JP2009128617A - Charger and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of image deletion due to corona discharge product. <P>SOLUTION: The charger 100 includes a casing 102 having an opening 106; and a shutter plate 130 for opening or closing the opening 106; and a moving means for moving the shutter plate 130. When the shutter plate 130 is moved from an opening position to a closing position by the use of the moving means, the casing 102 in a charging position is forcibly moved by the shutter plate 130, from the charging position to a retracting position against spring force of a compression coil spring 128. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a charger for charging the surface of a photosensitive drum, and an image forming apparatus (for example, an image forming apparatus such as an electrostatic copying machine, a printer, a facsimile, or a composite machine thereof) including the charger.

A charger that uniformly charges the surface of the photosensitive drum by corona discharge generates corona products such as ozone and nitrogen oxides. When the generated corona product adheres to the surface of the photosensitive drum, the surface resistance of the photosensitive drum is lowered under high humidity, and so-called image flow is generated. A charger for solving such a problem is disclosed in Patent Document 1, for example. The charger disclosed in Patent Document 1 includes a casing having a discharge wire and extending in the axial direction of the photosensitive drum and having an opening facing the photosensitive drum, a shutter plate that opens and closes the opening, and a shutter. Moving means for moving the plate in a tangential direction of the photosensitive drum that coincides with the width direction of the casing to move between a closed position for closing the opening and an open position for opening the opening is provided.
JP 2007-072121 A

In the charger, the shutter plate has a gap between the opening end of the casing disposed so as to face the surface of the photosensitive drum with a gap and the surface of the photosensitive drum. Is moved in the tangential direction. In a so-called scorotron type charger in which a grid is disposed at the opening end of the shutter plate, a grid and a photosensitive member arranged linearly in the tangential direction of the photosensitive drum as viewed in the axial direction of the photosensitive drum. The clearance between the surface of the body drum (the apex of the circumferential surface) is generally set to 0.1 mm to 1.0 mm in consideration of charging performance. In order to stably open and close a shutter plate that is thinner than such a narrow gap over a long period of time without contacting the surface of the photosensitive drum, high-precision technology is required and practical application is extremely difficult. It is. Further, when the grid is disposed in the casing so as to exist in an arc shape with a certain gap along the outer peripheral surface of the photosensitive drum as viewed in the axial direction of the photosensitive drum, the arc-shaped gap In order to open and close, it is necessary to form a thin shutter plate in the shape of an arc and open and close it without contacting the surface of the photosensitive drum, and practical application is practically impossible. Even in a so-called corotron type charger that does not use a grid, the same problem as described above exists when the gap between the casing and the surface of the photosensitive drum is narrow as described above.

An object of the present invention is to make it possible in practice to easily prevent the occurrence of image flow due to a corona product while ensuring a gap between a grid or casing and the surface of a photosensitive drum as required. And an image forming apparatus provided with the charger.

