JP2018173587A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device capable of preventing carriers from sticking to a surface of an image carrier during image formation and also capable of preventing the occurrence of leak at an electrification unit by performing operation to eject irregular-shaped carriers from developer.SOLUTION: An image formation device includes: an image carrier 1; electrification means 2 for electrifying the image carrier to form electrification potential Vd on a surface of the image carrier; electrostatic image formation means 3 for forming an electrostatic image on the electrified image carrier; and a developing device 4 for using developer containing toner and carriers to apply developing voltage including at least a direct current component Vdev to developer carriers. The image formation device is configured to make an absolute value of Vd smaller than a value at the time of image formation or Vd to nearly 0 V before forming a first image after prescribed timing when use of a new carrier is started at the developing device, make difference Vback between Vd and Vdev larger than difference at the time of image formation, and perform initial operation to drive the image carrier for a prescribed time.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus using an electrophotographic system or an electrostatic recording system.

  In an image forming apparatus using an electrophotographic method, a two-component developing method using a two-component developer including a toner and a carrier is used as a developer for developing an electrostatic image formed on an image carrier. There is something.

  In an image forming apparatus using the two-component development method, a phenomenon may occur in which a deformed carrier, a small-diameter carrier, a fine powder carrier or the like in the developer pierces the surface of the image carrier. The irregularly shaped carrier is a carrier having a shape that is considerably different from the ideal shape in design, and the small-diameter carrier or the fine powder carrier is a carrier having a particle size substantially smaller than the ideal particle size in design.

  When the carrier is pierced and fixed on the surface of the image carrier, discharge is concentrated on the carrier in the charging unit that charges the image carrier, causing a leak of excessive current, resulting in dot-like image defects. In some cases, the image carrier may need to be replaced.

  A deformed carrier, a small-diameter carrier, or a fine powder carrier may be generated when the carrier is crushed with the use of the developer, or a new developer may be generated during the manufacture of the developer. is there. A deformed carrier, a small-diameter carrier, or a fine powder carrier tends to have a lower holding force on the developer carrier than a normal carrier, and is easily attached to the image carrier. In addition, the deformed carrier is likely to pierce the surface of the image carrier due to its shape and the like. Further, in the configuration in which the intermediate transfer member is pressed against the image carrier, and in the configuration in which a peripheral speed difference is provided between the image carrier and the intermediate transfer member, the deformed carrier is a pressure contact portion between the image carrier and the intermediate transfer member. This makes it easier to pierce the surface of the image carrier.

  Japanese Patent Application Laid-Open No. H10-260260 discloses that the generation of a carrier that easily pierces the surface of an image carrier is suppressed by suppressing the progress of crushing of the carrier accompanying the use of the developer.

  In Patent Document 2, at an initial stage after a new developer is introduced into the developing means, the charged potential of the image carrier is set higher than usual, and the image carrier is driven for a predetermined time. And executing a foreign matter discharge mode for discharging the irregularly shaped carrier.

Japanese Patent No. 5194598 JP 2004-279490 A

  It may be difficult from the viewpoint of manufacturing cost to sufficiently remove the irregular carrier, small-diameter carrier, or fine powder carrier that easily pierces the surface of the image carrier from the new developer by classification during the production of the developer. The invention of Patent Document 1 does not solve the problem caused by the deformed carrier, small diameter carrier, or fine powder carrier contained in a new developer.

  In the invention of Patent Document 2, the charged potential of the image carrier is set higher than usual in the foreign matter discharge mode. However, in this configuration, a leakage may occur when the irregularly shaped carrier discharged on the image carrier reaches the charging unit during the foreign substance discharge mode. That is, it is expected that the deformed carrier discharged in the foreign matter discharge mode is removed from the image carrier by the cleaning unit and does not reach the charging unit. However, for example, in a configuration where the image carrier and the intermediate transfer member cannot be separated from each other, the deformed carrier discharged onto the image carrier may pierce the surface of the image carrier at the press contact portion between the image carrier and the intermediate transfer member. is there. The carrier that has pierced the surface of the image carrier in the foreign substance discharge mode can be expected to be removed from the image carrier while passing through the cleaning section a plurality of times during the foreign substance discharge mode. However, if a leak occurs due to the deformed carrier that reaches the charging unit during the foreign substance discharge mode, an image defect may occur in an image formed thereafter, and the image carrier needs to be replaced. Sometimes.

  In the following description, carriers having shapes and sizes that are quite different from the ideal shapes and sizes in design and that are easy to pierce the image carrier are collectively referred to as “deformed carriers”.

  The object of the present invention is to perform the operation of discharging the deformed carrier from the developer to suppress the carrier from sticking to the surface of the image carrier during image formation, and to prevent leakage at the charging part during the operation. An object of the present invention is to provide an image forming apparatus that can be suppressed.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier, charging means for charging the image carrier to form a charging potential Vd on the surface of the image carrier, and an electrostatic image on the charged image carrier. An electrostatic image forming means for forming; a developer container containing a developer including toner and carrier; and a developer carrier for carrying and transporting the developer contained in the developer container, the developer carrier A developing voltage including at least a DC component Vdev is applied to the developing device for supplying toner to the electrostatic image on the image carrier to form a toner image, and use of a new carrier in the developing device is started. After the predetermined timing and before forming the first image, the absolute value of Vd is made smaller than that at the time of image formation or Vd is set to approximately 0 V, and the difference Vback between Vd and Vdev is set to be smaller than that at the time of image formation. Enlarge, said A control unit for executing an initial operation for driving the carrier for a predetermined time, an image forming apparatus characterized by having a.

  According to the present invention, it is possible to suppress the carrier from sticking into the surface of the image carrier during image formation by performing the operation of discharging the irregularly shaped carrier from the developer, and to prevent leakage at the charging unit during the operation. Can be suppressed.

1 is a schematic sectional view of an image forming apparatus. FIG. 2A is a schematic cross-sectional view of an image forming unit, and FIG. 2B is a schematic cross-sectional view illustrating a layer configuration of a photosensitive drum and a charging roller. 3 is a schematic block diagram illustrating a control mode of a main part of the image forming apparatus. FIG. It is a flowchart figure of control of Example 1. FIG. FIG. 3 is a timing chart of control in Embodiment 1. It is a flowchart figure of control of Example 1. FIG. FIG. 6 is a timing chart of control in Embodiment 2.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[Example 1]
1. FIG. 1 is a schematic sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type multi-function machine that employs an intermediate transfer method and can form a full-color image using an electrophotographic method, and includes a copying machine, a printer, and a facsimile function. Yes.

