Diffractive optics for fabric fault detection

Several devices for textile fault detection, based on diffractive optics. have been proposed in the past without appreciable influence on direct on-loom inspections. Nevertheless, the use of diffractive optics cannot be considered surpassed by other inspection systems. Compared with procedures based on image processing, it is insensitive to dust and vibrations and does not suffer from the presence of ambient light. We have investigated and improved a method based on the optical detection of the Fourier power spectrum to survey and identify defects in textile structures. The optical set-up analyses the local behavior of the texture, which is converted in a power spectrum. This system can be easily inserted in an automatic inspection device, which determines the presence of a defect comparing the actual power spectrum with that of the good fabric assumed as a reference. The processing of data is rather simple since it is based on the number and position of peaks in the spectrum. A byproduct of our investigation is a device to measure the yam density in the fabric.