| After reviewing the previous investigations of unwinding in past half century, the fruitful areas of further research have been defined. The integrated model of three-region analysis, which covers the balloon region, the drag region on the package, and the stationary region on the package, has been developed. This model can predict the yarn path configuration and the tension distribution during unwinding, which are of practical significance in the optimization of the unwinding process and of unwinding machine design. A comprehensively parametric study has been carried out and the influences of key parameters on the yarn tension and balloon shape during unwinding have been studied. The instability of unwinding, associated with the change in the number of loops in the balloon, has been investigated by bifurcation phenomenon characterized by the nonlinear model of unwinding. The possible unstable regions in which yarn tension might vary violently due to the change in the number of loops in balloon have been presented. The influences of yarn elasticity on unwinding have been studied. Both the yarn tension and the balloon radius for highly elastic yarn are less than those for inextensible yarn. Finally, the unwinding yarn across the end region of package has been investigated. The yarn tension at the guide eye in an unwinding cycle when the unwind point moves along the height of the package has been examined. The tension reaches the maximum at the far end of the package, and the minimum at the near end of the package relative to the guide eye. |
