JP2010113144A - Charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clean a grid electrode 13 with a cleaning brush 22 because if the corona charging is performed in a state where toner is attached to a grid electrode 13 of a corona charger 2, the charge amount of the toner is increased and electrostatic adhesion is increased. Even if it is processed, it cannot be removed properly.
A conductive brush is used as a cleaning brush so that a cleaning process is performed while discharging toner adhering to a grid electrode.
[Selection] Figure 3

Description

  The present invention relates to a charging device that charges a member to be charged using a corona charger. This charging device is used in, for example, an electrophotographic image forming apparatus such as a copying machine, a printer, a FAX, and a multifunction machine having a plurality of these functions.

  In a conventional electrophotographic image forming apparatus, in a charging process, which is one of the electrophotographic processes, a process of uniformly charging a photosensitive member, which is an object to be charged, with a corona charger is performed.

  In the configuration in which the charging process is performed using the corona charger, foreign matter (attachment) such as dust or scattered toner floating in the apparatus is structurally attached to the grid electrode.

  If foreign matter adheres to the grid electrode in this way, the discharge efficiency at the site where the foreign matter has adhered decreases, causing unevenness in the charging potential of the photoconductor, causing unevenness in the density of the output image. End up.

In view of this, the apparatuses described in Patent Documents 1 to 3 employ a configuration in which a cleaning mechanism for the grid electrode using a cleaning pad or a cleaning brush is provided, and the foreign matter attached to the grid electrode of the corona charger is cleaned by this cleaning mechanism. ing.
Japanese Patent Laid-Open No. 06-43735 Japanese Patent Laid-Open No. 06-208283 JP 2005-338797 A

  However, the apparatuses described in Patent Documents 1 to 3 cannot properly remove foreign matters attached to the grid electrode.

  This is thought to be due to the fact that insulating foreign matter such as toner adhering to the grid electrode is subjected to corona discharge, increasing the amount of charge and increasing the electrostatic adhesion of the foreign matter to the grid electrode. It is done.

  This electrostatic adhesion force (referred to as mirror power) increases as the time of corona discharge increases, and can be expressed by electrostatic force with the mirror image charge generated on the grid electrode. It is proportional to the square.

  In order to remove the foreign substances that are firmly attached in this way from the grid electrode, a countermeasure can be considered such as increasing the cleaning capability of the cleaning mechanism, for example, pressing the cleaning brush strongly against the grid electrode.

  However, in such a countermeasure, on the contrary, the foreign matter is rubbed firmly against the grid electrode, which has an adverse effect. As a result, foreign matters are fused to the grid electrodes, causing unevenness in the charged potential of the photosensitive member, which causes unevenness in the density of the output image.

  Accordingly, an object of the present invention is to provide a charging device that can appropriately remove deposits attached to the grid electrode of a corona charger.

  Other objects of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings.

The present invention relates to a charging device having a corona charger for charging an object to be charged and a cleaning mechanism for cleaning a grid electrode of the corona charger.
The cleaning mechanism has a conductive member that performs a cleaning process while removing charges attached to the grid electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the deposit | attachment adhering to the grid electrode of a corona charger can be removed appropriately.

  Hereinafter, a charging device according to the present invention will be described in detail with reference to the drawings by taking an image forming apparatus equipped with the charging device as an example.

  FIG. 1 is a schematic side view of an electrophotographic image forming apparatus. First, the overall configuration of the image forming unit of the image forming apparatus will be described, and then the charging device will be described in detail.

(Image forming part)
As shown in FIG. 1, an electrophotographic photosensitive member (hereinafter referred to as a photosensitive member) 1 as a member to be charged is installed so as to be rotatable in the direction of an arrow.

  Around the photosensitive member 1, a charging device (corona charger) 2, an image exposure device 7, a developing device 3, a transfer device 4, a cleaning device 5, and a light neutralizing device 6 are arranged along the rotation direction of the photosensitive member 1. They are installed in order.

  In such an image forming unit, a toner image can be formed on a sheet P which is a recording paper by an electrophotographic process.

