JP2006267699A - Image forming apparatus, cleaning device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a charging means for charging a photoreceptor by impressing DC current to the photoreceptor hard to be soiled with simple structure. <P>SOLUTION: Even when toner on the photoreceptor 10 is scratched off by a blade 12, not all are scratched off and a part may stay as stay toner 25 between the blade 12 and the photoreceptor 10 (A). When the photo conductor 10 at a stopped state starts rotation, the stay toner 25 passes through between the blade 12 and the photoreceptor 10 ((B)) by oscillation of the blade 12 and the photoreceptor 10 to reach a charging roller 14 ((C), time t1). As it is, the stay toner 25 adheres to the charging roller 14. Then, the stay toner 25 is made to be hard to adhere to the charging roller 14 by impressing AC voltage to the charging roller 14 at the time of reach (time t1) when a part of the photoreceptor 10 positioned at a first position P1 reaches a second position P2 at the start (time t0) of rotation of the photoreceptor 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, a cleaning apparatus, and a method. More specifically, the image forming apparatus includes a charging unit that charges a photosensitive member by applying a DC voltage, and the charging unit is cleaned. The present invention relates to a cleaning apparatus and method.

  A cleaning blade used as a cleaning unit for a photoconductor in a conventional contact charging image forming apparatus is in contact with the photoconductor and scrapes off toner adhering to the photoconductor. Part of the toner removed from the photoconductor during the rotation of the photoconductor stays on the surface near the tip of the cleaning blade. When the photosensitive member stops, the toner staying on the surface near the tip of the cleaning blade adheres linearly on the photosensitive member. When the photosensitive member is rotated again, the cleaning blade and the photosensitive member are separated by the vibration at the start of the rotation of the photosensitive member, and the linear toner on the photosensitive member is cleared as the photosensitive member rotates. -Passes between the ning blade and the photoreceptor, reaches the contact charging means and adheres. As described above, when the toner adheres to the contact charging means, the charging performance of the portion where the toner adheres deteriorates, and as a result, a poorly charged portion also occurs on the photoreceptor. When the photoconductor is a reversal development system, the poorly charged portion is developed, resulting in horizontal black streaks, and the image quality is degraded. When the contact charging unit adopts a DC charging method in which a DC voltage is applied to charge the photosensitive member, the polarity of the applied voltage of the contact charging unit is not reversed, so that the adhered toner is difficult to leave once attached.

  In view of the above, conventionally, an apparatus has been proposed in which a cleaning member is brought into contact with the surface of a contact charging unit for a certain period of time at predetermined timing intervals (see Patent Document 1). Further, the contact blackout means is arranged so that the contact charging means is separated from the photosensitive body until the toner linearly attached to the photosensitive body passes through the position of the contact charging means, and is contacted with the photosensitive body after passing. An apparatus for moving (retracting) has been proposed (see Patent Document 2).

However, such an apparatus has a complicated structure, such as requiring a new member called a cleaning member or a mechanism for moving the contact charging means.
JP-A-7-128956 JP-A-9-179384

  The present invention has been made in view of the above-described facts, and provides an image forming apparatus, a cleaning apparatus, and a method capable of making a charging unit that is charged by applying a DC voltage to a photoconductor with a simple configuration and less likely to become dirty. The purpose is to provide.

  In order to achieve the above object, an image forming apparatus according to the first aspect of the present invention includes a rotary photoreceptor for forming an electrostatic latent image and developing the electrostatic latent image with toner, Forming means for forming an electrostatic latent image on the photosensitive member; rotating means for rotating the photosensitive member; scraping means for scraping toner in contact with the photosensitive member; A charging unit for contacting and charging the photoconductor at a second position spaced downstream from the first position in contact with the photoconductor; and a DC voltage from the charging unit to the photoconductor for the charging. And a voltage control unit capable of applying an AC voltage to the charging unit, and the rotation unit is controlled to start rotation of the stopped photoconductor, and at the start of rotation of the photoconductor positioned at the first position When the part reaches the second position, And a control means for controlling said voltage control means so that an AC voltage is applied to the conductive means.

