Abstract: A magnetic roller for image developing of a printer and having a roller body made of rubber, plastic, or artificial resin mixed with magnetic materials and formed as unity, and a plurality of S magnetic poles and N magnetic poles, which are formed in the outer circle of the roller body as a unity.

Abstract: An image forming apparatus includes plural toner image forming devices. Each of which has a rotating photoconductor, a charging device that uniformly charges a surface of the photoconductor, a latent image forming device that forms an electrostatic latent image on the surface of the charged photoconductor, a developing device that develops the electrostatic latent image on the surface of the photoconductor to a toner image, and a developing container that contains toner used by the developing device. A diameter of the photoconductor of at least one toner image forming device is formed larger than a diameter of the photoconductor of the other toner image forming devices. Each developing container of all the toner image forming devices is formed in equal-sized, and a center of rotation of a developing roll of each developing device is arranged in a position upper than a center of rotation of each photoconductor.

Abstract: A developing method of the present invention develops a latent image formed on an image carrier with a two-ingredient type developer, which consists of toner grains and carrier grains retaining the toner grains thereon, deposited on a developer carrier in the form of brush chains. Assume that the brush chains on the developer carrier has a height of h as measured at a zero field point where the magnetic field formed by a main magnet is zero, and that a gap for development that is the shortest distance between the developer carrier and the image carrier is a, then a and h are equal to each other. Image quality is estimated by varying the combination of an angle ? between the gap and the zero field point, the outside diameter of the image carrier and the outside diameter of the developer carrier and the height h. A desirable or an optimum range of the results of estimation are selected to set various conditions.

Abstract: A developing device for developing a latent image formed on an image carrier of the present invention includes a rotatable, nonmagnetic developer carrier, and a magnetic field generating member for generating a magnetic field in a developing zone where the developer carrier faces the image carrier. The magnetic field generated causes a developer deposited on the developer carrier to rise in the form of a magnet brush. A magnetic pole for development is located upstream of a position where the developer carrier and image carrier are closest to each other in a direction of rotation. A magnetic force, as measured on the surface of the developer carrier, increases from the position of the magnetic pole toward a position where the magnet brush finally leaves the image carrier.

Abstract: The invention relates generally to processes for electrographic image development. An electrographic development apparatus is provided wherein a film is adjacent a cylindrical toning shell and a mixture of toner and carrier is particles disposed on the cylindrical toning shell in contact with the film. The cylindrical toning shell is closest to the film at a first location, the mixture of toner and carrier particles being movable through the first location with a flow direction. A magnetic core disposed within the cylindrical toning shell offset toward the cylindrical shell such that a magnetic field strength is greater at the second location than the first location.

Abstract: The toner of the present invention is suitably used in SLIC development system where a liner velocity of a developer-bearing member is 150 to 500 cm/sec. The toner has resin particles containing at least a coloring agent, and a charge controlling agent fine articles, and a ratio M/T of the amount M (% by weight) of an element in the surface of toner particles as determined by X-ray photoelectron spectroscopy (XPS) to the amount T (% by weight) of the element in the entire toner particles of 20 to 500, which element is present only in a charge control agent among components of the toner and is an element belonging to one of the first, second, third, fourth, and fifth periods of the long form of periodic table of elements except hydrogen, carbon, oxygen, and rare gas elements.

Abstract: A developing device having a first developing sleeve for supplying developing agent to the first developing area A, and a second developing sleeve for supplying developing agent, handed from the first developing sleeve, to a second developing area B, the surfaces of the first developing sleeve and the second developing sleeve are subjected to roughening such that the average inter-peak distances thereof differ between the first developing sleeve and the second developing sleeve. This prevents fusion of toner due to toner particles becoming embedded in recesses of course formations on the surface of the developing sleeves, resulting in extensive usage periods yielding high image quality.

