JP2004212554A - Electrifying device and image forming apparatus using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying device that has a small size and stable strength, and to provide an image forming apparatus having the electrifying device. <P>SOLUTION: The electrifying device 52 is disposed opposite an image carrier and constructed so as to electrify the surface of the image carrier to a predetermined potential. The electrifying device 52 includes a long shield case 520 having a substantially U-shaped cross-section whose width increases from the bases 5211, 5221 toward an open edge; and a discharge wire 523 disposed in the shield case such that it extends in the direction of the length of the shield case. Side walls 521, 522 on both sides are bent inside and include first side walls 5212, 5222 and second side walls 5213, 5223 extending from the respective bases. A distance L1 between the first side walls 5212, 5222 and the discharge wire 523 and a distance L2 between the second side wall 5212, 5223 and the discharge wire 523 are substantially identical in cross-sectional view. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charging device that is arranged to face an image carrier and charges the surface of the image carrier to a predetermined potential, and an image forming apparatus using the same.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus such as a copying machine, a printer, and a facsimile is provided with a photosensitive drum for forming an image, and a charging device for charging the surface of the photosensitive drum to a predetermined potential is disposed in an appropriate place around the photosensitive drum. This charging device includes a long shield case having an open surface facing the photosensitive drum and having a U-shaped cross section, and a discharge wire stretched in a long direction in the U-shaped inner space (for example, Patent Document 1).
[0003]
When a voltage is applied to the discharge wire, corona discharge occurs in the charging device, and the surface of the photosensitive drum existing on the opening side of the case is charged to a predetermined potential. The photosensitive drum charged to a predetermined potential is irradiated with light by a laser or the like by an exposure device to lower a predetermined potential in a selected area, and an image to be formed is drawn as an electrostatic latent image. A toner is applied to the electrostatic latent image, and the toner image is transferred to a recording sheet, thereby forming an image on the recording sheet. Thereafter, the residual charge on the surface of the photoconductor drum is removed by the discharging lamp, and the photoconductor drum is brought into a state where the next electrostatic latent image can be drawn.
[0004]
[Patent Document 1]
JP-A-2000-162934 [0005]
[Problems to be solved by the invention]
In recent years, from the viewpoint of resource saving and space saving, there has been a high demand for downsizing of the image forming apparatus itself as well. Therefore, it is preferable that the image forming apparatus is provided closer to a device adjacent to the charging device, for example, to the side of the exposure device or the neutralization lamp. For this purpose, the case of the charging device is preferably compact. However, by simply reducing the size of the conventional case having a U-shape as described above, when a voltage is applied to the wire because the distance between the wire and the case is too short, current leaks to the case, and corona discharge occurs. May not be possible.
[0006]
In addition, the charging device has a possibility that paper dust and toner particles may adhere to the discharge wire and cause potential unevenness in the longitudinal direction, so that a cleaning tool sandwiching the discharge wire between the charging device and a driving mechanism such as a motor is used. It is also known to incorporate a cleaning means capable of reciprocating along the wire. However, in order to maintain the initial shape while incorporating such a mechanism, consideration must be given to strength. .
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a charging device that is small in size and stable in strength and an image forming apparatus using the charging device in order to solve the above-mentioned problems.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is a charging device that is arranged to face the image carrier and charges the surface of the image carrier to a predetermined potential. And a discharge wire extending in a longitudinal direction inside the shield case. The side walls on both sides are bent inward to form first and second side walls from the base side, respectively. The charging device is characterized in that the first and second side walls have substantially the same distance from the discharge wire as viewed in cross section.
[0009]
According to a fourth aspect of the present invention, there is provided an image forming apparatus including the charging device according to any one of the first to third aspects, wherein the image carrier is a photosensitive drum.
[0010]
According to these, the side wall of the shield case having a substantially U-shaped cross section that becomes wider toward the opening end is bent inward and formed with the first and second side walls from the base side. Since the distance between the first and second side walls and the discharge wire is substantially the same in a sectional view, the grounding action on the discharge wire is affected only by one side wall. Disappears. In addition, since the case has a substantially U-shaped cross section and both side walls are bent inward, a more robust case is formed as compared with a case where the case is formed in a semicircular shape and the other end is made smaller.
[0011]
According to a second aspect of the present invention, in the charging device according to the first aspect, among the side walls on the both sides, the second side wall becomes wider toward an opening end. Thereby, the charging device can be formed in a small size, and the area of the opening end can be ensured.