  That is, the image forming apparatus according to the present invention includes a rotating photosensitive member, and an electrostatic latent image is formed on the photosensitive member by the forming unit, the electrostatic latent image is developed with toner by the developing device, and the toner image is formed on the paper. The image is formed on the paper by transfer.

  Not all of the toner image is transferred to the sheet, and some of the toner image may remain on the photoreceptor. If the toner remains on the photosensitive member, it adversely affects the next image formation, and it is necessary to remove it. In view of this, there is provided a scraping means for scraping the toner in contact with the photosensitive member.

  On the other hand, in order to form an electrostatic latent image on the photoreceptor as described above, it is necessary to charge the photoreceptor. In view of this, there is provided charging means for contacting and charging the photoconductor at a second position spaced from the first position of the scraping means contacting the photoconductor downstream in the rotational direction. In the present invention, the voltage control means applies a DC voltage from the charging means to the photosensitive member for the charging. Note that the voltage control means can apply an AC voltage to the charging means.

  As described above, even if the toner on the photosensitive member is scraped off by the scraping means, not all of the toner is scraped off, and a part of the toner stays between the scraping means and the photosensitive member. There is a case. When the stopped photoconductor starts to rotate, the staying toner may pass between the scraping unit and the photoconductor and reach the charging unit to be attached.

  Therefore, the control means controls the rotation means to start rotation of the stopped photoconductor, and when the portion of the photoconductor positioned at the first position at the start of rotation reaches the second position, that is, The voltage control means is controlled so that an AC voltage is applied to the charging means at least when reaching this.

  As described above, the photosensitive member in a stopped state is started to rotate, and the portion of the photosensitive member positioned at the start of the rotation at the first position where the scraping unit contacts the photosensitive member is in contact with the charging unit. When the second position is reached, an AC voltage is applied to the charging unit, so that the toner staying between the scraping unit and the photosensitive member is less likely to adhere to the charging unit.

  In this way, the voltage control means for applying a DC voltage from the charging means to the photoconductor for charging is controlled to make it difficult for the toner staying between the scraping means and the photoconductor to adhere to the charging means. Therefore, it is possible to make the charging means difficult to get dirty with a simple configuration.

  According to a second aspect of the present invention, the control means controls the forming means so that an electrostatic latent image is formed on the photosensitive member after the application of the alternating voltage to the charging means is finished and the direct current is applied for a predetermined time. .

  Here, the predetermined time is a predetermined time until the voltage applied to the charging unit is switched from an AC voltage to a DC current so that the charging unit can properly charge the photosensitive member.

  According to a third aspect of the present invention, there is provided a cleaning device for cleaning a charging means for forming an electrostatic latent image and contacting and charging the rotating photosensitive member for developing the electrostatic latent image with toner. The charging means contacts the photosensitive member and scrapes off the toner at a second position spaced from the first position where the toner removing means contacts the photosensitive member to the downstream side in the rotation direction. A voltage control unit that can contact the body and apply a DC voltage from the charging unit to the photoconductor for the charging, and can apply an AC voltage to the charging unit; And a control means for controlling the voltage control means so that an AC voltage is applied to the charging means when the portion of the photoconductor located at the position 1 reaches the second position.

  That is, the present invention is a cleaning device that forms an electrostatic latent image and cleans a charging unit that contacts and charges a rotating photoreceptor for developing the electrostatic latent image with toner.

  The charging unit contacts the photoconductor at a second position spaced downstream from the first position in contact with the photoconductor of the detoning unit that contacts the photoconductor and scrapes off the toner. is there.

  The voltage control means can apply a DC voltage from the charging means to the photosensitive member for charging, and can apply an AC voltage to the charging means.

  The control means is configured to apply an AC voltage to the charging means when the portion of the photoconductor positioned at the first position reaches the second position at the start of rotation of the photoconductor in a stopped state. Control the voltage control means.

  As described above, the photosensitive member in a stopped state is started to rotate, and the portion of the photosensitive member positioned at the start of the rotation at the first position where the scraping unit contacts the photosensitive member is in contact with the charging unit. When the second position is reached, that is, at least when this is reached, an AC voltage is applied to the charging means, so that the toner staying between the scraping means and the photosensitive member is less likely to adhere to the charging means. .

