Sheet overlap detection apparatus and sheet overlap detection method

Abstract

In a sheet overlap detection apparatus, an amplification factor control unit changes the amplification factor of a second amplifier which amplifies the output from a first amplifier which receives the output from an ultrasonic receiver. A first overlap detection monitor output decision unit decides the output from the second amplifier as a sheet overlap detection monitor output when the amplification factor of the second amplifier is adjusted, and the output value of the second amplifier has become almost equal to a first set value while one sheet is sandwiched between an ultrasonic transmitter and the ultrasonic receiver. A second overlap detection monitor output decision unit decides the output from the third amplifier as a sheet overlap detection monitor output when the amplification factor of the second amplifier is adjusted, and the output value of the second amplifier has not become almost equal to the first set value, but the output value of the third amplifier has become almost equal to a second set value while one sheet is sandwiched between the ultrasonic transmitter and the ultrasonic receiver. An overlap detection unit detects, based on the output from the second or third amplifier, overlap of sheets which pass between the ultrasonic transmitter and the ultrasonic receiver.

1 . A sheet overlap detection apparatus comprising:
 an ultrasonic transmitter which transmits an ultrasonic wave;   an ultrasonic receiver which receives the ultrasonic wave from said ultrasonic transmitter;   a first amplifier which amplifies an output from said ultrasonic receiver;   a second amplifier which is configured to freely change an amplification factor and amplifies an output from said first amplifier;   a third amplifier which amplifies an output from said second amplifier;   amplification factor control means for changing the amplification factor of said second amplifier;   first overlap detection monitor output decision means for deciding the output from said second amplifier as a sheet overlap detection monitor output when said amplification factor control means adjusts the amplification factor of said second amplifier, and an output value of said second amplifier has become almost equal to a first set value while one sheet is sandwiched between said ultrasonic transmitter and said ultrasonic receiver;   second overlap detection monitor output decision means for deciding an output from said third amplifier as a sheet overlap detection monitor output when said amplification factor control means adjusts the amplification factor of said second amplifier, and the output value of said second amplifier has not become almost equal to the first set value, but an output value of said third amplifier has become almost equal to a second set value while one sheet is sandwiched between said ultrasonic transmitter and said ultrasonic receiver; and   overlap detection means for detecting, based on the output from one of said second amplifier and said third amplifier, overlap of sheets which pass between said ultrasonic transmitter and said ultrasonic receiver, the output being decided as the sheet overlap detection monitor output by one of said first overlap detection monitor output decision means and said second overlap detection monitor output decision means.   
   
   
       2 . An apparatus according to  claim 1 , further comprising:
 first amplification factor decision means for deciding, as a sheet overlap detection amplification factor, the amplification factor of said second amplifier when said first overlap detection monitor output decision means has decided the output from said second amplifier as the sheet overlap detection monitor output, and the output value of said second amplifier has become almost equal to the first set value; and   second amplification factor decision means for deciding, as a sheet overlap detection amplification factor, the amplification factor of said second amplifier when said second overlap detection monitor output decision means has decided the output from said third amplifier as the sheet overlap detection monitor output, and the output value of said third amplifier has become almost equal to the second set value,   wherein in sheet overlap detection, said amplification factor control means sets, in said second amplifier, the sheet overlap detection amplification factor decided by one of said first amplification factor decision means and said second amplification factor decision means.   
   
   
       3 . An apparatus according to  claim 1 , wherein said amplification factor control means comprises:
 change width control means for repeatedly changing the amplification factor of said second amplifier while reducing a change width; and   change direction control means for changing the amplification factor of said second amplifier in a direction different from that of previous time when a magnitude relationship between the first set value and the output value of said second amplifier, or the magnitude relationship between the second set value and the output value of said third amplifier has changed due to the change of the amplification factor of said second amplifier.   
   
   
       4 . An apparatus according to  claim 1 , further comprising:
 first equivalence determination means for determining that the output value of said second amplifier has become almost equal to the first set value when an absolute value of a difference between the first set value and the output value of said second amplifier is smaller than a first threshold value; and   second equivalence determination means for determining that the output value of said third amplifier has become almost equal to the second set value when an absolute value of a difference between the second set value and the output value of said third amplifier is smaller than a second threshold value.   
   
   
       5 . A sheet overlap detection method comprising the steps of:
 causing an ultrasonic transmitter to transmit an ultrasonic wave;   causing an ultrasonic receiver to receive the ultrasonic wave from the ultrasonic transmitter;   causing a first amplifier to amplify an output from the ultrasonic receiver;   causing a second amplifier to amplify an output from the first amplifier;   causing a third amplifier to amplify an output from the second amplifier;   adjusting an amplification factor of the second amplifier;   deciding the output from the second amplifier as a sheet overlap detection monitor output when the amplification factor of the second amplifier is adjusted, and an output value of the second amplifier has become almost equal to a first set value while one sheet is sandwiched between the ultrasonic transmitter and the ultrasonic receiver;   deciding an output from the third amplifier as a sheet overlap detection monitor output when the amplification factor of the second amplifier is adjusted, and the output value of the second amplifier has not become almost equal to the first set value, but an output value of the third amplifier has become almost equal to a second set value while one sheet is sandwiched between the ultrasonic transmitter and the ultrasonic receiver; and   detecting, based on the output from one of the second amplifier and the third amplifier, overlap of sheets which pass between the ultrasonic transmitter and the ultrasonic receiver, the output being decided as the sheet overlap detection monitor output.   
   
   
       6 . A method according to  claim 5 , further comprising the steps of:
 deciding, as a sheet overlap detection amplification factor, the amplification factor of the second amplifier when the output from the second amplifier is decided as the sheet overlap detection monitor output, and the output value of the second amplifier has become almost equal to the first set value; and   deciding, as a sheet overlap detection amplification factor, the amplification factor of the second amplifier when the output from the third amplifier is decided as the sheet overlap detection monitor output, and the output value of the third amplifier has become almost equal to the second set value,   wherein the detecting step comprises the step of setting the sheet overlap detection amplification factor in the second amplifier.   
   
   
       7 . A method according to  claim 5 , wherein the adjusting step comprises the steps of:
 repeatedly changing the amplification factor of the second amplifier while reducing a change width; and   changing the amplification factor of the second amplifier in a direction different from that of previous time when a magnitude relationship between the first set value and the output value of the second amplifier, or the magnitude relationship between the second set value and the output value of the third amplifier has changed due to the change of the amplification factor of the second amplifier.   
   
   
       8 . A method according to  claim 5 , further comprising the steps of:
 determining that the output value of the second amplifier has become almost equal to the first set value when an absolute value of a difference between the first set value and the output value of the second amplifier is smaller than a first threshold value; and   determining that the output value of the third amplifier has become almost equal to the second set value when an absolute value of a difference between the second set value and the output value of the third amplifier is smaller than a second threshold value.