Research On The Measuring Method Of Indentation Diameter In Ball Press Test Based On Digital Image Processing

In the electrical and electronic products,the heat resistance property of non-metallic materials and solid insulating materials is an important performance when they are used as an insulating materials.They can direct impact on the safety of the electrical and electronic products.Some safety standard requirements: ball pressure test shall be used to test material heat resistance for the shell component,other external insulating component,and the component supporting insulating material with dangerous voltages,which may affect equipment safety because of heating damage.If the indentation diameter is less than or equal to 2mm,heat resistance of the material can be considered to meet the requirements.Indentation area can be divided into real indentation and the transition indentation.Indentation diameter measurement is the key step to ball determine the accuracy of ball pressure test result.However,the commonly used methods for indentation diameter measurement cannot accurately distinguish between the true indentation area with the transition indentation area.The measurement result need to be compensated by inspectors based on the experience of the subjective experience.So the measurement accuracy is poor.In order to identify accurately the real indentation and the transition indentation and improve the measurement accuracy,an automatically measure method for indentation measuring which can identify accurately the real indentation region and the transition indentation region has been develop,which is based on visual measurement method.The principal research work are listed as follows:(1)Design and building indentation diameter measurement device.(2)The research of indentation image pre-process algorithm.The salt and pepper noise was reduced by median filter with square template,and the Gaussian noise was filtered by Gaussian filter algorithm with square template.Then the Wallis sharpening algorithm was used to eliminate blur caused by image filtering.Finally the histograms equalization method was used to enhance the contrast of the real indentation area and the transition indentation area.(3)The research of segmentation algorithm for the recognition of real indentation area and transition indentation area.(4)The research of indentation diameter measurement algorithms and the calibration methods.Hough transform was taken on the boundary of real indentation area and transition indentation area to select effective point on the boundary.Then the effective point on the boundary were fitted by circle fitting algorithm based on least squares method,and the pixel length of indentation diameter was calculated.At last,the standard distance method was used to calibrate the device for indentation diameter measuring.(5)Study accuracy checking methods.The indentation diameter measurement method based on reverse engineering was proposed.The measurement precision is about 1μm.So the measuring results can be considered as standard values of the indentation diameter,which was used to check the accuracy of the measurement method based on visual measurement.Finally the measurement accuracy and the repeatability accuracy were checked by experiment.Experimental results indicate that the measurement accuracy is no greater than 3.5μm and the repeatability accuracy is no greater than 1.2μm,which can fully meet the requirements of indentation diameter measurement and prove the correctness and effectiveness of this work.