JPH03279972A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To satisfy both of electrostatic charging efficiency and the control performance of an electrostatic charging potential even in the case of a photosensitive body having a small diameter by making the electrode density of a control electrode positioned at a part where an electrostatic charger is opposed to the photosensitive body get higher from an upstream side to a downstream side in the rotating direction of the photosensitive body. CONSTITUTION:In the electrostatic charger 52, the mesh of a grid part 53 by which the control performance of the electrostatic charging potential is enhanced is made to get smaller and smaller from the upstream side to the downstream side in the rotating direction of the photosensitive drum 4. Therefore, the charger 52 secures electrostatic charging ability by achieving electrostatic charging characteristic which approximates to that of a corotron type charger because the electrode density of the grid is low for the rotating photosensitive drum 4 at first, and then it secures the control performance of the electrostatic charging potential by achieving the electrostatic charging characteristic as a scorotron type charger because the electrode density of the grid is high. Thus, both of the electrostatic charging efficiency and the control performance of the electrostatic charging potential are secured and then stable electrostatic charging is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a charging device used in an image forming apparatus that forms an image by electrophotography, such as a copying machine, facsimile machine, or printer.

BACKGROUND OF THE INVENTION This type of charging device includes a scorotron type device with a grid electrode and a corotron type device without a grid electrode. The corotron type has high charging efficiency, but lacks controllability of charging potential. On the contrary, the scorotron type has good controllability of the charging potential, but the charging efficiency is low.

Conventionally, when using these, one type is simply selected depending on the performance of the photoreceptor, the control method of the image forming apparatus, and the like.

Problems to be Solved by the Invention Recently, due to the use of personal computers as printers, it has been desired to downsize the entire device, and along with the reduction in the diameter of the photoreceptor, the surrounding equipment and space have been arranged closer together. There is.

Reducing the diameter of the photoreceptor reduces the curvature of the photoreceptor surface. For this reason, the photoreceptor faces the corotron and scorotron with a highly curved surface, and even in an extremely narrow surface area there is a large difference in the distance between the photoreceptor and the corona wire, resulting in a significant drop in charging efficiency. Therefore, if a scorotron is used with emphasis on controllability of the charging potential, the charging efficiency will be extremely reduced. To avoid this, it is necessary to increase the number of corona wires or increase the applied voltage, which makes it difficult to meet the demands for downsizing and cost reduction of image forming apparatuses.

Therefore, the present invention provides a system for controlling the charging property of a charging charger. An object of the present invention is to improve the B electrode and provide a charging device that can solve the above problems.

Means for Solving the Problems In order to achieve the above-mentioned problems, the present invention includes a control electrode for controlling the charging property from the charger to the photoreceptor, in a portion of the charger facing the photoreceptor. This is characterized in that the electrode density increases from the upstream side to the downstream side in the rotational direction of the photoreceptor.

Function In the above structure of the present invention, the control electrode located in the portion of the charger facing the photoreceptor has an electrode density that increases from the upstream side to the downstream side in the rotational direction of the photoreceptor, and the electrode density increases in each portion. Since the controllability of the charging potential is exerted in proportion to the electrode density, the controllability of the charging potential increases from the upstream side in the rotational direction of the photoconductor to the downstream side, and from the downstream side in the rotational direction of the photoconductor to the upstream side. As the controllability of the charging potential decreases, the charging efficiency improves.

As a result, charging can be performed with priority given to charging efficiency on the upstream side in the rotational direction of the photoreceptor, and charging can be performed with priority given to controllability of the charging potential on the downstream side.

EXAMPLE A developing device as an example of the present invention shown in FIGS. 1 to 6 will be described below.

FIG. 1 shows an image forming cartridge 1 equipped with a charging device according to the present invention. As shown in the figure, this cartridge 1 is formed by connecting a developer casing 2 and a waste toner casing 3. A photosensitive drum 4 is provided at the connecting end of the waste toner casing 3 and is pivotally supported on the side wall of the waste toner casing 3 by a shaft 6. A cleaning blade 7 is brought into pressure contact with the back of the photosensitive drum 4, and residual toner scraped off from the top of the photosensitive drum 4 is stored in the waste toner casing 3. To accommodate this, a paddle 8 is provided near the bottom of the waste toner casing 3 behind the photosensitive drum 4 to scrape the toner scraped from the photosensitive drum 4 into the waste toner casing 3. The photosensitive drum 4 has a photoconductive layer made of zinc selenium oxide, organic photoconductive material, etc. formed on the surface of a metal base such as aluminum, and forms an electrostatic latent image by imagewise exposure.