Abstract: A developer carrier for an SLIC developing system includes a developing sleeve and a magnetic roll having a plurality of magnetic poles. A narrow development nip is formed by narrowing the width of a development pole forming a magnet brush and by narrowing a developer rising region in a developing region where a flux density attenuation ratio of the development pole is 40% or more. A half-value width of the flux density of the development pole is 22° or less and the flux density variation rate is 4.0 mT/Deg or more in a circumferential direction in a part where the flux density in at least half of that of a downstream side of a developer carrying direction from a peak magnetic force position of the development pole is 90% or less.

Abstract: A developing method and apparatus of the present invention develops a latent image formed on an image carrier with a two-ingredient type developer, which consists of toner grain and carrier grains, deposited on a developer carrier in the form of a brush. A distance L between a zero field point at which the magnetic field of a main magnet is zero and the image carrier is 4 mm or smaller.

Abstract: A developing apparatus for developing an electrostatic image formed on an image bearing member includes a first developer bearing member for bearing magnetic developer to transport it to a first developing portion, a first magnetic field generator stationarily provided in the first developer bearing member, a second developer bearing member for bearing magnetic developer to transport it to a second developing portion, and a second magnetic field generator stationarily provided in the second developer bearing member. The first developer bearing member and the second developer bearing member supply the magnetic developer to the electrostatic image on the image bearing member in the mentioned order. In addition, a peak value of a normal line direction component of a magnetic force generated in the vicinity of the second developing portion is greater than a peak value of a normal line direction component of a magnetic force generated in the vicinity of the first developing portion.

Abstract: A device (100) for the transport of particles (30), in particular development particles (30) with a first magnetic roller (11) and a second magnetic roller (22) , in which the first magnetic roller (11) and the second magnetic roller (22) form a gap, and with a photographic element (1) for the particles (30), which moves through the gap, while the magnetic rollers (11, 22) turn in the same direction.

Abstract: An electrophotographic image forming apparatus of the present invention frees images from various defects including the thinning of horizontal lines, the omission of the trailing edge of an image, background contamination, granularity particular to a halftone image, carrier scattering, and image noise. Further, the apparatus of the present invention solves problems ascribable to patches used to sense image density. Moreover, the apparatus of the present invention faithfully reproduces tonality and has a high developing ability.

Abstract: A developing apparatus includes a developer container containing a magnetic developer including a toner and a wax contained in the toner. First and second developer carrying members are rotatably provided in the developer container, for carrying the magnetic developer. A regulation member regulates a thickness of a layer of the magnetic developer carried on the first developer carrying member. A first magnet has a first magnetic pole disposed opposite to the second developer carrying member and a second magnetic pole, which is a subsequent magnetic pole, dispose downstream from the first magnetic pole in a rotation direction of the first developer carrying member and having a polarity identical to a polarity of the first magnetic pole. A second magnet has a third magnetic pole, which has a polarity opposite to a polarity of the first magnetic pole, is disposed opposite to the first developer carrying member.

Abstract: An image forming apparatus including a cleaning device for removing toner, paper dust and other impurities left on an image carrier after image transfer with a cleaning member is disclosed. The cleaning member contacts the surface of the image carrier with variable pressure and remains, about the time when the image carrier stops moving after image formation, in contact with the surface with pressure lower than pressure capable of scrapping off the impurities. Before movement for image formation, the image carrier is driven in a reverse direction opposite to a forward direction assigned to image formation, stopped, and again moved in the forward direction and then in the reverse direction at least one time.

Abstract: Apparatus and methods for electrographic image development, wherein the image development process is optimized by subjecting the developer to magnetic field maxima, thereby imparting to the developer a velocity component in a direction perpendicular to the process direction, ensuring that the toner particles thus accelerated have sufficient kinetic energy to overcome the binding energy binding the toner particles to the carrier particles in the developer, and to be deposited on a receiver bearing an electrostatic latent image. The optimized image is developed to completion, where development to completion is characterized by a proportionality between the cube of the toner charge to mass ratio and a quantity consisting of the magnitude of the voltage of the toning shell minus the magnitude of the voltage of the toned image.