[0012]
According to a third aspect of the present invention, in the charging device according to the first or second aspect, the base portion has a pair of shapes extending in parallel in a longitudinal direction at upper ends of the side walls on both sides. Thereby, it is possible to reduce the size of the upper end portions of the side walls on both sides.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment in which the image forming apparatus according to the present invention is applied to a printer will be described with reference to FIGS. FIG. 1 is a schematic side view of the printer 1. In FIG. 1, a printer 1 has a recording paper storage section 2 in which recording papers are stacked on the bottom side of the main body, and is fed out of the recording paper storage section 2 at an upper side of the main body, and the recording paper after image formation is discharged. A transport section 4 and a transport belt 42 each including a transport path 41 for transporting the recording sheet over the discharge section 3 and an endless transport belt 42 for transporting the recording sheet at image forming sections 5 to 8 described below. The image forming units 5 to 8 are provided in series in the conveyance direction at the upper part of the image forming unit and form images of respective colors on recording paper, and the fixing unit 10 is provided downstream of the conveyance belt 42 in the sheet conveyance direction. .
[0014]
The transport section 4 has a required number of transport roller pairs 43 arranged at required positions along the transport path 41 from the upstream side, and these transport roller pairs 43 are driven to rotate by a motor or the like (not shown). ing.
[0015]
The image forming units 5 to 8 are arranged along the sheet conveying surface of the conveying belt 42 and form images of cyan (C), magenta (M), yellow (Y), and black (B) from the upstream side. The details will be described later. The transport belt 42 is stretched between rollers 44 and 45 on the upstream side and the downstream side, and a tension roller 46 is disposed at a suitable lower portion therebetween. The roller 44 forms a roller pair together with the pressure roller 44a, and can guide the conveyed sheet onto the conveyance belt 42.
[0016]
The fixing unit 10 includes a heat roller 101 having a heater source therein and a pressure roller 102, and fuses a toner of a given color transferred onto recording paper in the image forming units 5 to 8. The image forming units 5 to 8 have the same structure except that the toner colors are different, and the image forming unit 5 will be described below as an example.
[0017]
FIG. 2 is a side view for explaining the structure of the image forming unit 5. 2, the image forming unit 5 includes a photosensitive drum 51 as a carrier at the center, and a charging device 52, an exposing device 53, a developing device 54, a transfer roller 55, and a cleaning device around the photosensitive drum 51 from the upstream side in the drum rotation direction. A device 56 and a static eliminator 57 are provided.
[0018]
The photosensitive drum 51 has a cylindrical shape with a photosensitive layer formed on its surface, and is rotated at a constant speed by a drive mechanism (not shown). The charging device 52 applies a predetermined potential to the surface of the photoconductor using a corona discharge phenomenon. The exposure device 53 is disposed substantially downward, and the lower part is smaller than the upper part. The exposure device 53 includes, for example, an LED light emitting unit and a scanning polygon mirror, modulates image data transferred from an external memory or the like, emits the light as light, and outputs this light via the polygon mirror to the photosensitive drum 51. The electrostatic latent image is formed on the surface of the photosensitive drum 51 by scanning in the length direction.
[0019]
The developing device 54 applies an electric field to the surface of the photoconductor drum 51 with toner made of cyan to make the electrostatic latent image visible. The transfer roller 55 is for transferring a toner image to recording paper, and the cleaning device 56 is for removing residual toner. The static eliminator 57 is configured by arranging small LED elements on the array in the length direction of the photosensitive drum 51 and removing residual charges by light emission of the LED elements, and has a rectangular parallelepiped shape as a whole. .
[0020]
FIG. 3 is a perspective view of the charging device 52 shown in FIG. As shown in FIG. 3, the charging device 52 is made of metal and has a shield case 520 having long side walls 521 and 522 on both sides, and a long discharge wire 523 stretched inside in a long direction. And a grid electrode 524 formed of a conductive material in a mesh shape and disposed at an end opening of the shield case 520 via an insulating material (not shown).
[0021]
The shield case 520 is divided on the base end side so as to have a gap in the longitudinal direction on the upper surface, or a cutout portion is formed at both ends in the longitudinal direction, and the photosensitive drum 51 is formed on the distal end side. It has an opening surface on the side. The discharge wire 523 is surrounded by the shield case 520 and the grid electrode 524.
