KR20090063072A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus is provided to suppress an increase of electric charge smudge of a photoconductor by the synchronization of each member change, thereby forming a uniform image. The diameter of a photoconductor(1), the diameter of a roll type charger(2), and the diameter of a roll type cleaning member(20) are respectively set up so that electric charge smudge at a photoconductor surface periodically generated with the rotation of the photoconductor, electric charge smudge of the photoconductor surface periodically generated with the rotation of the roll type charger, and electric charge smudge of the photoconductor surface periodically generated with the rotation of the roll type cleaning member are not overlapped within the range of a image forming length which is the length of an image formed with the photoconductor.

Description

Image forming apparatus {IMAGE FORMING APPARATUS}

The present invention relates to an image forming apparatus for charging a cylindrical photosensitive member from a roll charger.

Conventionally, a corotron type or a contact charging type is used as a charging device for charging a cylindrical photosensitive member in an image forming apparatus. Here, in the contact charging type, since discharge is performed in the gap between the roll charger and the photoconductor called bias charge roll (BCR), the density pitch unevenness of the BCR / photoreceptor is likely to occur due to the gap shape. For this reason, in the conventional image forming apparatus, the charging uniformity is covered by the alternating current charging.

Moreover, in alternating current charging, since there exist subjects, such as high cost of an apparatus, damage to a photosensitive member, a cleaning roll, and deletion, direct current charging is also used (for example, refer patent documents 1-3).

[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-034760

[Patent Document 2] Japanese Patent Application Laid-Open No. 2001-002164

[Patent Document 3] Japanese Patent Application Laid-Open No. 7-129055

However, compared to alternating current charging, in the direct current charging, subtle photosensitive film thickness unevenness, rotational vibration, and resistance unevenness or change in shape of BCR become charge unevenness. For this reason, BCR and a photosensitive member which are highly accurate compared with AC charging are needed. In addition, due to the sensitivity of the charging, even the fluctuation of the BCR and the cleaning roll becomes a fluctuation in pressure to the BCR, resulting in a problem of charging unevenness (concentration unevenness). In addition, even for very small fluctuations of the photoconductor, the BCR, and the cleaning roll, if the pitch of the fluctuations is synchronized, the fluctuation becomes larger and the charge unevenness (density unevenness) also increases, resulting in image quality defects. The problem arises.

The present invention has been made to solve these problems. That is, the present invention provides a cylindrical photosensitive member, a roll charger disposed to face the outer circumferential surface of the photosensitive member, a roll type cleaning member disposed to face the outer circumferential surface of the roll charger, and an exposure machine for forming an electrostatic latent image on the surface of the photosensitive member. A developer for developing the latent electrostatic image into a toner image, a transfer machine for transferring the toner image to paper, a photosensitive member cleaning member for removing unnecessary toner remaining on the surface of the photosensitive member, and fixing the toner image to paper An image forming apparatus comprising a fixing apparatus, comprising: charging spots on the surface of the photoconductor periodically generated by rotation of the photosensitive member; charging spots on the surface of the photoconductor periodically generated by rotation of the roll-type charger; The charging unevenness of the surface of the photoconductor periodically generated by the rotation of the roll-type cleaning member, The diameter of the photosensitive member, the diameter of the roll-type charger, and the diameter of the roll-type cleaning member are set so as not to overlap within the range of the image forming length which is the length of the image formed by the photosensitive member, respectively. Device.

The present invention also provides a cylindrical photosensitive member, a roll charger disposed to face the outer circumferential surface of the photosensitive member, a roll type cleaning member disposed to face the outer circumferential surface of the roll charger, and an exposure machine for forming an electrostatic latent image on the surface of the photosensitive member. A developer for developing the latent electrostatic image into a toner image, a transfer machine for transferring the toner image to paper, a photosensitive member cleaning member for removing unnecessary toner remaining on the surface of the photosensitive member, and fixing the toner image to paper An image forming apparatus comprising a fixing apparatus, wherein the outer circumferential length of the photosensitive member is A, the outer circumferential length of the roll-shaped charger B is the outer circumferential length of the roll-shaped cleaning member C, and the contact portion of the photosensitive member and the roll-type charger When the nip width is N, ± (N / 2) centering on the position of each interval of A on the outer circumferential surface of the photoconductor, and B Each numerical value of ± (N / 2) centered on the positions of the intervals and ± (N / 2) centered on the positions of the intervals of C are different within the range of the image forming length, respectively. It is an image forming apparatus.

