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Optical Metrology for Manufacturing

Thursday 12th October

This meeting will bring together leaders in industry, research institutes and universities to discuss the latest developments and new applications for optical metrology. This conference will highlight principles and systems available for metrology along with detailed examination of selected applications.

PROGRAMME

10.30 Introduction & Welcome
Dr Roger Groves, Delft University of Technology, Netherlands
SESSION 1 : CHAIR | Caroline Gray
10.40 KEYNOTE SPEAKER
Technical aspects of optical metrology for machine calibration
Dr Anas Jarjour, Technical Fellow, Renishaw PLC, UK

The reporting accuracy of any motion system, whether it is a machine tool or a coordinate measuring machine, is key to its performance. The detailed knowledge of the geometric errors allows for the machine capabilities to be assessed and tracked over time thus increasing its uptime. Furthermore, the calibration of these errors can improve the machine performance through numerical error-compensation techniques.

In this talk, we give an overview of the different optical methods employed in machine calibration, with a focus on how these methods can be combined in a single system to provide a direct measurement of all errors in six degrees of freedom (three linear and three angular) along an axis of motion. Particular attention is given to the sources of measurement errors and their effects. The direct measurement of roll errors along an axis using optical techniques has been especially challenging. We give technical details of an innovative optical system capable of measuring these errors and present an assessment of its performance.

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11.10 Optical metrology of laser welding of metal components
Daniel Lloyd, Laser Optical Engineering Ltd, UK

The Radicle consortium is developing a prototype system for measuring a range of emissions from laser welding in manufacturing environments. A number of optical metrology techniques are being employed including spectral and image analysis, to determine a number of critical features in the weld keyhole. In addition optical sensors are being used to determine physical criteria such as position and fume size and density which influence the process. These features will be detected using a combination machine learning, direct image analysis and signal processing techniques.

Laser Optical Engineering has been tasked with measuring a number of the output signals from the welding region and synchronising these values with the measurements generated by existing commercial systems. This will require the development of a metrology tool that will be integrated onto a bespoke processing head. The combined data will be used to allow real time analysis of the weld performance and corrective action taken to optimise production performance. The Radicle project is EU H2020 funded and involves a mix of companies that intend to supply components for, or use the developed system as well as research organisations that will demonstrate and prove its functionality. When fully developed and commercialised this system is expected to reduce the reject part rate in a number of manufactured parts.

This presentation will give an overview of the optical metrology techniques used in the Radicle system and their application to both high value-low volume and high volume parts in a range of industries.

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11.30 Metrology challenges presented by the fabrication of large and high-value optics
Prof Paul Rees & Dr John Mitchell, Glyndŵr Innovations Ltd, OpTIC Technology
Centre - Glyndŵr University, UK

The fabrication of large and high-value optics presents a set of quite unique metrology challenges that must be overcome in manufacture. By “large optics”, we mean optics whose optical surfaces are greater than 350mm in diameter. By “high-value optics” we mean large optics that have either one or more aspherical surfaces or have difficult surface quality specifications to meet. Whilst the weight and size of the optic may increase, the manufacturing tolerances remain representative of optical manufacture. The verification of these optics must take into account both the handling and risk of large high-value glass substrates; instrumentation used for optical verification must be able to accommodate large and massive artefacts; and the support of the optic during the verification process becomes of key importance. Glyndwr Innovations Limits has a track record of manufacturing optics in the size range 150mm to 1600mm diameter. We present a review of some of these manufacturing challenges and how they need to be addressed to avoid costly non-conformances.

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11.50 Optical metrology of composite structures using laser shearography
Daniel Lloyd, Laser Optical Engineering Ltd, UK

Laser shearography has been an established optical metrology technique for a number of years and has gained acceptance in a number of industrial applications. Laser Optical Engineering (LOE) has been using shearography in a number of industrial and commercial sectors for over 15 years. During this time LOEs technology has found applications ranging from the marine to power sectors for newly manufactured and on-going condition monitoring of items.

This presentation will show case a number of case studies ranging from lifeboats to wind turbines and discuss the challenges in applying appropriate test conditions to the different materials and structures employed. Examples will be given of typical as well as more unusual defects to demonstrate the sensitivity of the technique. This will primarily focus on use of LOEs range of standard instruments but will also cover bespoke modifications for more unusual products and developments for testing during manufacture to obtain best performance from the technique as well as reducing production wastage.  Discussion will be made of the system design features which are required to allow the instruments to operate in a range of environments, from Scottish boat yards to air conditioned laboratories.