A developing roller 11 for developing an electrostatic latent image on the photosensitive drum 4 with toner is provided at the connecting end of the developing device casing 2 and is pivotally supported by a shaft 12 on a side wall. A sponge roller 13 is provided on the back of the developing roller 11 and is pivotally supported on the side wall of the developing device casing 2 by a shaft 14, which charges the developer and supplies it to the developing roller 11. A developer supply paddle 15 is provided inside the developer casing 2 and is pivotally supported on a side wall by a shaft 16 for agitating the developer in the developer casing 2 while supplying it to the sponge roller 13 . The shaft 16 is equipped with stirring blades 17 to prevent toner from forming into blocks.
is installed.

A wire 82 for scraping off the developer is provided on the back of the sponge roller 13. This wire 82 is stretched between the opening edges of a partition plate 95 in the developer casing 2 and is pressed against the back surface of the sponge roller 13. As a result, when the residual developer that has been supplied to the developing roller 11 on the sponge roller 13 returns to the back side of the sponge roller 13, this residual developer is scraped off from the surface of the sponge roller 13 by the wire 82. Returned to unused developer. Therefore, the residual developer that remains after being supplied to the developing roller 11 does not leave the surface of the developing roller 11 and is repeatedly supplied to the developing roller 11 as it is, or is scraped off once from the surface of the developing roller II. This prevents the developer from being captured by the sponge roller 13 and supplied to the developing roller 11 without being mixed with unused developer. For this reason, the sponge roller 13
It is possible to prevent the stress of the residual developer not supplied to the developing roller 11 from affecting the developing characteristics.

The developer casing 2 and the waste toner casing 3 are connected to the shaft 2.
Positioning rollers 23 and 24 provided on the shafts 6 and 12 of both the photosensitive drum 4 and the developing roller 11 are connected to each other so as to be swingable by the shafts 6 and 1 of the photosensitive drum 4 and the developing roller 11.
They are brought into pressure contact with each other, and a predetermined gap is maintained between the photosensitive drum 4 and the developing roller 11 while absorbing manufacturing and assembly errors of each part.

A lid 30 is attached to an upwardly opened developer input port 83 of the developer casing 2, and is fixed to the developer casing 2 by an appropriate method such as adhesion, welding, or screwing. The lid 30 extends to the waste toner casing 3 and covers the waste toner casing 3, making it easy to handle the image forming cartridge 1 as an integral part. In particular, the lid 30 is heavier than the waste toner casing 3 and is fixed to the side of the larger developer casing 2 to serve as the gripping portion H for integral handling, so that the stability of the image forming cartridge 1 during handling is improved. This makes it easier to handle. Note that a play is provided between the lid 30 and the waste toner casing 3 to an extent that does not prevent the necessary rocking of the waste toner casing 3 relative to the developer casing 2 due to pressure contact between the positioning rollers 23 and 24.

This image forming cartridge 1 is used by being attached to a printer 31 shown in FIG. 3, for example. In this printer 31, an upper frame 33 can be opened and closed vertically about a hinge shaft 34 with respect to a lower frame 32, and the image forming cartridge 1 is mounted on the upper frame 33 as shown in FIG. This attachment is performed detachably from the rear of the upper frame 33 that opens upwardly along guides (not shown) provided inside both side walls of the upper frame 33. When the upper frame 33 of the image forming cartridge 1 is closed with respect to the lower frame 32,
Transfer charger 3 provided on the lower frame 32 side
A paper passing bus 37 for printing is formed between the upper frame 33 and the upper frame 33 as shown in FIG. 3, and the paper passing path 37 is opened to facilitate troubleshooting such as jams. .

A laser scanning unit 38 is provided above the portion of the upper frame 33 where the image forming cartridge 1 is mounted. This laser scanning unit 38 deflects a laser beam 39 from a laser emission source modulated according to an image signal provided by a personal computer, an image reader, etc., onto the photosensitive drum 4 using an appropriate scanning means such as a polygon mirror. image exposure on the photosensitive drum 4. For this image exposure, the image forming cartridge 1 has an M
An exposure slit 51 is provided in a part of the photosensitive drum 4 so that an electrostatic latent image is formed in the image forming cartridge 1 by image exposure. A charger 52 that uniformly charges the surface of the photosensitive drum 40 is provided in front of the exposure position.

