JPH07230199A - Image forming device and electrifier - Google Patents

Abstract

PURPOSE:To excellently electrify the surface of a photoreceptor drum by precisely holding a very small gap between the surface of the photoreceptor drum and the electrifying surface of an electrifying plate, with a simple constitution. CONSTITUTION:Resinous spacers 11 are formed on both end parts in the longitudinal direction of a proximity electrifying plate 2 (in the generatrix direction of the photoreceptor drum 1). The sliding surfaces 11a of the spacers 11 are abutted on the surface of the photoreceptor drum 1, to confront the electrifying surface 2a of the proximity electrifying plate 2 with the surface of the photoreceptor drum 1. In the upstream side in the rotational direction of the photoreceptor drum 1 (the direction of the arrow R1), the very small gap is formed between the surface of the drum 1 and the electrifying surface 2a. It is arranged on the side nearer to the photoreceptor drum 1 than a plane passing through the very small gap and being in contact with the surface of the drum 1. At this time, the spacers 11 are integrally outsert-molded with the proximity electrifying plate based on the electrifying surface 2a as a reference, on both end parts of the proximity electrifying plate 2. Thus, a highly accurate very small gap depending on a die used for molding can be obtained.

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 such as a copying machine or a laser beam printer and a charging device, and more specifically, to a charging member to which an oscillating voltage (voltage whose voltage value changes periodically) is applied. The present invention relates to an image forming apparatus and a charging device that charge a surface of an image carrier by bringing the image carrier into contact with or close to the image carrier.

[0002]

[Prior art]

<Prior Art of the First Invention> In a contact charging device used in a copying machine or the like, a charging member to which a voltage is applied is brought into contact with an object to be charged to directly transfer the electric charge to the object to be charged. ,
The surface of the body to be charged, which is the surface to be charged, is charged to a predetermined potential. This contact charging device has a lower applied voltage required to charge a surface to be charged to a predetermined potential than a corona discharge device (contact charging device) which has been widely used as a charging device. It has the advantages that the amount of ozone generated in the charging process is very small and the need for an ozone removal filter is eliminated, the exhaust system configuration of the device can be simplified, and that it is maintenance-free. ing.

The contact charging device having the above-mentioned advantages is, for example, in an image forming apparatus such as an electrophotographic apparatus (copier, laser beam printer, etc.), an electrostatic recording apparatus, etc., which carries an image of a photoconductor, a dielectric or the like. As a substitute for the corona discharge device, it has been put to practical use as a means for charging the body and other charged bodies.

In this contact charging device, a superposed voltage obtained by superposing a DC voltage and an oscillating voltage is applied to a conductive charging member in order to uniformly charge the surface to be charged, and the charging member is applied to the member to be charged. A method of charging by contact is proposed (Japanese Patent Laid-Open No. 63-149669).

FIG. 6 shows an example of the contact charging device. In FIG. 1, reference numeral 1 denotes a drum type electrophotographic photosensitive member as an object to be charged, which is rotationally driven in the direction of arrow R1 at a predetermined peripheral speed (process speed), an electrostatic recording dielectric, etc. (hereinafter referred to as "photosensitive drum"). It is).

Reference numeral 2 denotes a conductive charging roller as a contact charging member, which is composed of a cored bar 21 and a conductive roller body 23 made of conductive rubber or the like formed on the outer periphery thereof. The charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force by the pressing force of a pressing spring (not shown) that urges both end portions of the cored bar 21 to rotate the photosensitive drum 1. Followed by the rotation.

Reference numeral 4 denotes a voltage application power source for the charging roller 2. The voltage applied to the charging roller 2 by the power source 4 via the contact leaf spring 3 brought into contact with the cored bar 21 of the charging roller 2 is a peak-to-peak voltage V which is at least twice the charging start voltage of the photosensitive drum 1. Oscillation voltage V _ac with _PP and DC voltage V
_dc is the superimposed voltage (V _ac + V _dc ). As a result, the outer peripheral surface of the photosensitive drum 1 that is being rotationally driven is uniformly charged.

However, the following problems have been pointed out in the image forming apparatus as described above, that is, in the image forming apparatus in which the voltage applying type contact charging device is used as the charging means of the image carrier.

That is, the transfer material 14 after the image formation shown in FIG.
As shown in FIG. 5, when the horizontal line pattern image 14a is output, the horizontal line pattern interval is determined by the frequency of the power supply 4 that applies a voltage to the charging roller 2. The drum surface potential unevenness (cycle unevenness; When it comes close to 14b,
That is, the interference fringes 14c are generated on the image surface.

The frequency f of the power source 4 has a variation of about plus or minus 10% from the value determined by the component precision, and depending on the power source 4, it approaches the spatial frequency of the horizontal line pattern image 14a, and the level is terrible. Interference fringe 14
In some cases, c was generated.

There has also been proposed a method of increasing the frequency f of the power source 4 applied to the charging roller 2 in accordance with the process speed as a countermeasure against the interference fringes 14c. However, as the image forming apparatus has become faster and the process speed has become faster as in recent years, the charging sound caused by the vibration voltage V _ac of the power source 4 (mainly, the surface of the charging roller 2 having elasticity is the photosensitive drum 1). The sound that hits the surface.) Becomes louder as the frequency f increases, which has become a problem.