[0022]
The charging device 52 applies a predetermined high voltage to the discharge wire 523 by a voltage applying unit (not shown), thereby causing a corona discharge in a gas around the discharge wire 523 to generate, for example, positive ions. Positive ions are emitted from the opening surface of the shield case 520 to the photosensitive drum 51. The charging device 52 is controlled so that a bias voltage is applied to the grid electrode 524 by a voltage applying unit (not shown), so that the surface of the photosensitive drum 51 has a predetermined potential. The ozone generated by the corona discharge is discharged to the outside of the device through a gap or a cutout on the upper surface by an air current generated by a fan or the like (not shown).
[0023]
FIG. 4 is a side sectional view of the charging device shown in FIG. As shown in FIG. 4, the shield case 520 has left and right symmetrical side walls 521 and 522 extending from opposite ends (hereinafter, referred to as bases) 5211 and 5221 of the opening surface to the other end (hereinafter, referred to as open end). It is formed to have a generally U-shape that becomes wider. On both side walls 521 and 522 of the shield case 520, bent portions 521a and 522a that are parallel to the long direction are formed at symmetrical positions in the middle of the opening ends from the base portions 5211 and 5221. It is bent inward at the bent portions 521a and 522a, whereby the side walls 5212 and 5222 (first side wall) are formed on the base side and the side walls 5213 and 5223 (second side wall) are formed on the tip side. The side walls 5212, 5222 are formed in a wide direction from the base portions 5211, 5221, and the side walls 5213, 5223 are formed in parallel with each other by bending portions 521a, 522a.
[0024]
Such a shape and dimensions of the shield case 52 are bent so that a perpendicular distance L1 from the discharge wire 523 to the side walls 5212 and 5222 and a perpendicular distance L2 from the discharge wire 523 to the side walls 5213 and 5223 are substantially the same. The bending angles of the portions 521a and 522a and the position of the discharge wire 523 are set.
[0025]
Note that, in the present embodiment, in a space surrounded by the bases 5211 and 5221 of the shield case 520, the space extends so that a cleaning mechanism storage space for storing a cleaning mechanism for cleaning the discharge wire 523 can be provided. However, a shield case shape without providing a storage space for the cleaning mechanism may be used.
[0026]
As described above, in the printer 1 according to the present embodiment, since the shield case 520 of the charging device 52 has a shape in which the side walls 521 and 522 expand toward the opening end, the bases 5211 and 5221 are small in width. In addition, since the opening side can have a required width dimension, a member (here, the exposure device 53 and the static elimination device) provided adjacent to the charging device 52 is provided in the space between the narrow bases 5211 and 5221. 57) can be arranged adjacent to each other, so that the degree of freedom in arranging the adjacent members is increased, and the printer 1 can be made compact. In particular, in the present embodiment, the arrangement of the exposure device 53 having a large size at the base side is more generous, so that the size of the printer 1 can be further reduced.
[0027]
Further, since the shield case 520 of the charging device 52 has a shape having the bent portions 521a and 522a, the shield case 520 can be formed more robustly than providing a semicircular shape in cross-sectional view and reducing the size of the upper end portion. It is. In particular, as in the present embodiment, a notch is formed on the upper surface of the shield case 52 so that the cleaning device is housed.
[0028]
The lengths L1 and L2 are substantially equal to each other. When a voltage is applied to the discharge wire 523, the current does not leak to the shield case 520, and the grounding action is greatly affected by any of the side walls. Therefore, the potential can be stabilized.
[0029]
In this embodiment, only the perpendicular dimensions L1 and L2 are substantially the same, but in order to secure a distance between the cleaning mechanism and the discharge wire 523, a distance L3 from the discharge wire 523 to a line segment L0 connecting the bases 5211 and 5221 respectively. The shape of the side wall and the position of the discharge wire 523 may be set in consideration of the dimensions L1 and L2.
[0030]
In the cross-sectional view of FIG. 4, the distance from the discharge wire 523 to the entire side wall 5212 (5222) varies with the perpendicular dimension L1 as a minimum, and the distance from the discharge wire 523 to the entire surface 5213 (5223) varies with the perpendicular dimension L2 as a minimum. Can be considered as substantially equivalent.