  In this way, the voltage control means for applying a DC voltage from the charging means to the photoconductor for charging is controlled to make it difficult for the toner staying between the scraping means and the photoconductor to adhere to the charging means. Therefore, it is possible to make the charging means difficult to get dirty with a simple configuration.

  By the way, as in claim 4, the control means may further control the voltage control means so that an alternating voltage is applied to the charging means every time the charging means makes at least one rotation from the time of arrival. .

  As described above, when an AC voltage is applied to the charging unit at the time of arrival, the toner staying between the scraping unit and the photosensitive member becomes difficult to adhere to the charging unit, but the toner does not necessarily adhere to the charging unit completely. It doesn't mean you don't.

  As described above, when the toner adheres to the charging unit, the toner comes into contact with the photosensitive member every time the charging unit rotates from the arrival time. If this is left as it is, charging failure may occur.

  Therefore, as described above, when an AC voltage is applied to the charging unit every time the charging unit rotates at least once from the time of arrival, the toner adhering to the charging unit can be cleaned, and a charging failure can be caused. .

  If attention is focused only on this point, the following invention is proposed. That is, a cleaning device that forms a latent electrostatic image and cleans a rotary charging unit that contacts and charges a rotary photosensitive member for developing the electrostatic latent image with toner, The charging unit contacts the photoconductor at a second position spaced from the first position of the detoning unit that contacts the photoconductor to contact the photoconductor and downstream in the rotational direction. A voltage control unit capable of applying a DC voltage from the charging unit to the photoconductor for the charging and an AC voltage to the charging unit; and a first position at a start of rotation of the photoconductor in a stopped state. Control means for controlling the voltage control means so that an alternating voltage is applied to the charging means every time the charging means makes at least one rotation from the time when the portion of the photoconductor located at the position reaches the second position; Is a cleaning device.

  The example described above is an example in which the toner stays between the scraping unit and the photosensitive member, but this occurs between the charging unit and the photosensitive member although the amount is small.

  Accordingly, in claim 5, the control means further controls the voltage control means so that an AC voltage is applied to the charging means at least when the rotation of the charging means is started. Therefore, it is possible to prevent the toner staying between the charging unit and the photosensitive member from passing between the charging unit and the photosensitive member, and to contaminate the charging unit.

  If attention is focused only on this point, the following invention is proposed. That is, a cleaning device that forms a latent electrostatic image and cleans a rotary charging unit that contacts and charges a rotary photosensitive member for developing the electrostatic latent image with toner, The charging unit contacts the photoconductor at a second position spaced from the first position of the detoning unit that contacts the photoconductor to contact the photoconductor and downstream in the rotational direction. A voltage control unit capable of applying a DC voltage from the charging unit to the photosensitive member for charging and applying an AC voltage to the charging unit; and an AC voltage applied to the charging unit at least when the charging unit starts rotating. It is a cleaning apparatus provided with the control means which controls the said voltage control means so that may be applied.

  In some cases, the toner adheres to the entire peripheral surface of the charging unit that contacts the photosensitive member.

  Therefore, in claim 6, the control means further controls the voltage control means so that an AC voltage is applied to the charging means during at least one rotation of the charging means from the start of rotation of the charging means. The peripheral surface in contact with the photoreceptor can be cleaned.

  If attention is focused only on this point, the following invention is proposed. That is, a cleaning device that forms a latent electrostatic image and cleans a rotary charging unit that contacts and charges a rotary photosensitive member for developing the electrostatic latent image with toner, The charging unit contacts the photoconductor at a second position spaced from the first position of the detoning unit that contacts the photoconductor to contact the photoconductor and downstream in the rotational direction. The charging means applies a DC voltage from the charging means to the photoconductor, and the charging means can apply an AC voltage to the charging means, and at least one rotation of the charging means from the start of rotation of the charging means. During this period, the cleaning device includes a control unit that controls the voltage control unit so that an AC voltage is applied to the charging unit.

  The start of rotation of the charging unit may coincide with the start of rotation of the photosensitive member.

  Further, the maximum value of the applied alternating current is at least twice the discharge start voltage.

