Positive yarn feeder with tension limiter
A motorized yarn-winding drum holds a plurality of loops of yarn wound thereon and is driven to rotate for drawing said yarn from a reel and feeding it to a general downstream machine. A movable guiding member is biased to slideably engage the yarn unwinding from the drum and to deviate its path, 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. The stroke of the guiding member is limited by a stop defining a position of maximum deviation of the yarn. The spring has one end operatively connected to the guiding member and one opposite end connected to driving elements operable for applying a load to the spring, with the guiding member abutting against said stop. The driving elements are controlled by a control unit which is programmed to adjust the load as a function of a desired feeding tension.
1. 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,
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 stop that defines a position of maximum deviation of the yarn by limiting a stroke of said guiding member,
driving means operable for applying a load to the spring with the guiding member abutting against said stop, and
a control unit for controlling said driving means, which is programmed to adjust said load as a function of a desired feeding tension,
said spring having one end operatively connected to the guiding member and an opposite end connected to the driving means, and
said driving means comprising a linear actuator having an operating rod, said spring being a coil spring suitable to act by traction and having a first end attached to said operating rod of said linear actuator, said coil spring having a second end that is arranged opposite to said first end, said guiding member being attached to said second end.
2. The positive yarn feeder of claim 1 , wherein said guiding member has a radial enlargement and said stop consists of a wall, which has a slot in which said guiding member is inserted, and against which said radial enlargement abuts with the guiding member in said position of maximum deviation of the yarn.
3. The positive yarn feeder of claim 1 , wherein said guiding member is made enbloc with said spiral spring.