Abstract: An overlap detection apparatus having a conveyance path for conveying letters including a letter release section where the letters are not held, a bending section formed in the letter release section, and a butt into which the forward end of the letters released from the conveyance path in the bending section is brought into contact. A detector is provided for detecting the forward end of a letter on the butt and an overlap judging arrangement for judging an overlap of letters based on the result of detection by the detector. The detector includes a light source for projecting light on the surface of a letter and a line sensor having a plurality of light receiving elements arranged in a line, wherein the line sensor detects a shadow of the forward end of the letters cast by the light source.

Abstract: An overlapped mail detection apparatus and method are disclosed. Since the postcard is shorter than the letter, the change in length is not sometimes detected even when the postcard is displaced. In the case where the exterior of the letter is deformed outward and an overlap is detected from the rise of the tail end of the letter after passing a guide, a thin letter or the like low in rigidity is hard to detect due to the slow rise after deformation in the guide. In view of this, a separator has a bent conveyance path for deforming the exterior of the letter outward. The conveyance surfaces constituting the inner and outer sides of the bent portion of the separator are spaced appropriately from each other. A detector detects the state of the letter surface in the neighborhood of the outer conveyance surface with which the forward end of the letter first comes into contact. An overlap of letters is judged from the result of detection by the detector.