JP2011070038A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device achieving formation of a high-quality image over a long term without causing deterioration in developer further than required while suppressing the occurrence of developing history (ghost) by reducing contrast of residual toner left after development in a hybrid developing system, and to provide an image forming apparatus. <P>SOLUTION: The developing device includes a leveling member for leveling the residual toner left after development on a surface of a toner carrier. Voltage that is between voltage applied to the toner carrier and voltage applied to a developer carrier is applied to the leveling member. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a toner carrier for developing a latent image formed on an image carrier with toner carried on the surface, a developer carried on the surface, and the toner in the developer on the toner carrier. The present invention relates to a developing device having a developer carrier to be supplied and an image forming apparatus including the developing device.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method, as a developing device for developing an electrostatic latent image formed on an image carrier, a one-component developing method using only toner as a developer and two using a toner and a carrier are used. Component development methods are known.

  In the one-component development method, the toner is generally charged by passing the toner through a regulating portion formed by a toner carrier and a regulation plate pressed against the toner carrier, and a desired toner thin layer can be obtained. Therefore, it is advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus.

  On the other hand, the deterioration of the toner is likely to be promoted due to the strong stress of the regulating portion, and the charge acceptability of the toner is likely to be lowered. Further, the charge imparting property to the toner is also lowered by the contamination of the regulating member, which is a charge imparting member to the toner, and the surface of the toner carrying member with the toner or the external additive. For this reason, the life of the developing device is short, for example, the toner charge amount is further reduced, causing problems such as fogging.

  In comparison, in the two-component development method, the toner is mixed with the carrier and charged by frictional charging, so that the stress is small, and the carrier surface area is large, so that it is relatively strong against contamination by the toner and external additives. It is advantageous for life.

  However, in the two-component development method, when developing the electrostatic latent image on the image carrier, the surface of the image carrier is rubbed with the magnetic brush formed by the developer, so that the developed image has magnetic brush marks. It has a problem that it occurs. Furthermore, there is a problem that the carrier easily adheres to the image carrier and causes an image defect.

  As a development method that solves the problem of image defects and achieves the same high image quality as the one-component development method while having the long-life characteristics of the two-component development method using a two-component developer, it is on the developer carrier. A so-called hybrid development system is disclosed in which a two-component developer is carried and only toner is supplied from the two-component developer to a toner carrier and used for development (see, for example, Patent Document 1).

  However, the hybrid development method described in Patent Document 1 has the following development history (ghost) problem.

  The problem of development history (ghost) is a problem that the hybrid development system generally has, and the pattern of residual toner that has not been used for development on the toner carrier is developed history (ghost) in the next development process. As a phenomenon that appears on the image.

  In the hybrid development, a bias voltage for supplying toner is applied to the toner carrier at a portion (toner supply region) between the developer carrier and the toner carrier to supply the toner.

  On the toner carrier, toner is used for development, and there is a portion where there is no or little development residual toner, and other portions where the toner layer is not used for development and are repeatedly supplied in layers, The difference between the two toner amounts generated in the undeveloped toner layer cannot be filled by the next one toner supply.

  For this reason, there is a difference in the amount of toner between the portion where the toner is not consumed and the portion where the toner is consumed in development at the time of the next development. The development history (ghost) is a problem that the difference in toner amount affects the development process and appears as a contrast of density on the image.

  An example of a typical ghost image is shown in FIG.

  As a method for solving the problem of development history (ghost), conventionally, cleaning is performed to electrically collect the entire development residual toner, facing the region downstream of the developing portion of the toner carrier and upstream of the supply portion. A technique for providing a roller has been proposed. (For example, see Patent Document 2)

JP-A-5-150636 JP 2001-265118 A

  As a method for solving the development history (ghost) which is a problem of the hybrid development method, as described in Patent Document 2, a technique of providing a cleaning roller for collecting the development residual toner has been proposed.

  However, although the problem of development history (ghost) is improved by providing the cleaning roller and collecting the development residual toner in this way, a large amount of toner adheres to the surface of the cleaning roller within a short period of time, and the cleaning roller Since the surface potential is increased, the recovery capability is not sustained.

  Therefore, in this method, it is essential to provide a toner removing means such as a scraper for removing the toner from the cleaning roller.

  However, if a scraper or the like is provided, the stress caused by this will cause toner deterioration. Therefore, the advantage of the hybrid development that the stress on the toner is small cannot be utilized, and it is not practical.

  In addition to this, as a method for reducing the contrast of the residual toner after development, a method in which a scraper is directly provided on the toner carrying member or a brush is brought into contact can be considered. It is not.

  The present invention has been made in view of the above technical problems. The object of the present invention is to reduce the contrast of residual toner and suppress the development history (ghost) in the hybrid development system, while preventing the deterioration of the developer more than necessary, and maintaining high image quality over a long period of time. It is an object of the present invention to provide a developing device that enables easy image formation and an image forming device using the developing device.

  In order to solve the above problems, the present invention has the following features.

1. A toner carrier that carries and conveys toner on the surface and develops the electrostatic latent image formed on the opposite image carrier with the toner;
A toner carrier bias power source for applying a voltage to the toner carrier to provide the toner for development;
A developer carrying body that carries and conveys a developer composed of toner and a carrier on the surface and supplies the toner in the developer to the toner carrying body facing the surface;
In a developing device having a developer carrier bias power source for applying a voltage to the developer carrier to supply the toner,
A leveling member for leveling development residual toner on the surface of the toner carrier;
A leveling member bias power source for applying a voltage to the leveling member,
The leveling member is
On the downstream side in the rotation direction of the toner carrier from the facing portion of the toner carrier and the image carrier,
And the upstream side of the rotation direction of the toner carrier from the facing portion of the toner carrier and the developer carrier,
Arranged to face the toner carrier,
The voltage applied to the leveling member by the leveling member bias power source is:
A voltage applied to the toner carrier by the toner carrier bias power source;
The developing device, wherein the developing device is a voltage positioned between the developer carrier bias power source and a voltage applied to the developer carrier.

