We focus on the subaperture polishing tool concept development for suppressing midspatial frequencies (MSF) arising from computer numerical control machining of aspherical optical surfaces. The selective effect in the MSF range is achieved by setting the tool viscoelastic properties so that rigidity increases in the frequency-domain generated by the rotational tool movement over the aspheric surface with the MSF while the tool remains flexible in the lower frequency range associated with tool radial direction movement. The mechanism of MSF removal is discussed in detail, including in terms of elasticity module frequency dependences, and is also experimentally verified. In order to monitor and optimize viscoelastic properties, especially in regard to frequency dependences, the dynamic mechanical analysis method has been developed and applied and is presented in the paper as well.
The aim of this work is an exploration of the options for optical surface polishing using the Zeeko IRP 100 machine and raster kinematics suitable for free-form polishing. For this purpose, aspheric surfaces were polished in raster prepolishing mode and then in Precession raster 3D shape correction, which is based on the Dwell time tool movement control. It was found that shape accuracy can achieve the value of approximately 35 nm RMS. The main inaccuracy was caused by the mid-spatial frequencies generated by the kinematics of the applied tools, which also limited the achievable values of microroughness.
The paper describes an achromatic Steinhal type doublet that employs an aspherical surface to allow wide angle imaging. A design criteria, optimization techniques and tolerancing of the doublet are described. Further a manufacturing process of the system and achieved optical performance measurement is discussed. Benefits of the wide angle imaging doublet are recently planned to be used in automotive industry application, namely for optimizing of head-light performance and their final evaluation. The final device is planned to be part of the production line.
We have realized an optical design of air space doublet of 100 mm clear aperture and 520 mm focal length that is optimized with respect to a quality of wavefront error better than 0.07 λ RMS for on-axis imaging at wavelengths of 633 nm and 450 nm. To minimize optical aberrations we have designed one of the four surfaces to be an aspherical. Based on a tolerance analyses those take into account planned spherical and aspherical technologies for surfaces realization and measurement equipment we have realized the doublet. In the paper there is described a technique of the optical design, tolerance analysis, technique of objective realization and results of the optical elements realization.
This paper describes a quest to find simple technique to superpolish Zerodur asphere (55μm departure from best fit sphere) that could be employed on old fashion way 1-excenter optical polishing machine. The work focuses on selection of polishing technology, study of different polishing slurries and optimization of polishing setup. It is demonstrated that either by use of fine colloidal CeO2 slurry or by use of bowl-feed polishing setup with CeO2 charged pitch we could reach 0.4nm RMS roughness while removing <30nm of surface layer. This technique, although not optimized, was successfully used to improve surface roughness on already prepolished Zerodur aspheres without necessity to involve sophisticated super-polishing technology and highly trained manpower.
In recent times, resin bond grinding wheels have often been used for the precise grinding of aspheric surfaces. In this paper, the influence of changes in the circumferential speed of the resin bond grinding wheel on the microroughness of the produced surface and also on the volume of the structures and the scratches is presented. The article also discusses how the cutting wear of the tool affects the surface quality and shows the correlation between the circumferential speed and the rate of degradation of the resin bond grinding wheel. A circumferential speed interval from 12 m/s to 24 m/s was investigated and the effect of tool degradation was observed at 1.9-hour intervals. The results of the experiment show that the optimal circumferential speed of the tool lies around 20 m/s. At this speed, the tool produces a perfectly polishable surface and tool degradation is minimized.
The aim of this study was to determine the optimal subaperture polishing procedure for aspherical surfaces on the Optotech MCP 250 CNC machine. Due to the fact that the CNC subaperture polishing process runs along well defined paths, certain frequencies develop on the polished surface, which can be limiting for the resulting microroughness. A proper sequence of polishing steps in different tool motion control modes can minimize these frequencies and help to substantially reduce microroughness. In this context, various tool motion control modes ("Spiral spindle mode", "Spiral axis mode" and "Raster mode") in combination with different tools were tested. The resulting microroughness values were observed in the defined mid-frequency and high-frequency areas. The best results, i.e. the lowest microroughness values were obtained using a combination of the processes "Ball spiral axis mode", "FEM raster mode", "spiral spindle 2D FEM correction mode" and "AFJ spiral axis mode"
The developed method is used for subsurface damage evaluation. It is based on CNC subaperture asymmetric polishing of the surface, which leads to the formation of a wedge with decreasing depth, depending on the diameter and a subsequent analysis of the surface using White - Light Interferometry. In the evaluation, 'negative PV value' method was used enabling the detection of the depth of damage with the accuracy of 1 micron.
The aim of this work was an investigation of surface microroughness and shape accuracy achieved on an aspheric lens by subaperture computer numeric control (CNC) polishing. Different optical substrates were polished (OHARA S-LAH 58, SF4, ZERODUR) using a POLITEX™ polishing pad, synthetic pitch, and the natural optical pitch. Surface roughness was measured by light interferometer. The best results were achieved on the S-LAH58 glass and the ZERODUR™ using the natural optical pitch. In the case of SF4 glass, the natural optical pitch showed a tendency to scratch the surface. Experiments also indicated a problem in surface form deterioration when using the natural optical pitch, regardless of the type of optical material.