JP2012128076A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce stains due to toner or external additives attached to the discharge surface side of a charging blade.SOLUTION: An image forming apparatus applies only a DC voltage to a charging blade when driving an image carrier, and applies an AC voltage to the charging blade when not driving the image carrier.

Description

  The present invention relates to a rotatable image carrier on which an electrostatic latent image is formed, and a blade-like shape for charging the surface of the image carrier by contact with the image carrier and applying a voltage. The present invention relates to an image forming apparatus that has a charging member and forms an image on a recording medium.

  In the above, representative examples of the rotatable image carrier on which the electrostatic latent image is formed include a drum type or endless belt type electrophotographic photosensitive member, and an electrostatic recording dielectric. Examples of the image forming apparatus include an electrophotographic type or electrostatic recording type copying machine, a printer, a facsimile, a composite function machine thereof, and an image display display device.

  A transfer type electrophotographic image forming apparatus will be described as an example. This apparatus generally includes a charging means and a drum for uniformly charging a drum surface to a predetermined polarity and potential with respect to an electrophotographic photosensitive member (image carrier: hereinafter referred to as a drum) represented by a rotating drum type. An electrostatic latent image of image information is formed by exposure means that selectively exposes the charged surface. The latent image is visualized (developed) as a toner image by a developing means using a developer (hereinafter referred to as toner). The toner image is transferred onto a recording material (recording medium) by a transfer unit. The toner image on the recording material is fixed as a fixed image by the fixing means, and the recording material is output as an image formed product.

  In recent years, the charging means is a contact type using a rotating charging member such as a belt shape, a roll shape or a brush shape made of semiconductive rubber or resin, or a fixed charging member such as a blade shape or a film shape. Chargers have been attracting attention. As a feature of the contact-type charger, there are advantages such as lowering of the power source and less generation of ozone compared to the non-contact-type corona charger.

  In order to charge the drum surface, such a contact-type charger usually charges the drum surface to about -500 V by applying a DC voltage of -1.0 to -1.5 kV. Further, when only a DC voltage is used, a method is used in which charging is stabilized by superimposing an AC voltage on the DC voltage due to instability of charging.

  Here, contact charging type charging means, in particular, a blade-shaped charging member (hereinafter referred to as a charging blade or blade) is a contact type, and as the durability increases, dirt adheres due to toner or the like, resulting in poor charging. There was a problem that occurred.

  That is, in order to ensure charging, a cleaning means is provided for removing toner remaining on the drum surface before normal charging. Normally, the toner remaining without being transferred by the cleaning means is removed from the drum, but the toner having a small particle diameter, the external additive, and the like are not always removed. The cleaning means may slip through the image to the extent that no streak is generated on the image. For this reason, the toner and the external additive that have passed through the cleaning means stay at the tip of the charging blade.

  Naturally, since the charging blade is not set for cleaning the drum, the toner and the external additive staying at the tip pass through the tip of the blade. At that time, there arises a problem that the toner and the external additive are contaminated on the drum surface side of the blade. In particular, it is known that the amount of adhesion to the blade is larger when the AC voltage is superimposed on the DC voltage than when the DC voltage is applied.

  If the amount of deposits on the charging blade increases, gap fluctuation and resistance fluctuation with the drum on the discharge surface of the charging blade will eventually occur, causing discharge unevenness and causing vertical streaks due to poor charging and excessive charging. It was.

  Various means have been disclosed for removing the contamination of the charging blade. Patent Document 1 discloses a means for preventing contamination by applying an AC voltage while the drum is rotating forward.

JP-A-9-319188

  However, in the case of the above-described prior art, if an AC voltage is applied while the drum is rotating, toner and external additives may slip through the blade, and dirt may be reattached due to the AC application. Patent Document 1 also describes an example in which an alternating current is applied without separating the charging blade. That is, alternating current is applied while the drum is rotating. When alternating current is applied while the drum is rotating, the toner and external additives slip through, and the charging blade is contaminated.

  The present invention relates to a further improvement of the prior art. The purpose is to reduce adhesion of toner and external additives due to long-term use of the blade-shaped charging member.

  In order to achieve the above object, a typical configuration of an image forming apparatus according to the present invention includes a rotatable image carrier on which an electrostatic latent image is formed, and a voltage applied in contact with the image carrier. Thus, a blade-shaped charging member for charging the surface of the image carrier, a voltage applying unit for applying a voltage to the charging member, and a control unit are provided, and an image is formed on a recording medium. In the image forming apparatus, the control unit applies only a DC voltage to the charging member during forward rotation of the image carrier during image formation, and stops driving the image carrier or reversely rotates the image carrier. Is characterized in that the voltage applying means is controlled to apply an alternating voltage to the charging member.

  According to the present invention, since only a DC voltage is applied to the blade-shaped charging member when driving the image carrier during image formation, the amount of deposits on the charging member can be reduced, and the apparatus can be increased in size and cost. Thus, contamination of the charging member can be reduced. Therefore, stable charging can be performed over a long period of time.

Sequence diagram according to Embodiment 1 Schematic configuration diagram showing an example of an image forming apparatus 1 is a schematic configuration diagram illustrating a charging blade according to a first embodiment. (A) thru | or (c) is a schematic block diagram which shows the other structural form of the charging blade which concerns on Example 1, respectively. Arrangement diagram of charging blade according to embodiment 1 Schematic diagram of calculation of charging blade intrusion amount δ and set angle θ according to embodiment 1 Bias schematic diagram according to the first embodiment Flow chart at the time of continuous paper passing according to the first embodiment Schematic which shows the charging blade which contact | abuts only the edge part which concerns on Example 1. FIG. Sequence diagram according to embodiment 2 Dirty adhesion schematic diagram during reverse rotation according to Example 2 Schematic sequence diagram according to the second embodiment Schematic configuration diagram of charging blade according to embodiment 3 Schematic diagram of bias according to Example 3 Schematic sequence diagram according to embodiment 3 Schematic configuration diagram of the contact charging blade only at the end according to the third embodiment Schematic sequence diagram according to embodiment 4 Schematic sequence diagram according to embodiment 4

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the scope to the following embodiments.

