Design And Development Of A Portable Brinell Hardness Measurement Device Based On Machine Vision

Hardness is one of the most important parameters of materials,partly reflects properties like strength and stiffness,so the hardness test plays a significant role in industry production.As the first proposed method Brinell hardness tests are widely applied because of its high precision and repeatability.Reading microscopes are employed for the measurement of the size of indentations in traditional hardness test,which need much workload and brought in personality error.Therefore,it’s urgently needed in industrial fields of a portable hardness testing device to achieve accurate automatic measurement.Considering features of the hardness test indentation images,an improved existence probability map based circle detection method is proposed in this paper to locate the center point,and another one-dimension accumulator method based on radical projection of gradient vectors is proposed to recognize all the circles with the same center point.To solve the problem of concentric circles,effective selection logic is applied to identify the right indentation.For higher accuracy of the match with indentations,an iterative least square fitting algorithm is proposed to eliminate the noise edge points.Based on the effective algorithm of accurate indentation detection,a novel pixel size calibration of image sensors method is proposed.The algorithm of center and radius extraction in two phases effectively overcame the shortcomings of traditional circle detection method and achieved the indentation extraction in complex situations.By canceling the interference of noises,the iteration fitting algorithm,greatly improved the accuracy of the match with indentations.Based on the whole indentation extracting algorithm,a portable device was designed,which realized the automatic Brinell hardness measurement with high accuracy.