Method for separating worn bank notes from a quantity of bank notes in bank note processing machines

A method for separating worn bank notes from a plurality of bank notes in a bank note processing machine comprising:

• specifying a target rate for separating the worn bank notes from the plurality of bank notes;
• assessing each one of the plurality of bank notes individually and sequentially;
• counting the plurality of bank notes during the assessing of the plurality of bank notes;
• measuring, during the assessing, a value of at least one physical variable of each one of the plurality of bank notes;
• comparing the measured value, or a derivative thereof, of each one of the plurality of bank notes with a threshold value during the assessment;
• separating from the plurality of bank notes, worn bank notes in which the measured value thereof exceeds the threshold value;
• counting the separated worn bank notes during the assessing of the plurality of bank notes;
• and
• modifying the threshold value each time one of the plurality of bank notes is assessed, or after a subgroup of the plurality of bank notes is assessed, by feedback control;
• wherein a control variable of the feedback control is a rate of previously separated worn bank notes from the plurality of bank notes.