An image forming apparatus according to the present invention includes: a driver that presses and separates two rollers via a belt; a detector that detects a position of the belt in an axial direction of one roller of the two rollers; and a hardware processor that calculates, based on a detection result by the detector, a first movement amount of the position of the belt in the axial direction when the belt is made to travel for a predetermined time in a state where the two rollers are separated and a second movement amount of the position of the belt in the axial direction when the belt is made to travel for the predetermined time in a state where the two rollers are pressed.

A transfer device for an image forming apparatus includes a frame, a driving roller, a backup roller, and a transfer belt to travel between the driving roller and the backup roller. The transfer device further include meandering prevention members to rotate independently of the backup roller, the meandering prevention members including a first meandering prevention member located between a first end portion of the backup roller and the frame, and a second meandering prevention member located between a second end portion of the backup roller and the frame. When the transfer belt meanders and contacts one of the first and second meandering prevention members, the one of the first and second meandering prevention members is to be rotatably driven to increase a tension of the transfer belt.

The present invention provides a fixing device including a flexible cylindrical rotary member and an inner-surface opposing portion that opposes an inner surface of the rotary member at an end portion of the rotary member in a generatrix direction. The inner-surface opposing portion moves upstream in a recording material conveying direction in accordance with lateral shift of the rotary member in the generatrix direction. This restricts the lateral shift of the rotary member.

A pair of pressure members are disposed at both ends of a pressure roller and rotatably support the pressure roller to press the pressure roller against a fixing roller including an elastic layer via a fixing belt. One of the pressure members that includes a fulcrum engaging section engaged with a rotation fulcrum at one end and is locked to a biasing member at a side opposite to the fulcrum engaging section is moved by a moving member in a direction intersecting a pressing direction of the pressure roller in a state where deformation of the elastic layer is regulated. Thus, a force acting on a fixing nip formed by the deformation of the elastic layer of the fixing roller is stabilized. As a result, the traveling performance of the fixing belt is stabilized, whereby the offset control can be performed with high accuracy.

A belt driving device includes plural rotating members around which a belt member extends, each rotating member rotating about a rotating shaft; and contact members disposed at both sides of the belt member in a width direction. The rotating members include a first rotating member, having a dimension less than a width of the belt member in a direction of the rotating shaft. Each contact member has a first contact point at which the contact member contacts the belt member and a second contact point closer to a corresponding one of the end portions in the width direction than the first contact point and at which the contact member contacts the belt member such that an angle between the contact member and the rotating shaft at the second contact point is greater than an angle between the contact member and the rotating shaft at the first contact point.

A belt driving device includes an annular belt member, rotary members, a protrusion, and a contact member. The belt member includes first and second edges. The belt member is wound around the rotary members. The protrusion protrudes from an inner peripheral surface of the belt member. The protrusion and each rotary member are arranged in an extending direction of the rotary member. The protrusion is provided at the second edge. The contact member is closer to the first edge. When the belt member deviates, the contact member comes into contact with the belt member. A difference between a position of the belt member when the protrusion comes into contact with an end surface of one of the rotary members and a position of the belt member when the belt member comes into contact with the contact member is equal to or less than a width of the protrusion.

A transfer device having a structure for preventing the meandering of a transfer belt, an image forming apparatus including a structure for preventing the meandering of a transfer belt, and a method for preventing meandering of the transfer belt. The image forming apparatus including a main body. The main body including an image forming member and a transfer device which transfers an image formed through the image forming member to a printing medium. The transfer device includes a frame, a driving roller, a backup roller being rotatably supported to the frame, a transfer belt to travel between the driving roller and the backup roller; and meandering prevention members located at both end portions of the backup roller to independently rotate. The meandering prevention members being driven by contact with the transfer belt to control tension of the transfer belt.

A belt drive device includes a first pulley, a second pulley, a first bulging portion, a belt, and a pressing portion. The first bulging portion is formed along an outer periphery of the second pulley to bulge outward in a radial direction of the second pulley at a center of the second pulley in an axial direction of the second pulley. The belt is stretched between the first pulley and the first bulging portion. The pressing portion presses an outer peripheral surface of the belt at a center of the belt in a width direction of the belt.

The present invention provides a fixing device including a flexible cylindrical rotary member and an inner-surface opposing portion that opposes an inner surface of the rotary member at an end portion of the rotary member in a generatrix direction. The inner-surface opposing portion moves upstream in a recording material conveying direction in accordance with lateral shift of the rotary member in the generatrix direction. This restricts the lateral shift of the rotary member.

An image forming apparatus includes a belt rotating member forming, with the rotating member, a nip portion for fixing a toner image to the recording medium, first and second rollers rotatably supporting the belt rotating member, a stepping motor tilting the first roller, an output unit outputting an amount-of-rotation signal instructing an amount of rotation of a rotor in the stepping motor, an electric current control unit controlling electric current to be fed to a coil in the stepping motor based on the amount-of-rotation signal, and a notifying unit. The notifying unit provides a predetermined notification in a state that an image formation process can be executed based on an output from a detecting unit configured to detect a position of the first roller and a value counted by a measuring unit counting the amount of rotation instructed by the output unit.