Patent Publication Number: US-7583561-B2

Title: Feed detecting system

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This present invention relates to a sensor system, and more specifically to a feed detecting system for processing a feed detecting signal which is used in a scanner and a printer, etc. 
   2. The Related Art 
   Conventionally, a sheet-feeding apparatus is arranged in a scanner or a printer, for static electricity between papers or others reasons, two papers or more are fetched by the sheet-feeding apparatus in one time, the papers will block a paper passageway in the scanner or the printer, or a part of the paper will not be scanned or printed for being sheltered. 
   U.S. Pat. No. 7,172,195 has disclosed an image reading apparatus, the image reading apparatus comprises an ultrasonic wave sensor, the ultrasonic wave sensor includes a wave sending element and a wave receiving element having a same structure with the wave sending element. The wave receiving element and the wave sending element are arranged in the top and the bottom sides of the transport path of the image reading apparatus respectively. While a sheet passes through the image reading apparatus along the transport path, the wave sending element sends an ultrasonic signal to the sheet, the ultrasonic wave passes through the sheet, the ultrasonic wave is attenuated differently in case of one sheet and in case of two or more sheets. Then the ultrasonic wave is amplified, rectified and converted to digital signal, the digital signal is compared with a standard value stored in a control CPU, the standard value is indicated by the ultrasonic wave passing through a sheet. If the digital signal is greater than the standard value, no sheet passes through the transport path; if the digital signal is less than the standard value, two sheets or more pass through the transport path; if the digital signal equals with the standard value, one sheet passes through the transport path. 
   For converting the ultrasonic wave to a digital signal, an A/D converter is arranged in the image reading apparatus. In order to exactly detecting the ultrasonic wave, the A/D converter must be a high frequency A/D converter, the high frequency A/D converter is a high cost, so the cost of the image reading apparatus is improved. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide a feed detecting system, the feed detecting system includes a sending element, a receiving element, a filtering-amplifying circuit, a peak-holding circuit, an A/D converter and a processing unit. The sending element is used to send an ultrasonic signal. The receiving element is used to receive the ultrasonic signal sent by the sending element, and the receiving element converts the ultrasonic signal to an electric signal. The filtering-amplifying circuit connects to the receiving element, and is used to receive, filter and amplify the electric signal, and then outputs the electric signal. The peak-holding circuit connects to the filter-amplifying circuit, and is used to receive the electric signal from the filtering-amplifying circuit, and hold a peak value of the electric signal for a span. The A/D converter connects to the peak-holding circuit, the A/D converter is used to receive and convert the peak value of the electric signal into a digital signal, then output the digital signal. The processing unit connects to the A/D converter, a standard value is stored in the processing unit, the processing unit reads the digital signal and compares the digital signal with the standard value. The standard value is a critical value between the ultrasonic wave from the sending element passing through one sheet and the ultrasonic wave passing through two sheets. 
   As above description, the peak-holding circuit receives the electric signal and holds the peak value of the electric signal for a span, the A/D converter may be a lower frequency A/D converter, but can satisfy the present feed detecting system, so the cost of the feed detecting system is reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with its objects and the advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram showing a feed detecting system according to the present invention; 
       FIG. 2  is a circuit diagram of a filtering-amplifying circuit according to an embodiment of the present invention; and 
       FIG. 3  is a circuit diagram of a peak-holding circuit according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   First referring to  FIG. 1 , a feed detecting system  1  according to the invention is shown. The feed detecting system  1  is arranged in a printer or a scanner, etc. The feed detecting system  1  includes a sending element  10 , a receiving element  20 , a filtering-amplifying circuit  30 , a peak-holding circuit  40 , an A/D converter  50  and a processing unit  60 . 
