Image forming apparatus and control method thereof

Abstract

To provide an image forming apparatus that develops an electrostatic latent image formed on an image carrier by using developer including toner and carrier, and to efficiently remove the toner attached to electrifying means that electrifies the image carrier.SOLUTION: An image forming apparatus executes an image forming operation of forming an image on a transfer target body in a state in which a developing member supplying developer including toner and carrier onto a surface of an image carrier to form a developer image is located at a first position for supplying the developer to the surface of the image carrier and a first electrification voltage is applied to electrifying means, subsequently a first rotation operation of rotating the image carrier in a state in which the developing member is located at the first position and a second electrification voltage with a smaller absolute value than that of the first electrification voltage is applied, and a second rotation operation of rotating the image carrier in a state in which the developing member is located at a second position for not supplying the developer to the surface of the image carrier and a third electrification voltage with a smaller absolute value than that of the second electrification voltage is applied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and a control method thereof.

Background Art

[0002] In an image forming apparatus that forms an image using an electrophotographic process, the toner image formed on the surface of the photosensitive drum is electrostatically transferred to an intermediate transfer member or a recording material by applying a voltage to a transfer member disposed opposite to the photosensitive drum. When forming toner images of a plurality of colors, the transfer process is repeatedly executed for each toner image of each color. By fixing the toner image to the recording material with a fixing device, image formation is performed on the recording material. Patent Document 1 describes a technique in which fine particles are previously adhered to the surface of the photosensitive drum, the fine particles are interposed between the photosensitive drum and the toner image, the adhesion force of the toner to the photosensitive drum is reduced, and the transfer efficiency is improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique of Patent Document 1, fine particles (hereinafter referred to as carriers) that assist transfer are previously adhered to the toner, and the carriers are separated from the toner and adhered to the photosensitive drum, so that the carriers are made to stay on the photosensitive drum. When the toner remaining on the photosensitive drum (hereinafter referred to as transfer residual toner) that has not been transferred in the transfer process passes through the contact portion with the charging roller, the transfer residual toner may be electrically adhered to the charging roller due to the influence of the electric field between the charging roller and the photosensitive drum. By forming an electric field opposite to that during image formation between the charging roller and the photosensitive drum and moving the toner adhered to the charging roller to the photosensitive drum, the cleaning process of the charging roller can be performed.

[0005] If there is an uneven distribution of carriers on the photosensitive drum, the charging performance will differ between areas with a high carrier concentration and areas with a low carrier concentration, resulting in uneven surface potential of the photosensitive drum. In this case, unevenness occurs in the electric field between the charging roller and the photosensitive drum, and uneven transfer of toner from the charging roller to the photosensitive drum occurs. Therefore, even after cleaning, the toner adhering to the charging roller cannot be uniformly cleaned, which can lead to density unevenness during subsequent image formation.

[0006] The present invention aims to efficiently clean toner adhering to a charging means for charging an image carrier in an image forming apparatus that develops an electrostatic latent image formed on an image carrier using a developer containing toner and a carrier. [Means for solving the problem]

[0007] The present invention comprises an image carrier and A charging means for charging the image carrier, An exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image, A developing member that forms a developing image by supplying a developer containing toner and a carrier onto the surface of an image carrier at a developing position facing the image carrier, the developing member being movable between a first position for supplying the developer to the surface of the image carrier and a second position for not supplying the developer to the surface of the image carrier, A transfer means for transferring the developer image to a transfer object, A charging voltage application unit that applies a charging voltage to the charging means, A control unit that controls the charging voltage application unit, It has, The control unit, Image forming operation in which the developing member is positioned in the first position and an image is formed on the transfer surface while a first charging voltage is applied, With the developing member positioned in the first position and a second charging voltage having a smaller absolute value than the first charging voltage applied, a first rotational operation is performed to rotate the image carrier, With the developing member positioned at the second location and a third charging voltage having a smaller absolute value than the second charging voltage applied, a second rotational operation is performed to rotate the image carrier. It is possible to do this, The image forming apparatus is characterized in that the control unit controls the first rotation operation and the second rotation operation to be performed after the image forming operation.

[0008] Furthermore, the present invention includes an image carrier and A charging means for charging the image carrier, An exposure means for exposing the image carrier charged by the charging means to form an electrostatic latent image, A developing member for forming a developing image by supplying a developer charged with normal polarity, including toner and carrier, onto the surface of the image carrier at a developing position facing the image carrier, the developing member being movable between a first position for supplying the developer to the surface of the image carrier and a second position for not supplying the developer to the surface of the image carrier, A supply member that supplies the developer to the surface of the developing member, A transfer means for transferring the developer image to a transfer object, A developing voltage application unit that applies a developing voltage to the developing member, A supply voltage application unit that applies a supply voltage to the supply member, A control unit controls at least one of the developing voltage application unit and the supply voltage application unit so that a potential difference is formed between the developing member and the supply member in a direction in which an electrostatic force acts on the developer, which is charged with normal polarity, in the direction from the supply member toward the developing member, It has, The control unit, An image forming operation in which the developing member is positioned at the first position and a first potential difference is formed between the developing member and the supply member, in which case an image is formed on the object to be transferred. With the developing member positioned in the first position and a second potential difference smaller than the first potential difference formed between the developing member and the supply member, a first rotational movement is performed to rotate the image carrier, With the developing member in the second position, a second rotational movement is performed to rotate the image carrier, It is possible to do this, The image forming apparatus is characterized in that the control unit controls the first rotation operation and the second rotation operation to be performed after the image forming operation.

[0009] Furthermore, the present invention includes the step of forming an electrostatic latent image on an image carrier that has been charged by a charging means, A developing member that forms a developing image by supplying a developing agent containing toner and a carrier onto the surface of the image carrier at a developing position facing the image carrier is moved between a first position where the developing agent is supplied to the surface of the image carrier and a second position where the developing agent is not supplied to the surface of the image carrier. A step of transferring the developer image to the transfer object, The process involves positioning the developing member at the first position and performing an image forming operation to form an image on the transfer object while applying a first charging voltage to the charging means, The steps include: positioning the developing member at the first position and applying a second charging voltage to the charging means, which has an absolute value smaller than the first charging voltage, and then performing a first rotation operation to rotate the image carrier; The steps include: positioning the developing member at the second position and applying a third charging voltage to the charging means, which has an absolute value smaller than the second charging voltage, and then performing a second rotation operation to rotate the image carrier; It has, The control method for an image forming apparatus is characterized in that, after the step of performing the image forming operation, the steps of performing the first rotation operation and the second rotation operation are performed.

