Novel Mathematical Techniques for Advanced Tool-paths to Transform High-value Optical Fabrication

Lead Research Organisation: Glyndwr University
Department Name: Engineering Research Centre

Abstract

Precision lenses and mirrors are used for a host of applications - ground-based telescopes for astronomy, satellites looking up at space or down at the ground, machines to make semiconductor 'chips' (for computers to mobile phones...), defence systems, laser-systems and numerous other applications.

The manufacture of precision optics is basically a two-stage process. First a glass blank is ground with a hard grinding wheel that cuts the material, to hog out the glass to the basic curved form. The glass is then polished using some form of pad that rubs the surface, using a water-slurry of a polishing compound - red rouge in the old days, white cerium oxide powder today.

Over the last decade, the optics industry has experienced a revolution in computer numerical control (CNC) of both the grinding and polishing processes. The project involves two partner companies pre-eminent in both types of machine and processes. Zeeko Ltd (originally spun out of UCL research in this field) manufactures CNC polishing machines and measurement equipment. Cranfield Precision Ltd (a division of Cinetic Landis) produces CNC grinding machines.

Such CNC machines almost always move the grinding or polishing tool across the surface in a standard back-and-forth raster pattern, or in a spiral path (by rotating the work-piece). A raster or spiral is a special case, because it crosses itself nowhere, and this simplifies calculating how the removal adds up. But, just like a tractor ploughing a field, these paths leave regular 'furrows' in the surface. Whilst these might be only nanometres deep (just tens of atoms) they cause stray light around an image in a telescope or camera.

There are various ways of smoothing surfaces to remove these regular features, but this takes additional times. Moreover, each extra process leaves its own signature, which itself has to be removed ... in what sometimes seems like an endless circle!

The new research will break out of this mould by using advanced mathematical methods to generate more complex tool-paths, which cross each other at myriads of points, and give a natural averaging effect. We call these 'hyper-crossing paths'. Furthermore, the polishing machines are able to change the polishing spot size 'on the fly'. In principle (and with the right mathematics) spot-size could be actively tuned to attack different sizes of surface-feature as the tool moves across a surface. We plan to develop this new idea, and are confident it will lead to a break-through in superior surfaces in less time.

And what of the results? These will be incorporated in the standard software of the partner companies, enhancing their competitive position. The results will also be used on the machines at the National Facility for Ultra-precision Surfaces in North Wales, operated by Glyndwr University in partnership with University College London. This will give enhanced capability for manufacturing optics to support British Science and our overseas collaborators. Beyond this we plan to disseminate the findings to the wider UK academic and and manufacturing communities to collaborate on and develop applications and prototypes for applications in high precision surfaces outside of the optics sector e.g. medical - prosthetic joints.

Publications

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Related Projects

Project Reference Relationship Related To Start End Award Value
ST/L001985/1 01/02/2014 30/04/2016 £72,079
ST/L001985/2 Transfer ST/L001985/1 01/05/2016 31/12/2016 £18,076
 
Description Using newly developed method, the efficiency of optical fabrication has been greatly improved.
Exploitation Route This method has been associated to a software package. Other manufacturers can purchase this software or software add-ons.
Sectors Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology

 
Title Epicyclic smoothing tool 
Description An Epicyclic smoothing tool has been developed to be able to used at robot facilities to smooth grinding marks. This tool is much more efficient in coping mid-spatial features. 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact This tool will enable a fast process of mirrors or lens from grinding state to polishing state. This will bridge the gap between these two stage on processing and metrology. 
 
Title Epicyclic database 
Description This database provide recommanded process parameters when input with parts size, shape, form target. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact This database will potentially be used by our research collaborators in their research and development programmes. 
 
Description Collaboration agreement with Harbin Institute of Technology (HIT) 
Organisation Harbin Institute of Technology
Country China 
Sector Academic/University 
PI Contribution We at Glyndwr University agreed to provide technical assistance and training opportunity for students and academic visitors. We also agreed to submit joint papers to peer-reviewed journals.
Collaborator Contribution Collaborator at HIT agreed to provide experimental work, including technican's access of the lab equipments.
Impact * One conference paper has been published * One journal paper is being edited * The PI Glyndwr has visited HIT * The collabator from HIT has visited Glyndwr University
Start Year 2014
 
Description Collaboration with Changchun Institute of Optics and Fine Mechanics, the Chinese Academy of Science 
Organisation Chinese Academy of Sciences
Department China Changchun Institute of Optics Fine Mechanics and Physics
PI Contribution I have visited this institute on 12/10/2017 and have given an invited talk at 2nd Aviation Metrology Department of Changchun Institute of Optics and Fine Mechanics, the Chinese Academic of Science. We have agreed on the further possibility of collaboration on research and development.
Collaborator Contribution The Institute agreed to subsidize academic students/ visitors to our University for further training.
Impact One PhD student is supported to visit the UK.
Start Year 2017
 
Description Collaboration with Zeeko Ltd. 
Organisation Zeeko Ltd
Country United Kingdom 
Sector Private 
PI Contribution We have developed software that is suitable for industrial robots to perform intermediate process between polishing and grinding.
Collaborator Contribution Zeeko has provided a FANUC robot to facilitate research and development programmes and some technical assistant on facility development.
Impact 1. The process developed from this project will be adopted by other projects. e.g. LOCUS M1 processing. 2. Zeeko has commercial interest for this process.
Start Year 2014
 
Title Epicyclic Toolpath Generation with ABB and FANUC machine settings 
Description This is an add-on package to a commercial software which enable intelligent polishing machines to produce ultra precision optical surfaces. This software package can generate optimised toolpath to minimise surface error. This software also have the option to operate on ABB and FANUC industrial robots. 
Type Of Technology Software 
Year Produced 2015 
Impact This software will enable a process that will shorten total fabrication time by parallel processing. In addition, the optimised toolpath offer a surface with improvement on mid-spatial errors. 
 
Description Facility introduction to AstroTrac 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Introduction of staffs from AstroTrac about the role of robot processing for high precision optics.
Year(s) Of Engagement Activity 2015
 
Description Invited seminar on Advanced Ultra Precision Surfaces Processing 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact This invited seminar is to present our recent work on processing ultra precision surfaces. The audiences are mainly scientists and postgraduate students. There are more than 30 people attended.
Year(s) Of Engagement Activity 2017
 
Description Invited seminar on Autonomous Manufacturing in Ultra Precision Section 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact This invited seminar was presented mainly towards postgraduate students and academics. Some undergraduates also turned up so that there were nearly 80 people attended. The students asked some relevant questions after the talk. One academic wish to visit our laboratory in 2018. The university all inquiry about joint degree scheme in the future.
Year(s) Of Engagement Activity 2017