Positive yarn feeder with control of the feeding tension

摘要

A yarn feeder comprises a housing (12) and a yarn-winding wheel (16), which is driven to rotate by motor means for feeding a yarn (Y) wound on it to a textile machine (M). A brake (18) applies a slight, static braking action upon the yarn (Y) upstream of the yarn-winding wheel (16). A control unit (CU) modulates the speed of rotation of the yarn-winding wheel (16) on the basis of a tension signal received from a tension sensor (26) engaged by the yarn (Y) downstream of the yarn-winding wheel (16), in order to maintain the yarn tension substantially constant on a desired level. The yarn (Y) is wound, in the form of a single loop, in a circumferential groove (32) of the yarn-winding wheel (16) which has a substantially V-shaped profile defined between two counterposed annular toothings (38, 40) in an alternated configuration. A deviating arm (42) has yarn-guiding means (44) which are slidably engaged by the yarn (Y) between the brake (18) and the tension sensor (26) in a position such that the yarn input to the yarn-winding wheel (16) is prevented from contacting the yarn delivered from the same.