Determination of the roughness of a precision surface by the correlation method of image processing of its microrelief

Background. Numerous studies have established that the roughness of the microrelief of the working surface of various parts of machines and mechanisms largely determines their operational reliability and durability. In this regard, the research and development of non-contact methods for the rapid assessment of the characteristics of microrepelops is an urgent task at present. Aim. The aim of the work is to study and develop an optoelectronic method, algorithms and software for processing raster images of the studied microreliefs obtained by small-sized video cameras, for the prompt assessment of its roughness directly in the course of the technodolic process. Methods. The method is based on computer processing of images of the studied microreliefs, as a result of which the roughness parameters of these microreliefs are determined. For this purpose, halftone images of microreliefs of reference samples, with certain GOST methods, roughness parameters, are first converted into binary images. Then, two-dimensional correlation functions are calculated from binary images using a quasi-optimal correlation algorithm. For these functions, the average amplitudes Ucp of the variable components of the correlation coefficients are calculated and the analytical dependence of the GOST roughness parameter Ra from Ucp is constructed. To depict the studied microrelief with unknown roughness parameters, the variable component of the two-dimensional correlation function is also determined and according to the obtained dependence Ra = (Ucp), the arithmetic mean deviation of the profile from the mean line Ra is found. Results. A new optoelectronic method for assessing the roughness parameters of microreliefs of precision surfaces is proposed, which is based on correlation processing of images of the studied microreliefs.The results of applying this method to the assessment of the roughness parameters of the surfaces of gas turbine engine. Defined fields roughness fields of the surfaces of the trough and the back of the blade of the 1st stage of gas turbine engine. Conclusion. The expediency of applying a correlation approach to processing images of microreliefs in order to determine the roughness parameters of precision surfaces is shown. At the same time, the negative influence of side uninformative factors on the results of measuring the parameters of the microrelief, in particular, fluctuations in the power of the light flux and the angle of its incidence on the surface under study, is also eliminated. In order to reduce the time spent on correlation image processing, a quasi-optimal correlation algorithm was used. Roughness fields for the working surfaces of the gas turbine engine blade were determined, on the basis of which it became possible to determine dangerous areas with unacceptable values of stress concentration.