Abstract: There are disclosed a magnet roller which includes a magnet main body portion and a shaft portion, wherein the magnet main body portion includes a composition for magnets and has at least one hollow portion in the inside thereof; a process for producing a magnet roller having a magnet main body portion and a shaft portion, which includes arranging in advance, at least one member for forming a hollow portion in a cavity of a mold which has generated a magnetic field on the circumference of the cavity, pouring a composition for magnets into the mold, and thereafter withdrawing the member for forming the hollow portion so that at least one hollow portion is formed in the inside of the magnet roller; and a developing unit which includes a developing roller constituted of a sleeve installed in a freely rotatable manner and the above magnet roller installed inside the sleeve.

Abstract: A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, the process cartridge includes an electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on the photosensitive drum; a magnet disposed inn the developing roller; a drum frame supporting the photosensitive drum; a developing device frame supporting the developing roller and the magnet; an engaging member mounted to one longitudinal end of the developing device frame in engagement with one end of the developing roller and with one end of the magnet, the engaging member is provided with a projected portion at an opposite end from the end where it is in engagement with one end of the developing roller and one end of the magnet; an elastic member urging the projected portion by its elastic force so as to urge the developing roller to the photosensitive drum.

Abstract: A ferrite powder for bonded magnets having a substantially magnetoplumbite-type crystal structure and an average diameter of 0.9-2 &mgr;m, the ferrite powder having a basic composition represented by the following general formula: (A1-xRx)O.n[(Fe1-yMy)2O3] by atomic ratio, wherein A is Sr and/or Ba; R is at least one of rare earth elements including Y, La being indispensable; M is at least one element selected from the group consisting of Co, Mn, Ni and Zn; and x, y and n are numbers meeting the conditions of 0.01≦x≦0.4, [x/(2.6n)]≦y≦[x/(1.6n)], and 5≦n≦6, (Si+Ca) being 0.2 weight % or less, and (Al+Cr) being 0.13 weight % or less, can be produced by mixing iron oxide containing 0.06 weight % or less of (Si+Ca) and 0.

Abstract: The present invention provides a developing apparatus which has a developer carrying member opposed to an image bearing member for bearing a latent image and adapted to carry magnetic developer, a magnet provided within the developer carrying member and having one end secured to a frame of the apparatus, and a bearing fitted on other end of the magnet and adapted to rotatably support the developer carrying member, wherein a fitting portion between the magnet and the bearing has a non-circular shape.

Abstract: When the structure is arranged such that one of the repulsion poles is used as a developer layer thickness regulation pole, screw pitch-shaped density unevenness occurred at the rear end of a solid black image.

Abstract: An image forming apparatus of the present invention includes a developing roller accommodating a magnet roller therein. The magnet roller includes a main pole forming a magnetic flux whose attenuation ratio is 40% or above in the direction normal to the developing roller. The axis A of the developer carrier, the axis B of the image carrier and the peak C of the magnetic force of the main pole in the above direction are positioned such that an angle between a line AB and a line AC is substantially zero degree.

Abstract: An image forming apparatus of the present invention includes a developing device including two developing rollers arranged in parallel in a direction in which an image carrier moves each for forming a magnet brush thereon. The magnetic poles of the developing rollers for effecting hand-over of a developer between the rollers are provided with the same polarity. An optical writing device optically writes an image on the image carrier in accordance with tonality data of four levels or less for a single dot. The developing device prevents the developer from moving through a gap between the developing rollers and bringing about irregular image density and background contamination. In addition, the optical writing device successfully obviates ghosts, which are likely to appear when a uniform halftone image including solid portions or bold characters is reproduced.

