JP6971725B2 - Charging device - Google Patents

Description

The present invention relates to a charging device suitable for use in an image forming apparatus such as a printer, a copier, a facsimile or a multifunction device using an electrophotographic method.

In an image forming apparatus using an electrophotographic method, a corona charger is used as a charging device in order to uniformly charge the surface of the photosensitive drum to a predetermined polarity and potential. The corona charger is arranged so as to face the photosensitive drum in a non-contact manner, and the photosensitive drum is charged by charged particles (corona ions) generated by the corona discharger. As a corona charger, a scorotron type is known. The corotron type corona charger has a discharge electrode that generates charged particles and charges the surface of the photosensitive drum, and a control electrode that controls the amount of charge on the surface of the photosensitive drum. A wire-shaped discharge electrode (called a discharge wire) is used, and a plate-shaped member having a large number of holes formed in a mesh shape (called a grid electrode) is used as a control electrode. Used.

In the case of the scorotron method, discharge products generated together with charged particles during corona discharge, or deposits such as toner and toner external agents tend to adhere to the grid electrodes. Deposits adhering to the grid electrodes can oxidize the grid electrodes and cause rust. When the grid electrode is rusted, it becomes difficult to uniformly charge the photosensitive drum to a predetermined potential, and uneven charging tends to occur. Therefore, in order to remove the deposits adhering to the grid electrode, a charging device including a cleaning member that slides on the grid electrode to clean the grid electrode has been proposed (Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-186269

The apparatus described in Patent Document 1 described above can clean both the surface of the grid electrode facing the discharge wire (referred to as a wire surface) and the surface of the grid electrode facing the photosensitive drum (referred to as a drum surface). It is equipped with a cleaning member. When cleaning the grid electrode, the drum surface cleaning pad for cleaning the drum surface is pressed against the grid electrode by the movable holding member. By doing so, even if the drum surface cleaning pad is worn due to repeated cleaning operations, the ability to remove the deposits (cleaning power) can be maintained, and the replacement cycle of the drum surface cleaning pad can be made as long as possible. However, when the grid electrode is not cleaned, it is necessary to retract the drum surface cleaning pad to the standby position by the movable holding member, and the device is required to secure the arrangement space for the movable holding member and the retracting space for the drum surface cleaning pad. It is easy to increase the size, which is contrary to the recent demand for miniaturization. In addition, the cost tends to be high because the movable holding member is provided. Therefore, a device having a simple structure that can clean both the wire surface and the drum surface of the grid electrode and can maintain the ability to remove the deposits on the drum surface for a relatively long time has been desired, but it is still so. Nothing has been proposed.

The present invention has been made in view of the above problems, and is a charging device having a simple structure capable of cleaning both the wire surface and the drum surface of the grid electrode, and in particular, maintaining the ability to remove deposits on the drum surface for a relatively long time. The purpose is to provide.

The charging device according to the embodiment of the present invention is arranged facing the surface of the photoconductor and has an opening formed on the surface facing the photoconductor, and the housing is arranged in the housing and the photosensitive member is exposed to light. The first of the discharge electrode that charges the surface of the body, the control electrode that is arranged between the photoconductor and the discharge electrode and controls the amount of charge on the surface of the photoconductor, and the control electrode that faces the discharge electrode. A first cleaning member that slides on a surface to clean the first surface, a main body portion that is flexible in the direction toward the second surface of the control electrode facing the photoconductor, and the main body portion are provided. A second cleaning member having a sliding portion that slides on the second surface to clean the second surface, and a moving means for moving the second cleaning member with respect to the control electrode are provided. Eh, the first cleaning member and the second cleaning member are L1 when the amount of penetration of the first cleaning member into the control electrode is L1 and the amount of penetration of the second cleaning member into the control electrode is L2. > It is characterized in that the relationship of L2 is satisfied.

According to the present invention, with respect to the second cleaning member for cleaning the second surface of the control electrode facing the photoconductor, a simple configuration in which a sliding portion sliding on the second surface is provided on the flexible main body portion. Therefore, the ability of the second cleaning member to remove the deposits on the second surface can be maintained for a relatively long time.

The schematic diagram which shows the structure of the image forming apparatus to which the charging apparatus of this embodiment can be applied. The schematic which shows the image formation part. The external perspective view which shows the charging apparatus of this embodiment. The cross-sectional view which shows the charging apparatus of this embodiment. The schematic diagram explaining the grid electrode. It is a side view which shows the charging apparatus of this embodiment, (a) shows the state which the shutter is open, (b) shows the state which the shutter is closed. The control block diagram of the movement control system of a cleaning member. It is a partially enlarged perspective view which shows the pull-in member, (a) shows before pulling in a grid electrode, (b) shows after pulling in a grid electrode. It is a figure explaining the cleaning range of a grid electrode, (a) shows the charging apparatus, (b) shows the charge current distribution flowing through a photosensitive drum. It is a figure which shows the wire surface cleaning brush, (a) is a bottom view seen from the grid electrode side, (b) is a side view. The schematic diagram explaining the penetration amount of the wire surface cleaning brush. The schematic diagram explaining the protrusion amount of the wire surface cleaning brush. The schematic diagram explaining the cleaning of the grid electrode by the wire surface cleaning brush. It is a figure explaining the cleaning mode of the grid electrode by the wire surface cleaning brush and the drum surface cleaning brush, (a) shows the time of an outward trip, and (b) shows the time of a return trip. A partially enlarged perspective view showing a charging device of another embodiment in which a drum surface cleaning brush is arranged on a shutter.

