Research On Three-Degree-of-Freedom Grating Displacement Measurement With Absolute Zero Alignment

Due to its high precision,less susceptible to environmental disturbance,small size,easy to operate,and low cost advantages,Grating displacement measuring technology is widely used as one of ultra-precision measuring tools.At present,there is an urgent need for a large range,high resolution multi-degree-of-freedom grating displacement measurement system with absolute zero alignment function.In view of the above requirements,this paper designs a large-scale,high-resolution three-degree-of-freedom grating displacement measurement system with absolute zero alignment function to solve the problem of micro-displacement measurement of the work piece table in the lithography system.Zero alignment function is used to solve the displacement measurement before the scanning grating and ruler grating positioning problem.The main research topics are as follows,Firstly,designed the optical path structure of the three-degree-of-freedom grating displacement measurement system,and analyzed the principle of X-direction,Y-direction and Z-direction displacement measurement.The realization of the X-direction and Y-direction displacement measurements is based on the dual-grating interference measurement principle.The Z-direction displacement measurement is based on the Michelson interferometer principle.In order to improve the optical subdivision factor to achieve high resolution,In the X-direction and Y-direction displacement measurement,the second-order diffracted light of the sca le grating is used for the interference measurement to realize the 2×2^1/2 optical subdivision.And designed transmission type combination scanning grating structure,analyzed the relationship between the parameters of each grating when the three degrees of freedom is measured.By means of vector diffraction analysis,designed the structural parameters of transmission type combination scanning grating and two-dimensional reflective scale grating.Secondly,analyzed the principle of zero alignment system.By introducing the laser light from the fiber and using the 2 quadrant detector,the problem of excessive use of the laser as a light source and focusing the beam with lens is avoided,achieved the design of the miniaturization principle of the alignment system.And designed photoelectric conversion and filter circuit for two quadrant detectors.For zero alignment system,designed the grating overall dimensions,the grating encoding,the internal structure of the grating.Finally,according to the requirements of the grating displacement measurement system and the zero alignment system,designed the data acquisition board,processed the grating of the measuring system and alignment mark,verified the grating measurement system and the doub le grating zero alignment through experiments.Experiments show that for X and Y axis grating displacement measurement system,the displacement measurement system realized optical subdivision of 2×2^1/2 times.For Z displacement measurement,the system realized optical subdivision of 1/2 wavelength of light source.For the zero-alignment system,the alignment accuracy is in the micron level when the speed of the micro-displacement table is 400 ?m/s at a working distance of 21 mm.