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

Lead Research Organisation: University of Huddersfield
Department Name: Sch of Computing and Engineering

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/L001950/1 01/02/2014 30/04/2016 £281,780
ST/L001950/2 Transfer ST/L001950/1 01/05/2016 31/12/2016 £49,556
 
Description EPSRC Manufacturing Prioritisation Panel
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
 
Description Glyndwr internal funding
Amount £12,500 (GBP)
Organisation Glyndwr University 
Sector Academic/University
Country United Kingdom
Start 05/2012 
End 06/2012
 
Description Huddersfield QR funding
Amount £31,200 (GBP)
Organisation University of Huddersfield 
Sector Academic/University
Country United Kingdom
Start 03/2017 
End 03/2017
 
Description Network Plus
Amount £76,789 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 04/2017 
End 03/2018
 
Description Research Grant, Follow on Fund
Amount £106,994 (GBP)
Funding ID ST/P003648/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Academic/University
Country United Kingdom
Start 04/2017 
End 12/2017
 
Description Technology Strategy Board: North Wales Photonics Launchpad
Amount £61,103 (GBP)
Funding ID TSB Ref 102745 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 06/2017 
End 06/2018
 
Title Epicyclic tool 
Description Development of a novel polishing tool with three heads that describe an epicyclic motion, whilst always pointing in the same direction in lab coordinates. Used with non-Newtonian materials adapting to variations in topography over a tool-path, but stiffening in the presence of local defects (mid spatial frequencies). Deployed on an industrial robot. Development of technologies to polish bare aluminium to a few nm surface texture (aluminium mirrors are usually nickel-coated, and this hard material is easily polished) 
Type Of Material Improvements to research infrastructure 
Provided To Others? No  
Impact Tool and the aluminium polishing technology is being used to smooth a part with intractable mid spatial frequency defects, originating in prior single point diamond turning at another UK institute. The part is the 480mm diameter bare-aluminium off-axis parabolic primary mirror for the CEOI-funded LOCUS project. LOCUS is a demonstrator for a future space-mission to measure pollutants in the terrestrial atmosphere. 
 
Title Pseudo random hyper-crossing tool-paths 
Description This work comprises the mathematical basis and software implementation fo the opposite extreme to zero-crossing tool-paths - 'hyper crossing paths'. These randomise surfaces by crossing the surface essentially everywhere. This method is more suitable to robot implementation, where speeds and accelerations can be much higher than with Cartesian CNC machine-tools. 
Type Of Material Improvements to research infrastructure 
Year Produced 2016 
Provided To Others? No  
Impact This work has been central to the success of developing our new robot laboratory and, with it, the concept of the Autonomous Manufacturing Cell. It has also bee key to polishing various components using robots, including the LOCUS mirrors. We are currently seeking advice on whether to patent this work or publish. 
 
Title Robot facility 
Description Establishment at the National Facility for Ultra Precision Surfaces,OpTIC Centre, N Wales, of a robot laboratory. This has three robots and a 1.2m air-bearing table, located in interlocked enclosures. This facility supports research in i) robotic automation of manual processes using ultra-precision CNC machines, ii) advanced polishing and grolishing processes, and iii) new methods of non-contact profilometry 
Type Of Material Improvements to research infrastructure 
Year Produced 2015 
Provided To Others? Yes  
Impact This facility is available to Glyndwr University, operators of the national Facility. 
 
Title Data for polishing and associated processes 
Description Data on polishing, grolishing and metrology results for a wide range of removal technologies, and operating parameters, including deployment on CNC polishing machines and robots, and using both free and bound abrasives. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact This data is the bedrock on which we are researching advanced ultra-precision surface techniques, and methods of process automation. It is also being used in processing real components, for example the primary and secondary mirrors for LOCUS. 
 