<Image forming device>
The schematic configuration of the image forming apparatus of this embodiment will be described with reference to FIGS. 1 and 2. The image forming apparatus 100 of the present embodiment is an electrophotographic tandem full-color printer. The image forming apparatus 100 has first, second, third, and fourth image forming portions PY, PM, PC, and PK that form yellow, magenta, cyan, and black images, respectively. The image forming apparatus 100 records a toner image according to an image signal from an external device such as a document reading device (not shown) connected to the apparatus main body 100A or a personal computer communicably connected to the apparatus main body 100A. Form to. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

As shown in FIG. 1, the image forming portions PY, PM, PC, and PK are arranged side by side along the moving direction of the intermediate transfer belt 8. The intermediate transfer belt 8 is stretched on a plurality of rollers and is configured to travel in the direction of arrow R2. Then, the intermediate transfer belt 8 carries and conveys the primary transferred toner image as described later. A secondary transfer roller 10 is arranged at a position opposite to the roller 9 on which the intermediate transfer belt 8 is stretched across the intermediate transfer belt 8, and the secondary transfer is to transfer the toner image on the intermediate transfer belt 8 to the recording material. It constitutes a part T2. A fixing device 11 is arranged downstream of the secondary transfer unit T2 in the recording material transport direction.

A cassette 12 containing a recording material is arranged below the image forming apparatus 100. The recording material is conveyed from the cassette 12 toward the registration roller 14 by the transfer roller 13. After that, the registration roller 14 starts rotating in synchronization with the toner image on the intermediate transfer belt 8, so that the recording material is transferred to the secondary transfer unit T2.

The four image forming units PY, PM, PC, and PK included in the image forming apparatus 100 have substantially the same configuration except that the developed colors are different. Therefore, here, the image forming unit PK will be described as a representative, and the description of other image forming units will be omitted.

As shown in FIG. 2, a cylindrical photosensitive drum 1 is arranged as a photoconductor in the image forming portion PK. The photosensitive drum 1 is rotationally driven in the direction of arrow R1. A charging device 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a cleaning device 6 are arranged around the photosensitive drum 1.

The process of forming, for example, a four-color full-color image by the image forming apparatus 100 having the above-described configuration will be described. First, when the image forming operation is started, the surface (photoreceptor surface) of the rotating photosensitive drum 1 is uniformly charged by the charging device 2. The charging device 2 irradiates the charged particles associated with the corona discharge to charge the photosensitive drum 1 to a uniform negative electrode dark potential. The details of the charging device 2 of this embodiment will be described later. Next, the photosensitive drum 1 is scanned and exposed by the laser beam L corresponding to the image signal emitted from the exposure apparatus 3. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum. The electrostatic latent image on the photosensitive drum is visualized by the toner contained in the developing device 4 and becomes a visible image.

The toner image formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 8 by the primary transfer unit T1 configured between the primary transfer rollers 5 arranged with the intermediate transfer belt 8 interposed therebetween. At this time, a primary transfer bias is applied to the primary transfer roller 5. Toner and the like remaining on the surface of the photosensitive drum 1 after the primary transfer are removed by the cleaning device 6.

Such an operation is sequentially performed in each of the image forming portions of yellow, magenta, cyan, and black, and the toner images of four colors are superimposed on the intermediate transfer belt 8. After that, the recording material stored in the cassette 12 is conveyed to the secondary transfer unit T2 at the timing of forming the toner image. Then, by applying the secondary transfer bias to the secondary transfer roller 10, the toner images of the four colors on the intermediate transfer belt 8 are collectively secondarily transferred onto the recording material.

Next, the recording material is conveyed to the fixing device 11. The fixing device 11 heats and pressurizes the recorded material to be conveyed. As a result, the toner on the recording material is melted and mixed, and is fixed to the recording material as a full-color image. After that, the recording material is discharged to the discharge tray 15. In this way, a series of image forming processes is completed.

<Charging device>
The configuration of the charging device 2 of the present embodiment will be described with reference to FIGS. 3 to 5. The charging device 2 of the present embodiment is a corona charging device of a scorotron type, and FIG. 3 shows the charging device 2 viewed from the photosensitive drum side. The charging device 2 is provided so as to be removable from the device main body 100A (see FIG. 1) of the image forming apparatus 100, and faces the photosensitive drum 1 along the rotation axis direction (longitudinal direction) of the photosensitive drum 1 as shown in FIG. It is placed in the position to be. For convenience of illustration, FIG. 3 omits the illustration of the cleaning member 250 described later, and FIG. 4 omits the illustration of the shutter 210 described later.

As shown in FIG. 3, the charging device 2 includes a pair of shield electrodes 203, a front block 201 arranged on the front side in the insertion direction of the charging device 2 (arrow X direction in the figure), and an insertion direction of the charging device 2. It has a back block 202 arranged on the back side of the. The shield electrode 203 is formed in a plate shape using stainless steel (SUS), and is arranged so as to face each other at predetermined intervals (for example, 30 mm) in the width direction (short direction) intersecting the rotation axis direction of the photosensitive drum 1. ing. The shield electrode 203, the front block 201, and the back block 202 form a housing 90 having an opening having a substantially U-shaped cross section. In the front block 201 and the back block 202, a discharge wire 205 (see FIG. 4) described later is stretched in the direction of the rotation axis of the photosensitive drum 1 and holds a grid electrode 206.

