| Aspheric surface optics has the excellent characteristics of simplifying optical system structure,expanding optical system functions,and improving imaging quality,and has become the core component in many fields such as laser fusion,aerospace remote sensing,and space telescopic observation.The high-precision manufacturing technology on it has always been the difficulty and hot spot of modern optical manufacturing.Traditional optical manufacturing methods have been unable to meet the growing requirements for aspheric surface applications.As a highly deterministic sub-aperture processing technology,magnetorheological finishing has the advantages of controllable material removal,accurate polishing results,and high surface accuracy,and is expected to solve the related problems in the manufacturing process of aspheric surfaces.At present,the research on magnetorheological finishing for optical components of the aspherical surfaces is not thorough and systematic,and it is difficult to realize the collaborative convergence of full-spatial frequency errors on the component surface,which to some extent limits the application of magnetorheological finishing in the field of high-precision machining of aspheric surfaces.Hence,the work on controlling the full-spatial frequency errors of the aspheric surface optical components in magnetorheological finishing is carried out in this paper,which is of great significance for the creation of ultra-precision and ultra-smooth aspheric surfaces with accurately controllable full-spatial frequency errors.The specific research work includes the following aspects:Based on the Preston equation and rheological properties of magnetorheological fluids,the correlation equation between plane and sphere tool influence functions was constructed,and the existing magnetorheological finishing process of spherical components was optimized,thereby improving the matching between theoretical prediction and actual processing.For the continuous variation of aspherical curvature,a dynamic regionalized modeling method of aspheric tool influence function was proposed,and then the pulse iterative algorithm for solving residence time was improved.And the edge continuation method was used to make the surface shape errors of the aspherical element converge largely.The experimental results show that the regionalized modeling of the dynamic tool influence function and the improved dwell time solution algorithm can effectively improve the surface shape accuracy of aspherical components after magnetorheological finishing.Aiming at the deterioration of middle-spatial frequency errors on the component surface after magnetorheological finishing,the main influencing factors of the middlespatial frequency errors were analyzed,and the influence law of each factor on it was obtained.Considering the removal efficiency and the surface shape errors correction effect comprehensively,it was proposed to use the characteristic length coefficient of polishing spot to evaluate the smoothing ability to the middle-spatial frequency errors.The influence weights of various factors on the tool influence function were obtained,and then the optimization of process parameters was realized.Based on k-means clustering,an adaptive grating trajectory planning method was proposed to reduce the introduction of middle-spatial frequency errors by reducing the periodicity of polishing trajectory.The effectiveness of the optimization of tool influence function and trajectory to suppress the middle-spatial frequency errors was verified by the experiment.Experiment showed that the optimization of tool influence function and trajectory can make the middle-spatial frequency errors of the component converge to the target accuracy,but the processing efficiency still needs to be further improved.Given the lack of smoothing post-processing technology for middle-spatial frequency errors,a conformal vibration polishing method combined with short-stroke forced vibration of polishing tools was proposed,and the and device construction of the method was completed.A tool influence function model was established and the corresponding verification experiment was carried out.The relative error between the theoretical calculation results of the material removal depth and the actual removal depth did not exceed 10 %.The effect mechanism of the polishing disc on the middle-spatial frequency errors and the low-spatial frequency surface errors in the process of conformal vibration polishing was analyzed,and a time domain smoothing prediction model of the middle-spatial frequency errors was established.Conformal vibration polishing experiments were carried out on the components with different surface types.The results show that the conformal vibration polishing method using flexible polishing tool is not limited by the component surface type,and can achieve better processing results.The accuracy of each moving axis of magnetorheological finishing machine was tested,and the Renishaw error compensation process software was used to compensate the accuracy of the moving axis to make it reach the predetermined accuracy,which provided a guarantee for the deterministic correction of the surface error.Through experiments,it was verified that magnetorheological finishing has good low-frequency modification ability,and the influence of various factors on the high-frequency errors of optical components was studied.The results show that the surface roughness of the components can be quickly converged to less than 1 nm by using high-precision machine tools and common process parameters.A combined processing method based on magnetorheological finishing and conformal vibration polishing was proposed,which realizes the synergistic control of errors in all spatial frequencies.The combined processing experiment of aspheric wedge-shaped lens was carried out.The experimental results show that the aspheric components processed by the combined processing method can meet the requirements of each spatial frequency,and the error convergence limit is significantly improved,which verifies the effectiveness of the combined processing method.The full-spatial frequency errors suppression method in magnetorheological finishing for aspherical optical components proposed in this paper provides theoretical basis and technical support for the high-precision and high-efficiency manufacturing of large-diameter aspherical optical components. |
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