A developing device for forming an image by developing an electrostatic latent image formed on an image carrier with a developer, includes: a developing container that accommodates the developer, a developing roller that faces the image carrier, is disposed adjacent to the developing container, and conveys the developer accommodated in the developing container to the image carrier, and a developer discharging part that is provided in the developing container and discharges a part of the developer, wherein a discharge amount of the developer discharged by the developer discharging part is controlled on the basis of a charge amount of a toner included in the developer.

In one example, a method for calibrating a position of a charge roller is described. The method may include a processor positioning a first end of a charge roller to a first plurality of index positions, determining a capacitance between the charge roller and a photoconductor imaging plate at each of the first plurality of index positions, determining a first index position of the first plurality of index positions with a greatest change in capacitance, and calibrating a position of the charge roller based upon the first index position.

A method of controlling transfer power of an image forming apparatus includes: determining a sensing feedback voltage by applying a set sensing current and measuring a first output voltage during a time period before an image is transferred to a transfer medium; measuring humidity and comparing the measured humidity with a set value; setting a target voltage based on the determined sensing feedback voltage when the measured humidity is equal to or higher than the set value; and adjusting the transfer current to apply the target voltage during a time period in which the image is transferred to the transfer medium.

In one example, a method for calibrating a position of a charge roller is described. The method may include a processor positioning a first end of a charge roller to a first plurality of index positions, determining a capacitance between the charge roller and a photoconductor imaging plate at each of the first plurality of index positions, determining a first index position of the first plurality of index positions with a greatest change in capacitance, and calibrating a position of the charge roller based upon the first index position.

An embodiment provides an image forming apparatus that has a first operation mode and a second operation mode. The first operation mode forms an image on a sheet with toner. The second operation mode decolorizes the toner on the sheet on which the image is formed with a decolorable toner having a decoloring function. In the first operation mode, when the sheet passes through a transfer unit, a transfer bias having the same polarity as that of a charge of the toner is applied to the transfer member and a toner image formed on a surface of the transfer member is transferred to the sheet. In the second operation mode, when the sheet passes through the transfer unit, a cleaning bias having a reverse polarity to that of the transfer bias is applied to the transfer member.

In an image forming apparatus, a control unit performs a control for determining a surface potential A to determine a first voltage to be applied to a charge roller by a charge voltage application circuit so that a surface potential of a photosensitive drum becomes a first potential. The charge voltage application circuit thereafter applies the first voltage to the charge roller to charge the photosensitive drum. In such a state, the control unit performs a second control to determine a light amount of a laser light source, so that the surface potential of the photosensitive drum becomes a second potential. In such a manner, a potential of a photosensitive drum surface is detected with high accuracy. Moreover, a time taken to detect the potential of the photosensitive drum surface is shortened.

An image forming apparatus includes an image bearing member, an intermediary transfer belt, a primary transfer roller provided so that a contact region between the roller and the belt and a contact region between the image bearing member and the belt are in a non-overlapping state with each other with respect to a movement direction of the belt, a primary transfer voltage source, a current detecting portion, an executing portion configured to acquire information on a discharge start voltage on the basis of a detection result of the detecting portion in a period other than a period of primary transfer by applying the voltage to the roller and a setting portion configured to set, on the basis of an execution result of the executing portion, a primary transfer voltage applied to the roller by the primary transfer voltage source in the period of the primary transfer.

In the image forming apparatus, a controller makes a reference image formed on an outer circumferential surface of an image carrier and transferred to a belt. Then, uncollected toner of the reference image, which is part of after-transfer remaining toner of the reference image that has missed being collected so as to remain even after one-round rotation of the image carrier, is transferred to the belt. The controller measures a collectable toner quantity corresponding to an applied voltage of the cleaning roller on a basis of an uncollected toner quantity estimated based on a toner concentration of the uncollected toner, and executes such adjustment that the collectable toner quantity becomes equal to or larger than a maximum value of the after-transfer remaining toner quantity and moreover the applied voltage becomes equal to or lower than a maximum applicable voltage.

A heating member of a fixing unit is situated in a fixing portion, and a commercial power source applies an alternating-current voltage to the heating member so that the heating member heats a transfer medium held in the fixing portion. In a case of transferring the toner image from an image bearing member onto the transfer medium in a transfer portion, a control unit controls a transfer power source based on a result of a comparison between a frequency obtained from a first detection result input from a detection unit with a predetermined frequency range including the frequency of the alternating-current voltage.

An image forming apparatus which forms an image on a recording material includes a transfer unit which transfers a toner image formed on an image bearing member to a recording medium, an applying unit which applies a predetermined current or voltage to the transfer unit, a detection unit which detects a voltage value with respect to the predetermined current applied by the applying unit or a current value with respect to the predetermined voltage applied by the applying unit, an environment detection sensor which detects an environment, and a determination unit which compares a detection result of the detection unit with a predetermined value according to a detection result of the environment detection sensor to determine whether or not predetermined discharge occurs in the transfer unit.