Patent ID: 8356765

Claim:
A positive yarn feeder, comprising: a motorized yarn-winding drum adapted to have a plurality of loops of yarn wound thereon and driven to rotate for drawing said yarn from a reel and feeding said yarn to a general downstream machine, and a movable guiding member, which is biased to slideably engage the yarn unwinding from the drum and to deviate a path of the yarn by a spring acting in contrast to the tension of the yarn, thereby generating a reserve releasable in response to tension peaks on the yarn, a stroke of said guiding member being limited by a stop defining a position of maximum deviation of the yarn, and said spring having one end operatively connected to the guiding member and an opposite end connected to driving means operable for applying a load to the spring, with the guiding member abutting against said stop, said driving means being controlled by a control unit which is programmed to adjust said load as a function of a desired feeding tension, said driving means being rotating driving means and said spring is a flat spiral spring having an inner end coaxially attached to an output shaft of said rotating driving means, and said flat spiral spring having an outer end from which said guiding member projects into the shape of an arm, said rotating driving means comprising a stepping motor, and said rotating driving means comprising a ratio-motor driven by said stepping motor.