Direction of Groove Detection for Wear Image of Four-Ball Friction Test Based on Gray Difference of Inclination Angle

In order to avoid subjective estimation of the direction of groove by using a tester in the four-ball friction test, an automatic wear angle detection method based on gray difference of inclination angle is proposed in this paper. First, the gray difference between the pixel and its W × 2W neighborhood pixels is acquired, in which each neighborhood pixel corresponds to an inclination angle. Second, a row’s grayscale difference of inclination angle is calculated, which is the sum of grayscale difference of all pixels in the same row with the same inclination angle. Third, the inclination angle corresponding to the minimum row’s grayscale difference is defined as the approach angles. Finally, the first t approaching angles with the highest frequency determine the wear angles. Compared with true angles determined manually, the simulation results of 200 samples show that the average absolute error is 2.1238° and the average running time is 1.3 s per frame. The influence of the algorithm parameters on detection precision is also analyzed.