According to one aspect of the present invention,
A casing having a built-in discharge wire and extending in the axial direction of the photosensitive drum and having an opening facing the surface of the photosensitive drum, a shutter plate for opening and closing the opening, and the shutter plate coincide with the width direction of the casing In a charger comprising moving means for moving between a closed position for closing the opening and an open position for opening the opening by moving in a tangential direction of the photosensitive drum,
The casing is movable between a charging position where the surface of the photosensitive drum can be charged and a retracting position where the surface is retracted from the charging position outward in the radial direction of the photosensitive drum, and is moved to the charging position by the biasing unit. Always energized,
When the shutter plate is moved from the open position to the closed position by the moving means, the casing in which the shutter plate is in the charging position is forcibly moved from the charging position to the retracted position against the biasing means.
A charger characterized by that,
Is provided.
The casing is formed in a channel shape having a pair of side walls facing each other with a gap in the tangential direction of the photosensitive drum, and the open position of the shutter plate is disposed on the outer side of one side wall of the casing. An inclined protrusion is formed extending outward in the radial direction of the photosensitive drum from the one side wall at the opening end toward the outer side, and the inclined protrusion of the photosensitive drum is in a state where the casing is at the charging position. A part of the inclined surface on the front side is positioned so as to exist on the movement trajectory of the shutter plate. When the shutter plate is moved from the open position to the closed position by the moving means, the tip of the shutter plate is inclined to the inclined protrusion of the casing. After the casing at the charging position in contact with a part of the inclined surface of the portion is forcibly moved from the charging position to the retracted position against the biasing means, the shutter plate moves the opening end of the casing laterally in the tangential direction. Is positioned me, it is preferable.
At the opening end of the casing, with the casing positioned at the charging position, a gap is formed on the surface of the photosensitive drum, and the linear ends extend linearly in parallel to the axial direction of the photosensitive drum. A grid provided with grid lines that are spaced apart from each other so as to form an arc shape along the surface is disposed, or a photoreceptor is provided with a gap on the surface of the photoreceptor drum. It is preferable that a grid made of a grid plate extending linearly in the axial direction of the drum is disposed.
According to another aspect of the invention,
An image forming apparatus comprising a charger for charging the surface of a photosensitive drum, wherein the charger is composed of any one of the chargers described above,
Is provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a charger configured according to the present invention and an image forming apparatus including the charger will be described below in detail with reference to the accompanying drawings.

First, an embodiment of a laser printer which is an image forming apparatus provided with a charger configured according to the present invention will be described with reference to FIG.

The laser printer 2 (hereinafter, abbreviated as “printer 2”) includes a printer main body 4 that is a substantially rectangular parallelepiped image forming apparatus main body. On the upper surface of the printer main body 4, a step portion 6 that extends vertically downward from the left end portion in FIG. 9 and a paper discharge tray 8 are formed. The paper discharge tray 8 is formed so as to rise from the lower end of the step portion 6 toward the upper right in FIG. 9 with a gentle curve and then to extend horizontally at the right end in FIG. A discharge port 9 is formed in the stepped portion 6.

In a substantially central region in the printer main body 4, a photosensitive drum 10 as an image carrier is disposed so as to be rotated in the clockwise direction in FIG. Around the photosensitive drum 10, a charger 100, a developing sleeve 12A of the developing device 12, a transfer roller 14, a cleaning roller 16A of the cleaning device 16, a static eliminator (not shown), and the like are provided. A laser scanning unit LSU that converts input image information into laser light and irradiates the surface of the photosensitive drum 10 is disposed at an upper position in the printer body 4.

A transport path 18 for transporting paper is disposed at a substantially central portion of the printer main body 4 in the vertical direction, and a paper feed cassette 20 is mounted at the lower end. The conveyance path 18 passes between the photosensitive drum 10 and the transfer roller 14 and extends substantially horizontally in the tangential direction thereof. The upstream end region of the transport path 18 is inverted downward and connected to the paper feed cassette 20. On the upstream side of the photosensitive drum 10 in the conveyance path 18, a separation roller pair 22, a conveyance roller pair 24, and a registration roller pair 26 are arranged along the conveyance path 18 in that order from upstream to downstream. Yes. In the paper feed cassette 20, there are disposed a bottom plate 30 which is a paper placement plate supported at one end so as to be rotatable around a shaft 28, a compression coil spring 32 which pushes up the other end of the bottom plate 30 and the like. ing. The upper surface of the front end portion of the paper P stacked and accommodated on the bottom plate 30 is pressed against a pickup roller 34 provided in the printer main body 4.

