Mid-spatial frequency error restraint based on variable optimal angle-step trajectory strategy for the removal attenuation effect of magnetorheological finishing

In the field of ultra-precision manufacturing, such as lithography lenses, achieving nanometer-level errors across the entire frequency range is crucial. Magnetorheological finishing (MRF) technology, a high-precision processing method with high efficiency and low subsurface damage, often introduces mid-spatial frequency (MSF) error due to the removal attenuation effect and regular polishing trajectory in the long continuous polishing process. It causes various imaging and light transmission defects that limit the performance of precision optical instruments. The attenuation of material removal capacity of MRF is characterized by the attenuation of the tool influence function, which is obtained by an equal time interval point removal experiment. The variable optimal angle-step trajectory strategy is proposed to mitigate the removal attenuation effect of MRF and suppress MSF error. To validate the effectiveness and practicability of the proposed method, a uniform polishing experiment is performed on fused silica components. The experimental results show that the 90° grating trajectory introduces significant MSF error on surface shape with PV = 0.008 λ, and the variable optimal angle-step trajectory strategy does not introduce MSF error, which confirms the variable optimal angle-step trajectory strategy effectively eliminates the removal attenuation effect of MRF and suppresses MSF error. The study presents a general approach for ultra-precision optical processing and improves the manufacturing accuracy of optical components.