JP7326723B2 - Charging device and image forming device - Google Patents

Description

The present invention relates to charging devices and image forming apparatuses.

2. Description of the Related Art In a conventional electrophotographic image forming apparatus, techniques disclosed in the following Patent Documents 1 to 3 are conventionally known regarding a charging device that charges the surface of an image carrier.

Japanese Patent Application Laid-Open No. 2004-138848 as Patent Document 1 and Japanese Patent Application Laid-Open No. 2004-138849 as Patent Document 2 disclose that the photosensitive layer (21b) has a film thickness between the upper part of the dip (21b2) and the lower part of the dip (21b1). In response to the difference, a technique is described in which the opening width of the grid (22b) is increased on the dip upper (21b2) side and decreased on the dip lower (21b1) side to make the charging potential more uniform. .

Japanese Patent Application Laid-Open No. 2003-15384 as Patent Document 3 discloses that in the corona discharge device (710), the opening area of the opening (71b) of the shield plate (71) is set to the outside of the photosensitive drum (31) in the axial direction. It describes a technology to uniformly charge the photosensitive drum (31) even under the influence of the ion wind by forming the opening area as wide as possible.
Further, Patent Document 3 discloses a technique of forming an opening (71b) so that the opening area increases from one end side to the other end side according to the direction of air blown by an air blowing means (78). is also listed.

Japanese Patent Application Laid-Open No. 2004-138848 (“0015” to “0020”, FIGS. 2 to 5) Japanese Patent Application Laid-Open No. 2004-138849 (“0015” to “0018”, FIGS. 2 to 4) Japanese Patent Application Laid-Open No. 2003-015384 (“0038” to “0051”, FIGS. 2 to 5)

SUMMARY OF THE INVENTION It is a technical object of the present invention to reduce the size of the charging means and suppress charging defects over time at the ends of the image holding means as compared with the case where the auxiliary charging means is added to the ends of the charging means.

In order to solve the technical problem, the charging device of the invention according to claim 1 is
a first charging means having a discharge electrode and a counter electrode facing the discharge electrode and charging the image holding means;
a second charging means arranged downstream of the first charging means with respect to the direction of movement of the surface of the image holding means and charging the image holding means;
with
an area of the counter electrode facing the discharge electrode outside the medium passage area is smaller than inside the passage area with respect to the width of the medium onto which the image is transferred from the image holding means;
The width direction end of the counter electrode is notched to reduce the area of the counter electrode,
A wall portion extending toward the image holding means on the upstream side of the counter electrode with respect to the movement direction of the image holding means is formed to have a constant height inside the medium passage area, Outside the passing area, the edge on the side of the image holding means is notched so that the height is smaller than inside the passing area of the medium .
It is characterized by

The invention according to claim 2 is the charging device according to claim 1 ,
The notch of the counter electrode is formed larger toward the outside in the width direction.

The invention according to claim 3 is the charging device according to claim 1 or 2 ,
A portion of the counter electrode farther from the image holding means with the discharge electrode interposed therebetween is cut out.

In order to solve the above technical problem, the image forming apparatus of the invention according to claim 4 ,
an image holding means;
a charging device according to any one of claims 1 to 3 , which charges the surface of the image holding means;
characterized by comprising

According to the inventions of claims 1 and 4 , compared with the case where the auxiliary charging means is added to the ends of the charging means, the charging means can be downsized and the charging failures of the ends of the image holding means over time can be suppressed. can do.
Further, according to the first aspect of the present invention , charging failure can be suppressed by a simple method of notching the ends in the width direction.
Furthermore, according to the first aspect of the present invention, compared to the case where the edge portion of the wall portion on the upstream side of the counter electrode on the side of the image holding means is not notched, the first charging means charges the edge portion. It is possible to suppress defects and level them by the second charging means.
According to the second aspect of the invention , it is possible to suppress a rapid change in the charge distribution at the boundary between the inside and the outside of the medium passage area, compared to the case where the notch does not become larger toward the outside. can be done.