A contact charging device using a long plate-shaped contact charging plate in place of the charging roller 2 is known as a measure for reducing the charging noise and eliminating the interference fringes 14c. With the longitudinal direction of the contact charging plate oriented parallel to the axis of the photosensitive drum, a part of the charging surface facing the surface of the photosensitive drum 1 is brought into contact (contact) with the surface of the photosensitive drum 1. As a result, a linear nip is formed as a contact surface between the charging surface and the photosensitive drum 1. Further, at this time, the position of the charging surface of the contact charging plate is set to be closer to the photosensitive drum 1 than the plane including the nip and contacting the surface of the photosensitive drum. As a result, the charging sound and the interference fringes 14c are suppressed to a level at which there is no practical problem.

The charging plate described above does not necessarily have to come into contact with the surface of the photosensitive drum 1. What is necessary is to secure a minute gap as a dischargeable area between the surface of the photosensitive drum 1 and the charging surface of the contact charging member. That is, as long as this condition is satisfied, the charging surface may be brought into close contact with the surface of the photosensitive drum 1 without being in contact therewith. Hereinafter, the above-mentioned charging plate will be referred to as a “proximity charging plate” in the sense that it suffices if the charging surface is at least close to the surface of the photosensitive drum 1.

Regarding the minute gap between the charging surface of the proximity charging plate and the surface of the photosensitive drum 1, when the upstream side and the downstream side of the proximity charging plate are determined with reference to the rotation direction of the photosensitive drum 1, a minute amount on the upstream side is determined. By maintaining the gap at about 0 to 100 μm, the charging surface of the proximity charging plate and the photosensitive drum 1
A reliable discharge is generated between the surface and the surface.

In the image forming apparatus shown in FIG.
Reference numeral 5 denotes exposure light for exposing the uniformly charged surface of the photosensitive drum 1 to form an electrostatic latent image, 6 a developing device for adhering toner to the electrostatic latent image to form a toner image, and 7 not shown. Of the transfer material supplied to the photosensitive drum 1 at a predetermined timing from the sheet feeding unit of the transfer roller 8, the transfer roller 8 for transferring the toner image on the photosensitive drum 1 onto the transfer material 7, and the transfer residual toner 9 on the photosensitive drum 1. The transfer material 7 is a cleaning blade for removing the toner image, and the transfer material 7 after the toner image is transferred is configured so that the toner image is fixed by a fixing device (not shown). <Prior Art of Second Invention> In a contact charging device mounted in an image forming apparatus such as a copying machine, a charging member to which a voltage is applied is brought into contact with a member to be charged, and the charge is directly transferred to the member to be charged. In this way, the surface to be charged is charged to a predetermined potential, and the applied voltage required to charge the surface to be charged to a predetermined potential is lower than that of a corona discharge device that has been widely used as a charging device. Voltage can be achieved, the amount of ozone generated in the charging process is very small and the need for ozone removal filters etc. is eliminated, therefore the configuration of the exhaust system of the device is simplified, maintenance free, It has advantages such as

As a charging member of the above-mentioned contact charging device, a charging roller in which a conductive rubber or the like is formed in a cylindrical shape on the outer circumference of a metal cored bar has been used in recent years.

The charging roller is rotatably supported and is a photosensitive drum (image carrier) which is a rotating drum type member to be charged.
It is configured to be rotated by the rotation of the photosensitive drum by being pressed by a spring or the like.

Further, a superimposing voltage obtained by superimposing an AC voltage and a DC voltage having a peak-to-peak voltage which is more than twice the charging start voltage of the photosensitive drum is applied to the charging roller from a power source through a core rod, and the photosensitive drum surface Are uniformly charged.

By the way, the charging roller as the charging member has the following problems.

That is, after winding the conductive rubber around the core metal as described above, it is necessary to form a high resistance layer on the surface of the conductive rubber in order to prevent current leakage from the charging roller to the photosensitive drum. Complex and expensive to manufacture.

Further, when the charging roller is used in an image forming apparatus such as a laser beam printer, that is, an image forming apparatus of the type which forms an image by writing image information by line scanning, for example, a horizontal line pattern image is output. At this time, when the unevenness of the potential on the surface of the photosensitive drum determined by the frequency of the AC component applied to the charging roller and the distance between the horizontal lines become close to each other, interference fringes occur.

In order to avoid the occurrence of the interference fringes, it is necessary to make the potential unevenness on the photosensitive drum smaller than the size of the pixels (dots) of the image forming apparatus. Therefore, the method of increasing the frequency has been adopted. . However, the charging roller vibrates at a frequency about twice the AC frequency due to the applied AC voltage, and the noise generated by the cylindrical photosensitive drum as a resonator, so-called charging sound, is emitted outside the apparatus main body. At this time, if the frequency of the AC voltage is high, there is a problem that the charging noise also becomes high.

Therefore, the applicant of the present invention, as a contact charging member which replaces the charging roller, has a charging surface facing a surface to be charged with a minute gap therebetween and a plane contacting the surface to be charged through the minute gap. Also proposes a charging member configured to be located on the charged side.

When a long plate-shaped conductor (proximity charging plate) as an electrode plate is brought into contact with or close to the photosensitive drum, the charging member is moved from the contact (proximity) position to the downstream side in the moving direction of the photosensitive drum. The charging surface is arranged closer to the photosensitive drum than the flat surface drawn so as to contact the surface of the photosensitive drum, and the structure is simpler than that of the charging roller described above, and the cost can be reduced.