  The image forming apparatus 100 includes first, second, and second toner images that form yellow (Y), magenta (M), cyan (C), and black (K) toner images, respectively, as a plurality of image forming units (stations). It has third and fourth image forming units PY, PM, PC, PK. Note that elements having the same or corresponding functions or configurations in each of the image forming units PY, PM, PC, and PK are Y, M, C, and K at the end of a symbol representing an element for any color. Omitted, may be explained comprehensively. In this embodiment, the image forming unit P includes a photosensitive drum 1, a charging roller 2, an image exposure device 3, a developing device 4, a primary transfer roller 5, a pre-exposure device 6, and a drum cleaning device 7 which will be described later. The FIG. 2A is a schematic cross-sectional view showing the configuration of one image forming unit P as a representative.

  The image forming apparatus 100 includes a photosensitive drum 1 that is a drum-type electrophotographic photosensitive member (photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure by a drum driving motor M1 as a driving means. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 which is a roller-type charging member as a charging unit. That is, in this embodiment, the regular charging polarity of the photosensitive drum 1 is negative. The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1, and is rotated following the rotation of the photosensitive drum 1. During the charging process, a charging voltage (charging bias), which is a negative DC voltage, is applied to the charging roller 2 from a charging power supply (high voltage power supply circuit) E1. That is, in this embodiment, the charging roller 2 charges the photosensitive drum 1 by applying a voltage composed only of a direct current component. The surface of the charged photosensitive drum 1 is scanned and exposed by laser light based on image information (here, “image exposure”) by an image exposure device (laser scanner) 3 as image exposure means (electrostatic image forming means). And an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. The image information is input from a document reading device (not shown) provided in the image forming apparatus 100, or input from an external device connected to the image forming apparatus 100 such as a personal computer, a digital camera, or a smartphone.

  The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner by a developing device 4 as a developing unit, and a toner image is formed on the photosensitive drum 1. During the development process, a development voltage (development bias) including a negative DC component is applied from a development power source (high-voltage power circuit) E2 to the development sleeve 4a described later. In this embodiment, the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) is applied to the exposed portion on the photosensitive drum 1 where the absolute value of the potential has been lowered by being exposed after being uniformly charged. ) Is charged with charged toner. That is, in this embodiment, the normal charging polarity of the toner, which is the charging polarity of the toner at the time of development, is negative. A toner bottle 13 containing toner as a replenishing developer to be replenished to the developing device 4 is detachable from the apparatus main body 110 of the image forming apparatus 100.

  An intermediate transfer belt 8 composed of an endless belt is disposed facing each of the photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 8 is an example of an intermediate transfer member that conveys the toner image primarily transferred from the photosensitive drum 1 for secondary transfer to the recording material S. The intermediate transfer belt 8 is stretched by a driving roller 81, a tension roller 82, and a secondary transfer counter roller 83 as a plurality of stretching rollers. The intermediate transfer belt 8 rotates (circulates) in the direction of the arrow R2 in the drawing when the driving roller 81 is rotationally driven by a belt driving motor M3 as driving means. On the inner peripheral surface side of the intermediate transfer belt 8, a primary transfer roller 5, which is a roller-type primary transfer member serving as a primary transfer unit, is disposed corresponding to each photosensitive drum 1. The primary transfer roller 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 8 to form a primary transfer portion (primary transfer nip) T1 where the photosensitive drum 1 and the intermediate transfer belt 8 are in contact with each other. As described above, the toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 8 as a rotating transfer object by the electrostatic force and pressure applied by the primary transfer roller 5 in the primary transfer portion T1. Primary transferred onto. During the primary transfer process, the primary transfer roller 5 receives a primary transfer voltage (positive voltage in this embodiment) from the primary transfer power supply (high voltage power supply circuit) E3 which is a reverse polarity (positive polarity in this embodiment) of the toner. Primary transfer bias) is applied. For example, when forming a full-color image, yellow, magenta, cyan, and black toner images formed on the photosensitive drums 1 are sequentially transferred so as to be superimposed on the intermediate transfer belt 8. In this embodiment, whenever the photosensitive drum 1 is driven, the primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 8, and the intermediate transfer belt 8 is also driven. That is, in this embodiment, the intermediate transfer belt 8 is always pressed against the photosensitive drum 1 while the photosensitive drum and the intermediate transfer belt 8 are driven. In particular, in this embodiment, the image forming apparatus 100 is not provided with a mechanism for separating the intermediate transfer belt 8 from the photosensitive drum 1 when the photosensitive drum 1 is driven.

  On the outer peripheral surface side of the intermediate transfer belt 8, a secondary transfer roller 9 that is a roller-type secondary transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 83. The secondary transfer roller 9 is pressed toward the secondary transfer counter roller 83 via the intermediate transfer belt 8, and a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 8 and the secondary transfer roller 9 are in contact with each other. T2 is formed. The toner image formed on the intermediate transfer belt 8 as described above is transferred to the intermediate transfer belt 8 and the secondary transfer roller 9 by the electrostatic force and pressure applied by the secondary transfer roller 9 in the secondary transfer portion T2. Is secondarily transferred onto the recording material S that is nipped and conveyed. During the secondary transfer process, the secondary transfer roller 9 receives a secondary voltage from the secondary transfer power supply (high voltage power supply circuit) E4, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner (positive in this embodiment). A next transfer voltage (secondary transfer bias) is applied. The recording material (transfer material, recording medium, sheet) S is conveyed to the registration roller pair 10 by a feeding / conveying device (not shown), and the registration roller 10 matches the timing of the toner image on the intermediate transfer belt 8 to the secondary. Supplied to the transfer portion T2. The recording material S is, for example, plain paper, a synthetic resin sheet that is a substitute for plain paper, cardboard, an overhead projector sheet, or the like.

  The recording material S to which the toner image has been transferred is conveyed to a fixing device 11 as a fixing unit, and the toner image is fixed (melted and fixed) on the surface by being heated and pressed by the fixing device 11. It is discharged (output) to the outside of the apparatus main body 110 of the forming apparatus 100.