Abstract: An image forming apparatus comprises a charging member, an image bearing member and a developer bearing member. The charging member comprises a first magnetic field generating device, wherein a first magnetic field with a first magnetic pole closest to the image bearing member has a half-value width &agr;°. Measuring from a center of the charging member, an angle between a closest point of the image bearing member and a maximum magnetic flux density of the first magnetic pole is &thgr;c°. The developer bearing member comprises a second magnetic field generating device, wherein a second magnetic field with a second magnetic pole closest to the image bearing member has a half-value width &bgr;°. Measuring from a center of the developer bearing member, an angle between a closest point of the image bearing member and a maximum magnetic flux density of the second magnetic pole is &thgr;d°.

Abstract: A method for manufacturing a magnetic roll for use in an electrophotographic printing machine of the type having an electrostatic latent image recorded on a photoconductive member is provided. The method includes the steps of placing a shaft in a mold cavity and molding a core in the mold cavity with the shaft in the cavity. The core defines a pocket on the periphery of the core. The method further includes the step of attaching a magnet to the pocket.

Abstract: A developing roller is made up of a magnet member and a sleeve surrounding the magnet member. A sophisticated magnetic characteristic including a repulsive pole can be easily formed on the surface of the sleeve. The repulsive pole causes a developer to be sharply released from the surface of the sleeve. A developing device including the developing roller is also disclosed.

Abstract: A development system is which includes a developer roll with a magnetic sleeve. The sleeve has a static magnetic field pattern for transporting developer material to a development zone; and a magnetic system for generating a superimposed alternating magnetic field to agitate developer material in the development zone in order to produce a charged toner cloud intended for the non-interactive development of latent electrostatic images.

Abstract: An image forming method for improving developer recirculation capability within a developer unit includes the steps of magnetically adsorbing a developer having magnetism onto a developer carrier by the action of a magnetic field generated by a magnetic field generating member to form a magnetic lobe, regulating the amount of developer in the magnetic lobe in accompaniment with rotation of the developer carrier about a longitudinal central axis by a developer regulating member disposed in a developer carrier rotating angular region extending from a position of a normal magnetic flux density inflection point, at which a component of the magnetic field normal to the developer carrier becomes zero, to a position of a normal magnetic flux density peak, at which the component of the magnetic field normal to the developer carrier exhibits a maximum value, in a direction in which the developer carrier is rotated, and developing a latent image on an image carrier using the magnetic lobe having a regulated amount of d

Abstract: An image forming method for developing an electrostatic latent image on a moving image-bearing member with a magnetic developer and for removing the residual toner after transfer of a developed toner image onto a transfer member is described. The method includes providing a rotatable, cylindrical permanent magnet having a plurality of magnetic poles on the surface for supporting and conveying the magnetic developer directly on the magnet surface; forming an electrostatic latent image into a toner image by attracting and conveying a magnetic developer including a nonspherical magnetic toner obtained by a polymerization or a nonspherical magnetic or non-magnetic toner obtained by a polymerization and magnetic carriers; and removing the residual toner remaining on the image-bearing member after transferring this toner image by a cleaning blade. The method also includes a surface magnetic flux density ranging from 50 to 1200 G, and a value of h, defined as .pi.D.multidot.Vp/(M.multidot.

Abstract: A developing roller is made up of a magnet member and a sleeve surrounding the magnet member. A sophisticated magnetic characteristic including a repulsive pole can be easily formed on the surface of the sleeve. The repulsive pole causes a developer to be sharply released from the surface of the sleeve. A developing device including the developing roller is also disclosed.

Abstract: A developing apparatus includes a developer bearing member, a first magnetic pole and a second magnetic pole of a same polarity as that of the first magnetic pole, and a regulating member. A regulating portion of the regulating member is provided within a range from a point of the maximum magnetic flux density of the second magnetic pole and an angular point corresponding to a half of the half value width of the second magnetic pole at the downstream side in the rotating direction of the developer bearing member.

