| Astronomical observations require ever-increasing resolution of telescopes.Increasing the caliber is an effective way to improve the resolution,but large-diameter telescopes are difficult to manufacture.Large modern telescopes use coherent synthetic aperture technology.The phase modulator is a key component of the beam synthesizing mechanism in the coherent synthetic aperture telescope.The detection accuracy and speed of the phase modulator motion information determine the modulation accuracy and control bandwidth of the phase modulator.It is helpful to improve the imaging resolution of synthetic aperture telescopes,to improve the modulation accuracy and control bandwidth of the phase modulator.The phase modulator motion information includes three degrees of freedom of pitch,azimuth,and piston.Real-time measurement methods with three or more degrees of freedom are still in the development stage.There are few methods for achieving multiple degrees of freedom measurement for a single system.The traditional multi-degree of freedom measurement method combines multiple sets of measurement equipment or sensors to measure the measured object at the same time.It is not only complicated in structure but also difficult to adjust and introduces more error.This work focuses on the three-degree-of-freedom(3-DOF)testing technology for phase modulators.It includes two rotating angles and one axial displacement measurement.The research content of this paper includes four parts as fellow.Optical interferometry has many advantages,such as high accuracy,traceability and non-contact measurement.It has become an important measure of precision measurement.This paper firstly conducts extensive research on optical interference precision measurement technology and multi-degree-of-freedom measurement technology based on related technologies of optical interference.Research,the article summarizes the latest achievements in the industry.In the second part,three displacement measurement sensors are proposed to achieve three-degrees of freedom measurement simultaneously.The displacements of three or more measurement points on the surface to be measured are measured in the measurement coordinate system,and the angle measurement and displacement are achieved based on the plane normal vector method.measuring.The measurement model and the error model were established.The theoretical analysis and error source analysis were performed on this method.The correctness of the method was illustrated and the simulation was performed in the computer.The result proved that the error source can be controlled effectively.The accuracy of the angle measurement is achieved at the micro-arc level,displacement measurement accuracy is at the nanometer level.In the third part,a multi-degree-of-freedom measurement system based on error interference is designed.The detailed description of the three-degree-of-freedom measurement system introduces the basic principles of laser heterodyne interference,structure composition and signal processing.The displacement measurement part is directly processed by the heterodyne interference signal processing method,and three phase extraction methods including least square method,IQ orthogonal solution and FFT(Fast Fourier Transform)are analyzed.The angle measurement uses CCD to collect interference fringes,and the spatial frequencies of the fringes are analyzed using FFT and fringe spacing methods.In the fourth part,a three-degree-of-freedom measurement experiment was designed and built.The experiment mainly verified the measurement scheme based on the plane normal vector in the second part.The experiment was performed on the installation position of the instrument and displacement sensor and the deflection experiment of the fast-reflection mirror.Measurement and displacement measurement,angular measurement range in the range of 0.45 mrad accuracy in the range of 0.39?rad;displacement measurement accuracy in the range of 50 nm.The positive determination and practicality of the proposed method are verified. |
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