JP2010276753A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that yields an excellent image over a long term by completely removing developer on a developing sleeve when forcibly consuming the developer of a developing device. <P>SOLUTION: The image forming apparatus 1 includes: the rotatable developing sleeve 26 supplying magnetic toner to a developing area D opposed to a photoreceptor drum 11; a magnetic pole member 25, included in the developing sleeve 26, capable of rotating in a periphery direction and having a plurality of magnetic pole parts N1, S1 and S2; and a power supply part 41 applying bias voltage to the developing sleeve 26. The image forming apparatus 1 includes a motor driving circuit 47 which rotates the developing sleeve 26 in a state where the magnetic pole part N1 of the magnetic pole member 25 is opposed to the developing area D when forming the image, and rotates the magnetic pole member 25 so that space between the adjacent magnetic poles S1 and S2 of the magnetic pole member 25 may be opposed to the developing area D, and also rotates the developing sleeve 26 when forcibly consuming the toner. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using the electrophotographic method, and more particularly to an image forming apparatus that forcibly consumes developer of a developing device.

  2. Description of the Related Art Conventionally, image forming apparatuses including a developing unit that develops an electrostatic latent image formed on the surface of a photoconductor as an image carrier with a one-component magnetic developer have been widely put into practical use. Such a developing device frictionally charges the developer by friction between the developers or by rubbing against the developing sleeve, etc., carries the developer on the developing sleeve, and supplies the carried developer to the photoreceptor. As a result, the developer in the developing device is consumed.

  When the developer is consumed in the developing device, it is replenished from the toner cartridge and a new developer is used for development. By repeating this, the developer in the developing device is replaced. However, when developing an image with a low printing rate, if the consumption of the developer is small and the image that consumes a small amount of the developer is continuously output, the change of the developer in the developing device is little. Not done. When the developer is present in the developing unit for a long time, the developer is rubbed with each other over a long period of time, and is rubbed against the developing sleeve to circulate in the developing unit. In addition, uneven distribution of particle size, abnormal charging and changes in charging characteristics occur, and further, the fluidity decreases due to aggregation of the developer. As described above, the developer is deteriorated, and when an image is formed with the deteriorated developer, the image quality is lowered.

  Therefore, in Patent Document 1, the developer in the developing device is forcibly consumed. The developing device of Patent Document 1 includes a rotatable developing sleeve and a fixed magnetic pole provided inside the developing sleeve. When the developer adheres to the developing sleeve by the magnetic field of the fixed magnetic pole and the developing sleeve supplies the developer to the photosensitive member, the electrostatic latent image on the photosensitive member is developed. When forced consumption is performed, the image area ratio per unit moving distance of the developing sleeve is calculated from the linear velocity of the developing sleeve and the image printing rate. In accordance with the image area ratio, the size of the black band image is determined outside the image area, and the developer corresponding to the black band image is supplied from the developing sleeve to the photoreceptor. This forcibly consumes the developer in the developing device and suppresses the deterioration of the developer.

  In the prior art described above, the fixed magnetic pole (main pole) is usually arranged in the developing region that faces the photoreceptor and supplies the developer. Due to the magnetic field of the fixed magnetic pole, the magnetic developer having a predetermined charge adheres to the developing sleeve, and the magnetic developer that is abnormally charged such as uncharged or lowly charged adheres to the developing sleeve. When a bias voltage is applied to the developing sleeve during development, only a predetermined charged developer flies from the developing sleeve to the photosensitive member against the magnetic force of the main pole in the developing region, and a toner image without fogging is formed on the photosensitive member. Formed on top. However, in forced consumption of the developer, even if a bias voltage is applied as in the development, the developer with a predetermined charge will fly toward the photoreceptor, but the abnormally charged developer will be applied to the photoreceptor. There was a problem that the developer remained on the developing sleeve without flying toward the developing sleeve, and the developer on the developing sleeve was not sufficiently cleaned.

Japanese Patent Laying-Open No. 2005-43388 (paragraphs [0065] to [0078], FIG. 1)

  The present invention has been made to solve the above-described problems. When the developer in the developer is forcibly consumed, the developer on the developing sleeve is sufficiently cleaned, and a good image can be obtained over a long period of time. An object of the present invention is to provide an obtained image forming apparatus.