Abstract: A method for developing an electrostatic latent image, including forming a magnet brush of a developer including a toner and a carrier on a developing sleeve including a main magnet and auxiliary magnets; and developing the electrostatic latent image with the magnet brush to form a toner image at a rubbing region, wherein the magnetic flux density in a normal line direction, half width, and attenuation ratio of the main magnet and the angle between the main magnet and auxiliary magnets are specified, and the magnetic sleeve has specific grooves thereon, and wherein the toner has a volume average particle diameter of from 4.0 to 7.0 ?m, and includes fine particles having a circle equivalent diameter not greater than 2 ?m in an amount not greater than 20% by number.

Abstract: In a developing device having a developing zone where an image carrier and a developer carrier face each other, the developer carrier carrying a developer thereon moves at a linear velocity of 150 mm/sec or above, but below 500 mm/sec. The amount of the developer conveyed to the developing zone by the developer carrier is between 65 mg/cm2 and 95 mg/cm2. A magnetic flux generated on the developer carrier in the developing zone by a magnetic pole has a flux density having an attenuation ratio of 40% in the direction normal to the developer carrier. The flux density in the direction normal to the developer carrier, as measured on the surface of the developer carrier, is between 100 mT and 200 mT. Magnetic grains, which constitute the developer together with toner grains, have a saturation magnetization value of 40×10?7×4 ?Wb·m/kg or above, but below 50×10?7×4 ?Wb·m/kg.

Abstract: A composition for synthetic resin magnets (such as magnet rollers for electrophotography process) which is composed of a resin binder and a magnetic powder mixed and dispersed therein. The resin compound has improved melt flow rate because the binder contains a thermoplastic and an aliphatic polyamide. Owing to its improved melt flow rate, the resin compound can be incorporated with a large amount of magnetic powder without deterioration in moldability. Thus the resulting plastic magnet has a strong magnetic force. In addition, the composition for synthetic resin magnets may be incorporated with a hindered phenol antioxidant, so that it is molded at a higher temperature (120-180° C.) than usual to achieve the same object as mentioned above.

Abstract: A position where a transport amount regulation member is opposed to a developing roller is in an area wherein the magnetic flux density in the tangent line direction becomes 95% or less of the maximum value upstream in the developer transport direction from the position at which the magnetic flux density in the normal direction formed by two magnetic poles on both sides of the transport amount regulation member on the sleeve roller surface of the developing roller becomes 0 gausses and is in an area wherein the magnetic flux density in the normal direction becomes 90% or less of the maximum value of the upstream pole in the developer transport direction.

Abstract: A developing device developing a latent image on a latent image carrier with a developer, and including a casing having an opening facing the latent image carrier and a developer carrier. Also included is a magnetic field generating device including a first magnetic pole generating a magnetic field causing the developer to rise on the developer carrier in a form of a magnet brush in a developing region, and a second magnetic pole generating a magnetic field at a downstream side of the first magnetic pole in a rotating direction of the developer carrier. Further, a toner-scattering restraining device is provided on an end portion of the casing at the downstream side of the developing region, and a magnetic member provided on a side of the toner-scattering restraining device facing the latent image carrier. A peak of a magnetic flux density set by the second magnetic pole in its normal direction is located outside of the opening.

Abstract: The present invention is directed to layered magnets, magnetic rolls made therefrom, methods for increasing the magnetic field strength of a ferritic magnet, methods for increasing the magnetic field strength of a magnetic roll, methods for increasing the magnetic field uniformity of a rare earth magnet, and methods for increasing the magnetic field uniformity of a magnetic roll. Layered magnets include a rare earth magnet having a magnetic field, and superposed upon the rare earth magnet, a layer of ferritic magnet bonded thereto. Layered magnets exhibit greater magnetic field strength and a substantially more uniform magnetic field.

