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Poster presentation of research work at the EPSRC Centre for innovative manufacturing in ultra precision.

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

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.

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.

The following study is realised within the frame of the PACMAN project: a study on Particle Accelerator Components Metrology and Alignment to the Nanometre scale, which is a Marie Curie program supported by the European commission and hosted by CERN (European Organisation for Nuclear Research). The aim of this program is to develop and build a pre-alignment bench on which each component is aligned to the required level in one single step using a stretched wire. During the operation, the centre of the stretched wire is aligned with the magnetic axis of the magnet. Then, the position of the wire is measured to the highest possible accuracy using a 3D Coordinate Measuring Machine (CMM) Leitz PMM-C Infinity from HEXAGON Metrology. The research described in this paper is two-fold: on one hand we apply a strong magnetic field to the head of the CMM and evaluate its influence on the measurement accuracy; on the other hand we measure the position

L’étude suivante est réalisée dans le cadre du projet PACMAN (a study on Particle Accelerator Components Metrology and Alignment to the Nanometre scale) : une étude sur la métrologie et l’alignement à l’échelle nanométrique des composants d’un accélérateur de particules. C’est un programme Marie Curie supporté par la Commission Européenne et hébergé par le CERN. Le but de ce programme est de faire travailler en équipe de jeunes chercheurs sur le développement d’un banc de pré-alignement pour l’accélérateur linéaire CLIC (Compact Linear Collider). Sur ce banc, chaque composant sera aligné au niveau requis en une seule opération basée sur l’utilisation d’un fil tendu. Pendant cette opération, le fil matérialisera les axes magnétiques et électriques des composants, c’est-à-dire qu’il sera à la position théorique du faisceau de particules. Puis il servira de référence et la position de son axe sera mesurée avec autant de précision que possible par une machine de mesure tridimensionnelle. La recherche présentée dans ce papier est en deux parties : la première vise à présenter les propriétés du fil nécessaires au projet qui ont été mesurées, tandis que différents capteurs potentiels pour le banc final se trouvent dans la seconde.

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.

Roll-to-roll printing on continuous plastic films could enable the production of flexible electronics at high speed and low cost, but the granularity of feature sizes is limited by the system accuracy. Technologies such as gravure printing and nanoimprint lithography demand a level of rotary motion precision that cannot be achieved with rolling element bearings. Manufacturing tolerances of the rotating parts, thermal drift and process forces in combination with structural compliance add up to additional error motions. In this master by research an active magnetic bearing (AMB) solution is designed for a new, super-sized roll-to-roll flexible electronics production machine, which was so far based on hydrostatic bearings. The magnetic bearing could actively compensate the accumulated synchronous error and maintain high accuracy under all conditions. However, the asynchronous error of a conventional AMB with the required size and power is a problem. In order to reduce the relatively high positioning uncertainty of active magnetic bearings an innovative radial position measurement based on linear, incremental encoders with optical conversion principle is proposed. A commercial encoder scanning head faces a round scale with concentric, coplanar lines on its face. By counting these lines the radial position can be measured. Because such a scale is not readily available, it is made by micro-machining. In experiments, different machining methods are compared. Then a magnetic bearing is built to demonstrate the efficacy of the proposed sensor. As a result, the best measurement noise is 3.5nm at 10kHz and a position uncertainty of approximately 0.25µm has been achieved for the magnetic bearing. These promising results are especially interesting for applications with high precision requirements at low speed of rotation.

The aims of this MSc research project are to investigate the application of aluminium for the main components of an ultra-precision spindle defined for use in R2R production systems and to produce a reel to reel rotary aluminium hydrostatic bearing system of high accuracy to meet the demand of manufacturing the flexible displays with an effective production capability for this special kind of film-based product. The original concept design was already finished to manufacture the bearing components and the objective of this project was to test the functionality of this new hydrostatic bearing system. Firstly, theoretical were performed to work out the output responses, including temperature rise, flow rate, load capacity etc., of the hydrostatic bearing system under different input design parameters, including supply pressure, fluid viscosity, the rotational speed etc. Then ANSYS software was used to build a FEA model to simulate the actual working conditions of the hydrostatic bearing system and to obtain the theoretical output parameters, especially the deflection conditions of the bearing shaft. Finally the experimental validation tests were conducted to verify the actual output responses to check correlation with the modelled results.