According to the third aspect of the invention , compared with the case where the portion of the counter electrode on the far side from the image holding means with the discharge electrode interposed therebetween is not notched, the first charging means suppresses charging defects at the end portion. and leveled by the second charging means .

FIG. 1 is an explanatory diagram of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is an explanatory diagram of the charging device of the first embodiment. FIG. 3 is an explanatory view of the upstream wall of the shield electrode of Example 1, viewed from the direction of arrow III in FIG. 4A and 4B are diagrams for explaining the operation of the first embodiment, FIG. 4A is a diagram for explaining the charging state by the conventional charging device, and FIG. 5A and 5B are explanatory diagrams of a modification of the first embodiment, FIG. 5A is an explanatory diagram of a convex notch shape, FIG. 5B is an explanatory diagram of a case where the notch becomes smaller toward the outside, and FIG. FIG. 5D is an explanatory diagram of a case where the notch becomes larger toward the outside, and FIG. 5E is an explanatory diagram of a case where the notch gradually becomes larger exponentially. FIG. 6 is an explanatory diagram of the charging device of the second embodiment, and is a diagram corresponding to FIG. 2 of the first embodiment.

Next, specific examples of embodiments of the present invention (hereinafter referred to as examples) will be described with reference to the drawings, but the present invention is not limited to the following examples.
To facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, the vertical direction is the Z-axis direction, and arrows X, -X, Y, -Y, The directions or sides indicated by Z and -Z are forward, rearward, rightward, leftward, upward and downward, or frontward, rearward, rightward, leftward, upward and downward, respectively.
Also, in the figure, the “・” in the “○” means an arrow pointing from the back to the front of the paper, and the “×” in the “○” means the front of the paper shall mean an arrow pointing backwards from the
It should be noted that in the following explanation using the drawings, illustration of members other than those necessary for the explanation is omitted as appropriate for ease of understanding.

FIG. 1 is an explanatory diagram of an image forming apparatus according to Embodiment 1 of the present invention.
In FIG. 1, a copier U as an example of an image forming apparatus according to the first embodiment has a printer section U1 as an example of an image recording apparatus, which is an example of a recording unit. A scanner unit U2, which is an example of a reading unit and an example of an image reading device, is supported above the printer unit U1. An auto feeder U3 as an example of a document feeder is supported above the scanner unit U2. A user interface U0 as an example of an input unit is supported by the scanner unit U2 of the first embodiment. The user interface U0 allows the operator to operate the copier U by inputting.

A document tray TG1 as an example of a medium containing unit is arranged above the auto feeder U3. A plurality of originals Gi to be copied can be stacked and accommodated in the original tray TG1. Below the document tray TG1, a document discharge tray TG2 as an example of a document discharge unit is formed. A document transport roll U3b is arranged along a document transport path U3a between the document tray TG1 and the document discharge tray TG2.

A platen glass PG as an example of a transparent document table is arranged on the upper surface of the scanner unit U2. In the scanner unit U2 of the first embodiment, an optical system A for reading is arranged below the platen glass PG. The reading optical system A of Example 1 is supported along the lower surface of the platen glass PG so as to be movable in the left-right direction. The reading optical system A is normally stopped at the initial position shown in FIG.
An imaging element CCD as an example of an imaging member is arranged on the right side of the optical system A for reading. An image processing unit GS is electrically connected to the imaging device CCD.
The image processing section GS is electrically connected to the writing circuit DL of the printer section U1. The writing circuit DL is electrically connected to an exposure device ROS as an example of latent image forming means.

