Abstract: The yarn is formed into a loop and a loop sensor monitors the variations in length in the loop of yarn. The variations in the size of the loop result from a difference in the speed between the speed of the yarn and the speed of the draw-off or delivery member. The draw-off or delivery member is driven by an asynchronous motor having a slip-clutch drive with an assembly for braking in response to eddy currents. In particular, a disc is connected to the motor and a magnetic field is applied to the disc, the magnitude of the field which is applied to the disc directly dependent upon the size of the loop. In the preferred embodiment, the regulation of the speed of a pilot roller of a winder as a function of the delivery speed of the yarn is accomplished.