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12.10 Non-contact metrology for advanced optical surfaces
Neil Fitzgibbon, Taylor Hobson Ltd, UK

The advances in technology have driven the need for optics to have more extreme surface geometries, such as Asphero-Diffractive, Fresnel, and Freeforms.  These changes have driven the need for more advanced and accurate 3D measurement capabilities, especially within the non-contact measurement field. Already capable of very high accuracy measurements on conventional optical forms, spheres and aspheres, the Luphoscan now provides a solution to these more demanding surfaces.

The Luphsoscan enables fast non-contact measurements using a MWLI point sensor (MWLI – multi-wavelength interferometer).  Measurements are obtained by rotating a part on a C-axis, whilst the sensor tracks across it following a path defined by the part design.  It is the precision control of this path that allows the senor to track over more complex surfaces such as fresnels and freeforms.  A point cloud is generated from the measurement data that is an accurate representation of the surface.  By using advanced analysis techniques, the point cloud can be compared to the part design and the residual surface error shown.  

Examples of measurements and analysis on these advanced forms will be discussed.


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  in the Launchpad and tutorials session, theatre 2 there is a opportunity to hear:
12.40 Swept Source Optical Coherence Tomography (SS-OCT) for industrial metrology
Andrea G Gletrude, Santec Europe Ltd

OCT technology is widely used to perform surface and cross section measurements (and imaging) for different materials. Compared to other technologies, such as X-Ray and Ultrasound, OCT techniques guarantee a non-invasive approach and higher resolution.
Furthermore, the use of swept sources with OCT systems, allows faster more accurate measurements compared to other OCT techniques, such as Time Domain (TD) and Spectral Domain (SD) OCT.

Consequently, SS-OCT has been used in a wide range of applications. From biomedical equipment (eye imaging) to industrial inspection processes, SS OCT succeeds in providing fast measurements and high resolution images.

This presentation will show the results achieved in several metrology related applications using the Santec (Komaki, Japan) OCT systems and sources.

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12.30 Conclusion and close of morning session
SESSION 2: Chair | Dr Andrew Henning  
13.55 Introduction to session.  
14.00 Position measurements for manufacturing applications using range-resolved interferometry
Dr Thomas Kissinger, Research Fellow, University of Cranfield, UK

Range-resolved interferometry (RRI) is a new interferometric position and displacement measurement technique based on sinusoidal optical frequency modulation of highly coherent, robust and cost-effective DFB-type laser diodes originating from the telecoms industry, exploiting their potential for precision optical measurements. In RRI, the use of interferometric phase evaluation allows relative displacement measurements at nanometre resolutions for applications such as laser vibrometry. Furthermore, RRI allows the evaluation of the range of the return signals in a manner similar to optical coherence tomography, enabling the additional capability of absolute position measurements at resolutions of 10 to 100 μm over kHz bandwidths.

In this presentation, we highlight some of our recent measurements from the application of absolute position measurements to manufacturing problems. Using a compact, fibre-coupled optical head, we demonstrate how measurements of welding layer heights have been carried out even during operation of the welding arc and show how this can be used to optimise welding and additive manufacturing applications. Furthermore, we highlight the possibility of this approach in related areas, such as robotic manufacturing.

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14.20 Wavelength scanning interferometry as used for in process metrology during roll to roll manufacture
Professor Liam Blunt, Director of the Centre for Precision Engineering,
University of Huddersfield, UK
14.40

Dual-plane optical coherence tomography imaging for velocity measurement in small-scale flows
Evangelos Rigas, Postgraduate Researcher, Cranfield University, UK

E. Rigas, J.M. Hallam, H.D. Ford, T.O.H. Charrett and R.P. Tatam

Micro particle image velocimetry (μPIV) is often used to investigate small-scale flows, but optical coherence tomography (OCT), originally developed for medical imaging applications, is also well-suited also to velocity measurement in milli- and micro-fluidic systems. Spatial resolutions of 5-15 μm are accessible, depending on centre wavelength, source bandwidth and numerical aperture. Processing and scanning can be adjusted to enable imaging in any of three orthogonal planes via a single optical access port, alleviating difficulties sometimes experienced with μPIV due to optical access limitations. An additional advantage of the OCT imaging technique is that channel topography imaging is available alongside the particle imaging required for velocity measurement.

A novel dual-beam OCT system has been developed to image few-micrometre particles in microfluidic flows, and to determine flow velocity using particle tracking or correlation methods. A galvanometer-scanned mirror sweeps two sample beams simultaneously through the measurement plane. Depending on the orientation of the beams, this technique can either (a) reduce the image acquisition interval by a factor of approximately 20 in a 2-velocity-component measurement (compared with an equivalent single-beam system), extending the upper limit on accessible velocities, or (b) allow, via a light-gating arrangement, a 3-velocity-component measurement.