A fixing device 36 is disposed on the downstream side of the photosensitive drum 10 in the conveyance path 18. The fixing device 36 includes a heat roller 36A and a pressure roller 36B pressed against the heat roller 36A from below. On the downstream side of the fixing device 36 in the conveying path 18, a conveying roller pair 38 is disposed. A discharge conveyance path 40 is disposed on the downstream side of the conveyance roller pair 38. The discharge conveyance path 40 extends upward along the inside of the rear wall of the printer main body 4 (the wall located on the left side in FIG. 9), and curves to the front side of the printer main body 4 at the upper end portion to discharge the discharge port 9. It is connected to the. A pair of conveyance rollers 42 is disposed at a substantially central position in the vertical direction of the discharge conveyance path 40, and a pair of discharge rollers 44 is disposed at the upper end (downstream end).

When a print signal is transmitted to the printer 2, the surface of the photosensitive drum 10 uniformly charged by the charger 100 is exposed by the laser scanning unit LSU, whereby an electrostatic latent image is formed on the surface. This electrostatic latent image is developed by the developing sleeve 12A of the developing device 12 to become a toner image. This toner image is transferred onto one side of the paper P conveyed from the paper feed cassette 20 at a predetermined timing by the transfer roller 14. The sheet P on which the toner image has been transferred is guided by the conveyance path 18 and conveyed to the fixing device 36, where it is thermally fixed while passing through the nip portion between the heat roller 36 and the pressure roller 36A. The sheet P on which the toner image is fixed is discharged face down from the discharge port 9 to the discharge tray 8 through the discharge transfer path 40 by the transfer roller pair 38, the transfer roller pair 42, and the discharge roller pair 44. .

Next, the charger 100 will be described. 1 to 4, the charger 100 includes a casing 102. A casing 102 made of an appropriate synthetic resin includes a ceiling wall 104 that extends linearly in the longitudinal direction with a constant width, and a pair that extends perpendicularly from both sides in the width direction of the ceiling wall 104 to one side of the ceiling wall 104. The side wall 105 is formed in a channel shape having an opening 106 (FIG. 4) on the opposite side to the top wall 104. End walls 107 are integrally formed at both ends of the casing 102 in the longitudinal direction. Each of the end walls 107 is disposed to be orthogonal to each of the side walls 105. The front end surface of each of the side walls 105 and each of the end walls 107 on the opening 106 side is positioned on a substantially common virtual plane (not shown).

In each of the regions extending from both longitudinal end regions of the casing 102 to a part of the intermediate region, one of the side walls 105 (one side wall 105 positioned upstream in the rotation direction of the photosensitive drum 10) from the front end of the opening 106 side to the outside. On the other hand, an inclined protrusion 105A that extends straight in the opposite direction to the direction in which the opening 106 opens is formed. There is another embodiment in which each of the inclined protrusions 105A extends from the front end of the side wall 105 on the side of one opening 106 while gently curving in this direction.

A shield case 108 formed in a channel shape from a metal plate such as stainless steel is fitted and attached to the intermediate region excluding both end regions in the longitudinal direction of the casing 102 so as to cover the three outer sides. In the casing 102, two discharge wires 110 are provided with tension so as to extend in the longitudinal direction. A grid 112 is disposed at the end of the opening 106 of the casing 102 in an arc shape so as to bulge inwardly from the opening end between the front end portions of the opening 105. The grid 112 extends linearly parallel to the longitudinal direction of the casing 102 and has an arc shape that bulges inwardly from the opening end between the front ends of the opening 105 when viewed in the longitudinal direction of the casing 102. Grid lines arranged with a gap between each other are provided. There is another embodiment in which the grid 112 is configured from a grid plate extending linearly with a predetermined width in the longitudinal direction of the casing 102 at the end of the opening 106 of the casing 102. In FIG. 3, reference numeral 113 denotes a terminal for applying a voltage to each of the discharge wires 110, and reference numeral 114 denotes a terminal for applying a voltage to the grid 112, each from one end of the casing 102. It is arranged to project outward.