[Example 1]
(1) Overall schematic configuration and image forming operation of an example of an image forming apparatus FIG. 2 is a schematic configuration diagram of an example of an image forming apparatus 1 according to the present invention. The apparatus 1 is a process cartridge detachable electrophotographic image forming apparatus (printer) using an electrophotographic process. The apparatus 1 forms an image on a recording material (recording medium, recording medium) P based on an electrical image signal inputted to a control circuit unit (control means: CPU) 100 from a host device 300 such as a personal computer, an image reader, or a facsimile machine. Execute.

  The recording material P is a sheet-like material on which an image can be formed by an electrophotographic process, and examples thereof include paper, a resin sheet, and a label. The control circuit unit 100 exchanges various types of electrical information with the operation unit 200 and the host device 300, and performs overall control according to a predetermined control program and a reference table stored in the storage unit of the image forming operation of the device 1. To control.

  In the apparatus main body of the apparatus 1, a cartridge housing portion 1A is provided. The process cartridge 2 is detachably attached to the cartridge housing portion 1A by a predetermined operation procedure. In this embodiment, the cartridge 2 is an integral process cartridge. That is, the electrophotographic photosensitive drum 3 as a rotating drum type image carrier on which an electrostatic latent image developed by the developer T is formed, and the charging means 4 and the developing means as process means acting on the drum 3 6. The cleaning means 8 is integrally assembled in a common housing.

  In this embodiment, the charging means 4 is a charging blade (blade-shaped charging member). The charging blade 4 will be described later. The developing means 6 is a non-contact developing device using magnetic one-component toner as the developer T. Hereinafter, the developer T is referred to as toner. The toner T used in this embodiment is a magnetic one-component negative toner composed of a base material and a plurality of external additives and having an average particle diameter of 8 μm. The cleaning means 8 is a blade cleaning device using an elastic blade (cleaning blade) 8a as a cleaning member.

  The developing device 6 includes a developing container 6a as a developer containing portion that contains toner T. Further, a developing sleeve 6b as a developer carrying member that develops the electrostatic latent image formed on the drum 3 as a toner image, a non-rotating magnet roller 6c disposed in the sleeve 6b, and toner on the developing sleeve 6b. It has a developing blade 6d for regulating the amount.

  A laser scanner unit (laser optical device) 5 as an image exposure unit is disposed above the cartridge housing portion 1A. The unit 5 outputs a laser beam L modulated in accordance with image information input from the host device 300 to the control circuit unit 100. The laser light L enters the cartridge 2 through the exposure window 2 a on the upper surface side of the cartridge 2. Thereby, laser scanning exposure is performed on the surface of the drum 3.

  A transfer roller 7 abuts on the lower surface of the drum 3 of the cartridge 2 to form a transfer nip portion N. The cartridge 2 accommodated in the cartridge accommodating portion 1A is pressed and fixed to a positioning portion (not shown) on the apparatus main body side by a pressing means (not shown). A drive output unit (not shown) on the apparatus main body side is coupled to a drive input unit (not shown) of the cartridge 2. Further, various electrical contacts (not shown) on the apparatus main body side are electrically connected to various electrical contacts (not shown) of the cartridge 2. The drum 3 is subjected to forward drive control, reverse drive control, and stop control by a drive source (not shown) controlled by the control circuit unit 100.

  The image forming operation is as follows. The drum 3 is driven to rotate at a predetermined process speed, in the present embodiment, at 105 mm / sec in the clockwise direction of the arrow A (at the time of forward rotation) during image formation. Unit 5 is also driven. In synchronization with this drive, a predetermined charging bias is applied to the charging blade 4 from a bias applying power source (voltage applying means) H at a predetermined control timing, and the surface of the drum 3 is contacted by the charging blade 4 in a non-contact manner. Uniformly charged to polarity and potential. The unit 5 scans and exposes the surface of the drum 3 with a laser beam L modulated in accordance with an image signal. As a result, an electrostatic latent image corresponding to the image signal is formed on the surface of the drum 3.

  The formed electrostatic latent image is supplied with toner by a developing sleeve 6b of the developing device 6 and developed as a toner image. The developing sleeve 6b is driven to rotate at a predetermined speed in the counterclockwise direction indicated by the arrow. A predetermined developing bias is applied to the developing sleeve 6b at a predetermined control timing from a developing bias applying power source (not shown).

  On the other hand, the sheet feeding roller 14 of the sheet feeding mechanism unit 13 is driven, and the recording material (recording medium) P is separated and fed. The recording material P passes through a sheet path 15 including registration means (not shown), is introduced into the transfer nip portion N at a predetermined control timing, and is nipped and conveyed through the nip portion N. While the recording material P passes through the nip portion N, a predetermined transfer bias is applied to the transfer roller 7 from a transfer bias application power source (not shown). As a result, the toner image on the drum 3 side is sequentially transferred onto the surface of the recording material P.

  The recording material P that has exited the nip portion N is separated from the surface of the drum 3 and introduced into the fixing device 10. In this embodiment, the fixing device 10 is a heat roller fixing device, and the recording material P is nipped and conveyed at the fixing nip portion and receives heat and pressure. As a result, the unfixed toner image on the recording material P is fixed by heat and pressure as a fixed image. Then, the recording material P exiting the fixing device 10 passes through the sheet path 16 and is sent to the paper discharge tray 12 on the upper surface of the apparatus 1 as an image formed product.

