Patent ID: 7583561
Filing Date: 2009-09-01
Classification: B65H

Abstract:
1. A feed detecting system, comprising: a sending element used to send an ultrasonic signal; a receiving element used to receive the ultrasonic signal sent by the sending element, the receiving element converting the ultrasonic signal to an electric signal; a filtering-amplifying circuit connected to the receiving element, used to receive, filter and amplify the electric signal, and then output the electric signal; a peak-holding circuit connected to the filter-amplifying circuit, used to receive the electric signal from the filtering-amplifying circuit and hold a peak value of the electric signal for a span; an A/D converter connected to the peak-holding circuit, used to receive and convert the peak value of the electric signal into a digital signal, then output the digital signal; a processing unit connected to the A/D converter, a standard value stored in the processing unit, the standard value corresponding to a critical value between the ultrasonic wave from the sending element passing through one sheet and the ultrasonic wave passing through two sheets, the processing unit reading the digital signal from the A/D converter and comparing the digital signal with the standard value; and wherein the filtering-amplifying circuit includes three capacitances, four resistances and a first OPAMP, a single electric source supplies the first OPAMP, the first capacitance, the first resistance and the third capacitance connect in series and connect to an anti-phase input point of the first OPAMP, a Vbias point connects to an in-phase input point of the first OPAMP via the fourth resistance, the second capacitance and the second resistance connect in series and connect a signal output point of the first OPAMP to GND, a connecting wire connecting the second capacitance and the second resistance connects to a connecting wire connecting the first resistance and the third capacitance, the third resistance connects the signal output point to the anti-phase input point, a signal input point delivers the signal from the receiving element to the first capacitance, the signal is processed by the filtering-amplifying circuit and then delivers to the peak-holding circuit.