  In addition, since invention of Claims 7-10 produces the effect | action and effect similar to invention of Claims 3-6, the description is abbreviate | omitted.

  In addition, the inventions according to claims 4 to 6 can be applied to the inventions according to claims 1 and 2.

  As described above, the present invention controls the voltage control means for applying a DC voltage from the charging means to the photosensitive member for charging, so that the toner stayed between the scraping means and the photosensitive member is charged. Therefore, it is possible to prevent the charging unit from becoming dirty with a simple configuration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus provided with the cleaning device according to the present embodiment forms an electrostatic latent image and is a rotary photosensitive device for developing the electrostatic latent image with toner. The body 10, the optical scanning device 18 as a forming unit for forming an electrostatic latent image on the photoconductor 10, the motor 20 (see also FIG. 2) as the rotating unit for rotating the photoconductor 10, and the photoconductor 10. Then, the blade 12 as a scraping means for scraping off the toner, and the photosensitive member 10 is contacted at the second position P2 spaced from the first position P1 where the blade 12 contacts the photosensitive member 10 to the downstream side in the rotation direction. Charging roller 14 as charging means for charging, and voltage control means capable of applying a DC voltage from the charging roller 14 to the photoconductor 10 for charging and applying an AC voltage (see FIG. 8) to the charging roller 14. Voltage system as The circuit 16 and the motor 20 are controlled to start rotation of the stopped photoconductor, and when the portion of the photoconductor 10 located at the first position P1 reaches the second position P2 when the rotation starts, that is, A control device 22 is provided as control means for controlling the voltage control circuit 16 so that an AC voltage is applied to the charging roller 14 at least when the charging roller 14 is reached. In addition, a developing device, a transfer device, and a static eliminator (not shown) are also provided.

  As shown in FIG. 2, the controller 22 is connected to a motor 24 as a charging means rotating means for rotating the charging roller, in addition to the motor 20, the optical scanning device 18, and the voltage control circuit 16.

  In the image forming apparatus in the present embodiment, an electrostatic latent image is formed on the photoconductor 10 by the optical device 18, the electrostatic latent image is developed with toner by the developing device, and the toner image is transferred to the paper by the transfer device. Thus, an image is formed on the paper.

  Not all of the toner image is transferred to the sheet, and some of the toner image may remain on the photoreceptor 10. If toner remains on the photoconductor 10, it adversely affects the next image formation, and it is necessary to remove it. Therefore, as described above, in the present embodiment, the blade 12 is provided, and the toner remaining on the photoconductor 10 is scraped off.

  The photosensitive member 10 from which the remaining toner has been scraped is also charged by the charging roller 15 after being neutralized by the neutralizing device for the next image formation.

  As described above, the charging roller 14 contacts the photoconductor 10 at the second position P2 that is a predetermined distance away from the first position P1 of the blade 12 that contacts the photoconductor 10 at the downstream side in the rotation direction. To charge. The voltage control circuit 16 applies a DC voltage from the charging roller 14 to the photoconductor 10 for the above charging. The voltage control circuit 16 can apply an AC voltage to the charging roller 16.

  By the way, even if the toner on the photoconductor 10 is scraped off by the blade 12, not all of the toner is scraped off. As shown in FIG. Then, the toner is retained as the retained toner 25. When the photoconductor 10 in a stopped state starts to rotate, the staying toner 25 passes between the blade 12 and the photoconductor 10 due to vibration of the blade 12 and the photoconductor 10, reaches the charging roller 14, and adheres. (Stain).

  As described above, when the stationary toner 25 adheres to the charging roller 14, the charging performance of the portion where the stationary toner 25 adheres deteriorates, and as a result, a defective charging portion also occurs on the photoconductor 10. When the photoconductor 10 is of a reversal development method, the poorly charged portion is developed, resulting in horizontal black streaks, and the image quality is degraded. When the charging roller 14 employs a DC charging method in which a DC voltage is applied to charge the photoreceptor 10, the stuck toner 25 that has adhered is difficult to separate once attached.

  Therefore, in the present embodiment, the charging roller 14 is cleaned (that is, dirt (toner) is less likely to adhere to the stationary toner 25 and more specifically dirt is removed). FIG. 4 shows a flowchart illustrating a cleaning process program for the charging roller 14.