<Discharge wire>
As shown in FIG. 4, the charging device 2 has a discharge wire 205 as a discharge electrode and a grid electrode 206 as a control electrode. The discharge wire 205 is arranged inside (inside the housing) of the pair of shield electrodes 203. The discharge wire 205 generates a corona discharge by applying a charging voltage from a high voltage power source (not shown). For the discharge wire 205, for example, stainless steel, nickel, molybdenum, tungsten, or the like is used, and these are formed in a wire shape. As the diameter of the discharge wire 205 becomes smaller, it becomes easier to cut the discharge wire 205 due to the collision of ions generated by the discharge. On the contrary, as the diameter of the discharge wire 205 increases, the charging voltage needs to be higher in order to generate a stable corona discharge. However, if the charging voltage is set too high, ozone is likely to be generated with the discharge. In view of the above points, it is preferable that the discharge wire 205 has a diameter of 40 μm to 100 μm.

<Grid electrode>
The grid electrode 206 is provided between the photosensitive drum 1 and the discharge wire 205 in the opening 90a of the housing 90 so as to be close to the surface of the photosensitive drum 1. The grid electrode 206 can control the amount of current flowing to the photosensitive drum side when a high voltage voltage is applied from a high voltage power source (not shown). Thereby, the amount of charge on the surface of the photosensitive drum 1 is controlled. When the grid electrode 206 is brought closer to the surface of the photosensitive drum, the effect of uniformly charging the surface of the photosensitive drum can be enhanced. In this embodiment, the closest contact distance (GD gap) between the grid electrode 206 and the photosensitive drum 1 is set to "1.3 ± 0.3 mm". The closest contact distance between the grid electrode 206 and the discharge wire 205 was set to 8 mm.

The grid electrode 206 has a so-called etching grid having a mesh-like portion in which a large number of through holes are formed by, for example, etching a thin plate-shaped metal flat plate (thin plate) base material 206c having a thickness of 1 mm or less. Is. In this embodiment, a thin plate made of austenitic stainless steel (SUS304) and having a thickness of about 0.1 mm is used as the base material 206c. In addition, martensitic stainless steel, ferritic stainless steel, or the like may be used as the base material 206c.

The shape of the grid electrode 206 will be described with reference to FIG. In FIG. 5, reference numerals “a to f” are added for convenience in order to explain the shape of the grid electrode 206. The through hole 206a has an opening width of "0.3 ± 0.03 mm" (see reference numeral a in FIG. 5), and the remaining portion of the base material 206c (see FIG. 4) other than the through hole 206a has a width of "0". It is formed so as to be ".07 ± 0.03 mm" (see reference numeral b in FIG. 5). Further, the through hole 206a is formed at an angle of "45 ± 1 °" (see reference numeral c in FIG. 5) with respect to the virtual line extending in the longitudinal direction. The larger the area ratio between the portion of the through hole 206a and the remaining portion other than the through hole 206a, the higher the effect of uniformly charging the surface of the photosensitive drum 1. In the lateral direction of the grid electrode 206, the width is "0.1 ± 0.03 mm" (see FIG. 5) at intervals of "6.9 ± 0.1 mm" (see reference numeral e in FIG. 5) to prevent bending. The beam 206b (see reference numeral d in the inside) is provided in the longitudinal direction. It is preferable to leave the base material 206c having a width of about "1.5 ± 0.1 mm" at both ends of the grid electrode 206 in the width direction (see reference numeral f in FIG. 5). Further, the grid electrode 206 is not limited to being formed in a mesh shape, and may be formed in a honeycomb shape, for example.

The surface of the grid electrode 206 is surface-treated (so-called coating) for the purpose of improving corrosion resistance to form a protective layer having a rust preventive effect. For example, a protective layer of tetrahederal amorphous carbon (ta-C), which is a material having a high degree of chemical inactivity with respect to the discharge product generated by the corona discharge, is formed. Compared with other materials, ta-C is excellent in inertness to air, water and the like at room temperature, corrosion resistance, low wear resistance, self-lubricating property, high hardness and surface smoothness. In addition, ta-C is less likely to undergo chemical adsorption and oxidation reactions, and is less likely to undergo partial deterioration due to wear and scratches. Therefore, it is suitable for use as a protective layer on the surface of the grid electrode.

<Shutter>
Further, as shown in FIG. 3, the charging device 2 has a shutter 210 that can move between the grid electrode 206 and the photosensitive drum 1. The shutter 210 moves in the longitudinal direction between the grid electrode 206 and the photosensitive drum 1, and has an open position in which the opening 90a (see FIG. 4) of the housing 90 is opened and a closed position in which the opening 90a is shielded. It is provided so that it can be moved freely. The shutter 210 is formed in the form of a thin sheet having a thickness of about 100 μm by using a soft flexible non-woven fabric such as rayon fiber. Of course, the shutter 210 is not limited to this, and may be formed by knitting nylon fibers or a film such as urethane or polyester as long as it can be formed into a thin sheet shape. The shutter 210 is formed so that the length in the width direction (short direction) is wider than the distance between the pair of shield electrodes 203 so as to cover the opening 90a of the housing 90.

As shown in FIGS. 6A and 6B, one end of the shutter 210 in the longitudinal direction is connected to the winding mechanism 211, and the shutter 210 is moved in the longitudinal direction by the winding mechanism 211. The take-up mechanism 211 winds up and stores the shutter 210 in a roll shape. As shown in FIG. 6A, when all the shutters 210 are in the position (open position) wound by the winding mechanism 211, the opening 90a (see FIG. 4) of the housing 90 is in the opened state. be. On the contrary, as shown in FIG. 6B, when all the shutters 210 are in the position (closed position) pulled out from the winding mechanism 211, the opening 90a of the housing 90 is in a shielded state. That is, the shutter 210 is moved to one end side (right side of FIG. 6B) of the photosensitive drum 1 to shield the opening 90a of the housing 90, and the other end side (left side of FIG. 6A). The opening 90a of the housing 90 is opened by being moved to.

