JP2009294239A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus suppressing unwanted toner adhesion and carrier adhesion to a photoreceptor drum by turning on or off developing bias in appropriate timing even when angular acceleration of the photoreceptor drum changes because of friction change of a driving member and fluidity change of two-component developer. <P>SOLUTION: The image forming apparatus includes: an optical sensor 26 detecting a rotational angle of the photoreceptor drum 16; and a controller 34 applying the developing bias for making toner adhere to an electrostatic latent image to a developing device 19 when the rotational angle of the photoreceptor drum 16 since starting electrification of the photoreceptor drum 16 by an electrifying device 17, which is detected by the optical sensor 26, becomes a reference angle, assuming that an angle to the center shaft of the photoreceptor drum 16 from an electrifying area to a developing area is the reference angle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus.

  An electrophotographic image forming apparatus (hereinafter simply referred to as an “image forming apparatus”) that forms an image based on electrophotography can form high-quality images with simple operations and is easy to maintain. Therefore, it is applied to copying machines, printers, facsimiles, multifunction machines, and the like, and is widely used. The image forming apparatus includes, for example, a photosensitive drum, a charging device, an exposure device, a developing device, a transfer device, a cleaning device, a charge eliminating device, and a fixing device. The surface of the photoconductive drum that is driven to rotate is uniformly charged by a charging device, and the charged photoconductive drum surface is irradiated with laser light by an exposure device to form an electrostatic latent image. Subsequently, the electrostatic latent image on the surface of the photosensitive drum is developed with toner by the developing device, and a toner image that is a visible image is formed on the surface of the photosensitive drum. The toner image on the surface of the photosensitive drum is transferred to a recording material by a transfer device, and then heated and pressurized by a fixing device to be fixed on the recording material. As a result, an image is formed on the recording material. The toner remaining without being transferred to the surface of the photoconductive drum is removed by a cleaning device, and the surface of the photoconductive drum after being cleaned is charged by a static eliminator to form a new image on the photoconductive drum. Is possible.

  As a developer for developing the electrostatic latent image on the surface of the photosensitive drum, there are a one-component developer composed only of toner and a two-component developer composed of toner and carrier. Since the one-component developer does not use a carrier, there is no need for a stirring mechanism for uniformly mixing the toner and the carrier, so that there is an advantage that the developing device is simplified, but the charge amount of the toner is difficult to stabilize. There are drawbacks. Since the two-component developer requires a stirring mechanism for uniformly mixing the toner and the carrier, there is a disadvantage that the developing device becomes complicated. Since it is excellent, it is used for a high-speed image forming apparatus and a color image forming apparatus.

  As a developing method, a reversal developing method is known in which toner adheres to a portion where the surface potential is lowered by light irradiation from an exposure apparatus, and a toner image is formed. In an image forming apparatus using a reversal development method, toner or carrier is applied to a photosensitive drum when the timing of applying a developing bias for attaching toner to an electrostatic latent image to the developing roller is early or late at the start of image formation. There is a problem of sticking.

  FIG. 11 is a graph schematically showing changes in the potential of the development region when the development bias application timing is early. As shown in FIG. 11, at the same time as the rotation of the photosensitive drum is started, charging of the photosensitive drum by the charging device and application of a voltage of +150 V to the developing roller are started. Here, the surface potential of the photosensitive drum in the developing region rises with a delay corresponding to the rotation angle from the charging device to the developing region. Therefore, a developing bias of −500 V is applied to the developing roller when a predetermined time (in this case, 0.1 second) assumed for the surface of the photosensitive drum charged by the charging device to reach the developing region has elapsed. The However, when the rotational speed of the photosensitive drum is slowed down due to some influence, the potential of the photosensitive drum surface in the development region is delayed from the assumed time (here, 0.1 seconds) (here, after 0.15 seconds). It will change. In such a case, the potential of the developing roller becomes −500 V higher than the surface potential of the photosensitive drum as a potential difference (arrow N), and the two-component developer contacts the surface area of the uncharged photosensitive drum. As a result, there is a problem that toner adheres to the surface of the photosensitive drum and waste toner is consumed for each image formation.

  On the other hand, FIG. 12 is a graph schematically showing changes in the potential of the development region when the development bias application timing is late. Contrary to the above, in FIG. 12, when the surface potential of the photosensitive drum in the developing region changes faster (here, 0.1 second) than the assumed time (here, 0.05 second), the surface potential of the photosensitive drum. Becomes -800 V higher than the potential of the developing roller as a potential difference (arrow P). As a result, the carrier adheres while the two-component developer is in contact with the surface area of the uncharged photosensitive drum, so that the carrier disappears every time the image is formed.

In order to solve such a problem, an image forming apparatus that applies a developing bias to a developer roller after a charged region on the surface of the photosensitive drum passes through the developing roller and then drives the developing roller is disclosed in Patent Document 1. Is disclosed.
JP 2006-258840 (released September 28, 2006)

  However, the image forming apparatus disclosed in Patent Document 1 applies a developing bias after the charged area on the surface of the photosensitive drum reaches the developing roller after the charging device starts charging, and then starts driving the developing roller. Therefore, there is a problem that it takes a long time until the rotation of the developing roller is stabilized.

  Also, after the image forming apparatus has been used for a long period of time, if the fluidity of the two-component developer decreases or the wear of the rotating shaft of the photosensitive drum or the developing apparatus proceeds, The angular acceleration becomes slow, and the time until the charged area of the photosensitive drum reaches the position of the developing roller becomes long. In consideration of this, in order to prevent the toner from adhering to the photosensitive drum by applying the developing bias before the charged region reaches the developing roller in any case, it is necessary to use a charging device. It is necessary to set a time with a certain margin as the time from the start of charging to the development bias application timing. As a result, there is a problem that the application timing of the developing bias is delayed more than necessary, and the start of image formation is further delayed.

  As described above, conventionally, since the developing bias cannot be applied at an appropriate timing at the start of image formation, there is a problem that toner or carrier adheres to the photosensitive drum or the start of image formation is delayed. there were.

  Also, as shown in FIGS. 11 and 12, if the toner or carrier unnecessarily adheres to the photosensitive drum due to the difference between the surface potential of the photosensitive drum and the potential of the developing roller, the problem is that The same happens at the end of formation. That is, there is a problem that toner or a carrier adheres to the photosensitive drum when the potential lowering start point on the surface of the photosensitive drum deviates from the change point of the potential of the developing roller due to the stopping of charging by the charging device. .

  The object of the present invention has been made in view of the above problems, and even when the angular acceleration of the photosensitive drum changes due to a change in friction of the driving member or a change in fluidity of the two-component developer. Another object of the present invention is to realize an image forming apparatus that can turn on or off the developing bias at an appropriate timing and can suppress unnecessary toner adhesion and carrier adhesion to the photosensitive drum.