2. The voltage applied to the leveling member by the leveling member bias power source is:
A voltage applied to the toner carrier by the toner carrier bias power source;
2. The developing device according to item 1, wherein the developing device is a voltage intermediate to a voltage applied to the developer carrying member by the developer carrying member bias power source.

3. Toner layer detecting means for detecting the amount of toner in the toner layer on the toner carrier;
2. The developing device according to claim 1, further comprising: a voltage control unit that controls a voltage applied to the leveling member by the leveling member bias power source based on a detection result of the toner layer detection unit. .

4). 2. The developing device according to claim 1, further comprising voltage control means for controlling a voltage applied to the leveling member by the leveling member bias power source based on a print ratio of image data to be output.

5). An image forming apparatus comprising: an image carrier; and a developing device that develops the electrostatic latent image formed on the image carrier with toner,
The image forming apparatus, wherein the developing device is the developing device according to 1 or 2 above.

6). An image forming apparatus comprising the developing device according to 1 above,
Toner layer detecting means for detecting the amount of toner in the toner layer on the toner carrier;
An image forming apparatus comprising: a voltage control unit that controls a voltage applied to the leveling member by the leveling member bias power source based on a detection result of the toner layer detection unit.

7). An image forming apparatus comprising the developing device according to 1 above,
An image forming apparatus comprising voltage control means for controlling a voltage applied to the leveling member by the leveling member bias power source based on a printing ratio of image data to be output.

  According to the developing device and the image forming apparatus of the present invention, in the hybrid developing system, the leveling member for leveling the development residual toner on the surface of the toner carrying member has a voltage applied to the toner carrying member, A voltage located between the voltage applied to the developer carrier and the leveling member is applied.

  This makes it possible to reduce the contrast of undeveloped toner and suppress the development history (ghost), and to form a high-quality image over a long period without causing unnecessary deterioration of the developer. Can do.

1 is a diagram illustrating a configuration example of a main part of an image forming apparatus according to a first embodiment. It is a figure which shows the example of the image of a typical ghost. FIG. 6 is a graph plotting a change in the amount of toner on a toner carrier in a developing device not provided with a leveling member. FIG. 6 is a schematic diagram showing that a difference in toner amount generated in a development residual toner layer on a toner carrier cannot be filled with a single toner supply. It is the schematic diagram showing the electric potential relationship of each member when a leveling member is not installed. It is the schematic diagram showing the electric potential relationship of each member at the time of installing a leveling member. FIG. 6 is a schematic diagram showing the maximum contrast when the leveling member application voltage is changed between the developer carrier application voltage and the toner carrier application voltage. 6 is a diagram illustrating a configuration example of a main part of an image forming apparatus according to a second embodiment. FIG. A circuit (voltage control means) for detecting the amount of toner in the toner layer and reflecting it in the leveling member applied voltage is shown. FIG. 6 is a schematic diagram showing the maximum contrast when the leveling member applied voltage is changed between the developer carrier applied voltage and the toner carrier applied voltage when the black toner remains after passing through the developing unit. 7 is a flowchart illustrating a procedure for detecting the amount of toner in a toner layer and reflecting the detected amount in setting of a leveling member bias voltage. It is a schematic diagram which shows that the appropriate setting of the voltage applied to a leveling member differs according to an image part ratio. The circuit (voltage control means) for controlling the leveling member applied voltage according to the image part ratio is shown. It is a flowchart which shows the procedure which sets a leveling member bias voltage according to an image part ratio.

  An embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
(Configuration and operation of image forming apparatus)
FIG. 1 shows a configuration example of a main part of an image forming apparatus according to the first embodiment of the present invention. The schematic configuration and operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.

  This image forming apparatus is a printer that performs image formation by transferring a toner image formed on an image carrier (photoconductor) 1 to a transfer medium P such as paper by an electrophotographic method.

  This image forming apparatus has an image carrier 1 for carrying an image. Around the image carrier 1, there are a charging member 3 as a charging means for charging the image carrier 1, and an image carrier. A developing device 2 for developing an electrostatic latent image on 1 and forming a toner image, a transfer roller 4 for transferring a toner image on the image carrier 1, and cleaning for removing residual toner on the image carrier 1 The blades 5 are sequentially arranged along the rotation direction A of the image carrier 1.

  The image carrier 1 is charged by the charging member 3 and then exposed by an exposure device 6 equipped with a laser emitter and the like, and an electrostatic latent image is formed on the surface thereof. The developing device 2 develops the electrostatic latent image to form a toner image. The transfer roller 4 transfers the toner image on the image carrier 1 to the transfer medium P, and then discharges it in the direction of arrow C in the figure. The cleaning blade 5 removes the residual toner on the image carrier 1 after the transfer with its mechanical force.

  The image carrier 1, the charging member 3, the exposure device 6, the transfer roller 4, the cleaning blade 5 and the like used in the image forming apparatus may arbitrarily use a known electrophotographic technique. For example, although a charging roller is shown in the drawing as the charging means, a charging device that is not in contact with the image carrier 1 may be used. Further, for example, there may be no cleaning blade.

  The configuration of the basic part of the developing device 2 of the hybrid developing system according to this embodiment will be described.

  The developing device 2 includes the following components. That is, a developer tank 17 that contains a developer 23 containing a carrier and toner, a developer carrier 13 that carries and conveys the developer 23 supplied from the developer tank 17 on the surface, and a toner from the developer carrier 13 The toner carrier 7 for developing the electrostatic latent image formed on the image carrier 1 and the toner carrier 7 is disposed in a non-contact manner on the downstream side of the development area 10 of the toner carrier. To apply a voltage to each of the leveling member 12 for supplying toner to the toner carrier or recovering from the toner carrier according to the amount of residual toner, and the developer carrier, toner carrier, and leveling member Developer carrier bias power source 24, toner carrier bias power source 25, and leveling member bias power source 26.

