Abstract
In order to remove mid-spatial frequency errors on aspheric and freeform surfaces, we have developed an aspheric smoothing tool which, unusually, is rigid. This has been proved feasible in the special case where the abrasive grit size exceeds the aspheric misfit, providing a cushion. Firstly, experimental parameters were derived from simulation of Influence Functions regarding misfit between the tool and the surface, which leads to dynamic Influence functions. Then the experimental part was polished into an aspheric surface from generated spherical surface. Thirdly, the choice of tool’s shape parameters was completed with optimisation of conic constant and tilt angle. The tool was machined into aspheric shape with a single-point cutter. Finally, experiments were carried out to compare this tool with a standard spherical smoothing tool. The results showed that this aspheric smoothing tool can removal mid-spatial errors effectively on aspheric surfaces.
Highlights
There has been considerable progress on advanced manufacturing of optical surfaces since the introduction of computer numerical controlled (CNC) polishing machines
We report a novel method of applying aspheric rigid smoothing tool to aspheric surfaces to remove mid-spatial frequency (MSF) errors
Part and tool preparation To verify the effectiveness of the aspheric smoothing tool and of the simulation result, the part was generated and polished to be the same prescription of the part in the simulation
Summary
There has been considerable progress on advanced manufacturing of optical surfaces since the introduction of computer numerical controlled (CNC) polishing machines. Despite the success in form figuring, there are issues with the CNC machines in dealing with the mid-spatial frequency (MSF) errors This type of surface irregularity has been describes and studied extensively before [8,9,10,11] and research to control MSF errors reported e.g [12,13,14,15] The MSF errors originate from various sources. They may arise from a prior generating process where hardgrinding was used, or coarse loose-abrasive grits or wide scope to improve such techniques when applied to aspheric or freeform surfaces.
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