Concentrating solar power systems currently have a high capital cost when compared with other energy generating systems. The solar energy is captured in the form of thermal energy rather than direct electrical, which is attractive as thermal energy is more straightforward and currently more cost-effective to store in the amounts required for extended plant operation. It is also used directly as industrial process heat, including desalination and water purification. For the technology to compete against other generating systems, it is crucial to reduce the electrical energy cost to less than $0.10 per kilowatt-hour. One of the significant capital costs is the solar field, which contains the concentrators. Novel constructions and improvements to the durability and lifetime of the concentrators are required to reduce the cost of this field. This paper describes the development and validation of an inexpensive, highly portable photogrammetry technique, which has been used to measure the shape of large mirror facets for solar collectors. The accuracy of the technique has been validated to show a whole surface measurement capability of better than 100 m using a large coordinate measuring machine. Qualification of facets of the MATS plant was performed during its installation phase, giving results of the shape, slope and intercept errors over each facet.

The reflctor characteristics are negatively affcted by the harsh desert weather conditions and hence the performance of the system decreases. Ths paper investigates the effct of two diffrent types of moving sands “A” and “B” from Libya on the performance and safety of the solar reflctors. Samples are collected from areas that are suitable for installing CSP plants. Thy are in diffrent particle sizes and chemical compositions: sand “A” with size ranges between 0.025-0.355 mm, and “B” is within 0.124-0.479 mm. Thexperiment outcome using sand blasting indicated that sand “A” has more inflence than sand “B” as the small particles of “A” spread over a large area of the reflctor. It is also noticed in the range studied that the speed variation effct has more impact than the mass quantity changing. For clean surfaces, the reflctivity is dropped by 2.2%, and the damaged surfaces increased about 1 mm in case of 0.5 g mass at 27 m/s storm speed. For 2g mass at 21 m/s storm speed, the roughness is found 3 mm.

a.r.graham@cranfield.ac.uk Abstract Reel to reel manufacturing is a mature technology that involves the passing of a flexible substrate or web continuously through one or more processes. The web is typically much longer than it is wide, and the width in turn is much greater than its thickness. It is a continuous process that results in high output at a low unit cost when compared with other production methods. Historically this has included newspaper printing and textile manufacture, but more recent research is being conducted in developing printed electronics, such as solar cells (Organic Photo-Voltaic or OPV), and wearable tech and flexible screens (Polymer LEDs or PLEDs). These devices consist of up to five layers, with a separate printing or coating process needed for each. Greater accuracy is necessary than for traditional industries and advances are required in three areas: control of the web; measurement and registration of the printed web; and flexible semi-conductor materials. In this paper we present a new methodology to improve printing accuracy by combining an advanced metrology system with an innovative process design.

This paper presents a methodology to predict the optical performance and physical topography of the glass collector surfaces of any given CSP plant in the presence of sand and dust storms, providing that local climate conditions are known and representative sand and dust particles samples are available. Using existing meteorological data for a defined CSP plant in Egypt, plus sand and dust samples from two desert locations in Libya, we describe how to derive air speed, duration, and sand concentrations to use within the Global CSP Laboratory sand erosion simulation rig at Cranfield University. This then allows us to predict the optical performance of parabolic trough collector glass after an extended period by the use of accelerated ageing. However the behavior of particles in sandstorms is complex and has prompted a theoretical analysis of sand particle dynamics which is also described in this paper.

This paper describes work to compare the optical properties and surface texture of glass and polymer film collectors. We also present the results of experiments designed to simulate collector cleaning processes (both contact and non-contact), and the degradation of glass and polymer reflecting surfaces owing to sand and dust abrasion. Finally we present initial results on the applicability of anti-soiling and self-cleaning coatings on glass and polymer film collector surfaces. Measurements, which include specular and hemispherical reflectance, surface roughness, and electron microscopy, indicate the excellent performance of currently available polymer film in terms of its optical performance and robustness in comparison with traditional glass collectors in CSP applications.

INTRODUCTION There are numerous applications demanding the use of medium to large freeform surfaces and optics. These include short wavelength microlithography, segmented ground based telescopes, compact space based observers, high power laser systems, IR defence systems and even international temperature definition apparatus. The authors have been engaged in developing effective fabrication of freeform surfaces demanded for all of the above mentioned applications [1,2,3,4].