Abstract: An improved developer roll magnet for a toner cartridge provides a strip of magnetic material that extends axially along a surface of the developer roll magnet located coaxially within a developer roll sleeve. The strip of magnetic material can be seated within a groove in the magnet and can extend radially outwardly above the surface of the magnet. The strip is generally adhered to the magnet by mutual magnetic attraction and can be made adjustable to move toward and away from the developer roll sleeve. The strip is typically located adjacent a nip formed between the developer roll sleeve and the image transfer drum of the cartridge to provide enhanced toner release for greater print yield and quality.

Abstract: A developing apparatus includes a developing device having a first magnetic pole opposed to an image carrier on which an electrostatic latent image is formed, and a second magnetic pole of the developing device arranged at a predetermined angle to the first magnetic pole, for supplying the electrostatic latent image with a developing agent having toner and carrier, where the second magnetic pole is of one polarity.

Abstract: For realizing a satisfactory and stable developing process, the charge state of a developer and the density of toner particles contained in the developer is kept constant in the developing process. A developing roller to be driven rotationally is provided in a developing tank containing a developer. The developer is sucked magnetically using the magnetic force of a magnet provided in a developing sleeve composing the developing roller. The developer is then fed into a developing area opposed to a photosensitive member, then collected into the developing tank after the developing process is ended. The magnet is composed of an odd number of magnetic poles; developing pole, feeding pole, magnetic force distribution adjusting pole, developer sucking pole, developer separating pole, auxiliary collecting pole, and collecting pole. Between the sucking pole and the developing pole, an even number of poles are disposed. Between the developing pole and the separating pole are disposed an even number of poles.

Abstract: In a developing device for visualizing an electrostatic latent image using two-component developer containing toner and magnetic carrier, excellent development will be performed and deterioration of the developer will be prevented. A developer carrier opposite to an image carrier having an electrostatic latent image formed thereon is prepared by forming a thin layer of aluminum with a thickness of 3 .mu.m or less on the peripheral surface of a roll-shaped member made of ferrite, and the surface roughness Rz of the peripheral surface of the foregoing ferrite roll is set to 50 .mu.m or less. N-poles and S-poles are alternately magnetized at a 50-to-250-.mu.m pitch along the peripheral surface of this ferrite roll. These magnetic poles can be magnetized to have uniform intensity because the peripheral surface of the roll has been smoothly finished, and a developer layer having only substantially one layer of the carrier uniformly attracted is formed on the peripheral surface.

Abstract: A magnet roller capable of adjusting the height and position of a magnetic force peak after formation of a roller, and easily meeting a requirement to attain a complex magnetic force pattern without significantly increasing the cost. In the magnet roller, at least two kinds of first magnet pieces and second magnet pieces different from each other in orientation characteristic of magnetic powders are fixedly disposed around the outer periphery of a shaft. The first magnet pieces is a magnet piece in which anisotropic magnetic powders are oriented in such a manner to converge from both the side surfaces and the back surface to a specific position on the front surface side.

Abstract: A developing apparatus employing a three-pole stationary magnetic roller for use with a uni-component magnetic developer or toner. The apparatus includes a rotational sleeve which accommodates the stationary roller, a mixer disposed in a toner vessel for stirring the toner, and a toner layer thickness regulator disposed upstream in the sleeve rotation direction from the developing position at which the image on a photo-sensitive drum is developed. The magnetic roller has a developing pole located near the developing position, a blade-facing pole facing the toner layer thickness regulator, and a shield pole located downstream in the sleeve rotation direction from the developing position, where the blade-facing pole and the shield pole are of the opposite polarity to the developing pole. The blade-facing pole and the shield pole generate a repulsive magnetic field therebetween, where the toner that has been stirred in the vessel comes in contact with the sleeve.

