Sheet feeding apparatus and method of detecting double feed

Abstract

A sheet feeding apparatus includes a stacker for stacking a sheet; a feeding device for feeding the sheet on the stacker to a predetermined processing position; a drive device for driving the feeding device; a double feed detection device having a sending element and a receiving element arranged at a downstream side of the feeding device for detecting a double feed of the sheet; a sensitivity adjustment device for comparing a detected value of the receiving element with a predetermined reference value for adjusting an output of the sending element; and a control device for controlling a transport speed of the feeding device. The sensitivity adjustment device adjusts the output of the sending element when the control device controls the drive device to stop the sheet or to decelerate the sheet at a predetermined speed.

1 . A sheet feeding apparatus comprising: 
 a stacker for stacking sheets;    a feeding device for feeding the sheets on the stacker to a predetermined processing position;    a drive device for driving the feeding device;    a double feed detection device arranged at a downstream side of the feeding device for detecting a double feed of the sheets and having a sending element and a receiving element;    a control device for controlling a transport speed of the feeding device; and    a sensitivity adjustment device for comparing a detected value of the receiving element with a predetermined reference value for adjusting an output of the sending element, said sensitivity adjustment device adjusting the output of the sending element in a condition such that the control device controls the drive device to stop the sheet or to decelerate the sheet at a predetermined speed.    
   
   
       2 . A sheet feeding apparatus according to  claim 1 , wherein said sending element includes an ultrasonic wave sending element and said receiving element includes an ultrasonic wave receiving element, said sensitivity adjustment device having an amplifier device for increasing or decreasing amplitude of the ultrasonic wave sending element.  
   
   
       3 . A sheet feeding apparatus, comprising: 
 a stacker for stacking sheets;    a feeding device for separating the sheets on the stacker into a single sheet and feeding the sheet to a predetermined processing position;    first and second transport devices arranged between the stacker and the sheet processing position with a predetermined distance therebetween;    a double feed detection device arranged between the first and the second transport devices for detecting a double feed of the sheets, and having a sending element and a receiving element disposed oppositely;    a control device for controlling transport speeds of the first and second transport devices;    a sheet sensor for detecting that the sheet fed from the stacker reaches a downstream side of the first and second transport devices; and    a sensitivity adjustment device for comparing a detected value of the sending element with a predetermined reference value for adjusting an output of the sending element so that the sensitivity adjustment device increases or decreases the output of the sending element according to a sheet leading edge detection signal from the sheet sensor.    
   
   
       4 . A sheet feeding apparatus according to  claim 3 , wherein said control device stops the drive device according to the sheet leading edge detection signal from the sheet sensor, and restarts the drive device after the sensitivity adjustment device increases or decreases the output of the sending element.  
   
   
       5 . A sheet feeding apparatus according to  claim 3 , wherein said control device drives the drive device at a predetermined speed according to the sheet leading edge detection signal from the sheet sensor, and drives the drive device at a speed higher than before after the sensitivity adjustment device increases or decreases the output of the sending element.  
   
   
       6 . A sheet feeding apparatus according to  claim 3 , wherein said first and said second transport devices have a first operation mode to transport the sheet to the sheet processing position at a first speed to perform a specific process, and a second operating mode to transport the sheet to the sheet processing position at a second speed without performing the specific process, said first speed being higher than the second speed.  
   
   
       7 . A method of detecting a double feed of sheets transported from a stacker, comprising: 
 a transport step for transporting the sheet on the stacker to a predetermined processing position;    a double feed detection step arranged between the stacker and the sheet processing position for detecting the double feed of the sheets with an ultrasonic wave sensor having a sending element and a receiving element;    a sensor sensitivity adjustment step for changing an output of the sending element while the sheet is stopped or is decelerated at a predetermined speed between the stacker and the sheet processing position; and    a discharging step for discharging the sheet by restarting the sheet or moving the sheet at a speed higher than the predetermined speed after the sensor sensitivity adjustment step.    
   
   
       8 . A method according to  claim 7 , wherein said sensor sensitivity adjustment step is executed when the sheet is nipped by at least two transport devices arranged at an upstream side and a downstream side in a direction that the sheet is transported.