The take-up mechanism 211 is held in the front block 201 together with the holding case 214 that holds the take-up mechanism 211. A guide roller that guides the shutter 210 so that the shutter 210 does not come into contact with the edge of the grid electrode 206, the holding portion 207, the knob 208, or the like in the vicinity of the shutter pull-out portion of the holding case 214, and the pull-out operation of the shutter 210 is not hindered. 215 is arranged. Here, the holding portion 207 (209) is arranged in the front block 201 and the back block 202, respectively, to hold the grid electrodes 206, and the knob 208 holds the grid electrodes 206 in the holding portions 207 and 209 according to the operation by the user. It is for removing from.

The other end of the shutter 210 on the opposite side of the take-up mechanism 211 is held by the leaf spring 212. The leaf spring 212 can urge the shutter 210 toward the grid electrode side and maintain the shutter 210 in an arch shape in the closed position. The shutter 210 is maintained in the closed position so that the vicinity of the center in the width direction (short direction) is convex toward the grid electrode side, thereby making it difficult for the discharge product to leak to the outside of the housing.

The leaf spring 212 holding the shutter 210 is connected to the carriage 213. The carriage 213 is driven by the rotation of the drive screw 217. The drive screw 217 is rotationally driven by the motor M. As the carriage 213 moves in the closed position direction, the shutter 210 is pulled out from the take-up mechanism 211. On the contrary, as the carriage 213 moves in the open position direction, the shutter 210 is wound by the winding mechanism 211. The leaf spring 212 is formed of, for example, a metal having a thickness of 0.10 mm, and is thin but has sufficient strength to withstand holding the shutter 210.

<Optical sensor>
In order to detect whether the shutter 210 is in the open position or the closed position, the charging device 2 has a first optical sensor PS1 and a second optical sensor PS2. The optical sensors PS1 and PS2 detect the position of the shutter 210, specifically, whether the shutter 210 is wound by the winding mechanism 211 (open position) or not (closed position). In the case of the present embodiment, the optical sensors PS1 and PS2 are arranged at two locations above the axis of the drive screw 217 so that predetermined signals can be output depending on whether the shutter 210 is in the open position or the closed position. There is.

As the optical sensors PS1 and PS2, for example, it is preferable to use a photointerruptor type sensor in which a light emitting unit that irradiates light and a light receiving unit that receives light emitted from the light emitting unit are arranged so as to face each other. In the case of a photointerruptor type sensor, a shielding member 220 is provided on the carriage 213. The shielding member 220 is moved in response to the movement of the carriage 213, that is, the shutter 210. When the shielding member 220 is in a shielding position that shields the optical sensors PS1 and PS2, the optical sensors PS1 and PS2 output a predetermined signal (here, a signal corresponding to the amount of light). On the contrary, when the shielding member 220 is in the non-shielding position where the optical sensors PS1 and PS2 are not shielded, the optical sensors PS1 and PS2 do not output a predetermined signal. In the present embodiment, as shown in FIG. 6A, when a predetermined signal is output from the optical sensor PS1 arranged closer to the winding mechanism 211 side, the shutter 210 is in the open position. On the other hand, as shown in FIG. 6B, when a predetermined signal is output from the optical sensor PS2 arranged far from the winding mechanism 211 side, the shutter 210 is in the closed position.

<Cleaning pad and cleaning material>
Further, the charging device 2 has a cleaning pad 216 for cleaning the discharge wire 205 and a cleaning member 250 for cleaning the grid electrode 206. In the case of the present embodiment, the cleaning pad 216 and the cleaning member 250 are held by the carriage 213. Therefore, the cleaning pad 216 and the cleaning member 250 are reciprocated in the longitudinal direction according to the drive of the motor M, that is, according to the movement between the open position and the closed position of the shutter 210. The cleaning pad 216 is formed by using, for example, a sponge, and cleans the discharge wire 205 by reciprocating with the discharge wire 205 sandwiched from above and below in the direction of gravity. The detailed configuration of the cleaning member 250 will be described later.

Here, the movement control of the cleaning member 250 will be described. In the case of the present embodiment, as described above, since the cleaning member 250 is reciprocated in accordance with the movement of the shutter 210, the cleaning member 250 is substantially moved according to the movement control of the shutter 210. The shutter 210 is moved under the control of the control unit 300 (see FIG. 1). FIG. 7 shows a control block of the movement control system of the cleaning member 250 (substantially the shutter 210) in the control unit 300. As shown in FIG. 7, a memory 301, a motor M, optical sensors PS1, PS2, and the like are connected to the control unit 300. In addition to the illustrations, various devices such as a motor and a power source for operating the image forming apparatus 100 are connected to the control unit 300, but the illustration and description thereof are omitted here because it is not the main purpose of the invention.

The control unit 300 controls various types of the image forming apparatus 100 such as an image forming operation, and has a CPU (Central Processing Unit) (not shown). A memory 301 such as a ROM or RAM as a storage means or a hard disk device is connected to the control unit 300. Various programs, data, and the like for controlling the image forming apparatus 100 are stored in the memory 301. The control unit 300 may execute the image forming job stored in the memory 301 to operate the image forming apparatus 100 so as to perform image forming. In the case of the present embodiment, the control unit 300 can execute the cleaning control for cleaning the grid electrode 206 by operating the cleaning member 250. It should be noted that the memory 301 can temporarily store the calculation processing results and the like accompanying the execution of various control programs.

