Theoretical Research On Orthogonal Diffraction Grating-based 3D Displacement Sensor

The rapid development of industrial production technology,especially aerospace measurement and control technology,the development and application of technologies such as MEMS manufacturing technology and nano-processing technology,put forward higher requirements on the precision displacement measurement technology,promote the precision displacement measurement technology in a large range,multi dimension and high speed in the direction of development.In this paper,a three-dimensional displacement sensor based on orthogonal diffraction gratings is theoretically studied to solve the contradiction between the tracking speed and the subdivision multiple of the grating,expand the dimension of displacement measurement,and achieve the measurement of three directions of XYZ displacement.The main work of this article includes1.Based on the theoretical analysis of the diffraction characteristics and the grating displacement measurement of one-dimensional and twodimensional gratings,the traditional orthogonally-based diffraction gratingbased displacement sensor is improved by using a two-dimensional orthogonal motion grating and reference grating with a grating pitch of 1um to construct the optical path.By detecting the ±1 order diffraction fringes,the displacement in three directions of XYZ is measured.In the design of optical path,a light splitting optical path based on the reflector is designed to reduce the energy loss of the beam and improve the signal to noise ratio.The ZEMAX software is used to verify the principle of optical path measurement and the function of the light splitting optical path.In the optical path structure,the self collimating structure of the grating is used to expand the displacement range of the Z axis.2.The signal processing scheme based on USB bus is designed.In the scheme,STM32F407 is used as the main control unit,and the number of the whole period changes of the interference fringes is counted by STM32F407.For the phase change less than one peroid,the software subdivision method is used to solve the problem.The method of tangent quantization lookup table is adopted to realize 200 times subdivision,which overcomes the influence of signal amplitude fluctuation on subdivision precision.3.In the signal processing scheme,the integral circuit in the traditional displacement discrimination and counting circuit is eliminated and the sinusoidal waveform is not subdivided,which reduces the limitation of the system to the movement speed of the grating displacement sensor.In the scheme,the data acquisition of grating interference signal is completed by A/D sampling circuit,and the calculation of signal subdivision and displacement is realized by PC processing,which reduces the computation amount of lower computer and breaks the bottleneck with limited computing power of lower computer.And the use of USB3300 to achieve high-speed USB transmission can also improve the measurement system's processing speed of displacement data.4.The performance of the signal processing circuit is tested and analyzed.The measurement error of the grating sensor system is analyzed.