| The airborne optoelectronic stabilized platform is a high-precision reconnaissance equipment equipped on drones and other aircrafts.It is optical,mechanical,electrical,computer and control interdisciplinary equipment,widely used in military and civil fields.Various frame structures have been derived from the development so far,among which the advantages of two axes and four frames and the number of equipment are strong.It can greatly improve the stability accuracy of the line of sight,enhance the ability of target search and tracking,and overcome the "over the top" problem of two axes and two frames.This article focuses on the small-sized,lightweight and high-precision photoelectric stabilized platform carried by the UAV.Because the classic control cannot solve the problems of nonlinear controlled objects,system parameter changes,internal and external complex disturbances,etc.,it develops a more efficient and reliable servo control method explore.Firstly,the overall composition of the two-axis and four-frame airborne optoelectronic platform(hereinafter referred to as airborne optoelectronic platform)system was introduced,indicating that the design of servo control control system is crucial to the stability of the line of sight of the optoelectronic platform.The advantages and characteristics of the two-axis four-frame structure were analyzed to meet the requirements of small volume and light weight,and provided favorable conditions for high precision and stability in the structure.At the same time,the small-angle movement of the inner frame overcomes the problem of "overhead"structurally.Then the working principle of the servo control system was analyzed,and the performance requirements of high precision stability control for all kinds of sensors and drive motors were analyzed and the selection was given.Secondly,the axis coordinate system is established based on the frame structure of the airborne optoelectronic platform,and the coupling relationship between the frames is derived using kinematics and mechanics theories.Next,a disturbance model is established for the internal disturbance and external torque disturbance of the system,and the main disturbance is overcome after quantitative calculation.Then,a mathematical model is established for each part of the airborne optoelectronic platform control system,which is convenient for the algorithm design in the servo control loop.Then,due to the movement complexity of the optoelectronic platform,the traditional control ability is limited,the sliding mode variable structure control method in advanced control theory was adopted.According to its parameter perturbation insensitivity and strong robustness,combined with the disturbance observer and the nonlinear extended observer,two effective cascade composite control strategies were designed.Simulation experiments were carried out to verify its observation ability to disturbance and performance in closed loop system.At the same time,a method to reduce the chattering problem of the sliding mode variable structure was proposed.Finally,against the hardware circuit and the composite control strategy software of the airborne optoelectronic platform were designed.The servo control processing module designed in thesis was implanted into the existing optoelectronic platform for experiment.Through laboratory tests and field experiments,nonlinear interference and mounted flight were added to collect a large number of data for analysis and verification.Compared with the 100～200urad level stability accuracy of the traditional light-weight two-axis two-frame photoelectric stabilized platform,the structure of this subject adopts two-axis four-frame form,and the servo control algorithm adopts sliding mode variable structure compound control,which improves its stability accuracy to Within 50urad.Experimental results show that the servo control strategy designed in this paper can meet the requirements of stability precision and response.It has more engineering significance and research value for the development of airborne optoelectronic platforms. |
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