The casing 102 has a charging position (a position shown in FIG. 1) at which the surface of the photosensitive drum 10 can be charged, and a retreat position (shown in FIG. 7) that retreats outward from the charging position in the radial direction of the photosensitive drum 10. In the printer main body 4 so as to be movable between the two positions. More specifically, the casing 102 is formed longer than the entire length of the photosensitive drum 10. In the printer body 4, positioning guides 116 that extend straight in the tangential direction are disposed at axially outer positions near the outer peripheral surface at both ends of the photosensitive drum 10. Each of the positioning guides 116 formed of an appropriate synthetic resin includes an elongated substantially rectangular guide plate portion 118 and inner side surfaces (inner axial side surfaces of the photosensitive drum 10) at both longitudinal ends of the guide plate portion 118. And the positioning protrusions 120 are arranged at symmetrical positions in the axial direction of the photosensitive drum 10 and are symmetrical to each other.

Each of the guide plate portions 118 of the positioning guide 116 is located at a position radially spaced from the outer peripheral surface (surface) of the photosensitive drum 10 when viewed in the axial direction of the photosensitive drum 10. One surface 118A (upper surface 118A in FIG. 1) extending straight in the tangential direction of the photosensitive drum 10 and the other surface 118B extending parallel to the one surface 118A at a position spaced radially inward of the photosensitive drum 10 with respect to the one surface 118A. (The lower surface 118B in FIG. 1), one end surface 118C in the longitudinal direction, and the other end surface 118D, and have a certain thickness (the axial thickness of the photosensitive drum 10). Each one surface 118A of the guide plate portion 118 is gently curved toward the other surface 118B toward one end surface 118C. This curve indicates that when the shutter plate 130, which will be described later, moves from the closed position (FIG. 1) toward the open position (FIG. 7), the front end of the shutter plate 130 is smoothly placed on each side 118A of the guide plate 118. Contributes to guiding. One end surface 118C of each guide plate portion 118 is located upstream in the rotation direction of the photoconductive drum 10 and downstream of the cleaning device 16 in the tangential direction, and the other end surface 118D is rotated in the photoconductive drum 10. Located downstream in the direction. Each of the positioning protrusions 120 extends from the inner surface of the corresponding guide plate 118 at a right angle so as to have the same thickness in the axial direction of the photosensitive drum 10 and is constant when viewed in the axial direction of the photosensitive drum 10. The tangential width extends from the other surface 118B of the corresponding guide plate 118 to the one surface 118A by the same length, and the top surface is formed in a semicircular shape. The top surfaces of the positioning protrusions 120 having substantially the same shape and size as each other are located at a position retracted in the direction of the other surface 118B by the same distance with respect to the one surface 118A.

As shown in FIG. 5, one guided plate 122 is disposed on one end wall 107 of the casing 102. The guided plate 122 extends from one end wall 107 at a right angle outward in the longitudinal direction of the casing 102, and is disposed so that both surfaces thereof face the width direction of the casing 102. Corresponding to the guided plate 122, a channel-shaped guide 124 is disposed in the printer body 4. Two guided plates 122 are also disposed on the other side of the end wall 107 at intervals in the width direction. Correspondingly, two channel-shaped guides 124 are arranged in the printer main body 4. In the casing 102, each of the guided plates 122 is slidably fitted to the corresponding guide 124, so that the end surface of each end wall 107 on the opening 106 (FIG. 4) side corresponds to the corresponding guide plate portion 118. The positioning projection 120 is supported in the printer main body 4 so as to be movable in the direction approaching and separating from the top surface of each positioning projection 120, that is, in the radial direction of the photosensitive drum 10.