  On the other hand, the surface of the photosensitive drum 1 after the primary transfer process is irradiated with light (herein also referred to as “pre-exposure”) by a pre-exposure device 6 as a pre-exposure unit, and after the primary transfer process, the photosensitive drum 1. At least a part of the charge (residual charge) remaining on the top is removed (static elimination). Further, the toner (primary transfer residual toner) remaining on the photosensitive drum 1 during the primary transfer process is removed from the photosensitive drum 1 and collected by the drum cleaning device 7 as a photosensitive member cleaning means. A belt cleaning device 12 as an intermediate transfer member cleaning unit is disposed at a position facing the driving roller 81 with the intermediate transfer belt 8 interposed therebetween. The toner (secondary transfer residual toner) remaining on the intermediate transfer belt 8 during the secondary transfer process is removed from the intermediate transfer belt 8 by the belt cleaning device 12 and collected.

  In each image forming portion P, the photosensitive drum 1, the charging roller 2, and the drum cleaning device 7 constitute a drum cartridge that can be attached to and detached from the apparatus main body 110 integrally. For example, the drum cartridge is replaced with a new one when the photosensitive drum 1 reaches the end of its life. Further, in each image forming unit P, the developing device 4 is detachable from the apparatus main body 110. The developing device 4 is removed from the apparatus main body 110, for example, for replacement of the developing device 4 itself or replacement of a carrier in the developing device 4.

  Here, the position where the charging process is performed by the charging roller 2 in the rotation direction (surface movement direction) of the photosensitive drum 1 is a charging position a. In the present exemplary embodiment, the charging roller 2 is a minute gap between the charging roller 2 and the photosensitive drum 1 formed on the upstream side and the downstream side of the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1. The photosensitive drum 1 is charged by electric discharge generated at least one of the gaps. However, for simplicity, it may be assumed that the contact portion between the charging roller 2 and the photosensitive drum 1 is the charging position a. Further, a position where image exposure is performed by the image exposure device 3 in the rotation direction of the photosensitive drum 1 is an image exposure position b. A developing position c is a position where toner is supplied from a developing sleeve 4a, which will be described later, to the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 (in this embodiment, a portion where the developing sleeve 4a and the photosensitive drum 1 face each other). . Further, the position where the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 8 in the rotation direction of the photosensitive drum 1 (the contact portion between the photosensitive drum 1 and the intermediate transfer belt 8 in this embodiment) is the primary transfer position ( Primary transfer portion) T1. The position where the pre-exposure by the pre-exposure device 6 in the rotation direction of the photosensitive drum 1 is the pre-exposure position d. Further, a contact portion between a later-described cleaning blade 7a and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is a cleaning position e. In this embodiment, the positions are arranged in the order of the charging position a, the image exposure position b, the development position c, the primary transfer position T1, the pre-exposure position d, and the cleaning position e along the rotation direction of the photosensitive drum 1. ing.

  The image forming apparatus 100 executes a job (printing operation) that is a series of operations for forming and outputting an image on a single or a plurality of recording materials S, which is started by one start instruction. In general, a job includes an image forming process, a pre-rotating process, an inter-sheet process when images are formed on a plurality of recording materials S, and a post-rotating process. The image forming process is a period in which an electrostatic latent image of an image that is actually formed and output on the recording material S, a toner image, a primary transfer or a secondary transfer of the toner image is performed. This is the period. More specifically, the timing at which the image is formed differs depending on the position where the electrostatic latent image formation, the toner image formation, and the primary transfer and secondary transfer of the toner image are performed. The pre-rotation process is a period for performing a preparatory operation before the image forming process from when the start instruction is input until the actual image formation is started. The inter-sheet process is a period corresponding to the interval between the recording material S and the recording material S when image formation is continuously performed on a plurality of recording materials S (continuous image formation). The post-rotation process is a period during which an organizing operation (preparation operation) after the image forming process is performed. The non-image forming period is a period other than the image forming time, and is a preparatory operation at the time of turning on the power of the image forming apparatus 100 or returning from the sleep state. The pre-multi-rotation process is included.

2. Photosensitive Drum FIG. 2B is a schematic cross-sectional view showing the layer structure of the photosensitive drum 1 and the charging roller 2. In this embodiment, the photosensitive drum 1 is a negatively chargeable organic photoreceptor (OPC) drum. In this embodiment, the photosensitive drum 1 has an outer diameter of 30 mm and is driven to rotate at a peripheral speed (process speed) of 210 mm / sec. As shown in FIG. 2B, the photosensitive drum 1 is composed of an aluminum cylinder (conductive drum base) 1a, an undercoat layer 1b, a photocharge generation layer 1c, and a charge transport layer 1d. Has a surface layer (photosensitive layer) laminated in this order. In the present embodiment, each layer 1b, 1c, 1d of the surface layer of the photosensitive drum 1 is a cured layer containing a curable resin as a binder resin. In the present embodiment, as a means for curing the surface of the photosensitive drum 1, the surface layer of the photosensitive drum 1 is a cured layer made of a material containing a curable resin, but is not limited thereto. . For example, a charge transporting cured layer formed by polymerizing and curing a monomer having a carbon-carbon double bond and a charge transporting monomer having a carbon-carbon double bond by heat or light energy. It may be used. Alternatively, for example, a charge transporting cured layer formed by curing and polymerizing a hole transporting compound having a chain polymerizable functional group in the same molecule by the energy of electron beam may be used.

3. Charging roller In this embodiment, the charging roller 2 is an elastic roller having an elastic layer (in this embodiment, a rubber roller). In this embodiment, the length of the charging roller 2 in the rotation axis direction is 320 mm. As shown in FIG. 2B, the charging roller 2 includes an elastic layer in which three layers of a lower layer 2b, an intermediate layer 2c, and a surface layer 2d are laminated in this order on a core metal (core material) 2a. It is configured. The lower layer 2b is a foamed sponge layer for reducing charging noise. The surface layer 2d is a protective layer provided in order to suppress the occurrence of leakage even if there is a pinhole or the like on the surface of the photosensitive drum 1. An uneven shape is formed on the surface layer 2d. By forming the concavo-convex shape on the surface layer 2d, the pressure applied by the charging roller 2 to the photosensitive drum 1 due to the concave portion can be reduced, and contamination of the charging roller 2 due to toner or the like can be reduced. As a method for forming the uneven shape on the surface layer 2d, there are a method of containing fine particles in the surface layer 2d, a method of processing by mechanical polishing, and the like. The electrical resistance of the charging roller 2 is typically 1 × 10 ⁵ Ω or less. The specifications of the charging roller 2 used in this example are as follows.
(1) Core metal 2a: Stainless steel round bar with a diameter of 6 mm (2) Lower layer 2b: Foamed EPDM with carbon dispersion, specific gravity 0.5 g / cm ³ , volume resistivity 10 ² to 10 ⁹ Ωcm, layer thickness 3.0 mm
(3) Intermediate layer 2c: carbon-dispersed NBR rubber, volume resistance value 10 ² to 10 ⁵ Ωcm, layer thickness 700 μm
(4) Surface layer 2d: tin oxide and carbon are dispersed in a resin resin of fluorine compound, volume resistance value 10 ⁷ to 10 ¹⁰ Ωcm, layer thickness 10 μm, surface roughness (JIS standard 10-point average surface roughness Ra) 1.5 μm

