The present invention has a purpose of providing a paper sensor device capable of measuring measurement light with high precision to detect a paper property with high precision without adding to printing time. A paper sensor device includes: a light-emitter that emits emission light; a photodetector that receives emission light in a first state and receives light transmitted through a sheet of paper in a second state; and a transporting unit that transports the sheet of paper. The transporting unit, including a transport roller and a paper guide, transports the sheet of paper while sandwiching the sheet of paper between the transport roller and the paper guide. The light-emitter is embedded in the transport roller. The photodetector is disposed on the back of the paper guide to receive light via a window.

A paper feeder includes a lift plate, a pickup roller, a feed roller, a retard roller, a rotation-count detection sensor, and a control unit. The rotation-count detection sensor outputs a rotation-count detection signal. The rotation-count detection signal indicates a rotation count of the retard roller. The control unit detects the rotation count of the retard roller based on the rotation-count detection signal. The lift plate separates from the pickup roller before the control unit detects the rotation count of the retard roller. The feed roller is driven when the control unit detects the rotation count of the retard roller. The retard roller is in abutting contact with the feed roller when the control unit detects the rotation count of the retard roller. The control unit determines whether replacement of the retard roller is necessary or not, based on the detected rotation count of the retard roller.

In accordance with an embodiment, a sheet conveyance apparatus comprises a roller, an acceleration sensor, and a controller. The roller conveys a sheet. The acceleration sensor is attached to the roller to output a signal indicating a direction of gravitational acceleration applied to the roller at the time the roller rotates. The controller acquires cumulative angle at which the roller rotates based on the signal output by the acceleration sensor. The controller determines whether to replace the roller based on the cumulative angle acquired by the rotation angle acquisition section.

A paper feeder includes a lift plate, a pickup roller, a feed roller, a retard roller, a rotation-count detection sensor, and a control unit. The rotation-count detection sensor outputs a rotation-count detection signal. The rotation-count detection signal indicates a rotation count of the retard roller. The control unit detects the rotation count of the retard roller based on the rotation-count detection signal. The lift plate separates from the pickup roller before the control unit detects the rotation count of the retard roller. The feed roller is driven when the control unit detects the rotation count of the retard roller. The retard roller is in abutting contact with the feed roller when the control unit detects the rotation count of the retard roller. The control unit determines whether replacement of the retard roller is necessary or not, based on the detected rotation count of the retard roller.