Rotational speed measurement using self-mixing interferometry

Self-mixing interferometry (SMI) is a technique that is capable of measuring rotational speed in a direct way. Thus, SMI is an attractive alternative to optical encoders with respect to speed detection. But problems such as additive noises as well as amplitude and frequency modulation due to spectral broadening make the usage of self-mixing interferometry challenging. In this paper, a signal processing method with relative high accuracy is presented for rotational speed measurement using SMI. The method uses of signal selection, autocorrelation, zero-crossing detection, as well as an averaging filter to determine the Doppler frequency of a SMI signal more accurately.Results of experiments showthe method's potential, as the linearity of the measuring system is≤±0.5% and the normalized root mean square error is≤0.2%.