Details of a Researcher - Beaucamp, Anthony

Papers - Beaucamp, Anthony

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Use of the 'Precessions'™ process for prepolishing and correcting 2D & 21/2D form

David D. Walker, Richard Freeman, Roger Morton, Gerry McCavana, Anthony Beaucamp

Optics Express 14 ( 24 ) 11787 - 11795 2006.11

Accepted, ISSN 10944087

The Precessions™ process polishes complex surfaces from the ground state preserving the ground-in form, and subsequently rectifies measured form errors. Our first paper introduced the technology and focused on the novel tooling. In this paper we describe the unique CNC machine tools and how they operate in polishing and correcting form. Experimental results demonstrate both the '2D' and '21/2D' form-correction modes, as applied to aspheres with rotationally-symmetric target-form. © 2006 Optical Society of America.

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Automated optical fabrication: First results from the new "Precessions" 1.2m CNC polishing machine

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Evans, R. Freeman, J. Kelchner, G. McCavana, R. Morton, D. Riley, J. Simms, G. Yu, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 6273 I 2006.10

Accepted, ISSN 0277786X

The requirements of space and defence optical systems and ground-based astronomy (especially extremely large telescopes) are providing optical fabricators with new challenges. These challenges particularly concern process speed, determinism and automation, and tighter tolerances on surface form and texture. Moreover, there is a growing demand for complex off-axis and 'freeform' surfaces and for larger components of the ~lm scale. With this in view, we first report on form-correction on a smaller analogue of the LRP1200 - an IRP400 in service in industry. We then report on the design, commissioning and preliminary process-development results from the first of the scaled-up 1.2m capacity CNC polishing machine from Zeeko, Ltd. This machine delivers the 'Classic' bonnet-based process, together with two new processes - fluid-jet polishing and the hybrid soft-grinding/polishing process called 'Zeeko-Grolish.' We indicate how this trio of processes running on the same machine platform with unified software can provide an unprecedented dynamic range in both volumetric removal rate and removal spot-size. This leads into a discussion of how these processes may be brought to bear on optimal control of texture and form. Preliminary performance of the 1.2m machine is illustrated with results on both axially-symmetric and more complex removal regimes. The paper concludes with an overview of the relevance of the technology to efficient production of instrumentation-optics, space optics and segmented telescope mirrors.

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Precessions 2.5D correction of an aspheric mirror

D. Walker, A. Beaucamp, R. Freeman, R. Morton, G. McCavana, J. Kelchner

FRONTIERS IN OPTICS - OSA TECHNICAL DIGEST PDPOF ( A1 ) 2006.08

Accepted

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New developments in the Precessions process for manufacturing free-form, large-optical, and precision-mechanical surfaces

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Freeman, G. Hobbs, G. McCavana, R. Morton, D. Riley, J. Simms, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 6148 2006.03

Accepted, ISSN 0277786X

The recent upsurge in the demand for off-axis and complex "freeform" optical surfaces is driving the development of novel processes for their fabrication. This paper focuses on recent developments of the Precessions CNC polishing process for freeform surfaces, including off-axis as a special case. First, the surface-prescription and metrology-data, and their relation to the data-input for the polishing machines, are considered. The relevance of consistent coordinate frames is emphasised. An outline of how the process can 'polish' a ground freeform part (improve the texture), and then 'figure' the part (reduce the form errors) is given. Specific experimental case-studies are then presented, illustrating the versatility of the process on different materials and forms. Recent work is included in which the process-speed has been moderated in order to remove tens of nanometres of stock material, rather then the more usual hundreds of nanometres to tens of microns as in the standard Precessions process. The relevance of this to improving the ultimate surface-precision that should be achievable by this method is described. As a final illustration, the potential of the process to the rapid fabrication of the hundreds to thousands of 1-2 metre class mirror segments required for extremely large telescopes is considered.