  Specifically, the charging device 2 uniformly charges the surface of the photoreceptor 1 to the negative polarity. Then, the surface of the photoreceptor 1 is irradiated with laser light L corresponding to the image signal from the image exposure device 7. As a result, the potential of the portion irradiated with light on the photosensitive member 1 is attenuated, and an electrostatic latent image corresponding to the image signal is formed. Next, a toner image corresponding to the electrostatic latent image is formed on the electrostatic latent image formed on the photosensitive member 1 by attaching a negatively charged toner to the developing device 3. The toner image formed on the photoreceptor 1 is electrostatically transferred to the sheet P by the transfer device 4. Thereafter, the toner image transferred onto the sheet P is fixed by a fixing device (not shown) and discharged outside the apparatus.

  The transfer residual toner remaining on the photoreceptor 1 is scraped off by the cleaning device 5 and collected by the cleaning device 5. Thereafter, the potential history remaining on the photoconductor 1 is erased by the photostatic device 6 and used for the next image formation.

(Charging device)
Next, the charging device will be described with reference to FIGS. 2 is a cross-sectional view of the charging device 2 viewed from the long side (front side), and FIG. 3 is a cross-sectional view of the charging device 2 viewed from the short side (side surface).

  In this example, as shown in FIGS. 2 and 3, a corona charger is used as the charging device 2. The corona charger 2 includes a U-shaped shield case 10 (hereinafter referred to as a shield) having insulating support portions 11 at both ends, and a discharge as a discharge electrode stretched along the longitudinal direction inside the shield 10. A wire (also referred to as a wire electrode) 12 is provided. Further, a grid electrode 13 is provided in the opening of the shield 10 facing the photoreceptor 1.

  In this example, a tungsten wire having a diameter φ of 60 μm is used as the discharge wire 12, and this tungsten wire is stretched over a wire holding portion 9 provided on the insulating support portion 11 via a spring. Further, a power source S1 is connected to the discharge wire 12, and a DC voltage is applied when the photosensitive member is charged. At this time, the direct current voltage (DC voltage) applied to the discharge wire 12 is controlled so that the discharge current becomes −800 μA (constant current control).

  In this example, SUS304 having a thickness of 0.1 mm is used as the grid electrode 13, and a large number of openings are formed in the SUS304 by an etching process. The distance between the grid electrode 13 and the photosensitive member at the closest position is 1.0 mm. Furthermore, the surface of the grid electrode 13 is subjected to nickel plating so as to have a thickness of 1 μm as a rust prevention treatment.

  From the above configuration, the charging process range by the corona charger 2 is a region W1 corresponding to the installation range of the grid electrode 13. In other words, the shield opening described above is provided in a range corresponding to the region W1.

  The grid electrode 13 is connected to a power source S2, and a DC voltage of −400 to −900 V is applied when the photosensitive member is charged. This is to stabilize the amount of ions traveling from the discharge wire 12 to the photoconductor, and as a result, the photoconductor can be charged to a desired potential (in this example, −600 V).

  As will be described later, when the grid electrode 13 is cleaned, the switch 190 as the switching means shown in FIGS. 3, 5, and 6 is grounded (0 V) as the charging voltage from the power source S2 is stopped. Is switched to.

(Charging device cleaning mechanism)
The charging device 2 of this example is provided with a cleaning device for cleaning the discharge wire 12 and the grid electrode 13 respectively.

(Discharging wire cleaning mechanism)
The cleaning mechanism for cleaning the discharge wire 12 is provided with a discharge wire cleaning member 15 as shown in FIG. As shown in FIG. 2, the discharge wire cleaning member 15 has a pair of sponge pads 15, which are disposed so as to press the discharge wire 12 from both sides. Polishing paper or the like may be attached to the sliding surface of the pair of sponge pads with the discharge wire 12.

  Further, the discharge wire cleaning member 15 is configured to reciprocate in the direction b of FIG. 3 (a direction substantially parallel to the stretching direction of the discharge wire 12) by a moving mechanism.

  Specifically, the discharge wire cleaning member 15 is held by a holder 16, and the holder 16 is engaged with a screw shaft 17 disposed on the side opposite to the side facing the photosensitive member of the corona charger 2. .

  The screw shaft 17 is a so-called screw shaft in which a spiral groove is formed on the circumferential surface in the longitudinal direction. Further, the screw shaft 17 is held by a bearing 18 included in the insulating support portion 11, and is configured to be rotationally driven in the a direction by a motor M1 having a drive connection relationship.

