An image forming apparatus includes an transfer section including a transfer roller and a rotatable member and performing transfer processing in which it transfers a developer to a recording medium; a power source controller that applies a voltage to the transfer roller and measures a current value of a current that flows through the transfer roller and the rotatable member; and a main controller that calculates a first electrical resistance value between the transfer roller and the rotatable member in if the recording medium is absent between the transfer roller and the rotatable member and a second electrical resistance value between the transfer roller and the rotatable member if the recording medium is present between the transfer roller and the rotatable member on the basis of the current value measured by the power source controller, and determines a transfer voltage value for the transfer processing.

An image forming apparatus includes an image bearing member, a transfer member, a voltage source, a speed setting portion, a test mode executing portion, a renewing mode executing portion, and a setting portion for setting a voltage applied to the transfer member. In a period in which the toner image exists at the transfer portion when image formation is executed at a first speed, the setting portion sets the voltage applied to the transfer member at a first target voltage last renewed. In a period in which the toner image exists at the transfer portion when the image formation is executed at a second speed, the setting portion sets the voltage applied to the transfer member at a voltage on the basis of the first target voltage last renewed and a conversion coefficient last renewed.

An image forming apparatus includes a toner image forming unit, a nip formation member, a transfer power source, an information acquisition device, and a controller. The information acquisition device acquires specific information that specifies whether a recording sheet as a transfer target of a toner image is an uneven surface sheet having an uneven surface. The controller outputs a bias including a superimposed voltage, in which an alternating current (AC) voltage is superimposed on a direct current (DC) voltage, as a transfer bias from the transfer power source when the specific information acquired by the information acquisition device is not information corresponding to the uneven surface sheet and to output a bias including only the DC voltage as the transfer bias from the transfer power source when the specific information is the information corresponding to the uneven surface sheet.

An image forming apparatus includes: an image forming unit configured to form an image on a recording medium which is unwound from a state of being wound in a roll shape; and a control unit configured to change an image forming condition of the image forming unit such that image quality becomes uniform before and after an unwinding start position of the recording medium at the time of start of an image forming operation.

An improved image forming apparatus includes an image bearer, a nip forming member, a transfer power source, and a controller. The controller switches a transfer mode between a first mode to transfer the toner image onto a first type sheet having a surface smoothness higher than a surface smoothness of a second type sheet and a second mode to transfer the toner image onto the second type sheet. The controller controls the transfer power source to output the transfer bias having an opposite-peak duty of greater than or equal to 50% that is a duty on the side of the opposite-peak value in the first mode. The controller controls the transfer power source to output the transfer bias having an opposite-peak duty of less than 50%, which is different from the opposite-peak duty of the first mode, in the second mode.

An image forming apparatus includes an image bearer to bear a toner image, a nip forming member contacting the image bearer to form a transfer nip, and a transfer power source. The transfer bias has a transfer peak value to electrostatically move toner from the image bearer to the recording sheet and an opposite-peak value to electrostatically move less toner from the image bearer to the recording sheet than the transfer peak value. An opposite-peak duty of the transfer bias is less than 50%. The opposite-peak duty is tr/T×100% where T is one cycle of the transfer bias and tr is a time period during which the transfer bias is on a side of the opposite-peak value relative to an offset voltage of the transfer bias in the one cycle T.

An imaging system includes a transfer roller, a bias application device, and a controller. The transfer roller forms a transfer nip region between the transfer roller and a transfer belt, and the transfer roller transfers toner images carried on the transfer belt, onto media conveyed through the transfer nip region, during a print job. The bias application device applies a bias to the transfer roller. The controller controls the bias application device to apply a first bias to the transfer roller so that the toner image is transferred to a first medium during the printing job, apply a second bias having a polarity opposite to the first bias to the transfer roller between the first medium and a second medium following the first medium, and apply a third bias having the same polarity as the first bias to the transfer roller between the first medium and the second medium.

A rotation center of a secondary transfer inner roller located at a first position is located downstream of a rotation center of a secondary transfer outer roller in a movement direction of an intermediate transfer belt tensioned by the secondary transfer inner roller and an idler roller. The rotation center of the secondary transfer inner roller located at a second position coincides in position with the rotation center of the secondary transfer outer roller, or is located upstream of the rotation center of the secondary transfer outer roller in the movement direction of the intermediate transfer belt tensioned by the secondary transfer inner roller and the idler roller.

An image forming apparatus, having a photosensitive drum, a developing roller movable between a contacting position, in which the developing roller contacts the photosensitive drum, and a separated position, in which the developing roller is separated from the photosensitive drum, a moving mechanism to move the developing roller between the contacting position and the separated position, a fuser including a heating member and a pressing member to nip a sheet at a position between the heating member and the pressing member, a nipping-force adjuster to switch a nipping force in the fuser between a first nipping force and a second nipping force being greater than the first nipping force, a motor, and a driving-force transmitter to transmit a driving force from the motor to the developing roller, is provided. The driving-force transmitter transmits the driving force further to the moving mechanism and the nipping-force adjuster.

An image forming device that forms image by transferring toner image formed by developing electrostatic latent image formed on a photoreceptor from the photoreceptor to an intermediate transfer body by applying a transfer bias to a transfer member and putting the transfer member in contact with the intermediate transfer body. The device includes: a current supplier selectively supplying a first constant current and a second constant current to the transfer member; a first voltage acquirer acquiring a first voltage occurring between the transfer member and the intermediate transfer body while the transfer member is supplied with the first constant current; a second voltage acquirer acquiring a second voltage occurring between the transfer member and the photoreceptor while the transfer member is supplied with the second constant current; and a thickness acquirer acquiring a value indicating photoreceptor layer thickness of the photoreceptor by using the first and second voltages.