| Unmanned aerial vehicle photoelectric reconnaissance platform is an important load of military combat aircraft,unmanned aerial vehicle,armed helicopter and other aircraft.It is required to ensure that the imaging equipment maintains high-precision line-of-sight stability under severe conditions such as strong vibration,friction moment and wind resistance moment,and to take high-resolution images.According to the development of airborne photoelectric reconnaissance platform in recent years,with the application of new technologies and new materials,the imaging quality and resolution of optical cameras have made breakthrough progress,and high-resolution detector imaging system needs high-performance servo control system to cooperate with it in order to play its good performance.The key to improve the performance of the servo system is to improve the stability accuracy of the LOS and the image motion compensation ability of the system.In order to meet the higher requirements of the airborne photoelectric reconnaissance platform for the stabilization accuracy of lineof-sight and imaging resolution,based on the current domestic situation,this paper studies the following contents:The control system structure,hardware structure and work flow of the airborne photoelectric reconnaissance platform are introduced in detail.The main factors affecting the stability accuracy of LOS are analyzed.A new composite control strategy is proposed for the outer frame servo system according to the main characteristics of the disturbance to the outer frame.The main disturbance torque friction moment in the system is modeled and compensated accurately.The ADRC is designed for secondary disturbances except friction moment disturbance.The rationality and feasibility of the composite control strategy are verified by simulation and practical experiments.Experiments show that the stability accuracy of a single external frame can be less than 20 urad.The basic principle of in-scan imaging of airborne photoelectric reconnaissance platform and the principle of compensating scanning image motion by Fast Steering Mrror(FSM)are introduced.It is pointed out that there are two kinds of image shifts in the practical application of the airborne photoelectric reconnaissance platform studied in this paper: aircraft flight image shifts and platform scanning image shifts.Two kinds of image motion compensation formulas are calculated by using FSM,in which the influence of flight altitude,flight speed,aircraft attitude and platform attitude are taken into account.Finally,combined with the specific optical parameters of the airborne photoelectric reconnaissance platform involved in the project and the derived formula,the maximum scanning angle of the system scanning imaging is calculated to be 8.5944 degree/s,and the image displacement is 30 pixels at the maximum scanning angle,which proves that the existing scanning image displacement of the system will seriously reduce the imaging performance of the optical system.FSM is an important component of secondary stability and the core device of image motion compensation.In practical application,uncertainties such as carrier vibration,eddy current sensor noise,zero drift and mechanical resonance will change the model parameters of FSM in a certain range,which will seriously affect the control accuracy of FSM.To solve this problem,a model reference adaptive control strategy is proposed.The resonance in the sweep curve of the FSM is suppressed by introducing speed feedback.Then a reference model is designed according to the requirements of the project.Finally,the simulation results of MATLAB verify that the output of the controlled object can follow the reference model well after the model reference adaptive knowable scheme is adopted,which effectively improves the response performance of the controlled object.The final system performance test shows that the step response stability time of the FSM is 3 ms,the overshoot is less than 10%,the closed-loop bandwidth can reach 210.8 Hz,and the stability accuracy of the FSM can reach 20 Urad under the given 5 g vibration of the external shaking table.The final image motion compensation imaging experiment proves that the FSM can compensate for the scanning imaging process of the external frame successfully.The results of two-stage stabilization experiment of the combination of the FSM and the external frame show that the overall stabilization accuracy of the system can reach 4.628 Urad under the disturbance of 2 2Hz of the swing table.The final image motion compensation imaging experiment proves that the FSM can compensate the image motion brought by the scanning imaging process of the external frame,and meet the requirements of the stability accuracy of the line of sight and the image motion compensation performance under flight conditions. |
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