Tension-controlling method for a yarn unwinding from a storage yarn feeder to a textile machine
The yarn tension is modulated by a yarn-braking device controlled by a control unit which receives signals of measured tension from a tension sensor and compares them with a reference tension signal in a control loop; as long as the reference tension remains unchanged, a first set of coefficients is used in the control loop causing the control loop to have a relatively slow behaviour in relation to the error-compensating action; when a change in the reference tension occurs, the system switches to a second set of coefficients causing the control loop to have a relatively fast behaviour; the second set of coefficients is maintained as long as the difference between the second value of the reference tension and the measured tension remains greater or equal to a predetermined minimum value, then the system switches again to the first set of coefficients.