Heterodyne Meter of Transverse and Longitudinal Displacements of Objects

Abstract

Nowadays, optical methods are widely used to measure the movements of various objects. In this case, it is necessary to measure both longitudinal displacements at a large distance, and transverse ones. Such tasks have to be solved when measuring the displacements of the cutting tools of machine tools. Among the optical methods, the most accurate is the method of heterodyne interferometry. However, this method does not allow making absolute measurements, since the period of the interference pattern is commensurate with the wavelength of light, which requires counting the number of stripes. In addition, the readjustment of this method requires two-frequency lasers and rather complex optical and electronic systems, which significantly complicates their application. To solve this problem, we used the method of heterodyne interferometry developed by the authors, which, in contrast to the known methods, allows us to make absolute measurements of the parameters of objects. This is achieved by creating a period of the interference pattern, which is equal to the speed of sound in the acousto-optical modulator divided by the modulator control frequency. The result was aa block diagram of a device for measuring transverse and longitudinal displacements of objects by the heterodyne method is developed. Analytical expressions are obtained for calculating the signal strength at the photodetector, the periods of interference patterns, the phase shift depending on the transverse and longitudinal displacements, the measurement range and the measurement accuracy, which allowed us to determine the main parameters of the device. To confirm the results obtained, an experiment was carried out. For this, a block diagram of the experiment was developed, with the help of which the influence of the beam divergence on the period of the interference pattern was determined. The experiment showed good agreement between theory and experiment.