The minimum common multiple of the diameter of the said photosensitive member, the diameter of the said roll type charger, and the diameter of the said roll type cleaning member is a value larger than an image formation length, The image forming apparatus of Claim 1 or 8 characterized by the above-mentioned.

The image forming apparatus according to claim 1 or 8, wherein the roll charger is applied with a direct current voltage.

The image forming apparatus according to claim 1 or 8, wherein the image forming length is 420 mm or less.

The said roll type cleaning member is comprised by the foam member, The image forming apparatus of Claim 1 or 8 characterized by the above-mentioned.

The image forming apparatus according to claim 1 or 8, wherein the roll type cleaning member has a shaft pressed in the direction of the roll type charger by a spring.

The image forming apparatus according to claim 1 or 8, wherein the roll charger and the roll cleaning member are fixed at a positive displacement.

In the present invention, not a length of one circumference of the photoconductor, but a cycle of fluctuations applied to the charging of each of the photoconductor, the roll charger, and the roll cleaning member within the range of the length (image formation length) for forming one image by the photoconductor. Is not duplicated, and it is possible to suppress an increase in electrification stain (concentration stain).

Therefore, according to the present invention, since the cycles of the fluctuations of the photoconductor, the roll charger, and the roll-type cleaning member do not overlap, the increase in charging unevenness of the photoconductor can be suppressed in synchronization with the fluctuation of each member. It becomes possible to perform uniform image formation.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described based on drawing.

<Schematic Configuration of Image Forming Apparatus>

1 is a schematic view showing a configuration example of an image forming apparatus according to the present embodiment. In FIG. 1, the cylindrical photosensitive member 1 used as a consultation member is rotatably provided in the arrow direction (counterclockwise rotation direction) in the figure. Around the photosensitive member 1, along the drum rotation direction, a roll-type charger 2, a laser scanner (exposure) 3, a developer 4, a transfer machine 5, a drum cleaner 6, a static eliminator (除 電器) 7 is arranged in sequence. Moreover, on the conveyance path R of a sheet | seat, the fixing | fixing machine 8 is arrange | positioned downstream of the paper conveyance direction rather than the transfer machine 5.

Since the roll type charger 2 is for uniformly charging the surface of the photosensitive member 1, it is arrange | positioned facing the outer peripheral surface of the photosensitive member 1, and follows the rotation of the photosensitive member 1, and the photosensitive member 1 is carried out. Rotate oppositely. The roll type charger 2 is provided with a roll type cleaning member 20 to face the outer circumferential surface, and serves to remove the toner attached to the roll type charger 2.

The laser scanner 3 forms an electrostatic latent image on the surface of the photoconductor 1 by exposing and scanning the surface of the photoconductor 1 according to a raster image. The developing device 4 develops an electrostatic latent image on the photosensitive member 1 into a toner image by supplying toner to the surface of the photosensitive member 1.

The transfer machine 5 transfers the toner image on the photoconductor 1 onto the paper by imparting a charge of opposite polarity to the toner on the back surface side of the paper conveyed along the conveyance path R. As shown in FIG. The drum cleaner 6 removes unnecessary toner remaining on the surface of the photoconductor 1 without being transferred to the paper. The static eliminator 7 removes unnecessary charges remaining on the surface of the photoconductor 1. The fixing unit 8 fixes the toner image on the paper by sandwiching the paper on which the toner image has been transferred by the heating roller 8A and the pinch roller 8B.

<Configuration of Roll Type Charger>

Fig. 2 is a schematic diagram for explaining the configuration of the roll charger used in the image forming apparatus of this embodiment. In this figure, the photosensitive member 1 and the roll type cleaning member 20 which oppose the roll type charger 2 are also shown.

That is, the roll charger 2 is called a bias charge roll BCR and is arranged to face the surface of the cylindrical photosensitive member 1. The roll charger 2 is made of, for example, a foam member, and the shaft is pressed to the photosensitive member 1 side by a spring and fixed at a positive displacement. Thereby, it rotates following the rotation of the photosensitive member 1. As shown in FIG. At this time, the length along the direction of rotation at the contact portion between the roll charger 2 and the photosensitive member 1 is set as the nip width. The nip width is approximately 0.5 mm to 3 mm.

