Postal-item processing method, including rank monitoring

A method of processing postal items in order to prepare delivery rounds by performing a plurality of sorting passes through a postal sorting machine having a carrousel of trays in which the postal items travel in trays above sorting outlets and are deposited in the appropriate sorting outlets, the method comprising the steps of:

• checking in the machine during a sorting pass and for each current item, data representative of an order number or rank allocated to the distribution point corresponding to the current postal item in a predetermined sequence of distribution points to run through this sorting pass in order to prepare each delivery round;
• said checking comprising monitoring how rank varies for successive postal items in order to detect any difference relative to said predetermined sequence;
• wherein in response to said detection of a difference for a current postal item:
• the rank of the current postal item is observed in a portion, or “observation window”, of a sequence constituted by a certain number of consecutive postal items;
• and
• if the rank of the current postal item is one less than a current rank,
• a first number of postal items of rank one more than the current postal item is counted in the observation window and a second number of postal items having the same rank as the rank of the current postal item is counted in said window;
• and
• if the first number is lower than a determined first threshold S1 and the second number is greater than a determined second threshold S2, then the machine is controlled so as deposit the current postal item in the appropriate sorting outlet;
• while
• if the first number is greater than the determined first threshold S1 and/or the second number is less than the determined second threshold S2, then the machine is controlled so as to cause the current postal item to return to the observation window after making one complete revolution round the carrousel.