Abstract: A development system is disclosed including a developer roll adapted for depositing developer material on an imaging surface having an electrostatic latent image thereon. The development system which includes a developer roll with a magnetic sleeve having a static magnetic field pattern for transporting developer material to a development zone. In operation the stationary magnetically patterned sleeve holds a thin well-defined blanket of magnetic developer on the sleeve surface. Magnetic assembly rotates and thereby generating a tangential magnetic field to move the developer blanket along the surface of sleeve; The developer blanket passes over zones on sleeve where developer material is picked up, self metering, mixing, blanket homoginization, tribo charging and developer transport occurs. The developer blanket moves to the development zone which is defined by a planar portion on the sleeve; parallel and adjacent to the imaging surface whereupon the blanket is compressed.

Abstract: A developing device which regulates the amount of developer transported on a developing sleeve via a regulating member constructed as a magnetic member, so as to not have large fluctuation in the amount of developer transported by a developing sleeve to a developing region even when there is dislocation in the install position of the regulating member, and which produces excellent images having stable density without image noise.

Abstract: A developing device for an electrophotographic apparatus and a developing roller therefor are disclosed. Polarity identical throughout a range between a magnetic conveying pole and a magnetic depositing pole on a sleeve forms a repulsive magnetic field. Therefore, even when the diameter of the sleeve is reduced for the miniaturization of the developing device, a developer can be surely released from the sleeve despite a decrease in the width of a developer releasing portion in the direction of rotation of the sleeve.

Abstract: In a development device for developing an electrostatic latent image formed on an image bearing body, the development device includes: a developer bearing body for conveying a developer borne thereon to a developing area on the image bearing body; a plurality of magnetic poles provided inside the developer bearing body; a detaching magnetic pole including optional two adjoining poles of the plurality of magnetic poles which are arranged to have the same polarity as each other for forming a repulsive magnetic field to remove the developer on the developer bearing body; and a magnetic body provided in the vicinity of and spaced away from the detaching magnetic pole, for forming a repulsive magnetic field having the same polarity as that of the detaching magnetic pole.

Abstract: An apparatus and method for non-interactive, dry powder development of electrostatic images including: an image bearing member bearing an electrostatic image; two component developer including toner and permanently magnetized carrier beads, the carrier having average diameter (2a) and magnetization M.sub.b a developer transporting member having a thickness t for transporting a developer layer of the two component developer, the layer spaced close to and out of contact with the image bearing member, and wherein the developer layer is substantially without chains of carrier beads, a multipole magnet member disposed in close proximity behind the transporting member and moving relative to it so as to sweep poles across its surface, the magnet member having a periodic magnetization of spatial frequency k and a peak magnetization M.sub.0wherein M.sub.b, t, k, and M.sub.0, are chosen such that M.sub.b is sufficiently large to prevent the escape of developer, and a quantity ##EQU1## is greater than about 1/3.

Abstract: Disclosed is a highly noiseless magnet roller capable of reducing occurrence of noise upon operation as much as possible. The magnet roller includes a magnet main body and a shaft portion projecting from each or either of both ends of the magnet main body, wherein the magnet main body and the shaft portion are integrally molded from a bond magnet composition in which a magnetic powder is dispersed in a resin binder. In this magnet roller, the roundness of the shaft portion is specified to be in a range of 30 .mu.m or less.

Abstract: An image development system for developing a latent image on an imaging surface, such as a xerographic photoreceptor, with plural development rollers having internal axially extending developer magnets with relatively offset axial end positions, and wherein at least one development roller has a smooth surface area at that same end, to reduce edge banding image defects from the interaction of the axial ends of the magnets of adjacent development rollers, especially for large size copy sheets being printed, such as B4 size. The image developer unit may have three development rollers with three different lengths of developer magnets to provide three different magnetic end positions staggered on opposite sides of the end position of the large sheet (relative to the imaging surface).