Moreover, the roll type | mold cleaning member 20 is arrange | positioned on the opposite side to the photosensitive member 1 of the roll type charger 2. The roll type cleaning member 20 is pressed in the direction of the roll type charger 2 by a spring, and is fixed to positive displacement.

In the roll charger 2 having such a configuration, discharge is performed at a charging gap between the surface of the photoconductor 1 generated when it rotates (a gap at the point where it passes through the nip position), so that the photoconductor 1 is discharged. The surface of the photosensitive member 1 is sequentially charged as it rotates. The charging gap is approximately 100 μm to 200 μm. Therefore, the charging unevenness (concentration unevenness) of the photosensitive member 1 is likely to occur due to the gap shape in the charging gap (change of the gap along the axial direction at the discharge position of the photosensitive member surface).

Here, as shown in FIG. 3, the roll type charger 2 has the direct contact type with the photosensitive member 1, and the indirect contact type. That is, in the roll type charger 2 shown in Fig. 3A, the surface of the photosensitive member 1 and the surface of the roll type charger 2 are in direct contact with each other, so that the rotation of the photosensitive member 1 is maintained as it is. Pass on the roll). In the direct contact type, the direct contact portion between the roll charger 2 and the photosensitive member 1 is in the nip position.

On the other hand, in the roll charger 2 shown in FIG. 3B, the surface of the roll charger 2 does not directly contact the surface of the photosensitive member 1, and is driven at the roll end of the roll charger 2. The roller 2a is in contact with the photoconductor 1 and is driven, and the roll of the roll type charger 2 rotates by this rotation. In either configuration, discharge is performed by a gap between the roll surface of the roll-shaped charger 2 and the surface of the photoconductor 1, thereby charging the surface of the photoconductor 1. In the indirect contact type, the contact portion between the driven roller 2a and the photosensitive member 1 in the roll-type charger 2 is in the nip position.

As described above, in the roll-type charger 2, the discharge is performed by the charging gap with the surface of the photosensitive member 1, so that the unevenness (charge unevenness) is generated by the uniformity of the charging due to the variation of the charging gap. In addition to affecting the film thickness unevenness or rotational vibration of the photosensitive member 1, the resistance unevenness and the variation of the shape of the roll-type charger 2, the charged unevenness also affects the shape and rotational vibration of the roll-type cleaning member 20. Is given. In addition, the influence of the rolls on each of these rolls overlaps, which causes a larger charge unevenness.

In this embodiment, in the charging configuration using the roll type charger 2, the photosensitive member 1, the roll type charger 2, and the roll type cleaning member 20 are disposed so that the influence of the charging unevenness on each roll does not overlap. It is characterized by the fact that the diameter is set.

Specifically, the charging unevenness on the surface of the photosensitive member 1 periodically generated by the rotation of the photosensitive member 1, and the unevenness of the surface of the photosensitive member 1 periodically generated by the rotation of the roll-type charger 2; And the diameter of the photosensitive member 1, the diameter of the roll-type charger 2, and the roll-type so that charging irregularities on the surface of the photosensitive member 1 periodically generated by the rotation of the roll-shaped cleaning member 20 do not overlap within the range of the image forming length. The diameter of the cleaning member 20 is set, respectively. In addition, the diameter of the roll type charger 2 mentioned here is the diameter of the roll for charge contacting the photosensitive member 1 in the direct contact type shown to Fig.3 (a), and the indirect contact shown to Fig.3 (b). In the mold, the diameter of the driven roller 2a in contact with the photosensitive member 1 is assumed.

Here, the image forming length refers to the length of one image forming area along the rotational direction of the photosensitive member 1, and refers to the length along the conveying direction at the largest size among the media (paper) handled by the image forming apparatus. . For example, when an image forming apparatus handles a paper size such as B4, B5, A3, or A4, which is defined by JIS (Japanese Industrial Standards), it refers to the length of the paper having the largest length along the conveying direction. .

As an example for realizing the prevention of the overlapping of the charging unevenness in each of these rolls, the outer circumferential length of the photosensitive member 1 is A, the outer circumferential length of the rolled charger 2 is B, the outer circumferential length of the roll-type cleaning member 20 is C, When the nip width (see FIG. 2) at the contact portion between the photosensitive member 1 and the roll-shaped charger 2 is N, ± (N based on the position of each interval of A on the outer circumferential surface of the photosensitive member 1 / 2), ± (N / 2) centered on the position every interval of B and ± (N / 2) centered on the position every interval of C so that they do not overlap within the range of the image formation length It is.

