Reduction of the nonlinearity error of a computerized contact interferometer using digital scale image processing

A computerized contact (vertical) interferometer developed at the Moscow State University of Technology “STANKIN” and based on the Uversky interferometer is described. The computerized interferometer with a resolution of 1 nm is designed for automated calibration of gauge blocks of 0, 1, 2 ISO tolerance grades with 0.1–100 mm nominal length range. Computerization of the Uversky interferometer significantly increases the calibration procedure efficiency, but at the same time causes an additional measurement error due to digital camera aberrations. A method and algorithm for computer aided correction of this error is proposed. The correction is provided by digital processing of the image from the video camera. The method is based on approximation of experimental data by polynomials of one variable of various degrees. It experimentally confirms the effectiveness of the method by its application to the computerized Uversky contact interferometer. The advantages of the method include ease of implementation in the form of a computer program and the ability to quickly transform one-dimensional algorithms and programs for polynomials of two or three variables. The results of the proposed work are useful in improving the accuracy of measurement software for computerized interferometers and other optical mechanical measuring devices.