  The detailed configuration and operation of the developing device 2 will be described later.

(Developer composition)
The configuration of the developer used in the developing device according to this embodiment will be described.

  The developer 23 used in the present embodiment includes toner and a carrier for charging the toner.

<Toner>
The toner is not particularly limited, and a known toner that is generally used can be used, and a colorant, a charge control agent, a release agent, and the like are contained in the binder resin, and external additives are added. What processed the agent can be used. The toner particle diameter is not limited to this, but is preferably about 3 to 15 μm.

  In producing such a toner, it can be produced by a publicly known method. For example, it can be produced using a pulverization method, an emulsion polymerization method, a suspension polymerization method or the like.

  The binder resin used in the toner is not limited to this. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene-substituted product), polyester resin, epoxy resin, vinyl chloride Resins, phenol resins, polyethylene resins, polypropylene resins, polyurethane resins, silicone resins and the like can be mentioned. It is preferable to use those having a softening temperature in the range of 80 to 160 ° C. and those having a glass transition point in the range of 50 to 75 ° C., depending on the resin alone or the composite.

  Further, as the colorant, known ones that are generally used can be used. For example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultra Marine blue, rose bengal, lake red, or the like can be used, and it is generally preferable to use 2 to 20 parts by mass with respect to 100 parts by mass of the binder resin.

  As the charge control agent, known ones can be used. Examples of the charge control agent for positively chargeable toners include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazoles. System compounds and polyamine resins. Examples of charge control agents for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkylsalicylic acid metal compounds, and calixarene compounds. In general, the charge control agent is preferably used at a ratio of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  In addition, as the above-mentioned mold release agent, known ones that are generally used can be used. For example, polyethylene, polypropylene, carnauba wax, sazol wax and the like can be used alone or in combination of two or more. In general, it is preferably used at a ratio of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  Also, as the above external additives, publicly known publicly known materials can be used. For example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicone resin, fluorine resin Resin fine particles such as silane coupling agent, titanium coupling agent, and silicone oil are preferably used. Such a fluidizing agent is added at a ratio of 0.1 to 5 parts by mass with respect to 100 parts by mass of the toner. The number average primary particle size of the external additive is preferably 10 to 100 nm.

  Further, as the external additive, reverse polarity particles having a chargeability opposite to that of the toner may be used. The reverse polarity particles preferably used are appropriately selected depending on the charging polarity of the toner.

  For example, when the toner is negatively charged by the carrier, the opposite polarity particles are positively charged particles that are positively charged in the developer. Also, for example, when the toner is positively charged by the carrier, the opposite polarity particles are negatively charged particles that are negatively charged in the developer. By incorporating reverse polarity particles in the two-component developer and accumulating the reverse polarity particles in the developer with durability, the chargeability of the carrier decreases due to the spent of the toner or the post-treatment agent on the carrier. However, since the reverse polarity particles can also charge the toner to the normal polarity, the chargeability of the carrier can be effectively compensated, and as a result, the deterioration of the carrier can be suppressed.

  When a negatively chargeable toner is used as the toner, fine particles having positive chargeability are used as the reverse polarity particles. For example, inorganic fine particles such as strontium titanate, barium titanate, and alumina, acrylic resin, benzoguanamine resin, and nylon resin are used. Fine particles composed of a thermoplastic resin such as a polyimide resin or a polyamide resin or a thermosetting resin can be used. Further, a positive charge control agent imparting positive chargeability may be contained in the resin, or a copolymer of nitrogen-containing monomers may be constituted.

  As the positive charge control agent, for example, nigrosine dye, quaternary ammonium salt and the like can be used, and as the nitrogen-containing monomer, 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-Dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinylpyridine, N-vinylcarbazole, vinylimidazole and the like can be used.

  On the other hand, in the case of using a positively chargeable toner, fine particles having negative chargeability are used as the reverse polarity particles. For example, in addition to inorganic fine particles such as silica and titanium oxide, fluorine resin, polyolefin resin, silicone resin, polyester resin Fine particles composed of a thermoplastic resin such as a thermosetting resin or the like can be used. Further, a negative charge control agent imparting negative chargeability may be contained in the resin, or a copolymer of a fluorine-containing acrylic monomer or a fluorine-containing methacrylic monomer may be constituted. Examples of the negative charge control agent include salicylic acid-based and naphthol-based chromium complexes, aluminum complexes, iron complexes, and zinc complexes.

  In addition, in order to control the chargeability and hydrophobicity of the reverse polarity particles, the surface of the inorganic fine particles may be surface treated with a silane coupling agent, a titanium coupling agent, silicone oil, etc. When imparting positive chargeability, surface treatment with an amino group-containing coupling agent is preferred, and when imparting negative chargeability, surface treatment with a fluorine group-containing coupling agent is preferred.

  The number average particle diameter of the reverse polarity particles is preferably 100 to 1000 nm. It is used by adding 0.1 to 10 parts by mass with respect to 100 parts by mass of toner.

<Carrier>
The carrier is not particularly limited, and a commonly used carrier can be used, and a binder type carrier, a coat type carrier, and the like can be used. The carrier particle size is not limited to this, but is preferably 15 to 100 μm.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and positive or negative chargeable fine particles can be fixed on the surface of the carrier, or a surface coating layer can be provided. The charging characteristics such as the polarity of the binder type carrier can be controlled by the material of the binder resin, the chargeable fine particles, and the type of the surface coating layer.

  Examples of the binder resin used in the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like typified by polystyrene resins, and curable resins such as phenol resins. .

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having an oxide layer on the surface can be used. The shape may be granular, spherical, or needle-shaped. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added to the magnetic resin carrier in an amount of 50 to 90% by mass.