  Further, the transfer residual toner remaining on the drum 3 without being transferred to the recording material P in the transfer nip N is scraped off by the cleaning blade 8a of the cleaning device 8 and stored in the waste toner container 8b. The cleaned drum 3 is repeatedly used for image formation.

(2) Charging blade The charging blade 4 is in contact with the drum 3 which is a rotatable image carrier on which an electrostatic latent image is formed, and is charged with a blade to charge the surface of the drum 3 by applying a voltage. It is a member. 3A is a side view of the charging blade 4 in this embodiment, FIG. 3B is a side view of the charging blade 4 in a state of being disposed with respect to the drum 3, and FIG. FIG. 4 is a perspective model view of the tip side of the charging blade 4 in a state where it is installed.

  The charging blade 4 in this embodiment includes an electrode 33 for applying a voltage. In this embodiment, a phosphor bronze plate (hereinafter referred to as an electrode plate) having a thickness of 100 μm, which is a conductive elastic plate member, is used as the electrode 33. The electrode plate 33 is long in the generatrix direction (drum axis direction) of the drum 3 and has a length corresponding to the entire width of the image formable region width G of the drum 3.

  The distal end side of the electrode plate 33 (one end side in the short direction of the electrode plate 33) is covered with insulating urethane rubber as a non-charging portion 34 along the length of the electrode plate 33. In this embodiment, the non-charging portion 34 is the tip portion of the charging blade 4. This leading end abuts over the entire width of the image formable area width G of the drum 3 and rubs the surface of the drum 3.

A charging portion 35 is attached to the surface of the electrode plate 33 facing the drum 3 along the length of the electrode plate 33 in order to charge the drum surface using discharge. In this embodiment, the charging portion 35 is a medium resistance conductive rubber, and is joined to the electrode plate 33 by a conductive adhesive. The resistance of the conductive rubber is about 10 ⁸ Ωcm. Accordingly, the charging unit 35 is electrically connected to the electrode plate 33. The base side of the electrode plate 33 (the other end side in the short direction of the electrode plate 33) is joined to the rigid metal plate 32 as a holder by a conductive adhesive. Accordingly, the charging unit 35 is electrically connected to the holder 32 via the electrode plate 33.

  The charging blade 4 is arranged with respect to the drum 3 with the longitudinal direction parallel to the generatrix direction of the drum 3. In this embodiment, the charging blade 4 is disposed in the counter direction with respect to the positive rotation direction A of the drum 3 during image formation. Then, the edge portion of the non-charging portion 34 on the front end side of the electrode plate 33 is brought into contact with the drum 3, the holder 32 is fixed to the housing (not shown) of the cartridge 2, and the edge portion is subjected to the bending reaction force of the electrode plate 33. In this state, the drum 3 is brought into contact with the drum 3 with a predetermined pressing force.

  In this contact state, the charging surface E of the charging unit 35 is disposed so as to face the non-contact with the drum 3. The discharge position S of the charging surface E is disposed in a non-contact manner with a dischargeable gap α between the charging surface E and the drum 3. In this embodiment, the voltage for the charging blade 4 is applied to the conductive holder 32 from a bias application power source H which is a voltage application means. The structure applied with respect to the electrode plate 33 may be sufficient. The power supply H is controlled by the control circuit unit 100 which is a control means. The control circuit unit 100 applies only a DC voltage as a predetermined charging bias from the power source H during the forward rotation of the drum 3 in the direction of arrow A during image formation.

  A bias applied to the holder 32 is applied to the charging unit 35 via the electrode plate 33. As a result, the surface of the rotating drum 3 is uniformly discharged to a predetermined polarity and potential by being discharged with respect to the surface of the drum 3 in a dischargeable micro gap between the charging surface E of the charging unit 35 and the drum 3. Charged.

  In the charging blade 4 of this embodiment, the electrode plate 33 is separated from the tip by 200 μm, and the non-charging portion 34 has a free end d. This is because, when a DC voltage is applied to the charging blade 4 during image formation, vertical streaks due to discharge from the cut surface F of the non-charging portion 34 occur. This vertical streak is generated slightly from the cut surface F, because the electric discharge is generated and the normal electric discharge is disturbed. Therefore, in order to eliminate discharge from the cut surface F, the cut surface F side is insulated so as not to discharge. The electrode plate 33 is disposed at a distance of 50 μm from the charging surface E of the charging unit 35.

  The charging blade 4 does not need to be insulated particularly if there is no discharge from the tip. For example, as shown in FIGS. 4A and 4B, the tip of the electrode plate 33 is formed of an insulating urethane rubber (insulating member) 34, and the tip is further insulated from the electrode plate 33. And formed of conductive rubber (conductive member) 35a. The conductive rubber 35a may be in contact with the drum 3 as a contact portion.

  Further, as shown in (c), the tip of the electrode plate 33 is formed of insulating urethane rubber (insulating member) 34. Further, the tip is formed of a conductive rubber (conductive member) 35a while being insulated from the electrode plate 33, and the tip thereof is formed of an insulating urethane rubber (insulating member) 34a. The insulating urethane rubber 34a may be in contact with the drum 3 as a contact portion.

  As described above, the charging blade 4 is disposed in contact with the drum 3. And it is arrange | positioned in the counter direction with respect to the normal rotation direction A of a drum. The charging blade 4 is in contact with the drum surface with a dischargeable gap in order to charge the drum surface to a predetermined voltage. In particular, charging does not need to be in the counter direction, but toner and external additives that have passed through the cleaning blade 8a stay in the charging blade 4, so that the discharge area does not become dirty when the counter abuts to prevent contamination. More optimal.