  When an instruction to rotate the photoconductor 10 in a stopped state for image formation is input to the control device 22, the cleaning process program starts. In step 32, the motor 20 is controlled to rotate the photoconductor 10. Let it begin.

  In step 34, a cleaning process (details will be described later) for applying an AC voltage to the charging roller 14 for a certain period of time is performed in order to make the staying toner 25 less likely to adhere to the charging roller 14 and to clean it.

  In step 36, it is determined whether or not a predetermined time has elapsed. Here, the predetermined time is a predetermined time until the charging roller 14 can properly charge the photosensitive member 10 by switching the voltage applied to the charging roller 14 from an alternating voltage to a direct current. It is.

  When this predetermined time has elapsed, in step 38, an image forming process is executed. That is, an electrostatic latent image is formed on the photoconductor 10 by the optical device 18, the electrostatic latent image is developed with toner by a developing device, and the toner image is transferred onto a sheet by a transfer device. The photoconductor 10 continues to rotate, and the toner remaining on the photoconductor 10 without being transferred to the paper is scraped off by the blade 12. The photosensitive member 10 from which the remaining toner has been scraped is also charged by the charging roller 15 after being neutralized by the neutralizing device for the next image formation.

  Next, the cleaning process of applying AC voltage to the charging roller 14 for a certain period of time in order to make it difficult for the stationary toner 25 to adhere to the charging roller 14 and to clean the charging roller 14 in the above step 34 is shown in each timing chart and FIG. This will be described in detail with reference to the state of adhesion of the residual toner 25 to the charging roller 14 shown in FIG.

  FIG. 5 shows a timing chart (FIG. 5C) of the AC voltage for the cleaning process, together with the rotation state of the photoconductor 10 (FIG. 5A) and the operating state of the optical scanning device (FIG. 5B). ing.

When the photosensitive member 10 is started to rotate (time t0) in step 32 as described above, in the present embodiment, the motor 24 is controlled to start the rotation of the charging roller 14. An AC voltage is applied to the charging roller 14 from the start of rotation of the photosensitive member 10 (time t0). The AC voltage is applied to the charging roller 14 when the portion of the photoconductor 10 located at the first position P1 reaches the second position P2 (time) at the start of rotation of the photoconductor 10 (time t0). In this embodiment, every time the charging roller 14 rotates at least once from the time of arrival (time t1) after the time t1), the charging roller 14 rotates once from the time of arrival (time t1) (time t2). Continue until. Note that the image forming process is executed when the predetermined time has elapsed (time t3) from the end of application of the AC voltage to the charging roller 14 (time t2).

  Next, when the rotation of the photoconductor 10 (time t0) is reached, the portion of the photoconductor 10 located at the first position P1 reaches the second position P2 (time t1). The reason for applying the voltage will be described.

  Even if the toner on the photoconductor 10 is scraped off, not all of the toner is scraped off. As shown in FIG. 6A, a part of the toner stays between the blade 12 and the photoconductor 10. The toner 25 may be stopped. When the stopped photosensitive member 10 starts to rotate, the stationary toner 25 passes between the blade 12 and the photosensitive member 10 due to the vibration of the blade 12 and the photosensitive member 10 as shown in FIG. 6C, the charging roller 14 is reached (time t1). In this state, the stationary toner 25 adheres to the charging roller 14.

  Therefore, when the rotation of the photoconductor 10 (time t0) is reached (time t1) when the portion of the photoconductor 10 located at the first position P1 reaches the second position P2, an AC voltage is applied to the charging roller 14. Is applied to make it difficult for the staying toner 25 to adhere to the charging roller 14.

  Next, the reason why the AC voltage is applied to the charging roller 14 when the charging roller 14 makes one rotation (time t2) from the time of arrival (time t1) will be described.

