On line conformity analysis on perforated plastic films by automated visual inspection

The Guial company produces the top veil of sanitary towels for women or baby napkins. The raw material is a plastic film that passes through a process to make holes. The success of the company is closely linked to the high and permanent quality control of its products. The amount of holes on the film (i.e. the percentage of open area) is the principal criterion that guarantees the quality of the final product. The film must be perforated so that the open area stands between 25% and 30% for a good absorption. The requirements from our industrial partner was to develop a low cost automatic system to inspect the perforated film on the production lines i.e. based on a personal computer architecture. The challenge was to implement algorithms on a PC based system, with high efficiency computational time and of course a good robustness versus different kinds of perturbations. From the images acquired by a CCD line scan camera, we compute the percentage of open area by the estimation of the cyclic ratio