Research On Equipment And Technology Of Ion Beam Figuring For Space Complex Optical Surface

High precision complex optical surface(off-axis aspheric and free-form surface)is the core components of high-resolution space optical remote sensing system.The manufacturing precision and processing capacity is one of the development bottlenecks of high resolution optical system.A new type of large F# optical system has a higher requirement on the reflection mirror shape,which is difficult to meet by the existing optical processing technology.Therefore,it is of great significance to study the fabrication technology of ultra-high precision optical components for improving the imaging quality of the optical remote sensing system.The traditional method of optical processing technology,such as Computer Controlled Optical Surfacing(CCOS),Stress Lap Polishing(SLP)will introduce mid-and-high frequency errors due to the mismatch between the complex optical surface and the grinding lap.Besides,the grinding lap will apply a positive pressure on the mirror which can lead to edge effect,sub-surface damage and copying effect etc.These problems existing in the traditional processing methods greatly limit the efficiency and precision of complex optical surface machining.In order to realize the high precision machining of the space complex optical surface,the new technology,Ion Beam Figuring(IBF)has been applied in the field of optical processing.The IBF technology is a kind of computer control optical surfacing technology.It replaces the traditional small grinding lap by the ion beam source,which can realize the removal of surface material of the optical element on the atomic scale.Under the same condition,the removal function of IBF will change with the change of incident angle.Generally,IBF with three axis machining and removing function correction is used.However,for high gradient complex optical surface,mathematical compensation has been unable to meet the requirement of processing precision,five axis motion system is required to ensure the stability of the removal function.In addition,the mid-and-high frequency errors caused by the previous procedure,the thermal effect in the processing of complex surface also have severely limited the processing precision.Therefore,to improve the efficiency and accuracy of IBF,this paper conducts research on IBF equipment and technology which mainly includes the following aspects:1.Study on the new type of IBF machineCombined with the advantages and disadvantages of the series and parallel machine,this paper presents the configuration of a new type of five axis motion system based on hybrid machine tool.The Jacobian matrix of the parallel mechanism is established with the closed vector method.In order to ensure the stability of the ion beam source in the process of machining,the singularity of the parallel mechanism is analyzed and verified.Finally,the workspace of the hybrid machine tool is presented.2.Study on IBF of complex optical surface based on hybrid machine toolThe processing strategy according to the best fitting spherical surface is presented combined with the characteristics of ion beam figuring.According to the best fitting spherical surface,the inverse kinematics algorithm of five axis hybrid motion system is presented.The approaches realization of dwell time are analyzed,the proessing mode based on speed is given.Besides,in order to remove the pose error of the optical element,the paper analyzes the relative error between the removal function and the workpiece and the inverse kinematics error of the hybrid machine tool.The method of correcting the pose error by Faraday scan and Renishaw border patrol mode is given based on the datum transfer.Using the dual frequency laser interferometer,the positioning error of the hybrid machine tool is analyzed and corrected.3.Analysis and suppression of thermal effect in ion beam machiningIn this study,a full-path simulation method based on a moving heat source to predict the temperature distribution of the space mirror during IBF is developed.In addition,the multistep figuring method is proposed for thermal suppression of the adhesive layer temperature.Finally,an experiment on a rectangular SiC space mirror is conducted to prove the effectiveness of the thermal analysis and suppression method.4.A combined machining method based on deconvolution algorithmBased on the deconvolution algorithm,this paper proposes a combined machining method using CCOS and IBF which can effectively reduce the mid-and-high frequency surface error.The simulation results show that this method can both improve the final ion beam machining precision and shorten the total processing time of the optical element.5.IBF experiment of space complex optical surfaceBased on the research above,IBF experiment is done for a high gradient spherical optical surface mirror with the independently developed machine FSGJ800-IBF.During the experiment,the RMS value of the surface error is converged from 0.032λ to 0.014λ,which prove the feasibility of the research.