| Micro-vibration from the survey camera will inevitably lead to line of sight jitter of the space optical telescope,which is one of the core problems that restrict high-precision deep sky survey.The deep sky survey task have very high requirements on the micro-vibration suppression.However,it is difficult to suppress the micro-vibration of the survey camera with multiple vibration source,so the breakthrough of micro-vibration suppression technology has become one of the key factors in the successful development of the survey camera.The dissertation takes the multi-source and multi-directional micro-vibration suppression of the survey camera as the research goal.By breaking through the key technologies such as micro-vibration suppression of large-size mechanical shutter under the limited installation space of the rotor shaft and passive vibration isolation of cryocoolers with large cooling capacity,the effective suppression of micro-vibration of the large focal plane multi-vibration source survey camera was realized for the first time in China,which laid the technical foundation for the successful development of the survey camera in related aspects.The innovative results of the dissertation are as follows:1)By modelling and characteristic analysis of micro-vibration sources of the survey camera,it reveals that excitation force of the mechanical shutters is canceled in one direction but is doubled in the other direction,and micro-vibration resonance frequency of the cryocooler is piston’s operating fundamental frequency and multiples.Firstly,the mathematical model of rigid rotor rotation is studied,a mathematical model of the mechanical shutter micro-vibration is established to analyse its vibration characteristics.It is revealed that vibration of the mechanical shutter is a low-frequency harmonic micro-vibration.Exciting force generated by the vibration is canceled in the face-to-face direction of the two blade and doubled in the normal direction of plane defined by two parallel rotation axes.Both results of the finite element simulations and the experimental results of the shutter verify the mathematical model of the opposed-open mechanical shutter.Secondly,micro-vibration mechanism of a Stirling-type pulse tube cryocooler is studied,and its micro-vibration mathematical model is established to analyse its vibration characteristics.It is revealed that vibration of the cryocooler is a harmonic vibration of its operating fundamental frequency and its multiples.Test results show that vibration of the cryocooler in three directions is a harmonic micro-vibration with the operating fundamental frequency and its multiple frequency,and verified the validity of the mathematical model of the cryocooler.Mathematical models of the mechanical shutters and cryocoolers are a prerequisites for the study of micro-vibration suppression.2)Due to low operating frequency of the mechanical shutters and limited installation space of the shutter shaft system,passive isolation of the shutter and dynamic balancing of shafts are not suitable for the shutter micro-vibration suppression.Therefore,normal excitation force suppression method by optimizing driving curve and dynamic compensation suppression method by combining CAM and lever are proposed and used to suppress micro-vibration of the mechanical shutter.Firstly,response of the shutter excitation force for different driving curve of square,triangular and sine waves was analyzed and it was found that optimizing driving curve could reduce the shutter excitation force.With the goal of minimizing absolute value of residual vibration force of the shutter,a mathematical optimization model was established and modified,and a simple method was used to optimize driving curve.Normal excitation force of the shutter before and after optimization was reduced from 2.92 N to 1.72 N,a reduction of 41%,and was validated by simulation.Secondly,excitation force of the shutter is canceled in the lateral direction and is doubled in the normal direction.Mechanism of the rotation of the lever with opposite forces on both sides,which is proportional to the distance,and produces an axial component is studied.A dynamic compensation method using CAM and levers is proposed,where excitation force is suppressed by equating the shutter normal excitation force with inertial force on the amplified side of the lever.The symmetrical arrangement of the cam and lever mechanism is used to cancel axial vibration force component.With the aim of minimizing residual of normal excitation force of the shutter,a CAM curve was obtained by optimizing polynomial with the simple method.The numerical solution of micro-vibration model and motion simulation analysis are carried out,and results of the two methods are consistent: excitation force was reduced from 2.38 N before suppression to 0.29 N after suppression,and suppression rate is 87.8%.So validity of the dynamic compensation method is verified.These methods solve the problem of suppressing normal excitation force of the shutter in conditions of extremely limited space.3)With conventional elastic element isolation systems,multi-degree of freedom vibration decoupling is not possible because there is not enough space making the support centre of the isolation system to coincide with centre of gravity of the cryocoolers assembly.A passive isolation system based on three orthogonal elastic elements is proposed to suppress multi-directional micro-vibration of large cooling capacity cryocoolers assembly.Isolation model of rigid system and coupling isolation model of elastic system are established respectively.The isolation modeling of rigid system can be used for the design and analysis of the stiffness and damping parameters,while coupled isolation modeling with elastic system is used for the performance analysis of passive isolation system.A principles of isolation systems design are proposed.Aiming at the multi-degree-of-freedom vibration characteristics of the cryocoolers,a passive vibration isolation system based on the new three-orthogonal elastic element is proposed.Parameter design and analysis of the three orthogonal flexible elements show that structural shape of new elastic element realizes decoupling in three translation directions.Design of decoupling isolation system of the cryocoolers is completed.Layout design and coupling analysis of the isolation system show that its six degrees of freedom are decoupled and verified by modal analysis.Thus,design problem of the cryocoolers decoupling isolation system under limited space is solved.Transfer rate of undamped and damped isolation system is analyzed.After micro-vibration of the cryocoolers is isolated by the damping vibration isolation system,vibration transmission rate at fundamental frequency of 50 Hz is 94%-97%.Goal of vibration suppression of the cryocoolers is achieved.So a technical breakthrough has been made in multi-directional micro-vibration suppression of cryocoolers with large cooling capacity.Finally,the dissertation develops integrated micro-vibration suppression of the entire Survey Camera,and simulates and verifies various vibration suppression technologies and methods proposed in this dissertation.Based on the above mentioned micro-vibration suppression techniques and methods,integrated modelling analysis of micro-vibration on the Survey Camera is carried out,and result show that suppressed micro-vibration meets mission requirements of the Survey Camera and achieves target of micro-vibration suppression. |
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