A novel inspection method for determining the cosmetic quality of automotive skin panels

The cosmetic quality of automotive skin panels affects the perceived valuation and quality of an automotive vehicle. The human eye is sensitive to optical distortions caused by geometric deviations and the severity of these distortions is related to wavelength and depth of the defects. This paper describes the development and evaluation of a physically based inspection method that uses the wavelet transform to identify shapes in panel topology that the human eye is specifically sensitive to and to estimate their depths. We then relate their depths to a perceived severity. Using a structured lighting system, geometric data was first collected from panels at each stage of a five-stage stamping process and then analysed with the wavelet-based inspection method. The results were then compared to a conventional inspection and two outcomes were found. First, the wavelet-based method was capable of detecting the location and sizes of subtle cosmetic defects in the panel and secondly, the stages of the stamping process were found to influence the location and severity of the defects found in panels.