Patent ID: 8740326

Claim:
A recording medium lift detection apparatus for detecting a lift of a recording medium that is conveyed on a predetermined conveyance surface along a predetermined conveyance path, the recording medium lift detection apparatus comprising: a light projection/receiving device which has a light projection unit for emitting a detection beam and a light receiving unit for receiving the detection beam, the light projection unit and the light receiving unit being disposed so as to face each other across the conveyance path; a light projection parallel flat plate, installed on an optical path of the detection beam between the light projection unit and the conveyance path, for causing parallel shift of the optical path of the detection beam; a light projection turning device for turning the light projection parallel flat plate; a control device for controlling the light projection turning device; and a recording medium lift detection control device that monitors an amount of light received by the light receiving unit, and stops conveying the recording medium or outputs an alarm when the amount of light received by the light receiving unit is equal to or lower than a predetermined value, wherein: the light projection/receiving device is installed in such a manner that the detection beam is positioned at a predetermined height above the conveyance surface, the light projection parallel flat plate has a beam entrance surface and a beam emission surface parallel to each other, and is configured to turn about a rotational axis perpendicular to the detection beam, so as to refract the detection beam having entered from the beam entrance surface to cause the parallel shift of the optical path of the detection beam in a direction away from the conveyance surface and emit the detection beam from the beam emission surface, the light projection turning device is connected to the rotational axis of the light projection parallel flat plate, and the control device controls the light projection turning device at predetermined timing so as to turn the light projection parallel flat plate to cause the parallel shift of the detection beam in the direction away from the conveyance surface.