  As a result of intensive investigations in view of the above problems, the applicant of the present application can easily implement the development bias ON / OFF timing appropriately by providing a rotation angle detection unit that detects the rotation angle of the photosensitive drum. As a result, the present invention has been made.

  In other words, in order to solve the above-described problems, the image forming apparatus according to the present invention exposes the photosensitive drum, the charging device for charging the photosensitive drum, and the charged surface of the photosensitive drum to perform static exposure. An electrostatic latent image formed on the photosensitive drum is formed using an exposure apparatus for forming an electrostatic latent image and a two-component developer containing toner and a carrier and utilizing a potential difference between the surface of the photosensitive drum. An image forming apparatus including a developing device for developing, a rotation angle detection unit for detecting a rotation angle of the photosensitive drum, and the charging device of the surface of the photosensitive drum with respect to a central axis of the photosensitive drum When the angle from the charging area to which the charging potential is applied to the developing area on the surface of the photosensitive drum that is in contact with the developer included in the developing device is a reference angle, the rotation angle detection unit In order to cause toner to adhere to the electrostatic latent image when the rotation angle of the photosensitive drum after the charging of the photosensitive drum detected by the charging device reaches the reference angle. And a controller for applying the developing bias to the developing device.

  According to the above configuration, when the rotation angle of the photosensitive drum detected by the rotation angle detection unit after the charging device starts to be charged reaches the reference angle, the electrostatic latent is detected. A developing bias for attaching toner to the image is applied to the developing device. Here, the reference angle refers to the developing device on the surface of the photosensitive drum from a charging region to which a charging potential is applied by the charging device on the surface of the photosensitive drum with respect to the central axis of the photosensitive drum. Is the angle to the development area where the developer is supplied. Therefore, when the rotation angle of the photosensitive drum after starting charging of the photosensitive drum by the charging device reaches the reference angle, the location on the photosensitive drum charged by the charging device reaches the development area. When Since the rotation angle of the photoconductive drum is actually detected, the angular acceleration of the photoconductive drum changes due to some influence, and even if there is a change in the time to reach the reference angle, It is possible to accurately detect the timing at which the portion charged by the apparatus reaches the developing region. Since the developing bias is applied at this timing, the surface potential of the photosensitive drum and the potential of the developing device always change at the same timing in the developing region. However, it does not become faster or slower than the change point of the surface potential of the photosensitive drum. That is, the developing bias can be applied at an optimal timing. As a result, unnecessary toner adhesion and carrier adhesion to the photosensitive drum can be suppressed.

  In addition, since the developing bias can be applied at an optimum timing, the time required to start image formation is not unnecessarily delayed.

  Furthermore, in the image forming apparatus of the present invention, the control unit rotates the photosensitive drum, and the rotation angle of the photosensitive drum after the charging device starts charging the photosensitive drum is determined. Until the reference angle is reached, it is preferable to apply a voltage having a polarity opposite to the charging polarity of the toner to the developing device.

  The period from when the photosensitive drum is rotationally driven to when the rotational angle of the photosensitive drum reaches the reference angle after charging of the photosensitive drum by the charging device is equal to the reference angle. The surface potential of the photosensitive drum is zero. According to the above configuration, during this period, since a voltage having a polarity opposite to the charging polarity of the toner is applied to the developing device, the toner is attracted to the developing device rather than the photosensitive drum. Thereby, it is possible to prevent the toner from adhering to the photosensitive drum during this period.

  Note that the reference angle is downstream from the downstream end in the rotation direction of the photosensitive drum in the charging area with respect to the central axis of the photosensitive drum from the downstream in the rotation direction of the photosensitive drum in the development area. The angle to the side end is preferred.

  Furthermore, the image forming apparatus according to the present invention further includes a rotation driving unit for rotating the photosensitive drum, and the control unit starts the driving of the rotation driving unit and simultaneously starts the rotation of the photosensitive drum by the charging device. It is preferable to start charging.

  According to the above configuration, the idling time of the photosensitive drum can be shortened, and the electrostatic latent image forming operation can be performed quickly.

  Further, the developing bias is preferably a voltage having the same polarity as the charging polarity of the toner. Thereby, it is possible to prevent the carrier from adhering to the surface of the photosensitive drum which is not charged.

  The image forming apparatus of the present invention includes a photosensitive drum, a charging device that charges the photosensitive drum, and an exposure device that forms an electrostatic latent image by exposing the surface of the charged photosensitive drum. And a developing device that develops an electrostatic latent image formed on the photosensitive drum using a two-component developer containing toner and a carrier and utilizing a potential difference from the surface of the photosensitive drum. In the forming apparatus, a rotation angle detection unit that detects a rotation angle of the photosensitive drum, and a charging region to which a charging potential is applied by the charging device on the surface of the photosensitive drum with respect to a central axis of the photosensitive drum The charging device detected by the rotation angle detection unit when the angle from the surface of the photosensitive drum to the developing region which is a contact region with the developer of the developing device on the surface of the photosensitive drum is a reference angle Thus, when the rotation angle of the photosensitive drum after the charging of the photosensitive drum reaches the reference angle, a developing bias for applying toner to the electrostatic latent image is applied to the developing device. And a control unit for stopping the operation.

  According to the above configuration, when the rotation angle of the photosensitive drum detected by the rotation angle detection unit after the charging of the photosensitive drum by the charging device stops becomes the reference angle, the electrostatic latent is detected. Application of the developing bias for attaching the toner to the image to the developing device is stopped. When the rotation angle of the photosensitive drum after the charging of the photosensitive drum by the charging device reaches the reference angle, the portion on the photosensitive drum that is not charged by the charging device has reached the development area. Is the time. Since the rotation angle of the photosensitive drum is actually detected, even if the angular acceleration of the photosensitive drum changes due to some influence and the time until the reference angle is reached changes, It is possible to accurately detect the timing at which a spot on the photosensitive drum that is not charged reaches the developing region. Since the application of the developing bias is stopped at this timing, the surface potential of the photosensitive drum and the potential of the developing device always change at the same timing in the developing region. That is, the development bias application can be stopped at an optimal timing. As a result, unnecessary toner adhesion and carrier adhesion to the photosensitive drum can be suppressed.

  Furthermore, in the image forming apparatus of the present invention, the control unit charges the toner after the rotation angle of the photosensitive drum after the charging device stops charging the photosensitive drum reaches the reference angle. It is preferable to apply a voltage having a polarity opposite to that of the polarity to the developing device.

