Research On Key Techniques Of Three Degrees Of Freedom Grating Displacement Measurement

Grating displacement measurement technology has great advantages in ultra-precision measurement due to its high precision,good stability,small size,flexibility,low cost,etc.,especially in the measurement system of ultra-precision machining equipment.In the field of ultra-precision machining,the requirements for grating displacement measurement technology are mainly high resolution and multiple degrees of freedom.In order to realize high-resolution and multi-degree-of-freedom displacement measurement,this paper studies key techniques such as optical subdivision factor,electrical subdivision factor and three-degree-of-freedom measurement of displacement measurement system,and uses micron in double grating interferometry system.The second-order diffracted light of the periodic grating is used to achieve 4x optical subdivision,and the electrical subdivision processing method of the optical signal is studied to improve the resolution of the system by using the direct reflection of the two gratings in the double grating interference system.The interference between the two causes the displacement measurement in the Z-axis direction,simplifies the system structure,and realizes the three-degree-of-freedom displacement measurement.The main work of the thesis is as follows:First,the optical structure of a three-degree-of-freedom high-resolution dual-grating interferometry system is designed.The displacement measurement in the X-axis direction and the Y-axis direction is based on the principle of double-grating interferometry,using the 0-order diffracted light of the scanning grating to reflect the diffracted light at the 2nd order of the scale grating,and the 2nd-order diffracted light of the scanning grating in the scale grating.-2 levels of reflected diffracted light,so that the two converge at the scanning grating and split the light to achieve 4 times optical subdivision measurement;the displacement measurement in the Z-axis direction is 0-order diffracted light and 1 level directly reflected by the scanning grating The diffracted light is respectively interfered with the 0th-order diffracted light and the 1st-order diffracted light which are emitted from the 0th-order diffracted light reflected by the scanning grating and reflected by the scale grating on the scanning grating,and forms an optical subdivision measurement of 2 times the wavelength of the optical light;The scalar diffraction theory is used to analyze the relationship between the diffraction efficiency and the structural parameters of the scanning grating 1D and 2D gratings and the scale grating in the principle of double grating interference.According to the diffraction efficiency requirements of the diffracted light,the simulation design and optimization are designed.The step height h and the duty ratio r of the one-dimensional and two-dimensional scanning gratings and the reflective scale grating.Secondly,the X-axis and Y-axis double-grating interferometry and the Z-axis interferometric measurement respectively acquire two interfering signals,and divide the multiple phase intervals according to the intersection and zero-crossing points generated by the normalized two signals due to the phase difference.Let the two signals mutually assist each other to realize phase subdivision of two signals with arbitrary phase difference signals.An algorithm for solving the phase of two signals as an auxiliary reference is designed and implemented on the digital signal processor DSP.Phase subdivision of two 120° phase difference signals in the X-axis and Y-axis directions and two 90° phase difference signals in the Z-axis direction are respectively realized.Finally,the scale grating and scanning grating of the measurement system are processed according to the requirements of double grating displacement measurement.The photoelectric conversion circuit,low-pass filter circuit and data acquisition module are designed.The optical test bench is built and the measurement signal is processed.Displacement information.The test analysis shows that the grating displacement measuring system realizes 4 times optical subdivision of the scale grating period in the X-axis direction and the Y-axis direction,and realizes the optical subdivision of the laser wavelength twice in the Z-axis direction.By designing a subdivision method for two arbitrary phase difference signals,128 times electrical subdivision of the period measurement signals in the X-axis,Y-axis,and Z-axis directions is realized.