A photosensitive drum PR as an example of an image holding unit is arranged in the printer unit U1. A charging device CC as an example of a charging device, a developing device G as an example of a developing device, a transfer unit TU as an example of a transfer device, and a drum cleaner CLp as an example of a cleaning device are arranged around the photosensitive drum PR. It is
In the first embodiment, the photosensitive drum PR, charging device CC, and drum cleaner CLp are configured as an image forming unit. The image forming unit of the first embodiment is detachably attached to the printer unit U1. Further, in the first embodiment, the developing device G is also detachably attached to the printer unit U1 as a developing unit. In Embodiment 1, the image forming unit and the developing unit are configured as separate units, but the present invention is not limited to this. It is also possible to

Below the transfer unit TU, paper feed trays TR1 to TR4 are arranged as an example of a storage means for media. A transport path SH1 extends from each of the paper feed trays TR1 to TR4. The transportation path SH1 includes a pickup roll Rp as an example of a medium take-out unit, a handling roll Rs as an example of a handling unit, a transportation roll Ra as an example of a medium transportation unit, and a registration roll Rr as an example of a medium delivery unit. are placed.
A fixing device F having a heating roll Fh and a pressure roll Fp is arranged to the left of the transfer unit TU. A discharge path SH2 connects the fixing device F as an example of the fixing means to the discharge tray TRh. The discharge path SH2 and the registration roll Rr are connected by a reversing path SH3. A transport roll Rb and a discharge roll Rh that can rotate forward and backward are arranged in the discharge path SH2.

(Explanation of image forming operation)
A plurality of documents Gi accommodated in the document tray TG1 sequentially pass through the document reading position on the platen glass PG and are ejected to the document ejection tray TG2.
When the auto feeder U3 is used to automatically feed and copy documents, the optical system A for reading is stopped at the initial position, and each document sequentially passes through the reading position on the platen glass PG. Expose Gi.
When the operator manually places the document Gi on the platen glass PG to make a copy, the optical system A for reading moves in the horizontal direction, and the document on the platen glass PG is scanned while being exposed.
Reflected light from the document Gi passes through the optical system A for reading and is condensed on the imaging element CCD. The imaging element CCD converts the reflected light of the document condensed on the imaging surface into an electric signal.

The image processing unit GS converts the read signal input from the imaging element CCD into a digital image signal and outputs the digital image signal to the writing circuit DL of the printer unit U1. The writing circuit DL outputs a control signal corresponding to the input image writing signal to the exposure device ROS.
The exposure device ROS outputs a laser beam L to form a latent image on the surface of the photosensitive drum PR charged by the charging device CC. A developing device G develops the latent image on the surface of the photosensitive drum PR into a visible image. A transfer roll TR of the transfer unit TU transfers the image on the surface of the photosensitive drum PR onto a recording sheet S, which is an example of a medium conveyed along the conveying path SH1. The image transferred to the recording sheet S is fixed by the fixing device F. FIG. The recording sheet S that has passed through the fixing device F is conveyed to the reversing path SH3 in the case of double-sided printing, and is discharged by the discharge roll Rh in the case of being discharged to the discharge tray TRh.

(Description of charging device)
FIG. 2 is an explanatory diagram of the charging device of the first embodiment.
In FIG. 2, the charging device CC of the first embodiment has an upstream charger 1 as an example of first charging means and a downstream charger 2 as an example of second charging means. The downstream charger 2 is arranged downstream in the rotational direction of the photosensitive drum PR. The upstream charger 1 has an upstream wire electrode 3 as an example of a discharge electrode. The upstream wire electrode 3 is formed in a string shape extending in the front-rear direction. The downstream charger 2 also has a downstream wire electrode 4 parallel to the upstream wire electrode 3 as an example of a discharge electrode.
An upstream shield electrode 6 as an example of a counter electrode is arranged around the upstream wire electrode 3 so as to surround three sides except for the side of the photosensitive drum PR. The upstream shield electrode 6 has an upstream wall 6a, a partition wall 6b arranged on the downstream side facing the upstream wall 6a, and a top wall 6c. Also, a downstream shield electrode 7 as an example of a counter electrode is arranged around the downstream wire electrode 4 so as to surround three sides except for the photosensitive drum PR side. In the downstream shield electrode 7 of the first embodiment, the upstream wall is shared with the partition wall 6b, and the partition wall 6b, the downstream wall 7b arranged on the downstream side facing the partition wall 6b, and the top wall 7c. have

The top walls 6c and 7c of the first embodiment are provided with openings 8 for discharging discharge products, ozone, etc. together with the airflow.
A grid electrode 9, which is an example of an electrode member, is supported between the wire electrodes 3 and 4 and the photosensitive drum PR, that is, on the side of the charging area Q0, which is the area facing the photosensitive drum PR. . The grid electrode 9 is formed in a net shape.
In the charging device CC of Example 1, the outer sides of the shield electrodes 6 and 7 are surrounded by a housing 10 as an example of support means. The housing 10 of Example 1 is made of a resin material as an example of insulating means.