  The period after the rotation angle of the photosensitive drum becomes the reference angle after the charging of the photosensitive drum by the charging device is stopped is that the surface potential of the photosensitive drum is 0 in the development region. . According to the above configuration, during this period, since a voltage having a polarity opposite to the charging polarity of the toner is applied to the developing device, the toner is attracted to the developing device rather than the photosensitive drum. Thereby, it is possible to prevent the toner from adhering to the photosensitive drum during this period.

  The reference angle is upstream of the upstream end in the rotation direction of the photosensitive drum in the charging area with respect to the central axis of the photosensitive drum from the upstream end in the rotation direction of the photosensitive drum in the development area. The angle to the side end is preferred.

  Furthermore, the image forming apparatus according to the present invention further includes a rotation driving unit for rotating the photosensitive drum, and the controller is configured to stop the rotation driving unit and stop the rotation of the photosensitive drum by the charging device. It is preferable to stop charging.

  According to the above configuration, the time required to stop the rotation of the photosensitive drum can be shortened, and wear and deterioration of the photosensitive drum and the two-component developer can be suppressed.

  Furthermore, in the image forming apparatus of the present invention, it is preferable that the control unit stops applying the voltage to the developing device after the rotation of the photosensitive drum is stopped.

  According to the above configuration, it is possible to prevent toner from adhering to the surface of the photosensitive drum that is not charged.

  In the image forming apparatus of the present invention, a plurality of markers having different light reflectivities from the surface of the photosensitive drum are formed on the surface of the photosensitive drum along the rotation direction of the photosensitive drum. The rotation angle detection unit is disposed at a position facing the marker, and detects the marker based on a difference in light reflectance between the surface of the photosensitive drum and the marker, thereby detecting the marker on the photosensitive drum. Preferably, the rotation angle is detected.

  According to said structure, a rotation angle detection part is realizable with a simple structure.

  In the image forming apparatus according to the present invention, a charging potential is applied by a rotation angle detection unit that detects a rotation angle of the photosensitive drum and a charging device on a surface of the photosensitive drum with respect to a central axis of the photosensitive drum. When the angle from the charged area to the developing area of the surface of the photosensitive drum to which the developer is supplied by the developing device is defined as a reference angle, the photosensitive device by the charging device is detected by the rotation angle detection unit. A control unit that applies a developing bias for attaching toner to the electrostatic latent image to the developing device when the rotation angle of the photosensitive drum after the charging of the photosensitive drum reaches the reference angle With.

  In the image forming apparatus of the present invention, a charging potential is applied by a rotation angle detector that detects a rotation angle of the photosensitive drum and a charging device on the surface of the photosensitive drum with respect to the central axis of the photosensitive drum. When the angle from the charged area to the developing area of the surface of the photosensitive drum to which the developer is supplied by the developing device is defined as a reference angle, the charging device detects the rotation detected by the rotation angle detection unit. When the rotation angle of the photosensitive drum after the charging of the photosensitive drum reaches the reference angle, the application of the developing bias for attaching the toner to the electrostatic latent image to the developing device is stopped. A control unit.

  As a result, the developing bias can be turned on / off at an optimal timing, and unnecessary toner adhesion and carrier adhesion to the photosensitive drum can be suppressed.

  An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

(Overall configuration of image forming apparatus)
FIG. 2 is a diagram schematically illustrating the overall configuration of the image forming apparatus according to the present exemplary embodiment. As shown in FIG. 2, the image forming apparatus 100 is a tandem color image forming apparatus that includes four image forming units 1 to 4, a transfer unit 88, and a fixing unit 15. The four image forming units 1 to 4 and the transfer unit 88 correspond to toner image forming means.

  The four image forming units 1 to 4, that is, the first image forming unit 1, the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 are an intermediate transfer belt 5 that is a recording sheet carrier. Are arranged in a line in this order from the upstream side to the downstream side in the direction of arrow R (hereinafter referred to as “rotation direction R”), which is the conveyance rotation direction of the recording sheet.

  Each of the four image forming units 1 to 4 includes a photosensitive drum 16. Then, in each of the image forming units 1 to 4, an electrostatic latent image corresponding to the image information of each hue is formed on the surface of the photosensitive drum 16, the electrostatic latent image is developed using toner, and each color toner Form an image. The first image forming unit 1 forms a toner image corresponding to black image information. The second image forming unit 2 forms a toner image corresponding to cyan image information. The third image forming unit 3 forms a toner image corresponding to the magenta image information. The fourth image forming unit 4 forms a toner image corresponding to yellow color image information.

  The transfer unit 88 includes the intermediate transfer belt 5, the secondary transfer roller 8, the primary transfer roller 7, and the two support rolls 6.

  The intermediate transfer belt 5 is provided above the four image forming units 1 to 4. The intermediate transfer belt 5 is an endless belt-like member that forms a loop-like moving path that is stretched around the two support rolls 6 and 6, and is a recording sheet carrier that carries and conveys a recording sheet. The intermediate transfer belt 5 can be driven to rotate in the rotation direction R and is provided so as to be in pressure contact with each photosensitive drum 16. As a raw material of the intermediate transfer belt 5, for example, a material in which an appropriate amount of an electron conductive conductive material is contained in a polyimide or polyamide resin is used.

  A position where the intermediate transfer belt 5 is in pressure contact with each photosensitive drum 16 is a transfer position of each color toner image. On the intermediate transfer belt 5, the respective color toner images are superimposed and transferred at a transfer position with the photosensitive drum 16, thereby forming a multicolor toner image.

  The four primary transfer rollers 7 are provided on the inner side of the intermediate transfer belt 5, are in pressure contact with the respective photosensitive drums 16 via the intermediate transfer belt 5, and can be driven to rotate around its axis by driving means (not shown). It is a roller-shaped member provided. The pressure contact position between each primary transfer roller 7 and each photosensitive drum 16 is the transfer position of each color toner image onto the recording sheet carried and conveyed by the intermediate transfer belt 5. In order to transfer the toner image on the surface of the photosensitive drum 16 to the intermediate transfer belt 5, a transfer bias having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roller 7.

  A secondary transfer roller 8 for transferring the color image formed on the intermediate transfer belt 5 to the recording sheet is disposed downstream of the fourth image forming unit 4 in the rotation direction R of the intermediate transfer belt 5.

  The secondary transfer roller 8 of the transfer unit 88 transfers a color image formed on the intermediate transfer belt 5 by the primary transfer roller 7 to a recording sheet carried and conveyed from a supply unit 84 described later, thereby forming a multicolor toner image. To do. The recording sheet carrying the multicolor toner image is supplied to the fixing unit 15.

