Sheet-conveying apparatus and method for detection of multifeed thereof

Abstract

A sheet-conveying apparatus and a method for detection of the multifeed thereof are provided. The sheet-conveying apparatus includes a passageway, a sheet-transporting mechanism and a sheet-detecting device. The sheet-detecting device disposed in the passageway includes a first transmitter, a first receiver, a second transmitter and a second receiver. A first signal is transmitted from the first transmitter along a first transmitting path and received by the first receiver. A second signal is transmitted from the second transmitter along a second transmitting path and received by the second receiver. The second transmitting path is oblique to the first transmitting path. The sheet-detecting device further includes a control-process unit for determining if the condition of the multifeed has occurred in the sheet-conveying apparatus according to the variations in the first signal and the second signal respectively received by the first receiver and the second receiver.

1 . A sheet-conveying apparatus, comprising:
 a passageway for a sheet to be conveyed along a conveying path;   a sheet-transporting mechanism for conveying the sheet through the passageway; and   a sheet-detecting device disposed in the passageway, having:
 a first transmitter for transmitting a first signal along a first transmitting path; 
 a first receiver for receiving the first signal; 
 a second transmitter for transmitting a second signal along a second transmitting path; and 
 a second receiver for receiving the second signal; 
   wherein the second transmitting path is oblique to the first transmitting path.   
   
   
       2 . The sheet-conveying apparatus according to  claim 1 , wherein the first transmitting path is perpendicular to the conveying path. 
   
   
       3 . The sheet-conveying apparatus according to  claim 1 , wherein the first transmitter transmits the first signal and the second transmitter transmits the second signal at the same time or at different times. 
   
   
       4 . The sheet-conveying apparatus according to  claim 1 , wherein the first transmitter transmits the first signal at a first frequency same as a second frequency at which the second transmitter transmits the second signal. 
   
   
       5 . The sheet-conveying apparatus according to  claim 1 , wherein the first transmitter transmits the first signal at a first frequency different from a second frequency at which the second transmitter transmits the second signal. 
   
   
       6 . The sheet-conveying apparatus according to  claim 1 , wherein when the weight of the sheet ranges from 50 g/m 2  to 120 g/m 2 , at least one of the first transmitter and the second transmitter transmits a signal whose frequency is higher than 40 kHz. 
   
   
       7 . The sheet-conveying apparatus according to  claim 6 , wherein at least one of the first transmitter and the second transmitter transmits a signal whose frequency ranges from 200 kHz to 300 kHz. 
   
   
       8 . The sheet-conveying apparatus according to  claim 1 , wherein the first transmitter and the second transmitter are ultra-sound wave transmitters, and the first receiver and the second receiver are ultra-sound wave receivers. 
   
   
       9 . The sheet-conveying apparatus according to  claim 1 , wherein the sheet-detecting device further comprises a control-process unit electrically connected to the first receiver and the second receiver for determining if multiple sheets are conveyed in the passageway according to the variations in the first signal and the second signal respectively received by the first receiver and the second receiver. 
   
   
       10 . The sheet-conveying apparatus according to  claim 1 , wherein the first transmitter and the first receiver are respectively disposed on opposite sides of the passageway. 
   
   
       11 . The sheet-conveying apparatus according to  claim 1 , wherein the second transmitter and the second receiver are respectively disposed on opposite sides of the passageway. 
   
   
       12 . A method for detecting multiple sheets, comprising:
 transmitting a first signal along a first transmitting path by a first transmitter;   transmitting a second signal along a second transmitting path oblique to the first transmitting path by a second transmitter;   receiving the first signal by a first receiver;   receiving the second signal by a second receiver; and   determining if multiple sheets are conveyed along a conveying path according to the variations in the first signal and the second signal.   
   
   
       13 . The method according to  claim 12 , wherein the step of determining if multiple sheets are conveyed along a conveying path according to the variations in the first signal and the second signal comprises:
 detecting the decay in the amplitude of the first signal and the second signal.   
   
   
       14 . The method according to  claim 12 , wherein the step of determining if multiple sheets are conveyed along a conveying path according to the variations in the first signal and the second signal comprises:
 detecting the phase shift of the first signal and the second signal respectively.   
   
   
       15 . The method according to  claim 12 , wherein the first transmitter transmits the first signal and the second transmitter transmits the second signal at the same time. 
   
   
       16 . The method according to  claim 12 , wherein the first transmitter transmits the first signal and the second transmitter transmits the second signal at different times. 
   
   
       17 . The method according to  claim 12 , wherein the first transmitter transmits the first signal at a first frequency same as a second frequency at which the second transmitter transmits the second signal. 
   
   
       18 . The method according to  claim 12 , wherein the first transmitter transmits the first signal at a first frequency different from a second frequency at which the second transmitter transmits the second signal. 
   
   
       19 . The method according to  claim 12 , wherein when the weight of the sheet ranges from 50 g/m 2  to 120 g/m 2 , at least one of the first transmitter and the second transmitter transmits a signal whose frequency is higher than 40 kHz. 
   
   
       20 . The method according to  claim 19 , wherein at least one of the first transmitter and the second transmitter transmits a signal whose frequency ranges from 200 kHz to 300 kHz.