  In this embodiment, as shown in FIG. 5A, edge contact is made at a set angle θ = 24 ° and an intrusion amount δ = 0.8 mm. Here, the intrusion amount δ is a virtual amount in which the tip of the charging blade 4 has entered the drum 3 without being deformed, and the set angle θ is a point at which the tip of the charging blade 4 and the drum 3 intersect. The angle formed by the tangent line D and the charging blade 4. When the charging blade 4 actually comes into contact with the drum 3, the result is as shown in FIG.

A method for obtaining the actual set angle θ and the penetration amount δ will be described with reference to FIG. The setting angle θ and the penetration amount δ are measured in a state where the drum 3 is removed from the arrangement state of the charging blade 4 and the drum 3 at the time of image formation. In FIG. 6, a position where the drum 3 is arranged at the time of image formation is a virtual drum 3. An axis that passes through the center of the virtual drum 3 and includes an edge portion at the tip of the charging blade 4 (the tip is described in the example of the non-charging portion 34 in FIG. 6) and that is parallel to the surface facing the drum 1 is X Axis. An axis that passes through the center of the virtual drum 1 and is perpendicular to the X axis is defined as a Y axis. As shown in the figure, the coordinates of the leading edge of the charging blade 4 from the virtual drum center 0 are measured.
From the drum center 0, the coordinate x in the x direction, the coordinate y in the y direction, and the radius r of the drum 3 can be used to obtain the set angle θ and the intrusion amount δ using the equations (1) and (2).

δ = √ (r ^ 2-x ^ 2) -y (1)
θ = sin ⁻¹ (x / r) Equation (2)
(3) Description of Charging Voltage (3-1) During Image Formation The control circuit unit 100 applies only a DC voltage to the charging blade 4 during normal rotation of the drum 3 during image formation (rotation in the direction of arrow A). The power supply H is controlled as follows. Here, during the forward rotation of the drum 3 at the time of image formation, in addition to the image formation operation with respect to the drum 3, the rotation of the drum 3 before image formation (during the pre-rotation process), the rotation drive of the drum 3 after image formation Time (during post-rotation process) is also included.

  This is because, when an AC voltage is applied to the charging blade 4 when the drum is driven, the charging sound is loud, and toner and external additives that have passed through adhere to the charging blade 4, so it is necessary to prevent this. At this time, in order to be charged with a DC voltage, the above-described charging blade is required to prevent unnecessary discharge.

(3-2) When Drum Driving is Stopped The control circuit unit 100 controls the power supply H so that an alternating voltage is applied to the charging blade 4 when the driving of the drum 3 is stopped. In this embodiment, having the charging application means for applying the alternating voltage separately from the image formation increases the size of the apparatus and increases the cost. Therefore, the same DC application power source H as that used for the image formation is used. By turning on / off the DC voltage of the power supply H, the same action as the AC voltage (alternating voltage) can be performed.

  Specifically, as shown in FIG. 7, the on / off of applying −1.0 kV is performed at a frequency of 100 Hz. At this time, the drum surface is first charged to -500 V when -1.0 kV is applied. Thereafter, an electric field difference (500 V) is generated between the drum surface and the charging blade 4 in order to turn off the voltage application. Therefore, the positive deposit adhered to the charging blade 4 is transferred onto the drum. After that, −1.0 kV is applied to the charging blade 4 again, so that the drum surface receives an oscillating electric field alternately about −500V.

  For this reason, the toner and external additives adhering to the charging blade 4 are caused by the action of the electric field between the charging blade 4 and the drum 3, and are shaken off by the vibration of the charging blade itself due to the application of an alternating voltage, and return to the drum surface. (Cleaning operation of the charging blade). Regularly charged polarity toner and external additives are transferred from the charging blade 4 to the drum 3 by the vibration of the charging blade itself by application of an AC voltage.

  In this embodiment, the AC voltage application time at this time is applied for 3 seconds after the drum drive signal is turned off for 0.2 seconds (because the drum 3 rotates due to inertia after the drum drive signal is turned off).

(3-3) Sequence Chart A series of operations for removing deposits from the charging blade 4 by applying an AC voltage when the drum drive is stopped in this embodiment will be described with reference to the sequence chart of FIG.

  First, a print signal is input (step S1), and an image forming operation is started. The drum starts to rotate (S2), and it takes time for the scanner 5 to reach a predetermined rotation speed before image formation. Therefore, the drum is driven to rotate for a predetermined preparation time (pre-rotation step). Thereafter, the image forming operation is started by the image forming start signal.

  First, by applying a charging voltage of -1.0 kV, the drum surface is applied to a predetermined voltage of -500 V and exposed by the exposure means 5 to form a latent image pattern. Thereafter, the latent image pattern is visualized with toner at a position facing the developing device 6, and transfer and cleaning operations are performed. Thereafter, a rotation operation after image formation (post-rotation process) is performed for cleaning the drum surface and discharging the transfer paper, and finally the drum is stopped (S3-S7).

  After 0.2 sec after the drum drive signal is turned off, an AC voltage (in this embodiment, DC voltage is turned on / off) is applied to the charging blade 4 (S8). Due to the vibration of the charging blade 4 itself generated by an alternating voltage and the action of an electric field, deposits (toner and external additives) attached to the charging blade 4 are returned to the drum surface (cleaning operation of the charging blade 4). At this time, in this embodiment, the charging blade 4 was turned on / off (application of AC voltage) for 3 seconds (S8-S9).

  When an AC voltage is applied to the charging blade 4 when the drum is driven, toner and external additives slip through and the drum facing surface of the charging blade 4 is soiled. However, if the AC voltage is applied when the drum drive is stopped as in this embodiment, it is possible to clean only the blade surface without any toner or external additive slipping through. Deposits (toner and external additives) returned to the drum surface from the charging blade 4 reach the cleaning device 8 by the rotation of the drum 3 in the pre-rotation process of the next print job and are removed from the drum surface. .