Description Fisba collaboration 
Organisation Fisba AG
Country Switzerland 
Sector Private 
PI Contribution Provision of research infrastructure and skilled CNC machine operators and measurement experts.These experiments have demonstrated that there are significant effects on removal profiles due to acceleration / deceleration effects.
Collaborator Contribution Development of a novel technique for allowing for acceleration / deceleration effects in precision CNC bonnet-polishing, consultancy, and provision of glass sample.
Impact Work very much in progress, developing this new technique as a collaboration. Anticipate results will be incorporated in Zeeko tool-path generator software when the effects are fully characterised. Meeting with Zeeko has been scheduled April 2018.
Start Year 2015
 
Description LOCUS 
Organisation UK Space Agency
Department Centre for Earth Observation Instrumentation
Country United Kingdom 
Sector Academic/University 
PI Contribution Developing the processing methods to light-weight, and then polish, diamond-turned bare aluminium mirrors to circa 5 nm surface roughness
Collaborator Contribution LOCUS systems design. Provision of the design data for the M1 and M2 mirrors for the LOCUS project.
Impact A validated process for CNC polishing of bare aluminium mirrors. This led to another project with an industrial partner who has a continuing requirement for high-quality metre-class aluminium mirrors in significant quantities. That project is commercially highly-sensitive, and under strict terms of confidentiality. Neither the application nor company can be disclosed.
Start Year 2015
 
Description New collaboration on applications of AI to ultra-precision surface processing 
Organisation University of Nottingham
Department Centre of Evidence Based Dermatology
Country United Kingdom 
Sector Academic/University 
PI Contribution I initiated this collaboration, recognising that the next step-change in ultra-precision surface processing will arise from applications of AI both to define, and then to close, the process loop with reduced (and eventually no) human intrventions.
Collaborator Contribution Input of AI expertise lacking in the ultra-precision community, leading to a joint grant proposal which has been shortlisted.
Impact Grant proposal to Network Plus scheme, aiming to kick-start a new are of research
Start Year 2016
 
Description Non Newtonian Materials 
Organisation Sheffield Hallam University
Department Materials and Engineering Research Institute (MERI)
Country United Kingdom 
Sector Academic/University 
PI Contribution Development of tooling, and non-Newtonian polishing slurries, and conducting polishing trials.
Collaborator Contribution As part of this research project (and as per the grant proposal) we have been working with Prof Andrew Alderson at Sheffield Hallam University - an expert in non-Newtonian materials. Huddersfield is employing him as a consultant. He is advising on these advanced materials and their action within polishing slurries.
Impact Theory predicts that a non-Newtonian polishing slurry should harden as it is drawn under a precessed, rotating polishing bonnet, and then preferentially remove mid spatial frequency features from surfaces. Within this 9-month grant we have conducted experimental trials with different non-Newtonian slurries, in combination with advanced tool-paths, with inconclusive results. We are currently standing back and, with Prof Alderson, working to understand and interpret these results, We expect to conduct more trials with a view to diagnosing the physics of what is going on, and hopefully arrive at process parameters that demonstrate the positive effects of the non-Newtonian slurries. In response to this we are, in parallel, also considering non-Newtonian materials inside polishing bonnets. Whilst this has been done before using 'Silly Putty'( as reported by U. Arizona and used extensively by us), the new understanding from the STFC grant is expected to lead to alternative non-Newtonian materials in tools, with potentially superior performance. This in turn has led to the concept of actively stimulating non-Newtonian behaviour in a tool where, on the surface of the part, it should optimally be targeted. This is novel. These future developments are included as a work-package in our Programme Grant proposal, which is at the final stages of assessment by EPSRC. Sheffield Hallam is a partner in that proposal, and Prof Alderson is a Co-I.
Start Year 2017
 
Description Zeeko Ltd 
Organisation Zeeko Ltd
Country United Kingdom 
Sector Private 
PI Contribution There has been a strong synergistic relationship between Zeeko Ltd and my research group, since Zeeko's formation in 2000. This continues, with bi-directional technology transfer. Research results from my group are commercialised by Zeeko Ltd, and technical advances undertaken by Zeeko directly benefit my group's research. This has been formalised through several research grants where Zeeko is an industrial partner. Furthermore, Zeeko was the organisation invited by the European Southern Observatory to tender for the manufacture of prototype segments for the European Extremely Large Telescopes.As Zeeko's business is machines and processes, it passed the opportunity to OpTIC, who tendered and won the contract. Zeeko was a collaborator in this project, to mutual advantage.
Collaborator Contribution Process, mathematical tools and software development for aspheric and freeform surfaces in general, and edge-control in particular.
Impact Process, mathematical and software tools embodied in enhanced Zeeko products, and made available to my research group. ESO prototype segment contract. Several collaborative research grants. Development of the whole concept of the Autonomous Manufacturing Cell.
 