Abstract: A developing unit includes a developer containing unit that contains developer, a developer carrier that has a moving surface, and carries the developer, a magnetic force generator that attracts the developer onto the moving surface by a magnetic force generated from a plurality of magnets, and a restricting member that restricts a layer thickness of the developer. The magnets includes a restricting magnet arranged closest to the restricting member and has a restricting magnetic pole of which a first surface toward the moving surface and a second surface toward an upstream adjacent magnet that is arranged so as to be adjacent to an upstream side of the developer carrier in a direction of movement of the moving surface and has an upstream adjacent magnetic pole form a ridged corner portion, and the ridged corner portion is chamfered.

Abstract: The long magnet includes a magnet block made of a mixture of rare earth magnetic powder, thermoplastic resin particles, fluidity additive, pigment, wax and charge control agent, and a reinforcing member to reinforce the magnet block. At least part of the reinforcing member is arranged inside of the magnet block.

Abstract: A developer carrier used for an SLIC developing system. Characteristic values contributing to provide high image quality, which cannot be covered by the stipulations of the attenuation ratio and half-value width of the flux density are clarified. The developer carrier is constituted to be composed of the developing sleeve for carrying and transporting the developer, and a magnetic roll disposed in the developing sleeve, having a plurality of magnetic poles P1-P5. A narrow nip for development is realized by narrowing the width of the pole for development P1 forming the magnet brush by raising the developer in the developing region facing the latent image carrier, and by narrowing the rising region of the developer in the developing region and the flux density attenuation ratio of the pole for development P1 is 40% or more. The half-value width of the flux density of the pole for development P1 is 22% or less, and the flux density variation rate is 4.

Abstract: An image forming apparatus develops a latent image formed on an image carrier with a developer that forms a magnet brush on a developer carrier. The developer carrier is made up of a sleeve and a stationary magnet roller accommodated in the sleeve. The magnet roller includes a main pole for causing the developer to form the magnet brush and auxiliary poles for helping the main pole exert a magnetic force. An electric field including an oscillation component is formed between the image carrier and the developer carrier. A particular ratio is set up between a distance between the image carrier and the developer carrier, as measured at the boundary of a nip, and the shortest distance between them, between the above shortest distance and the shortest distance between the developer carrier and a metering member, or between the shortest distance between the image carrier and the developer carrier and the amount of developer scooped up to the image carrier.

Abstract: An image forming method including providing a developer including a toner and a magnetic carrier, a developer carrier configured to convey the developer deposited thereon, and magnetic field generating means fixed within the developer carrier, and forming a magnetic field which forms a magnet brush between the image carrier and the developer carrier such that the magnet brush rises, contacts the image carrier and collapses within a range in which the magnetic field is more intense than an electric field capable of separating the toner and the magnetic carrier from each other by using the magnetic field generating means. The magnetic brush rubs the image carrier to thereby develop a latent image formed on the image carrier.

Abstract: An image forming apparatus of the present invention includes a developing device including a sleeve and a magnet roller fixedly accommodated in the sleeve. The magnet roller includes a main magnetic pole and an auxiliary magnetic pole adjoining it at a downstream side in the direction of rotation of the sleeve. A magnetic collection pole is positioned on the edge of an opening formed in a casing and facing a photoconductive drum. The collection pole forms a magnetic field that prevents a developer falling away from the sleeve from escaping the developing device via the opening.

Abstract: A developing apparatus of an electric photographic printer supplying a two-element developing agent to develop an electrostatic latent image formed on a photosensitive medium includes: a housing; a developing agent supplying roller; a developing agent mixing roller; a developing sleeve to transfer mixed developing agent to the photosensitive medium through a developing area formed between the developing sleeve and the photosensitive medium; a fixing magnet disposed inside of the developing sleeve to have a plurality of magnetic poles arranged from the developing area in a circular direction about a center of the fixing magnet; and a magnetic bar disposed on an inside surface of the housing to face one of the magnetic poles of the fixing magnet through the developing sleeve to form a magnetic force brush preventing the developing agent from being scattered as the developing agent passes through the developing area.