  Silicone resin, acrylic resin, epoxy resin, fluorine resin, etc. are used as the surface coating material of the binder type carrier, and these resins are coated on the surface and cured to form a coating layer, thereby providing a charge imparting ability. Can be improved.

  For example, the charging fine particles or the conductive fine particles are fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly, adhering these fine particles to the surface of the magnetic resin carrier, and then mechanically and thermally. By applying a strong impact force and fixing the fine particles so as to be driven into the magnetic resin carrier. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier.

  As the chargeable fine particles, organic or inorganic insulating materials are used. Specifically, organic insulating fine particles such as polystyrene, styrene copolymer, acrylic resin, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof may be used as the organic type. Regarding the charge level and polarity, a desired level of charge and polarity can be obtained by a material, a polymerization catalyst, surface treatment, and the like. Further, as the inorganic type, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  On the other hand, a coated carrier is a carrier in which a carrier core particle made of a magnetic material is coated with a resin, and in a coated carrier, positive or negatively chargeable fine particles are fixed on the surface of the carrier as in a binder type carrier. it can. Charging characteristics such as polarity of the coat type carrier can be controlled by the type of the surface coating layer and the chargeable fine particles, and the same material as the binder type carrier can be used. In particular, the coating resin can be the same resin as the binder resin of the binder type carrier.

  The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount. The mixing ratio of the toner is 3 to 50% by mass, preferably 6 to 30% by mass with respect to the total amount of the toner and the carrier. Is suitable.

(Configuration and operation of developing device 2)
A detailed configuration example and operation example of the developing device 2 according to this embodiment will be described with reference to FIG.

<Device configuration>
The developer 23 used in the developing device 2 is composed of toner and carrier as described above, and is stored in the developer tank 17.

  The developer tank 17 is formed by a casing 20 and normally contains mixing and agitating members 18 and 19 therein. The mixing stirring members 18 and 19 mix and stir the developer 23 and supply the developer 23 to the developer carrier 13. An ATDC (Automatic Toner Density Control) sensor 21 for detecting the toner concentration is preferably disposed at a position facing the mixing and agitating member 19 of the casing 20.

  The developing device 2 normally has a replenishing unit 15 for replenishing the developer tank 17 with toner that is consumed by the image carrier 1. In the replenishment unit 15, replenishment toner 22 sent from a hopper (not shown) that stores replenishment toner is replenished into the developer tank 17.

  The developing device 2 also has a regulating member 16 for thinning the developer for regulating the amount of developer on the developer carrying member 13.

  The developer carrier 13 is generally composed of a magnet roller (magnet body) 8 that is fixedly arranged and a rotatable sleeve roller 9 that encloses the roller, and supplies toner to the toner carrier 7 during image formation. The toner supply bias voltage is applied.

  The toner carrier 7 is arranged so as to face the developer carrier 13 and the image carrier 1, and a developing bias voltage for developing the electrostatic latent image on the image carrier 1 is applied.

  The toner carrier 7 may be made of any material as long as the voltage can be applied. For example, an aluminum roller having a surface treatment such as anodized may be used. In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate You may use what gave resin coatings, such as resin, a silicone resin, a fluororesin, and rubber coatings, such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. The coating material is not limited to this.

  Further, a conductive agent may be added to the bulk or surface of the coating. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include carbon black such as kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles, but are not limited thereto. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials, but they are not particularly limited. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

<Operation of the device>
An example of operation of the developing device 2 shown in FIG. 1 will be described in detail.

  The developer 23 in the developer tank 17 is mixed and agitated by the rotation of the mixing and agitating members 18 and 19 and is frictionally charged. At the same time, the developer 23 is circulated and conveyed in the developer tank 17 to the sleeve roller 9 on the surface of the developer carrier 13. Supplied.

  The developer 23 is held on the surface side of the sleeve roller 9 by the magnetic force of the magnet roller 8 inside the developer carrier 13, and rotates with the sleeve roller 9 so as to face the developer carrier 13. The passage amount is regulated by the regulating member 16.

  Thereafter, the developer 23 is conveyed to a supply nip portion where the developer carrier 13 faces the toner carrier 7.

  In FIG. 1, the toner carrier 7 and the developer carrier 13 are set in the rotation direction (counter direction) so that the surfaces of the toner carrier 7 and the developer carrier 13 move in opposite directions, but they move in the forward direction. You may set to a rotation direction (with direction).

  In the toner supply region 11 at the opposite portion between the toner carrier 7 and the developer carrier 13, the potential difference between the development bias voltage applied to the toner carrier 7 and the toner supply bias voltage applied to the developer carrier 13 is based on the potential difference. The toner in the developer 23 is supplied to the toner carrier 7 side by the force that the formed electric field gives to the toner.

  Usually, a bias obtained by superimposing an AC voltage on a DC voltage is applied to the toner carrier 7, and only a DC voltage or a bias obtained by superimposing an AC voltage on a DC voltage is applied to the developer carrier 13, and the toner supply region 11. An electric field is formed in which an alternating electric field is superimposed on a DC electric field.

  The toner layer supplied from the developer carrier 13 onto the toner carrier 7 in the toner supply region 11 is conveyed to the development region 10 as the toner carrier 7 rotates, and the development applied to the toner carrier 7 is performed. It is used for development by an electric field formed by a bias voltage and a latent image potential on the image carrier 1.

  In the development area 10, development is performed by the toner moving by an electric field in the development interval provided between the toner carrier 7 and the image carrier 1.

  Various known biases can be applied as the developing bias voltage. Usually, a bias obtained by superimposing an AC voltage on a DC voltage is applied. Thereafter, the toner layer (development residual toner) in which the toner is partially consumed in the developing region 10 is conveyed to the facing portion between the toner carrier 7 and the leveling member 12 as the toner carrier 7 rotates.

<Configuration and operation of leveling member>
The leveling member 12 is at least a part of a conductive roller installed at a predetermined gap from the toner carrier 7. The leveling member 12 forms an electric field at a portion facing the toner carrier 7 by applying a bias voltage.