  A charging power source E1 is connected to the cored bar 2a of the charging roller 2. The charging roller 2 is applied with a charging voltage (hereinbelow simply referred to as “Vcr”), which is a negative DC voltage, from the charging power supply E1 through the core 2a. The charging roller 2 charges the surface of the photosensitive drum 1 by electric discharge in a minute gap between the charging roller 2 and the photosensitive drum 1. Therefore, a DC voltage that is equal to or higher than a certain threshold voltage is applied to the charging roller 2. In this embodiment, by applying a negative DC voltage having an absolute value of about 600 V or more to the charging roller 2, the absolute value of the surface potential of the photosensitive drum 1 starts to increase, and thereafter, the absolute value of the applied voltage is increased. On the other hand, it rises linearly with a slope of about 1. In this embodiment, for example, in order to set the charging potential (dark portion potential) Vd (hereinafter also simply referred to as “Vd”) of the photosensitive drum 1 to −300 V, a DC voltage of −900 V is applied to the charging roller 2. do it. Further, in order to set Vd to −500 V, a DC voltage of −1100 V may be applied to the charging roller 2. The above threshold voltage is called a discharge start voltage (charging start voltage) Vth. That is, in order to obtain Vd required for electrophotography, the DC voltage Vd + Vth may be applied to the charging roller 2. In this embodiment, at the time of image formation, in order to set Vd to −900 V, a DC voltage of −1500 V as Vcr is applied to the charging roller 2 from the charging power source E1.

4). Developing Device In the present embodiment, the developing device 4 is a two-component magnetic brush developing type developing device. The developing device 4 includes a developing container 4b that contains a two-component developer including toner (nonmagnetic toner particles) as a developer and a carrier (magnetic carrier particles), and a developing device that is rotatably provided in the developing container 4b. And a developing sleeve 4a as an agent carrier. In the hollow portion of the developing sleeve 4a, a magnet roll 4d as a magnetic field generating means is disposed. In the developing container 4b, a conveying member 4c that conveys the developer to the developing sleeve 4a while stirring is disposed. In the present embodiment, the conveying member 4c is configured by a rotatable screw-shaped member. The developing sleeve 4a is rotationally driven by a developing driving motor M2 as driving means. In this embodiment, the driving force of the developing drive motor M2 is transmitted to the developing sleeve 4a and also to the conveying member 4c, and the developing sleeve 4a and the conveying member 4c are rotationally driven in synchronization. The developer in the developing container 4b is conveyed while being agitated by the conveying member 4c, whereby the toner and the carrier are triboelectrically charged. In this embodiment, the toner is negatively charged and the carrier is charged positively. The toner adheres to the carrier.

  The developing sleeve 4a carries the developer by the action of the magnetic field generated by the magnet roll 4d and transports the developer to the opposed portion to the photosensitive drum 1, and the developer (magnetic) that stands out by the action of the magnetic field generated by the magnet roll 4d. A brush) is brought into contact with the surface of the photosensitive drum 1. Further, a developing voltage including a negative direct current component whose absolute value is smaller than Vd is applied to the developing sleeve 4a from the developing power source E2. In this embodiment, at the time of image formation, a developing voltage including a DC component of −800 V is applied to the developing sleeve 4a from the developing power source E2 (here, the DC component of the developing voltage is also simply referred to as “Vdev”). . Note that an oscillating voltage including a DC voltage (DC component) and an AC voltage (AC component) may be used as the development voltage.

  The toner consumed for the image formation is appropriately supplied from the toner bottle 13 to the developing device 4. When the image is formed, only the toner is consumed from the developer. Therefore, the toner corresponding to the amount consumed by forming the previous image is formed from the toner bottle 13 every time the image is formed. 4 is replenished. Further, when the toner is replenished by such a method, an error with respect to a desired toner concentration (a weight ratio of the toner to the developer) may occur. Therefore, the toner replenishment amount obtained by the above method is based on the output of a toner concentration sensor (magnetic permeability sensor) (not shown) provided in the developing device 4 so that the toner concentration of the developer in the developing container 4b is 8 to 8. It is corrected to be maintained at 10%. The toner replenished from the toner bottle 13 to the developing container 4b is conveyed while being stirred by the conveying member 4c, thereby being mixed with the developer in the developing container 4b.

5. Pre-exposure device In this embodiment, the pre-exposure device 6 includes an exposure lamp as a light source and an exposure guide that diffuses light from the exposure lamp. In this embodiment, the wavelength of light that the exposure lamp irradiates the photosensitive drum 1 has a peak at 400 nm to 800 nm. The amount of light on the surface of the photosensitive drum 1 can be controlled in the range of 0.1 μW to 40 μW, and this amount of light can be adjusted by adjusting the voltage applied to the exposure lamp. The charge removal amount of the photosensitive drum 1 can be controlled by the exposure amount of the pre-exposure device 6.

6). Drum Cleaning Device In this embodiment, the drum cleaning device 7 includes a cleaning blade 7a as a cleaning member disposed in contact with the photosensitive drum 1, and a cleaning container 7b. The drum cleaning device 7 scrapes off the primary transfer residual toner from the surface of the rotating photosensitive drum 1 by the cleaning blade 7a and stores it in the cleaning container 7b. The cleaning blade 7a is a plate-like (blade-like) member made of rubber (urethane rubber or the like) as an elastic material. The cleaning blade 7a is arranged such that its longitudinal direction is substantially parallel to the longitudinal direction (rotation axis direction) of the photosensitive drum 1, and the edge portion of one end portion (free end portion) in the lateral direction is subjected to a predetermined pressing force. 1 is in contact with the surface. The cleaning blade 7 a is in contact with the photosensitive drum 1 in a direction (counter direction) in which the free end portion in the short direction faces the upstream side in the rotation direction of the photosensitive drum 1. In this embodiment, the free length in the short direction of the cleaning blade 7a is 8 mm, and the contact pressure (about linear pressure) against the photosensitive drum 1 is 35 gf / cm.

