charging member in order to secure a minute gap between the surface of the image carrier and the charging surface of the charging member. In addition, the charging member does not damage the surface of the image carrier. Therefore, the degree of freedom in designing the material and shape of the charging member is greatly improved. Thereby, for example, the charging member is made of a metal material, and it is easy to suppress the deformation (warpage) in the longitudinal direction.
In addition, the minute gap between the surface of the image carrier and the charging surface of the charging member does not depend on the accuracy of other constituent members and the like,
Since it is uniquely determined by the thickness of the sheet member, sufficient accuracy can be ensured.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a longitudinal sectional view showing the vicinity of an image carrier of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer by an electrophotographic process using a proximity charging plate as a charging member of the image carrier.

This laser beam printer is provided with a rotary drum type electrophotographic photosensitive member (photosensitive drum) 1 as an image bearing member. The photosensitive drum 1 includes an organic photoconductor (OP) as a photosensitive layer on the outer peripheral surface of a drum base body 1a made of aluminum.
C) The layer 1b is provided and has an outer diameter of 30 mm. The photosensitive drum 1 is rotatably supported and is rotationally driven in the direction of arrow R1 at a peripheral speed Vps by a driving unit (not shown).

A proximity charging plate 2 as a charging member is arranged above the photosensitive drum 1. The proximity charging plate 2 is an electrode plate made of a metal plate, a conductive plastic, a conductive rubber, or the like, is formed to be long in the axial direction of the photosensitive drum 1, and the photosensitive drum 2 is provided on the surface facing the surface of the photosensitive drum 2. A charging surface 2c that is gently curved in an arc shape is formed along the rotation direction of. The configuration for disposing the proximity charging plate 2 at a predetermined position with respect to the surface of the photosensitive drum 2 will be described in detail later. A bias voltage (Vdc + Vac) obtained by superimposing an alternating current having a frequency f on the direct current is applied to the proximity charging plate 2 by the power supply 5, and the surface of the photosensitive drum 1 is charged to a predetermined potential.

An electrostatic latent image is formed by the exposure device 6 on the surface of the photosensitive drum 1 which has been charged. The exposure device 6 is
A constant print density Dd corresponding 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)
The laser light image-modulated by pi is output. As described above, the surface of the photosensitive drum 1 that has been subjected to the charging process is subjected to the main scanning exposure in the drum generatrix direction with the laser light output from the scanner controlled by the controller, and the main scanning and the sub scanning based on the rotation of the photosensitive drum 1 are performed. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1. Then, the latent image is transferred to the developing sleeve 7 of the developing device.
The toner image is developed with the toner, and the developed image is transferred from the paper feed unit (not shown) at appropriate timing to the photosensitive drum 1 and the transfer roller 9
The image is transferred to the transfer material P introduced into the transfer section between and. The transfer material P that has passed through the transfer section is separated from the surface of the photosensitive drum 1 and is conveyed to an image fixing section (not shown). After the image transfer, the surface of the photosensitive drum 1 is cleaned by a cleaning blade 10 of a cleaning device to remove adhering contaminants such as transfer residual toner, and is repeatedly used for image formation.

Next, a method of bringing the proximity charging plate 2 close to the photosensitive drum 1 will be described.

The proximity charging plate 2 is held by holders 21 arranged near both ends in the longitudinal direction thereof. The holder 21 is supported by a container (support member) 11 to which the above-mentioned cleaning blade 10 and the like are fixed so as to freely come into contact with and separate from the surface of the photosensitive drum 1, and further, between the container 11 and the holder 21. It is urged toward the surface of the photosensitive drum 1 by the interposed compression spring 22. By the biasing of the holder 21 by the compression spring 22, the proximity charging plate 2 held by the holder 21
Is also urged toward the surface of the photosensitive drum 1 and is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. At this time, in the vicinity of both ends in the longitudinal direction of the proximity charging plate 2, the sheet member 23 is provided between the surface of the photosensitive drum 1 and the upstream side 2d of the proximity charging plate 2.
Is sandwiched and interposed. The sheet member 23 is sandwiched at its intermediate portion between the upstream side of the proximity charging plate 2 (referred to the rotation direction of the photosensitive drum 1; the same applies hereinafter) and the surface of the photosensitive drum 1 to form a minute gap S at this portion. In addition, the one end 23a on the upstream side and the other end 23b on the downstream side are fixed by the container 11 holding the holder 22, respectively.

