Research On Vibration Isolation And Angular Vibration Active Compensation Of Aerial Camera

As one of the important payloads of aerial remote sensing,aerial cameras can obtain ground information through a variety of imaging methods such as visible light,infrared and multispectral.Due to its advantages of good mobility,high timeliness,strong purpose and low investment,it is widely used in resources survey,topographic mapping,military reconnaissance and other fields around the world.As one of the most important performance indicators of aerial cameras,imaging quality is not only restricted by the optical system and the electronics system,but also affected by a variety of complex factors such as carrier motion,carrier vibration,and environmental conditions.Among them,the angular vibration of the aerial camera has serious impact on the imaging quality,which will cause the line-of-sight(LOS)of the aerial camera to jitter,and lead to image motion during its exposure process,resulting in blurred imaging.Therefore,how to reduce the impact of angular vibration on aerial cameras is one of the problems that must be solved in the development of high-performance aerial cameras.There are two main ways to reduce the impact of angular vibration on aerial cameras: one is to use the vibration isolation system to attenuate the amplitude of angular vibration as much as possible;the other is to actively compensate the impact caused by angular vibration through a compensation mechanism.The vibration isolation system has a strong ability to suppress high frequency vibration,and the active compensation method has obvious compensation effect on low frequency angular vibration.Only the combination of these two methods can minimize the effects of angular vibration in the entire frequency band.This paper conducts research work from two aspects of the design method of aerial camera vibration isolation system and the active compensation method of angular vibration:The source and cause of angular vibration are analyzed.It is confirmed that the angular vibration source of the aerial camera is not only the angular vibration excitation from external environment and the moving device inside the camera,but also the angular vibration due to the coupling after the linear vibration passed the vibration isolation system.By establishing the dynamic model of the aerial camera,the coupling characteristics of the aerial camera are analyzed,and the concepts of stiffness center,damping center,stiffness moment center and damping moment center are introduced.By analyzing the coincidence of the stiffness center,damping center,stiffness moment center,and the damping moment center and the center of mass,the different coupling forms caused by the layout and parameter selection of the isolators of the vibration isolation system are discussed.By analyzing the vibration transmissibility of the vibration isolation system,the relationship between the layout and parameter selection of the aerial camera vibration isolators and the vibration transmissibility is obtained.Based on the analysis and discussion of the coupling characteristics and vibration transmissibility of the vibration isolation system,a design method of passive vibration isolation system for aerial cameras based on coupling constraints,layout constraints and performance constraints is proposed.Using this method,a vibration isolation system was designed for a certain aerial camera,and its effectiveness was verified by finite element simulation.Based on the research of active compensation method of angular vibration,an active compensation simulation model was established to analyze the active compensation capability.A verification system of aerial camera angular vibration active compensation is established by using a fast steering mirror and a fiber optic gyro as the compensation mechanism and angular vibration measuring device,respectively.In order to provide a stable and controllable angular vibration excitation for the test experiment of the angular vibration active compensation verification system,a voice coil motor(VCM)driven angular vibration generating device based on flexible guidance mechanisms is designed and built,and a verification test is performed.Through the method of sampling a fixed cross target continuously and rapidly by a high-speed camera which is mounted on the angular vibration generating device,the compensation experiments of the angular vibration active compensation verification system under angular excitation with different amplitudes and frequencies are recorded.The image processing method is used to obtain the center coordinates of the cross target on sampled pictures.According to the change of the target center coordinates,the LOS jitter induced by angular vibration can be obtained.The performance evaluation of the angular vibration active compensation verification system is realized by comparing the amplitude change of the target center before and after the intervention of the angular vibration active compensation mechanism.After comparing 60 experimental results of active compensation under different angular vibration excitations with amplitudes of 0.045°,0.09°,0.135°,0.18°,0.225°,and 0.27°,with frequencies in the range of 5Hz-50 Hz,and intervals of 5Hz,the following phenomena is found: in the case of the same excitation amplitude,the active compensation effect continues to decline as the excitation frequency increases;under the same frequency,as the excitation amplitude increases,the active compensation effect continues to decrease.In all 60 experiments with different excitation amplitudes and excitation frequencies,the vibration suppression rate of the angular vibration active compensation verification system is above 70%,and the angular vibration suppression effect is good.It lays a technical foundation for the application of the active camera angle vibration compensation system.