   The sending element  10  is used to send an ultrasonic wave. The receiving element  20  is used to receiving the ultrasonic wave from the sending element  10 , and converts the ultrasonic wave to an electric signal. The filtering-amplifying circuit  30  connects to the receiving element  20  for receiving the electric signal, then filtering and amplifying the electric signal. The peak-holding circuit  40  connects to the filtering-amplifying circuit  30  for receiving the electric signal from the filtering-amplifying circuit  30 , the peak-holding circuit  40  holds a peak value of the electric signal for a span. The A/D converter  50  connects to the peak-holding circuit  40  for receiving the peak value of the electric signal from the peak-holding circuit  40  and converting the peak value of the electric signal to a digital signal. The processing unit  60  connects to the A/D converter  50  for receiving the digital signal from the A/D converter  50  and comparing the digital signal with a standard value stored in the processing unit  60 , and then the processing unit  60  sends a resetting signal to eliminate the peak value in the peak-holding circuit  40 . 
   The standard value is corresponding to a critical value between the ultrasonic wave from the sending element  10  passing through one sheet and the ultrasonic wave passing through two sheets. The processing unit  60  reads the digital signal from the A/D converter  50  and compares the digital signal with the standard value. If the digital signal is more than the standard value, the feed detecting system decides that no sheet passes through between the sending element  10  and the receiving element  20 ; if the digital signal is less than the standard value, the feed detecting system decides that two sheets or more pass through between the sending element  10  and the receiving element  20 , the feed detecting system  1  sends a warning to the printer or the scanner; and if the digital signal nearly equals to the standard value, the feed detecting system decides that one sheet passes through between the sending element  10  and the receiving element  20 , the sheet is processed unceasingly in the printer or the scanner. 
   The filtering-amplifying circuit  30  showing in  FIG. 2  is an embodiment. The filtering-amplifying circuit  30  includes three capacitances C 1 , C 2  and C 3 , four resistances R 1 , R 2 , R 3  and R 4 , and a first OPAMP (operational amplifier). A single electric source supplies the first OPAMP. The first capacitance C 1 , the first resistance R 1  and the third capacitance C 3  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 R 4 . The second capacitance C 2  and the second resistance R 2  connect in series and connect a signal output point of the first OPAMP to GND. A connecting wire connecting the second capacitance C 2  and the second resistance R 2  connects to a connecting wire connecting the first resistance R 1  and the third capacitance C 3 . The third resistance R 3  connects the signal output point to the anti-phase input point. A signal input point delivers the signal from the receiving element  20  to the first capacitance C 1 . The signal is processed by the filtering-amplifying circuit  30  and then delivers to the peak-holding circuit  40 . 
   The peak-holding circuit  40  in  FIG. 3  is an embodiment. The peak-holding circuit  40  includes three resistances R 5 , R 6  and R 7 , two diodes D 1  and D 2 , two capacitances C 5  and C 6 , and a second OPAMP. A single electric source supplies the second OPAMP. An input signal from the filtering-amplifying circuit  30  is delivered to an in-phase input point of the second OPAMP via the fifth resistance R 5 . The sixth resistance R 6 , the first diode D 1  and the seventh resistance R 7  connect in series and connect a signal output point of the second OPAMP. A signal processed by the peak-holding circuit  40  is output from the end of the seventh resistance R 7 . The second diode D 2  connects the in-phase input point to the end of the seventh resistance R 7 . The fifth capacitance C 5  parallel connects with the sixth resistance R 6  and the first diode D 1 . The end of the first diode D 1  connects to an anti-phase input point of the second OPAMP. The sixth capacitance C 6  connects the end of the first diode D 1  to GND. The second resistance R 2  and the first diode D 1  composes a half-wave recti-circuit to restore a high voltage in the second capacitance C 2 , then an MCU (microprocessor control unit) or an ASIC (application specific integrated circuit) reads the high voltage and then sends a resetting signal to eliminate the high voltage to provide next restoring. 
   As above description, the peak-holding circuit  40  receives the electric signal from the filtering-amplifying circuit  30  and holds the peak value of the electric signal for a span, so the A/D converter  50  may be a lower frequency A/D converter, but can process exactly the electric signal, therefore the cost of the feed detecting system  1  is reduced. 
   An embodiment of the present invention has been discussed in detail. However, this embodiment is merely a specific example for clarifying the technical contents of the present invention and the present invention is not to be construed in a restricted sense as limited to this specific example. Thus, the spirit and scope of the present invention are limited only by the appended claims.