  In this embodiment, the cleaning operation for the charging blade 4 is performed when the drum drive is stopped after image formation. However, the present invention is not limited to this, and may be performed when the drum is stopped before the drum drive is started. In this case, the adhering matter (toner and external additive) returned from the charging blade 4 to the drum surface reaches the cleaning device 8 by the rotation of the drum 3 in the pre-rotation process to be executed next, and is on the drum surface. Removed from. Alternatively, it is removed by development simultaneous cleaning by the developing device 6.

(3-4) Continuously Passing Here, heretofore described the case where one or several printing passes have been performed and the driving of the drum is stopped. A case where a large number of sheets are also passed will be described with reference to FIG.

  In this embodiment, the vertical streak due to the charging failure occurred in about 150 sheets as the number of sheets in which the toner or the external additive adhered to the charging blade 4 and caused the charging failure. Therefore, when a print signal of 100 or more continuous sheets is sent, the printing operation is stopped once for 100 sheets, and the charging blade cleaning operation is performed. Thereafter, the remaining number of sheets is passed again to prevent the occurrence of vertical stripes due to charging failure.

  In this embodiment, the cleaning operation is performed in units of 100 sheets. However, this is not particularly limited, and the printing operation is stopped before the charging blade becomes dirty, and the cleaning operation of the charging blade 4 is performed. FIG. 8 shows an operation in which the printing operation is stopped once for 100 sheets and the cleaning operation is performed when 100 or more sheets are continuously printed. Thereafter, the remaining number of prints is printed, and driving is stopped, or when 100 sheets are printed, a cleaning operation is performed.

(4) Verification Experiment Next, a verification experiment was conducted to see how much deposits on the charging blade 4 can be removed in the above-described embodiment. The environment was 23 ° C. and humidity 50%. At this time, the application voltage and application time of the AC voltage applied when the drum drive was stopped were varied to investigate the degree of deposit removal and its adverse effects.

  As shown in Table 1, the applied voltage is -500 V, -1 kV, -1.5 kV, the application time is swung as 1, 2, 3, 4, 5 seconds. I checked the memory of a drum 3. At this time, 100 sheets of the charging blade 4 are continuously passed, so that toner and an external additive are once attached to the charging blade 4, and then 50 sheets are passed to check the occurrence of vertical stripes due to charging failure. The evaluation was made.

  Further, the horizontal stripe of the drum cycle by the memory of the drum 3 is confirmed by passing one halftone after the application of the AC voltage. Table 1 summarizes the case where it does not occur, ◯, the case where there is an occurrence but no problem on the image, Δ, and the case where it occurs.

  As shown in Table 1, when the voltage application time was short, the adhering material was not removed and remained on the charging blade 4, and vertical streaks due to poor charging occurred after 50 sheets were passed. Further, if the voltage application time is long, a memory due to the voltage application is generated on the drum, resulting in a horizontal streak of the drum cycle. Therefore, it may be set according to each applied voltage and time, such as about 5 seconds at -500 V, 2 to 4 seconds at -1.0 kV, and 1 to 2 seconds at -1.5 kV. In this example, the voltage was applied at -1.0 kV, which was the best, for 3 seconds.

  In the present embodiment, the charging blade 4 has been described. However, the present invention is not limited to the charging blade, and the same holds true for the charging and cleaning blade in contact with the drum surface. Further, the case where the tip end portion of the charging blade 4 has been arranged over the entire width of the image formable region width G of the drum 3 has been described so far (FIG. 3C), but as shown in FIG. Even in the case where only the longitudinal end portion 34b is in contact with the tip portion, the same effect as described above is exhibited.

[Example 2]
In the second embodiment, an AC voltage for cleaning operation is not applied to the charging blade 4 when the drum drive is stopped as in the first embodiment, but the drum 3 is controlled to rotate reversely after the drum drive is stopped. Then, an AC voltage is applied to the charging blade 4 during the reverse rotation to remove the deposits on the charging blade 4. The configuration of the charging blade 4 and the applied bias applied to the charging blade 4 are the same as those in the first embodiment. The non-charging portion 34 abuts over the entire width of the image formable region width G on the surface of the drum 3 and rubs the surface of the drum 3.

  With reference to the sequence chart of FIG. 10, a series of operations for removing the adhering matter on the charging blade by applying an AC voltage to the charging blade 4 during the reverse rotation of the drum after the drum driving is stopped will be described. Steps S1-S7 are the same as steps S1-S7 in the sequence chart of FIG.

After stopping the drum drive in step S7, the control circuit unit 100 rotates the drum 3 backward at a speed of 5.0 mm / sec (S8). At this time, the charging blade 4 is turned on and off at −100 kV (application of AC voltage) for 3 seconds as in the first embodiment (S8). After 3 seconds, reverse rotation of the drum 3 and AC voltage application are stopped (S9). When the AC voltage is applied, the drum 3 is charged to -500 V, and then the charging blade is repeatedly turned on and off at -1.0 kV, so that the charging blade itself is vibrated by an alternating electric field centered on -500 V. .
Therefore, due to the vibration of the charging blade itself and the effect of the electric field, the deposit t ((a) in FIG. 11) on the charging blade surface (charging surface E) moves to the drum 3 side and is removed (cleaning operation of the charging blade 4). .

  Further, since the drum 3 rotates in the reverse direction B, the drum surface charged to -500 V always moves the adhering matter upstream in the forward rotation direction A, and the toner and external additives staying at the edge of the charging blade 4. At the same time. This is to prevent the external additive and drum shavings staying at the tip of the charging blade 4 from being pressed against the tip edge of the charging blade 4 and sticking strongly to the drum surface.