FIG. 3 is an explanatory view of the upstream wall of the shield electrode of Example 1, viewed from the direction of arrow III in FIG.
2 and 3, in the upstream shield electrode 6 of the first embodiment, a notch shape 11 is formed by notching the lower end of the upstream wall 6a outside L2 of the predetermined passage area L1 of the recording paper S. It is Therefore, in the first embodiment, the area of the upstream shield electrode 6 is set smaller on the outside L2 of the passage area L1 than on the inside of the passage area L1. In particular, the notch shape 11 of Example 1 is formed so that the notch becomes larger toward the outside of the passing region L1, that is, the area of the upstream shield electrode 6 becomes smaller.

In the first embodiment, as an example of a predetermined recording sheet S, the length of A4LEF: Long Edge Feed is set. That is, the width of the most frequently used recording paper S is set as the width of the passage area L1 instead of A3LEF as an example of the maximum width of the recording paper S that can be used in the copier U. Note that the width of the passage area L1 is not limited to the one exemplified in the first embodiment, and can be arbitrarily changed according to the design, specifications, usage environment, and the like.

(Action of Example 1)
In the charging device CC of Embodiment 1 having the above configuration, when image formation is started, current is supplied to the wire electrodes 3 and 4, and the shield electrodes 6 and 7 and the grid electrode 9 and the wire electrode 3 are grounded. , 4 to discharge. Along with this discharge, the surface of the photoreceptor drum PR is charged.
At this time, in the charging device CC of the first embodiment, the upstream wall 6a of the upstream shield electrode 6 is formed with a notch shape 11 on the outer side L2 in the width direction. Charges that have not reached the photosensitive drum PR during discharge are recovered via the shield electrodes 6 and 7 and the grid electrode 9 . At this time, the area of the shield electrode 6 is small in the area of the outer side L2. Therefore, the amount of charge collected is reduced, and as a result, the amount of charge in the area of the outer side L2 of the photoreceptor drum PR is increased.

4A and 4B are diagrams for explaining the operation of the first embodiment, FIG. 4A is a diagram for explaining the charging state by the conventional charging device, and FIG.
In FIG. 4A, the conventional charging device without the notch shape 11 can charge uniformly in the initial state where the photosensitive drum is not worn, as indicated by the solid line 01 in FIG. 4A. However, when printing is repeated, the photosensitive drum deteriorates over time. In particular, when there is a large amount of printing of the width L1 of the recording paper S, which is frequently used, the photoreceptor drum is in the transfer area (Q3) at the outer edge of the width L1 of the high frequency paper due to the influence of edge discharge. Deterioration and wear of the outer side L2 area of are likely to progress. Therefore, as time passes, charging failure tends to occur at the end portion 02a as indicated by the solid line 02 in FIG. 4A. If charging failure occurs at the end portion 02a, the impact of the charging failure is less likely to affect the printing of high-frequency paper. However, when printing on recording paper having a size larger than high-frequency paper, in the first embodiment, when printing on B4 or A3 paper, in the area of the outer side L2, the potential difference between the developing roll R0: developing bias is insufficient, image quality may deteriorate due to charging failure. Even if the configuration includes both the upstream charger 1 and the downstream charger 2 as in the first embodiment, if there is a charging failure at the end L2 after passing through the upstream charger 1, the downstream charger 2 passes through. Even if the end L2 is additionally charged, there is a high possibility that insufficient charging will remain.