  To achieve the above object, the present invention provides a rotatable developing sleeve for supplying a magnetic developer to a developing region facing an image carrier, and a plurality of magnetic poles included in the developing sleeve and rotatable in the circumferential direction. A magnetic pole member having a portion, a power supply portion for applying a bias voltage to the developing sleeve, and at the time of image formation, the magnetic sleeve of the magnetic pole member is opposed to a developing region, and the developing sleeve is rotated to forcibly consume the developer. Sometimes, the magnetic pole member is rotated so that the adjacent magnetic poles of the magnetic pole member are opposed to the developing region, and a drive unit that rotates the developing sleeve is provided.

  According to this configuration, at the time of image formation, the charged magnetic developer adheres onto the developing sleeve and is conveyed onto the developing region on the developing sleeve. When a bias voltage is applied to the developing sleeve, in the developing area, a predetermined charged developer flies from the developing sleeve to the image carrier against the magnetic force of the magnetic pole portion facing the developing area, and the toner image is image-bearing. Formed on the body. When the developer is forcibly consumed, the adjacent magnetic poles of the magnetic pole member are opposed to the development region.Therefore, in the development region, there is almost no magnetic force and does not act on the developer. The abnormally charged developer together with the predetermined charged developer moves from the developing sleeve to the image carrier.

  According to a second aspect of the present invention, the adjacent magnetic poles of the magnetic pole member are repulsive magnetic pole regions formed with the same polarity, and when the developer is forcibly consumed, the drive unit develops the repulsive magnetic pole region. The magnetic pole member is rotated so as to face the region. According to this configuration, when the developer is forcibly consumed, the repulsion magnetic pole area faces the development area, so that there is almost no magnetic force in the development area, and the bias voltage is applied to the development sleeve in this state. Then, the abnormally charged developer together with the predetermined charged developer moves from the developing sleeve to the image carrier.

  According to a third aspect of the present invention, there is provided a regulating member that regulates the amount of the developer on the developing sleeve, and when the developer is forcibly consumed, the drive unit is configured to be one of the plurality of magnetic poles. The magnetic pole member is rotated so that the portion faces the restriction member. According to this configuration, when the developer is forcibly consumed, the developer adheres to the developing sleeve by the magnetic pole portion facing the regulating member, and the regulating member regulates the developer deposited on the developing sleeve to a predetermined layer thickness. To do.

  According to a fourth aspect of the present invention, when a predetermined number of images are formed, the driving unit rotates the magnetic pole member so that the adjacent magnetic poles of the magnetic pole member are opposed to the development region. It is characterized by that.

  According to the first aspect of the present invention, at the time of image formation, the charged magnetic developer adheres on the developing sleeve and is conveyed onto the developing region on the developing sleeve. When a bias voltage is applied to the developing sleeve, in the developing area, the developer with a predetermined charge flies from the developing sleeve to the image carrier against the magnetic force of the magnetic pole portion facing the developing area, and there is no fog A toner image can be formed on the image carrier. When the developer is forcibly consumed, the adjacent magnetic poles of the magnetic pole member are opposed to the development region.Therefore, in the development region, there is almost no magnetic force and does not act on the developer. The abnormally charged developer together with the predetermined charged developer moves from the developing sleeve to the image carrier, and the developer on the developing sleeve is sufficiently cleaned, and a good image can be obtained over a long period of time.

  According to the second aspect of the present invention, when the developer is forcibly consumed, the repulsion magnetic pole region faces the development region, so that there is almost no magnetic force in the development region, and the developer does not act on this state. When a bias voltage is applied to the developing sleeve, the abnormally charged developer together with the predetermined charged developer moves from the developing sleeve to the image carrier, and the developer on the developing sleeve can be sufficiently cleaned.

  According to the third aspect of the present invention, when the developer is forcibly consumed, the developer adheres to the developing sleeve by the magnetic pole portion facing the regulating member, and the regulating member adheres to the developing sleeve. Is regulated to a predetermined layer thickness. As a result, there is no risk of excess developer coming into contact with the image carrier in the development area and contaminating the image carrier, and the developer is moved to the image carrier during forced consumption within the range of the bias voltage applied during image formation. Can be made.

  According to the fourth aspect of the present invention, the magnetic pole member is rotated so that the adjacent magnetic poles of the magnetic pole member are opposed to the development area when a predetermined number of images are formed. The developer is always cleaned, and a good image can be obtained over a long period of time.