Abstract: An image forming method for developing an electrostatic latent image on an image-bearing member that moves bearing electrostatic latent images formed of a two-component magnetic developer is described. The method includes the steps of providing a rotatable cylinder for supporting and conveying said magnetic developer, the cylinder including a permanent magnet with a plurality of magnetic poles provided on the surface. Magnetic carriers in the magnetic developer are attracted and conveyed on the surface of the permanent magnet, the magnetic carriers having an average particle size of 5 to 20 .mu.m and opposite to toner in polarity of charge. A carrier particle magnetization .sigma..sub.1000 in a magnetic field of 1000 Oe so as to amount to 50 emu/g or less is also used. The method also includes a surface magnetic flux density ranging from 50 to 1200 G, and a value of h, defined as .pi.D.multidot.Vp/(M.multidot.

Abstract: A development system including a developer transport adapted for depositing developer material on an imaging surface having an electrostatic latent image thereon, including a housing defining a chamber storing a supply of developer material including toner. A donor member is mounted partially in said chamber and spaced from the imaging surface, for transporting developer on an outer surface thereof to a region opposed from the imaging surface. The donor member has a magnetic assembly, which includes a plurality of poles, and a sleeve, enclosing said magnetic assembly and rotating about said magnetic assembly. A magnetic system generates a magnetic field to reduce developer bed height of said developer material on said donor member in a development zone.

Abstract: A solid-state selectably switchable combination cascade/magnetic brush for use in toner deposition or removal devices used in imaging machines of the electrostatic or magnetic type having one or more electro-magnets with one or more electro-magnetic windings and transfer heads placed inside, as well as outside, a photoconductor. Imaging mixture is agitated and conveyed to a transfer head which is exposed and adjacent to a photoconductor thereby eliminating the need for a drum or sleeve as the carrier/deposition agent for the imaging mixture. Transfer heads deposit imaging mixture directly onto a primary development zone with the excess cascading and attracting to a residual development zone and/or reclamation structure.

Abstract: A magnet roll including a cylindrical permanent magnet having a surface thereon a plurality of magnetic poles which extend along an axis of the magnet roll and an electroconductive ceramic layer formed at least on a circumferential surface of the cylindrical permanent magnet. The electroconductive ceramic layer may be TiC, WC, TiN, TiCN, CrN, ZrN, HfN, Ti+TiN, and Cr+CrN. The magnet roll is used in a developing method of developing a latent image on a photosensitive drum by a magnetic developer while applying a bias voltage to a developing zone, in which the number of the magnetic poles (N) satisfies the relation: N.gtoreq.(V.sub.1 /V.sub.2).times..pi.D/6, wherein V.sub.1 is a peripheral speed (mm/s) of the photosensitive drum, V.sub.2 is a peripheral speed of the magnet roll and D is an outer diameter (mm) of the magnet roll.

Abstract: A development system for developing an image with developer material including a housing containing developer material; and a magnetic roll for transporting the developer material from the housing to the image, the magnetic roll including an magnetic core and a cylindrical sleeve enclosing and rotating about the magnetic core, the sleeve having a thickness between 0.001 to 0.006 inches.

Abstract: By employing a developer using ferrite system carriers, a developing process can be carried out using a low brushing force by a magnetic portion having the same polarity in a developing unit in a developing roller. A relationship between a circumferential speed Up (mm/sec) of a photoconductor, a ratio K of a circumferential speed of a developing sleeve of the developing roller to the circumferential speed of the photoconductor, and a developing potential difference .DELTA.V (V) is set to 1.5.ltoreq.(K.times..DELTA.V/Up).ltoreq.2.1.

Abstract: A developing apparatus is provided for developing an electrostatic latent image on a latent image carrier by supplying the latent image carrier with a developer. This developing apparatus includes a toner accommodating chamber for accommodating magnetic toners. The apparatus also includes a developing roller, having a plurality of fixed magnetic pole members and sleeves provided along peripheries of the fixed magnetic pole members and rotating thereabout, for feeding the developer composed of magnetic carriers and magnetic toners to the latent image carrier. The apparatus further includes a developing chamber having a partition wall formed along the developing roller and assuming a configuration adapted to a shape of the developing roller, and a toner supply port for supplying the magnetic toners to the developing chamber from the toner accommodating chamber.