  The fixing unit 15 includes a heating roller 105 as a heating unit and a pressure roller 106. The heating roller 105 includes a heat source, for example, a heater lamp such as a halogen lamp, and is provided so as to be rotationally driven around an axis by a driving unit (not shown). The pressure roller 106 is provided in pressure contact with the heating roller 105 so as to be driven to rotate by the rotation driving of the heating roller 105. A recording sheet carrying a multicolor toner image is conveyed from the intermediate transfer belt 5 to a pressure contact portion between the heating roller 105 and the pressure roller 106, and the multicolor toner image is heated and pressed to form a multicolor toner image. It is fixed on the recording sheet. The recording sheet on which the multicolor toner image is fixed is discharged from the image forming apparatus 100 by the paper discharge roller 13a.

  A belt cleaning unit 10 for cleaning the surface of the intermediate transfer belt 5 is provided downstream of the secondary transfer roller 8 in the rotation direction R of the intermediate transfer belt 5 and upstream of the four image forming units 1 to 4. It has been. The belt cleaning unit 10 includes a belt cleaning brush 11 disposed in contact with the intermediate transfer belt 5 and a belt cleaning blade 12. The belt cleaning blade 12 is disposed downstream of the belt cleaning brush 11 in the rotation direction R of the intermediate transfer belt 5. The belt cleaning unit 10 removes toner remaining on the intermediate transfer belt 5 without being transferred to the recording material.

  A paper feed cassette 14 is provided below the four image forming units 1 to 4. The paper feed cassette 14 stores recording paper such as plain paper of various sizes such as B5, B4, A4, and A3, recording paper such as color copy paper, and overhead projector sheets (OHP sheets). The paper feed roller 13 assists the conveyance of the recording sheet in the conveyance direction P.

(Detailed configuration of image forming unit)
Next, the detailed configuration of the image forming units 1 to 4 will be described. FIG. 1 is a schematic diagram schematically showing the first image forming unit 1 of the image forming apparatus 100 shown in FIG. The second image forming unit 2, the third image forming unit 3 and the fourth image forming unit 4 are the same as the first image forming unit 1 except that a developer containing cyan toner, magenta toner or yellow toner is used. Since it is a structure, description is abbreviate | omitted.

  The first image forming unit 1 includes a photoconductive drum 16, a charging device 17 that charges the photoconductive drum 16, an exposure unit 18 that forms an electrostatic latent image on the photoconductive drum 16, and an electrostatic charge of the photoconductive drum 16. A developing device 19 for visualizing the latent image, an optical sensor 26 for detecting the rotation angle of the photosensitive drum 16, a cleaning device 20 for removing residuals such as toner remaining on the photosensitive drum 16, and a residual of the photosensitive drum And a slow electric lamp 25 for removing electric charges. The operation of each part of the first image forming unit 1 is controlled by a control device 34 realized by a central processing unit (CPU).

  Around the photosensitive drum 16, a charging device 17, an exposure device 18, a developing device 19, an optical sensor 26, a cleaning device 20, and a static elimination lamp 25 are arranged in this order along the rotation direction of the photosensitive drum 16. Yes.

  The photosensitive drum 16 is a roller-like member that is rotatably provided around an axis by a drum drive motor (not shown) that is a rotation drive unit, and on which an electrostatic latent image is formed. The photosensitive drum 16 rotates in the rotation direction indicated by an arrow Rd in the drawing. The rotation driving unit of the photosensitive drum 16 is controlled by the control device 34.

  The photosensitive drum 16 includes, for example, a cylindrical or columnar conductive substrate (not shown) and a photosensitive layer (not shown) formed on the surface portion of the conductive substrate. For example, an aluminum base tube can be used as the conductive substrate. The photosensitive layer may be formed by laminating a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material, and the charge generation material and the charge transport material are contained in one layer. It may be a thing. An underlayer may be provided between the photosensitive layer and the conductive substrate. Further, a protective layer may be provided on the surface portion of the photosensitive layer.

  In the present embodiment, a plurality of markers are arranged at equal intervals on the same circumference of the photosensitive drum 16 facing the optical sensor 26 (that is, along the rotation direction Rd of the photosensitive drum 16). The marker has a light reflectance different from that of the surface of the photosensitive drum.

  The optical sensor 26 is a sensor that measures the rotation angle of the photosensitive drum 16 by detecting a marker provided on the surface of the photosensitive drum 16, and functions as a rotation angle detection unit. Examples of the optical sensor 26 include a photosensor including a light emitting element and a light receiving element. In the photosensor, the light emitting element and the light receiving element are arranged to face a plurality of markers arranged at equal intervals on the same circumference on the photosensitive drum 16, and the light emitted from the light emitting element is irradiated onto the surface of the photosensitive drum 16. And the reflected light is received by the light receiving element. Since the reflectance of light differs between the marker and the surface of the photosensitive drum, the optical sensor 26 can detect the position of the marker based on a change in the amount of reflected light detected by the light receiving element. The measurement result of the optical sensor 26 is sent to the control device 34, and the rotation angle is calculated. That is, the rotation angle of the photosensitive drum 16 is calculated by counting the number of times the optical sensor 26 detects the marker.

  As will be described later, in the contact area between the photosensitive drum 16 and the developer included in the developing device 19 from the charging area that is the contact area between the photosensitive drum 16 and the charging device 17 with respect to the central axis of the photosensitive drum 16. A rotation angle corresponding to an angle to a certain developing area (that is, an angle formed by a line connecting the charging area and the central axis of the photosensitive drum 16 and a line connecting the developing area and the central axis of the photosensitive drum 16). In order to detect, it is preferable that 72 or more markers are arranged on the same circumference of the photosensitive drum 16.

  The charging device 17 charges the surface of the photosensitive drum 16 to a potential having a predetermined polarity (for example, minus). In the present embodiment, the charging device 17 includes a charging roller, and a charging voltage is supplied from the charging voltage supply device 31. As the charging device 17, a corona discharger or a brush charger can also be used. The output voltage of the charging voltage supply device 31 is controlled by the control device 34. In the following, it is assumed that the charging device 17 charges the surface of the photosensitive drum to a negative potential, but the present invention is not limited to this.

  The exposure device 18 is a device that irradiates the surface of the photosensitive drum 16 in a charged state with signal light corresponding to black image information, for example, laser light, and forms an electrostatic latent image corresponding to the black image information. is there. An LED array device can also be used as the exposure device 18. In the present embodiment, charges are generated by light irradiation at locations where light is irradiated by the exposure device 18 on the surface of the photosensitive drum 16, and the charged charges by the charging device 17 are removed. As a result, the potential is lowered at this location, and an electrostatic latent image is formed.

  The developing device 19 includes a developing roller 24, a stirring roller 40, a developing tank 41, and a toner supply container (not shown). The developing device 19 faces the surface of the photosensitive drum 16 and is provided so as to be separated from the photosensitive drum 16. The developing device 19 stores therein a two-component developer composed of a magnetic carrier and toner, and converts the toner into an electrostatic latent image corresponding to black image information formed on the surface of the photosensitive drum 16 by the two-component reversal development method. To form a black toner image.