The width of the minute gap S is determined by the thickness of the sheet member 23. The sheet member 23 is formed by, for example, banding a sheet made of a material such as PET. If a sheet having a thickness of 20 μm is used, the above-mentioned minute gap S is also set to 20 μm, which is almost the same as this. That is, by selecting a desired sheet member 23, the width of the minute gap S can be easily and accurately set to the same value as the thickness of the sheet member 23. In this manner, the sheet member 23 prevents the proximity charging plate 2 from directly contacting the surface of the photosensitive drum 1, and the proximity charging plate 23 does not contact the photosensitive drum 1 and damage it, and The degree of freedom in designing the material, shape, etc. of the proximity charging plate 23 is greatly increased. For example, the proximity charging plate 2 can be formed of an inexpensive and rigid metal material.

The charging surface 2c of the above-mentioned proximity charging plate 2 is arranged closer to the photosensitive drum 1 than the tangent line L (dotted line in FIG. 1) drawn to the surface of the photosensitive drum 1 at the minute gap S, and the upstream side 2d. From the photosensitive drum 1 toward the downstream side 2e.
The distance to the surface is gradually increasing. On the upstream side 2d, the distance between the surface of the photosensitive drum 1 and the charging surface 2a of the proximity charging plate 2 is a minute gap S (20 μm) based on the thickness of the sheet member 23.
m) with high accuracy, and in the downstream side 2e, the contact portion 21a protruding downward from the holder 21 contacts the surface of the photosensitive drum 1 so that the contact portion 21a is approximately 400-5.
It is held at 00 μm.

The proximity charging plate 2 is made of a metal plate as described above, and when a bias voltage is applied to the proximity charging plate 2 via the power source 5 to charge the surface of the photosensitive drum 1, the photosensitive drum 1 is charged. The sheet member 23 sandwiched between the surface and the proximity charging plate 2 can accurately hold the minute gap S between the two, so that charging noise, interference fringes, and the like are not generated, and it is excellent. Charging can be realized. In the above embodiment,
Proximity charging plate 2, holder 21, compression spring 22, power supply 5,
The sheet member 23 or the like constitutes a charging device. <Second Embodiment> Next, a second embodiment will be described. 2 shows the upstream side 2 of the proximity charging member 2 when fixing the one end 23a and the other end 23b of the sheet member 23 to the container 11.
The distance between the surface d of the photosensitive drum 1 and the distance d on the downstream side 2e is held by the sheet member 23.

This can be easily implemented by appropriately setting the length of the sheet member 23 when it is fixed to the container 11 (for example, shorter than that in the case of the first embodiment). <Third Embodiment> FIG. 3 shows a structure in which only one end 23a of the sheet member 23 is fixed to the container 11 and the other end 23b is not fixed and is free. The other configuration is the same as that of the first embodiment shown in FIG. In this way, by freeing the other end 23b of the sheet member 23 in the rotation direction of the photosensitive drum 1 (direction of arrow R1), the sheet member 23 is not wound around the photosensitive drum 1 and the proximity charging plate 2 and the photosensitive drum 1 are not wound. It is possible to maintain a minute gap S with the surface. <Embodiment 4> FIG. 4 shows an example in which the sheet member 23 is arranged so as to be wound around the proximity charging plate 2.
The intermediate portion of the sheet member 23 is applied to the charging surface 2c side of the proximity charging plate 2, and one end 2d and the other end 2e of the sheet member 23 are folded back to the back surface side of the proximity charging plate 2, respectively.
The folded-back portion is fixed with an adhesive or double-sided tape. This improves the assembling property when the proximity charging plate 2 is brought into contact with the photosensitive drum 1. <Embodiment 5> In Embodiment 5 shown in FIG. 5, two sheet members 23 and 25 having different thicknesses are used to form the upstream side 2d and the downstream side 2e of the proximity charging plate 2 to the surface of the photosensitive drum 1, respectively.
It is configured to secure the distance of. By sandwiching the thin sheet member 23 arranged on the inner side by the surface of the photosensitive drum 1 and the upstream side 2d of the proximity charging plate 2, a minute gap S is secured, while the thicker sheet member 25 arranged on the outer side is secured. The surface of the photosensitive drum 1 and the proximity charging plate 2
By sandwiching it with the downstream side 2e, the distance between them is secured. At this time, the thick outer sheet member 25
In order to prevent the interference with the upstream side 2d of the proximity charging plate 2, a notch 2f is provided in a part of the proximity charging plate 2.