  As a result, the holder 16 can reciprocate in the direction of the arrow b as the screw shaft 17 rotates. Specifically, the holder 16 moves forward by rotating the screw shaft 17 in the forward direction, while the holder 16 returns by rotating the screw shaft 17 in the direction opposite to the forward direction.

  Such a reciprocating operation is performed by controlling the motor M1 by the DC controller 32 shown in FIG. 6, and is controlled so that the moving speed of the discharge wire cleaning member 15 is 35 (mm / sec).

  FIGS. 4 and 5 show a state in which the discharge wire cleaning member 15 is in the retracted position outside the charging processing range W1, and the discharge is performed when the charging process is performed on the photoconductor to form a normal image. The wire cleaning member 15 is located at this retracted position. This retracted position becomes the home position of the discharge wire cleaning member 15 (hereinafter referred to as home position H (FIG. 5)).

  That is, as described above, when the cleaning process by the discharge wire cleaning member 15 is performed, the discharge wire cleaning member 15 is moved from the home position H to the reverse position to the right (in FIG. 3) of the charging process range W1. Let When the discharge wire cleaning member 15 reaches the reversal position, the DC controller 32 reverses the rotation direction of the screw shaft 17 to reverse the movement direction of the discharge wire cleaning member 15 and move it to the home position H.

  The timing for reversing the rotation direction of the motor M1 and the timing for stopping the motor M1 are controlled by the CPU 31 based on the operation time for driving (turning on) the motor M1. In addition, it is the structure which controls a motor M1 by installing a position detection sensor in the site | part corresponded to an inversion position and a retracted position (home position), and installing the detection flag detected by a position detection sensor in the holder 16. It does not matter. That is, the CPU 31 may control the timing for reversing the rotation direction of the motor M1 and the timing for stopping the motor M1 based on the output of the position detection sensor.

  By performing such a series of reciprocating operations, the cleaning process by the discharge wire cleaning member 15 is completed.

(Grid electrode cleaning mechanism)
As shown in FIGS. 2 and 3, a grid electrode cleaning member 14 is provided in the cleaning mechanism that cleans and removes foreign matters (attachments) attached to the inner surface of the grid electrode 13.

  The grid electrode cleaning member 14 is provided with a cleaning brush 22 as a conductive member (cleaning member) for removing friction while removing the foreign matter adhering to the grid electrode 13.

  Specifically, the grid electrode cleaning member 14 is obtained by attaching a base cloth 24 to which a conductive cleaning brush 22 is attached to a brush base 23, and a holder via an elastic member 19 which is a leaf spring. 16 is integrated. Further, as will be described later, the grid electrode cleaning member 14 is also electrically grounded since it also has a function of removing charges from foreign substances.

  And the conductive cleaning brush 22 is attached to the holder 16 so that the hair tip contacts the inner surface (surface on the discharge wire 12 side) of the grid electrode 13.

  In this example, the bristle length of the conductive brush 22 is set to 2.5 mm, and the amount of penetration of the cleaning brush 22 into the grid electrode 13 is set to 0.3 mm. If the amount of penetration of the cleaning brush 22 into the grid electrode 13 is too small, the cleaning processing capability is lowered, and if it is too large, the brush falls easily and the cleaning processing capability cannot be maintained. Therefore, it is desirable to optimize the penetration amount according to the characteristics of the selected brush (hair, fiber).

  In this example, conductive acrylic fibers are used as the brushes (hairs, fibers) constituting the cleaning brush 22. This acrylic fiber is made into a conductor with copper ions using a dyeing method. The brush has a flocking density of 200 denier / 80 filaments and a density of 150 per square millimeter.

  As a material for the brush, conductive rayon fiber, PVA fiber, amorphous fiber, or the like may be used. It should be noted that if hair breakage or the like occurs during the cleaning process, it causes a charging failure, so that the fiber desirably has sufficient tensile strength. In order to enhance the cleaning effect, the brush density is preferably set to 120 or more per square millimeter. This is because if the amount is less than this, a foreign object slips out due to insufficient brush contact during the cleaning process.

In addition, the electrical resistance of the cleaning brush 22 is an important factor for exerting the charge removal effect of the cleaning brush 22 during the cleaning process. The electrical resistance value of the cleaning brush 22 used in this example is 1 × 10 ¹ Ω.