At this time, the minute gap formed between the surface of the photosensitive drum and the charging surface of the proximity charging plate is the width of the above-mentioned proximity charging plate (the direction intersecting the longitudinal direction, that is, the moving direction of the surface of the photosensitive drum). When the width (along the width) is 12 mm, it is desirable to set 0 to 130 μm on the upstream side and 400 to 500 μm on the downstream side. <Prior Art of Third Invention> Conventionally, as a charging device of an image forming apparatus such as a copying machine laser beam printer, one shown in FIG. 20 is known. The figure shows a process cartridge C detachably attached to the main body of the image forming apparatus.
The longitudinal cross-sectional view of RG is shown. In the cartridge container 74, the photosensitive drum 7 as an image bearing member (charged member) is used.
7, a charging plate (charging member) 71, a developing device 109, a cleaning blade 83, a toner container 85 and the like are integrally incorporated.

The process cartridge C having such a structure
In the RG, the charging plate 71 is formed of metal, conductive plastic, conductive rubber, or the like, is supported by the cartridge container 74 so that it can come in contact with and separate from the surface of the photosensitive drum 77, and is interposed between the charging container 71 and the cartridge container 74. The compression spring 73 biases the surface of the photosensitive drum 77. As a result, the charging plate 71 causes the charging surface 71 a facing the surface of the photosensitive drum 77 to have the charging surface 71 a.
7 is placed close to (or in contact with) the surface and at a predetermined position. At the time of charging, a bias voltage is applied to the charging plate 71 to uniformly charge the surface of the photosensitive drum 77.

[0027]

[Problems to be Solved by the Invention]

<Problem of First Invention> However, according to the prior art of the first invention, there are the following drawbacks.

First, when the proximity charging plate is brought into contact with the photosensitive drum 1, (1) if the proximity charging plate is made of metal, it is easy to increase rigidity and prevent warpage in the longitudinal direction. Although the cost is low, the surface of the photosensitive drum 1 is easily damaged. (2) When the proximity charging plate is formed by a member that does not damage the surface of the photosensitive drum 1, the thickness tends to be thick when trying to secure the rigidity for preventing the warp in the longitudinal direction, which is also costly. It will be expensive.

Next, when the proximity charging plate is brought close to the photosensitive drum 1 without coming into contact with it, (3) In order to accurately maintain the minute gap on the upstream side of the proximity charging plate to 100 μm or less, all the constituent parts are The precision of parts must be kept high. (4) If the precision of the parts is not increased or cannot be increased, it becomes necessary to incorporate an adjustment mechanism for adjusting the minute gap, which complicates the configuration.

Therefore, it is an object of the first invention to provide an image forming apparatus equipped with a charging device capable of performing good charging with a simple structure. <Problem of Second Invention> Further, according to the conventional technique of the second invention, in order to accurately maintain the gap between the photosensitive drum surface and the charging surface of the proximity charging plate on the upstream side and the downstream side, There is a problem that the precision of parts such as the proximity charging plate and the container (housing) that supports the proximity charging plate must be increased.

Therefore, in the second invention, the surface of the image carrier (the photosensitive drum in the above description) and the charging surface of the charging member are set without increasing the precision of the parts such as the charging member (the above-mentioned proximity charging plate) and the container more than necessary. It is an object of the present invention to provide an image forming apparatus capable of accurately maintaining a minute gap between and. <Problem of the Third Invention> Further, according to the conventional technique of the third invention, a compression spring (elastic member) 73 for pressing the charging plate 71 against the surface of the photosensitive drum 77 is required separately from the charging plate 71. Therefore, there is a problem that the configuration becomes complicated.

Therefore, an object of the third invention is to provide a charging device in which the elastic member is omitted and the structure is simplified.

[0033]

The present invention (first to third inventions) has been made in view of the above circumstances, and has the following configurations, respectively. <Means of the First Invention> In the first invention, the surface of the image bearing member is opposed to the surface of the image bearing member through a minute gap, and the image bearing member is arranged closer to the image bearing member than a plane that is in contact with the surface of the image bearing member through the minute gap. In an image forming apparatus that includes a charging member having a charged surface, and applies an oscillating voltage to the charging member to charge the surface of the image carrier, the charging member causes the image carrier to pass through the minute gap. A charging plate having facing charging surfaces is provided, which is integrally formed at both ends of the charging plate and contacts a non-image forming area of the image carrier to secure a minute gap between the surface of the image carrier and the charging surface. The spacer is formed by outsert molding on both ends of the charging plate with reference to the charging surface of the charging plate.

Further, the charging member has a stepped portion in which the charging surface side is cut out at both ends of the charging plate on which the spacer is formed, and the spacer is in contact with the surface of the image carrier. The thickness between the sliding surface and both ends of the charging plate can be increased.

Further, the spacer may be directly held by a holding container. <Means of the Second Invention> The second invention is arranged so as to face the surface of the image carrier through a minute gap and to be closer to the image carrier than a plane contacting the surface of the image carrier through the minute gap. In an image forming apparatus that includes a charging member having a charged surface, and applies an oscillating voltage to the charging member to charge the surface of the image carrier, the charging member causes the image carrier to pass through the minute gap. The image carrier comprises a charging plate having a charging surface facing each other, and the image carrier has step portions in the non-image forming regions located on both sides of the central image forming region, and the both ends of the charging plate are respectively the image carrier. Abut the step of the body,
A minute gap is secured between the surface of the image carrier and the charging surface.

Each of the stepped portions is formed in at least two steps, and each end of the charging plate is brought into contact with the stepped portions so that the width of the minute gap is restricted to at least two points. May be.

The stepped portion may be formed by a coating agent for the surface of the image bearing member. <Means of Third Aspect> A third aspect of the present invention urges a charging member toward an object to be charged to bring the charging surface of the charging member into contact with or approach the surface to be charged of the object to be charged, and In a charging device for uniformly charging the surface to be charged by applying a voltage to a charging member, the charging member has an elastic portion at least in part, and the charging is performed based on the elastic force of the elastic portion. The surface is in contact with or close to the surface to be charged.