[0010] Furthermore, the present invention includes the step of forming an electrostatic latent image on an image carrier that has been charged by a charging means, A developing member that forms a developer image by supplying a developer charged with a normal polarity containing toner and a carrier onto the surface of the image carrier at a developing position facing the image carrier, and a step of moving the developing member between a first position for supplying the developer onto the surface of the image carrier and a second position for not supplying the developer onto the surface of the image carrier; A step of transferring the developer image onto a transfer body; By performing at least one of applying a developing voltage to the developing member and applying a supply voltage to a supply member that supplies the developer onto the surface of the developing member, a potential difference in a direction in which an electrostatic force from the supply member toward the developing member acts on the developer charged with the normal polarity is formed between the developing member and the supply member; A step of positioning the developing member at the first position and performing an image forming operation of forming an image on a transfer body in a state where a first potential difference is formed between the developing member and the supply member; A step of positioning the developing member at the first position and performing a first rotation operation of rotating the image carrier in a state where a second potential difference smaller than the first potential difference is formed between the developing member and the supply member; A step of performing a second rotation operation of rotating the image carrier in a state where the developing member is positioned at the second position; having A control method for an image forming apparatus, characterized in that after the step of performing the image forming operation, the step of performing the first rotation operation and the step of performing the second rotation operation are performed.

Effect of the Invention

[0011] According to the present invention, in an image forming apparatus that develops an electrostatic latent image formed on an image carrier using a developer containing toner and a carrier, toner attached to a charging means for charging the image carrier can be efficiently cleaned.

Brief Description of the Drawings

[0012] [Figure 1]Timing chart of the first rotational movement and the second rotational movement in Example 1 [Figure 2] Schematic cross-sectional view of the image forming apparatus in Example 1 [Figure 3] A schematic diagram showing how the carrier in Example 1 adheres to the photosensitive drum. [Figure 4] Schematic diagram showing the carrier adhesion pattern on the surface of the photosensitive drum in Example 1. [Figure 5] Timing chart of modified examples of the first and second rotational movements in Example 1 [Figure 6] Timing chart of modified examples of the first and second rotational movements in Example 1 [Figure 7] Timing chart of the first and second rotational movements in Example 2 [Figure 8] Schematic block diagram showing the control of the image forming apparatus in Example 1 [Modes for carrying out the invention]

[0013] (Example 1) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc., of the components described in the following embodiments should be appropriately modified depending on the configuration and various conditions of the apparatus to which the present invention is applied. Therefore, unless otherwise specified, the scope of the present invention is not intended to be limited to those embodiments.

[0014] Figure 2 is a schematic diagram showing an example of an electrophotographic image forming apparatus according to Example 1. The image forming apparatus 100 of Example 1 is a tandem type image forming apparatus having image forming stations a to d. The first image forming station a forms a yellow (Y) image, the second image forming station b forms a magenta (M) image, the third image forming station c forms a cyan (C) image, and the fourth image forming station d forms a black (Bk) image. The configuration of each image forming station is the same except for the color of the toner it contains. Common components in each image forming station are given a common code, and toner colors are distinguished by subscripts a, b, c, and d, while subscripts are omitted in descriptions that are common regardless of toner color. The configuration and operation of the image forming stations will be described below using the first image forming station a as an example.

[0015] The first image forming station a comprises a drum-shaped electrophotographic photoreceptor (hereinafter referred to as the photosensitive drum) 1, which is an image carrier; a charging roller 2, which is a charging means; an exposure means 3; a developing means 4; and a pre-charging exposure means 5. In the following description, the dimensions of the photosensitive drum 1 in the direction parallel to the rotation axis and in the direction of the rotation axis are referred to as the longitudinal direction and longitudinal width, respectively, and this applies not only to the photosensitive drum 1 but also to the description of various other components.

[0016] The photosensitive drum 1 is an image carrier that rotates at a peripheral speed (process speed) of 150 mm / sec in the direction of arrow Y and carries the toner image. The photosensitive drum 1 has a photosensitive layer and a surface layer on a φ20 mm aluminum tube, and the surface layer is a thin film layer with a thickness of 20 μm made of polycarbonate. When the control unit 99 receives an image signal, it starts the image forming operation of the image forming apparatus 100 and rotates the photosensitive drum 1. The rotating photosensitive drum 1 is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in Example 1) by the charging roller 2 and is exposed by the exposure means 3 according to the image signal. As a result, an electrostatic latent image corresponding to the yellow color component image of the color image based on the image signal is formed. Next, the electrostatic latent image is developed as a yellow toner image by the developing means (yellow developing means) 4.

[0017] The charging roller 2 contacts the surface of the photosensitive drum 1 with a predetermined pressure force, and rotates in a driven manner relative to the photosensitive drum 1 due to friction between the charging roller 2 and the surface of the photosensitive drum 1 at the contact portion (hereinafter referred to as the charging portion). A predetermined DC voltage is applied to the rotation axis of the charging roller 2 from a charging bias power supply (not shown) in accordance with the image forming operation. In this embodiment, the charging roller 2 is mounted on a metal shaft with a diameter of 5.5 mm, and has a thickness of 1.5 mm and a volume resistivity of 1 × 10⁻¹⁶. 6 An elastic layer made of a conductive elastic material with a thickness of approximately Ωcm was provided. In accordance with the image forming operation, a DC voltage of -1300V was applied as a charging bias to the rotation axis of the charging roller 2 to charge the surface of the photosensitive drum 1 to a predetermined potential of -600V. The surface potential of the photosensitive drum 1 was measured using a Trek Model 344 surface potential meter. This surface potential of the photosensitive drum 1 is the surface potential of the photosensitive drum 1 when no image is being formed, and no toner image is developed.

[0018] Exposure means 3 is an exposure means that forms an electrostatic latent image on the photosensitive drum 1 which has been charged by the charging roller 2. Exposure means 3 includes a laser driver, a laser diode, a polygon mirror, an optical lens system, etc. Based on image data input to the image forming apparatus 100 from, for example, an external computer (not shown), exposure means 3 irradiates the photosensitive drum 1 with laser light and forms an electrostatic latent image on the uniformly charged surface of the photosensitive drum 1. In this embodiment, exposure is performed by exposure means 3. The exposure amount is adjusted so that the potential (image formation potential) Vl of the photosensitive drum 1 in the electrostatic latent image area after the exposure is -100V.

[0019] The developing means 4 is a developing unit that develops an electrostatic latent image as a developing image using a developing agent containing a developer and a carrier. The developing means 4 has a developing roller 41 and a non-magnetic one-component toner (hereinafter referred to as toner) and a carrier as the developing agent. The developing roller 41 is a developing member that forms a developing image by supplying a developer of normal polarity containing toner and a carrier onto the surface of the photosensitive drum 1 at a developing position facing the photosensitive drum 1, which is an image carrier. The developing roller 41 is movable between a first position in which developer is supplied to the surface of the photosensitive drum 1 and a second position in which no developer is supplied to the surface of the photosensitive drum 1. In this embodiment, the first position is the position in which the developing roller 41 is in contact with the photosensitive drum 1, and the second position is the position in which the developing roller 41 is separated from the photosensitive drum 1.

[0020] The toner is a negatively charged, non-magnetic toner manufactured by suspension polymerization, with a volume-average particle size of 7.0 μm. It becomes negatively charged when supported on the developing roller 41. The volume-average particle size of the toner was measured using a Beckman Coulter LS-230 laser diffraction particle size analyzer.

