Research On Adaptive Sliding Mode Control Methods For An Airborne Three-axis Universal Electro-optical Stabilized Platform

Electro-optical stabilized platforms are widely used in the field of modern aerial remote sensing,such as military reconnaissance,target positioning,disaster monitoring and so on.In order to adapt to the complex terrain,weather and work environments,and meet requirements of rapid and reliable acquisition of all-weather disaster site information,a kind of three-axis universal Electro-optical stabilized platform mounted on the fixed-wing unmanned aerial vehicle platform has been developed Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences,which can realize to assemble different payloads rapidly via universal interfaces,and achieve multi-tasks such as the target search,swing scanning imaging,attitude compensation by high-precision compound motion of the three axes.Due to the three-axis universal electro-optical stabilized platform is affected by the influence of external nonlinear factors,such as the attitude change of the aviation platform and dynamic motion of target,the image quality is easily degraded.At the same time,different payloads have different masses and centroids which are difficult to be measured accurately.So it is a great challenge to obtain an exact dynamic model and design an effective servo control algorithm that takes into account both the video tracking and swing scanning imaging applications under the different payloads.Although,the traditional proportional-integral-derivative(PID)controller has been widely used in the motor drives due to its simplicity in implementation,with the increasing requirements of information task,higher positioning and tracking performances are needed,at this time,the PID controller often hit a bottleneck.In order to improve the performance in the practical engineering applications including so called low-speed video tracking and large-angle swing scanning imaging at the same time for the three-axis universal Electro-optical stabilized platform,we have studied adaptive sliding mode control strategy subjected to the uncertain disturbances.The main work of this paper is as follows:1.The system conposition and working principle of the three–axis universal electro-optical stabilized platform are described,the main disturbances of the platform are analyzed.The dynamic model and control model of the servo mechanism are established,and the influence of the servo control accuracy is analyzed.2.Aiming at the friction torque disturbance in video tracking,Lu Gre friction model is studied.Lu Gre friction model of the three-axis universal Electro-optical stabilized platform is established and parameters are identified.Adaptive sliding mode control method is constructed to compensate the friction online.Finally,simulation and experimental results show the method can significantly improve the control performance of low-speed video tracking.3.In order to improve the servo position tracking accuracy in engineering applications such as low-speed video tracking and large-angle swing scanning imaging,an adaptive nonsingular fast terminal sliding mode control strategy is proposed to solve the problems of system model uncertainty,external disturbance and input saturation,combining the advantages of sliding mode control and adaptive control.Firstly,all disturbances are lumped into the total disturbance,and the upper limitation of the lumped disturbance is designed as the function of position and velocity.Secondly,the sliding mode controller is designed according to the nonsingular fast terminal mode surface.At the same time,in order to meet the requirements of low-speed video tracking and large-angle swing imaging.For the dynamic performance of the position tracking control,a new reaching law is designed to accelerate the convergence process and alleviate the chattering phenomenon.Then,an adaptive controller is designed to estimate the disturbance parameters online.Finally,the stability of the control system is proved via Lyapunov stability theory.The simulation and experimental results show that the proposed method does not rely on the exact dynamic model,and does not need the prior knowledge of the upper bound of the lumped disturbance.It can achieve the fast convergence in finite time,and avoid the singularity problem.Owing to the new reaching law,the control parameters of the low-speed video tracking and large-angle swing scanning are unified,and chattering is effectively reduced,and the performance and robustness of the servo control system are improved.It has important engineering practical application value.In this paper,the system composite,principle and working mode of the three-axis universal Electro-optical stabilized platform are systematically introduced.Considering the model uncertainty and external disturbance factors,the adaptive sliding mode control method has been studied for the two practical applications including video tracking and swing scanning imaging with different payloads combinations,which improves the dynamic performance and position tracking precision of the servo control system,which provides an important reference value for the design batch production of this kind of electromechanical servo control system with multi-payload-combinations,multi-tasks and multi-uncertainties.