Abstract: A development station that improves toner halftone dot development over a wide range of environmental conditions includes a developer housing for retaining semi-conductive carrier particles and toner particles, a first magnetic roll having a stationary core with at least one magnet and a sleeve having longitudinal grooves that rotates about the stationary core of the first magnetic roll, a second magnetic roll having a stationary core with at least one magnet and a sleeve having longitudinal grooves that rotates about the stationary core of the second magnetic roll, an environmental sensor for generating an environmental condition signal, a variable voltage supply coupled to the first magnetic roll and the second magnetic roll, and a control circuit for adjusting an output level for the variable voltage supply.

Abstract: An electrophotographic image forming device is provided which includes an image holder on which an electrostatic latent image is formed. A magnetic roller has a magnetic brush including nonmagnetic toner and a magnetic carrier using a magnetic force. Donor rollers are provided which have toner layers that are received from the magnetic roller on an outer circumference of each of the donor rollers. The donor rollers are located opposite to the image holder to develop the toner onto the electrostatic latent image.

Abstract: An apparatus for loading one or more donor rolls of a developer unit, including: a developer housing having a reservoir for a developer material, the developer material comprising toner, a rotatable first donor roll that delivers the toner onto a moving photoconductive member, a rotatable trim roll that receives the developer material from the reservoir and delivers the developer material to a first magnetic brush roll that delivers the toner to the first donor roll, and a controller, responsive to a reload sensitivity signal, for controlling the speed of the trim roll.

Abstract: A developing device is provided with a developer accommodating vessel accommodating developer having as primary components a nonmagnetic toner and magnetic particles referred to as a carrier. The carrier is composed of a magnetic material as a core material that is uniformly covered with an insulating synthetic resin. The toner is mixed with the carrier at a weight ratio to the overall weight of the developer of 3-10%. The carrier has an average particle size of 65 ?m or less and a saturation magnetization of at least 70 emu/g. The developing device includes a developing roller and a sleeve roller that rotates about the developing roller. The surface of the sleeve roller is processed with metal shot to achieve a surface roughness of 0.45-1.08 times the average particle size of the carrier, or more specifically a roughness Rz of about 30 ?m.

Abstract: A developing unit includes a plurality of developing rolls over which a developer is conveyed and supplied onto an image carrier which is rotatably supported; and at least one pair of the developing rolls being adjacent to each other. In the pair of the developing rolls, one developing roll rotates in a direction opposite to a rotary direction of the image carrier, and the other developing roll rotates in the same direction of the rotary direction of the image carrier. A regulation member is interposed between the pair of the developing rolls. The regulation member regulates a conveyed amount of the developer. The regulation member is disposed to be opposed to a magnet which is provided within the two adjacent developing rolls. A polarity of the magnet in the pair of developing rolls opposed to each other is different from each other.

Abstract: A developing device includes a developer-bearing member supporting developer for developing electrostatic images, a first chamber supplying the developer to the developer-bearing member, a second chamber below the first chamber, first and second communicating portions connecting the first and second chambers, a first carrying member carrying the developer in the first chamber in a first direction from the first communicating portion to the second communicating portion, a second carrying member carrying the developer in the second chamber in a second direction from the second communicating portion to the first communicating portion, and a partition between the first and second chambers. A bottom portion of the first chamber is inclined such that a downstream end thereof in the first direction is higher than the other end at a position where the bottom portion faces the developer-bearing member.

Abstract: An apparatus for loading one or more donor rolls of a developer unit, comprising a developer housing having a reservoir for a developer material, a rotatable first donor roll that delivers the toner onto a moving photoconductive member, a rotatable first magnetic brush roll that receives the developer material from the reservoir and delivers the toner to the first donor roll, and a rotatable second magnetic brush roll that receives the developer material from the first magnetic brush roll and delivers the toner to the first donor roll. The apparatus may further comprise a rotatable second donor roll that receives the toner from the second magnetic brush roll and delivers the toner onto the photoconductive member, and a rotatable third magnetic brush roll that receives the developer material from the second magnetic brush roll and delivers the toner to the second donor roll.