  The electrical resistance value was measured under the conditions of an atmospheric temperature of 22.5 ° C. and a relative humidity of 55%. Specifically, from a current flowing when a voltage of 100 V is applied to a metal drum (in this example, made of aluminum) having a diameter φ of 30 mm, a 5 mm × 10 mm base fabric with a brush attached is brought into contact therewith. It is converted. The amount of penetration of the brush into the drum is 0.3 mm.

In this example, since the cleaning process is performed by rubbing the grid electrode while removing the foreign matter adhering to the grid electrode, it is more preferable to use a cleaning brush having a low electrical resistance value. Specifically, as described later, it is preferable to use one having an electric resistance value of 1 × 10 ⁵ Ω or less.

  Further, metal projections (guided portions) 20 are respectively provided on both side surfaces of the brush base 23 facing the shield 10, and these projections 20 are guided by guide rails 21 formed on the shield 10. It has a structure. The brush base fabric 24 is in contact with the metal protrusion 20. With such a configuration, the cleaning brush 22 is electrically connected to the shield 10 that is electrically grounded during the cleaning process. That is, the cleaning brush 22 is configured to be electrically grounded via the shield 10.

  As described above, since the grid electrode cleaning member 14 is attached to the holder 16 similarly to the discharge wire cleaning member 15, the grid electrode cleaning member 14 reciprocates in the direction b of FIG. 3 together with the discharge wire cleaning member 15 by the moving mechanism. It is configured.

  That is, the grid electrode cleaning member 14 reciprocates with the discharge wire cleaning member 15 by reciprocating the holder 16 along the longitudinal direction of the corona charger as the screw shaft 17 is rotated by the motor M1. ing.

  Therefore, when performing the cleaning process by the grid electrode cleaning member 14, the grid electrode cleaning member 15 is moved together with the discharge wire cleaning member 15 from the home position H (FIG. 5) to the reverse position to the right of the charging process range W1. When the grid electrode cleaning member 14 together with the discharge wire cleaning member 15 reaches the reverse position, the DC controller 32 reverses the rotation direction of the screw shaft 17 and reverses the movement direction of the grid electrode cleaning member 14 together with the discharge wire cleaning member 15. Let As a result, the grid electrode cleaning member 14 returns to the home position H together with the discharge wire cleaning member 15, and the cleaning process by the grid electrode cleaning member 14 is completed.

  Thus, the cleaning process by the grid electrode cleaning member 14 is performed simultaneously with the cleaning process by the discharge wire cleaning member 15.

(Insulation mechanism of cleaning brush)
In this example, since the grid electrode 13 is cleaned with the cleaning brush 22, the grid electrode 13 and the cleaning brush 22 to which a high voltage charging bias is applied are electrically connected during normal charging processing. Is insulative. Specifically, in this example, an insulating mechanism that causes the conductive brush 22 to be separated from the grid electrode 13 is employed.

  Specifically, as shown in FIG. 5, at the home position H, the guide rail 21 is disposed so as to be away from the grid electrode 13 side. Therefore, as the grid electrode cleaning member 14 reaches the home position H, the elastic member 19 contracts, so that the cleaning brush 22 is separated from the grid electrode 13. In addition, since the insulating support portion 11 includes an insulator including the guide rail 21, the cleaning brush 22 of the grid electrode cleaning member 14 is electrically insulated from the grid electrode 13.

  In addition, when the structure which separates the cleaning brush 22 from the grid electrode 13 is employ | adopted like this example, there also exists an advantage that it can prevent that the gap between the grid electrode 13 and the photoreceptor 1 fluctuates. This is because if the cleaning brush 22 remains in contact with the grid electrode 13 at the home position H, the grid electrode 13 tends to be pressed toward the photoreceptor 1 by the cleaning brush 22 and approach the photoreceptor 1. .

  When such a gap fluctuation occurs, the charged potential of the photoconductor cannot be set to a desired potential in the vicinity of the home position H, leading to a charging failure.

(Charging device cleaning sequence)
FIG. 6 shows a block diagram of a control circuit for controlling the cleaning device for cleaning the discharge wire 12 and the grid electrode 13 of the charging device 2.