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of a developing device and its control unit in the image forming apparatus according to the embodiment of the present invention. These are sectional views showing the main configuration of the developing device according to the embodiment of the present invention during image formation. These are sectional drawings which show the principal part structure at the time of forced consumption of the developing device according to the embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Further, the use of the invention and the terms shown here are not limited thereto.

  FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 1 includes a sheet feeding unit 2 disposed in a lower portion thereof, a sheet conveying unit 3 disposed on a side of the sheet feeding unit 2, and the sheet conveying unit 3. An image forming unit 4 disposed above the image forming unit 4, a fixing unit 5 disposed on the discharge side of the image forming unit 4, and an image reading unit disposed above the image forming unit 4 and the fixing unit 5. 6 is provided.

  The paper feed unit 2 includes a plurality of paper feed cassettes 7 for containing paper 9, and the paper 9 is fed from the selected paper feed cassette 7 among the plurality of paper feed cassettes 7 by the rotation of the paper feed roller 8. Each sheet is surely sent out to the sheet transport unit 3.

  The paper 9 sent to the paper transport unit 3 is transported toward the image forming unit 4 via the paper supply path 10. The image forming unit 4 forms a toner image on a sheet 9 by an electrophotographic process, and includes a photosensitive drum 11 that is rotatably supported in a predetermined direction (the arrow direction in FIG. 1), and the photosensitive drum 11. A charging unit 12, a developing device 14, a transfer unit 15, a cleaning unit 16, and a charge eliminating unit 17 are provided around the body drum 11 along the rotation direction.

  The charging unit 12 includes a charging wire to which a high voltage is applied. When a predetermined potential is applied to the surface of the photosensitive drum 11 by corona discharge from the charging wire, the surface of the photosensitive drum 11 is uniformly charged. . Then, when light based on the image data of the document read by the image reading unit 6 is irradiated to the photosensitive drum 11 by the exposure unit 13, the surface potential of the photosensitive drum 11 is selectively attenuated, and the photosensitive drum. 11 An electrostatic latent image is formed on the surface. Next, the developing device 14 develops the electrostatic latent image on the surface of the photosensitive drum 11, and a toner image is formed on the surface of the photosensitive drum 11. The toner image is transferred to the paper 9 supplied between the photosensitive drum 11 and the transfer unit 15 by the transfer unit 15.

  The sheet 9 on which the toner image has been transferred is conveyed toward the fixing unit 5 disposed on the downstream side of the image forming unit 4 in the sheet conveying direction. In the fixing unit 5, the sheet 9 is heated and pressed by the heating member 18 and the pressure roller 19, and the toner image is melted and fixed on the sheet 9. Next, the sheet 9 on which the toner image is fixed is discharged onto the discharge tray 21 by the discharge roller pair 20. After the transfer by the transfer unit 15, the toner remaining on the surface of the photoconductive drum 11 is removed by the cleaning unit 16, and the residual charge on the surface of the photoconductive drum 11 is removed by the charge eliminating unit 17. Then, the photosensitive drum 11 is charged again by the charging unit 12, and thereafter image formation is performed in the same manner.

  Next, the developing device will be described with reference to FIG. FIG. 2 is a cross-sectional view showing a schematic configuration of the developing unit and its control unit used in the image forming apparatus 1 according to the embodiment of the present invention.

  The developing device 14 includes a developing container 22 that contains a one-component magnetic developer, stirring members 23 and 24 that stir and transport the developer (hereinafter, sometimes referred to as “toner”), a developing sleeve 26, A magnetic pole member 25 and a regulating member 28 are provided. When the toner in the developing device 14 is consumed, the toner tank 31 supplies the toner to the developing device 14.

  The stirring members 23 and 24 are rotatably disposed at the bottom of the developing container 22 with a partition wall interposed therebetween. Moreover, the stirring members 23 and 24 are provided with blades formed in a spiral shape in the axial direction. When the agitating members 23 and 24 rotate, the toner is agitated, and the agitated toner circulates in the developing container 22 through a hole provided in the partition wall, and the toner is charged by friction between the toners. Then, the toner is conveyed to the developing sleeve 26 by the stirring member 24.

