| Laser guidance&communication system for UAV(Unmanned Aerial Vehicle,UAV)is a new kind of optoelectronic system which uses laser to measure and transmit UAV guidance information.It is mainly involved in UAV laser guidance technology,SLC(space laser communication,SLC)technology and their systems integration technology.Integration of discrete UAV laser guidance system and SLC system could avoid the hazard when using radio frequency transmit UAV guidance information,save resource requirements for install platform,and give full play to the dual advantages of the laser in measurement and communication.However,according to the existing publications,current research on UAV laser guidance and SLC technology are separate,and neither research team nor results have been published about the technology of their integration.Under the support of national defense pre-research project,a UAV laser guidance&laser communication experimental system is designed and realized in this dissertation originally,which is an innovative attempt to integrate UAV laser guidance and SLC technologies.In order to solve the three key technologies involved in this system:laser communication receiving technology without PAT(Pointing,Acquisition,Tracking,PAT)modules,fast acquisition technology and coarse/fine tracking control technology,deep researches and discussions have been done.The main contents of the dissertation are summarized as follows:1.On the foundations of the existing research results of our lab in SLC field,the typical structure of SLC system has been used as a reference in the experimental system design,and the functions related with UAV guidance have been embedded into the system.The experimental system includes four parts as a whole,which are optical subsystem,communication subsystem,PAT subsystems and guidance subsystem.In order to achieve integration of UAV laser guidance and SLC technologies,a dedicated communication subsystem for guidance was added to the communication subsystem,and a guidance subsystem was added to the overall structure.2.In order to acquire UAV quickly under the restraint that UAV could not emit beacon laser,a method based on a two-dimensional fast galvanometer and passive cooperation device(total reflection prism)is designed.Firstly,the fast acquisition and scanning mode is designed for passive cooperation device combined with the background of project,and also acquisition workflow diagram is given.Secondly,the mathematic expression of the acquisition time is derived,the opinion that when acquisition uncertain area,laser beam divergence,signal to noise ratio and other conditions is certainly,the scanning step performance of acquisition unit is the only factor that affect total acquisition time has been pointed out.And then,a novel acquisition method which uses a two-dimensional fast galvanometer that the scanning step performance is much higher than traditional coarse tracking turntable as the main scanning mechanism is proposed,so the acquisition time could greatly reduce in theory.Finally,the acquisition link for passive cooperation device is configured.The experimental results show that the acquisition time of this method is very shot,acquisition performance is much better than traditional acquisition methods.3.In order to improve the disturbance isolation degree of coarse tracking unit deeply,a novel control method based on modified extend state observer is proposed.Firstly,the composition and control structure of coarse tracking unit is introduced,coarse tracking control model is derived,the basic position controller form is determined which uses the PID(Proportional-Integral-Differential,PID)form,the PID parameters is calculated in accordance with the relevant technical parameters,and a satisfactory result of passive disturbance restrain is obtained.Secondly,the shortcomings of the PID controller are pointed out,the ADRC(Active Disturbance Rejection Control,ADRC)control theory which based on "active immunity" principle and its shortcomings during practical application are introduced.And then,focus on the ESO(Extended State Observer,ESO)which is the core part of ADRC theory,the disturbance observation theory of linear ESO is derived and demonstrated,and its disadvantages are pointed out theoretically,According to that,an modified linear ESO is proposed.Finally,the ADRC control of coarse tracking unit is realized with the improved linear ESO and PID adjuster.The experimental results show that as for the external position disturbance with the magnitude of 1 degree and frequency of 0.25Hz-1.25Hz,the disturbance isolation degree declines significantly with the increase of disturbance frequency adopting the traditional ADRC.While the disturbance isolation degree improves at least 4.26dB adopting the improved ADRC in this paper,and the disturbance isolation degree increases stably with the increase of disturbance frequency,which is almost the same at 1Hz and 0.25Hz.What's more,the proposed method is robust and the change within 15%of the controlled object is allowed.4.In order to improve the disturbance isolation degree of fine tracking unit deeply,a novel control method based on disturbance observer is proposed.Firstly,the optimal fine tracking control structure is determined,two kinds of fine tracking control structure that based on the motor position loop and current loop are introduced,their open loop transfer function,closed loop transfer function and the disturbance transfer function are derived,their basic position PD(Proportional-Differential,PD)controller parameters is calculated under the same forward path design index,after comparing the disturbance isolation degree of them,the opinion that the structure based on motor current loop is far superior to the structure based on the motor has been pointed out,in the subsequent study only fine tracking unit based on motor current loop is the research object.Secondly,the basic disturbance rejection principle and disturbance isolation degree limit in theory is analyzed.And then,DOB(Disturbance Observer-Based,DOB)theory based on the principle of "active immunity" is introduced.Finally,a novel control method based on DOB is proposed,the disturbance is observed from the position of the motor and the laser spot by DOB.The equivalent amount of disturbance compensation is added to the integration points in front of the current loop.The experimental results of fine tracking system show that compared with traditional PD controller,adding DOB can improve the disturbance isolation degree at almost all frequencies before the motor current saturates,and the optimal situation has reached 11.6dB.What's more,the proposed method is robust and the change within 15%of the controlled object is allowed.5.In order to realize guidance information reception under the restraint that UAV could not install PAT modules,a method based on a large receiver field of view and laser subcarrier modulation is designed.Firstly,the opinion that only a large receiver field of view could avoid link break caused by the laser beam alignment deviation when there is no PAT modules has been pointed out,and the effect of background light on receiver when using wide field of view is calculated,then the opinion that OOK signals will be submerged in the background light without special processing has been pointed out,and at last a method based on laser subcarrier modulation is proposed.Secondly,the physical implementation of the method is explained.And then,a special communication protocol for guidance is designed to improve the communication reliability and availability.Finally,laser communication link is configured;also the detailed design process is given.The experimental results show that compared with OOK modulation this method could suppress background light interference effectively and realize UAV laser communication data reception. |
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