On the other hand, a seal plate 25 is provided at the bottom edge of the connecting end opening of the developer casing 2 and extends to the circumferential surface of the developing roller 11 and comes into pressure contact therewith. A seal plate 26 is provided that extends to the photosensitive drum 4 and presses against it. As a result, the developer handling space of the image forming cartridge 1 formed by the developer casing 2 and the waste toner casing 3 becomes almost sealed, thereby preventing the developer from scattering to the outside. I can do it.

However, due to recent miniaturization and weight reduction, the thickness of each member forming the image forming cartridge 1 tends to become thinner and the rigidity tends to decrease. Therefore, when handling the image forming cartridge 1 alone, an external force for gripping the image forming cartridge 1 acts on the developing device casing 2 forming the grip part H of the image forming cartridge 1, causing temporary deformation such as twisting or denting. It may also occur. At this time, the volume of the developer casing 2 momentarily decreases, and the developer may be blown out along with the internal air from the weak portion of the seal.

Therefore, in this embodiment, an opening 84 is formed in the lid 30, and the opening 84 is closed with a semipermeable membrane 85. The semipermeable membrane 85 is made of a material that allows air to pass through but does not allow the developer to pass through. As a result, even if the developing device casing 2 is deformed as described above and the volume is reduced during handling of the image forming cartridge I, and the internal air blows out, the blowing out of the air is prevented by a semi-transparent structure with less resistance. Even if the developer tries to pass through the semi-permeable membrane 85 and the blown air is mixed with the developer, the semi-permeable membrane 8
5 to prevent the external −\ from blowing out. Such a structure can be applied to the waste toner casing 3 as well, if necessary.

Note that the sealing performance can be further improved by providing the seal plates 25 and 26 in the developer casing 2 and the waste toner casing 3 in multiple stages as necessary, and pressing them against the surfaces of the developing roller 11 and the photosensitive drum 4 in multiple stages in their rotational directions. improves.

An elastic blade 41 is pressed against the developing roller 11 . As the elastic blade 41, a rubber blade made of urethane rubber, silicone rubber, or the like, or a metal blade made of spring-use phosphor bronze, spring steel, or the like is useful. The upper end of the elastic blade 41 is attached by adhesive or the like to a metal support member 42 that is stretched between the side walls of the developer casing 2, and the lower end is attached to the developing roller 1.
It is pressed against the surface of 1.

Incidentally, the developing roller 11 has a developer carrying area X on the central side in the longitudinal direction formed with a satin surface by sandblasting or the like, which is advantageous for carrying the developer. Both ends of the developing roller 11 on both sides of the developer carrying area be. For this reason, the developer non-carrying area Y is kept as a smooth surface to avoid carrying the developer (FIGS. 4 and 5).

As a result, the developer carrying area X of the developing roller 1 has a satin-like unevenness formed on its surface, and the convex portion rises from the surface of the fabric, so that it has a slightly larger diameter than the developer non-carrying area Y. In addition, since the developer carrying area X of the developing roller 11 carries the developer supplied from the sponge roller 13, although the developer is thinned to a predetermined layer thickness by pressure contact with the elastic blade 41, the developing roller ] The diameter of the first developer carrying area X is further increased. Therefore, the diameter of the developer carrying area X of the developing roller 11 is somewhat different from that of the developer non-carrying area Y, and there is a gap between the developer carrying area X and the developer non-carrying area Y of the developing roller 11. Step Z (
(Fig. 5) will occur.

Therefore, if the elastic blade 41 is uniformly and continuously pressed over the entire length of the developing roller 11, it will not carry the developer, and moreover, the developer non-carrying area Y will have a small diameter.
Floating occurs between the two and causes the developer to leak forward.

In order to solve this problem, in this embodiment, a notch 86 cut from the tip is formed in the portion of the elastic blade 41 facing the boundary K between the developer carrying area X and the developer non-carrying area Y of the developing roller 11. is forming. As a result, the elastic blade 41 is divided by the notch 86 into the center side in the longitudinal direction facing the developer carrying area X and the developer non-carrying area Y of the developing roller 11, and the sections 41a and 41b on both sides thereof. Since the respective portions 41a and 41b independently press against the developer carrying area X and the developer non-carrying area Y of the developing roller 11 without being influenced by each other, there is a step Z between the respective areas X and Y. Part 4 of the elastic blade 41
1b can be brought into close contact with a portion of the developer non-carrying area Y, as shown in FIG. Therefore, the elastic blade 41
It is possible to eliminate the inconvenience in which the developer floats from the developing roller 11 in the developer non-carrying area Y and the developer leaks from the developer non-carrying area Y to the photosensitive drum 4 side.

