Research Of Grating Interferimetric Displacement Measuring Technology Based On The Principle Of Digital Phase

With the rapid development of precision and ultra-precision manufacturing technology,the higher requirements have been putted forward on displacement measurement technology.At present,micrometer grade of the displacement measurement technology could not meet the demand,so nanometer grade of the displacement measurement technology has been developed rapidly and it has become one of the research hotspots in the measurement industry.An interferometric displacement measuring technique based on diffraction grating as one of the ways of nanometer grade of displacement measurement technology has been used widely in the field of ultra-precision measurement technology.It has the advantages of high measurement precision,strong anti-interference ability and low manufacturing cost.Oversea researches have been developed earlier in the field and the relevant technology has been quite mature now.While the level of domestic technology is far away from the one of abroad.In this paper,a displacement measuring technology based on the diffraction of grating and the principle of light interference have both been studied.The diffraction principle of grating,the optical Doppler effect,the interference principle of coherent light and the optical-electrical conversion principle have been analyzed in detail.A measuring system has been designed according to the theories and a double-layer optical path structure has been putted forward especially.Using the structure,the space of system has been reduced and the practicality can also been improved.Signal conditioning circuits,including differential amplifier circuit,low-pass filter circuit and other part have been designed according to the characteristics of output signal.The signal-noise ratio(SNR)of the signal can be improved effectively by the method of multistage amplification.Moreover,the anti-interference mode has been used in the design process of the circuit to reduce the noise influence.However,the angle error about installing of photoelectric converter and the effects of delayed time of circuit can make the output of the two signals in a non-orthogonal state and bring a greater error to the subdivision calculation.A subdivision calculation method based on phase difference measurement principle is designed for the non-orthogonal generation calculation error of the signal.The principle and error source of the phase difference of the classical correlation principle have been analysed.Meanwhile,an improved algorithm of phase difference measurement based on the correlation principle have also been putted forward,which can overcome the limitation of the whole signal sampling in the classical calculation method.The result of the phase difference can been substituted into the calculation formula to obtain the final subdivision calculation result.Furthermore,a software method for calculating the number of a whole period and the direction of movement have been designed.Then the signal processing circuit would have been simplified.Under available experimental facilities,the experimental platform can be completed.In addition,the interference fringes containing the displacement signal are obtained.What is more,the output signals would have been obtained after optical-electrical conversion.The system's optical path structure,signal conditioning circuit and signal acquisition system modules have both been tested independently.The experimental results show that the resolution of the system is less than 5nm,and the system has good repeatability and linearity.