Production of electronics and photovoltaics using a reel-to-reel process

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

An accelerometer based-feedback technique for improving dynamic performance of a machine tool

A novel concept for improving machine dynamic performance was developed and realised, a virtual metrology frame, for a small size CNC machine with flexible frame. Its implementation in a simplified linear motion system shows a reduction in the magnitude of the first resonance in the plant frequency response function by 12 dB. Realising the concept required developing a real -time accelerometer-based measurement technique. It shows a low sensor noise σ=30 nm with optimal phase delay of <70 μs

A method for assessing measurement precision and stability of optical probes

The current strategy for measuring non-specular metre-scale surfaces – for instance segmented freeform optics post-grinding – in the mid- frequency bandwidths (S-filter), involves the use of contact probe based systems where measurement precision is a limiting factor. Equivalent non-contact optical probes claim accuracies up to an order of magnitude higher and could therefore improve current measurement systems. Chromatic confocal probes measure the distance to a surface using the principle of axial chromatic dispersion. The stability of a CHRocodile SE 300 μm probe was shown to be 200 ± 20 nm over an eight hour measurement period. A probe holder should be designed with a low thermal expansion material in order to thermally insulate the probe measurement for further investigation. The accuracy of the probe was assessed at the extremes of its measurement range. The maximum deviation over a 5 μm displacement was measured to be 85 nm. The entire measuring range should be investigated

Optimized estimator for real-time dynamic displacement measurement using accelerometers

This paper presents a method for optimizing the performance of a real-time, long term, and accurate accelerometer based displacement measurement technique, with no physical reference point. The technique was applied in a system for measuring machine frame displacement. The optimizer has three objectives with the aim to minimize phase delay, gain error and sensor noise. A multi-objective genetic algorithm was used to find Pareto optimal estimator parameters. The estimator is a combination of a high pass filter and a double integrator. In order to reduce the gain and phase errors two approaches have been used: zero placement and pole-zero placement. These approaches were analysed based on noise measurement at 0g-motion and compared. Only the pole-zero placement approach met the requirements for phase delay, gain error, and sensor noise. Two validation experiments were carried out with a Pareto optimal estimator. First, long term measurements at 0g-motion with the experimental setup were carried out, which showed displacement error of 27.6 ± 2.3 nm. Second, comparisons between the estimated and laser interferometer displacement measurements of the vibrating frame were conducted. The results showed a discrepancy lower than 2 dB at the required bandwidth

Fast figuring of large optics by reactive atom plasma

The next generation of ground-based astronomical observatories will require fabrication and maintenance of extremely large segmented mirrors tens of meters in diameter. At present, the large production of segments required by projects like E-ELT and TMT poses time frames and costs feasibility questions. This is principally due to a bottleneck stage in the optical fabrication chain: the final figuring step. State-of-the-art figure correction techniques, so far, have failed to meet the needs of the astronomical community for mass production of large, ultra-precise optical surfaces. In this context, Reactive Atom Plasma (RAP) is proposed as a candidate figuring process that combines nanometer level accuracy with high material removal rates. RAP is a form of plasma enhanced chemical etching at atmospheric pressure based on Inductively Coupled Plasma technology. The rapid figuring capability of the RAP process has already been proven on medium sized optical surfaces made of silicon based materials. In this paper, the figure correction of a 3 meters radius of curvature, 400 mm diameter spherical ULE mirror is presented. This work demonstrates the large scale figuring capability of the Reactive Atom Plasma process. The figuring is carried out by applying an in-house developed procedure that promotes rapid convergence. A 2.3 μm p-v initial figure error is removed within three iterations, for a total processing time of 2.5 hours. The same surface is then re-polished and the residual error corrected again down to& lambda;/20 nm rms. These results highlight the possibility of figuring a metre-class mirror in about ten hours

Microwaves enable activated plasma figuring for ultra-precision fabrication of optics

Activated plasma figuring using microwaves aims at providing highly efficient activated energy beams for rapid fabrication of optics. The chemical nature of this type of energy beam leads to targeting silicon-based materials. Furthermore this technology is proposed to address the needs of ultra-precision optical components. In this paper, we present a novel ADTEC microwavegenerated plasma torch design which is operated at atmospheric pressure. In this study, the plasma torch is fed with either argon or helium carrier gas. However this novel design for Plasma Figuring is targeted at local surface correction of crystal quartz which is a material of great interest for optical systems, such as acousto-optic devices. Also this novel design is targeted at reducing midspatial frequency errors such as waviness, ripple errors and residual sub-aperture tool footprints. These are responsible for the scattering of light at small angles, resulting in optical hazing effects, photonic energy loss and pixel cross-talk. Also the results of a preliminary investigation using Optical Emission Spectroscopy (OES) are reported and discussed. These results show the operat ing range when the main processing parameters are changed: microwave forward power values, gas flow rates and the types of gasses

