An automatic system, based on image analysis, is proposed to control the anisotropy of fiber webs to be used in nonwoven applications.
These fibre webs are cross lapped and preneedled. Submitted to a drafting process it is expected that the fibres may rotate around the fibre tufts inserted by the preneedling process and reorient themselves in order to reach a more isotropic state.
The critical point of the process is the control of the drafting degree. If the fibre web is too drafted, probably a new kind of orientation will arrive. If the drafting operation is not enough the material will keep the previous orientation. The mechanical properties of the final fabric depend on this phenomenon.
Using video cameras two sets of images are compared in terms of the distribution of gray levels and, consequently, the entropy of first order is calculated and compared. As the entropy increases the degree of anisotropy decreases revealing a state with less degree of order. The lowest degree of order gives the most homogeneous fabric.
A prototype with such a system controls automatically the drafting level, changing the speed of the rolls according with a computer program that rules the system to get the best possible results.
Finally and to control the process special methods such as laser diffraction of images collected in transparent replicas are used. The contour and respective axes of the ellipsis formed by the laser diffraction are calculated and the ellipticity of these contours are used to quantify the degree of order of the fibre webs.
By: Mário F. Nunes (*), Nuno R. Belino, Mário J. Pereira Universidade da Beira Interior,
Submit Date: 12/31/1999 20:00