Abstract: An apparatus for loading one or more donor rolls of a developer unit, comprising a developer housing having a reservoir for a developer material, a rotatable first donor roll that delivers the toner onto a moving photoconductive member, a trim roll that receives developer material from the reservoir and delivers the developer material to a first magnetic brush roller that delivers toner to the first donor roll, and a rotatable second magnetic brush roll that receives the developer material from the first magnetic brush roll and delivers the toner to the first donor roll. The apparatus may further comprise a rotatable second donor roll that receives the toner from the second magnetic brush roll and delivers the toner onto the photoconductive member, and a rotatable third magnetic brush roll that receives the developer material from the second magnetic brush roll and delivers the toner to the second donor roll.

Abstract: A development subsystem is used to develop toner particles transported by semiconductive carrier particles.

Abstract: A development station in an electrostatographic imaging machine supports longer operational life without undue variation in the mass of developer on roll parameter. The development station includes a developer housing, for retaining a quantity of developer having semi-conductive carrier particles and toner particles, a first magnetic roll having a stationary core with at least one magnet and a sleeve having longitudinal grooves that rotates about the stationary core of the first magnetic roll to transport developer to a photoreceptor, a second magnetic roll having a stationary core with at least one magnet and a sleeve having longitudinal grooves that rotates about the stationary core of the second magnetic roll to receive developer from the first magnetic roll and present the developer to the photoreceptor, the sleeve of the second magnetic roll being fabricated from a material that is softer than the sleeve of the first magnetic roll.

Abstract: A development subsystem is used to develop developer having semiconductive carrier particles and toner particles. The development subsystem includes a developer housing, for retaining a quantity of developer having semiconductive carrier particles and toner particles, a first magnetic roll having a stationary core with at least one magnet and a sleeve that rotates about the stationary core of the first magnetic roll, a second magnetic roll having a stationary core with at least one magnet and a sleeve that rotates about the stationary core of the second magnetic roll, and a motor coupled to the first and the second magnetic rolls to drive the rotating sleeves of the first and the second magnetic rolls in a direction that is against the direction of a photoreceptor that rotates in proximity to the first and the second magnetic rolls. The first and the second magnetic rolls carry semiconductive carrier particles and toner particles through a development zone formed by the first and the second magnetic rolls.

Abstract: A development station in an electrostatographic imaging machine impedes the flow of carrier particles out of the development station as the developer moves from an upper to a lower magnetic roll.

Abstract: A development station in an electrostatographic imaging machine may be controlled to improve toner halftone dot development over a wide range of environmental conditions.

Abstract: A development station in an electrostatographic imaging machine impedes the flow of carrier particles out of the development station as the developer moves from an upper to a lower magnetic roll.

Abstract: A developing method using a developing device including at least: a first developer bearing member arranged to be opposed to an image bearing member; and a second developer bearing member arranged on a downstream side of a rotation direction of the image bearing member with respect to the first developer bearing member, the developing method including developing a latent image formed on the image bearing member with a developer, in which: the developer is a two-component developer having toner and a magnetic carrier; and the developer has a degree of compression C in the range of 20 to 32% and a shearing stress obtained by shearing stress measurement under a consolidation load of 4.0×10?4 N/mm2 in the range of 0.5×10?4 to 2.5×10?4 N/mm2.

Abstract: A developing apparatus having: a first developer carrying member close to a developer regulating member for regulating an amount of developer; a second developer carrying member to which the developer is delivered from the first developer carrying member; and a mode for removing the toner on the surface of the second developer carrying member, in which mode, in a non-image-formation period, no toner transfer operation from the first developer carrying member to an image bearing member is substantially performed, but a toner transfer operation from the second developer carrying member to the image bearing member is performed.

Abstract: An image forming apparatus having an image bearing member on which an electrostatic image is formed, a first developer carrying member carrying a developer thereon, and a second developer carrying member disposed downstream of the first developer carrying member with respect to the direction of movement of the image bearing member, and designed such that one and the same electrostatic image on the image bearing member is developed with the developer carried on these developer carrying members, has a developer consumption mode in which during the other time than ordinary image formation, the developer borne on the first and second developer carrying members is shifted to the image bearing member, and during this developer consumption mode, control is effected so that the amount of developer consumed from the second developer carrying member to the image bearing member may be greater than the amount of developer consumed from the first developer carrying member to the image bearing member.

