spinning device 8 but without reaching the fiber collector groove of the rotor shortly before a time t2 is reached the computer 47 causes rotor run up to start by switching off the switch device 82 in this process the switch rod 83 of the switch device 82 releases the yoke 45 so that the billy rollers 44 can press the running tangential belt 43 against the shaft 40 of the rotor 8 the pairs of support disks also then begin to rotate with the shaft 40 and the photoelectric barrier 84 begins to count the pulses of the reflector 85 the computer 47 is programmed in such a way that the further piecing control is activated when the second reflector pulse appears the measuring channel 109 detects the acceleration which is calculated from the time elapsed between the second and third counting pulses the rotor acceleration is also ascertained in the same way in the computer 47 the appearance of the second reflector pulse is shown at the time t2 in fig5 if the rotor 8 is already rotating at the time t0 for any reason at all then a malfunction is occurring which causes the piecing program to be stopped and may cause.