Title Data Stitching software 
Description When measuring optics by interferometry or profilometry, it is often the case that the instrumental technique is incapable of measuring the size, or height-variation, on the surface. This work has enables overlapping linear profilometry scans to be stitched, and also full 3D interferometry maps. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2012 
Impact This technique has been exploited by Zeeko Ltd It was then a key method used to measure prototype mirror-segments for the E-ELT, as the full-aperture interferometric test had an obstruction that left a gap in the data. Similarly it is required in current work to measure the LOCUS off-axis parabolic primary mirror. 
 
Title Hyper crossing tool-path software suite and mathematical methods 
Description A mathematical description of novel hyper-crossing tool-paths for polishing and grinding, and their implementation within the Zeeko Ltd tool-path generator software suite. 
Type Of Technology Software 
Year Produced 2016 
Impact Has enabled the high speeds and accelerations of robots to be exploited in surface finishing 
 
Title Robot polishing software 
Description Software developed under a collaboration agreement with Zeeko Ltd, which enables existing Zeeko tool-path generating software to output tool-paths to an industrial robot, rather than a CNC polishing machine. Supports fabuc and ABB robots. 
Type Of Technology Software 
Year Produced 2015 
Impact Has enabled Zeeko to collaborate with a large industrial manufacturer for polishing complex moulds and dies (name is confidential) 
 
Description AOMATT Suzhou 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk, 'Closing the metrology / process loop in CNC polishing', invited contribution to 8th international Symposium on Advanced Manufacturing and Testing Technologies ('AOMATT'), Suzhou, China. Impact has been a string of Chinese academic visitors to my laboratory, who have played a material part in our research programme.
Year(s) Of Engagement Activity 2016
 
Description CEOI Workshop 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Invited talk, 'The future of autonomous manufacturing of precision surfaces', at CEOI Industry Consultation Workshop on Advanced Manufacturing Techniques for Space Instrumentation, London. This was part of a wider strategy to apprise the community of the opportunities presented by autonomous manufacturing of ultra-precision surfaces.
Year(s) Of Engagement Activity 2017
 
Description Green Optics Korea 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact 'Large optics at the large scale', general seminar presented to Green Optics and Korean Government institutes, S. Korea
Year(s) Of Engagement Activity 2015
 
Description Invited member of "Engaging Industry" discussion panel 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Part of Fundamentals of Technology Transfer course for university technology translators, run by PraxisUnico at Loughborough University . Awarding Body - PraxisUnico at Loughborough University, Name of Scheme - "Engaging Industry" discussion panel
Year(s) Of Engagement Activity 2011
 
Description Manchester Industry 4.0 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk entitled, 'Autonomous Manufacture of Ultra-Precision Surfaces - its Potential Realisation and Impact', Industry 4.0 Summit, Manchester Central Convention Centre. Purpose was to give an overview of a new approach to autonomous manufacture of ultra-precision surfaces, focussing on the unique challenges, and our approach to resolving them. As this was on March 1 2018, it is too early to aguge impact.
Year(s) Of Engagement Activity 2018
 
Description Manchester talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact 'The next generation of astronomical telescopes - a revolution in science & technology', Guest lecturer to Manchester University Astronomical Society
Year(s) Of Engagement Activity 2015
 
Description Photon 14 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact "Commercializing University Research - A Personal Experience - Warts and All", Invited plenary Optics and Photonics Prize talk, at Institute of Physics 'Photon14' conference, London
Year(s) Of Engagement Activity 2014
 
Description Swansea talk 2015 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact 'Telescopes - from the sublime to the ridiculous', Invited public lecture presented under the auspices of the Institution of Engineering and Technology, Swansea
Year(s) Of Engagement Activity 2015
 
Description Teisnach 2017 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Invited talk, 'More steps in process automation for optical fabrication', to the 4th European Seminar on Precision Optical Manufacturing, Teisnach, Germany Part of a strategy to apprise the wider community of developments in process automation. This has impact on the sales of Zeeko Ltd, as it embodies results of this research in its product range.
Year(s) Of Engagement Activity 2017