Further, the portion 41b of the elastic blade 41 is attached to the support member 42.
It is held down by presser metals 57 attached to both ends of the holder, which further prevents it from lifting up. Developing roller 1
A sealing material 88 is interposed between 1 and the side wall 87.

Further, in a long continuous portion of the elastic blade 4I, the pressure contact with the developing roller 11 tends to be stronger in the central portion of the continuous range than in other portions.
The layer thickness of the developer formed on the developing roller 11 tends to be non-uniform in the axial direction of the developing roller 11, which causes uneven development characteristics. Therefore, in this embodiment, in order to solve this problem,
A groove 81 as shown in FIGS. 1 and 5 is formed on the back surface of the elastic blade 41. This groove 81 is located approximately at the center in the width direction of the elastic blade 41, and is formed in a range excluding both ends of the portion 41a between the long cuts 86 of the elastic blade 41.

This allows the long portion 41a of the elastic blade 41 to
The bending rigidity at the central portion in the longitudinal direction is weakened by the concave groove 81, the pressing force against the developing roller 11 is reduced, and the pressing force against the developing roller 11 of the entire long portion 41a of the elastic blade 41 is reduced. become even.

Furthermore, stress is concentrated in the concave groove 81 portion of the elastic blade 41, and by equalizing the stress in other portions, the pressing force against the developing roller 11 can be made uniform.

Therefore, a thin layer of developer can be formed with a uniform layer thickness over the entire developer carrying area X of the developing roller 11, and uniform development characteristics can be expected over the entire developer carrying area X of the developing roller 11.

In addition, the elastic blade 41 is made of polyethylene terephthalate (
If it is formed by punching from a sheet such as PET, the cost will be lower than when a molded product such as urethane foam is used. In this case PET
Since it is made of a strong material, it does not damage the developing roller 11 or cause chattering, and it is preferable to press the developing roller 11 at the so-called abdomen in order to avoid contact with the tip edge.

Furthermore, since the elastic blade 41 is made of an insulating material, the frictional charging between the developer and the elastic blade 41 can be increased, and the overall charging state can be sufficiently stabilized. In this sense, forming a coating layer of an insulating material on the surface of the developing roller 11 can further improve the charging characteristics. Furthermore, since the insulating coating layer can form a matte surface during resin molding without sandblasting, the cost of the developing roller 11 is reduced accordingly, and the developer can be transported to areas where the electric field is not diffused. At the same time, the gap between the developing roller 11 and the photosensitive drum 4 can be shortened in a pseudo manner beyond the discharge limit.
Resolution in development is improved.

As another example, an insulating elastic roller may be used instead of the elastic blade 41, in which case the developing roller 11
You can set the relative speed in any way you like. This allows the charging characteristics to be adjusted in various ways,
Depending on whether the elastic roller is rotated in a subordinate direction to the developing roller 11 or in the opposite direction, the surface layer of the developer on the developing roller 11 is actively subjected to development;
It becomes possible to select whether to make it difficult to be subjected to development. Such selection is based on the developer, developer supply mechanism, and photosensitive drum 4.
This is useful when dealing with various types of image forming conditions, such as types, etc., or when responding to special requests.

In addition, a speed change mechanism is provided in the drive system of the developing roller 11 to increase the rotational speed of the developing roller 11 when forming an image with poor reproducibility such as a line drawing or a dot image. Increasing the supply amount improves reproducibility even for line drawings and dot drawings.

In this embodiment, the configuration of the charger 52 is devised in response to the fact that the photosensitive drum 4 is designed to have an extremely small diameter. The extremely small diameter photosensitive drum 4 faces the charging charger 52 with a curved surface having a sharp degree of curvature, resulting in low charging efficiency. If a scorotron type charger 52 having a grid portion 53 that improves the controllability of the charging potential is employed, the charging efficiency will further decrease, and sufficient charging will be difficult to achieve due to the effect of higher speed.

Therefore, the charger 52 has a mesh of the grid portion 53 that becomes gradually finer from the upstream side to the downstream side in the rotational direction of the photosensitive drum 4 (FIGS. 1 and 2). As a result, the rotating photosensitive drum 4 serves as the charger 52.
Initially, the electrode density of the grid was low and it exhibited charging characteristics similar to that of a corotron type charger, ensuring charging performance, and then the electrode density of the grid was high and it exhibited charging characteristics as a scorotron type charger. This ensures controllability of the charging potential. This makes it possible to achieve stable charging by ensuring both charging efficiency and controllability of charging potential.

