Displacement Measuring Technology Based On Diffractive Light Of Grating Interference

In order to develop compact high-precision nano-resolution displacement measuring device, diffraction grating-based optical interferometry measuring displacement theory and prototype machine was developed.Grating displacement measurement theory and methods was systematically analyzed. Based on the scalar diffraction theory, single-grating transmission system model was established and the effect of parameters such as grating pitch on the Moore fringe was analyzed. Using vector diffraction theory, generalized grating equation under the condition of any oblique incidence is given. The impact of Grating pitch and other parameters on diffraction orders and the diffraction efficiency was analyzed. The diffraction characteristics when the finite-size Gaussian beam incidence was discussed.A diffraction interference displacement measuring system was proposed and implemented which use a high-density single-grating whose length is 100mm, groove density is 400lp/mm. When the two diffracted beam with small frequency difference meet and interfere, the interference fringes changes four periods when the grating is moving a grating period relative the reading head, so the original signal period is 0.6μm. Stable signal phase difference was obtained by polarized light interference. The resolution of the system is 0.586nm after 1024-fold subdivision.Reflective intensity double-grating system model was established by three grating theory. The effect of system parameters on light intensity modulation was analyzed and the result was compared with two grating theory. The impact of Source size and other factors on system output signal was discussed. For the typical Littrow mode, the model of phase relationship between the output signal was established. The effect of parameters such as grating pitch on phase relationship was analyzed. Factors which affect the precision grating displacement measuring system were analyzed. The random error caused by environmental changes was processed by filtering. FIR digital filter was designed according to the signal characteristics which can effectively reduce the effect of low frequency noise. The general Kalman filter was given in a typical case of motor control. The simulation and experimental results showed the effectiveness of the method.