| The coating film quality of vehicle body is an important standard to evaluate the qualityand beauty of the car, which has a great effect to the company benefit due to the influence ofthe coating film defects on consumers’ buy satisfaction about the car. The artificial visualmethod is often used to test and evaluate the coating film quality of vehicle body intraditional method, however, it needs the inspector adjust repeatedly the observation angle tohave a comprehensive understand about it or touch the local film flatness to determinewhether the coating film defects exist, leading to the low work efficiency and the bigdifficulty. Besides, the film defect detection is will be probably affected by the objective andsubjective factors because of the different technical levels of the measurement personnel.The reflection ray of line structured light is conducted followed by classifying itaccording to the linear features in this detection method, which has characteristics ofnon-contact, wide field, high accuracy, strong real-time performance and the active control.The method used in this paper has great potential applications in on-line detection area ofbody coating film defects because the moving target is detected using the method ofstructured light scanning along the way. The defects with changed shape characteristics aredesigned and the key technologies of all the relevant method about film defect detection arestudied and verified by experiments.The improved morphological thinning algorithm and the method of gray extremum areadopted in extracting the structure light centerline, eventually making the error within acertain range without compromising on its shape information and increasing significantly thecenterline extraction speed. In improvement aspect of morphological thinning algorithm, theintegrity of the structure light information is ensured on the basis of reasonable cover to edgedetection missing point and the contrast with background region is increased through imagereconstruction in structured light areas. The automatic threshold extraction of the structuredlight centerline is realized based on the two improvement aspects, reducing influence of thedifferent image on the centerline extraction results due to external factors.The characteristics of the structured light in the defect area are analyzed in order to establish the relationship between the structured light centerline and coating film defectsshape. The comparative analyses of the defect area are conducted to test and verify theavailability of this identification method in this paper using slope method, finally theextraction algorithm in body coating film defects region is confirmed mainly based on thedirection code method of the pixel tracking and subsidiarily the slope method. It has anadvantage of extracting quickly and accurately defect area matrix. In addition, the pixeldistance search is conducted using the characteristics of the edge cover and the contrastanalysis is researched after setting the distance threshold in order to verify other fracturedefects expect the convex and concave shape.The characteristic shape of each extraction area and the relationship with coating filmdefects of is the three dimensional body are needed to determine after completing pixelextraction in the defect area. So the fitting for defect area is further researched using thescatter circle fitting method and the defect type is determined by the feature information ofboth structure light centerline and the adjacent one. The detection method of coating filmdefects based on structure light adopted in this paper has a good effect to the defectsdetection for the listed coating film by experimental validation for.specific types of bodycoating film defects. However, the hardware and software of experiment are needed tooptimization considering it still has certain distance with the requirement of high precisionfor coating film on-line detection of the car body. |
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