Thermal Control Design Of A Light-small Three Linear Array Aerial Camera

The rapid development of aviation technology makes aerial photogrammetric equipment widely used in military and civil fields.Aerial photogrammetry has become one of the important means to obtain ground information due to its low investment and high timeliness.Aerial cameras play an in-depth role in various fields,which puts forward higher and higher requirements for the imaging quality of its optical system.As an important aerial photogrammetry equipment,three-line array aerial camera provides accurate image information for the application of measurement technology in the form of optical photography.Therefore,the research on improving the imaging quality has become an imperative task.The three-line array aerial camera is mounted in the cabin of the uav,and its main working environment is the troposphere at medium and low altitudes.The temperature of the working environment is greatly affected by the flight height and flight season of the aircraft.Therefore,thermal perturbation has become an important factor affecting the imaging quality of the optical system and the measurement accuracy of the camera.It is of great practical significance to study the influence of different thermal environment on the optical system and design a reasonable and reliable thermal control system based on the integrated thermal/structural/optical(TSO)technique.For the problem of the complexity and variability of the UAV thermal environment,it is necessary to analyze the optical system in multiple thermal environments.As the design index of thermal control system,the temperature range that meets imaging quality requirements could be given by the change of defocusing amount and transfer function of the system in ZEMAX.To ensure that the temperature level of the optical system is within the index range,reduce the heat loss and heat leakage rate under the condition of extreme low temperature,the thermal insulation material and the layout of the thermal insulation mechanism is selected and designed,in the meantime,the lightweight passive thermal control design is completed.Based on that,the thermal network model is established to study the thermal characteristics of the aerial camera,analyze the heat leakage path and calculate heat loss of the aerial camera lens component.The research on thermal physic parameter analysis and correction method is applied to improve the accuracy of temperature distribution calculation.As the basis of hierarchical correction of thermal network model,parameters are classified according to the result of sensitivity analysis on the thermal physic parameters.After that,the transient thermal experiments are carried out,and the deviation analysis of experimental data is done.Latin hypercube sampling and unconstrained optimization are used for thermal analysis model's layered correction based on using the minimum deviation of transient temperature as object function.To ensure that the accuracy of the modified model meets the requirements of active thermal control design,the data of a new thermal experiment is used to be compared with the analysis of transient temperature distribution by using the modified model.The modified thermal network model will be used to calculate the heat leakage rate of each component of optical system which is the guidance of preliminary design of active thermal control,and the analysis results of finite element software guide further design iterative optimization,which reduces the heat loss of the lens and effectively compensates the heat loss in different part under low temperature environment.In order to ensure that the thermal control system can effectively control the camera temperature,a prototype is designed for transient thermal experiment.The experiment results show that optical system temperature can be controlled at 15~25? within 40 minutes and the temperature gradient is controlled in 4? with the active thermal control system turning on under low-temperature condition.This result indicated the rationality of the thermal control design in aspects of timeliness and effectiveness.