7). Control Mode FIG. 3 is a schematic block diagram showing a control mode of the main part of the image forming apparatus 100 of the present embodiment. In the present embodiment, the operation of each unit of the image forming apparatus 100 is comprehensively controlled by a control unit (control circuit) 50 provided in the apparatus main body 110. The control unit 50 includes a CPU 51 as arithmetic control means, a ROM 52 and RAM 53 as storage means, an input / output circuit (I / F) 54 for inputting / outputting signals to / from the outside, and the like. The CPU 51 is a microprocessor that controls the entire control of the image forming apparatus 100 and is a main body of the system controller. The CPU 51 is connected to each unit of the image forming apparatus 100 via the input / output circuit 54, exchanges signals with each unit, and controls the operation of each unit. The ROM 52 stores a program used by the CPU 51 for controlling an image forming operation and an initial operation described later. The RAM 53 is used for the CPU 51 to temporarily store data for control.

  In relation to this embodiment, the control unit 50 is connected to a charging power source E1, a developing power source E2, a drive circuit 20, and the like. The drive circuit 20 is a driver circuit for the drum drive motor M1, the development drive motor M2, and the belt drive motor M3 (FIG. 2A). In this embodiment, the photosensitive drum 1, the developing sleeve 4a, and the intermediate transfer belt 8 are rotationally driven in synchronization. At least two of the drum drive motor M1, the development drive motor M2, and the belt drive motor M3 may be shared. The controller 50 is connected to an attachment / detachment sensor 30 as attachment / detachment detection means for detecting attachment / detachment of the developing device 4 with respect to the apparatus main body 110. As the attachment / detachment sensor 30, any means such as a photo interrupter or a micro switch that switches between an ON / OFF state between the state in which the developing device 4 is attached to the apparatus main body 110 and the state in which the developing apparatus 4 is detached from the apparatus main body 110 is used. it can. Further, the operation unit 40 provided in the apparatus main body 110 is connected to the control unit 50. The operation unit 40 includes keys and switches as input means for inputting instructions relating to image formation to the control unit 50, and display means for displaying information to an operator such as a user or a service person in accordance with an instruction from the control unit 50. As a display.

  As will be described later, the control unit 50 turns ON / OFF the output of the charging power supply E1 and the development power supply E2 and the output value, ON / OFF of the drum drive motor M1, the development drive motor M2, and the belt drive motor M3 by the drive circuit 20. The initial operation is executed by controlling OFF and the like.

8). Initial Operation In this embodiment, the control unit 50 causes the following initial operation to be performed after a predetermined timing when the use of a new carrier is started in the developing device 4 and before the first image is formed. . That is, the absolute value of the charging potential Vd of the photosensitive drum 1 is made smaller than that at the time of image formation, and the difference Vback between the charging potential Vd of the photosensitive drum 1 and the DC component Vdev of the development voltage is made larger than that at the time of image formation. In this operation, the photosensitive drum 1 is driven for a predetermined time. Here, the difference between Vd and Vdev is also simply referred to as “Vback”. This Vback is a potential difference between Vd and Vdev at the development position c. Vback at the time of image formation works to urge toner charged to a normal charging polarity (negative polarity in this embodiment) from the photosensitive drum 1 side to the developing sleeve 4a side. The Vback during the initial operation is such that a carrier (particularly a deformed carrier) charged to a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is biased from the developing sleeve 4a side to the photosensitive drum 1 side. work.

  In particular, in this embodiment, Vd in the initial operation is a potential having the same polarity as the normal charging polarity of the photosensitive drum 1 (negative polarity in this embodiment), and Vdev in the initial operation is a normal charging of the photosensitive drum 1. The potential has the same polarity as the polarity (negative polarity in this embodiment). In the present embodiment, the predetermined timing is started after the new developing device 4 filled with the developer containing the new carrier is mounted on the apparatus main body 110 of the image forming apparatus 100, and then the use of the developing device 4 is started. Is the timing. This timing may be the following timing. For example, when the image forming apparatus 100 is shipped in a state where the developer (initial developer) used first in the new developing apparatus 4 is filled in the developing apparatus 4, the image forming apparatus is installed after the image forming apparatus 100 is installed. This is the timing when the use of 100 starts. Alternatively, for example, when the developing device 4 is replaced with respect to the apparatus main body 110, the use of the image forming apparatus 100 is started after the developing device 4 filled with the initial developer is mounted on the apparatus main body. is there.

  In other words, as described above, the new developer filled in the new developing device 4 may contain a deformed carrier. The irregularly shaped carrier easily adheres to the photosensitive drum 1 and easily sticks to the surface of the photosensitive drum 1. For this reason, if the irregularly shaped carrier is pierced and fixed on the surface of the photosensitive drum 1 at the time of image formation, there may be a leak in which excessive current flows due to concentration of discharge on the carrier in the charging portion a. When a leak occurs, dielectric breakdown of the photosensitive layer of the photosensitive drum 1 may occur, and a dot-like image defect may occur in an image to be formed thereafter. Therefore, the photosensitive drum 1 may need to be replaced. Therefore, when the developing device 4 filled with a new developer is attached to the apparatus main body 110, the deformed carrier is sufficiently obtained from the new developer at the time of non-image formation before the first image formation is performed thereafter. It is desirable to be removed. As will be described later, the irregularly shaped carrier tends to be relatively easily transferred from the developing device 4 to the photosensitive drum 1 by relatively increasing Vback which is a potential difference between Vd and Vdev. Therefore, the irregular carrier can be sufficiently discharged from the developing device 4 onto the photosensitive drum 1 by increasing the Vback to be larger than that at the time of image formation and driving the photosensitive drum 1 for a sufficient time (traveling distance).

