An image forming apparatus detects a first current value and a second current value of currents flowing between an image bearing member and a developer carrying member. When a difference between the detected first current value and the detected second current value exceeds a threshold in a state in which the image bearing member and the developer carrying member are rotated and a first developing voltage is applied to the developer carrying member, a controller controls AC voltage applied to the developer carrying member.

An image forming apparatus includes a developing device that forms a toner image, by developing an electrostatic latent image formed on a photoconductor drum, a charging device that electrically charges the photoconductor drum, a developing power source that applies a predetermined developing bias voltage to the developing device, and a calculation device that calculates a surface potential of the photoconductor drum, on a basis of the developing current flowing in the developing device. The developing power source applies the developing bias voltage in a plurality of levels, to the developing device. A current measurement device measures a developing current, with respect to the developing bias voltage of each level. The calculation device calculates the surface potential, on the basis of each developing current.

A control portion switches first and second modes based on information which influences a toner charging amount. In the first mode, a driving input to the developer bearing member is stopped in response to image formation completion before or at the same time when a trailing end of a charging area reaches the development position, and an application of the development voltage is stopped after the trailing end reaches the development position. In the second mode, The driving input to the developer bearing member is stopped in response to image formation completion before or at the same time when the trailing end reaches the development position, and the application of the development voltage is stopped at a timing after the trailing end reaches the development position and earlier than that in the first mode, or at the same time when the trailing end reaches the development position.

An image forming apparatus is operable in a normal image forming mode and an uneven lubrication detecting mode, and includes: an image carrier; a lubricant applying device that applies lubricant to the image carrier; and a processor that detects uneven lubrication on a surface of the image carrier in the uneven lubrication detecting mode in which an amount of the lubricant applied to the image carrier is increased to exceed an amount of the lubricant applied in image forming.

In an image forming apparatus, a fixing member has a surface layer having conductivity. A developer is a toner having a toner particle including a binder resin, a reactant of a polyhydric acid and a compound containing a group 4 element is present on a surface of the toner particle, and Tv/Fv>100 is satisfied where Tv represents a volume resistivity upon being unfixed, and Fv represents a volume resistivity after fixing. A bias applying unit can selectively apply a bias of a positive polarity and a bias of a negative polarity, and applies a bias of the same polarity as the charged polarity of a filler included in a recording material when the recording material passes through a fixing nip portion, and when the recording material does not pass through the fixing nip portion, respectively.

A developing device, including: a developer containing toner and carrier; and developer bearer configured to have surface thereof bear the developer and endlessly move, and to develop latent image over surface of latent image bearer by supplying toner in developer to latent image in developing region facing the latent image bearer, wherein carrier contains fine particles, value X in volume resistivity R (=10.sup.X) (Ω.Math.cm) of carrier is 11.5-16.0, developer bearer includes: magnetic field generating unit including a plurality of magnetic poles; and developing sleeve having a cylindrical shape enclosing magnetic field generating unit, and configured to bear developer over outer circumferential surface of cylindrical shape by magnetic force of the magnetic field generating unit and perform surface moving by rotating relative to developing device body, and developing device includes developing sleeve voltage applying unit configured to apply AC component-containing voltage to developing sleeve.

An image forming apparatus includes an image bearing member and a developing device having a first developer bearing member and a second developer bearing member, disposed with a gap therebetween. A controller executes a mode in which a first difference between an amplitude of an alternating current bias of a first developing bias applied to the first developer bearing member and an amplitude of an alternating current bias of a second developing bias applied to the second developer bearing member at a time of non-image formation is set to be large compared to a second difference between an amplitude of the alternating current bias of the first developing bias applied to the first developer bearing member and an amplitude of the alternating current bias of the second developing bias applied the second developer bearing member at a time of image formation.

An electrostatic charge image developing carrier includes a magnetic core particle, and a coating layer that coats surfaces of the magnetic core particle, wherein the coating layer includes a binder resin, thermosetting resin particles, and crosslinked resin particles, and the crosslinked resin particle contains a polymer formed by polymerizing a monomer component including the same monomer as a monomer used in the polymerization of the binder resin.

According to an aspect of the invention, a developing device includes a developer holding member that holds developer including toner which is charged to have a predetermined polarity on a surface and performs development of an electrostatic latent image with respect to an image holding member which holds the electrostatic latent image while being rotated; a storage member that stores the developer therein and has an opening portion for discharging air in which flow is generated by the rotation of the developer holding member; and a collection member that is provided in the opening portion of the storage member to be charged to the predetermined polarity, causes air to pass therethrough, and collects toner.

An image forming apparatus includes a rotatable image bearing member; a developing device including a rotatable developer carrying member, a toner content detecting portion, an electrostatic capacity detecting portion, and a switching portion configured to switch a developing condition on the basis of an output of the toner content detecting portion and an output of the electrostatic capacity detecting portion so that the developing condition is changed when the electrostatic capacity detected by the electrostatic capacity detecting portion reaches first electrostatic capacity at a first toner ratio and so that the developing condition is changed when the electrostatic capacity reaches second electrostatic capacity larger than the first electrostatic capacity at a second toner ratio smaller than the first toner ratio.