The size of the mesh can be changed freely. For example, in the second embodiment of the present invention shown in FIG. 7, the grid portion 53 is omitted on the upstream side of the charger 52 in the rotational direction of the photosensitive drum 4. This further improves the charging efficiency compared to the first embodiment. Although the electrode density of the grid portion 53 is made uniform to ensure controllability of the charging potential, it is also possible to design the grid portion 53 so that the electrode density changes as appropriate.

In either case, the charger 52 is formed into one for miniaturization, but two, a corotron type charger and a scorotron type charger, may be installed.

Returning to the first embodiment of the present invention, the charger 52 also has a grid portion 53 and a discharge stabilizing frame 54 integrally formed with a metal plate as shown in FIGS. 1 and 2 for miniaturization. It is. The corona wire 55 is installed between resin blocks 56 attached to both side walls of the developer casing 2, and a discharge stabilizing frame 54 is installed between the resin blocks 56.
holding the edge of the

Note that the corona wire 55 has a wire diameter of about 80 μm, which is extremely thin, so there is a problem with elongation and cutting, which makes it troublesome to handle during installation, and maintenance such as cleaning when it becomes dirty due to use is also troublesome. Therefore, it is conceivable that a metal plate is buried in a resin base (not shown) by insert molding or the like, and a part of the buried metal plate is exposed to be used in place of the corona wire. In this case, costs can be reduced and the strength of the corona electrode portion is improved, making assembly and cleaning easier. Alternatively, a predetermined metal material may be printed in a line shape on the surface of the resin base to serve as a substitute for the corona wire. In this case as well, the same effects as the above improvements can be expected.

Further, the discharge stabilizing frame 54 can also be formed by applying metal plating to the inner surface of the resin housing. In this case, the resin housing can be integrally formed with a part of the existing member such as the lid 30, and the structure can be simplified.

When the upper frame 33 is closed on the lower frame 32, the transfer charger 36 faces the photosensitive drum 4 of the image forming cartridge 1 with a certain gap, and is connected to the paper passing bus 37.
The developed toner image formed on the photosensitive drum 4 is transferred to the transfer paper 91 from the back side of the transfer paper 91 being conveyed.
Transfer it on top.

In addition, in the case of the transfer charger 36, the same improvement as that of the charging charger 52 can be made for the corona wire.

A timing roller pair 61 is provided in front of the transfer section of the paper passing bus 37, as shown in FIG. The timing roller pair 61 temporarily stops receiving the transfer paper 91 picked up and fed from the paper feed cassette 92 by the pickup roller 93 in a stopped state, and thereafter feeds the transfer paper 91 at a predetermined timing, and then feeds the transfer paper 91 to the photosensitive drum. The leading edge is aligned with the toner image formed on 4 and used for transfer.

A pair of fixing rollers 62 is provided behind the transfer section, and heat fixes the transfer sheet fed after the transfer.

The surface of the photosensitive drum 4 after the transfer is cleaned by a cleaning blade 7 to remove residual toner.

An eraser lamp 63 is provided immediately after the transfer charger 36 of the lower frame 32, and irradiates erase light onto the surface of the photosensitive drum 4 after transfer through the transfer paper 91 that is being passed, thereby eliminating any residue on the surface of the photosensitive drum 4. Remove charge. Near this eraser lamp 63, a light receiving end 65a of an optical fiber 65 is provided.
is positioned facing the photosensitive drum 4. This optical fiber 65 is adapted to guide reflected light when the toner image formed on the photosensitive drum 4 is illuminated by the eraser lamp 63 to a density sensor 64 provided at an appropriate position. As a result, the concentration sensor 64 is activated by the eraser lamp 6.
3 for illuminating the image to be inspected, and by using the eraser lamp 63 in common and using the optical fiber 65, the toner image can be detected without requiring any special space around the transfer section. The concentration can be detected, and the cost can be reduced because the eraser lamp 63 is shared.

By sending the detected density of the toner image to the control system, it is possible to determine whether there is a shortage or deterioration of the developer, and to take measures such as warning of the usage limit due to the life of the image forming cartridge 1 or stopping printing.

Note that if the eraser lamp 63 is installed within the discharge stabilizing frame of the transfer charger 36, further space saving can be achieved.

