| 1. A device for generating and controlling a yarn (F) reserve and for imparting a suitable tension for its winding on the
tapered bobbin (25), to be installed on service trolleys (C) for open-end spinning frames, for reattachment and start-up interventions on open-end
spinning units, consisting of a mouthpiece under low pressure equipped with approaching and distancing means towards the run
of the yarn (F), to suck it and generate a loop of reserve yarn in its interior, the service trolley (C) being equipped with
an auxiliary roll (50) for winding and unwinding operations of the yarn on the tapered bobbin (25), controlled by the control units of the trolley itself, characterized in that said sucking mouthpiece (40) is equipped with a series of sensors (41, 42, 43, . . . ) for detecting the presence of the yarn in its interior to reveal the dimension of the loop of reserve yarn (F) and
consequent piloting of the driving of the auxiliary roll (50) in the reattachment procedure and reconsignment phase of the tapered bobbin (25) in formation on its normally operating cylinder (29) wherein the auxiliary roll (50) is equipped with piloting means for driving at higher rates with respect to the normal rates for the collection of the yarn
(F).
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