Abstract: In a developing apparatus, a developing roller has a toner layer formed on a surface thereof, which toner layer is brought into contact with a photoconductor. A magnetic conveying roller having a magnet body is arranged rotatively close to the photoconductor. A regulating plate is provided at an outer periphery of the conveying roller.

Abstract: A development system is disclosed including a developer transport adapted for depositing developer material on an imaging surface having an electrostatic latent image thereon, said developer transport including a core; a magnetic transport member rotating about said core wherein said magnetic transport member has a static magnetic field pattern for transporting developer material to a development zone; and a magnetic system for generating a superimposed alternating magnetic field to agitate developer material in said development zone.

Abstract: A magnet system for an image-forming apparatus comprising an image-forming element which is capable of electrically and/or magnetically attracting a toner powder and is movable relative to the magnet system. The magnet system includes a support at least one ferromagnetic body and a clamping device. The support is surrounded by a rotatable sleeve and arranged such that the circumferential surface of the sleeve faces the surface of the image-forming element in a linear image-forming zone extending normal to the direction of movement of the image forming element. The at least one ferromagnetic body has magnets fixed in the support and defines a localized magnetic field in the image-forming zone. The clamping device will engage the ferromagnetic body to secure the body in the support in a non-positive manner, thereby allowing differential thermal expansion of the magnets and the support.

Abstract: A developing apparatus comprises: a developer support being disposed in the proximity of or in contact with an image support having a surface on which an electrostatic latent image is formed, the developer support having a peripheral surface supported turnably; and a developing bias power supply for supplying a developing bias voltage between the developer support and the image support, wherein a dual component developer including toner and magnetic carriers is supported on the peripheral surface of the developer support to be transported, and the toner is transferred to the image support in an electric field formed at a position where the image support faces the developer support for forming a toner image, and the developer support has a plurality of magnetic poles for attracting almost one layer of the carriers on the peripheral surface of the developer support almost uniformly.

Abstract: An improved developer roll magnet for a toner cartridge provides a strip of magnetic material that extends axially along a surface of the developer roll magnet located coaxially within a developer roll sleeve. The strip of magnetic material can be seated within a groove in the magnet and can extend radially outwardly above the surface of the magnet. The strip is generally adhered to the magnet by mutual magnetic attraction and can be made adjustable to move toward and away from the developer roll sleeve. The strip is typically located adjacent a nip formed between the developer roll sleeve and the image transfer drum of the cartridge to provide enhanced toner release for greater print yield and quality.

Abstract: In a developing unit used for an image forming apparatus to develop an electrostatic latent image on an image carrier, there are provided a developing agent carrying member for carrying a developing agent, a magnet roll disposed in the developing agent carrying member and a supporting member for supporting the magnet roll. A portion of the supporting member is melted so that a central shaft of the magnet roll is welded to the supporting member to attain fixation between the magnet roll and the supporting member.

Abstract: A developer roll for use in an electrophotographic printing machine of the type having an electrostatic latent image recorded on a photoconductive member in which a magnetic field attracts magnetic particles to form a magnetic brush on the periphery of a developer roll assembly. The developer roll assembly includes a sleeve and the developer roll. The developer roll is located at least partially within the sleeve. The developer roll includes a core having a core feature and a magnetic member having a member feature. The core feature and the member feature cooperate with each other so that the member and the core are mechanically interlocked with each other.

Abstract: A magnet roller including a columnar magnet with a through bore having a cross-section defining a thickness of the columnar magnet which is uneven along a circumference thereof, wherein a most thick portion of the columnar magnet has a strongest magnetic pole. The columnar magnet may be made from a resin material containing a magnetic powder. The bore cross-section may be non-circular, D-shaped, or rectangular. An insertion member may be inserted into the through bore to fixedly support the magnet roller.