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The application of optics polishing to free form knee implants

L. Blunt, P. Charlton, Anthony Beaucamp, X. Jiang

Proceedings of the 6th International Conference European Society for Precision Engineering and Nanotechnology, EUSPEN 2006 2 188 - 191 2006

Accepted

Free form surfaces have for some time played a part in the latest developments in the exploitation of new products in optics, from micro lenses up to ELT telescopes. The demands of the required tolerance on these "new" optics have led to significant improvements in manufacturing and metrology, as the capability to produce form in the tens of nanometre range coupled with nanometre surface roughness have become the critical enabler the their use. Free form surfaces are not limited to optics, and other product developments such as bio-implant surfaces in the prosthetics industry are utilising free form surfaces to make significant strides implant life. The prosthetic industry, have for some time, known from research into hip replacements, that significant reductions in the production of biologically damaging wear debris could be achieved by implementing hard on hard bearing couples rather than the traditional metal on polymer bearing couples. In these "new" knee joints the bearing couples comprise free form alumina on alumina or CoCr alloy on CoCr alloy surfaces. Unfortunately the application of these new materials for knee implants has been largely halted by the inability of manufacturers to polish their knee surfaces to the more demanding tolerances placed on free form hard on hard bearings of both form and roughness. These tolerances require micron level form deviation combined with nanometre surface finish in order to maintain full fluid film lubrication during in vivo functioning of the joint. This paper discusses the development of the capability to machine biomaterials for use as hard on hard knee joints. The surfaces are machined utilising a 7 axis CNC optics polishing machine, the Zeeko IRP200. The machine uses a novel precision technique to correctively polish components [1].

New results extending the Precessions process to smoothing ground asplieres and producing freeform parts

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Freeman, G. McCavana, R. Morton, D. Riley, J. Simms, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 5869 1 - 9 2005.12

Accepted, ISSN 0277786X

Zeeko's Precession polishing process uses a bulged, rotating membrane tool, creating a contact-area of variable size. In separate modes of operation, the bonnet rotation-axis is orientated pole-down on the surface, or inclined at an angle and then precessed about the local normal. The bonnet, covered with standard polishing cloth and working with standard slurry, has been found to give superb surface textures in the regime of nanometre to sub-nanometre Ra values, starting with parts directly off precision CNC aspheric grinding machines. This paper reports an important extension of the process to the precision-controlled smoothing (or 'fining') operation required between more conventional diamond milling and subsequent Precession polishing. The method utilises an aggressive surface on the bonnet, again with slurry. This is compared with an alternative approach using diamond abrasives bound onto flexible carriers attached to the bonnets. The results demonstrate the viability of smoothing aspheric surfaces, which extends Precessions processing to parts with inferior input-quality. This may prove of particular importance to large optics where significant volumes of material may need to be removed, and to the creation of more substantial aspheric departures from a parent sphere. The paper continues with a recent update on results obtained, and lessons learnt, processing free-form surfaces, and concludes with an assessment of the relevance of the smoothing and free-form operations to the fabrication of off-axis parts including segments for extremely large telescopes.

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Recent advances in the control of form and texture on free-form surfaces

D. D. Walker, A. T.H. Beaucamp, V. Doubrovski, C. Dunn, R. Freeman, G. Hobbs, G. McCavana, R. Morton, D. Riley, J. Simms, X. Wei

Proceedings of SPIE - The International Society for Optical Engineering 5965 2005.12

Accepted, ISSN 0277786X

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New results from the Precessions polishing process scaled to larger sizes

D. D. Walker, A. T.H. Beaucamp, D. Brooks, V. Doubrovski, M. Cassie, C. Dunn, R. Freeman, A. King, M. Libert, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 5494 71 - 80 2004.12

Accepted, ISSN 0277786X

The Precessions process uses an inflated membrane-tool that delivers near-Gaussian polishing spots. The tool-motion over the part can be constructed to preserve an aspheric form whilst removing damage from preceding processes, or control the form through a tool-path prescribed by numerical optimization. The process has previously been validated on surfaces up to 200mm diameter and used extensively in industrial environments. In this paper we report the first trials on a substantially larger part - a 500mm diameter f/1 ellipsoidal mirror - as part of the UK's technology-development for Extremely Large Telescopes. We draw attention to subtle problems that have arisen along the way. We also report on developing the process for free-form surfaces, in contrast to the axially-symmetric parts worked hitherto. The paper concludes with an assessment of the lessons learnt from the experiments, as they may impact on realization in a practical ELT segment fabrication facility.

