Drive for a yarn feeder for a textile machine

Claim 1

A drive for a yarn feeder for a textile machine comprising a yarn storage device having a storage drum for receiving yarn windings thereon; a yarn detector for sensing the presence of yarn at a preset point of said drum and for emitting a signal in response thereto, a drive motor for activating said storage device to cause a yarn to wind onto said drum, said motor having a three phase exciting winding therein; and a circuit arrangement for converting a direct current into a variable-frequency three-phase alternating current, said circuit arrangement being connected between said yarn detector and said drive motor for supplying said drive motor with said alternating current in response to the presence of yarn at said preset point of said drum, said circuit arrangement including an integrator responsive to said signal of said yarn detector to produce a trapezoidal control voltage having a value corresponding to a required speed of said motor and having a growth flank and a decay flank determinative of the acceleration time and deceleration of time of said motor; an oscillator for receiving said control voltage and emitting a control pulse sequence in response thereto, said sequence having a frequency proportional to the value of said control voltage; a digital counting circuit for receiving said control pulse sequence, said circuit having three output terminals corresponding to the three phases of said three-phase alternating current, each said output terminal being adapted to transmit of sequence of identical rectangular pulses with a 120° phase shift from the other of said outputs in consecutive order, each said sequence of rectangular pulses having a frequency of a value proportioned to said control voltage; three inverter stages, each said stage being connected to a respective terminal of said counting circuit to receive a sequence of rectangular pulses and having two output terminals to emit alternating control pulses in phase opposition to each other in response to said receive rectangular pulses, each said control pulse having a growth flank delayed by a preset time on the decaying flank of an immediately preceding opposed control pulse; and three switching amplifiers, each said amplifier having two input terminals for respectively receiving said control pulses to form a phase current therefrom, a choke for shaping said phase current into a sinusoidal pattern, and an output terminal for emitting said sinusoidal phase current to a respective winding of said drive motor.