  The developing roller 24 is a roller-like member that encloses the fixed magnetic pole body. The developing roller 24 is separated from the surface of the photosensitive drum 16 through an opening of the developing tank 41 with a slight gap, and can be driven to rotate. The black toner is supplied to the electrostatic latent image on the surface of the photosensitive drum 16. The developing roller 24 includes a developing sleeve that is a cylindrical member, and a fixed magnetic pole body provided inside the developing sleeve. In order to supply the black toner to the surface of the photosensitive drum 16, a voltage is applied to the developing roller 24 by the developing bias supply device 35.

  In the present embodiment, the developing bias supply device 35 outputs +150 V as a positive output voltage and outputs −500 V as a negative output voltage. In this embodiment, the voltage of −500 V is the same as the charging polarity of the toner, and is a developing bias for attaching the toner to the electrostatic latent image formed on the photosensitive drum. On the other hand, the voltage of +150 V is a voltage having a polarity opposite to the charging polarity of the toner, as will be described later. The output voltage of the developing bias supply device 35 is controlled by the control device 34.

  The agitation roller 41 is a roller-like member provided inside the developing tank 40 so as to be rotatable around an axis, and supplies black toner to the surface portion of the developing roller 24.

  The developing tank 41 contains the developing roller 24 and the stirring roller 40, and a two-component developer containing black toner and a magnetic carrier. The developing tank 41 is supplied with toner by a toner supply container (not shown). In this embodiment, the toner is charged to a negative potential, but the present invention is not limited to this.

  The black toner image developed by the developing device 19 is transferred to the intermediate transfer belt 5 shown in FIG.

  The cleaning device 20 removes and collects the black toner remaining on the surface of the photosensitive drum 16 after the black toner image on the surface of the photosensitive drum 16 is transferred to the intermediate transfer belt 5. The cleaning device 20 includes, for example, a cleaning blade provided so as to be in contact with the surface of the photosensitive drum 16 and a waste toner container for storing toner removed from the surface of the photosensitive drum 16 by the cleaning blade.

  The static elimination lamp 25 removes the electric charge remaining on the surface of the photosensitive drum 16.

(Regarding voltage application control to the developing roller)
Next, voltage application control to the developing roller 24 will be described with reference to FIGS.

(At the start of image formation)
First, the operation timing of the drum drive motor of the photosensitive drum 16, the timing of applying a charging voltage to the charging device 17, and the timing of applying a voltage to the developing roller 24 when starting image formation will be described. FIG. 3 shows the operation timing of the drum drive motor of the photosensitive drum 16, the application timing of the charging voltage to the charging device 17, and the voltage application timing to the developing roller 24 when image formation is started in the image forming apparatus 100. 5 is a timing chart showing a change with time in the rotation angle of the photosensitive drum 16.

  At the same time as the start of image formation, the control device 34 operates the drum drive motor of the photosensitive drum 16 and applies a charging voltage from the charging voltage supply device 31 to the charging device 17. As a result, charging of the photosensitive drum 16 is started and the photosensitive drum 16 starts to rotate. At this time, the control device 34 controls the developing bias supply device 35 and applies a positive voltage (+150 V) to the developing roller 24.

  FIG. 4 is a cross-sectional view showing the photosensitive drum 16, the developing roller 24, and the charging device 17. As shown in FIG. 4, an area in contact with the charging device 17 on the surface of the photosensitive drum 16 is a charging area. Here, the downstream end of the charging region in the rotation direction Rd of the photosensitive drum is a potential rise start point 16a on the surface of the photosensitive drum that is generated when charging of the photosensitive drum is started.

  When charging of the surface of the photosensitive drum 16 is started, a positive side voltage (+150 V) having a polarity opposite to the charging polarity of the toner is applied to the developing roller 24. At this time, the surface potential of the photoconductive drum 16 is 0 in the development area which is a contact area with the developer G on the surface of the photoconductive drum 16. Therefore, the toner is attracted to the developing roller 24 to which a voltage having a polarity opposite to that of the toner is applied, and the toner can be prevented from adhering to the surface of the photosensitive drum 16 by an electrostatic force.

  Further, the control device 34 calculates the rotation angle of the photosensitive drum 16 from the time when the operation of the drum drive motor is started. That is, the control device 34 counts the number of times the optical sensor 26 has detected the marker from the time when the operation of the drum drive motor is started, and multiplies the counted number by the angle of the adjacent marker with respect to the rotation axis of the photosensitive drum 16. Thus, the rotation angle of the photosensitive drum 16 is calculated.

  Then, the control device 34 controls the developing bias supply device 35 at the timing when the rotation angle of the photosensitive drum 16 from the time when the operation of the drum driving motor is started reaches the predetermined angle θ1, so that the developing bias is negative. A side voltage (−500 V) is applied to the developing roller 24.

  Here, the predetermined angle θ1 will be described. In FIG. 5, the potential rise start point 16 a is the downstream end in the rotation direction Rd of the photosensitive drum in the developing region where the two-component developer and the photosensitive drum are in contact (shown by the developing region end 16 c in the drawing). 2 is a cross-sectional view showing the photosensitive drum 16, the developing roller 24, and the charging device 17 when passing through the apparatus. As the predetermined angle θ1, the line connecting the potential rise start point 16a (that is, the downstream end portion in the rotation direction Rd of the photosensitive drum in the charging region) and the central axis of the photosensitive drum 16 and the developing region end 16c ( That is, the angle formed by the line connecting the photosensitive drum 16 and the central axis of the photosensitive drum 16 is set to the downstream end portion in the rotation direction Rd of the photosensitive drum in the developing region.

  Therefore, when the potential rise start point 16a reaches the developing region end 16c, a negative side voltage (−500 V) as a developing bias is applied to the developing roller 24. That is, the developing bias is applied to the developing roller 24 at the timing when the portion charged by the charging device on the surface of the photosensitive drum 16 reaches the developing region.

  FIG. 6 is a graph schematically showing changes in potentials of the photosensitive drum 16 and the developing roller 24 in the developing area at the start of image formation. As shown in FIG. 6, in the development area, the potential of the surface of the photosensitive drum 16 is 0 V until the portion charged by the charging device 17 arrives, and when the charged portion reaches, the charged potential ( −650V). On the other hand, the potential of the developing roller 24 is a positive potential (+150 V) until the portion charged by the charging device 17 arrives, and when the charged portion reaches, a negative potential (−500 V). It becomes. That is, in the development area, the potentials of the photosensitive drum 16 and the development roller 24 change at the same timing. As shown in FIG. 6, the difference between the surface potential of the photosensitive drum 16 and the potential of the developing roller 24 is within a range where toner adhesion or carrier adhesion to the photosensitive drum 16 does not occur (for example, 100 to 300 V). To be kept. As a result, it is possible to prevent toner or carrier from the developing device 19 from adhering to the photosensitive drum 16.