Sub-surface damage issues for effective fabrication of large optics

A new ultra precision large optics grinding machine, BoX®has been developed at Cranfield University. BoX®islocated at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium. This machine offers a rapidand economic solution for grinding large off-axis aspherical and free-form optical components.This paper presents an analysis of subsurface damage assessments of optical ground materials produced usingdiamond resin bonded grinding wheels. The specific materials used, Zerodur®and ULE®are currently understudy for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project.The grinding experiments have been conducted on the BoX®grinding machine using wheels with grits sizes of76 μm, 46 μm and 25 μm. Grinding process data was collected using a Kistler dynamometer platform. Thehighest material removal rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in lessthan 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurfacedamage was revealed using a sub aperture polishing process in combination with an etching technique.These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughnessof 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 400mm ULE®blank and a 1 metre hexagonal Z

A basis for the representation, manufacturing tool path generation and scanning measurement of smooth freeform surfaces

Freeform surfaces find wide application, particularly in optics, from unique single-surface science programmes to mobile phone lenses manufactured in billions. This thesis presents research into the mathematical and algorithmic basis for the generation and measurement of smooth freeform surfaces. Two globally significant cases are reported: 1) research in this thesis created prototype segments for the world’s largest telescope; 2) research in this thesis made surfaces underpinning the redefinition of one of the seven SI base units – the kelvin - and also what will be the newly (and permanently) defined value for the Boltzmann constant. Theresearchdemonstratestwounderlyingphilosophiesofprecisionengineering, the critical roles of determinism and of precision measurement in precise manufacturing. The thesis presents methods, and reports their implementation, for the manufacture of freeform surfaces through a comprehensive strategy for tool path generation using minimum axis-count ultra-precision machine tools. In the context of freeform surface machining, the advantages of deterministic motion performance of three-axis machines are brought to bear through a novel treatment of the mathematics of variable contact point geometry. This is applied to ultra-precision diamond turning and ultra-precision large optics grinding with the Cranfield Box machine. New techniques in freeform surface representation, tool path generation, freeform tool shape representation and error compensation are presented. A comprehensive technique for very high spatial resolution CMM areal scanning of freeform surfaces is presented, with a new treatment of contact error removal, achieving interferometer-equivalent surface representation, with 1,000,000+ points and sub-200 nm rms noise without the use of any low-pass filtering

A novel accelerometer based feedback concept for improving machine dynamic performance

Small size ultra-precision Computer Numerical Control (CNC) machines require high dynamic performance. Flexible frame phenomena can limit the machine dynamic performance, particularly in small size machines. A novel accelerometer based feedback concept for improving machine dynamic performance was developed and realised, a virtual metrology frame. It expends the limited techniques for improving dynamic performance of a small size machine by measuring the flexible frame displacement, and feeding it into the controller. The concept was implemented in a simplified linear motion system, and showed a 12dB reduction in the magnitude of the first resonance in the plant frequency response function. This allowed improving the servo bandwidth by 58% based on a PID controller. A new technique for real-time dynamic displacement measurements using accelerometer was developed. It shows a low sensor noise σ<30 nm; thus, accelerometers are used as a displacement sensor in a control system

Virtual metrology frame technique for improving dynamic performance of a small size machine tool

This paper presents a novel concept, a virtual metrology frame, for enhancing the dynamic performance of a machine tool with a flexible structural frame. The dynamic properties of a machine are directly affected by the stiffness of its frame, and its reference system; thus, by having an unstressed metrology frame, superior dynamic capabilities can be achieved. The developed concept does not require physical components associated with metrology frame; hence it is ideal for machine tools with requirements for small footprint and ultra-precision performance. The concept relies on an accelerometer based dynamic displacement feedback technique, where the accelerometer is used as a precision frame displacement sensor. The concept does not require a complex controller, and was realized in an off-the-shelf CNC controller. The concept was demonstrated on a linear motion system, a simplified version of a compact size CNC machine, and its servo bandwidth and dynamic stiffness were improved by 36% and 70% respectively, which are the key parameters for improving the machining accuracy