  As described above, even when the AC voltage is applied to the charging roller 14 at the time of arrival (time t1) to make it difficult for the stationary toner 25 to adhere to the charging roller 14, all of the stationary toner 25 is not necessarily completely. However, it does not mean that it does not adhere to the charging roller 14. That is, as shown in FIG. 6D, a part 25 A of the staying toner 25 is carried on the surface of the photosensitive member 10 without being attached to the charging roller 14, but the remaining part 25 B is the periphery of the charging roller 14. Adhere to the surface. As shown in FIGS. 6D and 6E, the residual toner remaining portion 25B adhering to the peripheral surface of the charging roller 14 contacts the charging roller 14 as the charging roller 14 rotates.

  Therefore, an AC voltage is applied to the charging roller 14 from the time of arrival (time t1) to the time when the charging roller 14 makes one rotation (time t2).

  As a result, the remaining toner remaining portion 25B is separated from the charging roller 14 and carried on the surface of the photosensitive member 10 as shown in FIG. 6F, so that the charging roller 14 can be cleaned. .

  Next, the reason why an AC voltage is applied to the charging roller 14 at the start of rotation of the photoconductor 10 (time t0) will be described.

  The example described above is an example in which the toner stays between the blade 12 and the photoconductor 10, but this amount is small, but as shown in FIG. It also occurs between the body 10.

  Therefore, at the start of rotation of the photoconductor 10 (time t0), that is, in the present embodiment, at the start of rotation of the charging roller 14, an AC voltage is applied to the charging roller 14, and as shown in FIG. As shown in FIG. 7B, the staying toner 27 staying between the charging roller 14 and the photosensitive member 10 is passed between the charging roller 14 and the photosensitive member 10.

  Next, the reason why the AC voltage is continuously applied to the charging roller 14 from the start of rotation of the photosensitive member 10 (time t0) will be described.

  As shown in FIG. 7C, a small amount of toner that has passed between the blade 12 and the photoreceptor 10 is attached (dirty) as attached toner 29 on the peripheral surface of the charging roller 14.

  Therefore, from the start of rotation of the photoconductor 10 (time t0), an AC voltage is continuously applied to the charging roller 14 for at least one rotation of the charging roller 14, and the adhering toner 29 adhered to the peripheral surface of the charging roller 14. 7D is moved (cleaned) from the charging roller 14 to the photoconductor 10 as shown in FIG.

  As described above, the rotation of the photosensitive member 10 (time t0), the rotation of the charging roller 14 from the rotation start of the photosensitive member 10 (time t0), the arrival time (time t1), and the arrival time (time) It is necessary to apply an AC voltage to the charging roller 14 when the charging roller 14 makes one rotation from time t1) (time t2), but it is complicated to apply an AC current or to stop applying the AC voltage according to each. It becomes. Therefore, in this embodiment, in order to realize simple control, from the start of rotation of the photoconductor 10 (time t0) to the time when the charging roller 14 rotates once (time t2) from the time of arrival (time t1). An alternating current is applied across.

  Next, the AC current will be described. In the present embodiment, the maximum value of the alternating current is set to be twice or more the discharge start voltage based on the following experimental results.

As shown in FIG. 8, the AC voltage oscillates between the maximum value V _D and the minimum value V _S around V ₀ , and in this embodiment, the photosensitive member 10 has the maximum value V _D and the minimum value V _S. It will be discharged at this part. The maximum value V _D is the discharge start voltage.

  As shown in FIG. 9, the AC voltage to be applied was gradually changed, and the contamination on the peripheral surface of the charging roller (BCR) 14 was measured. As shown in FIG. 9, when the maximum value Vpp of the alternating current was 1.2 [kV] or more, an experimental result was obtained that the contamination on the peripheral surface of the charging roller (BCR) 14 was reduced.

Here, the maximum value of the alternating current Vpp = 1.2 [kV] is twice the discharge start voltage V _D.

  Therefore, in the present embodiment, the maximum value of the alternating current is set to be twice or more the discharge start voltage.

  Further, the following experiment different from the above experiment (FIG. 9) was tried.

  First, the toner image shown in FIG. 10A is attached to the peripheral surface of the charging roller 14.

  Here, in the present embodiment, four toner images G1 to G4 obtained by gradually changing the density of three narrow toner images each having the same density, and a planar toner image having the same density on the entire surface are gradually obtained. Four toner images G11 to G14 having different densities were used.

