According to one embodiment, in an image forming apparatus, a frame that supports a transfer belt conveying a toner image in a conveyance direction and image forming units aligned along the transfer belt is provided with a dowel hole between the image forming units in a direction parallel to the conveyance direction and is also provided with an elongated hole having a long axis in a direction parallel to the conveyance direction, a dowel between the exposure units of a chassis supporting exposure units in a direction parallel to the conveyance direction is fitted to the dowel hole, and another dowel is inserted into the elongated hole.

An image forming apparatus includes a motor, an image formation-transfer section, a switching mechanism, a fixing section, and a controller. The motor generates driving force. The image formation-transfer section state-changes between a first contact state and a first separate state by the driving force. The switching mechanism transmits and cuts off the driving force to the image formation-transfer section. The fixing section includes first and second rotating members, and state-changes between a second contact state and a second separate state by the driving force. The controller controls the motor and the switching mechanism and thereby causes part or all of a first period, in which the fixing section state-changes from the second separate state to the second contact state, and part or all of a second period, in which the image formation-transfer section state-changes from the first separate state to the first contact state, to overlap each other.

An image forming apparatus includes a first image forming unit and a second image forming unit to form first toner images and second toner images, respectively, of different colors, a transfer member to transferred received toner images to a position, and a contact/separation unit to switch between first and second modes. Where a first, second, and third image are formed in order on sheets, the mode is switched from the first to the second mode after the transfer member receives the first image to the transfer member and before formation of the second image by the first image forming unit is started if a first image length in a conveyance direction is smaller than a predetermined length. After the sheet receives the first image, the contact/separation unit switches the mode from the first to the second mode if the first image length is greater than the predetermined length.

An image forming apparatus includes an image forming section, a driving unit and an operation unit. The image forming section includes one or more image forming units. The driving unit generates driving force. The operation unit selectively performs a first operation and a second operation. The first operation is an operation to change over from a coupled state of the one or more image forming units and the driving unit, which the driving force is transmitted to the one or more image forming units, to a released state of the one or more image forming unit and the driving unit, which the driving force from the driving unit is not transmitted to the one or more image forming units. When the second operation is performed, the released state is maintained.

An image forming apparatus includes: multiple image forming units that form toner images; an intermediate transfer belt that rotates so as to pass through the image forming units; multiple first-transfer rollers that are provided in a manner capable of being displaced between transfer positions, where the first-transfer rollers make the intermediate transfer belt come into contact with the image forming units, and retracted positions, where the first-transfer rollers make the intermediate transfer belt be separated from the image forming units, and that first-transfer the toner images to the intermediate transfer belt when the first-transfer rollers are located at the transfer positions; a displacement mechanism including a moving unit that comes into contact with and moves a first-transfer roller that is not involved in transfer in a first mode, in which an image is formed with one image forming unit, among the first-transfer rollers of the image forming units, so as to be displace the first transfer roller to the retracted position, and a rotating cam that comes into contact with a portion of the moving unit to move the moving unit in the first mode; and upstream-side and downstream-side retention rollers in contact with an inner circumferential surface of the intermediate transfer belt and supporting passing positions of the intermediate transfer belt at a position immediately upstream of the first-transfer roller that is disposed on the extreme upstream side in the rotation direction of the intermediate transfer belt and a position immediately downstream of the first-transfer roller that is disposed on the extreme downstream side in the rotation direction of the intermediate transfer belt, respectively. In a second mode, in which an image is formed with two or more image forming units of the image forming units, and when all the first-transfer rollers are located at the transfer positions, the displacement mechanism adjusts the passing position of the intermediate transfer belt by bringing a portion of the rotating cam into contact with the moving unit to move the moving unit and thus displacing one of the upstream-side and downstream-side retention rollers.

An image forming apparatus includes a first image forming unit and a second image forming unit to form first toner images and second toner images, respectively, of different colors, a transfer member to transferred received toner images to a position, and a contact/separation unit to switch between first and second modes. Where a first, second, and third image are formed in order on sheets, the mode is switched from the first to the second mode after the transfer member receives the first image to the transfer member and before formation of the second image by the first image forming unit is started if a first image length in a conveyance direction is smaller than a predetermined length. After the sheet receives the first image, the contact/separation unit switches the mode from the first to the second mode if the first image length is greater than the predetermined length.

An image forming apparatus includes: an image holding section; a transfer section that includes a transfer member, applies a transfer electric-field to a transfer region between the image holding section and the transfer member, and electrostatically transfers an image held by the image holding section onto a recording medium; a contact section that acts as an electrode to ground while being in contact with the recording medium when the recording medium passes through the transfer region; a first resistance detection section; a second resistance detection section; a comparison section that compares a first system resistance detected by the first resistance detection section with a second system resistance detected by the second resistance detection section; and a switching section that switches between constant voltage control and constant current control for the transfer electric-field produced by the transfer section depending on a result of comparison by the comparison section.

An image forming apparatus includes: a transport unit that transports a recording medium; a transfer unit that transfers an image formed with particles onto an image formation surface of the recording medium transported by the transport unit by an electric field formed between the transfer unit and the image formation surface by making contact with the image formation surface; and a support unit that supports the recording medium, is transported to the transfer unit together with the recording medium by the transport unit, and is not directly conductive with the transfer unit.

An image forming apparatus includes a photoconductor, a charger; a charge voltage applier that applies first and second charge voltages to the charger; an exposure device; a development device; a development voltage applier that applies first and second development voltages to the development device; a transfer device; a fixing device; a motor that drives the photoconductor simultaneously with at least one of the transfer device, the fixing device, and the transporter; and a controller. When the motor is driven for image formation, the first charge voltage and the first development voltage are respectively applied to the charge voltage applier and the development voltage applier. When the motor is driven for an operation other than image formation, the second charge voltage and the second development voltage are respectively applied to the charge voltage applier and the development voltage applier.

An image forming apparatus includes a mechanism configured to bring an intermediate transfer member into a first state contacting first and second drums and a second state separating from the first drum and contacting the second drum. The image forming apparatus is operable in a first mode of using the first and second drums in the first state, a second mode of using only the second drum in the second state, and a third mode of using only the second drum in the first state. If an image forming retry involving cleaning a transfer portion due to a recording medium conveyance delay in the third mode is to be performed, a controller changes over the third mode to the second mode without stopping rotation of the second drum to perform image formation on a recording medium fed by restart of a feeding operation.