  Here, it is expected that the irregular shaped carrier discharged on the photosensitive drum 1 in the foreign matter discharging mode is removed from the photosensitive drum 1 by the cleaning unit e and does not reach the charging unit a. However, for example, in the configuration in which the photosensitive drum 1 and the intermediate transfer belt 8 cannot be separated as in the present embodiment, the deformed carrier discharged onto the photosensitive drum 1 is exposed at the pressure contact portion between the photosensitive drum 1 and the intermediate transfer belt 8. The surface of the drum 1 may be stuck. It can be expected that the carrier pierced on the surface of the photosensitive drum 1 in this initial operation is removed from the photosensitive drum 1 while passing through the cleaning section e a plurality of times during the initial operation. However, when the absolute value of Vd is set larger than that at the time of image formation in the initial operation, a leak occurs when the irregularly shaped carrier discharged onto the photosensitive drum 1 reaches the charging unit a during the initial operation. May occur. If a leak occurs during the initial operation as described above, an image defect may occur in an image formed thereafter, and the photosensitive drum 1 may need to be replaced.

  Therefore, in the initial operation of the present embodiment, (1) Vd is set to a negative polarity potential whose absolute value is smaller than that during image formation, and (2) the difference Vback (= | Vd−Vdev |) between Vd and Vdev is an image. (3) The photosensitive drum 1 is driven for a predetermined time.

  FIG. 4 is a flowchart showing an outline of an operation procedure including an initial operation when the new developing device 4 in this embodiment is mounted on the apparatus main body 110. FIG. 5 is a chart showing the initial operation and the operation state of each part during image formation in this embodiment.

  For example, when the power of the image forming apparatus 100 is turned on, the control unit 50 determines whether or not a new developing device 4 is mounted (S1). In the present embodiment, the control unit 50 determines that a new developing device 4 is attached to the apparatus main body 110 based on the detection result of the attaching / detaching operation of the developing device 4 by the attaching / detaching sensor 30. However, the present invention is not limited to this, and it is only necessary to determine that the developing device 4 filled with the developer containing a new carrier is attached to the apparatus main body 110. For example, the determination may be made based on the execution of the reference adjustment of the toner density sensor provided in the developing device 4. Alternatively, the determination may be made based on information input from the operation unit 40 by the operator and indicating that a new developing device 4 is attached to the apparatus main body 110. Further, a storage unit (IC tag) for storing individual identification information or new product information indicating that the developing device 4 is new may be provided in the developing device 4 and the determination may be made based on the information in the storage unit.

  If the controller 50 determines in S1 that a new developing device 4 is mounted on the apparatus main body 110, the controller 50 performs an initial operation before forming the first image after the new developing device 4 is mounted. Execute (S2). In the initial operation, the charging voltage is turned on, the developing voltage is turned on, the transfer voltage is turned off, the image exposure is turned off, and the pre-exposure is turned on, and the photosensitive drum 1, the developing device 4 (the developing sleeve 4a, the conveying member 4c), and the intermediate transfer belt. 8 is driven. In the present embodiment, Vcr = −900V, Vd = −300V, Vdev = −100V, and Vback = 200V are set in the initial operation. In this embodiment, Vcr = −1500V, Vd = −900V, Vdev = −800V, and Vback = 100V are set during image formation. In other words, in the present embodiment, the absolute value of Vd is set to 600 V smaller and Vback is set to 100 V larger during the initial operation than during image formation. As shown in FIG. 5, when the initial operation is started, pre-exposure by the pre-exposure device 6 is started almost simultaneously with the start of driving of the photosensitive drum 1, the developing device 4, and the intermediate transfer belt 8. Then, the application of the charging voltage is started after the position on the photosensitive drum 1 at the pre-exposure position d when the pre-exposure by the pre-exposure device 6 has reached the charging part a. In addition, the application of the development voltage is started when the position on the photosensitive drum 1 at the charging portion a when the application of the charging voltage starts reaches the development position c. Thereafter, the driving (idle rotation) of the photosensitive drum 1, the developing device 4, and the intermediate transfer belt 8 is continued for a predetermined time (idle rotation time) set in advance. The idling time can be obtained in advance by experiments or the like so that the irregularly shaped carrier can be sufficiently discharged from the developing device 4 onto the photosensitive drum 1. In this embodiment, the idling time in the initial operation is set to 2 minutes.

  The controller 50 ends the initial operation after driving the photosensitive drum 1, the developing device 4, and the intermediate transfer belt 8 for a predetermined time (S3). As shown in FIG. 5, when the initial operation is finished, the application of the charging voltage is stopped, and the position on the photosensitive drum 1 that was in the charging unit a when the application of the charging voltage is stopped reaches the developing position c. The development voltage application is stopped at the same time. Thereafter, the driving of the photosensitive drum 1, the developing device 4, and the intermediate transfer belt 8 is stopped, and then the pre-exposure by the pre-exposure device 6 is stopped.

  Next, the control unit 50 determines whether or not there is an image formation request (S4). If there is an image formation request, the control unit 50 executes image formation (S5). If not, the image forming apparatus 100 is set in a standby state (S6). ), The process is terminated.

9. Evaluation Test Next, an evaluation test of the initial operation of this example and the comparative example was performed. First, an initial operation was performed on the new developing device 4 under the conditions of this embodiment and the following comparative example, and the presence or absence of leakage in the charging portion a during the initial operation was evaluated. The presence or absence of leakage during the initial operation was evaluated by measuring a direct current flowing between the charging roller 2 and the photosensitive drum 1 using a current measurement circuit. When a leak occurs, an excessively large current flows locally (instantaneously), so that it is possible to evaluate whether or not the leak has occurred. Thereafter, a printing durability test (10000 sheets of A4 paper (image duty 5%)) is performed using the developing device 4 that has been initially operated under a condition in which no leakage occurred, and leakage in the charging unit a during image formation is detected. The occurrence was evaluated. The presence or absence of leakage during image formation was evaluated by visually confirming the presence or absence of image defects considered to be caused by leakage in the entire halftone image.

  The conditions of the comparative example are as follows. In Comparative Example 1, Vd and Vdev at the initial operation were the same as those at the time of image formation (Vcr = −1500V, Vd = −900, Vdev = −800V, Vback = 100V, idling time = 2 minutes). In Comparative Example 2, Vd is the same as that at the time of image formation at the initial operation, the absolute value of Vdev is smaller than that at the time of image formation, and Vback is larger than that at the time of image formation (Vcr = −1500 V, Vd = − 900V, Vdev = −700V, Vback = 200V, idling time = 2 minutes). In Comparative Example 3, in the initial operation, the absolute value of Vd and the absolute value of Vdev were both made smaller than those at the time of image formation, and Vback was the same as at the time of image formation (Vcr = −900 V, Vd = −300 V, Vdev = −200V, Vback = 100V, idling time = 2 minutes). In Comparative Example 4, Vd and Vdev were the same as in this example, and the idling time was shorter than that in this example (idling time = 30 seconds).