  The toner images G1 to G4 and G11 to G14 were attached to the charging roller 14 to which the alternating current (the maximum value Vpp is at least twice the discharge start voltage) is applied as described above. For comparison, the toner images G1 to G4 and G11 to G14 were attached to the charging roller 14 to which a DC voltage was applied.

  As a result, when the charging roller 14 to which a DC voltage is applied is soiled with the toner images G1 to G4 and G11 to G14, a charging failure occurs in the portion where the toner images G1 to G4 and G11 to G14 are adhered. As shown in FIG. 10B, the toner images G1 to G4, G11 to G14, and the like, as shown in FIG. Images with the same pattern were generated, and the images W1 and W11 were remarkably recognized particularly in the case of poor charging at the portions where the toner images G1 and G11 having high density adhered.

  In the charging roller 14 to which a DC voltage is applied, since the polarity is not reversed, the peripheral surface of the charging roller 14 is not soiled. As shown in FIGS. 10C and 10D, the image formation is performed. The degree of contamination of the charging roller 14 was the same before and after.

  On the other hand, when the charging roller 14 to which the AC voltage is applied as described above is soiled with the toner images G1 to G4 and G11 to G14 as shown in FIG. The portions to which G4 and G11 to G14 were attached were removed from the charging roller 14 by an AC voltage as shown in FIG.

  As a result, no charging failure occurs, no charging failure occurs in the corresponding portion of the photoconductor 10, and an image having a uniform density on the entire surface is formed on the sheet, as shown in FIG. Further, images having the same pattern as the toner images G1 to G4 and G11 to G14 were not generated.

  Further, a plurality of toners having different toner amounts per unit area were passed between the charging roller 14 and the photoreceptor 10 (intrusion). That is, a plurality of toners having a toner amount per unit area of 1.144, 0.957, 0.709, 0.474, and 0.123 were passed. Also in this experiment, in addition to the case where an AC voltage was applied during passage (FIG. 11B), a DC voltage was applied for comparison (FIG. 11A).

  As can be understood by comparing FIG. 11 (A) and FIG. 11 (B), the amount of adhesion to the charging roller 14 with respect to the amount of rush (the portion indicated by hatching) is the case where an AC voltage is applied during passage. (FIG. 11 (B)) is less than the case where a DC voltage is applied (FIG. 11 (A)).

  As described above, in the present embodiment, the voltage control circuit that applies a DC voltage from the charging roller to the photosensitive member for charging is controlled for charging, and the toner retained between the blade and the photosensitive member is used as the charging unit. Since it does not adhere easily, the charging means can be made difficult to get dirty with a simple configuration.

1 is a schematic diagram of an image forming apparatus. It is a block diagram of an image forming apparatus (cleaning apparatus). FIG. 4 is a diagram illustrating a state in which toner staying between a blade and a photosensitive member passes through the toner and reaches a charging roller and adheres thereto. It is the flowchart which showed the cleaning processing program. It is a timing chart at the time of a cleaning process. It is a figure which shows the mode at the time of a cleaning process by seeing the surface of a photoreceptor to a plane. It is another figure which shows the mode at the time of a cleaning process by seeing the surface of a photoreceptor to a plane. It is a figure which shows the mode of an alternating current. It is the figure which showed the experimental result of the stain | pollution | contamination of the surrounding surface of a charging roller when the alternating voltage to apply is changed gradually. 2A and 2B are diagrams illustrating an image and a stain when a toner image is attached to a charging roller. FIG. 3A is a diagram illustrating a toner image that stains the charging roller, and FIG. FIG. 4C is a diagram illustrating an image formed on a sheet with a photosensitive member charged in FIG. 4C, and FIG. 4C is a diagram illustrating a state of contamination on the peripheral surface of the charging roller stained with a toner image, and FIG. It is the figure which showed the mode of the stain | pollution | contamination of the surrounding surface of the charging roller after applying a DC voltage to the charging roller which became dirty with an image, (E) is the photoconductor charged with the alternating voltage to the dirty charging roller. FIG. 4F is a diagram illustrating an image formed on a sheet, FIG. 5F is a diagram illustrating a state of contamination on the peripheral surface of the charging roller stained with a toner image, and FIG. It is the figure which showed the mode of the stain | pollution | contamination of the surrounding surface of the charging roller after applying an alternating voltage. FIG. 6 is a diagram illustrating the amount of rush and the degree of contamination when a plurality of toners having different toner amounts per unit area are passed (rushed) between the charging roller and the photosensitive member. A case where a DC voltage is applied is shown, and FIG. 5B is a diagram showing a case where an AC voltage is applied to the charging roller.