  The leveling member 12 may be made of any material as long as the voltage can be applied and the toner can be carried on the surface thereof, and examples thereof include an aluminum roller that has been subjected to a surface treatment such as alumite.

  In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate You may use what gave resin coatings, such as resin, a silicone resin, a fluororesin, and rubber coatings, such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. The coating material is not limited to this.

  Further, a conductive agent may be added to the bulk or surface of the coating. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent.

  Examples of the electronic conductive agent include carbon black such as kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles, but are not limited thereto. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials, but they are not particularly limited. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

  The rotation direction of the leveling member 12 is not particularly limited, and may be the width direction or the counter direction with respect to the toner carrier.

  The bias voltage applied to the leveling member 12 is set to an arbitrary voltage between the bias voltage of the toner carrier 7 and the bias voltage applied to the developer carrier 13.

  As the bias voltage applied to the toner carrier 7 or the developer carrier 13, not only a DC voltage but also a voltage obtained by superimposing various AC voltages on the DC voltage is used. Considering the potential, it is set so as to satisfy the aforementioned relationship.

  Note that the voltage applied to the leveling member 12 may be not only a DC voltage but also a voltage obtained by superimposing an AC voltage on a DC voltage. Various waveforms such as a sine wave, a rectangular wave, and a sawtooth wave can be used as the AC voltage waveform. The rectangular wave may be a symmetric waveform with a duty ratio of 50% or an asymmetric waveform. In this case as well, the above-described magnitude relationship may be satisfied by averaging the average potential of one cycle as the bias potential of the member 12.

  The toner layer conveyed to the opposite portion between the toner carrier 7 and the leveling member 12 is a development residual toner layer partly used for development, and a part used for development (hereinafter referred to as “after black”). ) And a portion not used for development (hereinafter referred to as “after white”), there is a difference in height in the toner layer.

  The leveling member 12 supplies toner to the “after black” portion and collects the toner from the “after white” portion or passes the toner without being supplied or collected. It acts to reduce the contrast of the toner amount after white (to level the toner layer). Details of this operation will be described later.

  The toner layer that has passed through the portion facing the leveling member 12 is returned to the toner supply region 11 as the toner carrier 7 rotates.

  On the other hand, the developer 23 that has passed through the toner supply area 11 is conveyed toward the developer tank 17 as the sleeve rotates, and the developer is generated by a repulsive magnetic field provided at a position corresponding to the developer recovery area 14 on the magnet roller 8. It is peeled off from the carrier 13 and collected in the developer tank 17.

  When a supply control unit (not shown) provided in the supply unit 15 detects from the output value of the ATDC sensor 21 that the toner density in the developer 23 has become equal to or lower than the minimum toner density for securing the image density, it is not shown. The replenishing toner 22 stored in the hopper by the toner replenishing means is supplied into the developer tank 17 through the toner replenishing section 15.

(Suppression effect of development history by leveling member)
<Development history (ghost) generation mechanism>
First, the development history generation mechanism will be described.

  FIG. 3 is a plot of changes in the amount of toner on the toner carrier in a developing device without a leveling member, with the horizontal axis representing the number of rotations of the toner carrier and the vertical axis representing the surface potential of the toner carrier. . The surface potential of the toner carrier on the vertical axis is a surface potential (toner layer surface potential) measured from above the toner layer with the conductive substrate of the toner carrier being zero, and is generally proportional to the amount of toner supplied.

  As can be seen from FIG. 3, the toner amount increases with each lap, and finally becomes substantially the same potential as the developer carrying member applied voltage Vs (P in the figure: after repeated non-image portions). Supply stops. Since the toner is supplied because there is a potential difference between the surface of the toner carrier and the developer carrier, the surface potential of the toner layer does not exceed the potential Vs of the developer carrier due to an increase in the amount of supplied toner.

  FIG. 4 is a schematic diagram showing that the difference in the amount of toner generated in the undeveloped toner layer T on the toner carrier surface S cannot be filled by one toner supply.

  In an image generally printed in an electrophotography represented by an office document output application, the image portion ratio is low and most of the image is a non-image portion. Therefore, the undeveloped toner layer is mostly non-toner (toner layer Tw) The surface potential of the toner layer after repeated image portions is reached, and the toner amount is saturated. If a portion of the image portion where the toner is used for development (toner layer Tk) is generated, the undeveloped toner is reduced to the amount of toner immediately after the image portion (after black) (FIG. 4 ( a)).

  Since the toner layer after black is supplied only once, it cannot supply the same amount of toner as after repeating the non-image part (after continuous white). A contrast Ct is generated between the toner amount after Tw) and after black (toner layer Tk) (see FIG. 4B).

  The toner amount contrast at this time is hereinafter referred to as “maximum contrast”. When this toner layer is subjected to development, a difference in development characteristics after white and after black occurs, and a development history (ghost) appears on the image.

  Hereinafter, the operation of the leveling member in the present embodiment will be described in more detail. Although the polarity of the toner is described as negative, the positive toner can be considered in the same way by reversing the direction of the bias, and the scope of the present invention is not limited to the negative toner.

  As shown in the upper part of FIG. 4, the toner layer on the toner carrier after passing through the developing portion has a difference in the height of the toner layer after white and after black.

  That is, as described with reference to FIG. 3, the toner layer after white has a toner amount corresponding to the surface potential of the toner layer being equal to the voltage applied to the developer carrier, while the toner layer after black is the toner amount. As a result of being used for development, there is no or very little toner.

  The maximum contrast at this time is a very large amount of toner after the continuous white. The leveling member reduces the contrast and reduces the contrast in the toner layer after the next supply, thereby realizing ghost suppression.

<Contrast reduction effect by leveling member>
The contrast reduction effect by the leveling member will be described with reference to FIGS.