  The counter 30 counts the number of output images at the image forming unit. The CPU 31 controls the DC controller 32 so that the cleaning process is performed every time the number of output images reaches a predetermined number (5000 in this example). Specifically, the operations of the switch 190, the motor M1, and the power sources S1 and S2 are controlled by the DC controller 32 so that the cleaning process is performed.

  In this example, a configuration is adopted in which the foreign matter adhering to the inner surface of the grid electrode 13 by the grid electrode cleaning member 14 is subjected to a cleaning process (rubbing process) while performing a static elimination process.

  Next, the cleaning sequence of the charging device will be described with reference to the flowchart shown in FIG. The entire steps are controlled by the CPU 31.

  When an image forming command is input to the image forming apparatus and the image forming process is started (step 1), image output is performed (step 2). Then, the number of output images (hereinafter referred to as output number) is counted by the counter 30 (step 3).

  It is determined whether or not the number of output sheets has reached the number of image formations based on the image formation command (hereinafter, “scheduled number”) (step 4). ). Further, it is determined whether the number of output sheets has not reached the predetermined number (step 4), and whether or not the predetermined number of cleaning sheets (5000 sheets) for cleaning the charging device has been reached (step 5). If the number of cleaning sheets has not been reached, image output is continued (step 2).

  On the other hand, if it is determined in step 5 that the number of output sheets has reached the cleaning number (5000 sheets) of the charging device, a command is sent from the CPU 31 to the DC controller 32, and the DC controller 32 turns off the power source S1 for the discharge wire. (Step 6).

  Then, the power source S2 for the grid electrode is also turned off (step 7), and the ground state is set by the switch 190 (step 8).

  Next, the motor M1 is turned on, and the discharge wire cleaning member 15 and the grid electrode cleaning member 14 are moved forward from the home position H to the reverse position (step 9).

  At this time, the grid electrode cleaning member 14 moves along the guide rail 20, and the cleaning process is performed by rubbing the grid electrode 13 in the charging region W1. Further, the discharge wire cleaning member 15 is simultaneously rubbed against the discharge wire 12 to perform a cleaning process.

  When the discharge wire cleaning member 15 and the grid electrode cleaning member 14 reach the reversal position, the rotation direction of the motor M1 is reversed, and the discharge wire cleaning member 15 and the grid electrode cleaning member 14 are returned (step 10). Then, the discharge wire cleaning member 15 and the grid electrode cleaning member 14 move toward the home position H. Again, the discharge wire 12 and the grid electrode 13 are cleaned.

  The grid electrode cleaning member 14 is separated from the grid electrode 13 by the separation mechanism (insulation mechanism) of the guide rail 20 after passing the charging region W1. Then, when the discharge wire cleaning member 15 and the grid electrode cleaning member 14 reach the home position H, the motor M1 is stopped and a series of cleaning processes is completed.

  Thereafter, the remaining image output is resumed until the output number reaches the planned number. That is, the switch 190 is switched to the grid electrode power source S2 (step 11), the power source S2 is turned on (step 12), and the discharge wire power source S1 is turned on (step 13).

  Then, when the number of output sheets reaches the predetermined number (step 4) as the image output is resumed (step 2), the series of image forming processing operations is terminated (step 14).

(Verification experiment)
First, in order to confirm the cleaning effect of the grid electrode 13 by performing the static elimination process of the foreign material adhering to the grid electrode 13 at the time of the cleaning process as described above, an endurance experiment was performed.

  In this durability experiment, image output was continuously performed on 100,000 sheets P in the image forming unit, and the degree of contamination of the grid electrode 13 and the occurrence of image defects were confirmed. The charging process of the charging device 2 was performed every time 5000 images were output as described above.

  As in this example, if the foreign matter such as toner adhering to the grid electrode 13 is removed by rubbing while removing the static electricity, the degree of contamination of the grid electrode 13 is slight even after 100,000 images are output. There was no image defect.

On the other hand, as a comparative example, instead of the conductive cleaning brush 22 described above, a similar durability experiment was performed using a high-resistance cleaning brush formed without conducting the conductive treatment of acrylic fibers. Specifically, in the comparative example, the cleaning brush has an electric resistance of 1 × 10 ¹³ Ω, a flocking density of 200 denier / 80 filaments, and the number of bristles per square millimeter is 150.