Abstract: An image forming apparatus includes an image bearing member for bearing and conveying an electrostatic image; a first developer carrying member for carrying and conveying a developer toward a first developing position; and a second developer carrying member for carrying and conveying the developer toward a second developing position, wherein when a time period required for a movement of the developer carried and conveyed by the first developer carrying member and the second developer carrying member from the first developing position through the developer delivering portion to the second developing position is assigned TA, and a time period required for a movement of the developer on the image bearing member from the first developing position to the second developing position is assigned TB, and wherein respective driving speeds of the image bearing member, the first developer carrying member, and the second developer carrying member are controlled so that TA and TB are different values.

Abstract: An image forming apparatus which can stably form an image of high quality by the use of a first developer carrying member and a second developer carrying member. On the first developer carrying member, development is performed by a method whereby a magnetic carrier contacts with an image bearing member, and on the second developer carrying member, development is performed by a method whereby the magnetic carrier does not contact with the image bearing member.

Abstract: A developing apparatus provided with first and second members disposed on an upstream and downstream sides, respectively, and opposed to an image bearing member. When a closest distance between the first developing member and the image bearing member is defined as SD1 (m), and the closest distance between the second developing member and the image bearing member is defined as SD2 (m), and the peak-to-peak voltage of a developing bias applied to the first developing member is defined as V1 (V), and the peak-to-peak voltage of the developing bias applied to the second developing member is defined as V2 (V), and the volume resistivity of the carrier is 1.0×10x?·cm, V1/SD1?V2/SD2?(0.65x?4.5)×106(V/m), 1.2×106?V1/SD1?(0.35x+3.5)×106(V/m), (0.30x?1.5)×106?V2/SD2?9.0×106(V/m), and 9.0?X?13.0 are satisfied.

Abstract: A developing device including: a first developer carrying member for carrying a developer to develop a latent image formed on an image bearing member; a first regulating member, disposed on one end of a longitudinal direction of the image bearing member, for regulating a gap between the image bearing member and the first developer carrying member; a second developer carrying member for carrying a developer to develop the same latent image formed on the image bearing member; and a second regulating member, disposed on the one end of the longitudinal direction of the image bearing member, for regulating a gap between the image bearing member and the second developer carrying member, wherein the first and second regulating members are disposed without being superposed upon each other in the longitudinal direction.

Abstract: A developing apparatus includes a developing container for containing a developer comprising toner and a carrier, said developing container is partitioned into a first chamber and a second chamber constituting a circulation path of the developer; a first developing rotatable member, provided in said first chamber, for developing an electrostatic image formed on the image bearing member with the developer in said first chamber; a regulating member for regulating a layer thickness of the developer on said first developing rotatable member; first magnetic pole and second magnetic pole, disposed in said first developing rotatable member in order named in a rotational direction of said first developing rotatable member, said first magnetic pole and second magnetic pole being defective to form a repelling magnetic field; a second developing rotatable member, disposed in said second chamber, for developing the the electrostatic image formed on the image bearing member with the developer magnetically received from sa

Abstract: An image forming apparatus includes an image bearing member having a surface on which an electrostatic latent image is to be formed; a black developing device, containing a black developer including toner and carrier, for developing the electrostatic latent image; at least one color developing device containing a color developer having a color other than black; a supplying device, provided for each of the black developing device and the color developing device, for supplying a supply material containing toner and carrier; a discharging device for discharging the developer. A resistivity of the carrier contained in the black developer is higher than resistivity of the carrier contained in the color developer, and a weight percentage of the carrier contained in the supply material for the black developing device is higher than a weight percentage of the carrier contained in the supply material for the color developing device.

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 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: An electrophotographic toner containing: a fixing resin, a colorant, and wax. The wax at least contains hydrocarbon wax having a number-average molecular weight of not higher than 600, and polyethylene wax having a number-average molecular weight of not higher than 600, a melting viscosity of lower than 15 mPa·s at 140° C. and a crystallinity of lower than 95%. A ratio of the hydrocarbon wax to the polyethylene wax is in a range of from 1:10 to 2:1. A maximum of absorption peaks in a heat-up time absorption calorie curve in a DSC curve of the toner measured by a differential scanning calorimeter is at a temperature not higher than 75° C. An onset temperature in absorption of heat is not higher than 65° C.