[0021] The carrier is a particle interposed between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1. Due to the function of the carrier, the adhesion force between the toner image and the photosensitive drum 1 is reduced, improving the primary transfer efficiency of the toner image. In this embodiment, the carrier is silica fine particles added externally to the toner. The particle size of the carrier is preferably 1000 nm or less, which is less affected by electrostatic forces. In this embodiment, the particle size of the carrier is 100 nm. The carrier added externally to the toner moves from the toner to the photosensitive drum 1 when the toner coated on the developing roller 41 comes into contact with the photosensitive drum 1, regardless of the potential difference between the developing roller 41 and the photosensitive drum 1.

[0022] The developing means 4 and the main body of the image forming apparatus 100 are equipped with a contact / separation mechanism 94 (see Figure 8) that controls the movement of the developing roller 41 between a first position and a second position. By controlling the contact / separation mechanism 94 according to the image forming operation, the developing roller 41 is switched between a state in contact with the photosensitive drum 1 and a state in which it is separated. When the developing roller 41 and the photosensitive drum 1 are in contact, the developing roller 41 contacts the photosensitive drum 1 with a pressing force of 200 gf. The width of the contact portion between the developing roller 41 and the photosensitive drum 1 (hereinafter referred to as the developing nip portion) is 2 mm in the rotational direction of the photosensitive drum 1 and 234 mm in the longitudinal direction of the photosensitive drum 1. The developing roller 41 is rotated in the same direction as the surface movement direction of the photosensitive drum 1 so that its surface movement speed (hereinafter referred to as the peripheral speed) in the developing nip portion is 140% of the peripheral speed of the photosensitive drum 1.

[0023] The developing roller 41 is a roller in which an elastic layer made of urethane resin is provided around a metal core. When the developing roller 41 and the photosensitive drum 1 come into contact during the image formation operation, a DC voltage of -300V is applied to the core of the developing roller 41 as a developing bias from a developing bias power supply (not shown). An electrostatic force is generated by the potential difference between the developing bias of the developing roller 41 -300V and the image formation potential Vl = -100V of the electrostatic latent image area of ​​the photosensitive drum 1. Due to this electrostatic force, the toner carried on the developing roller 41 moves to the electrostatic latent image area of ​​the photosensitive drum 1 during image formation, thereby developing the electrostatic latent image.

[0024] The supply roller 42 is a supply member that supplies developer to the surface of the developing roller 41. It is a sponge roller having a porous elastic layer around a metal core. The supply roller 42 is rotationally driven in the counter-direction with respect to the developing roller 41. At the contact point between the supply roller 42 and the developing roller 41, the toner coated on the developing roller 41 is scraped into the developer container, and new toner is supplied to the developing roller 41. The supply roller 42 is supplied with a voltage. A fixed DC voltage (supply roller voltage Vrs) is applied by the supply bias power supply 97 (see Figure 8), which is the supply voltage application unit. A predetermined DC voltage (developer roller voltage Vdc), which is the development voltage, is applied to the developer roller 41 by the developer bias power supply 93 (see Figure 8), which is the development voltage application unit. The control unit 99 controls at least one of the supply bias power supply 97 and the developer bias power supply 93 so that a potential difference in a predetermined direction is formed between the developer roller 41 and the supply roller 42. The potential difference in a predetermined direction is the potential difference in the direction in which an electrostatic force acts on the developer, which is charged with normal polarity, from the supply roller 42 toward the developer roller 41. The amount of toner supplied is controlled by controlling the potential difference between the supply roller voltage Vrs and the development voltage applied to the developer roller 41 (supply roller contrast ΔVrs = Vrs - Vdc).

[0025] The pre-charging exposure means 5 exposes the area of ​​the photosensitive drum 1 that has passed through the primary transfer section but has not passed through the charging section, thereby eliminating the unevenness of the surface potential of the photosensitive drum 1 after the primary transfer.

[0026] The intermediate transfer belt 10 is stretched and rotated by a plurality of tensioning members 11, 12, and 13. The intermediate transfer belt 10 is driven to move in the same direction as the rotation direction of the photosensitive drum 1 at the contact point with the photosensitive drum 1. The primary transfer roller 14 is a transfer means that contacts the photosensitive drum 1 via the intermediate transfer belt 10 and transfers the developer image formed on the photosensitive drum 1 to the intermediate transfer belt 10, which is an intermediate transfer body. The contact point between the primary transfer roller 14 and the photosensitive drum 1 via the intermediate transfer belt 10 is hereinafter referred to as the primary transfer section. During primary transfer in the image forming operation, a DC voltage of 300V is applied to the primary transfer roller 14 from a primary transfer power supply (not shown), and the first color yellow toner image formed on the photosensitive drum 1 is electrostatically transferred onto the intermediate transfer belt 10 as it passes through the primary transfer section.

[0027] The primary transfer roller 14 is a cylindrical metal roller with a diameter of φ6 mm, and its material is nickel-plated stainless steel. The primary transfer roller 14 is positioned 8 mm offset downstream of the intermediate transfer belt 10 in the direction of movement, relative to the center of the photosensitive drum 1. This ensures that the intermediate transfer belt 10 contacts the photosensitive drum 1 in a manner that it wraps around it. The primary transfer roller 14 is positioned 1 mm closer to the photosensitive drum 1 than the tangent plane to the photosensitive drum 1 at the upstream tangent in the direction of movement of the intermediate transfer belt 10. For example, if the plane that the tensioning member 13 and the photosensitive drum 1 commonly contact is a horizontal plane, the primary transfer roller 14 is positioned 1 mm vertically upward from the position where it contacts the horizontal plane from the side opposite to the photosensitive drum 1. This ensures that the primary transfer roller 14 presses the intermediate transfer belt 10 with a force of approximately 200 gf, thereby ensuring the amount of wrapping of the intermediate transfer belt 10 around the photosensitive drum 1. The primary transfer roller 14 rotates in conjunction with the rotation (movement) of the intermediate transfer belt 10.

[0028] Similarly, the second, third, and fourth image forming stations b, c, and d form images of the second color magenta toner, the third color cyan toner, and the fourth color black toner, which are then sequentially transferred onto the intermediate transfer belt 10. As a result, an image corresponding to the image data is formed on the intermediate transfer belt 10, which is the transfer target.

[0029] The secondary transfer roller 15, acting as a secondary transfer member, contacts the intermediate transfer belt 10 with a pressure of 50N, forming a secondary transfer section (hereinafter referred to as the secondary transfer nip section). The secondary transfer roller 15 rotates in a driven manner relative to the intermediate transfer belt 10. Recording material P is supplied to the secondary transfer nip section by the paper feeding means 50, and the four-color toner images on the intermediate transfer belt 10 are transferred collectively to the surface of the recording material P as they pass through the secondary transfer nip section (secondary transfer). When secondary transfer of the toner on the intermediate transfer belt 10 to the recording material P, a voltage of 1500V is applied to the secondary transfer roller 15 by a secondary transfer power supply (not shown).

[0030] Subsequently, the recording material P, which carries the four toner images, is introduced into the fuser 30, where it is heated and pressurized, causing the four toners to melt and mix, fixing them to the recording material P. After secondary transfer, any toner remaining on the intermediate transfer belt 10 is cleaned by the cleaning device 17 and removed from the intermediate transfer belt 10.

