According to an aspect of the invention, a developing device includes a developing container that accommodates a two-component developer, a toner concentration detecting unit that detects a toner concentration of the developer by a detecting unit exposed to an inner wall of the developing container, a transport member that is disposed within the developing container and stirs and transport the developer with a transport blade having a pitch that is equal to or less than a size of the detecting unit of the toner concentration detecting unit, and a plurality of gap holding members that is provided at a position facing the toner concentration detecting unit of the transport member and holds a gap such that a tip thereof is abutted against the inner wall of the developing container.

A developing device includes a developing container, first and second stirring-conveyance members, a developer carrier, a toner concentration sensor, a scraper, and a scraper attachment unit. The second stirring-conveyance member includes a rotation shaft, a first spiral blade to convey developer in an axial direction, and a second spiral blade to overlap a region where the first spiral blade is formed, which is opposite to the first spiral blade in phase, and lower than the first spiral blade in height in a radial direction. An absent region, where the second spiral blade does not exist, is formed in one pitch of the first spiral blade, the one pitch facing the toner concentration sensor. The scraper attachment unit is formed to extend, along a straight line passing through intersection points of the first and second spiral blades and parallel to the rotation shaft, into the absent region.

An object of the invention is to accurately grasp the fluidity of a developer and give proper feedback to an image forming process. An image forming device has a developing unit developing a latent image by transferring a developer to an image carrier, a fluidity measuring unit measuring fluidity of the developer, a correction amount computing unit computing a fluidity correction amount for correcting the fluidity of the developer measured by the fluidity measuring unit, and a process control unit changing a process condition of an image forming process. The process control unit selects, on the basis of the fluidity of the developer corrected based on the fluidity correction amount, an image forming process of changing a process condition from a plurality of image forming processes.

Provided is a magnetic carrier comprising a magnetic carrier particle having a magnetic body-dispersed resin carrier core material and a resin coating layer; the core material includes magnetic particles A and B having number average primary particle diameter of ra and rb (m), respectively, satisfying rarb; the particles A each include an oxide of at least one nonferrous metal of Mn, Al, Mg, Ti, and Ni; and an iron oxide; M1 represents total content of the nonferrous metal and F1 represents content of an iron of the magnetic carrier particle measured by XRF diffraction, M1/F1 is 0.010 to 0.100; M2 represents total content of the nonferrous metal and F2 represents content of an iron is F2 of the magnetic carrier particle measured by XPS, M2/F2 is 1.0 to 10.0.

A toner is provided. The toner contains a polyester resin. The toner has a glass transition temperature (Tg1st) at first temperature rising of differential scanning calorimetry (DSC) of from 45 C. to 65 C. The toner includes a component insoluble in tetrahydrofuran (THF) having two glass transition temperatures (Tga1st and Tgb1st) at the first temperature rising of DSC, where Tga1st is in a range of 45 C. to 5 C. and Tgb1st is in a range of 45 C. to 70 C. The toner includes a component soluble in THF having a glass transition temperature (Tg2nd) at second temperature rising of DSC of from 40 C. to 65 C.

An image forming apparatus includes a correction amount calculator, a fluidity measuring unit, and an external additive amount calculator. The correction amount calculator calculates a correction amount of fluidity to correct the fluidity of a two-component developer. The fluidity measuring unit measures the fluidity of the two-component developer. The external additive amount calculator corrects the measured fluidity on the basis of the correction amount of fluidity, calculates the amount of an external additive of a toner from the corrected fluidity of the two-component developer, and determines the state of the external additive.

A developing device includes a developer bearing member, a developing container which accommodates developer, a conveying screw which conveys the developer accommodated in the developing container, and an inductance sensor which includes a detecting portion which detects magnetic permeability of the developer accommodated in the developing container. The conveying screw includes a rotary shaft, a blade which is spirally formed on an outer circumference of the rotary shaft, and a rib formed to protrude outwardly from the outer circumference of the rotary shaft. The rib is disposed opposite the detection portion with respect to a conveying direction of the conveying screw and is provided with a magnet, with magnetic flux density of the magnet being in the range of 20 mT to 60 mT.

An image forming apparatus according to an embodiment includes an image bearing body, a developing roller, a housing, and a gap adjusting member. The image bearing body includes a first rotating shaft and includes a first surface on which a latent image is formed. The developing roller includes a second rotating shaft, includes a second surface, includes a bearing, and supplies a developer to the latent image and develops the latent image. The housing rotatably supports the second rotating shaft. The gap adjusting member includes a shaft hole for rotatably receiving one end of the first rotating shaft and includes a cam surface. The gap adjusting member is turned around the first rotating shaft and is fixed to the housing in a turning position where a gap is uniform in a direction of the second rotating shaft of the developing roller.

An image forming apparatus includes a developing unit attachment part to which developing units are to be attached, each of the developing units being associated with a first criteria for performing developer refreshing and a second criteria for performing developer refreshing, wherein the second criteria is defined so as to be met prior to the first criteria, and a controller configured to control a timing of developer refreshing executed for each of the developing units according to the first and second criteria values thereof, and a first developer tank that is located at a position higher than the developing unit and configured to contain the developer. When the first criteria for performing developer refreshing is met for at least one of the developing units, the controller causes developer refreshing to be performed for all developing units whose first or second criteria is met.

A carrier for developing electrostatic latent images is provided. The carrier includes a magnetic core particle and a resin layer coating a surface of the magnetic core particle. The resin layer includes a particulate material A having a volume average particle diameter (a) and a particulate material B having a volume average particle diameter (b). The volume average particle diameter (a) of the particulate material A is the largest among volume average particle diameters of all particulate materials included in the resin layer, and an inequation 100(a)/(b)5 is satisfied. The particulate material A is barium sulfate.