Research On The Laser Interferometer Vibration Measurement System Based On Orthogonal Signal

The demand of micro-vibration measurement by laser is increasing day by day with the rapid development of the modern life and industry, especially in some specific areas of research. Such as the micro-nano measuement in precision measurement technology, to monitor the safe operation in the construction and engineering equipment, health medical diagnosis in the heart and dental, and so on, micro-vibration application are urgently day after day. Therefore, the high-precision micro-vibration measurement has important practical significance.Laser interference technology is widely applied in the nanometer precise measurement. The demand of the measurement accuracy is also improved with the constant direction of scientific research toward the development of micro-areas. The demodulation technique of orthogonal laser interferometer is one of the crucial preconditions, it has been an important research topic in the field of the laser interference signal demodulation. The credible signal demodulation technique may improve the measurement precision of laser interferometer greatly. In this paper, we made a further study in demodulation of the orthogonal interference signals.In chapterⅠ, the significant of laser vibration measurement and the demodulation technique of the orthogonal interference signals are illustrated.In chapterⅡ, two methods which can both achieve orthogonal signals are elaborated:phase generated carrier (PGC) homodyne demodulation method, dual-optical-channel balancing detection method and quadrature detection method based on 1/8 wave plate. The two orthogonal signals generated in the phase generated carrier (PGC) homodyne demodulation method by circuit, but it's generated by optic path in other two methods.In chapterⅢ, two demodulation methods for the orthogonal signals are elaborated: phase generated carrier (PGC) homodyne demodulation method and arctangent method. By comparing the two mathods we can obtained:the weakness of PGC is affected by the carrier easily, the latter has the advantages that simple in principle and reduce signal processing time and so on.In chapter IV,the method to eliminate the DC component in the orthogonal signal are illustrated,by Matalab software simulation and experimental results prove that this method can be used to eliminate the DC component in the signal,and obtained the error percentage of arctangent algorithm results with the increase of DC value.Meanwhile, the micro-vibration signals can be measured accurately.In chapter V, experimental results show when the environmental disturbance is large,the range of the phase is beyond[-π/2,π/2],then the arctangent algorithm can not demodulate the signal.When use the feedback method,the range of the phase is limited between[-π/2,π/2],the micro-vibration signals can be demodulated by arctangent algorithm.The main works and contributions achieved in this dissertation were concluded as follows:Firstly,we designed a method to eliminate the DC component in the orthogonal signal,solve the problems that wrong result caused by DC values in the signals.Secondly,we designed the feed-back method to balance the frequency drifrt caused by environmental disturbance,the range of the phaseψ(t)+(φ1-φ2)is Iimited between[-π/2,π/2],the micro-vibrati.n signals can be measured accurately by the arctangent algorithm.