Further, the elastic portion may be provided at a portion having no charging surface.

[0039]

[Action]

<Operation of the First Invention> Based on the above configuration, according to the first invention, spacers for ensuring a minute gap between the surface of the image carrier and the charging surface of the charging plate are charged at both ends of the charging plate. By integrally molding outsert on the basis of the surface,
The precision of the minute gap can be increased. <Operation of the Second Invention> According to the second invention, step portions are provided in the non-image forming areas on both sides of the image forming area in the center of the image carrier, and both end portions of the charging member are brought into contact with these step portions. As a result, a minute gap between the surface of the image carrier and the charging surface of the charging member is secured, so that the precision of the minute gap can be easily improved by increasing the accuracy of forming the step. <Operation of the third invention> According to the third invention, at least a part of the charging member is formed of an elastic portion, so that the elastic force of the charging member itself causes a part of the charging member to abut the surface to be charged. The charged surface can be held at a predetermined position with respect to the surface to be charged.

[0040]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1 of the First Invention> FIG. 1 is a longitudinal sectional view showing a schematic configuration around a photosensitive drum 1 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 means for the image carrier.

In the figure, reference numeral 1 is a rotary drum type electrophotographic photosensitive member (photosensitive drum) as an image bearing member. In this embodiment, a photosensitive layer 1 is formed on the outer peripheral surface of an aluminum drum substrate 1b.
An organic photoconductor (OPC) layer is formed as a and has an outer diameter of 3
It has a diameter of 0 mm and is rotationally driven in the direction of arrow R1 at a predetermined process speed V _PS (peripheral speed).

Reference numeral 2 is a proximity charging plate (charging member), which is an electrode plate made of a metal plate. The proximity charging member 2 has a power supply 4
As a result, a bias voltage (V _dc + V _ac ) in which an alternating current with a frequency f is superimposed on a direct current is applied, whereby the peripheral surface of the photosensitive drum 1 is charged to a predetermined potential. In addition,
The proximity charging plate 2 and its attachment will be described later in detail.

A laser beam 5 is image-modulated with a constant print density D _dpi 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). is there.

As described above, the surface of the charged photosensitive drum 1 is subjected to main scanning exposure in the generatrix direction of the surface of the photosensitive drum 1 by the laser beam 5 output from the scanner controlled by the controller, and the photosensitive drum 1 is further exposed. Arrow R
By being sub-scanned by rotation in one direction, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1. Next, the electrostatic latent image becomes a toner image with toner (developer) attached by the developing sleeve 6 of the developing device. This toner image is transferred from a paper feed unit (not shown) to the transfer material 7 introduced into the transfer unit between the photosensitive drum 1 and the transfer roller 8 at an appropriate timing. The transfer material 7 that has passed through the transfer portion is separated from the surface of the photosensitive drum 1 and conveyed to a fixing portion (not shown), where the toner image is fixed. On the other hand, 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 9 of the cleaning device to be cleaned, and the photosensitive drum 1 is used for the next image formation.

Next, the proximity charging plate 2 and its mounting will be described.

As described above, the proximity charging plate 2 is an electrode plate made of a metal plate, and has a charging surface 2a on the surface facing the surface of the photosensitive drum 1. The charging surface 2a is the photosensitive drum 1
Is formed in a curved surface that is gently curved in the rotation direction (direction of arrow R1), and is configured by a curved surface having a curvature larger than that of the surface of the photosensitive drum 1, for example. Resin spacers 11 are integrally outsert-molded in the portions (non-image forming regions) outside the image forming regions at both ends in the longitudinal direction of the proximity charging plate 2. In this outsert molding, the proximity charging plate 2 is positioned and arranged in advance at a predetermined position of a mold for molding the spacer 11, and the spacer 11 is molded directly at both ends thereof. Therefore, the relative positional accuracy of the proximity charging plate 2 and the spacer 11 mainly depends on the accuracy of the mold. By increasing the precision of the mold, the precision of the proximity charging plate 2 and the spacer 11, that is, if the surface of the spacer 11 that contacts the surface of the photosensitive drum 1 is the sliding contact surface 11a, the charging surface 2 with respect to this sliding contact surface 11a.
It is possible to improve the positional accuracy of a. Specifically, the minute gap between the upstream side of the charging surface 2a in the rotation direction of the photosensitive drum 1 and the surface of the photosensitive drum 1 is accurately maintained at 100 μm or less, and further, the small gap is contacted with the surface of the photosensitive drum 1 through this portion. The charging surface 2a of the proximity charging plate 2 is arranged inside the plane S with respect to the plane S.
With this configuration, the minute gap between the surface of the photosensitive drum 1 and the charging surface 2a is 100 μm on the most upstream side.
In the following, it can be formed so as to gradually decrease toward the downstream side.

The spacers 11 formed at both ends of the proximity charging plate 2 are held by holders 13 arranged at both ends, respectively, and the holder 13 is vertically movable by a container 10 to which a cleaning blade 9 or the like is fixed. It is supported. Further, the holder 13 has a compression spring 12 interposed between the upper portion of the holder 13 and the container 10, whereby the spacer 11 is always in contact with the surface of the photosensitive drum 1 with an appropriate pressing force. As a result, between the surface of the photosensitive drum 1 and the charging surface 2a, 100 is provided on the upstream side as described above.
If the thickness is less than or equal to μm, a minute gap that gradually decreases toward the downstream side is formed.