That is, there is an area where charging unevenness occurs on each outer circumference of the photosensitive member 1, the roll-type charger 2, and the roll-type cleaning member 20, and the position where all the charged unevenness including the nip width overlaps on the photosensitive member 1 As a starting point, each roll rotates, and the length on the photosensitive member 1 becomes longer than the image forming length until all the charging spots overlap next. As a result, duplication of charging spots in each roll, including the nip width, does not occur within the range of the image forming length.

It is a schematic diagram explaining the state of electrification stain. Since the charging spot is caused by each of the photosensitive member, the roll charger, and the roll cleaning member, it occurs periodically with the rotation of the roll, and the maximum of the width of one charged spot (short side in the drawing) is the nip width. I think it becomes. In the example of the charging stain shown in Fig. 4, in order to make the description easy to understand, the charging stain which is the same as the nip width is shown in the form of a band, but in reality, the charging stain of various shapes occurs.

For example, in the example shown to Fig.4 (a), the state in which the charging stain a which originates in any one of the photosensitive member, a roll type charger, and a roll type cleaning member, and the charging stain b which originates in the other was adjacent | occur | produced is shown adjacently. have. In other words, the charging spots a and the charging spots b do not overlap within the range of the image forming region, and are generated at separate positions.

On the other hand, the example shown in Fig. 4B shows a state in which the charging stain a caused by any one of the photosensitive member, the roll charger and the roll cleaning member and the charging stain b caused by the other overlap in part. have. In this manner, when a plurality of charging spots a and b respectively generated for different rolls overlap within the range of the image forming region, the charging situation is greatly deteriorated for the overlapped portions. Therefore, it is possible to suppress the deterioration of the charging spots by preventing such charging spots from overlapping.

In this way, in order to prevent duplication of charging spots within the range of the image forming area, the roll diameters of the photosensitive member, the roll type charger, and the roll type cleaning member are set in this embodiment. That is, since the charge unevenness caused by each roll of the photosensitive member, the roll type charger, and the roll type cleaning member is generated with periodicity for each roll, each roll so that the minimum common multiple of the value based on the diameter of each roll becomes larger than the image forming length. Set the diameter. In addition, at this time, in consideration of the nip width (contact length according to the rotational direction of the contact portion) at the contact portion between the photosensitive member and the roll-type charger, the respective roll diameters are set so that charging staining does not occur even in a part of the nip width. do.

Thereby, the period of each charging stain (charge stain including a nip width) resulting from each roll of the photosensitive member, a roll type charger, and a roll type cleaning member does not overlap within the range of an image formation length, Deterioration can be suppressed. In addition, since it can cope only by setting the roll diameter, by not providing a special mechanism, it does not cause a large cost increase, and high density is not required more than necessary for each member, and image quality defects can be improved without a secondary obstacle. have.

<Example>

It is a figure explaining the specific example of the diameter of each roll of a photosensitive member, a roll type charger, and a roll type cleaning member. In addition, the unit of the numerical value shown in FIG. 5 is mm, and it is a value when the nip width is not considered in order to make description easy to understand. In addition, case1 and case2 do not set the diameter of each roll shown in this Example, and case3 is a case where the diameter of each roll shown in this Example is set. In addition, in case1, the maximum size of the paper to be imaged is A4, case2, and case3 are A3.

Here, an example of electrification stain in the case of each roll diameter shown by the case1 of FIG. 5 is shown to FIG. 6 (a). In case 1 of FIG. 5, the photosensitive member has a diameter of 24 mm and a roll-shaped cleaning member having a diameter of 8 mm. In these rolls, overlap occurs in a cycle of a circumferential length (approximately 75 mm) with a diameter of 24 mm. This is overlapped within the range of the image forming length (297 mm in A4 length) of the maximum size of the paper on which the image is formed (A4 in case1). As shown in FIG. Occurs.

In addition, the example of the charging unevenness in the case of each roll diameter shown by the case2 of FIG. 5 is shown to FIG. 6 (b). In case 2 of FIG. 5, the diameter of the photosensitive member is 30 mm and the diameter of the roll charger is 12 mm. In these rolls, overlap occurs in a cycle of a circumferential length (approximately 188 mm) by a diameter of 60 mm. This results in overlap within the range of the image forming length (420 mm in the A3 length) of the maximum size of the paper on which the image is formed (A3 in case2). Occurs.

