In a state that a first voltage is applied to a charging member so as to form a surface potential on a region of an image bearing member and a second voltage the same in polarity as the first voltage is applied to a transfer member, a detection unit detects a transfer current in the region of the image bearing member during one rotation of the image hearing member after the region passes through a charging portion, when an absolute value of the surface potential formed on the region immediately before entry into the charging portion is larger than an absolute value of the surface potential formed on the region when it is positioned upstream of a transfer portion and downstream of the charging portion in a rotational direction of the image bearing member.

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.

An image forming apparatus includes an image forming device, a corrector, and a controller. The image forming device is configured to form an image on a sheet using a rotating body under a predetermined image forming condition. The corrector is configured to correct the image forming condition to adjust image density unevenness corresponding to a rotation cycle of the rotating body. The controller is configured to control the image forming device to form on at least one sheet (i) plural test images that are different in correction amount for the image forming condition and (ii) pointing portions indicating intervals corresponding to the rotation cycle of the rotating body, in a state where the rotating body is continuously rotated.

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.

A control board configured to be mountable to a first image forming apparatus and to a second image forming apparatus of a type different from a type of the first image forming apparatus, the first image forming apparatus including a first load, the second image forming apparatus including a second load having a function different from a function of the first load. The control board comprising a connector to which the first load is to be connected in a case where the control board is mounted to the first image forming apparatus, and to which the second load is to be connected in a case where the control board is mounted to the second image forming apparatus, a common drive circuit configured to drive the first load and the second load via the connector, and one or more processors.

An image forming apparatus includes a rotatable image bearing member, a charging member, a charging voltage applying portion, a developer carrying member, a developing voltage applying portion, a detecting portion, and a controller. In a state in which the charging voltage is applied to the charging member, the controller controls the detecting portion so as to detect whether or not a change amount between a current value detected by the detecting portion when the surface of the image bearing member opposing the developer carrying member before application of the developing voltage passes through an opposing portion where the charging member and the image bearing member oppose to each other and a current value detected by the detecting portion when the surface of the image bearing member opposing the developer carrying member after the application of the developing voltage passes through the opposing portion is a threshold or more.

An image forming apparatus includes an image forming device, a corrector, and a controller. The image forming device is configured to form an image on a sheet using a rotating body under a predetermined image forming condition. The corrector is configured to correct the image forming condition to adjust image density unevenness corresponding to a rotation cycle of the rotating body. The controller is configured to control the image forming device to form on at least one sheet (i) plural test images that are different in correction amount for the image forming condition and (ii) pointing portions indicating intervals corresponding to the rotation cycle of the rotating body, in a state where the rotating body is continuously rotated.

Provided is an image forming apparatus having a simple configuration capable of measuring a toner current included in a developing current and accurately calculating a toner charge amount based on the measurement result. The developing device has a developer carrier that carries a two-component developer including a magnetic carrier and toner. The density detecting device detects the density of the toner image. The current detecting unit detects a DC component of a developing current that flows when a developing voltage is applied to the developer carrier. The control unit, in a state in which the image carrier is rotated at two or more different linear speeds during non-image formation, forms the same reference image on the image carrier by the developing device, and estimates the toner charge amount based on the developing current when the reference image is formed and the density of the reference image.

Provided is an image forming apparatus having a simple configuration capable of measuring a toner current included in a developing current and accurately calculating a toner charge amount based on the measurement result. A developing device has a developer carrier that carries a two-component developer including a magnetic carrier and toner. A developing voltage power supply applies a developing voltage obtained by superimposing an AC voltage on a DC voltage on the developer carrier. A control unit estimates a toner charge amount based on a toner current calculated by subtracting a carrier current from a developing current detected by a current detecting unit when a reference image is formed during non-image formation, and a toner developing amount calculated from the density of a reference image detected by a density detecting device.