Abstract: An electrically self-propelled pulsating multi-directional magnetic brush having an insert for use in toner deposition or removal devices associated with imaging machines of the electrostatic type (dry or liquid), the magnetic type, and the reprographic type. The insert further has skewed magnetic sections, made of permanent magnets or electro-magnets, therearound. The insert is used in conjunction with a permanent or electro-magnet and is contained within a rotatably mounted drum to provide an insulation for the drum and to further provide a driving force to uniformly rotate and multi-directionally pulsate developer mixture material around the drum.

Abstract: A developing apparatus includes a developing sleeve for carrying a developer; a hollow magnet roller in the sleeve; a supporting member inserted into the developing sleeve and the magnet roller to support an inside surface of the developing sleeve and the magnet roller.

Abstract: A method in which a photoconductive surface is charged to a uniform potential by a charging brush and a two-component magnetic developer is directly attracted on the surfaced of a sleeve-less developing roll formed from a permanent magnet member and transported by the rotation of the permanent magnet member. An electrostatic latent image is developed with the transported magnetic developer in a developing zone to form a visual toner image on the photoconductive drum. The toner image is transferred to a recording sheet by a transfer roll and permanently fixed thereon by a suitable fixing means. The specific volume resistance of the magnetic carrier is restricted to a particular range to prevent the magnetic carrier from adhering to the photoconductive surface.

Abstract: A system for forming desired magnetization patterns in permanent magnet structures such as magnetic brush cylinders cores, utilizes a fixture having a plurality of magnetizing members selectively orientable to the permanent magnet structures and couplable to a capacitor discharge magnetization apparatus. Magnetic tip members can have different flux focusing end configurations to form corresponding polarization patterns in the permanent magnet cylinder structures.

Abstract: A method for developing electrostatic latent image on a rotating photoconductive drum by a magnetic developer transported by a rotating developing roll disposed opposite to the photoconductive drum, the developing roll being made of a cylindrical permanent magnet having on circumferential surface thereof equispaced magnetic poles extending along the axial direction. In the method the magnetic poles are equispaced by an inter-pole pitch of 0.5-10 mm, the photoconductive drum and the developing roll are rotated so as to move in opposite directions in an developing zone, and the ratio of peripheral speeds of the developing roll and photoconductive drum are regulated within 1 to 5. By the above method, an electrophotographic imaging apparatus can be reduced in the size thereof while reproducing high-quality images.

Abstract: In a color image forming apparatus, as the second and subsequent development processes of the simultaneously transfer type, a non-contact type AC field double-element development is employed, and an absolute value of the difference between the maximum bias which provides the maximum toner developing electric field in the direction to the side of the latent image carrier and the average value of the developing bias is set larger than an absolute value of the difference between the minimum bias voltage which provides the minimum toner developing electric field in the direction to the side of the latent image carrier and the average value of the developing bias, while the bias voltage region located between the maximum bias voltage and the average bias voltage is set to a ratio of from 0.25 to 0.45 for one period of the AC voltage, and the frequency of the bias voltage is set from 4 kHz to 10 kHz.

Abstract: In an image printer performing multi-color printing, two magnetic poles having the same polarity are provided adjacent to each other in a position facing the printing body of the second developing agent holding body provided in the second developing unit, and development is performed under a condition satisfying the following formulas;B1.ltoreq.1100,1000.ltoreq.B2.ltoreq.1200,-300.ltoreq.B1-B2.ltoreq.0,F.apprxeq.0where B1 (gauss) is a magnetic flux density on the surface of the developing agent holding body of one magnetic pole of the magnetic poles arranged in the downstream side of the transmitting direction of the developing agent, and B2 (gauss) is a magnetic flux density on the surface of the developing agent holding body of the other magnetic pole of the magnetic poles arranged in the upstream side of the transmitting direction of the developing agent, and F (gf) is a rubbing force to the printing body of the magnetic brush in the second developing unit.