[0031] The cleaning device 17 uses a cleaning blade or the like to contact the outer surface of the intermediate transfer belt 10, scraping off any toner remaining on the intermediate transfer belt 10 and collecting it inside the cleaning device 17. The cleaning device 17 collects toner adhering to the intermediate transfer belt 10 downstream of the secondary transfer section in the rotational direction of the intermediate transfer belt 10.

[0032] Through the image formation operation described above, a color image based on image data is formed on the recording material. In this embodiment, the toner image, which is first transferred from the photosensitive drum 1 to the intermediate transfer belt 10, is shown to be transferred to the recording material in the secondary transfer section. However, a configuration in which the toner image is directly transferred from the photosensitive drum 1 to the recording material is also possible. Details of the image formation operation will be described later.

[0033] Next, the adhesion of toner to the surface of the charging roller 2 and the adhesion of carriers to the photosensitive drum 1 in this embodiment will be described.

[0034] First, let's explain the adhesion of toner to the surface of the charging roller 2. Due to the effects of transfer in the primary transfer section of the image forming operation, the remaining toner on the photosensitive drum 1 contains a certain proportion of toner charged with normal polarity and toner charged with opposite polarity (positive polarity in this embodiment). Therefore, as the remaining toner passes through the contact area with the charging roller 2 as the photosensitive drum 1 rotates, the electric field formed by the difference between the voltage applied to the charging roller 2 and the surface potential of the photosensitive drum 1 causes the positively polarized toner in the remaining toner to move to the charging roller 2. This adhesion of remaining toner to the surface of the charging roller 2 occurs each time the remaining toner passes through the contact area between the photosensitive drum 1 and the charging roller 2 as the photosensitive drum 1 rotates. Therefore, as the image forming operation and other processes are repeated, the remaining toner accumulates on the surface of the charging roller 2.

[0035] Next, the adhesion of the carrier to the photosensitive drum 1 will be explained. Figure 3(a) is a schematic diagram of the developing nip section when the developing roller 41 and the photosensitive drum 1 are in contact. As shown in Figure 3(a), in the developing nip section, the toner 300 supported on the developing roller 41 and the photosensitive drum 1 are in contact via the carrier 301, and the carrier 301 is interposed between the toner 300 and the photosensitive drum 1. Figure 3(b) is a schematic diagram showing the state after the toner 300 supported on the developing roller 41 and the photosensitive drum 1 shown in Figure 3(a) have passed through the developing nip section. The adhesion force Ft between the carrier 301 and the toner 300 in the developing nip section shown in Figure 3(a) is smaller than the adhesion force Fdr between the carrier 301 and the photosensitive drum 1. Therefore, as shown in Figure 3(b), the carrier 301 that was interposed between the toner 300 and the photosensitive drum 1 in the developing nip section moves from the toner 300 supported on the developing roller 41 to the photosensitive drum 1 after passing through the developing nip section. Furthermore, when toner 300 is transferred to the photosensitive drum 1 during the image forming operation, the carrier 301 attached to the toner 300 also moves to the photosensitive drum 1. Therefore, depending on the content of the image data involved in image formation, the amount of carrier 301 attached to the image forming area on the photosensitive drum 1 may become uneven. In other words, areas consisting of pixels with a large amount of toner transferred will have a larger amount of carrier 301 attached compared to areas consisting of pixels with a small amount of toner transferred or no toner transferred at all. If the amount of carrier 301 attached to the photosensitive drum 1 becomes uneven, it may become impossible to uniformly charge the surface of the photosensitive drum 1.

[0036] Thus, due to the uneven adhesion of residual toner accumulated on the charging roller 2 and carriers on the photosensitive drum 1, uneven density may occur in the formed image.

[0037] As a countermeasure, in this embodiment, the control unit 99 controls as follows. Specifically, the control unit 99 can perform an image forming operation in which the developing roller 41 is in a first position (contact position) and a first charging voltage is applied to the charging roller 2 to form an image on the intermediate transfer belt 10, which is the transfer target. The control unit 99 can also perform a first rotation operation in which the photosensitive drum 1 is rotated in which the developing roller 41 is in a first position (contact position) and a second charging voltage with an absolute value smaller than the first charging voltage is applied to the charging roller 2. The control unit 99 can also perform a second rotation operation in which the photosensitive drum 1 is rotated in which the developing roller 41 is in a second position (separated position) and a third charging voltage with an absolute value smaller than the second charging voltage is applied to the charging roller 2. By performing the first rotation operation, a supply operation is performed in which carriers are supplied from the developing roller 41 to the surface of the photosensitive drum 1, and excess carriers are recovered from the surface of the photosensitive drum 1. This controls the system to make the carriers on the surface of the photosensitive drum 1 uniform. By performing a second rotational movement, a cleaning operation is performed in which the developer is moved from the charging roller 2 to the photosensitive drum 1, thereby cleaning the charging roller 2. After the image forming operation, the control unit 99 performs the first rotational movement and the second rotational movement.

[0038] In Example 1, after the completion of the primary image transfer, a second rotation operation is performed in the post-rotation process, which is the final processing step of the image formation operation. Furthermore, in order to efficiently clean the charging roller 2 during the second rotation operation, the first rotation operation is performed before the second rotation operation to control the carrier of the photosensitive drum 1 to be uniform. Thus, in this embodiment, both the first and second rotation operations are performed after the image formation operation on the intermediate transfer belt 10. Alternatively, the first and second rotation operations may be performed after the image formation operation on the recording material is performed, or they may be started after the recording material has been discharged from the image forming apparatus 100. The first rotation operation will be described in detail below.

[0039] Figure 1 is a timing chart of the image forming operation, the first rotation operation, and the second rotation operation in this embodiment. As shown in Figure 1, the first rotation operation is performed after the image forming operation, and then the second rotation operation is performed. These operations are performed by a control unit 99 provided in the image forming apparatus 100. Figure 8 is a block diagram showing the control unit 99 and the various components of the image forming apparatus 100 that it controls. The control unit 99 controls the drum drive device 91 to rotate the photosensitive drum 1, controls the charging bias power supply 92, which is the charging voltage application unit, to apply a DC voltage, which is the charging voltage, to the charging roller 2, and controls the exposure means 3 to expose the photosensitive drum 1. The control unit 99 also controls the development bias power supply 93, which is the development voltage application unit, to apply a DC voltage, which is the development voltage, to the development means 4, and controls the contact / separation mechanism 94 to control the contact / separation state of the development roller 41 and the photosensitive drum 1. Furthermore, the control unit 99 controls the pre-charging exposure means 5 to expose the photosensitive drum 1 at a position upstream of the charging unit, and controls the primary transfer power supply 95 to apply a DC voltage to the primary transfer roller 14. The control unit 99 also controls the belt drive device 96 to rotate the intermediate transfer belt 10, and controls the supply bias power supply 97, which is the supply voltage application unit, to apply a DC voltage, which is the supply voltage, to the supply roller 42. Note that some of the various components shown in Figure 8 have been omitted from Figure 1 to avoid complexity in the drawing.