In the case of the present embodiment, the control unit 300 performs cleaning control for cleaning the grid electrode 206 every time the cumulative number of recording materials measured by the counter 302 reaches a predetermined number of image formations (for example, 6000). At that time, the control unit 300 controls the motor M as the drive means and operates the shutter 210 via the drive screw 217 and the carriage 213 described above to move the cleaning member 250. The movement of the cleaning member 250 with respect to the grid electrode 206 is detected by the optical sensors PS1 and PS2. The control unit 300 can acquire signals output from the optical sensors PS1 and PS2. When the movement of the cleaning member 250 is controlled, the control unit 300 controls the motor M so as to perform the outward path operation until a predetermined signal is output from the optical sensor PS2, and when the predetermined signal is output from the optical sensor PS2, the control unit 300 performs a return path operation. The motor M is reverse-controlled so as to be performed. After the image formation job is executed, the control unit 300 controls to close the shutter 210 when the elapsed time from the end of the image formation job has passed a predetermined time (for example, 2 hours), and enters the sleep mode. Further, when the image forming job is started from the sleep mode, the control unit 300 controls to open the shutter 210 and then starts the image forming.

Further, in the case of the present embodiment, in order to cause the cleaning member 250 to clean the grid electrode 206, the grid electrode 206 is moved (pulled in) from the photosensitive drum side to the discharge wire side before the start of the movement control of the cleaning member 250. That is, before cleaning, the grid electrode 206 stands by at a standby position where it does not come into contact with the cleaning member 250 on the photosensitive drum side. Then, during cleaning, the grid electrode 206 is moved between the standby position and the cleaning position in contact with the cleaning member 250 by the retracting members 252 (see FIG. 5) arranged at both ends in the lateral direction of the carriage 213. It is cleaned by the cleaning member 250.

<Retracting member>
The retracting member 252 will be described with reference to FIGS. 8 (a) and 8 (b). 8 (a) and 8 (b) show the charging device 2 viewed from the photosensitive drum side, and the upper side of the drawing is the direction of gravity. As shown in FIGS. 8A and 8B, the retracting member 252 is provided so as to project inward from the carriage 213 with respect to the shield electrode 203. The retracting member 252 extends in the moving direction of the carriage 213 and has a tapered portion 252a and a rubbing portion 252b. The tapered portion 252a is an inclined surface formed so as to approach the photosensitive drum side as it advances in the insertion direction (arrow X direction in the figure) of the charging device 2. On the other hand, the rubbing portion 252b is a horizontal plane formed on the front block 201 side of the tapered portion 252a.

As shown in FIG. 8A, the retracting member 252 moves in the direction of arrow X in the figure as the carriage 213 moves in the closed position direction. In response to the movement of the retracting member 252, the grid electrode 206 is moved along the tapered portion 252a so as to be pushed up toward the photosensitive drum side in the direction opposite to the direction of gravity (upper side in the drawing). The grid electrode 206 pushed up against gravity by the tapered portion 252a is locally deformed. Then, as shown in FIG. 8B, when the grid electrode 206 proceeds to the rubbing portion 252b, the grid electrode 206 receives a force F that is displaced toward the discharge wire side (lower side in the drawing) by the rubbing portion 252b and is in a displaced state. Retained. That is, the grid electrode 206 is pressed from the photosensitive drum side to the discharge wire side according to the movement of the carriage 213. As described above, since the cleaning member 250 is held by the carriage 213, the cleaning member 250 moves in the same manner as the carriage 213 moves. At that time, the cleaning member 250 is moved while contacting the grid electrode 206 pressed from the photosensitive drum side to the discharge wire side, and cleans the grid electrode 206.

As described above, since the pull-in member 252 is moved by rubbing against the grid electrode 206, the grid electrode 206 may be locally worn as the number of cleanings by the cleaning member 250 increases. FIG. 5 above shows the location of the grid electrode 206 that is worn by rubbing against the retracting member 252. The portion g of the grid electrode 206 shown in FIG. 5 is a portion that rubs against the retracting member 252. The portion h of the grid electrode 206 is a portion that does not rub against the retracting member 252. As shown in FIG. 5, the retracting member 252 is provided so as not to come into contact with the mesh portion of the grid electrode 206. This is because the remaining portion of the base material 206c (see FIG. 4) other than the through hole 206a in the mesh portion is thin and can be cut when rubbed by the pull-in member 252.

Next, the cleaning range of the grid electrode 206 by the cleaning member 250 will be described with reference to FIG. The reference numeral “G” shown in FIG. 9A indicates the distance between the discharge wire 205 and the shield electrode 203, and the reference numeral “H” indicates the distance between the discharge wire 205 and the grid electrode 206. Further, the reference numeral "R" shown in FIG. 9B indicates a range in which a current of half value or more flows with respect to the peak value of the charging current (Id) flowing on the photosensitive drum side. Further, the reference numeral "P" indicates the center of the grid electrode 206 in the width direction. Here, the range indicated by the reference numeral “R” indicates the range of ± (R / 2) with respect to the straight line connecting the discharge wire 205 and the center “O” of the photosensitive drum 1. The range represented by the reference numeral "R" is a range determined by the following equation 1.
R ² = G ² + H ² ... Equation 1

Then, as shown in FIG. 9B, the peak value of the charging current (Id) flowing through the photosensitive drum 1 becomes the largest immediately below (P) the discharge wire 205. In the case of the present embodiment, the cleaning range of the grid electrode 206 by the cleaning member 250 is the average of the squares of the interval “G” of the shield electrodes 203 and the interval “H” of the grid electrodes 206, as shown in the above equation 1. It has been set. This is because the larger the charging current (Id) flowing on the photosensitive drum side, the easier it is for deposits to adhere to the grid electrode 206. When the discharge wire 205 is arranged on either side of the shield electrode 203, the distance from the shield electrode 203 having a narrower distance from the discharge wire 205 is calculated as the above-mentioned distance "G". Is desirable.