Abstract: A developing device of the present invention includes stationary layer angle setting means. Assume that a developer layer, staying at a position upstream of a metering member in a direction in which a developer carrier conveys a developer, consists of a stationary layer in which the developer is not replaced and a flowing layer in which it is replaced, that an angle between, as seen from the axis of the developer carrier, the upstream edge portion, in the above direction, of the end portion of the metering member, which faces the developer carrier, and a position where the end of the stationary layer upstream of, but remote from the edge portion, is located is &thgr;d, and that an angle between, as seen from the above axis, the edge portion and a position where a magnetic pole is positioned just upstream of a doctor pole in the above direction is &thgr;1. Then, the angle &thgr;d lies in a preselected range relative to the angle &thgr;1.

Abstract: An electrographic development machine that utilizes magnetic toner particles includes a dielectric film member for carrying an electrostatic image thereon. A toner roller is disposed upon a first side of the dielectric film member. The toner roller has a core and an outer shell. The core includes a plurality of toner roller magnets, each of which have a respective north and south pole. The toner roller magnets are disposed such that adjacent pairs thereof have poles of opposite polarity disposed proximate the shell. The toner roller provides the dielectric film member with a supply of developer material. The machine further includes means for altering or balancing the magnetic forces acting on the developer.

Abstract: A process for preparing a magnet roller comprising a plurality of bar-like magnet pieces in a high working efficiency and in an improved adhesion accuracy, which comprises the steps of regulating the bonding position of at least two magnet pieces by their outer peripheral surfaces and their end surfaces, applying an adhesive from the inner surface side of the magnet pieces to the adhesion faces of the magnet pieces for bonding one magnet piece to another magnet piece to form a magnet block, and bonding and fixing the magnet block to a shaft. At least one of the adhesion faces which are in contact with each other may have a plurality of grooves to facilitate penetration of the adhesive into the interface of adjacent two magnet pieces.

Abstract: A development system optimized for efficient development of an electrostatic latent image on an imaging surface. The development system includes a development material sump, a magnetic developer roll including a rotatable sleeve having located therein a rotatable magnetic core, and a developer material delivery system for providing a metered supply of developer material to the rotatable sleeve. One or more stationary magnetic shunts are located with respect to the magnetic core, sleeve, and/or developer material delivery system so as to block the magnetic field effective for attracting developer material to the sleeve, thus allowing disengagement of the developer material therefrom at a drop-off zone.

Abstract: In a developing device including a plurality of developing sections each including a developer carrier that causes a developer deposited thereon to form a magnet brush and contact an image carrier, the developer carrier including: a rotatable nonmagnetic sleeve; and a stationary magnet roller accommodated in the sleeve and including a magnetic pole for scooping up the developer to the sleeve, a magnetic pole for conveying the developer deposited on the sleeve, and a main magnetic pole for causing the developer to rise on the sleeve in a form of the magnet brush. The plurality of developing sections include at least one developing section in which a flux density of the main magnetic pole in a normal direction has an attenuation ratio of 40% or above and at least one developing section in which said flux density has an attenuation ratio of 30% or below.

Abstract: An image forming apparatus of the present invention includes a lubricator for applying a lubricant to an image carrier or a process unit around the image carrier to thereby reduce friction. The apparatus of the present invention insures a uniform halftone image, prevents the trailing edge of an image from being lost, and faithfully reproduces even a horizontal line.

Abstract: The invention relates generally to processes for electrostatic image development, and setpoints that provide uniform image development. In particular, an apparatus and process having a magnetic brush that implements a rotating magnetic core within a shell is disclosed. The process implements one or more of the following optimum setpoints: a range of shell surface speeds that provide uniform toning density, a range of shell surface speeds that prevent toner plate-out, a skive spacing that minimizes sensitivity to variation, a magnetic core speed that minimizes sensitivity to variation, and an imaging member spacing that minimizes sensitivity to variation.