At this time, both ends of the one end 23a, 25a and the other end 23b, 25b of the sheet members 23, 25 may be fixed to the container 11, and as shown in FIG. If 23b and 25b are to be made free, the rotation direction of the photosensitive drum 1 (arrow R1
Direction) If the downstream side is free, these sheet members 2
The gap between the proximity charging plate 2 and the photosensitive drum 1 can be maintained at a predetermined value without the 3, 25 being caught in the photosensitive drum 1.

In the first to third embodiments and the fifth embodiment described above, the container 11 to which the sheet member 23 and the sheet member 25 are fixed is the container 11 to which the cleaning blade 10 of the cleaning device is fixed. However, it is not limited to this. For example, it may be a container that movably supports the holder 21 or a container that rotatably supports the photosensitive drum 1. That is, as long as the sheet members 23 and 25 can be effectively fixed, the member or the position to be fixed can be arbitrary.

[0031]

As described above, according to the present invention,
By sandwiching the sheet member between the surface of the image carrier and the charging member, it is possible to prevent the surface of the image carrier and the charging member from directly contacting each other. The degree of freedom of design can be increased, and an inexpensive charging member can be configured with a simple configuration. For example, even when the charging member is made of metal or the like so as to have sufficient rigidity, the surface of the image carrier is not damaged because the charging member and the image carrier are not in contact with each other. In addition, charging noise and interference fringes do not occur. Further, since the minute gap between the surface of the image carrier and the charging member can be accurately maintained by the thickness of the sheet member, good charging of the image carrier can be realized.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view illustrating a configuration of a charging device in an image forming apparatus according to a first exemplary embodiment.

FIG. 2 is a vertical cross-sectional view showing the configuration of a charging device in an image forming apparatus according to a second exemplary embodiment.

FIG. 3 is a vertical cross-sectional view showing a configuration of a charging device in an image forming apparatus according to a third exemplary embodiment.

FIG. 4 is a vertical cross-sectional view showing the configuration of a charging device in an image forming apparatus of Example 4.

FIG. 5 is a perspective view illustrating a configuration of a charging device in an image forming apparatus according to a fifth exemplary embodiment.

FIG. 6 is a schematic diagram showing a configuration of a charging device of a conventional image forming apparatus.

FIG. 7 is a diagram showing a generation state of interference fringes when an image is formed by a conventional charging device.

[Explanation of symbols]

 1 Image Carrier (Photosensitive Drum) 2 Charging Member (Proximity Charging Plate) 2c Charging Surface 5 Power Supply 6 Exposure Device 7 Developing Sleeve 9 Transfer Roller 10 Cleaning Blade 11 Supporting Member (Container) 23 Sheet Member 23a One End 23b Other End L Tangent Line P Transfer material S Small gap

Claims (3)

[Claims] 1. An image forming apparatus in which a charging member of a charging device is brought close to an image carrier and at least an oscillating voltage is applied to the charging member to charge the image carrier, wherein the charging member is , Having a charging surface facing the surface of the image carrier through a minute gap, and arranging the charging surface closer to the surface of the image carrier than a tangent line drawn to the surface of the image carrier at the minute gap. In addition, the charging device includes a sheet member that is interposed between the surface of the image carrier and the charging surface to secure the minute gap, and the image forming apparatus. 2. The sheet member has an intermediate portion sandwiched between the surface of the image carrier and the charging surface, and at least one end of the sheet member supports the charging member or the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is fixed to a supporting member. 3. The image forming apparatus according to claim 1, wherein the sheet member is fixedly disposed on the charging member.