The techniques described in Patent Documents 1 and 2 can deal with non-uniform film thickness in the axial direction of the photoreceptor drum in the initial state, but cannot deal with deterioration of the photoreceptor drum over time. Further, in the technique described in Japanese Patent Laid-Open No. 2002-200300, the structure in which the opening area is changed according to the flow of the ion wind cannot cope with deterioration of the photoreceptor drum over time.
Further, by increasing the number of chargers to three or more, that is, by adding auxiliary charging means and performing additional charging, it is also possible to increase the potential of the deteriorated end portion L2 to the potential of the inner side L1. is. However, in this case, there is a problem that the overall size of the charging device is increased.

On the other hand, in Example 1, the area of the upstream shield electrode 6 in the region of the outer side L2 is small, and as indicated by V2a in FIG. It is possible to ensure the same amount of charge as in the area L1 of . Therefore, in the charging device CC of the first embodiment, compared with the case where the auxiliary charging means is added to the end portion of the charging means, the size of the charging device CC can be reduced while the charging failure of the end portion L2 of the photosensitive drum PR over time can be prevented. Suppressible.
In the charging device CC of the first embodiment, the surface of the photosensitive drum PR has the potential indicated by V2a when it passes through the upstream charger 1, but when it passes through the downstream charger 2, the potential is leveled, and the initial state is reached. The charging state is the same as that of V1.

In addition, in the first embodiment, it is possible to suppress charging defects at the end portion by a simple method of cutting out a portion of the upstream wall 6a.
Furthermore, in Example 1, the notch shape 11 is larger toward the outer side, and the charge distribution changes more rapidly than in the case where the area changes rapidly at the boundary between the inner region L1 and the outer region L2. is suppressed. There are variations in the size of the recording paper S and in the accuracy of transportation, and the boundary portion may shift. get closer. Therefore, even if a part of the recording paper S, which is frequently charged, reaches the outer area L2, the adverse effect due to the difference in the charge distribution can be suppressed.

5A and 5B are explanatory diagrams of a modification of the first embodiment, FIG. 5A is an explanatory diagram of a convex notch shape, FIG. 5B is an explanatory diagram of a case where the notch becomes smaller toward the outside, and FIG. FIG. 5D is an explanatory diagram of a case where the notch becomes larger toward the outside, and FIG. 5E is an explanatory diagram of a case where the notch gradually becomes larger exponentially.
Note that the notch shape 11 is not limited to the form illustrated in FIG. 3, and can be arbitrarily changed according to the configuration and specifications of the copying machine U, the usage environment, the setting of the discharge voltage, and the like. For example, as shown in FIG. 5A, a convex cutout shape 11a is formed in which the central portion of the outer L2 region is cut out the most, or as shown in FIG. 5B, a cutout shape that becomes smaller toward the outside. 11b, or a stepped notch shape 11c as shown in FIG. 5C. It is also possible to form the notch so that it becomes larger toward the outside as shown in FIG. 5D, or to make the notch gradually become larger exponentially as shown in FIG. 5E.
Moreover, although the notch shape 11 is formed in the upstream wall 6a of the upstream shield electrode 6 in the first embodiment, the present invention is not limited to this. For example, it is possible to form a notch shape on the outside of the top wall 6c in the front-rear direction. It is also possible to form the notch shape 11 on both the upstream wall 6a and the top wall 6c. Moreover, if the partition wall 6b is not shared with the downstream shield electrode 7, the partition wall 6b can be formed with a notch shape.

FIG. 6 is an explanatory diagram of the charging device of the second embodiment, and is a diagram corresponding to FIG. 2 of the first embodiment.
In the description of the second embodiment, the same reference numerals are given to the components corresponding to the components of the first embodiment, and detailed description thereof will be omitted.
Although the second embodiment differs from the first embodiment in the following points, it is constructed in the same manner as the first embodiment in other respects.