  The developing sleeve 26 is formed in a cylindrical shape with a nonmagnetic material such as aluminum and incorporates a magnetic pole member 25. Further, the developing sleeve 26 is rotatably supported in the developing container 22 at a position adjacent to the stirring member 24, and is rotated in the arrow direction (counterclockwise direction) in FIG. Further, the developing sleeve 26 is exposed from the opening of the developing container 22 and is opposed to the photosensitive drum 11 that is an image carrier with a certain interval. A developing area D for supplying the toner adhering to the developing sleeve 26 toward the photosensitive drum 11 is formed in the opposed area. Further, in order to supply the toner on the developing sleeve 26 to the photosensitive drum 11, the developing sleeve 26 is connected to a power supply unit 41 in which alternating current is superimposed on direct current, and this bias voltage is applied to the developing sleeve 26.

  The regulating member 28 regulates the toner adhering to the surface of the developing sleeve 26 to a predetermined layer thickness. The regulating member 28 has a blade shape and has a predetermined shape with the surface of the developing sleeve 26 on the upstream side in the rotating direction of the rotating sleeve 26 in the developing region D. The developer container 22 is attached with an interval.

  The magnetic pole member 25 has a plurality of magnetic pole portions in the circumferential direction, and generates a magnetic field toward the surface of the developing sleeve 26. The magnetic pole member 25 is rotatably supported in the developing container 22 and is rotated by a motor 46. At the time of image formation, when the predetermined magnetic pole of the magnetic pole member 25 faces the development area D and the toner in the developing device 14 is forcibly consumed, the magnetic member 26 is rotated from the state at the time of image formation by the motor 46 and developed. The position of the magnetic pole portion changes with respect to the region D.

  At the time of image formation, the toner conveyed from the stirring member 24 adheres to the surface of the developing sleeve 26. The adhered toner is regulated to a constant layer thickness by the regulating member 28 and is conveyed toward the developing flow area D by the rotation of the developing sleeve 26 in the direction of the arrow in FIG. When a bias voltage is applied between the developing sleeve 26 and the photosensitive drum 11 by the power supply unit 41, the toner on the developing sleeve 26 is supplied to the photosensitive drum 11 in the developing region D, and the photosensitive drum 11. The upper electrostatic latent image is developed into a toner image.

  Further, the image forming apparatus 1 includes a motor drive circuit 47 as a drive unit that rotationally drives the motors 45 and 46. In addition, the image forming apparatus 1 connects the bias driving circuit 42 that drives the power supply unit 41, the counting unit 51 that counts the number of sheets on which image formation has been performed, and the counting unit 51, and the motor driving circuit 47 and the bias driving circuit. And a control unit 50 having a CPU, a ROM, a RAM, and the like for controlling 42.

  The control unit 50 controls the motor drive circuit 47 and rotates the motor 45 by turning on the power of the apparatus. The developing sleeve 26 is rotated by the rotation of the motor 45, and the toner on the developing sleeve 26 is charged (developing aging). In response to the print instruction signal, the control unit 50 controls the bias drive circuit 42 to drive the power supply unit 41. The electrostatic latent image on the photosensitive drum 11 is developed by applying a bias of the power supply unit 41. When the image formation is completed, the counting unit 51 adds the number of printed sheets, and inputs the total number of printed sheets to the control unit 50. When the cumulative number reaches the predetermined number, the control unit 50 controls the motor drive circuit 47 to rotate the motor 46. The rotation of the motor 46 moves the magnetic pole part of the magnetic pole member 25 facing the developing area D to a position different from that at the time of image formation, and the motor 46 stops. In the state where the magnetic pole member 25 is in the above state, for example, a solid image is continuously developed at the time of development aging, and the toner of the developing device 14 is forcibly consumed. Alternatively, when an image with a low printing rate is continuously output, the solid image may be developed outside the image area, such as during normal image formation. When the toner in the developing device 14 is forcibly consumed, new toner is supplied from the toner tank 31.

  Next, the configuration operation of the developing device 14 during image formation and forced toner consumption will be described in detail. FIG. 3 is a cross-sectional view showing a main configuration of the developing device during image formation, and FIG. 4 is a cross-sectional view showing a main configuration of the developing device during forced consumption.

  As shown in FIG. 3, the magnetic pole member 25 is disposed in the developing sleeve 26. In the magnetic pole member 25, magnetic pole portions S 1, S 2, and N 1 are arranged in order along the rotation direction of the developing sleeve 26.

  The magnetic pole portion S2 is disposed so as to face the regulating member 28, and generates a magnetic field toward the surface of the developing sleeve 26 at that position. The magnetic toner adheres to the surface of the developing sleeve 26 due to the frictional charging of the magnetic toner between the regulating member 28 and the developing sleeve 26 and the magnetic force of the magnetic pole S2. The thickness of the adhering toner is regulated by the regulating member 28.