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Recent development of Precessions polishing for larger components and free-form surfaces

D. D. Walker, A. T.H. Beaucamp, D. Brooks, V. Doubrovski, M. Cassie, C. Dunn, R. Freeman, A. King, M. Libert, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 5523 281 - 289 2004.12

Accepted, ISSN 0277786X

Since the 2003 Annual Meeting, the Precessions process has become accepted as an efficient method for polishing and figuring moderate-sized axially-symmetric aspheric parts in industry. In this paper, we report on some very significant new advances beyond this capability. The first is the demonstration of the process on substantially larger diameter parts than worked hitherto - in particular, a precision-ground 500mm diameter deeply-concave aspheric mirror. We describe the consequences of polishing large parts with the axis of the part vertical, in contrast to the horizontal axis of the smaller machines. Issues include slurry puddling and settlement in concave forms, process-uniformity, adequate support of the part and handling. We then report on recent work developing the Precessions process for non axially-symmetric surfaces including free-form. The correct relationship of the process with metrology has proved to be complex on several fronts, one example being differing descriptions of form either along a surface or its projection. We present our experience using profilometry and interferometry on precision-ground and polished surfaces, and in achieving absolute form with known base radius. Finally, we remark on the potential power of a priori predictions of achievable surface quality when optimizing optical system designs.

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Advances in small-tool polishing for free-form surfaces

R. R. Freeman, A. Beaucamp, D. Walker, R. Morton, G. McCavana

FRONTIERS IN OPTICS - OSA TECHNICAL DIGEST OM ( A4 ) 2004

Accepted

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Precessions aspheric polishing: - New results from the development programme

D. D. Walker, A. T.H. Beaucamp, R. G. Bingham, D. Brooks, R. Freeman, S. W. Kim, A. King, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 5180 15 - 28 2003.12

Accepted, ISSN 0277786X

The Precessions process for producing aspheric and other optical surfaces is undergoing rapid development. In this paper, we summarise the considerable success achieved in controlling the repeatability of the process on both the 200mm and 600mm machines, and illustrate this with examples of aspherics that have been produced. We particularly describe our approach to fine form-control. This has required the development of various strategies to moderate the volumetric removal rates, in order to give the required sensitivity of removal. We conclude with a discussion of the scaling laws that apply when adapting the process to smaller and larger sized parts. This is illustrated by predicting the process-parameters for mass-producing segments for extremely large telescopes.

New polishing technology for large mirrors and lenses

D. D. Walker, A. T.H. Beaucamp, D. Brooks, A. King, R. Morton, G. McCavana

Proceedings of SPIE - The International Society for Optical Engineering 10314 31 2003.05