15.00

Evaluation of an inverse rendering solution for the calibration of a
projector’s extrinsic parameters in fringe projection using CAD data

Dr Petros Stavroulakis, Research Fellow, University of Nottingham, UK

In order to calibrate a fringe projection setup, knowledge of the relative distance and pose between the camera and the projector are required. Once the setup is calibrated, the relative positions and poses of the camera and projector are assumed invariant during the measurement as they do not move with respect to each other. The calibration step usually requires a calibration plate placed within the measurement area and a set of calibration images is projected onto the plate to determine the correspondence with the camera pixels. This step is time consuming and frequently needs repeating if the calibration is unsuccessful thus wasting measurement time. In this work, we computationally evaluate a new inverse rendering approach to calibrating the projector’s position whereby no calibration plane or targets are required. Instead, the illuminated object is rendered and compared to the image acquired from the camera. The position of the light source is optimised until the rendered and target images are within tolerance. To accelerate convergence and to avoid converging to false local minima, a fast deep learning coarse classification algorithm of the projector’s azimuth and elevation is performed on the image before the optimisation begins. The proposed inverse rendering calibration method allows the extrinsic parameters of the projector to be quickly calibrated without any prior setup and can be performed after the measurement images have been taken, thus saving time during the acquisition of the measurements.

Petros I. Stavroulakis1, Shuxiao Chen1, Clement Delorme2 and Richard Leach 1
1Manufacturing Metrology Team, Faculty of Engineering, University of Nottingham, UK
2Ecole Nationale d’ Ingenieurs de Saint Entienne ENISE, Saint-Etienne, France


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15.20 Laser speckle correlation sensing for industrial robots
Dr Tom Charrett, Lecturer, University of Cranfield, UK

The use of speckle correlation sensing for robotic manufacturing has great potential to allow rapid robot characterisation and measurement of robot trajectory and end-effector speed. The technique utilises an end-effector mounted sensor acquiring and processing laser speckle patterns at high speeds (~500fps) to determine the robot end-effector translation and velocity in a horizontal plane. This can be used to characterise deviations from a desired tool speed which is of importance in many manufacturing operations, for example, in many continuous machining or processing operations the feed rate or tool speed is critical to process quality. By utilising an end-effector mounted sensor the need for expensive external measurement systems such as laser tracker systems, and their associated requirement for line-of-sight is avoided.

Here the application of a laser speckle correlation sensor for tool speed measurement of the end-effectors of industrial robots will be presented including the design and implementation of the sensor and signal processing.  Results of laboratory characterisation of the sensor and its practical application for tool speed measurement in a robotic additive manufacturing process - robotic wire and arc additive manufacturing (WAAM) will be presented.

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15.40 Concluding comments  
15:45 Close of meeting  
  The exhibition remains open until 5pm  



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PROGRAMME:

10.15 Registration  
10.30 Introduction and Welcome
Roger Groves, Delft University of Technology
 
Session 1: Techniques
Chair: Ian Johnstone
 
10.40 KEYNOTE SPEAKER :
Optical interferometry technology for embedded metrology

Professor Xiangqian (Jane) Jiang, Director of EPSRC Centre in Advanced Metrology, University of Huddersfield

High Value manufactured components range from optics, energy-efficient engines, aerodynamic components, roll to roll thin films, long-life human-joint implants to photovoltaic panels.  Many of these technologies have the potential to impact widely, but only if production costs are low enough to make them economical for mass consumption.  Precision measurement is a critical aspect of the production of these components. 

The requests for next generation instruments for the surface and geometric measurement are: no removal from the machine tool/production line, to on-line, non-contact, high speed, ease of use, small footprint and robustness. A more critical aspect is to reach the same level of accuracy as the state-of-the-art laboratory-based measurement systems, with affordable cost!

This talk focus on the creation of embedded measurement technologies for advanced manufacturing.

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11.10 Fast photocurrent mapping of photovoltaics using compressed sensing
Dr Matthew Cashmore, Research Scientist, National Physical Laboratory

With the current global drive for renewable energy solutions, the photovoltaic (PV) market has been increasing rapidly in terms of both demand, and production rates. As a result of this it is of paramount importance that the metrology used to measure the spatial efficiency of such devices improves to account for the increased need. One common method used is to scan a laser beam over the surface of the cell whilst recording the output current, known as Laser Beam Induced Current (LBIC) scanning. This method, although well characterised and highly established, is slow as a spot measurement scan has to be achieved, with large numbers of data samples required per point in order to overcome noise. A technique is demonstrated to obtain the spatial response map of a photovoltaic from a significantly reduced number of measurements, and hence over a much shorter timescale than LBIC allows for. This is achieved through the use of a digital micromirror array (DMD) which projects binary patterns onto the test PV, and then reconstructing the final response map through compressive sensing techniques.

