A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abrasive fine-finishing technology is often applied as a final finishing process, and the selection of the right technology is crucial to obtaining the desired performance of functions such as fatigue life. This paper begins with classifications of the technology along with fundamentals and brief histories of the individual methods. The material removal mechanisms, specific energies, and finishing characteristics of the various technologies are summarized giving assessments of the surfaces created by them. Guidelines developed for selecting the appropriate methods, and case studies illustrate the effectiveness of various methods. This paper ends with a discussion of the future prospects of the technology. (C) 2016

Abrasive fine-finishing technology

A method for null-testing fast convex aspheric optical surfaces is presented The method consists of using a cylindrical screen with a set of lines drawn on it in such a way that its image, which is formed by reflection on a perfect surface, yields a perfect square grid Departures from this geometry are due to imperfections of the surface, allowing one to know if the surface is close to the design shape Tests conducted with a full hemisphere and with the parabolic surface of a lens show the feasibility of the method Numerical simulations show that it is possible to detect surface departures as small as 5 microm

Null-screen testing of fast convex aspheric surfaces.

High Energy Fluid Jet Machining (HEFJet-Mach): From scientific and technological advances to niche industrial applications

Computer controlled polishing requires accurate knowledge of the tool influence function (TIF) for the polishing tool (i.e. lap). While a linear Preston's model for material removal allows the TIF to be determined for most cases, nonlinear removal behavior as the tool runs over the edge of the part introduces a difficulty in modeling the edge TIF. We provide a new parametric model that fits 5 parameters to measured data to accurately predict the edge TIF for cases of a polishing tool that is either spinning or orbiting over the edge of the workpiece.

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Parametric modeling of edge effects for polishing tool influence functions.

We have reproduced quantitatively the technique commonly used in optical shop to evaluate surface error from comparison between experimental and simulated Ronchigrams. We used this procedure to evaluate, from Ronchigrams of any number of fringes, the curvature radius and/or conic constant of conic surfaces. The error function is calculated without using integration (numerical or polynomial) so the corresponding problems were avoided. Furthermore, when the error function is described with cubic splines, then the local errors are very well reproduced, which is not the case with the polynomial description. We have described the error functions with conical surfaces or with cubic splines, and for the best reproduction of experimental Ronchigram we used genetic algorithms.

Local and global surface errors evaluation using Ronchi test, without both approximation and integration

To pass from a spherical surface to a conic one, it is possible to use a petal tool or a small solid tool that is placed at different time intervals at several radial zones of the glass. Genetic algorithms are applied to calculate the angular sizes of the incomplete annular tools that make up the petal tools. We also present the desired wear results carried out with the petal tool that was designed on the basis of the dwell times of complete annular tools. These dwell times are calculated by using base functions that are generated with annular tools and by applying the genetic algorithms.

Calculating petal tools by using genetic algorithms.

It is difficult to calculate the wear produced by free-pinned tools because their angular movement is not entirely predictable. We analyze the wear produced with free-pinned ring tools, using both simulations and experiments. We conclude that the wear of an incomplete ring is directly proportional to the ring’s angular size, independently of the mean radius of the ring. We present an algorithm for calculation of the wear produced by free-pinned petal tools, as they can be considered a linear combination of incomplete free-pinned ring tools. Finally, we apply this result to the enhancement of a defective flat surface and to making a concave spheric surface.

Experimental results and wear predictions of petal tools that freely rotate

A new tool for hydrodynamic radial polishing, HyDra, allows for the local polishing of optical surfaces with a controllable wear rate. The results of the removal rate for different polisher types and sizes, applied air pressures for slurry expulsion, and tool height with respect to the working surface, are reported. We present a numerical analysis of the volumetric removal rate for the dynamic experiments as well as a comparison with a similar technique.

Static and dynamic removal rates of a new hydrodynamic polishing tool

In Ronchi test Malacara formula is used to evaluate surface errors, which are represented by cubic splines. The spline coefficients are estimated by means of genetic algorithms.

Alberto Cordero-Dávila

Papers

Local and global surface errors evaluation using Ronchi test, without both approximation and integration

Calculating petal tools by using genetic algorithms.

Experimental results and wear predictions of petal tools that freely rotate

Static and dynamic removal rates of a new hydrodynamic polishing tool

Surface evaluation with Ronchi test by using Malacara formula, genetic algorithms, and cubic splines