[0040] First, the first rotational operation will be described. In this embodiment, the developing roller 41 has both the function of supplying carriers to the photosensitive drum 1 and the function of recovering carriers from the photosensitive drum 1. The first rotational operation involves setting a potential relationship so that toner charged with the correct polarity does not move from the developing roller 41 to the photosensitive drum 1, and then bringing the developing roller 41 into contact with the photosensitive drum 1 and driving it to rotate. The surface of the developing roller 41 has protrusions formed by rough particles that are higher than the average particle size of the toner, so that even when the developing roller 41 is covered with toner, the photosensitive drum 1 and the protrusions can be brought into direct contact. Carriers are recovered from areas on the photosensitive drum 1 where there is a lot of carrier by the protrusions on the developing roller 41 where toner is not attached. The areas on the photosensitive drum 1 where toner is attached to the 41 supply carrier to areas where carrier is scarce. In this way, the developing roller 41 can level the photosensitive drum 1 so that about one to two layers of carrier are attached to it.

[0041] Figure 4(a) is a schematic diagram showing the uneven distribution of carriers on the photosensitive drum 1. If the same area on the photosensitive drum 1 corresponds to an area with a large amount of toner transfer, the carriers on the photosensitive drum 1 will be uneven as shown in Figure 4(a). Figure 4(b) is a schematic diagram showing the state of the carriers on the photosensitive drum 1 after the first rotation operation has been performed. By performing the first rotation operation from the uneven carrier state shown in Figure 4(a), the carriers on the photosensitive drum 1 can be leveled to a state where they are stacked in approximately 1 to 2 layers, as shown in Figure 4(b).

[0042] In this embodiment, during the execution of the first rotational operation, the discharge amount from the charging roller 2 is controlled to be less than the discharge amount during the image forming operation. Specifically, as shown in Figure 1, at time t1, when the image forming operation is completed, the voltage applied to the charging roller 2 is changed from the first charging voltage (-1300V) during the image forming operation to a second charging voltage (-1200V) which has a smaller absolute value than the first charging voltage. By making the absolute value of the charging voltage smaller than the absolute value of the charging voltage during the image forming operation, the potential difference between the charging roller 2 and the photosensitive drum 1 is reduced, and the charging current decreases. As a result, the amount of discharge products such as nitrogen oxides can be reduced. By reducing the amount of discharge products, it is suppressed that carriers become embedded in deposits on the photosensitive drum 1 containing discharge products, which reduces the transfer efficiency.

[0043] Between time t2 and time t3, the developing roller 41 is brought into contact with the photosensitive drum 1 and rotated to perform the first rotation operation. By making the execution time of the first rotation operation after image formation (the contact time between the developing roller 41 and the photosensitive drum 1) at least the time it takes for the photosensitive drum 1 to rotate once, the carrier on the photosensitive drum 1 can be made well uniform. When images with similar patterns are formed consecutively, the degree of carrier non-uniformity on the photosensitive drum 1 is likely to be large, so it is preferable that the execution time of the first rotation operation be about the length of 5 rotations of the photosensitive drum 1. If the degree of non-uniformity is even greater, it is more preferable that the execution time of the first rotation operation be about the length of 10 rotations of the photosensitive drum 1. In this embodiment, the execution time of the first rotation operation was set to the length of 20 rotations of the photosensitive drum 1 so that the carrier can be sufficiently uniform when images of patterns that are commonly formed are formed consecutively. This balances the time required for the subsequent rotation process with the degree of carrier uniformity. Furthermore, in order to prevent the carrier from becoming embedded in deposits containing discharge products, it is preferable to start the first rotation operation immediately after the image forming operation is completed. The rotation speed of the photosensitive drum 1 associated with the first rotation operation can be adjusted as appropriate.

[0044] Next, the second rotation operation will be described. In the second rotation operation in this embodiment, the photosensitive drum 1 is rotated while a third charging voltage (0V), which has an absolute value smaller than the second charging voltage (-1200V), is applied to the charging roller 2. In addition, an electric field opposite to that during the image forming operation is formed between the photosensitive drum 1 and the charging roller 2, and between the photosensitive drum 1 and the primary transfer roller 14, thereby removing the positively charged toner on the charging roller 2.

[0045] In Figure 1, after the first rotational movement, the developing roller 41 is separated from the photosensitive drum 1 at time t3. After the separation of the developing roller 41 is completed at time t4, the developing voltage is set to 0V at time t5. In this embodiment, an example is shown where the developing voltage is set to 0V after the developing roller 41 has separated. However, the changed developing voltage is not limited to this example, as long as the change in developing voltage is performed after the developing roller 41 has separated.

[0046] On the other hand, regarding the charging voltage, after the first rotational movement, the charging voltage is changed from -1200V to -1300V at time t4, and the time it takes for the photosensitive drum 1 to complete one rotation (between time t4 and time t5) -1300V is continuously applied. This brings the total potential of the photosensitive drum 1 to -600V. By increasing the absolute value of the charging voltage, the electric field in the direction of the photosensitive drum 1 can be strengthened.

[0047] Next, at time t5, the charging voltage is changed towards the third charging voltage (0V), and the exposure means 3 is forced to emit light. The drum potential at the position exposed by the exposure means 3 changes from -600V to -100V. It is preferable that the forced exposure by the exposure means 3 is started at time t5 so that exposure occurs no later than before the toner that first moved from the charging roller 2 to the photosensitive drum 1 reaches the exposure position due to the rotation of the photosensitive drum 1. As a result, the drum potential at the position where the toner that moved from the charging roller 2 to the photosensitive drum 1 is attached becomes -100V.

[0048] Between time t4 and time t5, the portion of the photosensitive drum 1 that has a drum potential of -600V corresponding to the charging voltage of -1300V applied to the charging roller 2 comes into contact with the charging roller 2 to which a third charging voltage (0V) is applied between time t6 and time t7. As a result, an electric field is formed between the 0V charging roller 2 and the -600V photosensitive drum 1, and the positively charged toner attached to the charging roller 2 moves to the photosensitive drum 1. In this embodiment, the difference between the second charging voltage (-1200V) and the third charging voltage (0V) is greater than the difference between the first charging voltage (-1300V) and the second charging voltage (-1200V). This is because, during the first rotation operation, it is necessary to create a potential difference that prevents the movement of toner from the developing roller 41 to the photosensitive drum 1, while during the second rotation operation, it is necessary to cause active toner movement from the charging roller 2 to the photosensitive drum 1.

[0049] The primary transfer voltage is changed from 300V to -900V at the timing before the toner that has moved to the photosensitive drum 1 reaches the primary transfer section (immediately after time t5 in Figure 1). Because the potential of the photosensitive drum 1 at the position where the toner that has moved from the charging roller 2 is attached is -100V due to forced emission, an electric field is formed in the primary transfer section between the -100V photosensitive drum 1 and the -900V primary transfer roller 14. As a result, the positively charged toner attached to the photosensitive drum 1 moves to the intermediate transfer belt 10. Here, the primary transfer voltage is set to -900V, but it is sufficient to set it to a voltage that can transfer positively charged toner, and a voltage equivalent to the potential difference in the primary transfer section during image formation may also be applied.