  Further, the deposit t dropped on the drum 3 from the charging surface E of the charging blade 4 cannot stay through the blade contact portion due to the reverse rotation B of the drum 3, and therefore stays in the blade contact portion (FIG. 11 (b)). External additives accumulate on the blade contact portion. However, since the cohesive force between the external additives is large, it does not reattach to the blade 4 and moves on the drum along with the rotation of the drum 3 for cleaning during the forward rotation of the drum 3 in the pre-rotation process of the next print job. Device 8 is reached and removed from the drum surface. Further, the external additive moves to the drum side when the blade tip vibrates due to vibration at the time of starting the drum.

  Also, in order to prevent the deposit t (FIG. 11 (b)) staying at the blade contact portion from reattaching to the blade, the drum rotates backward and stops, and then rotates forward at 5.0 mm / sec for 2 seconds. A. Thereby, the external additive t staying at the blade contact portion is retracted from the blade as shown in FIG.

  That is, the following operation control is performed after the alternating voltage is applied when the driving of the drum 3 is stopped or when the reverse rotation B is performed. Before applying the DC voltage to the blade 4 for image formation, the drum 3 is configured such that the region of the drum 3 facing the blade 4 when the alternating voltage is applied is retracted from the region facing the blade 4. 3 is rotated forward. Thereby, the dirt of a blade can be removed more effectively and reattachment can be prevented. A sequence chart at this time is shown in FIG.

  According to this embodiment, by applying an AC voltage to the charging blade 4 during the reverse rotation of the drum 3, it is possible to reduce the deposits on the blade 4 and simultaneously remove the toner and external additives accumulated at the blade tip. Become.

  In the present embodiment, the charging blade 4 has been described. However, the present invention is not limited to the charging blade, and the same holds true for the charging and cleaning blade in contact with the drum surface. Further, the case where the tip end portion of the charging blade 4 has been arranged over the entire width of the image formable region width G of the drum 3 has been described so far (FIG. 3C), but as shown in FIG. Even in the case where only the longitudinal end portion 34b is in contact with the tip portion, the same effect as described above is exhibited. However, in the case of the charging / cleaning blade, the tip of the charging blade 4 abuts over the entire width of the image formable area width G of the drum 3.

[Example 3]
13A is a side view of the charging blade 4 in the present embodiment, FIG. 13B is a side view of the charging blade 4 in a state of being disposed with respect to the drum 3, and FIG. FIG. 4 is a perspective model view of the tip side of the charging blade 4 in a state where it is installed. The configuration of the charging blade 4 and the setting for the drum 3 in this embodiment are basically the same as those of the charging blade 4 of FIG. The non-charging portion 34 abuts over the entire width of the image formable region width G on the surface of the drum 3 and rubs the surface of the drum 3. Components and parts common to the charging blade 4 in FIG.

  In this embodiment, the charging blade 4 is an electrode for applying a voltage, and the electrode plate 33 is a first electrode. In addition to the electrode plate 33, the charging blade 4 is on the opposite side of the electrode plate 33 from the drum 3 side. It has the 2nd electrode 36 spaced apart from said 1st electrode.

  The control circuit unit 100 applies only a DC voltage from the first power source (voltage applying unit) H1 to the first electrode 33 during the forward rotation of the drum 3 during image formation (in the direction of arrow A). When the driving of the drum 3 is stopped, a direct current voltage is applied from the first power source H1 to the first electrode 33, and an alternating voltage is applied from the second power source H2 to the second electrode 36. Control H2.

  That is, the third embodiment is different from the first and second embodiments in the configuration of the charging blade 4 and has two electrodes (33, 36). One electrode 33 is used to apply a charging voltage in the same manner as in the first and second embodiments. The other electrode 36 is on the back surface of the charging blade 4. When the drum drive is stopped, an AC voltage is applied to the electrode 36, and a DC voltage is applied to the first electrode 33, thereby providing electrostatic effects and vibration effects. Are generated simultaneously.

  Thereby, the deposits on the charging blade 4 are removed. In addition, since an AC voltage is applied to the back surface of the charging blade 4, it is possible to generate vibrations by applying the AC voltage without generating a memory due to discharge on the drum 3.

  In this embodiment, a DC voltage is applied to the first electrode 33 during drum driving (during image formation, rotational driving before image formation, and rotational driving after image formation). This is because, when an AC voltage is applied when the drum is driven, the charging noise is large, and it is necessary to prevent slipped toner and external additives from adhering to the charging blade. At this time, in order to obtain a uniform charge by charging with a DC voltage, the structure of the charging blade is required to prevent unnecessary discharge.

  Moreover, the applied voltage applied when driving is stopped will be described with reference to FIG. When the drum driving is stopped, an AC voltage is applied to the second electrode 36 to cause the charging blade 4 to vibrate. Further, a positive DC voltage is applied to the first electrode 33 so as to generate an electric field in which deposits are liable to transfer on the drum surface. Therefore, vibration is generated at the second electrode 36 by an electrostatic electric field effect at the first electrode 33. Thereby, the deposit | attachment adhering to the charging blade surface (charging surface E) can be transferred to the drum 3 (cleaning operation of the charging blade 4).

  Specifically, a DC voltage of +200 V is applied to the first electrode 33, and an AC voltage of 1.5 kVpp and f = 1.5 kHz is applied to the second electrode 36. The application time at this time is 3 seconds after the drum drive signal is turned off, because 0.2 second after the drum drive signal is turned off (because the photosensitive drum rotates due to inertia after the drum drive signal is turned off).