  The evaluation results are shown in Table 1 below. Table 1 also shows the evaluation results of the initial operation of Example 2 described later.

  In this example, no leak occurred during both the initial operation and the durability test. This is considered to be due to the fact that the absolute value of Vd was made smaller during the initial operation than during image formation, and Vback was made larger than during image formation. In other words, it is considered that by increasing Vback, the irregularly shaped carrier in the developing device 4 that causes a leak is effectively discharged onto the photosensitive drum 1 in the initial operation. In addition, it is considered that the occurrence of leakage during the durability test could be suppressed because the deformed carrier in the developing device 4 was sufficiently removed by the initial operation. In addition, by reducing the absolute value of Vd (that is, decreasing the absolute value of the charging voltage), the occurrence of leakage during the initial operation due to the carrier that has passed through the cleaning unit e after being discharged onto the photosensitive drum 1 is suppressed. It is thought that he was able to.

  Here, the carrier that slips through the cleaning unit e during the initial operation is the following deformed carrier. That is, a carrier having an acute angle structure or a polyhedral structure pierced on the surface of the photosensitive drum 1 by pressing and rubbing with the intermediate transfer belt 8 or a small diameter carrier, or a fine powder carrier that has passed through the cleaning unit e without being scraped off by the cleaning blade 7a. Etc. These deformed carriers tend to have a weaker magnetic force acting on them than a normal carrier and a weak holding force on the developing sleeve 4a. In the initial operation, an electric field stronger than that at the time of image formation is generated by urging the carrier charged positively in the direction from the developing sleeve 4a toward the photosensitive drum 1 due to Vback larger than that at the time of image formation. Therefore, during the initial operation, it is considered that the irregularly shaped carrier is more likely to be selectively discharged onto the surface of the photosensitive drum 1 than the normal carrier. Further, it is considered that the carrier that has passed through the cleaning unit e is collected by the drum cleaning device 7 while passing through the cleaning unit e a plurality of times during the initial operation. Therefore, the carrier discharged from the developing device 4 onto the photosensitive drum 1 that may cause a leak is collected from the surface of the photosensitive drum 1 before image formation is started, and the absolute value of the charging voltage is set during image formation. It is considered that the occurrence of leaks could be suppressed even if it was increased.

  In Comparative Example 1, Vback was not made larger during the initial operation than during image formation, so that the irregularly shaped carrier in the developing device 4 could not be sufficiently removed, and a leak occurred during the durability test.

  In Comparative Example 2, the irregular carrier in the developing device 4 was effectively discharged onto the photosensitive drum 1 by making Vback larger during initial operation than during image formation. However, since the absolute value of the charging voltage is large, a leak occurred in the charging portion a due to the carrier that pierced the surface of the photosensitive drum 1 and passed through the cleaning portion e during the initial operation.

  In Comparative Example 3, the leakage during the initial operation was suppressed by making the absolute value of the charging voltage during the initial operation smaller than that during the image formation. However, since Vback was not made larger during the initial operation than during image formation, the irregularly shaped carrier in the developing device 4 could not be sufficiently removed, and a leak occurred during the durability test.

  In Comparative Example 4, because the idling time was short, the irregularly shaped carrier in the developing device 4 could not be sufficiently removed, and a leak occurred during the durability test.

  As described above, according to this embodiment, by performing the initial operation, it is possible to suppress the carrier from sticking to the surface of the photosensitive drum 1 during image formation and to cause a leak in the charging unit a during the initial operation. Can be suppressed.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, in the image forming apparatus according to the present embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted. To do.

  In the initial operation of this embodiment, (1) Vd is set to approximately 0 V (charging voltage is OFF), and (2) the difference Vback (= | Vd−Vdev |) between Vd and Vdev is set larger than that at the time of image formation. (3) The photosensitive drum 1 is driven for a predetermined time. That is, in this embodiment, Vd in the initial operation is substantially 0 V, and Vdev in the initial operation is a potential having a polarity opposite to the normal charging polarity of the photosensitive drum 1.

  FIG. 6 is a flowchart showing an outline of an operation procedure including an initial operation when the new developing device 4 according to this embodiment is mounted on the apparatus main body 110. FIG. 7 is a chart showing the initial operation and the operation state of each part during image formation in this embodiment.

  The processes in S1 to S6 in FIG. 6 are the same as the processes in S1 to S6 in FIG. However, in the present embodiment, the high pressure setting for the initial operation in S2 of FIG. 6 is different from the high pressure setting for the initial operation in S2 of the first embodiment. That is, in this embodiment, as shown in FIGS. 6 and 7, in the initial operation, the photosensitive drum 1 is set with the charging voltage OFF, the development voltage ON, the transfer voltage OFF, the image exposure OFF, and the pre-exposure ON. Then, the developing device 4 and the intermediate transfer belt 8 are driven. In this embodiment, Vcr = 0V, Vd = 0V, Vdev = + 200V, and Vback = 200V are set in the initial operation. In this embodiment, Vcr = −1500V, Vd = −900V, Vdev = −800V, and Vback = 100V are set during image formation. That is, in the present embodiment, the absolute value of Vd is set to 900 V smaller and Vback is set to 100 V larger during initial operation than during image formation.

  For the initial operation of this example, the same evaluation test as that described in Example 1 was performed. The evaluation results are shown in Table 1 below.

  In this example, no leak occurred during both the initial operation and the durability test. This is presumably because the voltage applied to the charging roller 2 during the initial operation was turned off and Vback was made larger than that during image formation. In other words, it is considered that by increasing Vback, the irregularly shaped carrier in the developing device 4 that causes a leak is effectively discharged onto the photosensitive drum 1 in the initial operation. In addition, it is considered that the occurrence of leakage during the durability test could be suppressed because the deformed carrier in the developing device 4 was sufficiently removed by the initial operation. In addition, by setting the charging voltage to OFF, it is considered that the occurrence of leakage during the initial operation due to the carrier that has passed through the cleaning unit e after being discharged onto the photosensitive drum 1 could be suppressed.

