Automatic document feeder and registration system therefor

摘要

A sheet feeder transports sheets from a sheet supply, such as a document tray, to a distant location, such as a registration position on the platen of an electrophotographic copier. A sensing device monitors a time period which starts when a sheet advancing mechanism is actuated and ends when a sheet reaches the distant location. An indication of abnormal operation is provided if the sheet does not reach the distant location within a preset time period. The preset time period is initially set at one period of time and subsequently set at a shorter period of time. The initial time period is longer to allow the sheets to become fully engaged with the sheet feeder after initial loading, while the subsequent period is shorter to provide a quicker indication of abnormal operation.