  Next, with reference to the sequence chart of FIG. 15, when the drum driving is stopped in this embodiment, a DC voltage is applied to the first electrode 33 of the charging blade 4 and an AC voltage is applied to the second electrode 36 to remove deposits. The operation of will be described. Steps S1-S7 are the same as steps S1-S7 in the sequence chart of FIG.

  After the drum driving is stopped, after the drum 3 is stopped (0.2 seconds after the drive signal is turned off), a DC voltage +200 V is applied from the first power source H1 to the first electrode 33 of the charging blade 4. Then, an AC voltage of 1.5 kVpp and f = 1.5 kHz is applied to the second electrode 36 from the second power source H1 (steps S8 to S9). As a result, electrostatic action between the charging blade 4 and the drum 3 and vibration of the charging blade 4 itself are generated at the same time, and deposits (toner and external additives) adhering to the charging blade 4 are deposited on the surface of the photosensitive drum. return.

  When an AC voltage is applied when the drum is driven, toner and external additives slip through and the drum facing surface of the charging blade 4 is soiled. However, if an AC voltage is applied when driving of the photosensitive drum is stopped as in the present embodiment, it is possible to clean only the blade surface without any toner or external additive slipping through.

  In this embodiment, the cleaning operation for the charging blade 4 is performed when the drum drive is stopped after image formation. However, the present invention is not limited to this, and may be performed when the drum is stopped before the drum drive is started. In this case, the adhering matter (toner and external additive) returned from the charging blade 4 to the drum surface reaches the cleaning device 8 by the rotation of the drum 3 in the pre-rotation process to be executed next, and is on the drum surface. Removed from. Alternatively, it is removed by development simultaneous cleaning by the developing device 6.

  Up to this point, the case where one or several printing sheets have been performed and the driving of the drum is stopped has been described. However, in actual use, several sheets may be continuously fed (during continuous feeding). is there. In that case, as in FIG. 8 of the first embodiment, when 100 or more sheets are continuously printed, the printing operation is stopped once and the cleaning operation is performed on the 100th sheet. Thereafter, the remaining number of prints is printed, and driving is stopped, or when 100 sheets are printed, a cleaning operation is performed.

(Verification experiment)
Next, a verification experiment was conducted to see how much deposits on the charging blade 4 could be removed in the above embodiment. The environment was 23 ° C. and humidity 50%. At this time, the applied voltage of the DC voltage applied when the drum drive was stopped and the applied voltage of the AC voltage were varied to investigate the degree of deposit removal and its adverse effects.

  As shown in Table 2, the applied voltage of the DC voltage is set to 200, 500, -500 V, and the applied voltage of the AC voltage is swung to 0.5 k, 1.0 k, and 1.5 kVpp, and the degree of deposit removal at that time, The memory of the photosensitive drum, which is the harmful effect, was confirmed. Moreover, the removal condition and the bad effect by the application time in each of the following cases 1) to 3) were confirmed.

1) When DC voltage 500V is applied to the first electrode 33 and AC voltage 1.5 kVpp is applied to the second electrode 36 2) DC voltage 200V is applied to the first electrode 33 and AC voltage 1.5 kVpp is applied to the second electrode 36 3) When a DC voltage of 200 V is applied to the first electrode 33 and an AC voltage of 1.0 kVpp is applied to the second electrode 36, the charging blade 4 at this time is charged once by passing 100 sheets continuously. Evaluation was performed by attaching toner and external additives to No. 4 and then passing 50 sheets to confirm the occurrence of vertical streaks due to poor charging. Further, the horizontal stripe of the drum cycle by the memory of the drum 3 is confirmed by passing one halftone after the application of the AC voltage. At this time, Table 2 shows ◯ when it does not occur, Δ when it occurs but there is no problem in the image, and × when it occurs.

  As shown in Table 2, the larger the width of the amplitude value of the AC voltage with respect to the DC voltage, and the more the electric field that returns the positive substance to the drum between the drum 3 and the charging blade 4, the charging failure after passing 50 sheets. No vertical streaks due to. Here, since the vibration of the charging blade 4 is more effective than the action of the electric field, the adhering substance can be removed more when the amplitude difference of the AC voltage with respect to the DC voltage is larger. By applying the DC voltage and the AC voltage at the same time, it is possible to further shorten the voltage application time without generating horizontal stripes of the drum cycle due to the memory on the drum.

  Further, when the voltage application time is long, the memory of the drum 3 is easily generated in the first embodiment. However, in the present embodiment, the memory of the drum 3 is not particularly generated because the AC voltage is applied by the back electrode 36. For this reason, in this embodiment, it is possible to remove the adhering matter on the charging blade 4 without generating a horizontal stripe having a drum cycle caused by the memory of the drum 3. In this embodiment, the DC voltage is 200 V and the AC voltage is 1.5 kVpp for 3 seconds. However, the present invention is not limited to this, and the optimum bias application voltage and application time can be obtained for the above reasons.

  In the present embodiment, the charging blade 4 has been described. However, the present invention is not limited to the charging blade, and the same holds true for the charging and cleaning blade in contact with the drum surface. Further, the case where the tip end portion of the charging blade 4 has been disposed over the entire width of the image formable area width G of the drum 3 has been described so far (FIG. 13C), but as shown in FIG. Even in the case where only the longitudinal end portion 34b is in contact with the tip portion, the same effect as described above is exhibited.

[Example 4]
Also in the fourth embodiment, as in the third embodiment, the charging blade 4 having the first electrode 33 and the second electrode 36 is used. Then, an AC voltage is not applied when the drum driving is stopped, but an AC voltage is applied when the drum is reversely rotated after the drum driving is stopped to remove deposits on the charging blade.