  In the initial operation, Vd is a negative potential having an absolute value smaller than that at the time of image formation, Vdev is a positive potential, and the difference Vback (= | Vd−Vdev |) between Vd and Vdev is an image. You may make it larger than the time of formation.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained.

[Other embodiments]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiment, the pre-exposure is turned on in the initial operation, but the pre-exposure may be turned off. The occurrence of leakage can be further suppressed by turning off the pre-exposure and reducing the discharge current flowing in the charging unit without gradually decreasing the surface potential of the photosensitive drum. In the above-described embodiment, the transfer voltage is set to OFF in the initial operation, but this also suppresses the neutralization of the surface potential of the photosensitive drum. Therefore, the discharge current flowing in the charging unit is reduced, This has the effect of suppressing the occurrence of leaks. However, for the purpose of suppressing the transfer of the carrier adhered to the photosensitive drum to the intermediate transfer belt, the transfer voltage having the same polarity as the charging polarity of the carrier (positive polarity in the above embodiment) is turned ON during the initial operation. Also good.

  In the above-described embodiment, the initial operation is performed after the developing device filled with the developer containing the new carrier is mounted on the apparatus main body and before the first image is formed. However, the present invention is not limited to this. After the developer in the developing device is replaced with a developer containing a new carrier, an initial operation may be performed before the first image is formed. In other words, the predetermined timing when the use of a new carrier is started in the developing device is the timing when the use of the developing device is started after the developer in the developing device is replaced with a developer containing a new carrier. Good. Further, there is a configuration in which the carrier is supplied to the developing device together with the toner as a supply developer. In this configuration, for example, after the replenishment developer containing a predetermined amount or more of new carrier is replenished to the developing device, the initial operation may be performed before the first image is formed. Note that the predetermined amount of the replenishment developer including a new carrier for which the initial operation is to be performed can be obtained in advance by experiments or the like according to the degree to which the carrier pierces the surface of the photosensitive drum. In addition, as a replenishment developer, a configuration in which toner and a carrier are individually replenished to the developing device can be considered. In this case as well, as described above, after a predetermined amount or more of new carrier has been replenished to the developing device, An initial operation may be performed before the formation is performed. That is, the predetermined timing when the use of a new carrier is started in the developing device may be a timing when a new carrier or a developer containing a new carrier is supplied to the developing device. The initial operation may be selectively executed at a plurality or one of the predetermined timings, including those described in the above embodiments.

  The present invention is not limited to a tandem type image forming apparatus, and can be applied to other types of image forming apparatuses such as a direct transfer system. The direct transfer type image forming apparatus has a recording material carrier constituted by an endless belt or the like, instead of the intermediate transfer member in the above-described embodiment. Then, the toner image formed in each image forming unit is directly transferred to the recording material carried and conveyed by the recording material carrier. Even in such an image forming apparatus, for example, in a configuration in which the recording material carrier cannot be separated from the image carrier, problems similar to those in the above-described embodiment can be significant. Further, the image forming apparatus is not limited to a color image forming apparatus, and may be a monochrome (monochrome or other single color) image forming apparatus. Even in such an image forming apparatus, for example, in a configuration in which a transfer member such as a transfer roller for transferring a toner image from an image carrier to a recording material cannot be separated from the image carrier, problems similar to those in the above-described embodiment become significant. obtain. In addition, the present invention can be implemented in image forming apparatuses used for various purposes such as printers, various printing machines, copiers, FAX machines, and multifunction machines.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 4 Developing apparatus 8 Intermediate transfer belt 50 Control part

Claims (10)

An image carrier;
Charging means for charging the image carrier to form a charging potential Vd on the surface of the image carrier;
Electrostatic image forming means for forming an electrostatic image on the charged image carrier;
A developing voltage that contains a developer containing toner and a carrier, and a developer carrier that carries and conveys the developer contained in the developer container, and the developer carrier contains at least a DC component Vdev. And a developing device that forms a toner image by supplying toner to the electrostatic image on the image carrier;
After a predetermined timing when the use of a new carrier is started in the developing device, before forming the first image, the absolute value of Vd is made smaller than that at the time of image formation or Vd is set to approximately 0 V, and Vd And a control unit that executes an initial operation of driving the image carrier for a predetermined time by making a difference Vback between Vdev and Vdev larger than that at the time of image formation;
An image forming apparatus comprising:   The predetermined timing is a timing at which use of the developing device is started after a new developing device filled with a developer containing a new carrier is mounted on the main body of the image forming apparatus. The image forming apparatus according to claim 1.   The image according to claim 1, wherein the predetermined timing is a timing at which use of the developing device is started after the developer in the developing device is replaced with a developer containing a new carrier. Forming equipment.   The image forming apparatus according to claim 1, wherein the predetermined timing is a timing when a new carrier or a developer containing a new carrier is supplied to the developing device.   Vd in the initial operation is a potential having the same polarity as the normal charging polarity of the image carrier, and Vdev in the initial operation is a potential having the same polarity as the normal charging polarity of the image carrier. The image forming apparatus according to any one of claims 1 to 4.   5. The Vd in the initial operation is substantially 0 V, and the Vdev in the initial operation is a potential having a polarity opposite to a normal charging polarity of the image carrier. The image forming apparatus described in the item.   7. The charging device according to claim 1, wherein the charging unit is in contact with the image carrier and charges the image carrier when a voltage including only a direct current component is applied thereto. Image forming apparatus.   An intermediate transfer member that conveys the toner image primarily transferred from the image carrier to the recording material for secondary transfer, and the intermediate transfer member is always in operation during driving of the image carrier and the intermediate transfer member; The image forming apparatus according to claim 1, wherein the image forming apparatus is pressed against the image carrier.   In the moving direction of the surface of the image carrier, downstream from a transfer position where the toner image formed on the image carrier is transferred to the transfer body, and upstream from a charging position where the charging means charges the image carrier. In the pre-exposure position, there is a pre-exposure unit that irradiates the surface of the image carrier with light, and at the time of image formation, the image carrier charged by the charging unit after being irradiated with light by the pre-exposure unit The electrostatic image is formed on the body by the electrostatic image forming unit, and light irradiation by the pre-exposure unit is not performed during the initial operation. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein no voltage is applied to a transfer unit that transfers a toner image from the image carrier to a transfer target during the initial operation.

Images