| 摘要 |
<p>A drum (12) has a yarn (Y) wound thereon which is adapted to be unwound upon request of a downstream textile machine. A passive weft-braking device (22) exerts a predetermined, uncontrolled braking action upon the yarn (Y). A controlled weft-braking device (24) arranged downstream of the passive weft-braking device (22) is provided with a first series of comb-like arranged prongs (36) and with a second series of comb-like arranged prongs (40) inserted in an alternated configuration between the prongs (36) of the first series. The yarn (Y) runs in a zig-zag manner between the two series of prongs (36, 40) and receives a braking action by friction from them, which changes in strength depending on their relative position. A motor (46) drives the second series of prongs (40) with respect to the first one for adjusting the strength of the braking action. A tension sensor (50) measures the tension of the yarn (Y) unwinding from the drum (12) and generates a corresponding tension signal (T). A control unit (CU) controls the motor (46) by feedback based on the tension signal (T), in such a way as to stabilize the tension of the yarn (Y) on a desired level.</p> |
