| Laser beam pointing control plays an important role in precision guidance,space laser communication and aerial imaging etc.in modern times.With compact structure,high tracking precision,wide control bandwidth,fast response speed and other outstanding advantages,fast steering mirror is one of the essential devices for fast and high-precision beam pointing control.By far,many developed countries in Europe and America have already developed advanced fast steering mirrors.In comparison,China still falls behind in terms of both researches and products.In addition,China has imposed some restrictions on introduction of advanced fast steering mirrors for high-end products.Therefore,researching and developing innovative and competitive fast steering mirrors are important to further research on advanced optical technologies for high-end products.In this paper,research was carried out on a fast steering mirror driven by piezoelectric ceramics for laser beam pointing control system,including structural design of the fast steering mirror system,study on micro-displacement amplification of rhomboid structure,study on a flexible support structure with three degrees of freedom,study on nonlinear compensation for hysteresis of piezoelectric ceramics and study on identification of fast steering mirror system and controller design as well as experimental study on test platform building.The said studies are specified as follows:The design scheme of the laser beam pointing control system was put forward in line with the fast steering mirror system.A four-point driver structure was adopted,with piezoelectric ceramics as the the driving element,an innovative grating encoder as the feedback element,a flexible structure as the support element,and DSP28335 as the key processor.Given the short stroke of the piezoelectric ceramic driver,research was carried out on micro-displacement amplification.Theoretical analysis was carried out on the correlations between deflection range and resonant frequency of the fast steering mirror and the displacement amplification ratio and rigidity of the rhomboid structure.Also,the key structural parameters affecting the performance of the rhomboid structure were analyzed,and the linear programming method for designing key structural parameters was put forward.Moreover,simulation analysis was carried out on the rhomboid structure by means of finite element method so as to verify the law of the influence of the key structural parameters of the rhomboid structure on its performance.Furthermore,the intensity of the designed rhomboid structure was checked under static load and harmonic response respectively.Finally,the performance of the rhomboid structure was tested in an experimental study,which proved that the test results and the results of theoretical analysis were consistent.A new flexible support structure with three degrees of freedom was studied in order to overcome the poor shear resistance of the piezoelectric ceramic driver which could elongate but couldn't shrink.Firstly,the flexible support structure composed of flexible rods and petal-shaped flexible ring was put forward.Secondly,the flexible support structure was modeled by means of Castigliano's Theorem.Also,the key structural parameters affecting the performance of the flexible rod were studied theoretically.Finally,simulation analysis was carried out on the flexible support structure by means of finite element method,which verified that this structure could protect the piezoelectric ceramics from shear failure while effectively transmitting the driving force.Moreover,it could restrain vibration mode in the non-working directions,thus ensuring first-order resonant frequency.Given the influence of hysteresis effect of piezoelectric ceramics on identification of the system,in the fast steering mirror system,the hysteresis effect of piezoelectric ceramics was compensated by means of Prandtl-Ishlinskii inverse model based on PLAY operator and Prandtl-Ishlinskii model based on STOP operator.Prandtl-Ishlinskii model based on STOP operator was improved to compensate for the influence of input rate on hysteresis effect,which enhanced the open-loop accuracy of the system.Furthermore,a third-order mathematical model was built by analyzing the mechanical structure and circuit hardware of the fast steering mirror system.Finally,the parameters of the linear system composed of the hysteresis compensator and the fast steering mirror were identified by means of sinusoidal frequency.A test platform was built;and the programs for the controllers were written in DSP28335 and FPGA to test the deflection range,pointing accuracy,resonant frequency and control bandwidth of the innovative fast steering mirror.Moreover,the deficiencies of the innovative fast steering mirror were analyzed through comparison with the product of PI,a German company.The test results show the follows: the parameters of a fast steering mirror with the load diameter of 90 mm are as follows: the deflection range is 5 mrad,the pointing accuracy is 20 ?rad,the resonant frequency is about 250 Hz and the closed loop bandwidth is 120 Hz.Hence,it can cater to laser beam pointing control system. |
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