| With the ever-increasing demand for measurement accuracy in the field of ultra-precision measurement,domestic and foreign scholars have conducted more detailed research work on heterodyne laser interferometers and sought to break through the measurement of nano-scale accuracy.The periodic nonlinear error is the main factor restricting the accuracy of the heterodyne laser interferometer.Therefore,periodic nonlinear error compensation and suppression techniques have received more and more attention.In this paper,the traditional periodic nonlinear error model does not consider the influence of the initial phase of the interference light,causing the actual signal to be inconsistent with the theoretical model.Under the condition that the initial phase influence factor is considered,a periodic non-linear error correction model is established.The mechanism of the influence of the initial phase on the periodic nonlinearity error is discussed.This paper proposes a feature parameter extraction algorithm to correct the periodic nonlinear error of a heterodyne laser interferometer.Based on the above principles,a nonlinear calibration system based on double-lock-up amplification demodulation and feature parameter extraction correction algorithm is designed.The main research contents are as follows:(1)A periodic nonlinear error correction model for a heterodyne laser interferometer was established.The traditional nonlinear error model is analyzed.This model has insufficient understanding of the influence of the initial phase,resulting in the signal in the compensation does not satisfy the basic symmetry.Re-model the periodic nonlinear error to achieve the purpose of matching the theoretical model with the actual measured signal form.Comparing and analyzing the influence mechanism of initial phase on unequal amplitude error,DC bias error and non-orthogonal error in traditional model and universal model,analyzing the mechanism of the effect of triple difference on the period nonlinear error,the effect of initial phase on periodic nonlinear error is analyzed.(2)Based on the periodic non-linear error universal model,a feature parameter extraction algorithm was proposed to correct the non-linear periodic errors.Real-time capture of the characteristic values of the two demodulated signals to obtain the amplitude of the input signal and the dc bias value,according to which the unequal amplitude error and dc bias error of the two signals are corrected;using a digital add/ subtractor.Two channels of equal-amplitude and non-DC offset error signals are processed for non-orthogonal error correction,and the unequal amplitude errors introduced in the process of signal orthogonalization are corrected twice.It solves the problem that the interference signal has the nonlinear error,and the nonlinear correction of the target under variable speed motion.(3)Based on the principle of double orthogonal phase-locked amplification and feature parameter extraction algorithm,a periodic nonlinear e rror correction system was designed.The system uses the pre-signal processing module to amplify and filter signals according to the characteristics of the reference signals and measurement signals emitted by the heterodyne laser interferometer,and then t he double orthogonal lock-in amplifier module utilizes the internally generated reference signals for the two channels.The output signal is mixed and filtered and demodulated.Finally,the feature parameter extraction algorithm is used to correct the non-linear periodic error.An experimental device of heterodyne laser interferometer is set up to analyze the accuracy of the universal model of periodic nonlinear error and the performance of the nonlinear correction system proposed in this paper.The experim ental results show that the nonlinear error before correction reaches ±9.07 nm,and the value of the nonlinear error after correction is only ±0.43 nm.Experiment result demonstrated that proposed compensation method is able to reduce the nonlinear error. |
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