Paper feeder

Abstract

A sheet feeding apparatus includes a sending element of an ultrasonic sensor for outputting ultrasonic waves, a drive circuit for supplying the sending element of the ultrasonic sensor with a drive signal for driving the sending element, a receiving element of the ultrasonic sensor disposed opposite the sending element of the ultrasonic sensor across a sheet transfer path in the sheet feeding apparatus, and for receiving the ultrasonic waves, a setting unit for setting a threshold for the detection of transfer of the plurality of paper sheets by using the output of the receiving element of the ultrasonic sensor at the time of stopping of the output of the sending element of the ultrasonic sensor as a basic value, and a detection unit for detecting transfer of the plurality of paper sheets by comparing the output of the receiving element of the ultrasonic sensor with the threshold.

1 . A sheet feeding apparatus for detecting transfer of a plurality of paper sheets by using ultrasonic waves, the apparatus comprising: 
 a sending element of an ultrasonic sensor for outputting ultrasonic waves;    a drive circuit for supplying the sending element of the ultrasonic sensor with a drive signal for driving the sending element;    a receiving element of the ultrasonic sensor disposed opposite the sending element of the ultrasonic sensor across a sheet transfer path in the sheet feeding apparatus, and for receiving the ultrasonic waves;    a setting unit for setting a threshold for the detection of transfer of the plurality of paper sheets by using the output of the receiving element of the ultrasonic sensor at the time of stopping of the output of the sending element of the ultrasonic sensor as a basic value; and    a detection unit for detecting transfer of the plurality of paper sheets by comparing the output of the receiving element of the ultrasonic sensor with the threshold.    
   
   
       2 . The sheet feeding apparatus according to  claim 1 , wherein the threshold for detecting transfer of the plurality of paper sheets is obtained by adding a fixed value to the output of the receiving element of the ultrasonic sensor at the time of stopping the output of the sending element of the ultrasonic sensor.  
   
   
       3 . The sheet feeding apparatus according to  claim 1 , wherein the threshold for detecting transfer of the plurality of paper sheets is obtained by adding, to the output of the receiving element of the ultrasonic sensor at the time of stopping of the output of the sending element of the ultrasonic sensor, a value calculated, correspondingly to the output of the receiving element of the ultrasonic sensor at the time the sending element of the ultrasonic sensor is driven stepwise by the drive circuit, according to the correlation between the output and a correction value determined based on the correlation between the sensitivity and the output of the receiving element of the ultrasonic sensor and the correlation between the fitting position and the output of the receiving element of the ultrasonic sensor.  
   
   
       4 . The sheet feeding apparatus according to  claim 1 , wherein the output of the receiving element of the ultrasonic sensor at the time of stopping of the output of the sending element of the ultrasonic sensor is the average of a plurality of the outputs.  
   
   
       5 . The sheet feeding apparatus according to  claim 1 , wherein the output of the receiving element of the ultrasonic sensor is the average of a plurality of the outputs.  
   
   
       6 . The sheet feeding apparatus according to  claim 1 , wherein the detection unit judges that, when the output of the receiving element of the ultrasonic sensor is lower than the threshold a prescribed number of times or more often, transfer of the plurality of paper sheets is taking place.  
   
   
       7 . The sheet feeding apparatus according to  claim 1 , wherein the detection unit uses the threshold as a threshold for detecting transfer of the plurality of paper sheets regarding a plurality of types of paper sheets differing in ream weight.  
   
   
       8 . The sheet feeding apparatus according to  claim 1 , further comprising: 
 a motor for transferring paper sheets,    wherein the detection unit, in the event of detecting transfer of the plurality of paper sheets, drives the motor to stop the transfer of the paper sheets.    
   
   
       9 . The sheet feeding apparatus according to  claim 1 , further comprising: 
 feed rollers for transferring paper sheets to a reading position,    wherein the sending element of the ultrasonic sensor and receiving element of the ultrasonic sensor are disposed upstream from the reading position on the transfer path and in the vicinity of downstream or upstream from the feed rollers.    
   
   
       10 . The sheet feeding apparatus according to  claim 1 , further comprising: 
 a first amplifying circuit for amplifying the output of the receiving element of the ultrasonic sensor;    a filter for removing noise from the output of the first amplifying circuit;    a second amplifying circuit for amplifying the signals cleared of noise;    a sample hold circuit for sampling and holding the peak value of the output of the second amplifying circuit; and    an AD converter for converting the value held by the sample hold circuit into a digital signal and inputting it to the setting unit.    
   
   
       11 . A sheet feeding apparatus for detecting transfer of a plurality of paper sheets by using ultrasonic waves, the apparatus comprising: 
 a sending element of an ultrasonic sensor for outputting ultrasonic waves;    a drive circuit for supplying the sending element of the ultrasonic sensor with a drive signal for driving the sending element;    a receiving element of the ultrasonic sensor disposed opposite the sending element of the ultrasonic sensor across a sheet transfer path in the sheet feeding apparatus, and for receiving the ultrasonic waves;    an amplifier, comprising an operational amplifier, for amplifying the output of the receiving element of the ultrasonic sensor; and    an adjusting unit provided in the amplifier, and for forming a control signal for adjusting the output of the amplifier, whereby the reference voltage of the operational amplifier is adjusted.    
   
   
       12 . A sheet feeding apparatus for detecting transfer of a plurality of paper sheets by using ultrasonic waves, the apparatus comprising: 
 a sending element of an ultrasonic sensor for outputting ultrasonic waves;    a receiving element of the ultrasonic sensor disposed opposite the sending element of the ultrasonic sensor across a sheet transfer path in the sheet feeding apparatus, and for receiving the ultrasonic waves;    an amplifier for amplifying the output of the receiving element of the ultrasonic sensor;    an adjusting unit for forming a control signal for adjusting the output of the amplifier; and    a drive circuit for supplying the sending element of the ultrasonic sensor with a drive signal for driving the sending element, the drive circuit varying the number of waves or the duty ratio of clocks supplied to the sending element of the ultrasonic sensor according to the control signal from the adjusting unit which is provided in the drive circuit.