  The magnetic pole portion N1 is disposed so as to face the developing region D, and generates a magnetic field toward the surface of the developing sleeve 26 in the developing region D. When the bias voltage of the power supply unit 41 (see FIG. 2) is applied to the developing sleeve 26, the magnetic toner having a predetermined charge flies from the developing sleeve 26 to the photosensitive drum 11 against the magnetic force of the magnetic pole portion N1. The magnetic toner that has been abnormally charged, such as uncharged or low-charged, is prevented from flying to the photosensitive drum 11 by the magnetic force of the magnetic pole portion N1, and remains on the developing sleeve 26. As a result, a good toner image free of fog or the like is formed on the photosensitive drum 11.

  The magnetic pole portions S1 and S2 have the same polarity. A repulsive magnetic pole region R is formed on the peripheral surface between the magnetic pole portions S1 and S2. In the repulsive magnetic pole region R, the magnetic flux density is approximately 0 Gauss. The repulsive magnetic pole region R faces the agitating member 24, and charged toner conveyed from the agitating member 24 adheres to the surface of the developing sleeve 26 in this region, while toner that is not consumed for development in the developing region D comes from the developing sleeve 26. It is peeled off and returned to the stirring member 24 side.

  At the time of image formation, the magnetic pole member 25 is in the above state. However, when the toner is forcibly consumed, the magnetic pole member 25 is rotated approximately 150 degrees in the counterclockwise direction of FIG. Become.

  When the toner is forcibly consumed as shown in FIG. 4, the magnetic pole S <b> 1 of the magnetic pole member 25 is disposed so as to face the regulating member 28, and a magnetic field is generated toward the surface of the developing sleeve 26 at that position. Magnetic toner adheres to the surface of the developing sleeve 26 due to frictional charging of the magnetic toner between the regulating member 28 and the developing sleeve 26 and the magnetic force of the magnetic pole S1. The thickness of the adhering toner is regulated by the regulating member 28.

  The repulsive magnetic pole region R is disposed so as to face the developing region D, and hardly generates a magnetic field in the developing region D. The magnetic force of the magnetic pole member 25 does not act on the magnetic toner on the developing sleeve 26 in the developing region D. As a result, when the developing sleeve 26 and the photosensitive drum 11 are rotated and a bias voltage of the power supply unit 41 (see FIG. 2) is applied to the developing sleeve 26, the magnetic toner having a predetermined charge is transferred from the developing sleeve 26 to the photosensitive drum 11. And the abnormally charged magnetic toner also moves to the photosensitive drum 11. When the developing sleeve 26 is continuously rotated in this manner, the toner on the developing sleeve 26 is cleaned.

  According to the above-described embodiment, the image forming apparatus 1 includes a rotatable developing sleeve 26 that supplies magnetic toner to the developing region D that faces the photosensitive drum 11, and is included in the developing sleeve 26 and is rotatable in the circumferential direction. A magnetic pole member 25 having a plurality of magnetic pole portions N1, S1, and S2, and a power supply portion 41 that applies a bias voltage to the developing sleeve 26. Further, the image forming apparatus 1 rotates the developing sleeve 26 with the magnetic pole portion N1 of the magnetic pole member 25 facing the developing region D at the time of image formation. A motor drive circuit 47 (drive unit) that rotates the magnetic pole member 25 and rotates the developing sleeve 26 so as to face the developing region D is provided.

  According to this configuration, at the time of image formation, the charged magnetic toner adheres to the developing sleeve 26 and is conveyed onto the developing region D on the developing sleeve 26. When the bias voltage of the power supply unit 41 is applied to the developing sleeve 26, in the developing region D, the magnetic toner having a predetermined charge flies from the developing sleeve 26 to the photosensitive drum 11 against the magnetic force of the magnetic pole portion N1, and is fogged. It is possible to form a good toner image without the like on the photosensitive drum 11. When the toner is forcibly consumed, the adjacent magnetic poles S1 and S2 of the magnetic pole member 25 are opposed to the developing region D. Therefore, in the developing region D, there is almost no magnetic force and the toner is not supplied to the developing sleeve 26 in this state. When the bias voltage of the portion 41 is applied, the abnormally charged magnetic toner together with the predetermined charged magnetic toner moves from the developing sleeve 26 to the photosensitive drum 11, and the toner on the developing sleeve 26 is sufficiently cleaned. A good image can be obtained.