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11.30 3D shape shearography for strain inspection of aerospace materials and structures
Dr Andrei Anisimov, Research Scientist, Delft University of Technology

Shearography (speckle pattern shearing interferometry) is a non-destructive testing technique that provides full-field surface strain measurement. It is used for both hidden defect detection and novel material characterization. The presentation covers practical questions of 3D shape shearography system development for surface strain measurement of curved objects together with experimental results on characterization of embedded aerospace smart materials. The complete procedure of calibration and data processing of a 3D shape shearography system with multiple view configuration is presented. A structured light projector is used for inline shape measuring that led to accurate measurement of surface strain of curved objects. The 3D shape shearography system performance was evaluated with a cylinder specimen with diameter of 190 mm loaded by internal pressure. Experimental part of the lecture covers the use of shearography for characterization of structural behaviour of fibre metal laminates with embedded heater elements. The embedded heater elements are introduced for thermal anti-icing and de-icing, so the material behaviour during thermal loading is of interest. Two GLARE (Glass Laminate Aluminum Reinforced Epoxy) specimens with different embedded heater elements were manufactured. The overall surface strain behaviour, zones with inner heater connections and manufacturing defects were experimentally investigated and analysed.

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11.50 Pros and cons of dfferent optical metrology techniques and correlation of stylus measurement
Dr Mike Conroy, Taylor Hobson Ltd

Abstract to follow

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12.10 Linear guide calibration of multi-dof interferometers
Dr Denis Dontsov, Head of Research & Development, SIOS Meßtechnik GmbH

The knowledge of the linear and angular deviations of linear guides is essential for their application in positioning systems.

According to current state of the art the positioning deviations are qualified by the interferometric measuring technologies. The angular deviations are measured either by the angular interferometers or by the autocollimators. Such measurements have to be done sequentially after the positioning measurements of the linear guides
.
This presentation shows a new long range multi-beam interferometer principle, which is capable of measuring the positioning deviations, the pitch and yaw angles and straightness of the linear guides simultaneously.

This method reduces the full characterization time of the position equipment significantly. Furthermore it allows the calculation of the center of rotation of the sliding element of the gauges and therefore the post-correction of the Abbe error. The high synchronization of the length measurements of all interferometric channels of the system allows dynamic measurements and features additional benefits comparing to the optical angular measurement equipment. The device also includes an optoelectronic sensor for detection of the directional deviation between the laser beam and the movement direction of the linear guides.
This minimizes the cosine error of the measurements which can be significant for the long range measurements.

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12.30 Conclusion and close of morning session  
13.55 Session 2 : Applications
Chair: Claudiu Giusca
 
14.00

Metrology requirements for the serial productions of ELT primary mirror segments
Dr Caroline Gray, Director, Optics KnowHow Ltd

The manufacture of the next generation of large astronomical telescopes, the extremely large telescopes (ELT), requires the rapid manufacture of greater than 500 1.44m hexagonal segments for the primary mirror of each telescope.

Both leading projects, the Thirty Meter Telescope (TMT) and the European Extremely Large Telescope (E-ELT), have set highly demanding technical requirements for each fabricated segment. These technical requirements, when combined with the anticipated construction schedule for each telescope, suggest that more than one optical fabricator will be involved in the delivery of the primary mirror segments in order to meet the project schedule. For one supplier, the technical specification is challenging and requires highly consistent control of metrology in close coordination with the polishing technologies used in order to optimize production rates. For production using multiple suppliers, however the supply chain is structured, consistent control of metrology along the supply chain will be required. This requires a broader pattern of independent verification than is the case of a single supplier.

This paper outlines the metrology requirements for a single supplier throughout all stages of the fabrication process. We identify and outline those areas where metrology accuracy and duration have a significant impact on production efficiency. We use the challenging ESO E-ELT technical specification as an example of our treatment, including actual process data. We further develop this model for the case of a supply chain consisting of multiple suppliers. Here, we emphasize the need to control metrology throughout the supply chain in order to optimize nett production efficiency.