Since the proximity charging plate 2 does not come into contact with the surface of the photosensitive drum 1 due to the above-mentioned structure, it does not damage the surface of the photosensitive drum even when it is formed of a metal that is inexpensive and has high rigidity and little warpage. Further, by forming by outsert molding, it is possible to accurately hold the minute gap without providing a special adjusting mechanism or the like. Therefore, the frequency f of the oscillating voltage is set to prevent the interference fringes 14c (see FIG. 7). Even when it is raised, good charging without charging noise can be performed. <Embodiment 2 of the first invention> FIG. 2 is a perspective view showing a state in which a spacer 11 is molded at the end of the proximity charging plate 2, and FIG.
Proximity charging plate 2 with spacer 11 removed from the state
FIG. In Example 1, the proximity charging plate 2 was formed so that the cross-sectional shape in the direction intersecting with the longitudinal direction would be the same regardless of the position in the longitudinal direction. Is formed to be thin. That is, as shown in FIG. 3, a stepped portion 2b is provided at the end of the proximity charging plate 2. In this way, when the spacer 11 is outsert-molded at both ends of the proximity charging plate 2, the stepped portion 2b is formed to increase the thickness of the spacer 11 as shown in FIG. That is, the wall thickness of the proximity charging plate 2 on the sliding contact surface 11a side can be increased from L ₁ to L ₂ . Thereby, the resin fluidity at the time of outsert molding becomes good, and the spacer 11 with more stable accuracy can be formed. <Third Embodiment of the First Invention> FIG. 5 shows a third embodiment. In this embodiment, when the spacer 11 is molded by outsert molding, the holder 13 and the spacer 11 are integrally molded. This reduces the number of parts and the number of assembly steps. <Embodiment 1 of the Second Invention> FIG. 9 is a schematic configuration diagram showing an example of an image forming apparatus according to the second invention. This image forming apparatus is a laser beam printer by an electrophotographic process using a contact charging device as a charging means of an image carrier. In the figure, reference numeral 51 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") as an image bearing member, and in the present embodiment, an aluminum drum base 51b.
On the outer peripheral surface of the organic photoconductor (OP
C) layer is formed. The photosensitive drum 51 is formed with an outer diameter of 30 mm, and is rotationally driven in the arrow R1 direction at a predetermined process speed V _PS (peripheral speed). 52
Is a proximity charging plate as a charging member, and is, for example, a metal plate or an electrode plate formed in a long plate shape with conductive plastic or conductive rubber. A bias voltage (V _dc + V _ac ) in which a direct current is superimposed on a direct current with an alternating current having a frequency f is applied to the proximity charging plate 52, whereby the surface of the photosensitive drum 51 rotating in the direction of the arrow R1 is predetermined. It is charged to the electric potential. _Reference numeral 55 denotes a laser beam which is image-modulated with a constant print density D _dpi 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).

As described above, the surface of the photosensitive drum 51 that has been subjected to the charging process is subjected to the main scanning exposure in the drum generatrix direction with the laser beam 55 output from the scanner controlled by the controller, so that the surface of the photosensitive drum 51 is exposed. An electrostatic latent image corresponding to the target image information is formed. Then, the latent image is toner-developed by the developing sleeve 56 of the developing device, and the developed toner image is introduced from a paper feeding unit (not shown) to a transfer unit between the photosensitive drum 51 and the transfer roller 58 at a predetermined timing. The image is transferred to the transferred transfer material 57. The transfer material 57 that has passed through the transfer portion is separated from the surface of the photosensitive drum 51 and is conveyed to a fixing portion (not shown) to fix the toner image on the surface. On the other hand, the photosensitive drum 51 after the toner image transfer is cleaned by the cleaning blade 59 to remove adhered contaminants such as transfer residual toner remaining on the surface, and is subjected to the next image formation.

The proximity charging plate 52 is the photosensitive drum 51.
Has a charging surface 52d on the lower surface facing the charging surface.
2d and the surface of the photosensitive drum 51 (the surface of the photosensitive layer 51a)
It is necessary to maintain a constant small gap between and. This minute gap is defined by the moving direction of the surface of the photosensitive drum 51 (arrow R
According to the experiment by the applicant, the minute gap La on the upstream side is 0 to 1 unlike the upstream side and the downstream side in one direction).
30 μm, the small gap Lb on the downstream side is 400 to 500 μm
It has been confirmed that the optimum charging state is obtained when m.

In order to keep the minute gaps La and Lb between the surface of the photosensitive drum 51 and the charging surface 52d of the proximity charging plate 52 constant, this embodiment has the structure described below.

As shown in FIG. 8, the close-up charging plate 52 is provided with cut-and-raised parts 52c. The cut-and-raised portion 52c is inserted into a compression spring 61 attached to a housing (container) 60 of the image forming apparatus main body, and the tip end side is supported by the housing 60 so as to be vertically movable. The proximity charging plate 52 is biased toward the surface of the photosensitive drum 51 by the elastic force of the compression spring 61. Cylindrical projections 52a and 52b as shown in FIG. 10 are provided at both ends of the proximity charging plate 52 in the longitudinal direction (however, in the figure, only one end of the proximity charging plate 52 is shown). , These protrusions 5
2a and 52b are pressed against stepped portions 51A and 51B at both ends of the photosensitive drum 51, which will be described below.