In FIG. 6, the notch shape 11 is not formed in the upstream wall 6a in the charging device CC of the second embodiment. Further, an end portion 10a of the housing 10, which is an example of an insulating means, is formed so as to extend from the outside to the inside of the upstream wall 6a corresponding to the area of the outside L2. Therefore, in the region of the outer side L2, the end 10a of the housing 10 is sandwiched and insulated between the upstream wire electrode 3 and the upstream wall 6a. Therefore, on the outer side L2, charges are not collected through the upstream wall 6a, and as a result, the charge amount of the end portion L2 of the photosensitive drum PR is increased. That is, the area of the upstream shield electrode 6 facing the upstream wire electrode 3 is smaller outside L2 than inside the passage area L1.

(Action of Example 2)
In the charging device CC of Example 2 having the above-described configuration, as in Example 1, even if the end portion of the photoreceptor drum PR deteriorates over time, charging defects at the end portion of the photoreceptor drum PR are reduced. be.
In addition, in the second embodiment, the end portion 10a of the housing 10 is integrally formed with the housing 10, which makes it possible to reduce manufacturing labor and cost compared to a configuration in which the housing is assembled separately.

It should be noted that it is not limited to the configuration in which the end portion 10a of the housing 10 is integrally formed as illustrated in the second embodiment, and may be configured separately. For example, it can be realized by attaching a tape-like insulating means made of an insulating material to the inner side of the upstream shield electrode 6 or by applying a paste-like insulating means. In this case, it is possible to easily modify the existing charging device CC. Further, the configuration is not limited to the configuration in which the seal-like insulating means is attached (supported) to the upstream shield electrode 6, and a configuration in which the insulating means is supported by the housing 10 is also possible.

(Change example)
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the invention described in the claims. Is possible. Modified examples (H01) to (H04) of the present invention are exemplified below.
(H01) In the above-described embodiments, the image forming apparatus is not limited to a copier as an example, and can be applied to an image forming apparatus such as a printer and a FAX. Further, the present invention is not limited to monochrome image forming apparatuses, and can also be applied to color image forming apparatuses.

(H02) In the above embodiment, it is desirable to use two wire electrodes 3 and 4, but it is also possible to use three or more wires.
(H03) In the above embodiment, it is possible to adopt a configuration without the grid electrode 9. FIG.
(H04) In the above embodiment, it is desirable to provide the upstream charger 1 with a notch shape, but it is also possible to provide the downstream charger 2 with a notch shape. The charging state of the surface of the photoreceptor drum PR after passing through the charging device CC is more stable in the configuration in which the deteriorated end portion is charged by the notch shape 11 of the upstream charger 1 and smoothed by the downstream charger 2. It is also possible to provide the downstream charger 2 with a notch shape according to the required uniformity of the charging state.

1... first charging means,
2 ... second charging means,
3... discharge electrode,
6... counter electrode,
6a: a portion on the upstream side of the counter electrode,
6c . . . a portion of the counter electrode farther from the image holding means;
10 ... supporting means,
10a... insulating means,
11... Notch,
CC... charging device,
L1 ... medium passage area,
L2: Outside the medium passage area,
PR... image holding means,
U: image forming apparatus.

Claims (4)

a first charging means having a discharge electrode and a counter electrode facing the discharge electrode and charging the image holding means;
a second charging means arranged downstream of the first charging means with respect to the direction of movement of the surface of the image holding means and charging the image holding means;
with
an area of the counter electrode facing the discharge electrode outside the medium passage area is smaller than inside the passage area with respect to the width of the medium onto which the image is transferred from the image holding means;
The width direction end of the counter electrode is notched to reduce the area of the counter electrode,
A wall portion extending toward the image holding means on the upstream side of the counter electrode with respect to the movement direction of the image holding means is formed to have a constant height inside the medium passage area, Outside the passing area, the edge on the side of the image holding means is notched so that the height is smaller than inside the passing area of the medium .
A charging device characterized by: 2. The charging device according to claim 1, wherein the notch of the counter electrode is formed larger toward the outer side in the width direction. 3. The charging device according to claim 1, wherein a portion of said counter electrode farther from said image holding means with respect to said discharge electrode is notched. an image holding means;
a charging device according to any one of claims 1 to 3, which charges the surface of the image holding means;
An image forming apparatus comprising:

Images