In recent years a number of high profile mooring failures have emphasised the high risk nature of this element of a floating structure. Semi-submersible Mobile Offshore Drilling Units (MODUs) operating in the harsh North Sea environment have experienced approximately 3 mooring failures every 2 years, based on an average population of 34 units. In recognition of the high mooring failure rates, the HSE has introduced recommendations for more stringent mooring strength requirements for units operating on the UK Continental Shelf (UKCS) [17]. Although strength requirements are useful to assess the suitability of a mooring design, they do not provide an insight into the question: what is the reliability of the mooring system?This paper aims to answer this question by evaluating failure statistics over the most recent decade of available data. Mooring failure rates are compared between the Norwegian Continental Shelf (NCS), the UKCS, and with industry code targets to understand how overall reliability is related to the strength capacity of a mooring system.The failure statistics suggest that a typical MODU operating in the UKCS would experience a mooring line failure in heavy weather approximately every 20 operating years. This failure rate appears to be several orders of magnitude greater than industry targets used to calibrate mooring codes. Despite the increased strength requirements for the NCS, failure rates do not appear to be lower than the UKCS. This suggests that reliability does not correlate well with mooring system strength. As a result, designing to meet the more rigorous HSE requirements, which would require extensive upgrades to existing units, may not significantly increase mooring system reliability. This conclusion needs to be supported with further investigation of failure statistics in both the UKCS and NCS. In general, work remains to find practical ways to further understand past failures and so improve overall reliability.

This paper describes the development of an inexpensive, highly portable photogrammetry technique for measuring the position and form of large mirror segments for solar collectors. The accuracy of the technique has been validated using a large Coordinate Measuring Machine (CMM) with results showing a measurement capability of better than 100μm. The surface form and resulting slope errors of the parabolic troughs have been measured and the impact of the mirror support system determined. This paper contains the results of photogrammetry and CMM comparison with details of the measurements, their analysis and further related experimental results obtained using both measurement techniques.

The demand for higher precision large optics has increased with major science and commercial projects running within the astronomy, fusion energy, and lithography sectors. The affordability of such projects necessitates reductions in cycle times and costs of the current optical process chains [1]. Recent developments in grinding and figure correction, using the BoX grinding machine and Reactive Atom Plasma (RAP) machine [2, 3] have demonstrated significant reduced processing times in the process chain. However, there remains scope for additional cost reduction within the polishing stage. To address this, a new industrial robot based polishing platform has been developed at Cranfield University. The platform offers an economic solution for processing ground surfaces for subsequent RAP processing and the application of a final neutral polishing to reduce surface roughness. This paper presents an analysis of polished fused silica surfaces; a material selected because of its use in lithography optics and fusion energy laser systems. The target surface roughness (Ra) was <10 nm while maintaining the surface form accuracy obtained from grinding.

Advances in technology are driving the requirement for metre-scale optics. Traditional optical process chains have used grinding for aspherisation, followed by sub-aperture CNC polishing, with the final form figure correction carried out with energy beam processes. With the trend for larger optics, this approach is slow thereby restricting capacity and increasing costs. The recent technological advances in grinding and final figure correction using Reactive Atom Plasma (RAP) technology have demonstrated significantly reduced cycle times. These reductions have yet to be matched by advances in polishing technology; therefore currently, multiple high performance sub-aperture polishing machines are required alongside a grinding and energy beam machine to achieve full utilisation in optical manufacturing process chains. To address this challenge, an industrial robot based polishing system has been developed using a standard Fanuc six axis robotic arm, aimed at bridging the aspherisation and final figure correction processes. The use of conventional industrial robots is a low capital cost alternative compared to conventional high cost sub-aperture polishing systems, offering the potential to employ higher numbers of low cost units within manufacturing cells. The robot based polishing system has been developed to remove subsurface damage and mid-spatials from the incoming surface, providing an optical quality finish suitable for interferometric measurement and subsequent RAP figure correction. A final neutral polish is employed using the robot system. The reported results demonstrate that this approach, in conjunction with BoX grinding and RAP figuring, provides a viable, faster and lower cost alternative to other current process chains. Laser Metrology and Machine Performance X

In this experimental study, diamond turning of single crystal 6H-SiC was performed at a cutting speed of 1m/s on an ultra-precision diamond turning machine (Moore Nanotech 350 UPL) to elucidate the microscopic origin of ductile-regime machining. Distilled water (pH value 7) was used as a preferred coolant during the course of machining in order to improve the tribological performance. A high magnification scanning electron microscope (SEM FIB- FEI Quanta 3D FEG) was used to examine the cutting tool before and after the machining. A surface finish of Ra=9.2nm, better than any previously reported value on SiC was obtained. Also, tremendously high cutting resistance was offered by SiC resulting in the observation of significant wear marks on the cutting tool just after 1km of cutting length. It was found out through a DXR Raman microscope that similar to other classical brittle materials (silicon, germanium, etc.) an occurrence of brittle-ductile transition is responsible for the ductile-regime machining of 6H-SiC. It has also been demonstrated that the structural phase transformations associated with the diamond turning of brittle materials which are normally considered as a prerequisite to ductile-regime machining, may not be observed during ductile-regime machining of polycrystalline materials.

