Patent ID: 6212130
Filing Date: 2001-04-03
Classification: B65H,G01N

Abstract:
A method for the detection of overlapped sheets, the sheets being conveyed along a transport path and being supported in a plane during movement, said method comprising the steps of:positioning an ultrasound beam generator on a first side of the transport path, the beam generator producing a beam of ultrasound energy having a frequency and an axis and being oriented such that the axis of the beam of ultrasound energy produced thereby intersects the plane in which the sheets are supported at an acute angle;locating an ultrasound receiver on the second side of the transport path and in axial alignment with the beam generator, an air gap through which the sheets are transported thus being present between the beam generator and beam receiver, the ultrasound receiver providing electrical signals commensurate with ultrasonic energy incident thereon;selecting the frequency of the ultrasound energy such that multiple sheets present in the air gap will function as an interference filter whereby the wavefronts of the transmitted ultrasound energy will destructively combine and the degree of attenuation will be substantially greater than that caused by a single sheet;energizing the ultrasound beam generator to cause the production of bursts of energy at the selected frequency;determining from the signals provided by the receiver whether the degree of attenuation of ultrasound energy which traverses the air gap between the beam generator and ultrasound receiver is commensurate with the presence of closely spaced plural sheets in the air gap; andproviding an alarm when the degree of attenuation of the ultrasound energy is indicative of plural sheets being present in the path of the beam of ultrasound energy.