Abstract: A magnetic core includes an array of permanent magnets bonded to a cylindrical core. The magnets are formed of an extruded magnetic composite material containing a neodymium-boron-iron alloy. The magnetic core contains regions of alternating magnetic polarization arranged to create a multipole structure. Such extruded magnets easily constructed at low cost and offer close magnetic pole spacing with little or negligible surface discontinuity.

Abstract: A developing device of the present invention includes a developing roller provided with a plurality of magnetic poles. The magnetic poles include a main pole and two auxiliary poles positioned at both sides of the main pole for helping the main pole form a magnetic force. The auxiliary poles reduce the half width of the main pole. An AC-biased DC bias for development is applied to the developing roller and disturbs carrier grains close to the developing roller. Images free from various defects including granularity and local omission are achievable with the developing device.

Abstract: In a magnet brush type developing method of the present invention, at least one position where brush chains formed by magnetic carrier grains rise exists in a portion where an electric field formed between a facing zone where an image carrier and a developer carrier face each other has a strength E (V/m) expressed as:

Abstract: A method for developing an electrostatic latent image, including forming a magnet brush of a developer including a toner and a carrier on a developing sleeve including a main magnet and auxiliary magnets; and developing the electrostatic latent image with the magnet brush to form a toner image at a rubbing region, wherein the magnetic flux density in a normal line direction, half width, and attenuation ratio of the main magnet and the angle between the main magnet and auxiliary magnets are specified, and the magnetic sleeve has specific grooves thereon, and wherein the toner has a volume average particle diameter of from 4.0 to 7.0 &mgr;m, and includes fine particles having a circle equivalent diameter not greater than 2 &mgr;m in an amount not greater than 20% by number.

Abstract: An electrophotographic image forming apparatus of the present invention frees images from various defects including the thinning of horizontal lines, the omission of the trailing edge an image, background contamination, granularity particular to a halftone image, carrier scattering, and image noise. Further, the apparatus of the present invention solves problems ascribable to patches used to sense image density. Moreover, the apparatus of the present invention faithfully reproduces tonality and has a high developing ability.

Abstract: In an image forming apparatus, a magnet brush forming device includes at least a first magnetic pole facing an image carrier carrying a latent image and a second magnetic pole positioned downstream of the first magnetic pole in the direction of rotation of a developer carrier. When a magnet brush formed on a developer carrier by the first magnetic pole forms a nip between it and the image carrier, flux density in the direction normal to the developer carrier has an attenuation ratio of 40% or above. The second magnetic pole has an upstream half-value point located downstream of a point upstream of and angularly spaced from the edge of a developer storing member by 15°. Flux density in the normal direction and flux density in the tangential direction between the first and second magnetic poles have vectors the sum of which is 85 mT or above.

Abstract: An image forming apparatus in which the flux density of a main magnetic pole for development has an attenuation ratio of 40% or above in the normal direction is disclosed. Assume that a period of time of T1 is necessary for a photoconductive element to move by a single dot at a nip for development. Also, assume that, in a single period of an alternating electric field applied to a developing sleeve as a bias, the duration of an electric field causing toner to move toward the photoconductive element is T2. Further, assume that the duration of an electric field causing the toner to move toward the sleeve is T3. Then, a relation of T1>T2>0 or a relation of T1>T3>0 holds.

Abstract: A magnetic core includes an array of permanent magnets bonded to a cylindrical core. The magnets are formed of an extruded magnetic composite material containing a neodymium-boron-iron alloy. The magnetic core contains regions of alternating magnetic polarization arranged to create a multipole structure. Such extruded magnets easily constructed at low cost and offer close magnetic pole spacing with little or negligible surface discontinuity.

Abstract: A development system optimized for localized agitation of developer material proximate to and within a development zone so as to provide cleaner and more efficient development of an electrostatic latent image on an imaging surface. The development system includes a development material sump, a magnetic developer roll including a rotatable sleeve having located therein an offset rotatable magnetic core, and a developer material delivery system for providing a metered supply of developer material. One or more stationary magnets located within the sleeve provide a static magnetic field pattern effective for attracting developer material to the sleeve and for aiding transport of the developer material therefrom to the development zone.

