An image forming apparatus includes a transferring belt, photosensitive drums along the belt, primary transferring parts transferring images from the drums to the belt, voltage applying parts applying transfer voltages to the respective transferring parts when each transferring part carries out transfer, a current detecting part and a resistance value measuring part. When the measuring part carries out resistance value measurement, if one transferring part is a measurement subject of the measuring part, the applying part applies zero or weak voltage to the one transferring part and applies the transfer voltage to other transferring parts at measurement timing when the one transferring part is between sheets. At the measurement timing, the detecting part detects a first total current value of currents flowing thorough the transferring parts and the measuring part measures the subject resistance value of the one transferring part based on the first total current value.

A relationship 150≦Rs (Ω)/Rm (Ω)≦4000 is established in an environment of a temperature of 15° C. and a humidity of 10% in a case where a surface resistance of a transfer roller is Rs (Ω) when a current is fed between a pair of electrodes facing each other in an axial direction of the transfer roller and arranged on a surface of the transfer roller with an interval of 5 mm therebetween, the electrodes having a width of 20 mm in a circumferential direction of the transfer roller in a state of being arranged on the transfer roller, and in a case where a combined resistance of a first layer and a second layer is Rm (Ω) when the current is fed from a core portion to an outer peripheral surface of the second layer.

An image forming apparatus includes an image bearing drum; a drum charging member at a charging position opposed to the drum, with a charging bias; a developing member for developing an electrostatic image formed on the drum with toner, with a developing bias; a transfer member for transferring a toner image from the drum onto a sheet, with a transfer bias; a transfer bias source for outputting transfer bias; and a controller for effecting control to start raising of the transfer bias so as to correspond to timing at which an area of the drum passing at a timing of starting of raising of the charging bias passes the transfer position and to complete the raising of the transfer bias so as to correspond to timing at which an area of the drum passing at a timing of completion of raising of the charging bias passes the transfer position.

An image forming apparatus includes a rotatable image bearing member, a developing member, a transfer member, and a brush contacting a surface of the image bearing member in a contact portion downstream of a transfer portion and upstream of a developing portion with respect to a rotational direction of the image bearing member. The toner which is not transferred onto a toner image receiving member is collected by the developing member. In a charging series, the toner is positioned on the same side as a normal charge polarity of the toner relative to the brush. In the contact portion, a maximum value of a contact pressure of 0.7 gf/mm.sup.2 or more and 3.5 gf/mm.sup.2 or less, a maximum contact area ratio is 18% or more and 74% or less, and a Clark-Evans index of the brush is 1 or more.

An image forming apparatus includes a photosensitive member, a charging member, an exposing device, a developing device, a transfer member, a brush, a voltage applying portion, and a control portion controlling a surface potential of the photosensitive member at the brush contacting position. When a value of subtracting a value of the surface potential of the photosensitive member in the brush contacting position from a value of the brush voltage is defined as a contacting position potential difference, the control portion controls the surface potential of the photosensitive member in the brush contacting position so that the contacting position potential difference is changed from a first potential difference to a second potential difference in a predetermined direction which is either one of an increasing direction or a decreasing direction, and then the contacting position potential difference is changed from the second potential difference to a third potential difference in the predetermined direction.

An image forming apparatus includes an image bearing member, an intermediary transfer member having ion conductivity and a rotatable endless belt shape, a primary transfer member, a secondary transfer member, a cleaning member, an environment sensor and a controller. Based on a result of the environment sensor, the controller controls so as to change a current balance based on an integrated value of a first current value and an integrated value of a second current value. The first current value is a current flowing from inside of the intermediary transfer member to outside thereof and the second current value is a current flowing from outside of the intermediary transfer member to inside thereof.

An image forming apparatus has an image carrier carrying a toner image; a transfer member made with an ion conductive material and forming a transfer nip by being pressed by the image carrier; and a power supply continuously applying a transfer bias voltage to the transfer member as a plurality of print media pass through the transfer nip. The transfer bias voltage has a predetermined polarity. A control section determines whether the resistance of a nip-margin area has exceeded a predetermined resistance threshold, the nip-margin area being a marginal portion of the transfer nip through which no print medium passes. When the determination of the control section is affirmative, the power supply applies a reverse-bias voltage to the transfer member, the reverse-bias voltage having an opposite polarity to the transfer bias voltage.

An image forming apparatus that includes an image bearing member which can bear a toner image, a transfer member used to transfer a toner image onto a recording material from the image bearing member, and a reading device which reads density information of images on recording material disposed on a platen. The image forming apparatus forms a first chart on a first recording material and a second chart on a second recording material by sequentially transferring a plurality of test images while applying a plurality of test voltages to the transfer member. The two charts are read by the reading device and the transfer voltage is adjusted based on the reading result.

An image forming apparatus includes an image bearing member; a transfer member configured to form a transfer portion where the toner image is transferred from the image bearing member by being supplied with a transfer bias; a carrier liquid supplying portion configured to supply the carrier liquid to the transfer portion; a transfer bias voltage source capable of applying the transfer bias to the transfer portion; a detecting portion configured to detect at least one of a voltage and a current at the transfer portion; and a setting portion configured to set the transfer bias during non-image-formation on the basis of a detection result of the detecting portion when a setting bias is applied from the transfer member in a state in which the carrier liquid is in the transfer portion.

A power supply is configured to apply voltage to a power feed roller. An elastic blade of a roller cleaning unit clean a surface of the power feed roller at a position different from an abutting position of the power feed roller and a secondary transfer outer roller. A control unit is configured to execute a secondary transfer cleaning mode at a timing when a transfer of a toner image in a secondary transfer portion is not performed. In the secondary transfer cleaning mode, a voltage of only one of the positive and negative polarities is applied to the power feed roller while the secondary transfer outer roller and the power feed roller are rotated.