Explanation of symbols

10 photoconductor 18 optical scanning device (formation means)
20 Motor (rotating means)
12 Blades
14 Charging roller (charging means)
16 Voltage control circuit (voltage control means)
22 Control device (control means)

Claims (12)

A rotating photoreceptor for forming the electrostatic latent image and developing the electrostatic latent image with toner;
Forming means for forming an electrostatic latent image on the photoreceptor;
A rotating means for rotating the photosensitive member;
Scraping means for scraping the toner in contact with the photosensitive member;
Charging means for contacting and charging the photoconductor at a second position spaced from the first position of the scraping means contacting the photoconductor downstream in the rotational direction;
A voltage control unit capable of applying a DC voltage from the charging unit to the photoconductor for the charging, and capable of applying an AC voltage to the charging unit;
The rotation unit is controlled to start rotation of the stopped photoconductor, and when the portion of the photoconductor positioned at the first position reaches the second position at the start of rotation, an AC voltage is applied to the charging unit. Control means for controlling the voltage control means to be applied;
An image forming apparatus including:   The control means controls the forming means so that an electrostatic latent image is formed on the photoconductor after the application of the alternating voltage to the charging means is finished and a direct current is applied for a predetermined time. The image forming apparatus according to claim 1. A cleaning device for cleaning a rotary charging unit that forms an electrostatic latent image and contacts and charges a rotary photosensitive member for developing the electrostatic latent image with toner,
The charging unit contacts the photoconductor at a second position spaced from the first position of the detoning unit that contacts the photoconductor to contact the photoconductor and downstream in the rotational direction. And
A voltage control unit capable of applying a DC voltage from the charging unit to the photoconductor for the charging, and capable of applying an AC voltage to the charging unit;
The voltage control means is arranged so that an alternating voltage is applied to the charging means when the portion of the photoconductor positioned at the first position reaches the second position at the start of rotation of the photoconductor in a stopped state. Control means for controlling;
A cleaning device.   4. The cleaning according to claim 3, wherein the control means further controls the voltage control means so that an alternating voltage is applied to the charging means every time the charging means makes at least one rotation from the arrival time. apparatus.   5. The cleaning apparatus according to claim 3, wherein the control unit further controls the voltage control unit so that an AC voltage is applied to the charging unit at least when the charging unit starts rotating.   6. The cleaning according to claim 5, wherein the control unit further controls the voltage control unit so that an AC voltage is applied to the charging unit during at least one rotation from the start of rotation of the charging unit. apparatus. The electrostatic latent image is formed, and the electrostatic latent image is contacted with the photosensitive member of the scraping means for contacting the rotating photosensitive member for developing with the toner and scraping off the toner. A cleaning method for cleaning a rotary charging means that is charged by applying a DC voltage by contacting the photoconductor at a second position spaced from the position downstream in the rotation direction,
A cleaning method, wherein an AC voltage is applied to the charging means when a portion of the photoconductor positioned at the first position reaches the second position at the start of rotation of the photoconductor in a stopped state. .   8. The cleaning method according to claim 7, wherein an AC voltage is applied to the charging unit every time the charging unit makes at least one rotation from the arrival time.   9. The cleaning method according to claim 7, wherein an AC voltage is applied to the charging unit at least at the start of rotation of the charging unit.   The cleaning method according to claim 9, wherein an AC voltage is applied to the charging unit during at least one rotation from the start of rotation of the charging unit.   The cleaning device according to any one of claims 3 to 6, wherein the maximum value of the alternating current to be applied is twice or more the discharge start voltage.   11. The cleaning method according to claim 7, wherein the maximum value of the AC current to be applied is twice or more the discharge start voltage.

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