action of electronic brake 28 in such a way as to maintain the tension substantially constant at reference value t_ref while yarn recovering device remains at a position of minimum interference with the yarn as shown in fig2 when signal le indicates that yarn is no longer unwound from the drum le 0 which circumstance is indicative of the fact that the downstream machine has either stopped to draw yarn or started to return it control unit cu u201c freezes u201d the braking action at the last value and if measured tension t_meas is lower than a lower threshold tension t_lim_inf than it enables yarn recovering device 32 to recover yarn while its speed v rr is continuously modulated in such a way as to maintain the tension substantially constant on reference value t_ref at this stage the number of revolutions and fractions of revolutions n completed by reel 34 is monitored it should be noted that with the method according to the invention reel 34 can rotate at a modulated speed in both directions in fact after an initial yarn recovering step during which the exceeding yarn is wound on reel 34 in order to maintain the tension at the desired level t_ref the subsequent request of yarn from the downstream machine will cause reel 34 to rotate in the opposite direction always at a controlled speed in order to return the yarn however before reaching the initial position n 0.