[0050] The forced light emission by the exposure means 3 is performed for a predetermined time (from time t5 to time t8). In this embodiment, the predetermined time is set to the time it takes for the photosensitive drum 1 to complete two rotations. This allows the positively charged toner on the photosensitive drum 1 to be transferred to the intermediate transfer belt 10 more reliably. Then, at time t9, the primary transfer voltage is changed from -900V to 0V. The positively charged toner that has moved to the intermediate transfer belt 10 is transported through the secondary transfer section to the section opposite the cleaning device 17 as the intermediate transfer belt 10 circulates, and at time t 10 Then it is recovered by the cleaning device 17. Here, from time t4 to time t 10 The execution time of the second rotational movement was set to 40 rotations of the photosensitive drum 1. In this embodiment, the execution time of the second rotational movement is longer than that of the first rotational movement. During the second rotational movement, the toner moves from the charging roller 2 to the photosensitive drum 1, then to the intermediate transfer belt 10, and finally to the intermediate transfer belt 10, where it is removed by the cleaning device 17. Therefore, by ensuring a longer time for the second rotational movement, the charging roller 2 can be cleaned more reliably. The rotational speed of the photosensitive drum 1 during the second rotational movement can be adjusted as appropriate. Furthermore, the execution time of the second rotational movement may be shorter than that of the first rotational movement.

[0051] As described above, the controlled first and second rotational movements allow for efficient removal of toner adhering to the surface of the charged roller 2.

[0052] Next, the effects of this embodiment will be described. In this embodiment, since the first rotation operation is performed before the second rotation operation, the charging roller 2 can be cleaned while the carrier on the photosensitive drum 1 is not uneven. As a result, the second rotation operation can be performed with the potential of the photosensitive drum 1 facing the charging roller 2 controlled to be uniform in advance. Therefore, the toner can be controlled to move uniformly from the charging roller 2 to the photosensitive drum 1 during the second rotation operation. To confirm the effects of this embodiment, the amount of carrier attached to the photosensitive drum 1 after the first rotation operation and the amount of toner attached to the charging roller 2 after the second rotation operation were verified.

[0053] Regarding the amount of carrier adhering to the photosensitive drum 1, five consecutive image formation operations were performed to create a vertical line image with a width of 25 mm in the longitudinal direction in the center of the photosensitive drum 1. The device was stopped at time t3 immediately after the first rotation operation and observation was performed. For the observation method, a laser microscope (VK-X200 Keyence) was set to a magnification of 3000x and images of the surface of the photosensitive drum 1 in the printed and non-printed areas were acquired. In the acquired images, it was observed that there was almost no difference in the amount of carrier adhering to the printed and non-printed areas of the photosensitive drum 1, indicating that the carrier was uniformly adhering to the photosensitive drum 1.

[0054] To determine the amount of toner adhering to the charging roller 2, an image of a vertical line with a length of 25 mm was formed in the center of the photosensitive drum 1, and the image formation operation was performed for five consecutive images. The toner density on the charging roller 2 was measured immediately after the first and second rotation operations. Specifically, the toner on the charging roller 2 was collected with transparent tape (polyester tape 5511 Nichiban) and attached to high-whiteness paper (GFC081 Canon). The toner density D1 of the transparent tape in the printed area and the toner density D2 of the transparent tape in the non-printed area were measured using a reflectometer (reflectometer model TC-6DS manufactured by Tokyo Denshoku Co., Ltd.). The difference in toner density between the printed and non-printed areas on the charging roller 2, calculated as the absolute value of the difference |D2-D1|, was 5% or less, indicating that the toner on the charging roller 2 was uniformly cleaned.

[0055] As explained above, in the first rotation operation, the developing roller 41 collects excess carriers attached to the photosensitive drum 1 and supplies carriers to areas on the photosensitive drum 1 where there are fewer carriers. This allows the amount of carriers attached to the photosensitive drum 1 to be controlled to be uniform, thereby reducing unevenness in the surface potential of the photosensitive drum 1. By performing this first rotation operation before the second rotation operation, the second rotation operation is performed with a uniform surface potential of the photosensitive drum 1, so that the toner from the charging roller 2 moves uniformly to the photosensitive drum 1. This allows the toner on the charging roller 2 to be uniformly reduced.

[0056] In this embodiment, an example was described in which the generation of discharge products is suppressed by reducing the absolute value of the charging voltage during the first rotation operation. However, other control methods are also acceptable as long as the generation of discharge products can be suppressed. For example, during the execution of the first rotation operation, the exposure intensity of the pre-charging exposure means 5 may be reduced to a lower level than the exposure intensity during the image forming operation. For example, as shown in Figure 5, by turning off the pre-charging exposure by the pre-charging exposure means 5 at time t2, the potential difference between the photosensitive drum 1 and the charging roller 2 immediately before the charging section is reduced, thereby reducing the amount of discharge products. Then, the developing roller 41 is brought into contact with the photosensitive drum 1 until time t3 to perform the first rotation operation. From time t0 to time t1, and from time t3 onward, the control is the same as described in Figure 1. In addition, during the first rotation operation, the developing roller 41 may be brought into contact with the photosensitive drum 1 and rotated without reducing the magnitude of the charging voltage. Even in this case, the control can be made so that the carriers on the photosensitive drum 1 are uniform.

[0057] Furthermore, in the second rotational movement, the toner moves from the charging roller 2 to the photosensitive drum 1 along with the carrier. As a result, the area of ​​the photosensitive drum 1 to which the toner that moved from the charging roller 2 has adhered has a larger amount of carrier compared to other areas. This causes the carrier of the photosensitive drum 1 If unevenness occurs in the rear, charging unevenness may occur in the next image forming operation, and this charging unevenness may result in image density unevenness.

[0058] Therefore, as shown in Figure 6, the first rotational movement may be performed again after the completion of the second rotational movement. Figure 6, time t 10 After the second rotational movement is completed, the developing roller 41 is brought into contact with the photosensitive drum 1 again, at time t 11 From time t 12 During this time, the first rotational movement is performed. This controls the carrier of the photosensitive drum 1 to be more uniform, and the next image formation takes place under these conditions, resulting in good image formation.

[0059] In this embodiment, an example has been described in which the first and second rotation operations are performed in a post-rotation step after the image formation operation, but the embodiment is not limited to this. Depending on the content of the image data involved in image formation, the timing of the first and second rotation operations between image formations may be determined. For example, the first and second rotation operations may be performed each time a series of image formations is completed, or each time a predetermined number of images are formed. This predetermined number may be a constant, or it may be variable depending on the content of the image data involved in image formation and environmental conditions such as temperature and humidity. Furthermore, the time for performing the first rotation operation may be variable depending on the content of the image data involved in image formation and the environmental conditions during image formation.

