Paper folding machine

A paper folding machine folding a printed paper sheet along at least one fold line preset on a printing surface of the paper sheet so as to form a signature, the paper folding machine comprising:

• a transport path for the paper sheet having an entrance, an exit and at least one folding position which is provided in an intermediate area of the transport path;
• at least one transport mechanism transporting the paper sheets one by one along the transport path between the entrance and a most upstream folding position, and between adjacent folding positions, and between a most downstream folding position and the exit;
• a folding mechanism arranged at each of the at least one folding position so as to fold the paper sheet along the associated fold line while the paper sheet is stopped at the associated folding position;
• at least one adjustable guide positioning the paper sheet relative to the at least one folding position by bringing at least one side of the paper sheet into contact with the at least one adjustable guide;
• an adjustable stopper arranged downstream of each of the at least one folding position so as to position and stop the paper sheet at the associated folding position by bringing a leading edge of the paper sheet into contact with the stopper;
• and
• a fold misalignment detection unit detecting, for each paper sheet and for each folding position, a fold misalignment amount, wherein
• the position of the at least one guide and/or the stopper associated with the corresponding folding position is adjusted based on detection data of the fold misalignment detection unit, characterized in that
• the paper folding machine further comprises:
• a drive mechanism capable of moving the at least one adjustable guide and the stopper;
• and
• a controller operatively connected to the drive mechanism, wherein
• the controller comprises
• a data receiving section receiving the detection data from the fold misalignment detection unit,
• a data counting section counting, for each folding position, the number of the detection data received by the data receiving section,
• a data storage section storing, for each folding position, the detection data received by the data receiving section,
• a statistical processing section calculating, for each folding position, an average fold misalignment amount using the detection data corresponding to a predetermined number of sample each time the number of detection data stored in the data storage section reaches, for each folding position, the number of sample, and
• an adjustment section adjusting the position of the at least one guide and/or the stopper associated with the corresponding folding position so as to correct fold misalignment corresponding to the average fold misalignment amount each time the average fold misalignment amount is calculated by the statistical processing section.