With reference to FIGS. 1 to 4, there are two each between the outer surface of the top wall 104 at both ends in the longitudinal direction of the casing 102 and the spring receivers 126 arranged at corresponding positions in the printer body 4. The compression coil spring 128 is disposed. The casing 102 has a positioning projection of the corresponding guide plate 118 at the end face on the opening 106 side at the corner where each of the end walls 107 and the side wall 105 intersect at right angles by the compression coil springs 128 constituting the urging means. By being in pressure contact with the top surface of each of the portions 120, it is positioned in a state of being constantly urged to the charging position. The opening 106 of the casing 102 extends in the axial direction of the photosensitive drum 10 and is positioned to face the surface of the photosensitive drum 10. Each outer surface of the end wall 107 of the casing 102 is positioned with a gap inside the corresponding guide plate portion 118. The end face on the opening 106 side of each side wall 105 of the casing 102 is positioned with a gap in the surface of the photosensitive drum 10. The end face of each end wall 107 of the casing 102 on the opening 106 side is positioned outside the both ends of the photosensitive drum 10 (not shown). Grid lines constituting the grid 112 of the casing 102 extend linearly in parallel with each other in the axial direction of the photosensitive drum 10 with a gap on the surface of the photosensitive drum 10 and are viewed in the axial direction. It arrange | positions at intervals so that it may become circular arc shape along the surface. When the grid 112 is constituted by a grid plate extending linearly with a predetermined width in the longitudinal direction of the casing 102 at the end of the opening 106 of the casing 102, the grid plate has a gap on the surface of the photosensitive drum 10. And extend linearly in the axial direction of the photosensitive drum 10.

The charger 100 has a shutter plate 130 that opens and closes the opening 106 of the casing 102, and a closed position that closes the opening 106 by moving the shutter plate 130 across the width direction of the casing 102 that coincides with the tangential direction of the photosensitive drum 10. (Position shown in FIG. 7) and a moving means for moving between the opening position for opening the opening 106 (position shown in FIG. 1). When the shutter plate 130 is moved from the open position to the closed position by the moving means, the casing 102 in which the shutter plate 130 is in the charging position (FIG. 1) moves the charging position (FIG. 1) against each spring force of the compression coil spring 128. ) To the retracted position (FIG. 7).

This will be described more specifically. As shown in FIG. 1, a cleaning device 16 is disposed on the outer side in the radial direction of the photosensitive drum 10 and upstream of the position where the charger 100 is disposed. A housing 132 is disposed above the cleaning device 16 in FIG. 1 and between the cleaning device 16 and the charger 100. The housing 132 is disposed so as to extend in the axial direction of the photosensitive drum 10, and guide plates 134 are disposed at both ends in the longitudinal direction (the axial direction) of the housing 132. Each of the guide plates 134 formed of an appropriate synthetic resin is disposed so as to extend straight on the extension of each guide plate portion 118 of the positioning guide 116, and is configured in substantially the same manner. That is, each of the guide plates 134 includes a single side (upper surface in FIG. 1) 134A, a longitudinal end surface 134C, and an arc-shaped other end surface 134D, and has a certain thickness (axial thickness of the photosensitive drum 10). ing. Each one side 134A of the guide plate 134 is disposed so as to extend straight on the extension of the one side 118A in the guide plate portion 118 of the corresponding positioning guide 116 (positioned on a common virtual plane), and is circular. The arc-shaped other end surface 134D is positioned so as to face the one end surface 118C of the guide plate portion 118.

The shutter plate 130 is made of a suitable synthetic resin and is formed in a rectangular flat plate shape. In the housing 132, both ends of the shutter plate 130 in the longitudinal direction are respectively placed and supported on one side 134A of the guide plate 134 so as to be slidable along the one side 134A. Note that guide flanges 136 (FIG. 2) are formed at both ends in the longitudinal direction of the shutter plate 130 so as to extend at right angles to the guide plate 134 direction. In a state where the shutter plate 130 is placed and supported on one side 134A of each guide plate 134, each of the guide flanges 136 is positioned outside the corresponding guide plate 134 in the axial direction. An opening 138 through which the shutter plate 130 can be opened and closed is formed on the charger 100 side of the housing 132.

