A contact-and-separation system includes a first roller, a second roller, and a contact-and-separation device. The first roller contacts a belt. The second roller is opposed to the first roller. The contact-and-separation device contacts or separates the belt to or from the second roller via a sheet conveyed. The contact-and-separation device includes an eccentric cam, a motor, and a circuitry. The eccentric cam is mounted on an end of a rotation shaft of the first roller. The motor rotates the eccentric cam. The circuitry controls the motor to rotate the eccentric cam to contact or separate the belt to or from the second roller via the sheet conveyed. The circuitry controls the motor to decelerate a rotation speed of the motor on contact or separation of the belt to or from the second roller between the first roller and the second roller.

A print head apparatus is provided for use with a xerographic printing device having a rotating photoreceptor with a curved conductive surface. The apparatus includes an LED bar print head configured for locating adjacent the photoreceptor; a first distance sensor located on the print head at a first location, the first distance sensor being configured for measuring a first gap between the print head and the photoreceptor at the first location; and a second distance sensor located on the print head at a second location, the second location being different from the first location, the second distance sensor being configured for measuring a second gap between the print head and the photoreceptor at the second location. The print head is configured such that the sensors are arranged on the print head such that the sensors are configured to enable a measurement of angular position of the print head relative to the surface of the photoreceptor.

An image-forming apparatus includes a main body, a belt unit detachably attachable to the main body, a coupling and a restricting part. The belt unit includes: a first roller defining an axis extending in an axial direction, a second roller opposing the first roller in a first direction perpendicular to the axial direction, and a belt looped over the first roller and the second roller. The coupling is configured to move in the axial direction to come into engagement with the first roller for inputting a drive force into the first roller. The restricting part is provided on the main body and is configured to restrict the first roller from moving in a second direction perpendicular to the axial direction and the first direction when the belt unit is attached to the main body.