The configuration of the cleaning member 250 will be described in detail. As shown in FIG. 4, the cleaning member 250 of the present embodiment has a wire surface cleaning brush 500 as a first cleaning member and a drum surface cleaning brush 600 as a second cleaning member. The wire surface cleaning brush 500 and the drum surface cleaning brush 600 each clean the front and back surfaces of the grid electrode 206. That is, the wire surface cleaning brush 500 slides on the surface (first surface, referred to as the wire surface) of the grid electrode 206 facing the discharge wire 205 to clean the wire surface. On the other hand, the drum surface cleaning brush 600 slides on the surface (second surface, referred to as a drum surface) of the grid electrode 206 facing the photosensitive drum 1 to clean the drum surface.

<Wire surface cleaning brush>
First, the wire surface cleaning brush 500 will be described with reference to FIGS. 10A to 13. As shown in FIGS. 10A and 10B, the wire surface cleaning brush 500 is a flame-retardant resin brush woven into a base cloth, and is composed of a brush portion 501 and a base cloth portion 502. Has been done. The brush portion 501 has a free length "L10" and is formed so as to cover the region (see FIG. 9B) indicated by the above-mentioned reference numeral "R" in the width direction of the grid electrode 206. In the case of the present embodiment, the brush portion 501 is ^{woven with a thickness of 11 decitex acrylic piles at a density of 60,000 / inch 2 so} that the free length “L10” is 3.0 mm. Was used. The brush portion 501 may use a resin brush such as nylon (registered trademark), polyvinyl chloride (PVC), or polyphenylene sulfide resin (PPS). The size of such a wire surface cleaning brush 500 is, for example, a width direction length of 21 mm and a length direction length of 5 mm. The brush portion 501 is formed so that the margin portion indicated by the reference numeral “Δg” is, for example, 1 mm.

As shown in FIG. 11, in the case of the present embodiment, the amount of penetration of the brush portion 501 into the grid electrode 206 (ΔX in the figure) in a stationary state in which the wire surface cleaning brush 500 is not sliding on the grid electrode 206 is, for example. It is set to 0.8 mm.

As shown in FIG. 12, when the wire surface cleaning brush 500 moves in the longitudinal direction and slides on the grid electrode 206, the brush portion 501 cleans the wire surface of the grid electrode 206 and the through hole 206a. It is divided into what you do. The “deflection amount” of the grid electrode 206 described in FIG. 12 indicates the amount by which the brush portion 501 cleaning the wire surface presses the grid electrode 206. In the case of this embodiment, the amount of deflection of the grid electrode 206 is suppressed to about 0.1 mm. Further, the protrusion amount (ΔL in the figure) of the brush portion 501 with respect to the grid electrode 206 in the operating state in which the wire surface cleaning brush 500 is sliding on the grid electrode 206 is set to, for example, 0.4 to 0.6 mm. .. The “protruding amount ΔL” is the length at which the brush portion 501 cleaning the through hole 206a protrudes from the grid electrode 206 toward the photosensitive drum.

FIG. 13 shows how the brush portion 501 having a free length “L10” comes into contact with the through hole 206a for cleaning. The cleaning force of the through hole 206a by the brush portion 501 is proportional to the distance that the brush portion 501 moves in contact with the through hole 206a. From this, if the "protrusion amount ΔL" (see FIG. 12) is increased, the contact movement distance between the brush portion 501 and the through hole 206a can be increased, so that the cleaning force of the through hole 206a by the brush portion 501 can be increased. Can be done. Further, the value of this "protrusion amount ΔL" is determined by the free length "L10" of the brush portion 501 and the penetration amount of the brush portion 501 into the grid electrode 206 (ΔX in FIG. 11). In the present embodiment, the amount of protrusion of the grid electrode 206 in the cleaning range (R region of FIG. 9B) is 0.4 to 0.6 mm described above, and the amount of protrusion at both ends in the other width directions is 0 to 0. It was set to 0.2 mm. That is, the cleaning power of the R region where the deposits are likely to adhere is higher than that of both ends in the width direction where the deposits are hard to adhere. It is preferable that the free length "L10" of the brush portion 501 and the penetration amount of the brush portion 501 into the grid electrode 206 (ΔX in FIG. 11) are set so as to be so.

Here, in order to clean both the wire surface of the grid electrode 206 and the through hole 206a, the protrusion amount ΔL (see FIG. 12) needs to be 0 mm or more. More preferably, it is desirable to set the protrusion amount ΔL to 0.1 mm or more in consideration of the plate thickness and the amount of bending of the grid electrode 206. Further, it is desirable to set the protrusion amount ΔL to be equal to the length J in the longitudinal direction of the through hole 206a shown in FIG. For example, when the formation angle of the through hole 206a is 45 degrees and the length J of the through hole 206a in the longitudinal direction is 0.3 mm, the protrusion amount ΔL is set to 0.4 mm or more. The upper limit of the protrusion amount ΔL is smaller than the distance (GD gap) between the grid electrode 206 and the photosensitive drum 1 so that the behavior of the brush portion 501 does not change due to contact with the photosensitive drum 1 when the grid electrode 206 is cleaned. It is desirable to do. By doing so, it becomes possible to suitably clean both the wire surface and the through hole 206a of the grid electrode 206 while suppressing the amount of bending of the grid electrode 206.