[0060] (Example 2) A second embodiment will now be described. In the image forming apparatus 100 according to this embodiment, components common to Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted. In this embodiment, the control unit 99 can perform an image forming operation in which an image is formed on the intermediate transfer belt 10, which is the transfer target, when the developing roller 41 is in a first position (contact position) and a first potential difference is formed between the developing roller 41 and the supply roller 42. The control unit 99 can also perform a first rotation operation to rotate the photosensitive drum 1 when the developing roller 41 is in a first position (contact position) and a second potential difference smaller than the first potential difference is formed between the developing roller 41 and the supply roller 42. The control unit 99 can also perform a second rotation operation to rotate the photosensitive drum 1 when the developing roller 41 is in a second position (separated position). By performing the first rotation operation, a supply operation is performed in which carriers are supplied from the developing roller 41 to the surface of the photosensitive drum 1, and excess carriers are recovered from the surface of the photosensitive drum 1. This controls the system to make the carrier on the surface of the photosensitive drum 1 uniform. By executing a second rotational movement, a cleaning operation is performed to clean the charging roller 2 by moving the developer from the charging roller 2 to the photosensitive drum 1. After the image forming operation, the control unit 99 performs the first rotational movement and the second rotational movement.

[0061] During the first rotation operation, the amount of developer carried on the developing roller 41 of the developing means 4 is less than during the image forming operation. In this embodiment, during the execution of the first rotation operation, the absolute value of the voltage applied to the supply roller 42 is made smaller than during the execution of the image forming operation, thereby making the potential difference (second potential difference) between the supply roller 42 and the developing roller 41 smaller than the first potential difference during the image forming operation. The potential difference Vrs-Vdc between the supply roller 42 and the developing roller 41 is called the supply roller contrast ΔVrs. In addition, in order to reduce the discharge products on the photosensitive drum 1, the absolute value of the primary transfer voltage is made smaller during or after the first rotation operation than during the execution of the image forming operation. By lowering the absolute value of the primary transfer voltage, the potential difference between the photosensitive drum 1 and the primary transfer roller 14 in the primary transfer section becomes smaller, and the potential fluctuation of the photosensitive drum 1 before and after the primary transfer section becomes smaller. As a result, the potential difference between the charging roller 2 and the photosensitive drum 1 in the charging section after passing through the primary transfer section becomes smaller, and the charging current decreases, thus reducing the discharge products.

[0062] As shown in Figure 7, at time t1 after image formation is complete, the supply roller voltage is changed from -400V to -350V. This causes the supply roller contrast ΔVrs to be Δ10 during the image formation operation. The voltage decreases from 0V to Δ50V. ​​That is, the control unit 99 sets the potential difference between the developing roller 41 and the supply roller 42 to a first potential difference of Δ100V during the image forming operation, and to a second potential difference of Δ50V, which is smaller than the first potential difference, during the first rotation operation. Thereafter, during the first rotation operation from time t2 to time t3, the supply roller contrast ΔVrs is maintained at Δ50V. ​​Reducing the supply roller contrast ΔVrs reduces the electric field required to move the negative polarity toner from the supply roller 42 towards the developing roller 41, thus reducing the amount of toner on the developing roller 41. As a result, the area of ​​the developing roller 41 where no toner is attached increases, increasing the area of ​​the surface of the developing roller 41 that is exposed on the contact surface of the developing roller 41 with respect to the photosensitive drum 1. Therefore, excess carriers attached to the photosensitive drum 1 can be effectively recovered. Consequently, the carriers on the photosensitive drum 1 can be made more efficiently uniform, thus shortening the execution time of the first rotation operation. In Example 2, the execution time of the first rotation operation was set to the time of 18 rotations of the photosensitive drum 1, making it shorter than in Example 1. In this example, an example was described in which the potential difference between the developing roller 41 and the supply roller 42 (supply roller contrast ΔVrs) during the first rotation operation was reduced from Δ100V during the image formation operation to Δ50V, but this is not the only example. For example, the supply roller contrast ΔVrs may be set to Δ0V (zero), or ΔVrs may be set to a negative value. When ΔVrs is negative, the potential difference between the developing roller 41 and the supply roller 42 during the first rotation operation (second potential difference) will be the opposite in sign to the first potential difference during the image formation operation. By controlling the supply roller contrast during the first rotation operation in this way, the amount of toner supplied to the developing roller 41 during the first rotation operation can be reduced.

[0063] After the first rotational movement is completed, the developing roller 41 is separated at time t4, and while a developing voltage of -300V is applied, the supply roller voltage is applied at -400V, the same as during image formation. This allows the amount of toner on the developing roller 41 to return to the same amount as the amount of developer used during the image formation operation, thus enabling good image formation for the next step. At time t5, as the developing voltage is changed from -300V to 0V, the supply roller voltage is changed to 0V so that the supply roller contrast becomes Δ0V.

[0064] The primary transfer voltage is changed in stages from 300V to 120V, and then to 0V, at the timing after the trailing end of the recording material, which has had its image formed up to time t1, has passed through the secondary transfer section. Figure 7 shows an example in which this primary transfer voltage change is performed after time t3, but this primary transfer voltage change may also be performed during the execution of the first rotation operation before time t3.

[0065] The control operations from time t5 onward are the same as in Example 1.

[0066] According to this embodiment, by reducing the supply roller contrast ΔVrs during the first rotational movement, the amount of toner transferred from the supply roller 42 to the developing roller 41 is reduced. This increases the area of ​​the contact surface between the photosensitive drum 1 and the developing roller 41 where the surface of the developing roller 41 is exposed, allowing for efficient collection of excess carrier material adhering to the photosensitive drum 1. As a result, the carrier material on the photosensitive drum 1 can be more reliably and uniformly distributed, enabling more uniform cleaning of the charging roller 2 during the second rotational movement. [Explanation of symbols]

[0067] 1a, 1b, 1c, 1d: Photosensitive drum (photoreceptor), 2a, 2b, 2c, 2d: Charging roller, 3a, 3b, 3c, 3d: Exposure means, 10: Intermediate transfer belt, 14a, 14b, 14c, 14d: Primary transfer roller, 41a, 41b, 41c, 41d: Developing roller, 42a, 42b, 42c, 42d: Supply roller, 92: Charging bias power supply, 93: Developing bias power supply, 97: Supply bias power supply, 99: Control unit

Claims

1. an image carrier; a charging means for charging the image carrier; an exposure unit that exposes the image carrier charged by the charging unit to light to form an electrostatic latent image; a developing member that forms a developer image by supplying a developer containing toner and a carrier onto a surface of the image carrier at a development position facing the image carrier, the developing member being movable between a first position at which the developer is supplied to the surface of the image carrier and a second position at which the developer is not supplied to the surface of the image carrier; a transfer means for transferring the developer image onto a transfer target; a charging voltage applying unit that applies a charging voltage to the charging means; a control unit that controls the charging voltage application unit; and The control unit an image forming operation in which the developing member is positioned at the first position and an image is formed on a transfer medium in a state in which a first charging voltage is applied; a first rotation operation of rotating the image carrier while the developing member is positioned at the first position and a second charging voltage having an absolute value smaller than that of the first charging voltage is applied; a second rotation operation of rotating the image carrier while the developing member is positioned at the second position and a third charging voltage having an absolute value smaller than that of the second charging voltage is applied; is executable, The image forming apparatus is characterized in that the control unit controls the first rotation operation and the second rotation operation to be executed after the image forming operation.

2. 2. The image forming apparatus according to claim 1, wherein the difference between the second charging voltage and the third charging voltage is greater than the difference between the first charging voltage and the second charging voltage.