In addition, the example of the charging unevenness in the case of each roll diameter shown by the case3 of FIG. 5 is shown in FIG. In case 3 shown in Fig. 5, the diameter of the photosensitive member is 30 mm, the diameter of the roll-type charger is 14 mm, and the diameter of the roll-type cleaning member is 11 mm. In these rolls, at a cycle of a circumferential length (approximately 7,253 mm) with a diameter of 2,310 mm Duplicate occurs. This is larger than the image forming length (420 mm in the A3 length) of the maximum size (A3 in case3) to form the image, and as shown in Fig. 7, no large charging unevenness occurs within the range of the image forming length.

Thus, in the case 1 and case 2 which did not set each roll diameter shown in this Example, large electrification | staining stain generate | occur | produced in the electrification area | region, while in case 3 which set each roll diameter shown in this example, the big electrification in the electrification area | region It can be seen that no staining occurs. That is, in case1 and case2, charging spots are overlapped by a plurality of rolls, and charging stains are increased, but in case3, charging spots are not overlapped by a plurality of rolls, and only charging spots appear in each roll alone. It is only possible to suppress the increase in electrification stain.

In addition, in the above specific example, the example in which the image forming length is the maximum size of the paper has been described, but the length of the range in which the image is actually formed among the maximum sizes of the paper is the image forming length, so that the charging spots do not overlap within the range. May be set.

<DC play and interchange play>

In contact charging using a roll charger, charging spots (concentration spots) are liable to occur due to subtle gap variations between the rolls of the roll charger and the surface of the photoconductor. In particular, in the direct current charging in which the direct current voltage is applied to the roll charger, the film thickness unevenness of the photoconductor, which is not a problem in the alternating current charge, also appears remarkably as the charging unevenness. In addition, when the pitches of the charging spots of each member are synchronized, the larger the spots, the more the image quality defects.

Here, a comparison between DC charging and AC charging will be described. Fig. 8 is a diagram showing the relationship of the photosensitive member charging potential to the voltage applied to the roll-type charger in the case of DC charging, and Fig. 9 is a diagram showing the relationship of the photosensitive member charging potential to the voltage applied to the roll-type charger in the case of AC charging. . In Fig. 8, the film thickness of the photoconductor is a parameter, but in either case of DC charging, the photoconductor charging potential increases in proportion to the voltage applied to the roll charger.

On the other hand, in the case of the alternating current charging shown in Fig. 9, the charging potential increases in proportion to the applied voltage, but the increase in the charging potential is saturated from a certain point. Therefore, in the case of alternating current charging, by setting the applied voltage in a range where the charging potential is saturated, the variation in the charging potential due to the variation in the applied voltage can be suppressed. On the contrary, in the case of direct current charging, the variation in the applied voltage greatly affects the variation in the charging potential.

10 is a diagram showing a change in the photoreceptor charging potential with respect to the photoreceptor film thickness in the case of DC charging, and FIG. 11 is a diagram showing a change in the photoreceptor charging potential with respect to the photoreceptor film thickness in the case of AC charging. In addition, in FIG. 10, FIG. 11, the measurement position of the film thickness in the photosensitive member is used as a parameter. In the DC charging shown in Fig. 10, as the film thickness of the photoconductor becomes thick, the photoconductor charging potential decreases. On the other hand, in the case of the alternating current charging shown in Fig. 11, even when the film thickness of the photosensitive member becomes thick, there is no significant change in the photosensitive member charging potential. Therefore, in the case of alternating current charging, the influence on the charging potential of the photosensitive member film thickness is not large, whereas in the case of direct current charging, the change in the photosensitive member film thickness greatly affects the variation in the charging potential.

From these facts, in the case of direct current charging, in particular, the diameter of each roll of the photosensitive member, the roll type charger, and the roll type cleaning member and the photoresist film thickness are difficult to manage, and the charging unevenness due to each roll overlaps to generate a large charge unevenness. .

Therefore, in the present embodiment, in addition to alternating current charging, in particular, in the case of direct current charging, the effect of suppressing deterioration of uniformity of the charging potential is increased by eliminating duplication of charging stains.

1 is a schematic diagram showing a configuration example of an image forming apparatus according to the present embodiment.

FIG. 2 is a schematic diagram illustrating a configuration of a roll charger in the image forming apparatus of this embodiment. FIG.

It is a schematic diagram explaining the form of a roll type charger.