  In this comparative example, streaky density unevenness occurred when 20,000 images were output. When the grid electrode of the corona charger in which the density unevenness occurred was observed, a lot of toner, dust, and the like were attached at a position corresponding to a place where streaks appear. These deposits are considered to be caused by toner scattered from the developing device 3 and the cleaning device 5 and dust entering from outside the apparatus. In some cases, the toner is fixed. This seems to be because the cleaning process with the cleaning brush was repeated while the toner hardly moved. Once the toner is fixed, it becomes almost impossible to remove.

  Next, the effect of removing electricity from the grid electrode 13 during the cleaning process of the grid electrode 13 will be described. Therefore, a verification experiment for evaluating the cleaning ability of the grid electrode cleaning member 14 was performed.

  In this verification experiment, the toner is uniformly attached to the inner surface of the grid electrode 13 (the surface opposite to the side facing the photoreceptor 1), and this is set on the corona charger 2, and the grid electrode 13 is cleaned by the grid electrode cleaning member 14. The cleaning process was performed. Thereafter, the change rate of the toner covering area ratio at the grid electrode 13 was obtained, and this was used as a measure of the cleaning ability.

  Specifically, “toner coverage area ratio after cleaning” is divided by “toner coverage area ratio before cleaning” and multiplied by 100, which is hereinafter referred to as cleaning efficiency Y (%). In this scale, the greater the rate of change Y, the higher the cleaning ability. In order to improve the reproducibility of this value, the toner coverage area ratio before cleaning is adjusted to 60 (%).

  First, before explaining the verification results, we verified how the cleaning effect changes when the foreign matter attached to the grid electrode is charged under normal image formation conditions. This will be explained. That is, FIG. 8 shows the relationship between the discharge time (charging time) and the cleaning efficiency Y (%). In this verification, a cleaning brush having the same conditions as those described in the comparative example is used.

  After the toner was adhered to the grid electrode 13, the cleaning efficiency Y under each condition was measured by changing the discharge time by the corona charger 2 to 0 seconds, 5 seconds, 20 seconds, and 40 seconds. The charging conditions at this time are the same as those in the normal charging process, the value of the current flowing through the discharge wire 12 is −800 μA, and the voltage applied to the grid electrode 13 is −700V.

  As shown in FIG. 8, it can be seen that the cleaning efficiency Y decreases rapidly as the discharge time increases. This is presumably because the toner, which is an insulator, receives corona discharge and is excessively charged, and the electrostatic adhesion force to the grid electrode 13 is increased. If the foreign matter adhering to the grid electrode 13 is conductive, no charge is accumulated, so that the adhesion force does not increase during the normal charging process.

  However, as in the comparative example, the result of the above experiment using an insulating cleaning brush indicates that if the foreign matter is strongly charged, it cannot be removed only by the cleaning brush scraping effect. Even if the height is increased, the cleaning efficiency cannot be improved.

  On the other hand, when a conductive brush is used as in this example, foreign matter (adhered matter) such as toner can be neutralized, so that the electrostatic adhesion force of the foreign matter to the grid electrode 13 is reduced. Cleaning efficiency can be improved. That is, according to the configuration of the present example, when the grounded cleaning brush comes into contact with the foreign matter, the accumulated charge is removed through the cleaning brush.

  Moreover, the direction which made the electrical resistance value of the cleaning brush low can raise the static elimination efficiency at the time of a cleaning process.

  Therefore, the relationship between the cleaning efficiency and the electrical resistance value of the cleaning brush will be described.

By adjusting the degree of conductive treatment of the acrylic fiber constituting the cleaning brush, a brush having an electric resistance value of 1 × 10 ³ Ω, 1 × 10 ⁵ Ω, 1 × 10 ⁷ Ω, 1 × 10 ⁹ Ω It made and verified experiment about each cleaning efficiency. The verification result is shown in FIG.

  The conditions for this verification experiment are the same as the verification experiment described with reference to FIG. However, the discharge time (charging time) is 60 seconds.

