Line-by-line document scanner equipped with a device for controlling the position of documents

Claim 1

A scanner for line-by-line scanning of a document, comprising: a surface for transfer of the document in continuous motion, means for causing the document to slide along the surface, n photosensors (where n is a whole number greater than 1) each having a reading field and adapted to deliver scanning signals, a registration mark drawn on a fixed support and located within the reading field of m out of the n photosensors (where m is a whole number with O<m<n+1), said registration mark and said n photosensors being respectively located on the two sides of said surface, comparison circuit for detecting the passage of the document between the registration mark and the m photosensors, comprising: a memory having an input coupled for receiving the signals of the m photosensors at least at the beginning of a reading process and one output; a comparator having a first input coupled for receiving the signals of the m photosensors at least starting from an instant located between the beginning of a reading process and the beginning of transfer of the document between the registration mark and the m photosensors, a second input coupled to the output of the memory at least slarting from said instant and one output; and a counting circuit connected to the output of said comparator for counting at the time of each line scan the number of times different signals are received on the first and on the second input of said comparator.