4 is a schematic diagram illustrating a state of electrification stain.

5 is a view for explaining a specific example of the diameter of each roll of the photosensitive member, the roll type charger, and the roll type cleaning member.

6 is a schematic diagram showing an example of electrification stain in cases 1 and 2;

7 is a schematic diagram showing an example of electrification stain in case 3;

Fig. 8 is a diagram showing the relationship of the photoconductor charging potential to the voltage applied to the roll charger in the case of DC charging.

Fig. 9 is a diagram showing the relationship of the photosensitive member charging potential to the voltage applied to the roll charger in the case of alternating current charging.

10 is a diagram showing a change in the photosensitive member charging potential with respect to the photosensitive member film thickness in the case of direct current charging.

Fig. 11 is a diagram showing the change of the photosensitive member charging potential with respect to the photosensitive member film thickness in the case of alternating current charging.

<Explanation of symbols for the main parts of the drawings>

1: photosensitive member 2: roll type charger

3: laser scanner 4: developer

5: transfer machine 6: drum cleaner

7: static eliminator 8: fuser

20: roll type cleaning member

Claims (14)

Cylindrical photosensitive member, A roll charger and disposed to face an outer circumferential surface of the photosensitive member; A roll cleaning member disposed to face an outer circumferential surface of the roll charger; An exposure machine for forming an electrostatic latent image on the surface of the photosensitive member; A developing unit for developing the latent electrostatic image into a toner image; A transfer unit for transferring the toner image onto a paper; A photosensitive member cleaning member for removing unnecessary toner remaining on the surface of the photosensitive member; An image forming apparatus comprising a fixing unit for fixing the toner image to a sheet, Periodically generated by the charging stain on the surface of the photosensitive member periodically generated by the rotation of the photosensitive member, by the charging stain on the surface of the photosensitive member periodically generated by the rotation of the roll-type charger, and by the rotation of the roll-type cleaning member The diameter of the photosensitive member, the diameter of the roll-type charger, and the diameter of the roll-type cleaning member are set so that the charging unevenness of the surface of the photoconductor does not overlap within the range of the image forming length which is the length of the image formed by the photoconductor. An image forming apparatus, characterized in that. The method of claim 1, And a minimum common multiple of the diameter of the photosensitive member, the diameter of the roll type charger, and the diameter of the roll type cleaning member is greater than the image forming length. The method of claim 1, And said direct current voltage is applied to said roll type charger. The method of claim 1, And the image forming length is 420 mm or less. The method of claim 1, The said roll type cleaning member is comprised by the foam member, The image forming apparatus characterized by the above-mentioned. The method of claim 1, And said roll type cleaning member has an axis pressed in the direction of said roll type charger by a spring. The method of claim 1, And said roll type charger and said roll type cleaning member are fixed to a positive displacement. Cylindrical photosensitive member, A roll charger and disposed to face an outer circumferential surface of the photosensitive member; A roll cleaning member disposed to face an outer circumferential surface of the roll charger; An exposure machine for forming an electrostatic latent image on the surface of the photosensitive member; A developing unit for developing the latent electrostatic image into a toner image; A transfer unit for transferring the toner image onto a paper; A photosensitive member cleaning member for removing unnecessary toner remaining on the surface of the photosensitive member; An image forming apparatus comprising a fixing unit for fixing the toner image to a sheet, When the outer circumferential length of the photosensitive member is A, the outer circumferential length of the roll-type charger is B, the outer circumferential length of the roll-shaped cleaning member is C, and the nip width at the contact portion between the photosensitive member and the roll-type charger is N. , On the outer circumferential surface of the photosensitive member, ± (N / 2) centered on the position of each interval of A, ± (N / 2 centered on the position of the interval of B, and the position every interval of C Each numerical value of ± (N / 2) is set to be different within the range of the image forming length. The method of claim 8, And a minimum common multiple of the diameter of the photosensitive member, the diameter of the roll type charger, and the diameter of the roll type cleaning member is greater than the image forming length. The method of claim 8, And said direct current voltage is applied to said roll type charger. The method of claim 8, And the image forming length is 420 mm or less. The method of claim 8, And said roll type cleaning member is made of a foam member. The method of claim 8, And said roll type cleaning member has an axis pressed in the direction of said roll type charger by a spring. The method of claim 8, And said roll type charger and said roll type cleaning member are fixed to positive displacement.

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