At both ends in the axial direction of the photosensitive drum 51, that is, at the non-image forming areas on both sides of the central image forming area,
The step portion 51A is formed inside and the step portion 51B is formed outside in a two-step configuration. The steps 51A and 51B are formed over the entire circumference of the surface of the photosensitive drum 1, and the height from the surface of the photosensitive drum 1 is 80
± 50 μm, and the step portion 51B is formed at 450 ± 50 μm. Then, in the inner step portion 51A having a small step,
The protrusion 52a of the proximity charging plate 52 and the protrusion 52b are in contact with the outer step portion 51B having a large step. As a result, the surface of the photosensitive drum 1 and the charging surface 5 of the proximity charging plate 52 are
The small gaps La and Lb between 2d and 2d are small on the upstream side having the projection 52a (approximately 80 ± 50 μm), and the projection 52b
Is set to be large (approximately 450 ± 50 μm).

By adopting the configuration as described above, the surface of the photosensitive drum 51 and the charging surface 52 of the proximity charging plate 52.
The minute gaps La and Lb between the upper end and the upper end are stepped portions 51.
A, the downstream side is regulated by the height of each step 51B. Therefore, with respect to the surface of the photosensitive drum 1, the step 5
By forming 1A and 51B with high precision, it becomes possible to hold these minute gaps La and Lb with high precision. That is, the accuracy of the minute gaps La and Lb is mainly determined by the accuracy of forming the stepped portions 51A and 51B, and the processing accuracy of the proximity charging plate 52 itself and the housing 60 of the image forming apparatus main body that supports the proximity charging plate 52 are used. Accuracy, and further, the mounting accuracy of the proximity charging plate 52 with respect to the housing 60, and so on.

The proximity charging plate 52 is positioned in the circumferential direction and the longitudinal direction by engaging the cut-and-raised parts 52c of the proximity charging plate 52 with the housing 60. <Second Embodiment of Second Invention> Next, a second embodiment will be described with reference to FIG.

As shown in the figure, the steps 51A and 51B at both ends of the photosensitive drum 51 may be formed by increasing the thickness of the photosensitive layer 51a when the photosensitive drum 1 is formed. That is, when the photosensitive layer 51a is formed on the central portion of the drum base body 51b in the axial direction by the coating agent to provide the image forming area, the thickness of the photosensitive layer 51a is adjusted at both ends corresponding to the non-image forming area. Make it a little thicker and step 51
A is formed and the thickness is further increased to form the step 51B.

According to this embodiment, when the photoconductor drum 51 is manufactured, the step portions 51A and 51B can be formed in the same working step when the photoconductor layer 51a is formed on the drum substrate 51b. After the formation of the layer 51a, it is not necessary to additionally provide a step for forming the stepped portions 51A and 51B. <Third Embodiment of the Second Invention> Next, a third embodiment will be described with reference to FIG.

As shown in the figure, the stepped portions 51A and 51B of the photosensitive drum 51 may be formed by integrally molding a sliding member 51c made of, for example, synthetic resin at the end portion with the drum base 51b. .

According to this embodiment, the friction between the protrusions 52a and 52b of the proximity charging plate 52 and the step portions 51A and 51B can be reduced, and the life of the image forming apparatus main body can be extended. it can. <Embodiment 1 of the third invention> FIG. 13 is a vertical sectional view of a process cartridge having a charging member according to the present invention, FIG. 14 is an enlarged sectional view of the charging member, and FIG. 15 is a laser beam printer equipped with the process cartridge. The cross-sectional view of (image forming apparatus) is illustrated.

First, a simple configuration and operation of the laser beam printer will be described with reference to FIGS.

Process cartridge CRG shown in FIG.
Is a cartridge container 7 that integrally includes a drum-shaped photosensitive drum 77 as an image carrier, a charging plate (charging device) 71, a developing device 109, a cleaning member 83, a toner container 85, and the like.
4 is incorporated. This process cartridge CRG can be easily mounted in the main body 86 and taken out from the main body 86 by releasing the upper cover 78 of the upper part of the printer main body (hereinafter simply referred to as “main body”) 86 shown in FIG. You can do it.
In FIG. 15, the process cartridge CRG is installed in the main body 8
6 shows a state in which the upper cover 78 is closed by mounting the same on No. 6, that is, a standby state in which an image can be formed.

When a print signal is sent from a control circuit (not shown) at the time of image formation, the paper feed roller 100 rotates, and the transfer material P loaded in the paper feed cassette is only the top one. The photosensitive drum 77 and the transfer roller are separated by the separation claw 101 and sent out, further guided by the conveyance roller 102 by the upper guide 103 and the lower guide 104, and further guided by the introduction guide 105 and the transfer guide 106 on the lower surface of the cartridge container 74. 10
7 is introduced into the transfer section. On the other hand, when the position of the transfer material P is detected by a transfer material sensor (not shown), the laser light L output from the exposure device 108 at a predetermined timing is
The surface of the photosensitive drum 77 reflected by the reflection mirror M and charged by the charging plate 71 to which a predetermined bias voltage has been applied is irradiated (exposed) to form an electrostatic latent image on the surface of the photosensitive drum 77. Power is transmitted from a drive unit (not shown) of the main body 86 to the photosensitive drum 77 and the developing device 109 in the process cartridge CRG, whereby each of them rotates in the arrow direction at a predetermined process speed. The electrostatic latent image formed on the surface of the photosensitive drum 77 by the exposure is developed by toner (developer) attached by the developing device 109 to form a toner image. The toner image on the photosensitive drum 77 is transferred onto the transfer material P, which has been conveyed, by the transfer roller 10.
Transferred by 7.

