Design of a large-angle magnetic field generator for virtual-axis MRF of high-steepness optics

With the continuous advancement of various advanced optical systems, the requirements for optical components have become increasingly stringent. Particularly for lithographic objectives in photolithography machines, the manufacturing difficulty of high-steepness, large-departure aspheric surfaces escalates as numerical aperture (NA) increases. Conventional magnetorheological finishing (MRF) technology typically performs normal-direction processing on workpieces using the lowest point of the polishing wheel, yet struggles to achieve high-precision machining of high-steepness optical components (surface slope exceeding ±25°) due to mechanical axis travel limitations and interference issues. While current variable contact-point polishing methods based on equivalent magnetic fields can extend machine tool processing ranges, the implementation techniques for achieving wide-angle equivalent magnetic fields remain unreported. To address these challenges, this study designed and optimized a magnetic field generator with a ±45° operational range. First, through theoretical magnetic field analysis, we identified key parameters affecting magnetic field strength and effective polishing area, thereby designing a wide-angle magnetic field generator. Second, orthogonal experimental methodology was employed to optimize critical parameters of magnetic poles according to magnetic field design specifications. Finally, finite element simulation results demonstrate that the optimized magnetic field generator achieves: (1) an effective polishing range of ±45°. (2) magnetic field strength of 255mT at 1mm from polishing wheel. (3) magnetic field strength about 30mT in non-processing areas. These specifications fully satisfy both polishing requirements and magnetorheological fluid circulation needs. This research provides a viable solution for MRF of high-steepness optics and establishes theoretical foundations for virtual-axis polishing technology applications.