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14.20 Ultra high intensity interactions and novel optics
Professor David Neely, (Acting) Head of High Power, Central Laser Facility

Ultra high intensity PW class lasers have been used to achieve some of the most extreme environments accessible within the modern laboratory in terms of density, pressure and temperature. Delivering the highest intensities (5x1020 Wcm-2) with pulses of sub ps duration requires accurate metrology and characterisation to ensure that the target is positioned at the optimum location. Plasma mirrors which can be used to improve the laser pulse contrast1 have been used for over a decade, with typical efficiencies of ~ 75%. However, utilising multi pulse excitation, plasma optics with reflectivities of 96% are now achievable2.  The new capabilities which such optics make available will be explored and the potential for such developments to play a major role in the next generation of facilities will be discussed.

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14.40 Applications of adaptive optics in vision science
Dr Karen Hampson, Postdoctoral Research Assistant, University of Bradford

The human eye is a biological adaptive optics system. The retina senses blur and the lens adapts its power to focus a given image on the retina. However the eye suffers from aberrations beyond those that can be corrected for by its lens or using conventional spectacles and contact lenses. These aberrations fluctuate at several Hertz owing to factors such as the heartbeat and changes in tear film. Since the advent of the Shack-Hartmann wavefront sensor, ocular aberrations can be rapidly and objectively measured. This has paved the way for adaptive optics systems that can non-invasively manipulate the eye's aberrations. This presentation will discuss the concept of the Shack-Hartmann sensor and adaptive optics and their use in vision science. This will include in-vivo imaging of individual retinal cells, investigation of the properties of the eye's own adaptive optics system, and assessing the limits of vision.

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15.00 High resolution point-sensing using template matching to extract phase from spectral interferograms
Dr Haydn Martin, Senior Research Fellow, University of Huddersfield

Dispersed reference interferometry (DRI) is a variant of spectral interferometry and has potential to improve on existing commercial single point measurement techniques such as chromatic confocal (CC) sensors by improving dynamic range. The DRI has previously been demonstrated with a resolution of only 250 nm over a range of 300 µm. However, because DRI is an interferometric technique, phase information is inherent in the generated spectral interferograms and nanometre resolution could be achieved if that information can be extracted efficiently from a single interferogram. This talk describes a method of phase calculation using template matching which is a technique commonly used in image processing. Template matching is used to extract high resolution phase information from an experimental DRI apparatus. Spectral interferogram templates, representing axial measurement positions are generated using a simple simulation of the optical apparatus. These templates are cross-correlated against a spectral interferogram generated from the DRI apparatus. The peak of the resulting correlogram indicates the closest matching template interferogram and allows the inference of a measured position with high resolution. The template matching phase extraction method is evaluated in terms of linearity, resolution and operating range. The computational requirements and avenues for optimisation in this area are also considered.

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15.20 The emergence of quantitative raman spectroscopy
Dr Debdulal Roy, Senior Research Fellow, National Physical Laboratory

Raman spectroscopy has multifaceted appeal but it requires an additional metrology dimension to make it truly competitive quantitative technology. Raman techniques offer many advantages including minimal sample preparation, non-destructive characterisation, chemical and structural measurements in aqueous media and air with sub-micron spatial resolution. Such a combination of characteristics is highly desirable for chemical analysis in many industries particularly in research and development and quality control or assurance. Raman spectroscopy has a growing family of applications with expanding needs and a lot of acronyms such as SERS (surface-enhanced Raman spectroscopy) TERS (tip-enhanced Raman spectroscopy), SRS (stimulated Raman scattering), CARS (coherent anti-Stokes Raman scattering) etc. All these techniques aim to quantify the amount of substance and accurately pin-point their locations. The traceability of measurements to the International System of Units is an absolutely necessity. In this talk, I intend to elucidate few applications of Raman spectroscopy in chemical measurements and the recent developments of standards to make Raman techniques reproducible and quantitative.

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15.40 Innovative vibration free large volume metrology
Prof Nigel Copner, WORIC, University of South Wales

abstract to follow
 
16:00 Concluding comments
Andrew Henning
 
16:05 end of meeting  


As always, it is free to attend this conference

The 2015 Conference and Industry Programme, run by Enlighten Meetings with its partners, covers application and technology advances, innovations and emerging technologies.

Sign up to our mailing listmailing list and receive all the latest Enlighten Conference news and information.

TECHNICAL PROGRAMME COMMITTEE

Dr Roger Groves
Delft University of Technology
E-mail: r.m.groves@tudelft.nl

Dr Andrew Henning

University of Huddersfield
Email: a.henning@hud.ac.uk

Caroline Gray
OpTIC Technology Centre
Email: c.gray@glyndwr.ac.uk

Dr Claudiu Giusca
Cranfield University
Email: c.giusca@cranfield.ac.uk


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