The next generation of ground based telescopes require many hundreds of metre scale off-axis mirrors. In this paper the grinding of a 1.45m scale Zerodur® mirror segment for the European Extremely Large Telescope (E-ELT) is introduced. Employing an R-theta grinding mode with a multi stage grinding process material removal rates of up to 187.5mm3/s are achieved, whilst typically removing up to 1mm depth of material in total. Results show a RMS form error of <1μm, with subsurface damage <10μm, and a production cycle time under 20h.

An ultra precision large optics grinding machine, BoX®, was developed and produced at Cranfield University. BoX® offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. Grinding high accuracy surfaces with low subsurface damage reduces subsequent polishing time. This efficient grinding process provides the capacity to grind 1.5 m parts. This paper presents an analysis of Astrositall® optical ground parts: a hexagonal 84 m radius of curvature mirror of 1 m across corners and an off-axis 350 mm diameter mirror. The 1 m hexagonal part is representative of segments under study for making extremely large telescope (ELT) segmented mirrors. The second part was machined off-axis to demonstrate free-form fabrication capability. These operations demonstrate the scalability of the rapid grinding process developed for large free-form optics. The use of an error compensation procedure improved an initial ground form accuracy to +/- 1 μm p-v over 1 metre surface. The results highlighted the effect of grinding parameters and machine dynamics on form accuracy and fabrication time.

The development of high performance grinding machines together with the latest superabrasive technology has the potential to impact significantly on existing process chains. Abrasive machining is one material removal process that has the potential to span several orders of magnitude in terms of stock removal. This ranges from high efficiency deep grinding (HEDG) which can now compete with conventional cutting processes and provides the potential for improved surface integrity, surface finish and form accuracy, through to superfinished surfaces with roughness values as low as 10nm Ra. Thus, using a single machine tool and a single set-up, exceptionally high stock removal rates are achievable in a roughing cycle followed by superfinishing to generate the required surface characteristics and profile, providing higher precision and reduced manufacturing costs.

In this paper the application of high efficiency deep grinding to cylindrical plunge grinding is demonstrated and thermal modelling used to optimise the grinding cycle for an automotive steel and cast iron. The benefits associated with the high work speed achievable in cylindrical grinding are highlighted and both thermal modelling and experimental measurements have established that low workpiece temperatures are possible even when specific material removal rates of 2000 mm3/mm.s are achieved. Surface integrity studies based on microstructural analysis and Barkhausen noise have also demonstrated the effectiveness of the process.

The introduction of high performance grinding machines in combination with the latest superabrasive technology has the potential to impact significantly on existing process chains. High efficiency deep grinding (HEDG) with its high material removal rates can now compete with conventional cutting processes whilst maintaining surface integrity and surface finish requirements.

Diamond coated fibres have been produced by a hot filament CVD technique, where the surface of the fibres has a faceted structure making them suitable for use as an abrasive medium. Grinding trials to determine the performance of a metal bonded diamond fibre grinding wheel have been carried out using a 'state of the art' machining centre developed for the high precision ductile regime grinding of optics. Further work has been undertaken using a single fibre placed radially in a titanium disc to assess wear. Ductile ground surfaces were produced in BK7 glass with a surface roughness figure of 70 nm Ra, and less than 2 mu m sub-surface damage. The wear behaviour of the single fibre mounted in a disc wheel was monitored. Measurements showed that the initially sharp leading edge broke down to form a chamfered wear face, the profile produced by the fibre remaining similar. Diamond fibre grinding wheels have been shown to be capable of ductile grinding. These initial trials suggest that diamond fibres have the potential for longer wheel life, when grinding in the ductile region, compared with existing resin bond wheels.

Research into the grinding of advanced ceramics and glasses has shown the importance of wheel conditioning. In order to reliably grind these materials in a “low damage” mode, the inherent variability of the grinding process has to be controlled.