In the transfer material P having the toner image transferred to the front surface at the transfer portion, the charge accumulated on the surface (rear surface) on the transfer roller 107 side is removed by the static elimination needle 110, and the unfixed toner image is carried on the front surface. In this state, it is conveyed to the fixing device 112 through the transfer material guide 111. The transfer material P on which the unfixed toner image is fixed here is changed by the flapper 113.
When it is discharged with the image surface facing up, it is transported in the arrow FU direction, and when it is discharged with the image surface facing down, it is transported in the arrow FD direction and then discharged to the outside of the main body 86.

Next, the structure of the charging device will be described with reference to FIGS.

The charging plate 71 is a long plate-shaped metal plate having a substantially constant thickness, and its upper end side is a cartridge container 74 with its longitudinal direction oriented in the horizontal direction (the generatrix direction of the photosensitive drum 77).
It is attached by means of screws 81, and the lower end side is a free end. At both ends of the charging plate 71 in the longitudinal direction, insulating abutting portions 72a and 72b having good slidability are provided on the photosensitive drum 7.
7 is projected on the surface side. These abutting portions 72a,
Regarding 72b, the abutting portion 72a on the upstream side in the rotation direction of the photosensitive drum 77 is the abutting portion 72 on the downstream side.
It is set lower than b. The charging plate 71 takes the position shown by the broken line in FIG. 14 when the photosensitive drum 77 is not mounted, and when the photosensitive drum 77 is mounted at a predetermined position, the position shown by the solid line in FIG. 14, that is, the charging plate described above. 71 abutting portions 72a and 72b at both end portions of the photosensitive drum 7
7 Contact the non-image forming area on the surface. At this time, the charging plate 71
Has an appropriate elasticity, and therefore these abutting portions 72
The a and 72b are brought into contact with the surface of the photosensitive drum 77 with an appropriate pressing force. As a result, the charging surface 71a facing the surface of the photosensitive drum 77 at the central portion in the longitudinal direction of the charging plate 71.
Forms a fine gap with the surface of the photosensitive drum 77 that is good for charging the surface of the photosensitive drum 1. This minute gap is regulated by the butting portion 72a on the upstream side and by the butting portion 72b on the downstream side. That is, by appropriately setting the heights of these abutting portions 72a and 72b, the minute gap can be set to a predetermined size on the upstream side and the downstream side. At this time, since the charging plate 71 itself has elasticity, a biasing member such as a compression spring, which is conventionally required to bias the charging plate toward the surface of the photosensitive drum, is positively omitted, and the structure is formed. Can be simplified.

By applying a bias voltage to part of the charging plate 71 in this state, the surface of the photosensitive drum 77 rotating in the direction of the arrow in FIG. 15 can be uniformly charged.

The charging plate 71 is a metal plate having a constant thickness in the above-described embodiment, and the contact portions 72a and 72 with the photosensitive drum 77 are used.
Although b is a resin member having good slidability, it is not limited to these. Second Embodiment of Third Invention FIG. 16 shows another shape of the charging plate 71. The charging plate 71 of this embodiment is bent in the middle of the direction intersecting the longitudinal direction. With such a shape, the spacer for mounting the charging plate 71 can be made small. <Third Embodiment of the Third Invention> FIG. 17 and FIG.
An example in which the thickness of 1 is not constant is shown. That is, the charging plate 71
Is thicker at the portion having the charging surface 71a and thinner at the other portion 71b. Since the charging surface 71a is gradually distant from the surface of the photosensitive drum 77 continuously as in the first embodiment, the boundary between the region where the discharge occurs and the region where the discharge does not occur is not clear, and when there is a problem in the image process, the above-mentioned case occurs. The other portion 71b of the above may be separated from the surface of the photosensitive drum 77 to the extent that no discharge occurs.

When the shape of the charging surface 71a facing the surface of the photosensitive drum 77 is important, the other portion 71b is used.
It is preferable that the thickness of the charged surface 71a is sufficiently thin with respect to the portion having the charging surface 71a so that the charging surface 71a is hardly deformed and only the other portion 71b is elastically deformed. <Embodiment 4 of the third invention> The photosensitive drum 7 on the charging plate 71.
The contact with 7 may be made on almost the entire charging surface 71a as shown in FIG. In this case, the charged surface 71a
Is formed of a high-resistance member and has a slidability that does not damage the surface of the photosensitive drum 77.

[0069]

As described above, according to the present invention,
It has the following effects. <Effect of First Invention> A first invention is to provide a spacer for ensuring a minute gap between the surface of the image carrier and the charging surface of the charging plate.
Outsert molding is performed integrally on both ends of the charging plate with the charging surface as a reference, so that the charging plate does not come into contact with the image carrier and the precision of the minute gap does not require a special adjusting mechanism. Since it can be a highly accurate one that mainly depends on the precision of the mold at the time of molding, even if the charging plate is formed of a metal that is inexpensive and has high rigidity and little warpage, it does not damage the surface of the photosensitive drum, and Even if the frequency of the oscillating voltage is increased to prevent interference fringes, good charging without charging noise can be performed. <Effect of the Second Invention> The second invention is to form an image carrier by forming a step portion in the non-image forming area at each end portion of the image carrier and bringing both end portions of the charging member into contact with the step portion. Since the minute gap between the body surface and the charging surface of the charging member is secured, the precision of the minute gap mainly depends on the forming precision of the step portion, and therefore,
The precision of the minute gap can be easily improved by increasing the precision of forming the step portion. <Effect of the third invention> According to the third invention, at least a part of the charging member is constituted by an elastic portion, so that the elastic force of the charging member itself causes a part of the charging member to abut the surface to be charged, The charged surface can be held at a predetermined position with respect to the surface to be charged. Therefore, an elastic member such as a spring for pressing the charging member against the surface to be charged, for example, a spring for pressing the charging member can be positively omitted, and the configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a charging member of Example 1 of the first invention.