(At the end of image formation)
Next, the operation timing of the drum drive motor of the photosensitive drum 16, the application voltage stop timing of the charging device 17 and the voltage application timing to the developing roller 24 when the image formation is completed will be described. FIG. 7 shows the operation timing of the drum drive motor of the photosensitive drum 16, the timing of stopping the application of the charging voltage to the charging device 17, and the timing of applying the voltage to the developing roller 24 when the image formation is completed in the image forming apparatus 100. 6 is a timing chart showing the change with time of the rotation angle of the photosensitive drum 16.

  The control device 34 first stops the operation of the drum drive motor of the photosensitive drum 16 and the application of the charging voltage from the charging voltage supply device 31 to the charging device 17. In this case, the drum drive motor only stops, and the photosensitive drum 16 stops after rotating for a while due to inertia.

  Therefore, the control device 34 calculates the rotation angle of the photosensitive drum 16 from the time when the operation of the drum drive motor is stopped. The calculation method is as described above.

  Then, the control device 34 controls the developing bias supply device 35 at the timing when the rotation angle of the photosensitive drum 16 from the time when the operation of the drum driving motor is stopped reaches the predetermined angle θ2, and applies it to the developing roller. The voltage is switched from a minus side voltage (−500 V) as a developing bias to a plus side voltage (+150 V).

  Here, the predetermined angle θ2 will be described. As shown in FIG. 4, the upstream end portion in the charging region in the photosensitive drum rotation direction Rd is a potential decrease start point 16 b on the surface of the photosensitive drum that occurs when charging to the photosensitive drum is stopped. A line connecting the potential drop start point 16b and the central axis of the photosensitive drum 16, the tip 16d of the developing area (that is, the upstream end in the rotational direction Rd of the photosensitive drum in the developing area), and the center of the photosensitive drum 16. The angle between the line connecting the axes is set.

  For this reason, the timing at which the portion charged by the charging device 17 on the surface of the photosensitive drum 16 has passed through the developing region, in other words, the portion not charged by the charging device 17 on the surface of the photosensitive drum 16 has reached the developing region. At the timing, a positive voltage is applied to the developing roller 24.

  FIG. 8 is a graph schematically showing changes in the potential of the photosensitive drum 16 and the developing roller 24 in the developing area at the end of image formation. As shown in FIG. 8, in the development area, the potential of the surface of the photosensitive drum 16 is a charging potential (−650 V) until all of the portion charged by the charging device 17 passes, and the charging is performed. When all of the portions pass (that is, when the uncharged portion reaches), the voltage becomes 0V. On the other hand, the potential of the developing roller 24 is a negative side voltage (−500 V) that is a developing bias until all the parts charged by the charging device 17 pass, and when all the charged parts pass. (In other words, when an uncharged portion arrives), a positive voltage (+150 V) is obtained. That is, in the development area, the potentials of the photosensitive drum 16 and the development roller 24 change at the same timing. As shown in FIG. 8, the difference between the surface potential of the photosensitive drum 16 and the potential of the developing roller 24 is within a range where toner adhesion or carrier adhesion to the photosensitive drum 16 does not occur (for example, 100 to 300 V). To be kept. As a result, it is possible to prevent toner and carrier from adhering to the photosensitive drum 16 from the developing device 19 even at the end of image formation.

(Processing flow of control device)
The operation processing flow of the drum drive motor, charging potential application, and voltage application to the developing roller 24 in the control device 34 of the present embodiment will be described. FIG. 9 is a flowchart showing a processing procedure of the control device 34. A processing procedure at the start and end of the image forming operation will be described with reference to the flowchart shown in FIG.

  First, an image forming process start signal is input to the control device 34. The start signal is input to the control device 34 from the operation unit when the user presses a copy start button in the operation unit of the image forming apparatus 100, for example. As another example, when the communication unit of the image forming apparatus 100 receives a print job from a computer device that is communicably connected to the image forming apparatus 100, the start signal is input to the control device 34 from the communication unit. Is done.

  Upon receiving the start signal, the control device 34 (1) starts driving the drum drive motor, and (2) controls the charging voltage supply device 31 to apply the charging voltage to the charging device 17. (3) The developing bias supply device 35 is controlled to apply a positive voltage (+150 V) to the developing roller 24 (S1). At this time, the control device 34 also starts the developing device 19, the optical sensor 26 and the slow power lamp 25 together.

  As described above, since the driving of the drum driving motor and the application of the charging voltage are simultaneously performed, the idling time of the photosensitive drum 16 can be shortened.

  Further, at the time when the application of the charging voltage is started, the surface potential of the photosensitive drum 16 is 0 in the developing region. At this time, since a positive voltage having a polarity opposite to the charging polarity of the toner is applied to the developing roller 24, the toner is attracted to the developing roller 24 rather than the photosensitive drum 16. Thereby, it is possible to prevent the toner from adhering to the photosensitive drum 16.

  Next, the control device 34 counts the number of times that the optical sensor 26 has detected the marker from the time when the operation of the drum drive motor is started (the processing time of S1), and the photosensitive drum 16 of the marker adjacent to the count number. By multiplying the angle with respect to the rotation axis, the rotation angle a of the photosensitive drum 16 is measured (S2).

  Further, the control device 34 determines whether or not the measured rotation angle a is less than the predetermined angle θ1 (S3).

  If the rotation angle a measured by the optical sensor 26 is less than the predetermined angle θ1 (Yes in S3), the process returns to S2.

  On the other hand, when the rotation angle a measured by the optical sensor 26 reaches the predetermined angle θ1 (No in S3), the control device 34 controls the developing bias supply device 35 to apply the voltage applied to the developing roller 24. The positive side voltage (+ 150V) is switched to the negative side voltage (−500V), which is a developing bias (S4). As a result, the carrier is attracted toward the developing roller 24, and the carrier can be prevented from adhering to the photosensitive drum 16.

  Further, as shown in FIG. 6, the difference between the surface potential of the photosensitive drum 16 and the potential of the developing roller 24 is within a range where toner adhesion or carrier adhesion to the photosensitive drum 16 does not occur (for example, 100 to 300 V). Thus, it is possible to prevent the toner and carrier from adhering to the photosensitive drum 16 from the developing device 19.

