Detection of shape manufacturing defects of flat fan-pattern nozzle orifices using elliptic fourier descriptors

Abstract

Shape defects originating from the manufacture in the orifice openings of the flat fan-pattern nozzles may result in deteriorating the spray pattern. This study has been conducted with the aim of detecting the manufacturing defects of the fan-pattern nozzle orifices in terms of shape uniformity using the elliptic Fourier descriptors (EFDs), and revealing the shape differences among the nozzle orifices made in polyacetal for various nominal sizes ranging from 01 to 06. At first, descriptive data describing dimensions (major and minor length, projected area, etc.) and shapes (shape factor, elongation and roundness) of the nozzle orifices were obtained using an image processing method. The next process, to evaluate the nozzles’ orifice shape using elliptic Fourier analysis (EFA), the progresses of generating the orifice’s contour data, derivation of EFDs, principal component analysis (PCA) of EFDs and visualization of shape variations estimated by the principal component scores (PCs) were followed respectively. Although the shape differences of the orifice outlines could be visually distinguished, the descriptive shape data were not able to discriminate the contour differences. The EFDs determined for each orifice size could individually detect the nozzle orifices with shape defect originating from the manufacture and they could be explicitly distinguished from the scatter plots. The results of the Hotelling’s pairwise comparison test showed that the nozzle orifices in shape were significantly different from each other. Linear discriminant analysis demonstrated that the group centroids of the orifices of 03, 04 and 06 were found close-range to each other. The orifice of 01 which is rectangular in shape had an extraordinary attribute compared to the other orifices. The orifice outline of 015 with a smooth shape was in appearance of an oblate ellipse in shape. The contour of the nozzle orifice of 02 size was explicitly found different from the others. It was concluded that the EF method can be used intended for the manufacturers inspect and improve the quality of nozzle orifices.