A drive shaft 140 extending in the longitudinal direction of the housing 132 (axial direction of the photosensitive drum 10) is rotatably supported inside the opening 138 in the housing 132, and the drive shaft 140 is spaced apart in the axial direction. The two drive rollers 142 are arranged so as to rotate together. A driven roller 144 is pressed against each of the drive rollers 142 by a spring member (not shown) from the bottom to the top in FIG. The central portion in the longitudinal direction of the shutter plate 130 on the opening 138 side is sandwiched between the driving roller 142 and the driven roller 144. One end (the upper end in FIG. 3) of the drive shaft 140 extends outward from one end in the longitudinal direction of the housing 132, and the driven gear 146 is disposed at the one end so that the driven gear 146 can rotate integrally. The driven gear 146 is meshed with a driving gear 148 of an electric motor M that is a driving source. Each of the drive shaft 140, each of the drive rollers 142, each of the driven rollers 144, and the like constitute moving means for the shutter plate 130.

As shown in FIG. 1, the shutter plate 130 is opened to the outside of the side wall 105 of the casing 102 of the charger 100 (one side wall 105 disposed upstream in the rotation direction of the photosensitive drum 10). Is arranged. It can be said that the inclined protrusion 105A of the casing 102 is formed to extend outward in the radial direction of the photosensitive drum 10 from the one side wall 105 at the end of the opening 106 toward the outer side. With the casing 102 positioned at the charging position (FIG. 1), the inclined protrusion 105A is positioned such that a part of the inclined surface 105f on the surface side of the photosensitive drum 10 exists on the movement locus of the shutter plate 130. It is done. With the shutter plate 130 positioned at the closed position (FIG. 1), the tip of the shutter plate 130 is positioned so as to be in contact with or spaced from a part of the inclined surface 105f of the inclined protrusion 105A.

1 to 3 and 6, when the electric motor M is driven and the driving roller 142 is rotated in the counterclockwise direction in FIG. 1, the shutter plate 130 is connected to the driving roller 142 and the driven roller 144. By the cooperation, it is moved from the open position (FIG. 1) to the closed position (FIG. 7), that is, toward the charger 100, to the right indicated by the arrow X in FIG. The first movement of the shutter plate 130 is performed by sliding both end portions of the shutter plate 130 on one side 134A of each guide plate 134, respectively. The movement of the shutter plate 130 in the longitudinal direction is restricted between each of the guide flanges 136 and the corresponding guide plate 134. Due to the movement of the shutter plate 130, the tip of the shutter plate 130 abuts a part of the inclined surface 105 f of the inclined protrusion 105 </ b> A of the casing 102 so that the casing 102 in the charging position moves the spring force of each compression coil spring 128. 1 is forced to move upward from the charging position (FIG. 1) to the retracted position (FIG. 7) as indicated by an arrow Y in FIG.

When the front end of the shutter plate 130 moves over the inclined surface 105f of the inclined protrusion 105A of the casing 102 while forcibly moving the casing 102 upward as indicated by the arrow Y in FIG. The upper surface in FIG. 1 moves to a position that covers a part of the end of the opening 106 of the casing 102, and the lower surface in FIG. 1 at both ends in the longitudinal direction of the shutter plate 130 is the guide plate portion 118 of the positioning guide 116. And supported on one side 118A. The distal end portions of the guide ribs 136 of the shutter plate 130 are positioned outside the guide plate portions 118, respectively. When the shutter plate 130 is further moved across the end of the opening 106 of the casing 102 to the closed position (FIG. 7), the rotation drive of the electric motor M is stopped and the shutter plate 130 is positioned at the closed position (FIG. 7). As shown in FIG. 7, the casing 102 is supported on one surface 118 </ b> A of each of the guide plate portions 118 via the shutter plate 130, and the photosensitive drum 10 is opposed to the top surface of each of the positioning projections 120. Is located at a retracted position (FIG. 7) spaced outward in the radial direction. The opening 106 of the casing 102 is closed by a shutter plate 130 positioned at the closed position. The rear end portion (left end portion in FIG. 7) of the shutter plate 130 is nipped by the driving roller 142 and the driven roller 144. In the printer 2, the opening 106 of the casing 102 is closed by the shutter plate 130 while the printing operation is stopped. During this time, the problem that the corona product generated in the charging device 100 adheres to the surface of the photosensitive drum 10 is prevented, so that the occurrence of image flow is prevented.

