Design And Analysis Of Flexible Frames For Airborne Optical Devices

The airborne optical device is usually mounted on a gyro frame which is supported by vibration isolation system to achieve high-precision angular positioning and broadband vibration isolation.For lightweight optical devices,the size and weight of traditional gyroscopic frames and vibration isolation system are relatively high,and bearing friction disturbances have significant influence on the angular control accuracy.Novel flexible frame with low torsional stiffness,which serves as both vibration isolator and rolling bearing,can significantly reduce extra payload and simplify the structure.It is of great significance for the improment of vibration isolation and angular positioning performance for airborne optical devices.Concerning the requirements of flexible frame for a small airborne optical device,this thesis focuses on the systematic solution and configuration design of the flexible frame.By means of comparative research on dynamic modeling and analysis of three kinds of flexible frames,an spatial-octagonal-supported flexible frame with positive and negative stiffness in parallel is proposed,and prototype development and performance verification of the flexible frame are then carried out.The main research achievements of the thesis are as follows:1.According to the requirements of the flexible frame performance index of an airborne optical device,an overall plan of the flexible frame with octagonal support is proposed.The feasibility of different flexible frame configurations based on series stiffness,positive and negative stiffness parallel connections,etc.Combining the requirements of low stiffness,large load,and small volume,a structural configuration scheme for a flexible framework of airborne optical equipment was proposed.2.For the requirement of high axial stiffness and low lateral stiffness for each flexible supporting elements,three kinds of configuration were proposed,including a flexible structure with multi-bars in series,series-parallel flexible bars combined with magnetic negative stiffness mechanism,and helical spring combined with pre-compressed negative stiffness mechanism.Structural design and stiffness characteristics modeling and simulation were carried out.Vibration isolation frequency,torsional stiffness and structural strength of the flexible frame for the above three kinds of flexible support elements were analyzed and compared,and helical spring combined with pre-compressed negative stiffness mechanism was chosen as solution for the flexible frame.3.The detailed design and prototyping of the flexible frame based on the helical spring preloaded spring negative stiffness mechanism were completed.The vibration isolation and torsional stiffness testing and analysis of the flexible frame under simulated load were carried out.The results show that the errors of the three-way vibration isolation simulation and the measured results of the prototype test system are 11.1%,2.5% and 3.0%,respectively,and the error between the torsional stiffness simulation and the measured results is within 6.7%.Further analysis of the source of the error and the influence rules provide directions for subsequent optimization and improvement.The research results show that the flexible frame structure proposed in this thesis is feasible and basically meets the design index requirements.The performances of the prototype can be improved in the future,by improving the manufacturing and assembly precision of structural components,and replacing ball joints with flexible hinges.