  Thereafter, when the photosensitive drum 16 rotates once, the entire surface of the photosensitive drum 16 becomes a charged region. FIG. 10 is a cross-sectional view showing the photosensitive drum 16, the developing roller 24, and the charging device 17 after the photosensitive drum 16 has rotated one or more times. As shown in FIG. 10, after the entire surface of the photosensitive drum 16 has become a charged region, the control device 34 controls the exposure device 18 to start forming an electrostatic latent image on the photosensitive drum 16 (see FIG. 10). S5). Thereafter, when the formation of the electrostatic latent images corresponding to all images is completed, the control device 34 stops the operation of the exposure device 18 (S6). Subsequently, the control device 34 stops driving the drum drive motor and controls the charging voltage supply device 31 to stop the application of the charging voltage to the charging device 17 (S7). Thereby, the idling time of the photosensitive drum 16 can be shortened, and wear and deterioration of the photosensitive drum 16 and the two-component developer can be suppressed.

  Next, the control device 34 counts the number of times that the optical sensor 26 has detected the marker from the time when the driving of the drum drive motor stops (the time of processing in S7), and rotates the photosensitive drum of the marker adjacent to the count. The rotation angle b of the photosensitive drum is measured by multiplying the angle with respect to the axis (S8).

  Further, the control device 34 determines whether or not the measured rotation angle b is less than the predetermined angle θ2 described above (S9).

  If the rotation angle b measured by the optical sensor 26 is less than the predetermined angle θ2 (Yes in S9), the process returns to S8.

  On the other hand, when the rotation angle b measured by the optical sensor 26 reaches the predetermined angle θ2 (No in S9), the control device 34 controls the developing bias supply device 35 to apply the voltage applied to the developing roller 24. The developing bias is switched from the minus side voltage (−500V) to the plus side voltage (+ 150V) (S10).

  Then, after a sufficient time (for example, 5 seconds) has passed for the rotation of the photosensitive drum 16 to stop, the control device 34 controls the developing bias supply device 35 to stop the voltage application to the developing roller 24. (S11).

  As described above, the rotation angle of the photosensitive drum 16 can be detected by the optical sensor 26, and the developing bias can be applied to the developing roller 24 at an appropriate timing. Therefore, the angular acceleration at the start of the rotational driving of the photosensitive drum 16 can be performed. Even if the change occurs, unnecessary toner adhesion and carrier adhesion to the photosensitive drum 16 can be suppressed.

  In the above description, the optical sensor 26 is provided as the rotation angle detection unit. However, as a member for detecting the rotation angle of the photosensitive drum 16, a drum drive motor that outputs the rotation position of the motor as a signal may be used instead of the optical sensor 26.

  As described above, in this embodiment, the optical sensor (rotation angle detection unit) 16 that detects the rotation angle of the photosensitive drum 16 is provided, so that the development bias ON / OFF timing is appropriately performed. .

  Specifically, the image forming apparatus 100 exposes the photosensitive drum 16, the charging device 17 that charges the photosensitive drum 16, and the surface of the charged photosensitive drum to form an electrostatic latent image. A developing device 19 that develops an electrostatic latent image formed on the photosensitive drum 16 by using a potential difference between the device 18 and a two-component developer containing toner and a carrier and utilizing the potential difference with the surface of the photosensitive drum 16; It has.

  Further, the image forming apparatus 100 includes an optical sensor (rotation angle detection unit) 26 that detects the rotation angle of the photosensitive drum 16 and the charging device 16 on the surface of the photosensitive drum 16 with respect to the central axis of the photosensitive drum 16. When the angle from the charging area to which the charging potential is applied to the developing area on the surface of the photosensitive drum 16 that is in contact with the developer G of the developing device 19 is defined as a reference angle, the optical sensor 26 detects the angle. The developing bias for attaching the toner to the electrostatic latent image when the rotation angle a of the photosensitive drum 16 after the charging device 17 starts charging the photosensitive drum 16 reaches the reference angle. And a control device (control unit) 34 that applies (−500 V) to the developing device 19.

  Here, the reference angle is, for example, the photosensitive region in the developing region from the potential rise start point 16a that is the downstream end portion in the rotation direction Rd of the photosensitive drum 16 in the charging region with respect to the central axis of the photosensitive drum 16. The angle θ1 is a predetermined angle θ1 up to the developing region end 16c, which is the downstream end in the rotation direction Rd of the body drum 16.

  According to the configuration of the present embodiment, the photosensitive drum charged by the charging device 17 is when the rotation angle a of the photosensitive drum after the charging of the photosensitive drum by the charging device reaches the predetermined angle θ1. This is when the spot on the drum reaches the development area. Since the rotation angle of the photosensitive drum 16 is actually detected, a portion on the photosensitive drum 16 that is not charged by the charging device 17 reaches the development region regardless of the time until the predetermined angle θ1 is reached. The arrival timing can be detected accurately. Since the developing bias is applied at this timing, even if the time for the rotation angle a of the photosensitive drum 16 to reach the predetermined angle θ1 changes, the surface potential of the photosensitive drum 16 and the developing roller 24 in the developing region are changed. The potential changes at the same timing, and the development bias application timing does not become faster or slower than the change point of the surface potential of the photosensitive drum 16 as in the conventional case. That is, the developing bias can be applied at an optimal timing. As a result, unnecessary toner adhesion and carrier adhesion to the photosensitive drum 16 can be suppressed.

  In addition, since the developing bias can be applied at an optimum timing, the time required to start image formation is not unnecessarily delayed.

  Similarly, when the rotation angle b of the photosensitive drum 16 detected by the optical sensor 26 and the charging of the photosensitive drum 16 after the charging device 17 stops charging becomes the reference angle, the control device 34 The application of the developing bias for attaching the toner to the electrostatic latent image to the developing device 19 is stopped.

  Here, the reference angle is, for example, the photosensitive region in the developing region from the potential decrease start point 16b that is the upstream end in the rotation direction of the photosensitive drum 16 in the charging region with respect to the central axis of the photosensitive drum 16. This is a predetermined angle θ2 up to the developing region tip 16d, which is the upstream end of the body drum 16 in the rotational direction Rd.

  According to the configuration of the present embodiment, when the rotation angle b of the photosensitive drum 16 detected by the optical sensor 26 after the charging of the charging drum 17 by the charging device 17 is stopped reaches the predetermined angle θ2. Is when the spot on the photosensitive drum 16 that is not charged by the charging device 17 reaches the developing region. Since the rotation angle b of the photoconductor drum 16 is actually detected, a portion on the photoconductor drum 16 that is not charged by the charging device 17 is not developed regardless of the time until the predetermined angle θ2 is reached. It is possible to accurately detect the timing of reaching. Since the application of the developing bias is stopped at this timing, even if the time for the rotation angle b of the photosensitive drum 16 to reach the predetermined angle θ2 changes, the surface potential of the photosensitive drum 16 and the developing roller in the developing region. The potential of 24 changes at the same timing. That is, the development bias application can be stopped at an optimal timing. As a result, unnecessary toner adhesion and carrier adhesion to the photosensitive drum 16 can be suppressed.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  Finally, each block of the image forming apparatus 100, in particular, the control device 34 may be configured by hardware logic, or may be realized by software using a CPU as follows.