  FIG. 5 shows a case where no leveling member is installed, and FIG. 6 shows a case where a leveling member is installed. FIG. 6 is a diagram schematically illustrating a potential relationship of a solder member including a toner layer potential.

  The horizontal broken lines indicate the voltages (Vb and Vs) applied from the bias power source to the toner carrier and the developer carrier, respectively, and the horizontal solid lines indicate the voltages (Vd) applied from the bias power source to the leveling member. is there.

  Here, since the toner polarity is described as negative, the relative position of the bias voltage to be applied is as follows. Regarding the potential relationship between the toner carrying member and the developer carrying member, the toner carrying member Vb> the developer carrying member Vs is satisfied from the request for the toner supply. Further, the leveling member Vd has a relative relationship such that it is positioned between them.

  White arrows represent potentials (Vtb and Vts) formed by the toner layer on the toner carrier or the leveling member, respectively.

  On the toner carrier after white, the toner layer is formed so that the surface potential thereof is equal to the developer carrier application voltage Vs.

  The leveling member initially does not have toner on its surface, but the bias voltage Vd applied to the leveling member is set to the positive side of the toner carrier surface potential after continuous white = developer carrier potential Vs. Therefore, toner is collected from the toner layer after continuous white in a state where no toner is present on the surface. Within a short period of time, the toner layer is held on the surface as indicated by the broken white arrow Vtd so that the surface potential is equal to the voltage applied to the developer carrier, and image formation is normally performed in that state. Is called.

  Now, when the undeveloped toner layer passes through the leveling member in this state, since the surface potentials of the toner carrier and leveling member are equal in the white rear portion, toner is not exchanged between the two. . On the other hand, after black, the surface potential Vtd of the leveling member is smaller than the surface potential Vb of the toner carrier, and toner movement from the leveling member to the toner carrier occurs according to the relationship.

  As a result, after passing the leveling member, a constant toner layer height is formed even after black. Compared to the case of FIG. 5 where there is no leveling member, in FIG. It can be seen that the maximum contrast Ct, which is the difference in layer height, is reduced.

  In addition, although it demonstrated paying attention after continuous white and after black here, in other cases, for example, there is a state after white but not reaching a saturated state after continuous white in FIG. Even in such a case, the contrast is reduced based on the above concept that the toner moves according to the relative relationship between the surface potential of the toner carrier and the leveling member.

  Since the development history (ghost) is most noticeable at the maximum contrast, it is important to reduce the development history.

<Setting applied voltage to leveling member>
Next, setting of the voltage applied to the leveling member will be described with reference to FIGS. 7 (a), (b), and (c). FIGS. 7A, 7B and 7C are schematic diagrams showing the maximum contrast when the voltage applied to the leveling member is changed between the developer carrier applied voltage and the toner carrier applied voltage. It is.

  First, in the case of FIG. 7A in which the potential Vd of the leveling member is set close to the developer carrier Vs, the difference between the leveling member applied voltage Vd and the white toner layer surface potential Vb−Vtb (= Vs) is Since it is small, the amount of the toner layer Vtd held on the leveling member is small. Therefore, the amount of toner that can be supplied onto the toner carrier after black is limited thereby.

  Next, in the case of FIG. 7B in which the potential Vd of the leveling member is set closer to the toner carrier Vb, the difference between the leveling member applied voltage Vd and the white toner layer surface potential Vb−Vtb (= Vs) is large. Therefore, the amount of the toner layer Vtd held on the leveling member is larger than in the previous case. However, since the potential difference between the leveling member applied voltage Vd and the toner carrier applied voltage Vb is small, the amount of toner that can be supplied onto the toner carrier after black is limited.

  Finally, in the case of FIG. 7C in which the potential Vd of the leveling member is set at substantially the center between the developer carrier applied voltage Vs and the toner carrier applied voltage Vb, the leveled member applied voltage is compared with the previous two. There is a good balance between the difference between Vd and the white toner layer surface potential Vb−Vtb (= Vs) and the potential difference between the leveling member applied voltage Vd and the toner carrier applied voltage Vb, and the leveling member to the toner carrier Since both factors that inhibit toner movement can be suppressed, the maximum contrast Ct can be reduced.

  Accordingly, the voltage Vd applied to the leveling member is not so close to the developer carrier Vs or the toner carrier Vb, and the effect of the leveling member can be sufficiently exerted by setting it near the center thereof.

(Second Embodiment)
(Configuration and operation different from the first embodiment)
A second embodiment of the present invention will be described with reference to FIG. FIG. 8 shows a configuration example of a main part of an image forming apparatus according to the second embodiment of the present invention.

  In the second embodiment shown in FIG. 8, members having the same functions as those in the first embodiment shown in FIG.

  In the following description, the polarity of the toner is described as minus, but the plus toner can be considered in the same way by reversing the direction of the bias, and the scope of the present invention is not limited to minus toner. Absent.

  The developing device 2 used in the image forming apparatus shown in FIG. 8 is provided with a toner layer detecting means 27 facing the toner carrier 7 after development.

  The toner layer detection means 27 is, for example, a surface potential meter or an optical density detection device, and is installed for the purpose of detecting the toner amount of the toner layer on the toner carrier 7.

  FIG. 9 shows a circuit (voltage control means) for detecting the amount of toner in the toner layer and reflecting it in the leveling member applied voltage.

  The toner layer detection means 27 and the leveling member bias power supply 26 are connected to the leveling member bias control circuit 31 and the toner layer detection means control circuit 32, respectively, as shown in FIG. The toner layer detection means control circuit 32 is connected to a calculation unit 35 including, for example, a CPU, a RAM, and a ROM.

  In the present embodiment, the circuit (voltage control means) is configured to control the bias voltage applied to the leveling member 12 based on the detection result from the toner layer detection means 27.

  Such a configuration is a particularly effective method when the undeveloped toner state changes with time due to factors such as environmental fluctuations and developer deterioration. For example, a case where the amount of the post-black toner that normally hardly remains on the toner carrying member remains so as to affect the proper leveling member potential due to the above factors can be considered as an example.

