Nonlinear Phenomena in High-Speed Yarn
Unwinding
Introduction
The process of removing yarn from a package by over-end withdrawal
through a guide eye is fundamental to many operations in the textile industry,
such as winding, unwinding, and two-for-one twisting. The surface generated by a
loop of yarn rotating rapidly about a fixed axis is called a balloon. The
balloon shape characteristics and operating speeds govern the yarn tension. Yarn
strength limits the maximum tension and therefore the operating speed and
productivity of the system. The properties of such balloons are important in
designing new machinery, improving the efficiency of existing processes, and
determining the limit of performance of these processes. The application of the
dynamical theory of rotating yarn loops to these processes and the experimental
studies of such balloons are therefore of considerable technological interest.
Theoretical studies
A complete analysis of the yarn dynamics has been conducted
over the range between the eyelet point and the unwind point (the point at which
yarn first starts moving away from its stationary position in the package
surface). The motion of the yarn is in two parts: the sliding movement on the
package surface and the ballooning movement. By applying dynamical theory, these
two parts of yarn motion were mathematically formulated, respectively. The
nondimensionalized Equations of Motion were then numerically solved by means of
a fifth order Runge-Kutta routine with the help of Matlab software
package.
The profile of a simulated one and a half balloon is shown in
Figure 1. Figure 2 illustrates the relationship between yarn tension at the
eyelet point T0 and the a/H ratio, where a is the radius of package, and H is
the distance between the eye-let and the point where yarn starts to fly into the
balloon.
Fig. 1 Profile of a simulated balloon |
Fig. 2 Relationship between the yarn tension at eyelet
and a/H ratio |
Experimental studies of the unwinding process
To get experimental results of the yarn unwinding process, a
video-based measurement system is being developed. This system comprises of the
following components: PC with Windows software, optical sensor, tension sensor,
video camera and stroboscope.
The optical sensor provides a trigger at every revolution of
the yarn balloon This makes it possible to freeze the yarn at a certain point of
rotation, independent of the varying rotation frequency. While the image is
captured with the video camera, the strobe flashes to freeze the high speed yarn
movement. Simultaneously, the tension is measured. The PC, equipped with video
capture board and high speed digital signal processing board, performs all
controls and data acquisition functions.
The captured image, the tension graph and the trigger signal
are displayed in a graphical user interface. The picture on the right shows a
typical screen of this user interface. Graph and image can be exported for
further processing and comparison to theory.
Results
The images made by the video camera provided a good capture of
the yarn path between package and eyelet. Dependent on the position of the
stroboscope and the camera, the yarn path on the package was visible, too.