  Further, according to the above embodiment, the adjacent magnetic poles of the magnetic pole member 25 are the repulsive magnetic pole regions R formed with the same polarity, and when the toner is forcibly consumed, the drive unit converts the repelling magnetic pole region R into the developing region D. The magnetic pole member 25 is rotated so as to face each other. As a result, when the toner is forcibly consumed, the repulsion magnetic pole region R faces the development region D. Therefore, in the development region D, there is almost no magnetic force and the toner does not act on the toner. When a voltage is applied, the abnormally charged magnetic toner together with the predetermined charged magnetic toner moves from the developing sleeve 26 to the photosensitive drum 11, and the developer on the developing sleeve 26 can be sufficiently cleaned.

  In addition, according to the above embodiment, the regulating member 28 that regulates the amount of toner on the developing sleeve 26 is provided, and when the toner is forcibly consumed, the driving unit is one of the magnetic poles N1, S1, and S2. The magnetic pole member 25 is rotated so that the portion faces the restriction member 28. Thus, when the toner is forcibly consumed, the magnetic toner adheres to the developing sleeve 26 by the magnetic pole portion S2 facing the regulating member 28, and the regulating member 28 causes the magnetic toner adhered on the developing sleeve 26 to have a predetermined layer thickness. Since the regulation is performed, there is no possibility that excess toner contacts the photosensitive drum 11 in the developing region D and contaminates the photosensitive drum 11. In addition, the toner can be moved to the photosensitive drum 11 during forced consumption within the range of the bias voltage applied during image formation, and the bias voltage can be easily controlled.

  Further, according to the embodiment, when a predetermined number of images are formed, the driving unit rotates the magnetic pole member 25 so that the adjacent magnetic poles S1 and S2 of the magnetic pole member 25 are opposed to the development region D. Therefore, the toner on the developing sleeve 26 is always cleaned, and a good image can be obtained over a long period of time.

  In the above-described embodiment, an example in which the present invention is applied to a developing device using a one-component magnetic developer has been described. You may apply to the developing device using.

  In the above-described embodiment, when the developer of the developing device is forcibly consumed, the repulsive magnetic pole region formed between the magnetic pole portions S1 and S2 is opposed to the developing region. Not limited to this, when the developer is forcibly consumed, a magnetic pole member having a magnetic flux density of approximately 0 gauss may be opposed to the development area. For example, a gap between the S pole and N pole of approximately 0 gauss is opposed to the development area. You may make it the structure to make. In this case, the same effect as described above is obtained.

  Moreover, in the said 1st Embodiment, although the magnetic pole member comprised 3 poles, S pole, N pole, and S pole, this invention is not restricted to this, A magnetic pole member is S pole, N pole, S pole, N pole. You may make it the structure which has various pole numbers, such as 4 poles.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 14 Developer 22 Developer container 23, 24 Stirring member 25 Magnetic pole member 26 Developing sleeve 28 Restricting member 41 Power supply part 42 Bias drive circuit 45, 46 Motor 47 Motor drive circuit (drive part)
50 Control part 51 Counting part D Development area N1, S1, S2 Magnetic pole part R Repulsive magnetic pole area

Claims (4)

A rotatable developing sleeve for supplying a magnetic developer to a developing region facing the image carrier;
A magnetic pole member included in the developing sleeve and having a plurality of magnetic pole portions rotatable in the circumferential direction;
A power supply for applying a bias voltage to the developing sleeve;
At the time of image formation, the magnetic pole part of the magnetic pole member is opposed to the development area, and the development sleeve is rotated. An image forming apparatus comprising: a drive unit that rotates the member and rotates the developing sleeve. Between the adjacent magnetic poles of the magnetic pole member is a repulsive magnetic pole area formed with the same polarity, and when the developer is forcibly consumed, the drive unit moves the magnetic pole member so that the repulsive magnetic pole area faces the developing area. The image forming apparatus according to claim 1, wherein the image forming apparatus is rotated.   Provided with a regulating member that regulates the amount of developer on the developing sleeve, and when the developer is forcibly consumed, the drive unit is configured so that any one of the plurality of magnetic pole units faces the regulating member. The image forming apparatus according to claim 1, wherein the magnetic pole member is rotated.   The drive unit rotates the magnetic pole member so that adjacent magnetic poles of the magnetic pole member are opposed to the development area when a predetermined number of images are formed. The image forming apparatus according to claim 3.

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