FIG. 2 is a perspective view showing a state in which a spacer is formed at an end portion of the proximity charging plate according to the second embodiment.

FIG. 3 is a perspective view showing a shape of an end portion of the proximity charging plate according to the second embodiment.

FIG. 4 is a side view showing a state in which a proximity charging plate is arranged via a spacer according to the second embodiment.

FIG. 5 is a vertical sectional view showing a schematic configuration of a charging member of Example 3 of the same.

FIG. 6 is a vertical sectional view showing a schematic configuration of a conventional image forming apparatus.

FIG. 7 is a diagram showing a transfer material after image formation in which interference fringes similarly occur.

FIG. 8 is a vertical cross-sectional view showing the configuration in the vicinity of the photosensitive drum of Example 1 of the second invention.

FIG. 9 is a diagram showing a minute gap formed between the surface of the photosensitive drum and the charging surface of the first embodiment.

FIG. 10 is a view of the stepped portion of the photosensitive drum and the proximity charging plate according to the first embodiment as viewed from above.

FIG. 11 is a view of the stepped portion of the photosensitive drum and the proximity charging plate in the second embodiment as viewed from above.

FIG. 12 is a diagram showing the stepped portion of the photosensitive drum and the proximity charging plate in the third embodiment as seen from above.

FIG. 13 is a vertical sectional view of a process cartridge having a charging plate according to the first embodiment of the third invention.

FIG. 14 is an enlarged vertical sectional view of the charging plate according to the first embodiment.

FIG. 15 is a vertical sectional view of the image forming apparatus according to the first embodiment.

FIG. 16 is a vertical sectional view of a process cartridge having a charging plate according to the second embodiment.

FIG. 17 is a vertical sectional view of a process cartridge having a charging plate according to the third embodiment.

FIG. 18 is an enlarged vertical sectional view of the charging plate according to the third embodiment.

FIG. 19 is an enlarged vertical sectional view of the charging plate according to the fourth embodiment.

FIG. 20 is a vertical sectional view of a process cartridge having a conventional charging plate.

[Explanation of symbols]

 1 Image Carrier (Photosensitive Drum) 2 Charging Plate (Proximity Charging Plate) 2a Charging Surface 4 Bias Power Supply 5 Laser Light 6 Development Sleeve 7, 14 Transfer Material 8 Transfer Roller 9 Cleaning Blade 10 Container 11 Spacer 12 Compression Spring 13 Holder 14c Interference Stripe 51 Image Carrier (Photosensitive Drum) 51a Photosensitive Layer 51b Drum Base 51A Step 51B Step 52 52 Charging Member (Proximity Charge Plate) 52a Upstream Projection 52b Downstream Projection 52c Cut and Raise 52d Charged Surface 54 Bias Power Supply 55 laser beam 56 developing sleeve 57 transfer material 58 transfer roller 59 cleaning blade La small gap on the upstream side Lb small gap on the downstream side 71 charging member (charging plate) 71a charging surface 72a, 72b abutting portion 74 cartridge container 77 charged body (Image carrier, photosensitive drum) 109 Vessel 83 cleaning blade 85 toner container CRG process cartridge P transfer material

Claims (8)

[Claims] 1. A charging member having a charging surface which faces the surface of the image carrier through a minute gap and is disposed closer to the image carrier than a plane which is in contact with the surface of the image carrier through the minute gap. An image forming apparatus comprising: an oscillating voltage applied to the charging member to charge the surface of the image carrier, wherein the charging member has a charging plate having a charging surface facing the image carrier through the minute gap. A spacer that is integrally formed at both ends of the charging plate and that contacts a non-image forming region of the image carrier to secure a minute gap between the surface of the image carrier and the charging surface. The image forming apparatus is characterized in that the both ends of the charging plate are outsert-molded with reference to the charging surface of the charging plate. 2. The charging member has stepped portions, which are notched on the charging surface side, at both ends of the charging plate on which the spacers are formed, and the spacers contact the surface of the image carrier. The image forming apparatus according to claim 1, wherein a thickness between a sliding surface and both ends of the charging plate is increased. 3. The image forming apparatus according to claim 1, wherein the spacer is directly held by a holding container. 4. A charging member having a charging surface which faces the surface of the image carrier through a minute gap and is arranged closer to the image carrier than a plane which is in contact with the surface of the image carrier through the minute gap. An image forming apparatus comprising: an oscillating voltage applied to the charging member to charge the surface of the image carrier, wherein the charging member has a charging plate having a charging surface facing the image carrier through the minute gap. The image carrier has a step in each of the non-image forming areas located on both sides of the central image forming area, and both ends of the charging plate are brought into contact with the step of the image carrier. An image forming apparatus, wherein a minute gap is secured between the surface of the image carrier and the charging surface. 5. The width of the minute gap is regulated at least at two or more places by forming each of the step portions in at least two steps and contacting each end of the charging plate with the step portions. The image forming apparatus according to claim 4, wherein. 6. The image forming apparatus according to claim 4, wherein the step portion is formed of a coating agent for the surface of the image carrier. 7. A charging member is biased toward an object to be charged, the charging surface of the charging member is brought into contact with or close to the surface to be charged of the object to be charged, and a voltage is applied to the charging member. In a charging device for uniformly charging the surface to be charged, the charging member has an elastic portion at least in part, and the charging surface is brought into contact with the surface to be charged based on an elastic force of the elastic portion. A charging device characterized by being brought close to each other. 8. The charging device according to claim 7, wherein the elastic portion is provided in a portion that does not have the charging surface.