Abstract: The present invention relates to a developing apparatus for developing an electrostatic image formed on an image carrier, comprising a developing container, a first developing member formed at the first chamber for conveying developer to a first developing portion, a second developing member provided with the second chamber for conveying the developer to a second developing portion and a magnetic field generating means for generating magnetic field for transferring the developer between the first developing member and the second developing member. The diaphragm is disposed in a non-contacting manner to the first developing member and the second developing member and has a restricting member for restricting entry of the developer out of an interior of the developing container to a space between the first developing member and the second developing member.

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: To control bending of a magnetic field generation unit provided inside a developer carrying member, a developing apparatus for developing an electrostatic image formed on an image bearing member according to the present invention includes: a developer container which contains a magnetic developer; first and second developer carrying members which carry the developer in the developer container to the image bearing member; and first and second magnetic field generation units which are fixedly arranged in the first and second developer carrying members. In the developing apparatus, the first magnetic field generation unit and the second magnetic field generation unit form a magnetic field for delivering the developer from the first developer carrying member to the second developer carrying member, and the developing apparatus further includes a magnetic unit which exerts a magnetic force, which resists a magnetic force caused by the magnetic field, on the first and second magnetic field generation units.

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: A developing apparatus includes a developing container for containing a developer comprising toner and a carrier, said developing container is partitioned into a first chamber and a second chamber constituting a circulation path of the developer; a first developing rotatable member, provided in said first chamber, for developing an electrostatic image formed on the image bearing member with the developer in said first chamber; a regulating member for regulating a layer thickness of the developer on said first developing rotatable member; first magnetic pole and second magnetic pole, disposed in said first developing rotatable member in order named in a rotational direction of said first developing rotatable member, said first magnetic pole and second magnetic pole being defective to form a repelling magnetic field; a second developing rotatable member, disposed in said second chamber, for developing the the electrostatic image formed on the image bearing member with the developer magnetically received from sa

Abstract: An image forming apparatus has a plurality of developing devices for developing an electrostatic image formed on an image bearing member, and a rotary member holding the plurality of developing devices and rotated in a route including a developing position, the rotary member selectively positioning any one of the developing devices at the developing position. Each of the plurality of developing devices has a plurality of developer carrying members carrying a developer thereon and carrying the developer to the image bearing 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: A developing device includes a developing container for accommodating a magnetic developer containing magnetic toner. First and second developer carrying members carry the developer from inside of the developing container toward an image bearing member by rotations thereof in the same rotational directions. The developer is fed by the first developer carrying member to and then is fed by the second developer carrying member to a latent image formed by the image bearing member. First and second magnetic field generation members are provided in the first and second developer carrying member 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.

Abstract: A developing device having a plurality of sleeves is provided for high-speed development and the prevention of an abnormal image, for example, thinning of a line image. An AC bias is effectively applied, so that the base contamination is suppressed to obtain a smooth image without obvious grains. Among the plural sleeves, a bias towards the photoreceptor side is applied to an upstream-side sleeve, and a bias in the reverse direction is applied to a downstream-side sleeve. Alternatively, an AC bias with a low frequency is applied to the upstream-side sleeve and an AC bias with a high frequency is applied to the downstream-side sleeve. In addition, an AC bias with a large amplitude is applied to the upstream-side sleeve, and an AC bias with a small amplitude is applied to the downstream-side sleeve.

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: The present invention relates to a developing apparatus comprisinga developing container for containing a developing agent and rotatable first and second developing members provided at the developing container as to face an image carrier for developing an electrostatic image formed on the image carrier. The first developing member is secured to the developing container to keep a gap to the image carrier and the second developing member has keeping members at both ends in a longitudinal direction thereof to keep a gap to the image carrier.

Abstract: A developing unit in an electro-photographic apparatus such as a printer, a facsimile and a copier for actualizing an image employing colored particles such as toner, and more particularly to a developing unit for forming a toner image on the surface of a photosensitive body. The developing unit includes a plurality of developing rollers each having a core and a sleeve. The sleeve accommodates the core. The plurality of developing rollers include a first developing roller and a second developing roller. The sleeve for the first developing roller is rotated to move in the same direction as a moving direction of the surface of the photosensitive body. The sleeve for the second developing roller is rotated to move in an opposite direction to the moving direction of the surface of the photosensitive body. The core of only one of the plurality of developing rollers is driven in rotation while the other core is fixed.

