A lubricant is a substance that lessens friction and wear between mechanical parts. A good quality lubricating oil is required for protecting the mechanical equipment and reducing energy consumption. Its performance index (friction coefficient) could be measured by the four-ball wear test. For the morphological analysis of testing data from the four-ball wear test, determination of wear angle is very important for measuring the wear spot diameter, validity of the four-ball wear test and recognition of abnormal wear scar. On the basis of character analysis and image processing technology, a novel wear angle determination algorithm for wear scar is presented in this article. The direction of the wear scar (wear angle) is determined based on angle transformation and grey consistency (the smallest change of grey level). Simulation results show that the algorithm has high precision, good robustness and less time consuming. The average absolute error of our method is 0.8° and the absolute error of 95% of samples is <4°. The average runtime per frame is 3.896 s in the simulation platform.

润滑剂是一种减少机械零件之间的摩擦和磨损的物质。需要高质量的润滑油来保护机械设备并减少能耗。其性能指标（摩擦系数）可以通过四球磨损试验测量。对于来自四球磨损测试的测试数据的形态分析，确定磨损角度对于测量磨损点直径，四球磨损测试的有效性以及识别异常磨损痕迹非常重要。在字符分析和图像处理技术的基础上，提出了一种新的磨损痕迹磨损角确定算法。磨损痕迹的方向（磨损角度）是根据角度变换和灰度一致性（灰度的最小变化）确定的。仿真结果表明，该算法精度高，鲁棒性好，耗时少。我们方法的平均绝对误差为0.8°，而95％的样本的绝对误差为<4°。在仿真平台中，每帧的平均运行时间为3.896 s。