When the electric motor M is driven again and the drive roller 142 is rotated in the clockwise direction in FIG. 1, the shutter plate 130 is reversely moved from the closed position (FIG. 7) to the open position (FIG. 1). When the shutter plate 130 reaches the open position (FIG. 1), the driving of the electric motor M is stopped and the shutter plate 130 is positioned at the open position (FIG. 1). During this time, the casing 102 is moved and positioned from the retracted position (FIG. 7) to the charging position (FIG. 1) by the spring force of each compression coil spring 128.

In the charger 100 according to the present invention, the casing 102 has a charging position (FIG. 1) that can charge the surface of the photosensitive drum 10, and retracts outward from the charging position (FIG. 1) in the radial direction of the photosensitive drum 10. 7 and is always urged to the charging position by each of the compression coil springs 128, and the shutter plate 130 is moved from the open position (FIG. 1) to the closed position (FIG. 7). ), The casing 102 in which the shutter plate 130 is in the charging position (FIG. 1) is forcibly moved from the charging position (FIG. 1) to the retracted position (FIG. 7) against the spring force of each compression coil spring 128. Let With this configuration, even if the gap between the surface of the photoconductor drum 10 and the grid 112 of the charger 100 is set to a narrow gap as required, the shutter plate 130 is placed in the tangential direction of the photoconductor drum 10. By moving the position not contacting the surface of the drum 10, the charger 100 can be moved from the charging position (FIG. 1) to the retracted position (FIG. 7). In practice, it is possible to easily prevent the occurrence of image flow due to the corona product while ensuring a gap with the grid 112 as required. In the case of the corotron system in which the grid 112 is not used for the casing 102, the embodiment has the tip on the opening 106 side of the casing 102 arranged on the surface of the photosensitive drum 10 with a slight gap as shown in FIG. Since the opening 106 of the casing 102 can be opened and closed in the same manner as the above scorotron system, the same effect as described above can be achieved.

In the charger 100 according to the present invention, the casing 102 is formed in a channel shape having a pair of side walls 105 facing each other at a distance in the tangential direction of the photosensitive drum 10, and the open position of the shutter plate 130 (FIG. 1) is An inclined protrusion that is disposed on the outer side of one side wall 105 of the casing 102 and extends outward in the radial direction of the photosensitive drum 10 from the one side wall 105 at the end of the opening 106 toward the outer side. In the state where 105A is formed and the casing 102 is at the charging position (FIG. 1), a part of the inclined surface 105f on the surface side of the photosensitive drum 10 of the inclined protrusion 105A exists on the movement locus of the shutter plate 130. When the shutter plate 130 is moved from the open position (FIG. 1) to the closed position (FIG. 7) by the moving means, the tip of the shutter plate 130 is moved to the case. The casing 130 at the charging position (FIG. 1) is in contact with a part of the inclined surface 105f of the inclined protrusion 105A of the ring 102 from the charging position (FIG. 1) against each spring force of the compression coil spring 128. After forcibly moving to the retracted position (FIG. 7), the shutter plate 130 is positioned across the end of the opening 106 of the casing 102 in the tangential direction. Such a configuration contributes to the achievement of the above effect.

In the charger 100 according to the present invention, at the end of the opening 106 of the casing 102, the casing 102 is positioned at the charging position (FIG. 1), and the shaft of the photosensitive drum 10 is spaced from the surface of the photosensitive drum 10. A grid 112 is provided with grid lines extending linearly parallel to each other and spaced apart from each other so as to form an arc along the surface when viewed in the axial direction. Alternatively, a grid 112 made of a grid plate extending linearly in the axial direction of the photosensitive drum 10 with a gap in the surface of the photosensitive drum 10 is disposed. Even in such a configuration, the above effect can be achieved, which is practically useful.