<Drum surface cleaning brush>
Next, the drum surface cleaning brush 600 will be described. As shown in FIG. 4, the drum surface cleaning brush 600 has a main body portion 601 and a sliding brush portion 602 as a sliding portion. The main body portion 601 is a leaf spring formed of, for example, stainless steel (SUS) having a thickness of 100 μm, and has flexibility in the direction toward the drum surface of the grid electrode 206. The sliding brush portion 602 is provided on the main body portion 601 using, for example, a flocked sheet in which a flame-retardant resin brush having a free length of 1.5 mm is flocked. The sliding brush portion 602 is formed so as to be in contact with the grid electrode 206 in the R region (predetermined region including directly under the discharge wire 205) shown in FIG. 9B. The sliding brush portion 602 is brought into contact with the grid electrode 206 by the main body portion 601. As the sliding brush portion 602, a flame-retardant treatment of acrylic, nylon (registered trademark), PVC (polyvinyl chloride), PPS (polyphenylene sulfide resin) or the like may be used. Further, the sliding brush portion 602 is not limited to the brush, and may be a sponge, rubber, or a resin sheet.

When the inventors conducted experiments by changing the contact area ratio between the drum surface and the wire surface with respect to the grid electrode 206, the relationship was "contact area ratio of the drum surface (S2)> contact area ratio of the wire surface (S1)". It was found that the grid electrode 206 was well cleaned. In the present embodiment, the contact area ratio (S2) of the drum surface cleaning brush 600 with respect to the grid electrode 206 is larger than the contact area ratio (S1) of the wire surface cleaning brush 500 with respect to the grid electrode 206. That is, in the case of the present embodiment, since the cleaning member for cleaning the wire surface is required to remove (remove) the deposits adhering to the wire surface as the main purpose, the wire surface cleaning brush 500 is used. Has been done. However, in this case, the deposits adhering to the wire surface cannot be removed and may be moved to the drum surface side through the through hole 206a. Therefore, in the cleaning member for cleaning the drum surface, in addition to removing the deposits adhering to the drum surface, the deposits that have moved from the wire surface to the drum surface can be removed by the wire surface cleaning brush 500. It is required to move. Therefore, as a cleaning member for cleaning the drum surface, an electrostatically transplanted drum surface cleaning brush 600, a sponge, high-density rubber, or the like is used. Therefore, the contact area ratio between the drum surface and the wire surface with respect to the grid electrode 206 is larger in the cleaning member for cleaning the drum surface than in the cleaning member for cleaning the wire surface. For the contact area ratio, a transparent glass plate that imitates the grid shape at the time of cleaning is prepared, and the cleaning member that cleans the wire surface and the cleaning member that cleans the drum surface with the above-mentioned intrusion amount are applied to the transparent glass plate. It is the contact area per unit area calculated by taking a picture of the contact state with a camera.

Further, in the present embodiment, the amount of penetration of the drum surface cleaning brush 600 (specifically, the sliding brush portion 602) into the grid electrode 206 is set to 0.3 mm. This is smaller than the penetration amount “0.8 mm” of the wire surface cleaning brush 500 (specifically, the brush portion 501) into the grid electrode 206. The inventors conducted experiments in which the penetration amounts of the drum surface cleaning brush 600 and the wire surface cleaning brush 500 were changed in the range of 0.05 to 3.0 mm, respectively. From the experimental results, it was found that the grid electrode 206 was satisfactorily cleaned when the relationship of "the amount of penetration of the wire surface cleaning brush 500 (L1)> the amount of penetration of the drum surface cleaning brush 600 (L2)" was established. Therefore, in the present embodiment, the penetration amount of the wire surface cleaning brush 500 is set to 0.8 mm and the penetration amount of the drum surface cleaning brush 600 is set to 0.3 mm as described above.

However, since the sliding brush portion 602 of the drum surface cleaning brush 600 is worn by repeatedly performing the cleaning operation, the free length of the sliding brush portion 602 is reduced. In that case, it becomes difficult to maintain the relationship between the contact area ratio and the intrusion amount described above. Therefore, as described above, the sliding brush portion 602 is provided on the flexible main body portion 601 and the sliding brush portion 602 is pressed against the drum surface side of the grid electrode 206 to obtain the sliding brush portion 602. Even if the free length is reduced, the deposits can be cleaned well.

Further, in the present embodiment, the wire surface cleaning brush 500 and the drum surface cleaning brush 600 are provided on the cleaning member 250 so as to slide with respect to the grid electrode 206 at different positions in the longitudinal direction. That is, during the cleaning operation of the cleaning member 250, the sliding brush portion 602 of the drum surface cleaning brush 600 moves with respect to the moving direction of the grid electrode 206 at a position different from the sliding position of the wire surface by the brush portion 501 of the wire surface cleaning brush 500. It is designed to slide on the drum surface. By doing so, the cleanability of the deposits adhering to the grid electrode 206 is improved. This point will be described with reference to FIGS. 14 (a) and 14 (b).

FIG. 14A shows a mode of cleaning the grid electrode 206 by the wire surface cleaning brush 500 and the drum surface cleaning brush 600 when the shutter 210 moves from the open position to the closed position. As shown in FIG. 14A, on the outward trip, the sliding brush portion 602 of the drum surface cleaning brush 600 is on the upstream side in the moving direction from the sliding position of the grid electrode 206 by the brush portion 501 of the wire surface cleaning brush 500. Slides on the grid electrode 206. In other words, the brush portion 501 of the wire surface cleaning brush 500 cleans the grid electrode 206 before the sliding brush portion 602 of the drum surface cleaning brush 600. In this case, the brush portion 501 moves the deposits adhering to the wire surface to the drum surface side through the through hole 206a (see FIG. 11). After that, the sliding brush portion 602 cleans the deposits moved to the drum surface side and the deposits originally adhered to the drum surface together. At this time, the deposit is made to fall on the shutter 210 so that the deposit does not fall on the photosensitive drum and adhere. As described above, by cleaning the wire surface having a relatively large amount of deposits first and then cleaning the drum surface, the cleanability of the deposits adhering to the grid electrode 206 is improved.

