Patent ID: 8061116

Claim:
Method for piecing a yarn at a rotor spinning machine comprising a plurality of spinning stations ( 1 ), in which a fiber band supplied by a fiber band feed from a band supply and opened by means of an opening mechanism is supplied as a single fiber flow to the spinning rotors and the yarn spun in the spinning rotor is drawn off by a draw-off device from the spinning rotor, with at least one control device ( 24 ) for detecting and evaluating data from an automatic piecing process at least one spinning station ( 1 ) as well as at least one sensor device ( 23 ) for measuring the yarn diameter and for detecting the position of the associated measuring point of a piecer produced during the piecing process, the successive production of a plurality of piecers being controlled by means of the control device ( 24 ) in a measuring phase without feed addition and with reduced drafting, characterised in that in the measuring phase, successively more than five piecers are produced, in that the coordinates of the measurement values together with the associated measurement values from the individual measurements of the piecers are supplied for an evaluation for averaging and for determining a fiber band function taking into account the drafting reduced for the measurement values, which reflects the fiber flow behaviour in the form of the respective fiber band quantity supplied to the rotor as a function of the transport path of the fiber band feed, and in that the speed of the fiber band feed is controlled in a delayed manner from the run-up of the yarn draw-off, which is dependent on the rotor speed, by means of the fiber band function, in such a way that the fiber shortfall quantity being produced from the fiber band function is compensated by dynamic feed addition with respect to height and length.