As shown in FIG. 9, when the electrical resistance value of the cleaning brush is larger than 1 × 10 ⁵ Ω, it can be seen that the cleaning efficiency rapidly decreases. This is considered to be because, when the electric resistance value of the cleaning brush is larger than 1 × 10 ⁵ Ω, the charge removal processing of foreign matters such as toner adhering to the grid electrode 13 is hardly performed. In this way, in the case of a cleaning brush having an electric resistance value larger than 1 × 10 ⁵ Ω, it cannot be said that “static discharge treatment” is performed in this example. Therefore, it is preferable to use a cleaning brush of 1 × 10 ⁵ Ω or less in order to appropriately remove the foreign matter such as toner adhering to the grid electrode 13.

  In this example, the outer surface of the grid electrode (the surface facing the photoconductor) is not cleaned, but it is considered that there is no problem with this. This is because dirt that affects the charging potential unevenness of the photosensitive member by the corona charger is more conspicuous when it adheres to the inner surface than the outer surface of the grid electrode. This is because the potential distribution in the corona charger is hardly affected by the foreign matter adhering to the outer surface of the grid electrode.

  On the other hand, the grid electrode has a structure like a saucer due to the structure, and foreign matter is likely to accumulate there. Further, the foreign matter adhering to the inner surface of the grid electrode disturbs the potential distribution in the corona charger, so that the discharge current distribution is likely to be non-uniform, and the charged potential unevenness of the photoreceptor is likely to occur.

  For this reason, the configuration for cleaning the inner surface of the grid electrode as in this example is effective in preventing the occurrence of uneven charging potential on the photoreceptor. Of course, if necessary, a cleaning device for cleaning the outer surface of the grid electrode may be further provided.

In this example, the cleaning brush 22 in which all the brushes (fibers) are conductive is used as the grid electrode cleaning member. However, the present invention is not limited to such a configuration. For example, a hybrid type configuration in which about 80% of the brushes (fibers) constituting the cleaning brush 22 are conductive and the remaining 20% are non-conductive with medium resistance may be used. At this time, it is desirable that the electric resistance value of such a cleaning brush is 1 × 10 ⁵ Ω or less.

Further, the grid electrode cleaning member is not limited to a brush, and for example, an elastic body such as a conductive sponge (electric resistance value is 1 × 10 ⁵ Ω or less) may be used. When the sponge is used in this manner, the electrical resistance value of the sponge can be performed in the same manner as the method for measuring the electrical resistance value of the brush described above.

  As described above, according to the configuration of this example, the grid electrode of the corona charger can be appropriately cleaned, and image density unevenness due to charging failure can be prevented.

  Next, Example 2 will be described with reference to FIGS. FIG. 10 is a schematic cross-sectional view of the charging device 2 as viewed from the long side, and FIG. 11 is a schematic cross-sectional view of the charging device as viewed from its short side.

  In this example, the insulation mechanism for bringing the grid electrode cleaning member 14 located at the home position H into an insulated state is different. Accordingly, since the configuration other than this is the same as that of the first embodiment, detailed description thereof will be omitted by adding the same reference numerals.

  In this example, the cleaning brush 22 is moved away from the grid electrode 13 as in the first embodiment, so that the cleaning brush 22 is not electrically insulated from the grid electrode 13 as follows. A simple insulation mechanism is adopted.

  That is, when the cleaning brush 22 is positioned at the home position H, the insulating sheet (insulating mechanism) 40 is configured to be in an insulating state by being positioned between the cleaning brush 22 and the grid electrode 13.

  Specifically, the insulating sheet 40 is bonded to the inner surface of the grid electrode 13 so as to cover the inner surface of the grid electrode 13 at the home position H. This insulating sheet 40 is a PET (polyethylene terephthalate) sheet having a thickness of 0.5 mm.

  A conductive brush 41 is provided on the surface of the brush base 24 facing the shield electrode 10, and the conductive brush 41 is electrically connected to the brush base cloth 24. In the grid electrode cleaning member 14 of this example, a brush base 24 to which the cleaning brush 22 is fixed is attached to the holder 16 by a rigid support arm 42. Therefore, in this example, unlike Example 1, the moving direction of the cleaning brush 22 remains linear even in the vicinity of the home position H.

  By adopting such a configuration, the cleaning brush 22 is electrically connected to the grounded shield electrode 10 during the cleaning process, and a static elimination effect by the cleaning brush 22 can be generated.

  With the configuration of this example, the separation mechanism as in the first embodiment is not necessary, so that the insulation mechanism can be simplified and the charging device can be made compact.

