Analysis And Optimization Of Nonlinear Vibration Characteristics Of Rough And Precision Tracking System For Near Ground Laser Communication Terminal

The stability of the APT(Acquisition Pointing and Tracking)system of laser communication terminal is the key to ensure the reliability of the communication link,it needs to maintain high accuracy and quick ness,so the mastery of its dynamic characteristics under the effect of working disturbance and background noise is particularly important.Even subtle vibration transmitted to communication system may have a large impact,also the system level research on the dynamic characteristics has a guiding significance for the selection of control bandwidth and simulation and optimization of the whole system.The terminal structures are often used to approximated by linear theory,but in the course of movement,system stiffness and boundary conditions may change at any time,the nonlinear effects caused by it will also lead to the introduction of huge errors in the analysis and calculation.Therefore,the analysis and consideration of the nonlinear factors of the precision tracking system is an important part to realize the dynamic and precise simulation of the system.The terminal tracking usually achieved by coarse and fine tracking together,the coarse tracking is realized by multi dimension photoelectric tracking turntable,fine tracking mainly realized through the quick control of FSM system.In a multidimensional photoelectric turntable,the nonlinear effect is mainly caused by the change of the contact state of the bolt connection and the instability movement caused by the misalignment of the shaft system.In the fine tracking system,its nonlinear influence mainly exists in the asymmetrical motion of the flexible rotating structure and the change of the contact state of the bolt connection area.This study focuses on the research of nonlinear dynamic characteristics in these aspects,to complete the study and analysis of the mechanism and influence of the dynamic characteristics.Multi parameter optimization is carried out for the frequency and the resonant frequency of the working state is maximized.The influence of the vibration characteristics,control bandwidth and optical system performance is also discussed.For the bolt connection part,firstly the theory and simulation of single bolt model are studied,linear model and nonlinear contact models are constructed considering the bolt pretightening force.The time domain explicit integration algorithm is introduced,single point white noise excitation isconstructed,according to the sampling law,the single step time and the total time are solved.The response of the single bolt model under this excitation is calculated,the frequency results of the simulation are obtained.Then a single bolt model is producted,the experimental results of the single bolt model are obtained by the hammering method.Compared with the simulation results,a model that considering both the accuracy of simulation and the complexity of simulation is fond.The accuracy of the model in the single bolt connection model is verified.Then,the whole bolt connection is simulated using the bolt contact model for the two dimensional photoelectric turntable.The modal simulation results of the whole machine are obtained by modal method,and the response of the whole machine system under unidirectional excitation is calculated by the explicit response analysis under unidirectional excitation.Finally,a response experiment is carried out,and the response of end machine system under different unidirectional excitation is obtained.Compared with simulation and experiment results,it is found that the bolt contact model is also suitable for the simulation of complex system.Through the motor swept experiment of the whole machine,the response of the terminal system under real working conditions can also be obtained.Compared with the simulation results of bolted connection models,the error of the bolt model under real working conditions can be understood.For the shaft misalignment section,the motion equation of the system can be established based on the lagrange equation,then the fourth order Runge-Kutta method is ultilized to get the steady state response of a rotor system,the response of frequency spectrum,rbit of shaft center and poincaré mapping are used to characterize dynamic characteristis of rotor system.For shafting simulation,the rotor system solid rotor model is established in Comsol.The Campell diagram of the influence of the rotational speed on the mode can be obtained from the response of system at different rotational speeds.The nonlinear response of the system is obtained by adding parallel misalignment conditions and rotating conditions.The dynamic characteristics of rotor system under different system parameters can also be obtained by analyzing the response results.Then,the experimental platform of the middle rotor is built,and the response of the system under different speeds and misalignment conditions can be obtained using acceleration sensor and laser displacement sensor.Compared with the simulation analysis,the accuracy of the analysis and simulation results can be verified.Finally,the misalignment rotor model is integrated into the whole machine system.Considering the bolt connection contact model and the shafting misalignment model,the response of the turntable under the working condition is obtained,and the accuracy of the simulation results a nd the model can be verified by comparing with the motor frequency swept experiment.For the fine tracking system,the flexure and rotation accuracy expressions of the main rotary link flexure hinges are obtained from the second law of Cartesian.Based on the minimum flexibility,the highest rotation accuracy and the allowable stress requirements law are applied to select the optimal parameters and the shape of the rotary parts.Then the simulation and experimental verification of the flexibility optimized structure are carried out to verify the accuracy of analysis results.Then consider the bolt connection in the model,the response of FSM system driven by motor is obtained.Finally,sweep experiment platform is established,amplitude frequency characteristic curve on two working direction is obtained.The single response resonant frequency is obtained which guides the selection of work control bandwidth and verifies the result of simulation analysis.After investigation of the nonlinear characteristics,according to the analysis results,multi-parameters are optimized based on response surface method,topology optimization of the key structure is carried out.Using the sub structure method,the overall response of the primary mirror surface performance para meters before and after optimization is obtained.It can be found the optimal structure not only improves the resonance frequency of working condition,but also the the primary mirror surface type under the vibration.