  The configuration of the charging blade 4 and the voltage applied to the first and second electrodes 33 and 36 are the same as those in the third embodiment. The non-charging portion 34 abuts over the entire width of the image formable region width G on the surface of the drum 3 and rubs the surface of the drum 3. For this reason, in the fourth embodiment, a series of operations for removing the adhering matter on the charging blade by applying an AC voltage during the reverse rotation of the drum after the drum driving is stopped will be described using the sequence chart of FIG. Steps S1-S7 are the same as steps S1-S7 in the sequence chart of FIG.

  After the drum drive is stopped, the drum 3 is rotated in reverse at a speed of 5.0 mm / sec. At the same time, a DC voltage of +200 V is applied to the first electrode 33 and an AC voltage of 1.5 kVpp is applied to the second electrode 36 for 3 seconds as in the third embodiment (S8, S9). Therefore, positive deposits on the surface of the charging blade (charging surface E) are removed from the surface of the charging blade onto the drum 3 by the action of the electric field between the drum 3 and the charging blade 4 and the vibration of the charging blade itself.

  At this time, since the drum 3 rotates in the reverse direction B, the toner and the external additive staying on the edge of the blade are also moved to the upstream side together with the deposits removed from the charging blade 4 onto the drum 3. This is to prevent the external additive and drum shaving powder staying at the tip of the cleaning blade from being pressed against the tip edge of the blade and strongly adhering to the drum surface.

  Further, as in the third embodiment, the deposits dropped from the blade cannot stay through the blade contact portion by the reverse rotation B of the drum 3 and therefore stay in the blade contact portion. However, since the external additive is concentrated in the blade contact portion, the cohesive force between the external additives is large, so that the external additive does not reattach to the blade. Accompanying movement on the drum. In addition, the external additive always moves to the drum side when the blade tip vibrates due to vibration at the time of starting the drum.

  Further, in order to prevent the reattachment to the blade, similarly to the second embodiment, after the drum 3 is reversely rotated B and stopped, the drum 3 is rotated forward at 5.0 mm / sec for 2 seconds. Thus, if the external additive staying in the blade contact portion is withdrawn from the blade, the contamination of the blade can be more effectively removed and reattachment can be prevented. A sequence chart at this time is shown in FIG.

  According to the present embodiment, the AC voltage is applied during the reverse rotation of the drum 3 to reduce the deposits on the charging blade 4 and to remove the toner and the external additive accumulated at the tip of the charging blade at the same time.

  In the present embodiment, the charging blade 4 has been described. However, the present invention is not limited to the charging blade, and the same holds true for the charging and cleaning blade in contact with the drum surface. Further, the case where the tip end portion of the charging blade 4 has been disposed over the entire width of the image formable area width G of the drum 3 has been described so far (FIG. 13C), but as shown in FIG. Even in the case where only the longitudinal end portion 34b is in contact with the tip portion, the same effect as described above is exhibited.

[Other matters]
1) The image carrier on which the electrostatic latent image is formed in the present invention is not limited to the electrophotographic photosensitive member in the electrophotographic system of the embodiment. It may be an electrostatic recording dielectric in an electrostatic recording system. Further, the rotatable image carrier is not limited to the drum type. It may be in the form of an endless rotating belt.

  2) The relative movement of the image carrier and the charging member is not limited to the form in which the image carrier moves relative to the fixed charging member as in the embodiment, and the charging member moves to the fixed image carrier. A form in which both the charging member and the image carrier move is also included.

  3) The contact of the charging member with the image carrier is not limited to the counter direction contact in the embodiment, and may be forward contact. Further, the contact is not limited to the edge contact, and abdominal contact may be used.

  4) In the present invention, the charging of the surface of the image carrier by the charging member includes a charge for neutralizing the surface of the image carrier. The blade-shaped charging member of the present invention can also be used as an image carrier cleaning and charging blade.

  3 .. Image bearing member 4.. Blade-shaped charging member, H... Voltage applying means 100... Control means P... Recording medium 1.

Claims (4)

A rotatable image carrier on which an electrostatic latent image is formed, a blade-shaped charging member for charging the surface of the image carrier by applying a voltage while abutting against the image carrier; An image forming apparatus that includes a voltage applying unit that applies a voltage to the charging member, and a control unit, and forms an image on a recording medium,
The control means applies only a DC voltage to the charging member during forward rotation of the image carrier during image formation, and an alternating voltage to the charging member when driving of the image carrier is stopped or during reverse rotation. An image forming apparatus that controls the voltage applying unit to apply the voltage. A rotatable image carrier on which an electrostatic latent image is formed, and a blade-like shape for charging the surface of the image carrier by a non-charged portion coming into contact with the image carrier and applying a voltage. An image forming apparatus that includes a charging member, a voltage applying unit that applies a voltage to the charging member, and a control unit, and forms an image on a recording medium,
An electrode for applying a voltage to the charging member is provided, and the electrode is separated from the first electrode on the opposite side of the image carrier from the first electrode. And a second electrode disposed
The control means applies only a DC voltage to the first electrode during forward rotation of the image carrier during image formation, and when the drive of the image carrier is stopped or during reverse rotation, An image forming apparatus, wherein the voltage application unit is controlled so that a DC voltage is applied to the electrode and an alternating voltage is applied to the second electrode.   After the alternating voltage is applied when the image carrier is stopped or reversely rotated, and before the DC voltage is applied to the charging member for image formation, the alternating voltage is applied to the charging member. The image forming apparatus according to claim 1, wherein the image carrier is rotated forward so that the region of the image carrier that has been moved away from the region facing the charging member.   The contact portion of the charging member with respect to the image carrier is in contact with the entire width of the image formable region on the surface of the image carrier to rub against the surface of the image carrier. The image forming apparatus according to any one of claims 1 to 3.