Study Of Laser Heterodyne Nano Measurement Technology Based On Backstepping Compensation

Nano displacement measurement technology is an important part of precision measurement.It can detect the state of nano materials and evaluate the nano scale.It is the cornerstone of the development of nanotechnology and it has a certain guiding role in the application of nanotechnology.Laser heterodyne detection is one of the main methods to realize nano measurement.The development and trend of laser nano measurement technology at home and abroad are analyzed.In order to improve the accuracy and stability of the system,taking the spindle of DM1007 CNC machine tool in precision machining center as the research object,the laser heterodyne nano displacement measurement technology based on backstepping compensation is proposed.Firstly,the design of laser heterodyne nano measurement system is studied and the mathematical model of response is built.The backstepping algorithm aims at constructing a Lyapunov stabilization function that can make the system work stably by means of step by step recursion,stabilizing the nonlinear influence caused by modulation and demodulation and high frequency signal in the system,and calibrating the measurement system with the algorithm.Laser Doppler effect and acoustooptic modulation are used to detect laser coherent heterodyne;The self mixing effect reduces the local frequency of the acoustooptic modulator,and the double frequency reduces the oscillation frequency,simplifies the system design and improves the system stability.The laser heterodyne nano measurement system is completed by optical devices,circuits and digital signal processing algorithm.Select the semiconductor laser with good coherence and the photodetector with high efficiency to receive the corresponding laser wavelength;Based on the principle of superheterodyne reception,the frequency spectrum shifting circuit is designed to move the modulation signal of to mid-frequency,which not only ensures the anti-interference of signal transmission,but also improves the circuit processing efficiency;The phase discrimination circuit demodulates the displacement information to improve the measurement accuracy;Backstepping algorithm analyzes system transfer function,builds Lyapunov function,flattens phase frequency characteristic curve,and improves low-frequency characteristics;According to the relationship between power spectral density function and correlation function,combined with recursive algorithm and fast Fourier algorithm,fast correlation function analysis is realized to effectively extract the amplitude and frequency of weak signal.Build a laser heterodyne nano measurement system,and carry out static and dynamic experiments.In the static experiment,the signal is concentrated at 2KHz,the phase shift per minute is 0.06°,the system works stably and reliably;In the dynamic experiment,the maximum error and the average error are improved to some extent by comparing the experimental results without backstepping and after backstepping.The maximum error is not more than ±0.5nm,and the maximum relative error is less than 0.6%;The confidence interval is 0.95(k=2),the displacement is 60 nm,and the expanded uncertainty is 0.608%,which meets the design requirements of the system.It shows that the system has the ability of nano displacement measurement and the scheme is feasible.