[0031]
The image forming apparatus according to the present invention includes, in addition to a printer, other apparatuses using electrophotography, such as a copying machine and a facsimile. Further, in the printer 1 according to the present embodiment, the members disposed adjacent to the charging device 52 are the exposure device 53 and the discharging lamp 57, but are not necessarily limited thereto, and are disposed around the photosensitive drum 51. Any device may be used as long as it is disposed adjacent to the charging device 51.
[0032]
In the present embodiment, the side walls 521 and 522 have the same shape. However, the side walls 521 and 522 do not necessarily have to have the same shape, and the distances to the side walls 5212, 5213, 5222, and 5223 are substantially different depending on the arrangement position of the discharge wire 523. It suffices that they are substantially the same as each other and that the grounding action is performed uniformly.
[0033]
Further, in the present embodiment, an example of one bent portion 521a (522a) has been described in order to facilitate the manufacturing process. However, the present invention is not limited to this, and it is symmetrical (or symmetrical) with respect to the side walls 521 and 522. It is possible to form the required number of bent portions, basically have a U-shape, and have a shape in which the opening side is wider at least with respect to the base side.
[0034]
In addition, the second side walls 5213 and 5223 forming the opening side of the side walls 521 and 522 may not be parallel to each other, and may have a shape that becomes wider toward the opening end. According to this, it is possible to reduce the size of the side walls 5213 and 5223 in the width direction, and it is possible to secure a required opening area for charging the photosensitive drum 51.
[0035]
Further, in the present embodiment, charging device 51 is a scorotron charging device having grid electrode 524 and generates positive corona discharge, but may generate negative corona discharge, or And a corotron charging device.
[0036]
【The invention's effect】
According to the first aspect of the present invention, it is possible to reduce the size of the case while securing the distance between the discharge wire and the first and second side walls of the case, and to adjoin the charging device of the present invention. It is possible to form a small-sized image forming apparatus by mounting the member close to the image forming apparatus. Further, since the case can be formed firmly, the initial shape can be maintained even when the cleaning means is built in the case.
[0037]
According to the second aspect of the present invention, the charging device can be formed in a small size and the area of the opening end can be secured, so that the second side wall can be reduced in the width direction. At the same time, the required area of the opening surface for charging the image carrier can be ensured.
[0038]
According to the third aspect of the present invention, it is possible to reduce the size of the upper end portions of the side walls on both sides, and to mount the charging device of the present invention and an adjacent member closer to each other and mount the charging device on the image forming apparatus. Can be formed.
[0039]
According to the fourth aspect of the present invention, it is possible to reduce the size of the case while securing the distance between the discharge wire and the first and second side walls of the case, and to adjoin the charging device of the present invention. It is possible to form a small-sized image forming apparatus by mounting the member close to the image forming apparatus. Further, since the case can be formed firmly, the initial shape can be maintained even when the cleaning means is built in the case.
[Brief description of the drawings]
FIG. 1 is a schematic side view of a printer.
FIG. 2 is a side view illustrating the structure of an image forming unit.
FIG. 3 is a perspective view of the charging device shown in FIG. 2;
FIG. 4 is a side sectional view of the charging device shown in FIG. 3;
[Explanation of symbols]
1 Printer 5-8 Image Forming Unit 51 Photoconductor Drum (Image Carrier)
52 Charging device 520 Shield case 521, 522 Side wall 5211, 5221 Base 5212, 5222 Side wall (first side wall)
5213, 5223 Side wall (second side wall)
521a, 522a, 521b, 522b Bent portion 523 Discharge wire 524 Grid electrode

Claims (4)

In a charging device that is arranged to face the image carrier and charges the surface of the image carrier to a predetermined potential, a long shield case having a substantially U-shaped cross section that becomes wider from the base toward the opening end, A discharge wire extending in a longitudinal direction therein, wherein the side walls on both sides are bent inward to form first and second side walls, respectively, from the base side, A charging device, wherein the first and second side walls have substantially the same distance from the discharge wire as viewed in cross section. 2. The charging device according to claim 1, wherein, of the side walls on both sides, the second side wall becomes wider toward an opening end. 3. 3. The charging device according to claim 1, wherein the base has a pair of shapes extending parallel to a longitudinal direction at upper ends of the side walls on both sides. 4. An image forming apparatus comprising: the charging device according to claim 1, wherein the image carrier is a photosensitive drum.

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