According to the printer 2 including the charger 100 that charges the surface of the photosensitive drum 10, it is practically easy to prevent image flow while ensuring the required charging performance.

1 is a schematic cross-sectional view showing a configuration of an embodiment of a charger configured according to the present invention. FIG. 2 is a partial view showing a left end portion of the casing of the charger shown in FIG. 1 when viewed in the A direction in FIG. 1. FIG. 2 is a plan view of the charger shown in FIG. 1, with a part thereof omitted. It is a figure which shows only the casing of the charger shown in FIG. FIG. 2 is a partial view of both ends of a casing of the charger shown in FIG. 1 as seen from the plane in FIG. 1. It is a cross-sectional schematic diagram which shows the other operation | movement aspect of the charger shown in FIG. FIG. 6 is a schematic cross-sectional view showing still another operation mode of the charger shown in FIG. 1. FIG. 8 is a partial view showing a left end portion of the charger casing shown in FIG. 7 when viewed in the A direction in FIG. 7. FIG. 2 is a schematic configuration diagram of a laser printer including the charger illustrated in FIG. 1.

Explanation of symbols

2: Laser printer 4: Printer main body 10: Photoconductor drum 100: Charger 102: Casing 105A: Inclined protrusion 105f: Inclined surface 106: Opening 112: Grid 128: Compression coil spring (biasing means)
130: shutter plate 140: drive shaft 142: drive roller 144: driven roller

Claims (4)

A casing having a built-in discharge wire and extending in the axial direction of the photosensitive drum and having an opening facing the surface of the photosensitive drum, a shutter plate for opening and closing the opening, and the shutter plate coincide with the width direction of the casing In a charger comprising moving means for moving between a closed position for closing the opening and an open position for opening the opening by moving in a tangential direction of the photosensitive drum,
The casing is movable between a charging position where the surface of the photosensitive drum can be charged and a retracting position where the surface is retracted from the charging position outward in the radial direction of the photosensitive drum, and is moved to the charging position by the biasing unit. Always energized,
When the shutter plate is moved from the open position to the closed position by the moving means, the casing in which the shutter plate is in the charging position is forcibly moved from the charging position to the retracted position against the biasing means.
A charger characterized by that. The casing is formed in a channel shape having a pair of side walls facing each other with a gap in the tangential direction of the photosensitive drum, and the open position of the shutter plate is disposed on the outer side of one side wall of the casing. An inclined protrusion is formed extending outward in the radial direction of the photosensitive drum from the one side wall at the opening end toward the outer side, and the inclined protrusion of the photosensitive drum is in a state where the casing is at the charging position. A part of the inclined surface on the front side is positioned so as to exist on the movement locus of the shutter plate,
When the shutter plate is moved from the open position to the closed position by the moving means, the tip of the shutter plate abuts a part of the inclined surface of the inclined protrusion of the casing to resist the casing at the charging position against the urging means. The charger according to claim 1, wherein the shutter plate is positioned across the opening end of the casing in the tangential direction after forcibly moving from the charging position to the retracted position. At the opening end of the casing, with the casing positioned at the charging position, a gap is formed on the surface of the photosensitive drum, the linear ends extend linearly in parallel to the axial direction of the photosensitive drum, and the axial direction A grid having grid lines arranged with a gap between each other so as to form an arc along the surface is arranged, or a photoconductor with a gap on the surface of the photoconductor drum The charger according to claim 1 or 2, wherein a grid composed of a grid plate extending linearly in the axial direction of the drum is disposed. An image forming apparatus provided with a charger for charging the surface of the photosensitive drum, wherein the charger comprises the charger according to any one of claims 1 to 3. apparatus.

Images