  On the other hand, since the grid electrode 13 is pressed by the cleaning brush 22 at the home position H, it is desirable that the gap between the grid electrode 13 and the photoreceptor 1 be uniform in consideration of this. Further, it is desirable to control the voltage applied to the grid electrode 13 within a range where no leakage occurs.

  In addition, as a material of the insulating sheet used as an insulating mechanism, you may use the well-known insulating material other than PET mentioned above.

  As described above, according to the configuration of this example, the grid electrode of the corona charger can be appropriately cleaned as in the first embodiment, and the grid electrode cleaning member is insulated from the grid electrode. The configuration of the insulation mechanism can be simplified.

  In the first and second embodiments, the example in which the charging device (corona charger) is used in the charging process for uniformly charging the photosensitive member has been described. However, the present invention is not limited to this example. Such a configuration may be used.

  For example, a charging device (corona charger) similar to that in Embodiments 1 and 2 is used for the purpose of charging the toner image formed on the photoreceptor before transferring it to the sheet.

  Further, instead of the transfer roller used in the transfer device 4, a charging device (corona charger) similar to those in the first and second embodiments may be adopted. That is, in this example, the charging device is used for the transfer process.

  In the first and second embodiments, the photosensitive member is described as an example of the member to be charged. However, the present invention is not limited to this example, and the following configuration may be used.

  For example, the case where the member to be charged is an intermediate transfer member may be used. This intermediate transfer member is a known one, and is used for the primary transfer of the toner image formed on the photosensitive member and the secondary transfer of the primary transferred toner image to the sheet. In this case, the charging device (corona charger) can be used as a device for subjecting the toner image primarily transferred from the photosensitive member to the intermediate transfer member, before the secondary transfer. The charging device (corona charger) can also be used in a primary transfer process from a photoconductor to an intermediate transfer body and a secondary transfer process from an intermediate transfer body to a sheet.

1 is a schematic sectional view of an image forming apparatus. It is the schematic sectional drawing which looked at the corona charger from the front. It is the schematic sectional drawing which looked at the corona charger from the side. It is the schematic sectional drawing which looked at the corona charger from the front. It is the schematic sectional drawing which looked at the corona charger from the side. It is a block diagram for controlling the cleaning apparatus of a corona charger. It is a flowchart which shows the flow of the cleaning process of a corona charger. It is a figure which shows the relationship between charging time and cleaning efficiency. It is a figure which shows the relationship between the electrical resistance of a cleaning brush, and cleaning efficiency. It is the schematic sectional drawing which looked at the corona charger from the front. It is the schematic sectional drawing which looked at the corona charger from the side.

Explanation of symbols

1 Photoconductor 2 Charging device (corona charger)
DESCRIPTION OF SYMBOLS 3 Developing device 4 Transfer device 5 Cleaning device 6 Photostatic device 7 Image exposure device 12 Discharge wire 13 Grid electrode 14 Grid electrode cleaning member 15 Discharge wire cleaning member 16 Holder 17 Screw shaft 20 Conductive protrusion 21 Guide rail 22 Cleaning brush 30 Counter 31 CPU
32 DC controller 40 Insulation sheet 41 Conductive brush 190 Switch (SW)
H Home position M1 Motor S1 Power supply for discharge wire S2 Power supply for grid electrode

Claims (5)

In a charging device having a corona charger for charging an object to be charged and a cleaning mechanism for cleaning a grid electrode of the corona charger,
The charging device according to claim 1, wherein the cleaning mechanism includes a conductive member that performs a cleaning process while removing charges attached to the grid electrode.   2. The insulating mechanism according to claim 1, further comprising an insulating mechanism that electrically insulates the conductive member from the grid electrode when the conductive member is in a retracted position that is out of a charging region of the corona charger. Charging device.   The insulating mechanism includes a separation mechanism that places the conductive member in a separated state with respect to the grid electrode when the conductive member is in a retracted position that is out of a charging region of the corona charger. Item 2. The charging device according to Item 2.   The charging device according to claim 1, wherein the conductive member is a brush.   5. The charging device according to claim 1, wherein the member to be charged is an electrophotographic photosensitive member, and the corona charger is used for uniformly charging the electrophotographic photosensitive member.

Images