Abstract: A developing device for an image forming apparatus of the present invention includes a developing roller made up of a sleeve and a magnet roller and a doctor facing the surface of the sleeve. The edge of the doctor faces the sleeve at a particular position selected to stabilize the amount of a developer to be scooped up, protect the developer from deterioration, and allow an adequate amount of charge to deposit on the developer by friction.

Abstract: An image forming apparatus of the present invention includes a developing device of the type causing a developer to form a magnet brush on the surface of a developer carrier in a developing region or nip for development. The magnet brush contacts and thereby develops a latent image formed on an image carrier. The apparatus of the present invention increases image density and faithfully reproduces even low-contrast images with a low-cost configuration. Further, the apparatus reduces image defects, including granularity and the omission of the trailing edge of an image, even if the range over which the magnet brush and image carrier contact is reduced.

Abstract: A developing device includes a developing container for accommodating a developer containing magnetic toner; first and second developer carrying members for carrying the developer from inside of the developing container toward an image bearing member by rotations thereof in the same rotational directions, wherein the developer is fed by the first developer carrying member to a latent image upper formed the image bearing member and then is fed by the second developer carrying member; and first and second magnetic field generation members provided in the first and second developer carrying member, for generating magnetic fields, wherein the first magnetic field has a first magnetic pole disposed at a position substantially opposed to the image bearing member, and a second magnetic pole disposed at a position substantially opposite the second developer carrying member and having a polarity opposite the first magnetic pole, the second magnetic field generation member has a third magnetic pole disposed at a positi

Abstract: An image forming apparatus is provided for obtaining excellent developing properties using toner with small particle diameters and for forming high-quality visual images. In a developing device of an image forming apparatus, a two-component developer is used which satisfies conditions that volume mean particle diameter dt of a toner is 3˜5 &mgr;m (Condition 1), volume mean particle diameter dc of a carrier is 5 dt˜10 dt (Condition 2), and a weight ratio Rw of the toner and the carrier is 1.6 (dt/dc) ×(&rgr;t/&rgr;c)˜2.4 (dt/dc)×(&rgr;t/&rgr;c) (Condition 3, where &rgr;t and &rgr;c are density of the toner and the carrier, respectively). A main magnetic pole M of a rotary sleeve is arranged in the vicinity of the closest position of the rotary sleeve and an image forming body, and the closest distance D between the rotary sleeve and the image forming body satisfies a condition that D is 0.5 H˜0.8 H for the free tip height H of a magnetic brush B of the main magnetic pole M.

Abstract: In a developing device according to the present invention, a developing roller 8 has a fixed shaft 12 and a sleeve 13. The length of a draw-up magnetic pole N3 provided in the fixed shaft 12 is made shorter than the length of a main magnetic pole N1. Accordingly, the amount of a developer adhering to both ends of an outer peripheral surface of the sleeve 13 is reduced, so that the density of the developer at both the ends of the sleeve 13 is maintained in suitable conditions in a state where the developer is over the main magnetic pole N1.

Abstract: A developing device includes a developing container for containing therein a developer provided with a carrier and a toner, a conveying device for conveying the developer in the developing container, a developer bearing member for bearing thereon the developer conveyed by the conveying device, the developer bearing member conveying the developer to a developing portion for developing a latent image formed on an image bearing member, a magnetic field generating device provided in the developer bearing member for generating a magnetic field, the magnetic field generating device being provided with a first magnetic pole and a second magnetic pole provided so as to be adjacent to the downstream side of the first magnetic pole in the direction of rotation of the developer bearing member and having the same polarity as the first magnetic pole, and a regulating device for regulating the layer thickness of the developer on the developer bearing member at a location substantially opposed to the second magnetic pole.