Furthermore, the cleaning blade 7 can be formed of a transparent resin material and used as a light guide to irradiate the surface of the photosensitive drum 4 with eraser light. According to such an erase method, the degree of freedom in selecting the installation location of the eraser lamp 63 increases. Furthermore, cleaning blade 7
Similarly to the elastic blade 41, a concave groove can be formed on the back of the blade to equalize the pressing force. In this case, the resonant frequency of the blade can be easily selected.

Furthermore, the cost can be reduced by punching out a PET sheet.

As shown in FIG. 6, the waste toner casing 3 is provided with an unused detection mechanism 71 that is linked to the drive system. This unused detection mechanism 71 is a gear 73 provided on one shaft of the drive system, for example, the rotating shaft 72 of the paddle 8 for scraping in waste toner.
The detection gear 74 is engaged. The detection gear 74 has teeth 75 only on a part of the outer periphery, and the other part of the outer periphery is a cam surface 77 having a recess 76 in a part. The waste toner casing 3 also includes a detection pin 78 facing the cam surface 77.
is held movably forward and backward, and this detection pin 78 is brought into contact with the cam surface 77 by a spring 79. When the image forming cartridge 1 is not in use, that is, when the drive system has never been operated and no developer is consumed, this abutment position is set a predetermined amount downstream from the recess 76 of the cam surface 77 in the driving direction. It's a remote location.

When the image forming cartridge 1 is installed in the printer 31 and is driven and used even once, the gear 7 that is interlocked with the drive is activated.
3 rotates the detection gear 74. The concave portion 76 of the cam surface 77 faces the detection pin 78 by an amount of rotation that is extremely small compared to the amount of drive required for use. At this opposing position, the detection pin 78 is fitted into the recess 76 by the force of the spring 79.

The detection pin 78 protrudes outside the waste toner casing 3 when the image forming cartridge 1 is not in use, and when the image forming cartridge 1 is mounted on the upper frame 33, the switch 94 provided on the upper frame 33 is activated. It is pushed by the detection pin 78 and automatically detects that the image forming cartridge l is unused. This detection signal is sent to the control system of the printer 31 to start counting the number of prints using the image forming cartridge 1 and to issue a restriction or warning against use of more than a predetermined number of prints based on this count. Conversely, if the image forming cartridge 1 to be installed has already been used, the detection pin 78 is retracted toward the waste toner casing 3, so even if the image forming cartridge 1 is installed in the upper frame 33, Switch 94 cannot be pressed. Therefore, no action is taken as would be the case when an unused image forming cartridge 1 is installed.

However, the usage status can also be detected at the necessary time. For example, by detecting the point in time when a predetermined number of sheets, such as 500 sheets, have been used and using this as a use start signal, it is possible to support test use of up to 500 sheets. In this case, it is preferable to employ a speed reduction mechanism. Furthermore, it can be said that the point in time when the image forming cartridge 1 has been used for printing the maximum number of sheets for use is detected and a warning is given for further use.

Effects of the Invention According to the present invention, the control electrode located in the portion of the charger facing the photoconductor has an electrode density that increases from the upstream side to the downstream side in the rotational direction of the photoconductor, and The controllability of the charging potential increases according to the electrode density, and the controllability of the charging potential increases from the upstream side to the downstream side in the rotational direction of the photoreceptor, and from the downstream side to the upstream side in the rotational direction of the photoreceptor. Charging efficiency improves as the controllability of the charging potential decreases toward the side, so charging is performed with priority given to charging efficiency on the upstream side in the direction of rotation of the photoconductor, and charging is performed with priority given to controllability of the charging potential on the downstream side. Therefore, both charging efficiency and controllability of charging potential can be satisfied even for a small-diameter photoreceptor.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an image forming cartridge having a charging device as a first embodiment of the present invention, FIG. 2 is an enlarged sectional view of the charging device, and FIG. 3 is a printer in which the image forming cartridge is used. FIG. 4 is a perspective view showing the developing roller section, FIG. 5 is an enlarged front view of a part of the developing roller section, and FIG. 6 is an unused detection mechanism section of the image forming cartridge. FIG. 7 is a cross-sectional view of a part of the waste toner casing, and FIG. 7 is an enlarged cross-sectional view of a charging device showing a second embodiment of the present invention.

Claims (1)

[Claims] (1) In the part of the charger facing the photoreceptor,
A charging device characterized in that a control electrode for controlling the charging property of a photoreceptor from a charger is provided such that the electrode density increases from the upstream side to the downstream side in the rotational direction of the photoreceptor.