FIG. 14B shows a mode of cleaning the grid electrode 206 by the wire surface cleaning brush 500 and the drum surface cleaning brush 600 during the return route in which the shutter 210 moves from the closed position to the open position. As shown in FIG. 14B, on the return trip, the sliding brush portion 602 of the drum surface cleaning brush 600 is on the downstream side in the moving direction from the sliding position of the grid electrode 206 by the brush portion 501 of the wire surface cleaning brush 500. Slides on the grid electrode 206. The grid electrode 206 is almost cleaned during the above-mentioned outward route, but if any deposits remain, the sliding brush portion 602 of the drum surface cleaning brush 600 first cleans the grid electrode 206. In this case, the sliding brush portion 602 moves the deposits adhering to the drum surface to the wire surface side through the through hole 206a (see FIG. 11). After that, the brush portion 501 cleans the deposits that have been moved to the wire surface side. At this time, deposits may fall on the photosensitive drum, but most of the deposits are cleaned on the outward trip, and in this case, very few deposits fall on the photosensitive drum, and most of them are rotating photosensitive drums. Since it is flown by the air flow of the drum 1, it is difficult to adhere to the photosensitive drum 1.

As described above, in the present embodiment, the wire surface cleaning brush 500 can be used to clean the wire surface, and the drum surface cleaning brush 600 can be used to clean both sides of the grid electrode 206 on the drum surface. Regarding the drum surface cleaning brush 600, the sliding brush portion 602 is provided on the flexible main body portion 601 and the sliding brush portion 602 is pressed against the drum surface side of the grid electrode 206. With a simple configuration that can clean both sides of the grid electrode 206 while preventing the size of such a device from becoming large, even if the sliding brush portion 602 is worn, the ability to remove deposits on the drum surface is maintained for a relatively long time. Can be done.

<Other embodiments>
In the above-described embodiment, an example is shown in which the wire surface cleaning brush 500 and the drum surface cleaning brush 600 are integrally provided as the cleaning member 250, but the present invention is not limited to this, and the drum surface cleaning brush 600 is used as the shutter 210. It may be arranged. The charging device 2 in such a case is shown in FIG. The cleaning member 250 shown in FIG. 15 is different from FIG. 8 in that the drum surface cleaning brush 600 is arranged on the shutter 210, and other configurations and operations are the same as those of the above-described embodiment. Have the same reference numerals and the description thereof will be omitted.

As shown in FIG. 15, in the present embodiment, the leaf spring 212 holding the other end of the shutter 210 is used as the main body portion described above, and the sliding brush portion 602 described above is attached to the leaf spring 212 to form a drum surface. The cleaning brush 600 is arranged on the shutter 210. In such a case, the sliding brush portion 602 of the drum surface cleaning brush 600 can be firmly slid on the grid electrode 206 while the shutter 210 is not brought into contact with the photosensitive drum 1. Further, since the leaf spring 212 is also used as the main body portion, it is possible to prevent an increase in cost due to the addition of parts.

1 ... Photoreceptor (photosensitive drum), 2 ... Charging device, 90 ... Housing, 205 ... Discharge electrode (discharge wire), 206 ... Control electrode (grid electrode), 210 ... Shutter, 500 ... First cleaning member (wire surface) Cleaning brush), 600 ... Second cleaning member (drum surface cleaning brush), 601 ... Main body, 602 ... Sliding part (sliding brush part), M ... Moving means (motor)

Claims (5)

A housing arranged facing the surface of the photoconductor and having an opening formed on the surface facing the photoconductor, and a housing.
A discharge electrode arranged in the housing and charging the surface of the photoconductor, and
A control electrode arranged between the photoconductor and the discharge electrode and controlling the amount of charge on the surface of the photoconductor,
A first cleaning member that slides on the first surface of the control electrode facing the discharge electrode to clean the first surface, and
A main body portion having flexibility in the direction toward the second surface of the control electrode facing the photoconductor, and a slide provided on the main body portion and sliding on the second surface to clean the second surface. A second cleaning member with a moving part,
E Bei and a moving means for moving the second cleaning member to said control electrode,
When the amount of penetration of the first cleaning member into the control electrode is L1 and the amount of penetration of the second cleaning member into the control electrode of the first cleaning member and the second cleaning member is L2.
Satisfy the relationship L1> L2,
A charging device characterized by that. The first cleaning member and the second cleaning member have a contact area ratio of S1 per unit area of the first cleaning member with respect to the first surface, and contact of the second cleaning member with respect to the second surface per unit area. When the area ratio is S2,
Satisfy the relationship S2> S1
The charging device according to claim 1. A shutter that can be moved between an open position where the opening is opened and a closed position where the opening is shielded is provided.
In the second cleaning member, when the shutter is moved from the open position to the closed position, the sliding portion is on the upstream side in the moving direction from the sliding position of the control electrode by the first cleaning member. Sliding on the control electrode,
The charging device according to claim 1 or 2 , wherein the charging device is characterized by the above. The shutter, the first cleaning member, and the second cleaning member are moved together by the moving means.
The charging device according to claim 3 , wherein the charging device is characterized by the above. The second cleaning member is arranged on the shutter and
The moving means moves the second cleaning member by moving the shutter.
The charging device according to claim 3 or 4.

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