Accepted, ISSN 0277786X

Copyright © 2017 SPIE. The Precessions™ process, and the 200mm capacity 'All' machine which embodies it, are outlined in the accompanying paper 'New method to control form and texture on industrially-sized lenses'. In this paper, we summarise the development of the process to address larger optical components. The first machines constructed for this application are of 600mm capacity. A conceptual design of a 1-2m class machine of bridge-configuration has also been produced. Unlike the All machine, the work-piece on these larger machines lies in a horizontal plane i.e. with the rotation axis of the work-piece spindle vertical. This configuration is preferred because it allows the use of a hydrostatic support-system for the work-piece; important for large optics in general, and particularly so for light-weight optics. The machine can also provide a clear vertical path above the work-piece for optical testing, or for access by lifting gear. It is interesting to consider how the Precessions™ process can be scaled. As an example, consider first that the type of surface-form remains the same; it might, for example, be an f/2 parabola. Consider then that the work-piece diameter, the bonnet-diameter, the polishing spot-sizes used, and the tool-path on the surface, are all stretched by a factor of two. The area of the polishing spot and that of the work-piece have both increased by a factor of 4, but the number of convolutions of the spiral tool-path remains the same. Since the spot instantaneously addresses the same fraction of the overall work-piece surface-area, the terms all cancels in relation to cycle-time. However, for the same tool-rpm, the larger bonnet delivers a proportionally higher surface-speed, because the polishing action is further from the axis of rotation. Therefore, the volumetric removal rate (proportional to contact-area times surface-speed) tends to vary as the cube rather than the square of the scale-factor. As a result, the larger bonnet working over the larger work-piece with the same polishing pressure, will remove twice the depth of material in the same time. The above scaling could, in principle, reduce cycle times on larger parts. In practice, we have found that excessive removal-rates lead to impractically short dwell-times, especially near the centre of a spiral tool-path. Such scaling also demands increased traverse-speeds and accelerations from the machine, and this rapidly becomes a limitation. Moreover, as the process converges on final form, smaller depths of material need to be removed. In practice, we have found it necessary to moderate the process by diluting the slurry and by moving from a polyurethane tool-surface to a material that delivers a lower-removal rate, such as Multitex. We are also developing bonnets that are compatible with operation at a reduced polishing pressure, in order to give additional control for fine-removal. The current status of the process development is as follows. A form error of ∼80nm peak-to-valley has been achieved aspherising a 100mm diameter part. This work revealed some subtle but significant limitations in the optimisation code, mostly concerned with convergence and residual ripples. Recent work has focussed on this aspect, and the revised code is now ready for polishing trials. A 150mm diameter part is currently in-process, and work is about to commence on a 300mm fused silica mirror for a space application.

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<title>Precessions aspheric polishing: new results from the development program</title>

David D. Walker and Anthony T. H. Beaucamp and Richard G. Bingham and David Brooks and Richard Freeman and Sug-Whan Kim and Andrew King and Gerry McCavana and Roger Morton and David Riley and John Simms

Optical Manufacturing and Testing V ($\lbrace$SPIE$\rbrace$) 2003

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Novel CNC polishing process for control of form and texture on aspheric surfaces

D. D. Walker, A. T.H. Beaucamp, D. Brooks, R. Freeman, A. King, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 4767 99 - 105 2002.12

Accepted, ISSN 0277786X

We first consider the potential impact of a technology that could deliver polished, accurate aspheric surfaces in a routine and automated manner. We then summarise the technical challenge, and present an appraisal of the performance of the novel 'Precessions' process, which is a major advance in this direction. We outline the design concepts behind the productionized CNC polishing machines which executes the process, and then describe the progress developing strategies to preserve form when polishing ground surfaces, and to correct form on both pre-ground and polished surfaces. Particular consideration is given to resolving the inherent difficulties of control of centres on rotationally-symmetric parts. We then report on experimental results achieved with the machines. Finally, we present our programme to extend the control-algorithms to handle fully free-form surfaces, and draw conclusions about the effectiveness and generality of the 'Precessions' technique.

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The precessions process for efficient production of aspheric optics for large telescopes and their instrumentation

D. D. Walker, A. T.H. Beaucamp, R. G. Bingham, D. Brooks, R. Freeman, S. W. Kim, A. King, G. McCavana, R. Morton, D. Riley, J. Simms

Proceedings of SPIE - The International Society for Optical Engineering 4842 73 - 84 2002.12

Accepted, ISSN 0277786X

We summarise the reasons why aspheric surfaces, including non-rotationally-symmetric surfaces, are increasingly important to ground and space-based astronomical instruments, yet challenging to produce. We mainly consider the generic problem of producing aspheres, and then lightweight segments for the primary mirror of an Extremely Large Telescope. We remark on the tension between manufacturability of spherical segments, and performance with aspheric segments. This provides the context for our presentation of the novel Precessions process for rapid polishing and form-correction of aspheric surfaces. We outline why this is a significant step beyond previous methods to automate aspheric production, and how it has resulted in a generalized, scaleable technology that does not require high capital-value tooling customized to particular types of optical form. We summarise implementation in the first two automated CNC machines of 200 mm capacity, followed by the first 600 mm machine, and the current status of the process-development programme. We review quantitative results of polishing trials, including materials relevant to large and instrumentation optics. Finally, we comment on the potential of the technology for space optics and for removing quilting in honeycomb substrates.

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