Patent ID: 8531742

Claim:
A sheet detecting device detecting a sheet being conveyed, comprising: an ultrasound generator generating ultrasound; a transmitting side opening, which includes a first opening and a second opening to transmit the ultrasound, wherein the transmitting side openings are arranged in an arrangement direction being vertical to a conveying direction, in which the sheet is to be conveyed, and provided above a face being parallel to a plane of the sheet to be conveyed; a transmitting side propagation unit, which is connected to the ultrasound generator and each of the transmitting side openings, and which transfers the ultrasound generated by the ultrasound generator to the transmitting side opening; a receiving side opening, which includes a third opening and a fourth opening to receives the ultrasound transmitted from the first opening and the second opening, wherein the receiving side openings are arranged in the arrangement direction to face the transmitting side opening; an ultrasound receiver receiving the ultrasound received by the receiving side openings; a receiving side propagation unit, which is connected to each of the receiving side openings and the ultrasound receiver, and which transfers the ultrasound received by the receiving side opening to the ultrasound receiver; and a first determining unit, which determines amplitude of the ultrasound received by the ultrasound receiver with corresponding to a time point, in which the ultrasound is received by the ultrasound receiver, wherein a first distance from the ultrasound generator to the first opening is different from a second distance from the ultrasound generator to the second opening, and wherein a third distance from the ultrasound receiver to the third opening is different from a fourth distance from the ultrasound receiver to the fourth opening.