An image forming apparatus includes: a photoconductor; a charging roller; an exposure device; a developing device that is provided on a downstream side of the charging roller in a rotation direction of the photoconductor, and forms a toner image by supplying toner to a latent image; a cleaning blade that is provided between a transfer part of a surface of the photoconductor located on a downstream side of the developing device in the rotation direction of the photoconductor and the charging roller, and removes residual toner adhering to a part of the surface of the photoconductor on a downstream side of the transfer part; a lubricant supplier that supplies a lubricant to the surface of the photoconductor; and a voltage controller that controls a charging voltage to be applied to the charging roller.

An image forming apparatus includes: a photoconductor; a charging roller; an exposure device; a developing device that is provided on the downstream side of the charging roller in the rotation direction of the photoconductor, and forms a toner image by supplying toner to the latent image; a cleaning blade that is provided between a transfer part of the surface of the photoconductor located on a downstream side of the developing device in the rotation direction of the photoconductor and the charging roller, and removes the residual toner adhering to a part of the surface of the photoconductor on a downstream side of the transfer part; a lubricant supplier that supplies a lubricant to the surface of the photoconductor; and a voltage controller that controls a charging voltage to be applied to the charging roller.

A bias condition determination portion of an image forming device executes each of: a first approximation expression determination operation that respectively acquires the DC component of the development current with at least three peak-to-peak voltages included in a first measurement range and determines a first expression showing a relation between the peak-to-peak voltage and the DC component of the acquired development current, a second approximation expression determination operation that respectively acquires the DC component of the development current with at least three peak-to-peak voltages included in a second measurement range larger than the first measurement range and determines a second approximation expression showing a relation between the peak-to-peak voltage and the DC component of the acquired development current, and a reference voltage determination operation that determines, as a reference peak-to-peak voltage, the peak-to-peak voltage at an intersection where the first approximation expression and the second approximation expression intersect each other.

A developing device includes a developer container, a rotatable developing member, a magnet, a rotatable magnetic member, a removing member, a first bias applying portion, and a second bias applying portion. An electric field for moving normally charged toner, existing between the rotatable developing member and the rotatable magnetic member, toward the rotatable developing member is generated by applying a first bias to the rotatable developing member by the first bias applying portion and by applying a second bias to the rotatable magnetic member by the second bias applying portion.

Provided is an image forming apparatus capable of suppressing the occurrence of image defects in response to a difference in carrier resistance and obtaining high image quality. A developing unit has a developing roller that carries the toner in a two-component developer that includes a toner and a magnetic carrier on the surface thereof, and forms a toner image on the surface of a photosensitive drum. A current detecting unit detects developing current flowing between the developing roller and the photosensitive drum when a developing voltage is applied to the developing roller by a developing power supply. When the developing voltage is applied to the photosensitive drum, the control unit derives a carrier resistance based on the developing current detected by a current detecting unit, and controls the AC amplitude of the AC voltage of the development voltage is based on the carrier resistance.

A bias condition determination portion of an image forming device executes each of: a first approximation expression determination operation that respectively acquires the DC component of the development current with at least three peak-to-peak voltages included in a first measurement range and determines a first expression showing a relation between the peak-to-peak voltage and the DC component of the acquired development current, a second approximation expression determination operation that respectively acquires the DC component of the development current with at least three peak-to-peak voltages included in a second measurement range larger than the first measurement range and determines a second approximation expression showing a relation between the peak-to-peak voltage and the DC component of the acquired development current, and a reference voltage determination operation that determines, as a reference peak-to-peak voltage, the peak-to-peak voltage at an intersection where the first approximation expression and the second approximation expression intersect each other.

Provided is an image forming apparatus capable of suppressing the occurrence of image defects in response to a difference in carrier resistance and obtaining high image quality. A developing unit has a developing roller that carries toner in a two-component developer that includes a toner and a magnetic carrier on the surface thereof, and forms a toner image on the surface of a photosensitive drum. A current detecting unit detects developing current flowing between the developing roller and the photosensitive drum when a developing voltage is applied to the developing roller by a developing power supply. When the developing voltage is applied to the photosensitive drum, a control unit derives a carrier resistance based on the developing current detected by a current detecting unit, and controls an AC amplitude of an AC voltage of the developing voltage based on the carrier resistance.

An image forming apparatus includes a rotatable image bearing member, a charging member, a rotatable developer carrying member, a developing voltage applying portion, a detecting portion for detecting a first current value and a second current value of currents flowing between the image bearing member and the developer carrying member, and a controller for controlling the applying portion. When a difference between the first current value and the second current value which are detected by the detecting portion exceeds a threshold in a state in which the image bearing member and the developer carrying member are rotated and the developing voltage is applied to the developer carrying member, the controller controls the AC voltage of the developing voltage applied to the developer carrying member.

An image forming apparatus includes an image forming portion, a high-voltage generation circuit, a current detection portion and a control portion. The image forming portion includes an image carrying member, a charging device, an exposure device and a developing device which includes a developer carrying member for carrying a developer including a carrier and a toner. The control portion can perform a development ghost prediction mode that includes a step of measuring the amount of charge of the toner within the developing device at the time of non-image formation, a step of measuring, as a carrier current, the direct-current component of a development current when the amount of development of the toner is 0 [mg/cm.sup.2] and a step of estimating the level of occurrence of development ghost and the cause of occurrence based on the amount of charge of the toner and the carrier current which are measured.

An image forming apparatus includes: a photosensitive drum; a magnetic roller; a transfer belt; a drum cleaning roller for collecting toner on the photosensitive drum and discharging collected toner to the photosensitive drum; a belt cleaner; a waste toner accommodating unit; and a controller configured to perform a printing operation for forming an image on a sheet and a cleaning operation for cleaning the drum cleaning roller. The controller is configured to perform: when performing the printing operation, collecting toner on the photosensitive drum using the drum cleaning roller; and when performing the cleaning operation, discharging the toner on the drum cleaning roller collected in the collecting to the photosensitive drum; transferring the toner on the photosensitive drum onto the transfer belt; and collecting the toner on the transfer belt using the belt cleaner so that the collected toner is accommodated in the waste toner accommodating unit.