  That is, the control device 34 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, a RAM (random access memory) that expands the program, A storage device (recording medium) such as a memory for storing the program and various data is provided. An object of the present invention is to provide a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program of the control device 34, which is software that realizes the above-described functions, is recorded in a computer-readable manner This can also be achieved by supplying the control device 34 and reading and executing the program code recorded on the recording medium by the computer (or CPU or MPU).

  Examples of the recording medium include a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The control device 34 may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available. Also, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  The present invention can be applied to an image forming apparatus such as a printer, a copier, or a multifunction peripheral.

FIG. 2 is a schematic diagram schematically showing an image forming unit provided in the image forming apparatus of the present embodiment. 1 is a diagram schematically illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment. 6 is a timing chart showing a change in rotation angle of the photosensitive drum with time, along with the timing for applying the developing bias of the operation timing of the drum drive motor and the timing for applying the charging voltage when starting image formation. FIG. 3 is a cross-sectional view illustrating a photosensitive drum, a developing roller, and a charging device. FIG. 3 is a cross-sectional view showing a photosensitive drum, a developing roller, and a charging device when a potential rise start point passes through a developing region end. 6 is a graph schematically showing changes in potentials of a photosensitive drum and a developing roller in a developing area at the start of image formation. 5 is a timing chart showing the operation timing of the drum drive motor, the charging voltage application stop timing, the developing bias application timing, and the change with time of the rotation angle of the photosensitive drum at the end of image formation. 6 is a graph schematically showing changes in potentials of a photosensitive drum and a developing roller in a developing area at the end of image formation. It is a flowchart which shows the process sequence of a control apparatus. FIG. 4 is a cross-sectional view showing the photosensitive drum, the developing roller, and the charging device after the photosensitive drum has rotated one or more times. 6 is a graph schematically showing a potential change in a development region when an application timing of a development bias is early. 6 is a graph schematically showing a potential change in a development region when a development bias application timing is late.

Explanation of symbols

1-4 Image forming unit 16 Photosensitive drum 17 Charging device 18 Exposure device 19 Developing device 24 Developing roller 26 Optical sensor (rotation angle detection unit)
31 Charging voltage supply device 34 Control device (control unit)
35 Development Bias Supply Device 100 Image Forming Device G Developer Rd Rotation Direction of Photosensitive Drum

Claims (11)

A photosensitive drum;
A charging device for charging the photosensitive drum;
An exposure device that forms an electrostatic latent image by exposing the surface of the charged photosensitive drum;
An image forming apparatus comprising: a two-component developer including a toner and a carrier, and a developing device that develops an electrostatic latent image formed on the photosensitive drum using a potential difference with the surface of the photosensitive drum. In the device
A rotation angle detector for detecting the rotation angle of the photosensitive drum;
Contact with the developer of the developing device on the surface of the photosensitive drum from a charging region to which the charging potential is applied by the charging device on the surface of the photosensitive drum with respect to the central axis of the photosensitive drum When the angle to the development area, which is an area, is set as a reference angle, the rotation angle of the photosensitive drum after the charging device starts charging the photosensitive drum detected by the rotation angle detector An image forming apparatus comprising: a control unit that applies a developing bias for attaching toner to the electrostatic latent image to the developing device when the reference angle is reached.   The controller is configured to rotate toner of the photosensitive drum until the rotation angle of the photosensitive drum reaches the reference angle after the charging device starts charging the photosensitive drum. The image forming apparatus according to claim 1, wherein a voltage having a polarity opposite to the charging polarity is applied to the developing device.   The reference angle is the downstream end in the rotation direction of the photosensitive drum in the developing region from the downstream end in the rotation direction of the photosensitive drum in the charging region with respect to the central axis of the photosensitive drum. The image forming apparatus according to claim 1, wherein the angle is an angle up to a portion. A rotational drive unit for rotationally driving the photosensitive drum;
4. The image forming apparatus according to claim 1, wherein the control unit starts charging of the photosensitive drum by the charging device simultaneously with the start of driving of the rotation driving unit. 5.   The image forming apparatus according to claim 1, wherein the developing bias is a voltage having the same polarity as a charging polarity of the toner. A photosensitive drum;
A charging device for charging the photosensitive drum;
An exposure device that forms an electrostatic latent image by exposing the surface of the charged photosensitive drum;
An image forming apparatus comprising: a two-component developer including a toner and a carrier, and a developing device that develops an electrostatic latent image formed on the photosensitive drum using a potential difference with the surface of the photosensitive drum. In the device
A rotation angle detector for detecting the rotation angle of the photosensitive drum;
Contact with the developer of the developing device on the surface of the photosensitive drum from a charging region to which the charging potential is applied by the charging device on the surface of the photosensitive drum with respect to the central axis of the photosensitive drum When the angle to the development area, which is the area, is set as a reference angle, the rotation angle of the photosensitive drum after the charging of the photosensitive drum by the charging device detected by the rotation angle detector is stopped. An image forming apparatus comprising: a control unit that stops application of a developing bias for attaching toner to the electrostatic latent image to the developing device when a reference angle is reached.   The controller is configured to apply a voltage having a polarity opposite to a toner charging polarity to the developing device after the rotation angle of the photosensitive drum after the charging device stops charging the photosensitive drum reaches the reference angle. The image forming apparatus according to claim 6, wherein the image forming apparatus is applied to the image forming apparatus.   The reference angle is an upstream end in the rotational direction of the photosensitive drum in the developing region from an upstream end in the rotational direction of the photosensitive drum in the charging region with respect to the central axis of the photosensitive drum. The image forming apparatus according to claim 6, wherein the angle is an angle up to a portion. A rotational drive unit for rotationally driving the photosensitive drum;
9. The image forming apparatus according to claim 6, wherein the control unit stops charging of the photosensitive drum by the charging device at the same time as the rotation of the rotation driving unit is stopped.   10. The image forming apparatus according to claim 6, wherein the control unit stops applying the voltage to the developing device after the rotation of the photosensitive drum is stopped. 11. A plurality of markers having different light reflectivities from the surface of the photosensitive drum are formed on the surface of the photosensitive drum along the rotation direction of the photosensitive drum.
The rotation angle detection unit is disposed at a position facing the marker, and detects the marker based on a difference in light reflectance between the surface of the photosensitive drum and the marker, thereby detecting the marker on the photosensitive drum. The image forming apparatus according to claim 1, wherein the image forming apparatus is an optical sensor that detects a rotation angle.

Images