3. a supply member for supplying the developer to a surface of the developing member; a developing voltage applying section that applies a developing voltage to the developing member; a supply voltage application unit that applies a supply voltage to the supply member; Furthermore, the control unit further controls at least one of the developing voltage application unit and the supply voltage application unit so that a potential difference is formed in a direction in which an electrostatic force acts on the developer charged to the normal polarity in a direction from the supply member toward the developing member, The control unit During the image forming operation, a control is performed so that an image is formed on a transfer medium in a state where a first potential difference is formed between the developing member and the supply member, 3. The image forming apparatus according to claim 1, wherein during the first rotation operation, the image carrier is rotated in a state in which a second potential difference smaller than the first potential difference is formed between the developing member and the supply member.

4. an image carrier; a charging means for charging the image carrier; an exposure unit that exposes the image carrier charged by the charging unit to light to form an electrostatic latent image; a developing member that forms a developer image by supplying a developer that contains toner and a carrier and is charged to a normal polarity onto a surface of the image carrier at a development position facing the image carrier, the developing member being movable between a first position at which the developer is supplied to the surface of the image carrier and a second position at which the developer is not supplied to the surface of the image carrier; a supply member for supplying the developer to a surface of the developing member; a transfer means for transferring the developer image onto a transfer target; a developing voltage applying section that applies a developing voltage to the developing member; a supply voltage application unit that applies a supply voltage to the supply member; a control unit that controls at least one of the developing voltage application unit and the supply voltage application unit so that a potential difference in a direction in which an electrostatic force acts on the developer charged to the normal polarity in a direction from the supply member toward the developing member is formed between the developing member and the supply member; and The control unit an image forming operation in which an image is formed on a transfer medium in a state in which the developing member is located at the first position and a first potential difference is formed between the developing member and the supply member; a first rotation operation of rotating the image carrier in a state in which the developing member is located at the first position and a second potential difference smaller than the first potential difference is formed between the developing member and the supply member; a second rotation operation of rotating the image carrier with the developing member positioned at the second position; is executable, The image forming apparatus is characterized in that the control unit controls the first rotation operation and the second rotation operation to be executed after the image forming operation.

5. 5. The image forming apparatus according to claim 3, wherein the control unit controls the second potential difference to be zero or a potential difference opposite in sign to the first potential difference during the first rotation operation.

6. 6. The image forming apparatus according to claim 1, wherein the transfer medium is an intermediate transfer medium.

7. The control unit a supplying operation of supplying the carrier from the developing member to the surface of the image carrier by performing the first rotation operation; The image forming apparatus according to any one of claims 1 to 6, wherein the second rotation operation is performed to move the developer from the charging means to the image carrier, thereby performing a cleaning operation to clean the charging means.

8. the first position is a position where the developing member abuts against the image carrier; 8. The image forming apparatus according to claim 1, wherein the second position is a position where the developing member is separated from the image carrier.

9. 9. The image forming apparatus according to claim 1, wherein the time during which the second rotation operation is performed is longer than the time during which the first rotation operation is performed.

10. The image forming apparatus according to any one of claims 1 to 9, wherein the control unit forms an electric field between the image carrier and the charging means and between the image carrier and the transfer means in a direction opposite to that during the image forming operation, during the second rotation operation.

11. 11. The image forming apparatus according to claim 1, wherein the control unit performs the second rotation operation after the first rotation operation.

12. The image forming apparatus according to claim 11 , wherein the control unit performs the first rotation operation again after the second rotation operation.

13. 13. The image forming apparatus according to claim 1, wherein the control section performs the first rotation operation immediately after the image forming operation.

14. a pre-charging exposure unit that exposes a portion of the image carrier that has passed through the transfer unit and that has not passed through the charging unit; 14. The image forming apparatus according to claim 1, wherein the control section reduces the exposure intensity of the pre-charge exposure means during the first rotation operation to be lower than the exposure intensity during the image forming operation.

15. 15. The image forming apparatus according to claim 1, wherein the control section reduces the absolute value of the transfer voltage in the transfer means during or after the first rotation operation to be smaller than that during the image forming operation.

16. 16. The image forming apparatus according to claim 1, wherein the control unit executes the first rotation operation for a period of time during which the image carrier rotates at least one revolution.

17. 17. The image forming apparatus according to claim 1, wherein the control section controls the amount of developer carried on the developing member during the first rotation operation to be less than that during the image forming operation.

18. 18. The image forming apparatus according to claim 17, wherein the control section, during the first rotation operation, makes the absolute value of the supply voltage applied to the supply member that supplies toner to the developing member smaller than that during the image forming operation.

19. 19. The image forming apparatus according to claim 17, wherein the control section returns the amount of developer carried on the developing member to the same amount as the amount of developer during the image forming operation after the first rotation operation.

20. 20. The image forming apparatus according to claim 1, wherein the control section exposes the image carrier to light by the exposure section for a predetermined time during the second rotation operation.

21. forming an electrostatic latent image on an image carrier charged by a charging means; a step of moving a developing member, which forms a developer image by supplying a developer containing toner and a carrier onto a surface of the image carrier at a development position facing the image carrier, between a first position where the developer is supplied to the surface of the image carrier and a second position where the developer is not supplied to the surface of the image carrier; transferring the developer image to a transfer medium; a step of positioning the developing member at the first position and performing an image forming operation to form an image on a transfer medium while applying a first charging voltage to the charging means; a step of performing a first rotation operation of rotating the image carrier while positioning the developing member at the first position and applying a second charging voltage, the absolute value of which is smaller than that of the first charging voltage, to the charging means; a step of performing a second rotation operation in which the developing member is positioned at the second position and the image carrier is rotated in a state in which a third charging voltage having an absolute value smaller than that of the second charging voltage is applied to the charging means; and a step of performing the first rotation operation and a step of performing the second rotation operation, the step of performing the image forming operation being carried out after the step of performing the image forming operation;

22. forming an electrostatic latent image on an image carrier charged by a charging means; At a development position facing the image carrier, a toner and a carrier are deposited on the surface of the image carrier. a step of moving a developing member, which forms a developer image by supplying a developer charged to a normal polarity, between a first position where the developing member supplies the developer to the surface of the image carrier and a second position where the developing member does not supply the developer to the surface of the image carrier; transferring the developer image to a transfer medium; applying a developing voltage to the developing member and / or applying a supply voltage to a supply member that supplies the developer to the surface of the developing member, thereby forming a potential difference between the developing member and the supply member in a direction such that an electrostatic force acts on the developer charged to the normal polarity in a direction from the supply member toward the developing member; a step of positioning the developing member at the first position and performing an image forming operation to form an image on a transfer medium in a state where a first potential difference is formed between the developing member and the supply member; a step of performing a first rotation operation of rotating the image carrier while positioning the developing member at the first position and forming a second potential difference between the developing member and the supply member, the second potential difference being smaller than the first potential difference; performing a second rotation operation of rotating the image carrier while the developing member is positioned at the second position; and a step of performing the first rotation operation and a step of performing the second rotation operation, the step of performing the image forming operation being carried out after the step of performing the image forming operation;

Images