  The control in this case will be described with reference to FIGS. 10 (a), (b), and (c).

<Applied voltage setting control of leveling member>
FIGS. 10A, 10B, and 10C illustrate the case where the toner after the black portion remains after passing through the developing portion, and the voltage Vd applied to the leveling member is expressed by the developer carrier applied voltage Vs to the toner carrier. It is the schematic diagram shown about the maximum contrast Ct when changing between body applied voltages Vb.

  In these drawings, compared to FIGS. 7A, 7B, and 7C, since the toner layer exists on the surface of the toner carrier after black, the surface potential Vtk of the toner layer after black is It is generated on the minus side of the toner carrier applied voltage Vb. The case where the potential Vd of the leveling member is changed from the developer carrier applied voltage Vs to the toner layer surface potential Vtk after black in such a case will be described.

  First, in the case of FIG. 10A where the potential Vd of the leveling member is set close to the developer carrier Vs, the difference between the leveling member applied voltage Vd and the white toner layer surface potential Vtw (= Vs) is small. The amount Vtd of the toner layer held on the leveling member is small. Therefore, the amount of toner that can be supplied onto the toner carrier after black is limited thereby.

  Next, in the case of FIG. 10B where the potential Vd of the leveling member is set closer to the toner carrier Vb, the difference between the leveling member applied voltage Vd and the white toner layer surface potential Vtw (= Vs) is large. The amount Vtd of the toner layer held on the leveling member is larger than that in the previous case. However, since the potential difference between the leveling member applied voltage Vd and the post-black toner carrier surface potential Vtk is small, the amount of toner that can be supplied onto the black toner carrier is limited thereby.

  Finally, in the case of FIG. 10C in which the potential Vd of the leveling member is set at substantially the center between the developer carrier applied voltage Vs and the post-black toner carrier surface potential Vtk, the leveling member is compared with the previous two. The difference between the applied voltage Vd and the toner layer surface potential Vtw (= Vs) after white and the potential difference between the smoothing member applied voltage Vd and the black toner carrier surface potential Vtk is well balanced. As a result, it is possible to reduce the maximum contrast Ct.

  Accordingly, the voltage Vd applied to the leveling member is not so close to the developer carrier Vs or the post-black toner carrier surface potential Vtk, and the effect of the leveling member can be sufficiently exerted by setting it near the center. .

<Setting flow of leveling member bias voltage by toner amount detection of toner layer>
When the development residual toner amount after black varies due to factors such as environmental fluctuations and developer deterioration, the appropriate value of the voltage applied to the leveling member changes.

  In this embodiment, since the toner amount of the toner layer after black and after white can be detected by the toner layer detection means, an appropriate value of the voltage applied to the leveling member is calculated according to the detection result, Feedback can be provided to the leveling member application bias.

  Hereinafter, a method for controlling the leveling member bias voltage will be described with reference to FIG. FIG. 11 is a flowchart showing a procedure for detecting the amount of toner in the toner layer and reflecting it in setting the leveling member bias voltage.

  When the power supply is turned on and started, the voltage applied to the leveling member is set to an initial set value that has been set in advance (S1).

  Next, in S2, a test pattern including a continuous non-image portion (continuous white portion) having a sufficient length and an image portion (black portion) formed thereafter is printed on the image carrier.

  In step S3, the development layer toner layer after the continuous white portion development and the development residual toner layer after the black portion development in the test pattern are respectively detected by the toner layer detecting means. The detection result is temporarily stored in the RAM.

  In S4, the appropriate value V1 of the voltage applied to the leveling member is calculated based on the detection result detected in S3.

  In S5, the leveling member bias voltage applied at the time of test pattern printing is compared with the leveling member bias voltage V1 calculated in S4.

  If they are different, the setting of the voltage applied to the leveling member in S6 is reset to the appropriate value V1 of the bias voltage calculated in S4, and the process proceeds to S7.

  In S7, based on a command from the user, a printing operation is performed with a preset number of sheets, span of time, and the like.

  At every constant span, at S8, it is checked whether or not the preset equalizing member bias adjustment timing has been reached. If not, the routine returns to S7 to continue the printing operation.

  If the leveling member bias adjustment timing has been reached, the process returns to S2 in order to adjust the leveling member bias voltage again.

(Third embodiment)
(Configuration and operation different from the first and second embodiments)
A third embodiment of the present invention will be described.

  The configuration of the developing device used in this embodiment is the same as that used in FIG. 1 (first embodiment) or FIG. 8 (second embodiment). Members having the same functions as those in FIG. 1 or FIG. 8 are given the same reference numerals as those in FIG. 1 and FIG.

  In the following description, the polarity of the toner is described as minus, but the plus toner can be considered in the same way by reversing the direction of the bias, and the scope of the present invention is not limited to minus toner. Absent.

  Since the image portion ratio (printing ratio) is generally low in an image that is generally printed with an electrophotographic image such as an office document output application, the configuration with the image portion ratio in mind has been described so far. However, in the case where the present invention is used for graphic applications or the like, an application in which a relatively large number of images with a high image ratio (printing ratio) are output can be considered. In such a case, an embodiment in which the voltage applied to the leveling member is controlled in accordance with the image portion ratio as described below is effective.

<Applied voltage setting control of leveling member>
This will be described with reference to FIG. FIG. 12 is a schematic diagram showing that the appropriate setting of the voltage applied to the leveling member differs according to the image portion ratio.

  In an image with a high image portion ratio, the ratio of the black rear portion with a small amount of toner in the undeveloped residual toner layer increases, so the amount of toner collected from the white rear toner layer to the leveling member decreases, and is always on the leveling member. It becomes impossible to maintain the toner amount at which the surface potential of the toner carrier after the non-image portion is repeated. Therefore, it is important to efficiently supply the collected toner to the black toner carrier.

