Research Of High-precision Displacement Measurement System Based On The Principle Of Diffraction And Interference

With the fast development manufacturing technologies, the stringentrequirements for length-scale measurements expedite the development andapplication of displacement measuring systems with nanometer resolution andaccuracy. And grating and laser interferometers are now widely used for long rangedisplacement measurements. Grating pitch is used as measurement basis in gratinginterferometers, compared to laser wavelength; measurement basis is fixed and canprovide good immunity against environmental factors. Grating interferometersrequire light source less of the frequency stabilization and cost lowly. Also gratinginterferometers have the advantages of simple optical structure, convenientoperation, easy miniaturization. So because of these obvious advantages, gratinginterferometers have been paid more and more attention in the research andapplication of nano-scale measurements. Oversea researches on gratingmeasurement are already very mature, and all types of grating measurementproducts have been mass production. Although in this respect our country has madesome achievements, but it is still a big gap abroad.This paper studies a nano-scale displacement measurement system based on theprinciple diffraction and interference, First, this paper analyzes the principle ofoptical Doppler effect and diffraction characteristics of diffraction grating, gives outtheoretical analysis and experimental verification of the grating displacementmeasurement system, and miniaturizes the optical reading head by integrating allthe optical components.Also, this paper analyses error sources of the grating displacementmeasurement system, and itemized gives out the various error factors including theoptical path error analysis, circuit error analysis. The optical path errors includeoptical alignment errors and errors introduced by the laser light source and grating.Circuit errors include photoelectric conversion errors and count errors. The opticaldesign software Lighttools is used to analyze optical alignment errors and achievesdeflection tolerance of the grating.Conditioning circuit design and signal processing circuit, the signalconditioning circuit to eliminate the presence of the error, including the DC leveldrift error, the non-orthogonal error, and unequal amplitude error and the like,improving the circuit board before the DC offset errors still exist problem, increasethe bias correction link. The signal processing circuit is the use of FPGA for datacollection, to distinguish, counting and segmentation processing and displacement calculations. And the realization of serial communication with the host computer,the display interface designed by LabVIEW can display the last displacement data.Then, conditioning circuit and signal processing circuit are designed. Thesignal conditioning circuit eliminates the presence of the errors, including the DClevel drift error, the non-orthogonal error, and unequal amplitude error. The signalprocessing circuit uses FPGA to collect, distinguish, count, process segmentationand calculate displacement.Finally, the optical platform is build, and the miniaturized reading head isassembled, and the entire displacement measuring system is build. Each module ofthe system performance is tested. Experiments show that, in the measurement rangeof (0~100) um, the system can achieve superior resolution of5nm and linearity,repeatability of the system is good.