Patent ID: 8752830
Filing Date: 2014-06-17
Classification: B65H

Abstract:
1. A sheet feeder comprising: a container unit configured to contain a plurality of sheets; a feeding unit configured to feed sheets from said container unit; a transmitter configured to transmit ultrasonic waves to a sheet being fed by said feeding unit; a receiver configured to receive ultrasonic waves transmitted by said transmitter; a first detection unit configured to detect a level of ultrasonic waves received by said receiver; a determination unit configured to determine whether or not sheets are being multi-fed, by comparing the level of ultrasonic waves detected by said first detection unit after lapse of a predetermined time period from transmission of the ultrasonic waves by said transmitter with a predetermined threshold value; a second detection unit configured to detect a distance between said transmitter and said receiver; and a changing unit configured to change at least one of the predetermined time period and the predetermined threshold value based on the distance detected by said second detection unit.