  As shown in FIG. 12A, if the voltage Vd applied to the leveling member is set improperly, the toner Vtd on the leveling member cannot be supplied to all areas after black, and the voltage from the leveling member The maximum contrast Ct is eventually increased in the portion where the toner supply could not be received and the portion after the white even though the leveling member was attached.

  For this reason, as shown in FIG. 12B, the voltage Vd applied to the leveling member is slightly closer to the toner carrier applied voltage Vb so that the toner Vtd recovered on the leveling member after whitening spreads over the entire area after black. Must be set.

  On the other hand, when it is determined that the image has a low image portion ratio, the voltage of the leveling member may be controlled based on the method described in the first or second embodiment.

<Setting flow of leveling member bias voltage according to image portion ratio>
Hereinafter, a method for controlling the leveling member bias voltage Vd will be described with reference to FIGS.

  FIG. 13 shows a circuit (voltage control means) for controlling the leveling member applied voltage according to the image portion ratio. 9 is different from FIG. 9 in that an image portion ratio calculating means 33 for receiving an image data input portion and calculating an image portion ratio (print ratio) is provided.

  FIG. 14 is a flowchart showing a procedure for setting the leveling member bias voltage Vd in accordance with the image portion ratio.

  When the image data is input in S11 after the power is turned on and started, the image portion ratio of the image data is calculated by the image portion ratio calculating means in S12.

  Next, in S13, based on the image portion ratio calculated in S12, an appropriate value V1 of the voltage Vd applied to the leveling member is calculated by the calculation unit.

  In S14, the leveling member bias voltage applied during the previous printing is compared with the leveling member bias voltage V1 calculated in S13. If both are the same, the process proceeds to S16.

  If the two are different, the setting of the voltage applied to the leveling member in S15 is reset to the appropriate value V1 of the bias voltage calculated in S13, and the process proceeds to S16 to perform the actual printing operation.

  When the printing operation for a certain period (for example, for each page) is completed, the process returns to input of the next image data.

  The above describes the method of controlling the leveling member voltage based on the ratio of the image portion for a certain period, for example, for each page. However, by further shortening this period, the appropriate leveling member voltage can be accurately and accurately set for each period. Can be set, and the effect of the present invention is enhanced.

  A configuration in which this idea is further advanced and the voltage of the leveling member is continuously controlled is also possible as an embodiment of the present invention. In addition, the third embodiment can be configured by combining the method of the second embodiment in which the toner layer detection unit is provided and controlled according to the detection result.

  As described above, according to the developing device and the image forming apparatus according to the embodiment of the present invention, in the hybrid developing system, the toner having the leveling member for leveling the development residual toner on the surface of the toner carrier is provided. A voltage located between the voltage applied to the carrier and the voltage applied to the developer carrier is applied to the leveling member.

  This makes it possible to reduce the contrast of undeveloped toner and suppress the development history (ghost), and to form a high-quality image over a long period without causing unnecessary deterioration of the developer. Can do.

  In addition, the above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Developing device 3 Charging member 4 Transfer roller 5 Cleaning blade 6 Exposure device 7 Toner carrier 12 Leveling member 13 Developer carrier 23 Developer 24 Developer carrier bias power source 25 Toner carrier bias power source 26 Leveler Bias member bias power supply 27 Toner layer detection means 31 Leveling member bias control circuit 32 Toner layer detection means control circuit 33 Image portion ratio calculation means 35 Calculation section

Claims (7)

A toner carrier that carries and conveys toner on the surface and develops the electrostatic latent image formed on the opposite image carrier with the toner;
A toner carrier bias power source for applying a voltage to the toner carrier to provide the toner for development;
A developer carrying body that carries and conveys a developer composed of toner and a carrier on the surface and supplies the toner in the developer to the toner carrying body facing the surface;
In a developing device having a developer carrier bias power source for applying a voltage to the developer carrier to supply the toner,
A leveling member for leveling development residual toner on the surface of the toner carrier;
A leveling member bias power source for applying a voltage to the leveling member,
The leveling member is
On the downstream side in the rotation direction of the toner carrier from the facing portion of the toner carrier and the image carrier,
And the upstream side of the rotation direction of the toner carrier from the facing portion of the toner carrier and the developer carrier,
Arranged to face the toner carrier,
The voltage applied to the leveling member by the leveling member bias power source is:
A voltage applied to the toner carrier by the toner carrier bias power source;
The developing device, wherein the developing device is a voltage positioned between the developer carrier bias power source and a voltage applied to the developer carrier. The voltage applied to the leveling member by the leveling member bias power source is:
A voltage applied to the toner carrier by the toner carrier bias power source;
The developing device according to claim 1, wherein the developing device has a voltage intermediate to a voltage applied to the developer carrying member by the developer carrying member bias power source. Toner layer detecting means for detecting the amount of toner in the toner layer on the toner carrier;
The developing device according to claim 1, further comprising: a voltage control unit that controls a voltage applied to the leveling member by the leveling member bias power source based on a detection result of the toner layer detection unit. apparatus. The developing device according to claim 1, further comprising a voltage control unit that controls a voltage applied to the leveling member by the leveling member bias power source based on a print ratio of image data to be output. An image forming apparatus comprising: an image carrier; and a developing device that develops the electrostatic latent image formed on the image carrier with toner,
The image forming apparatus according to claim 1, wherein the developing device is the developing device according to claim 1. An image forming apparatus comprising the developing device according to claim 1,
Toner layer detecting means for detecting the amount of toner in the toner layer on the toner carrier;
An image forming apparatus comprising: a voltage control unit that controls a voltage applied to the leveling member by the leveling member bias power source based on a detection result of the toner layer detection unit. An image forming apparatus comprising the developing device according to claim 1,
An image forming apparatus comprising voltage control means for controlling a voltage applied to the leveling member by the leveling member bias power source based on a printing ratio of image data to be output.

Images