Abstract: The present invention relates to a developing apparatus for developing an electrostatic image formed on an image carrier, comprising a developing container, a first developing member formed at the first chamber for conveying developer to a first developing portion, a second developing member provided with the second chamber for conveying the developer to a second developing portion and a magnetic field generating means for generating magnetic field for transferring the developer between the first developing member and the second developing member. The diaphragm is disposed in a non-contacting manner to the first developing member and the second developing member and has a restricting member for restricting entry of the developer out of an interior of the developing container to a space between the first developing member and the second developing member.

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 larger 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 developing device including: a developing container for containing a developer, the developing container being provided so as to oppose an image bearing member; first and second developer bearing members for bearing and carrying the developer in the developing container to the image bearing member; and a pressurizing member for pressurizing the vicinity of an end of the second developer bearing member toward the image bearing member side, in which the developing container has a first supporting portion for rotatably supporting the vicinity of an end of the first developer bearing member and a second supporting portion for supporting the vicinity of the end of the second developer bearing member rotatably and swingably with the first supporting portion as a swinging center such that a distance between the first developer bearing member and the second developer bearing member does not substantially vary.

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: A developing apparatus includes a developer container containing a magnetic developer comprising a toner and a wax contained in the toner, first and second developer carrying member, rotatably provided in the developer container, for carrying the magnetic developer, a regulation member for regulating a thickness of a layer of the magnetic developer carried on the first developer carrying member, and magnetic field generation means for generating a magnetic field for transferring the magnetic developer from the first developer carrying member to the second developer carrying member. A common electrostatic latent image formed on an image bearing member is developed with the developer carried on the first developer carrying member and the developer carried on the developer carrying member in this order.

Abstract: A developing apparatus includes a developing container for containing a developer comprising toner and a carrier, said developing container is partitioned into a first chamber and a second chamber constituting a circulation path of the developer; a first developing rotatable member, provided in said first chamber, for developing an electrostatic image formed on the image bearing member with the developer in said first chamber; a regulating member for regulating a layer thickness of the developer on said first developing rotatable member; first magnetic pole and second magnetic pole, disposed in said first developing rotatable member in order named in a rotational direction of said first developing rotatable member, said first magnetic pole and second magnetic pole being defective to form a repelling magnetic field; a second developing rotatable member, disposed in said second chamber, for developing the the electrostatic image formed on the image bearing member with the developer magnetically received from sa

Abstract: The present invention relates to a developing apparatus comprisinga developing container for containing a developing agent and rotatable first and second developing members provided at the developing container as to face an image carrier for developing an electrostatic image formed on the image carrier.

Abstract: A developing device includes rotatable first and second developer carrying members carrying developer thereon to develop an electrostatic image formed on an image bearing member. The first and second developer carrying members are provided with a plurality of nonrotary magnetic poles therein, respectively a developer regulating member regulates the amount of the developer carried on the second developer carrying member.

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 transfer 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 unit in an electro-photographic apparatus such as a printer, a facsimile and a copier for actualizing an image employing colored particles such as toner, and more particularly to a developing unit for forming a toner image on the surface of a photosensitive body. The developing unit includes a plurality of developing rollers each having a core and a sleeve. The sleeve accommodates the core. The plurality of developing rollers include a first developing roller and a second developing roller. The sleeve for the first developing roller is rotated to move in the same direction as a moving direction of the surface of the photosensitive body. The sleeve for the second developing roller is rotated to move in an opposite direction to the moving direction of the surface of the photosensitive body. The core for at least one of the plurality of developing rollers is driven in rotation.

Abstract: A developing device having a plurality of sleeves is provided to be able to perform a high-speed development. The developing device is provided to be able to prevent the abnormal image, for example, blur at the rear end of a solid image or a thinning of the line image. An AC bias is effectively applied, so that the base contamination is suppressed to obtain a smooth image without obvious grains. Among the plural sleeves, a bias towards the photoreceptor side is applied on an upstream-side sleeve, and a bias in the reverse direction (towards the sleeve side) is applied to the downstream-side sleeve. Alternatively, a bias with a low frequency is applied to the upstream-side sleeve and a bias with a high frequency is applied to the downstream-side sleeve. In addition, a bias with a large frequency amplitude is applied to the upstream-side sleeve, and a bias with a small frequency amplitude is applied to the down stream-side sleeve.

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.