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Table of Contents
Micromachining of Optical Fibres with a Nanosecond Laser for Optical Communication and Sensor Applications
LTI Modelling of Active Magnetic Bearings by Means of System Identification
Multivariable H∞ or Centre of Gravity PD Control for an Active Magnetic Bearing Flywheel System
Micromachining of Optical Fibres with a Nanosecond Laser for Optical Communication and Sensor Applications by D. Schmieder, R. Samaradiwakera and J. Meyer
Abstract: Micromachining of single-mode telecommunication fibres (SMF28) was accomplished with a Nd:YAG laser at a wavelength of 355 nm. Micromachining is important for the manufacturing of Bragg gratings and long period gratings which are used in add-drop filters and wavelength division multiplexers. Manufacturing of miniature Fabry-Perot interferometers used for temperature sensors is also possible. A short overview of micromachining concepts is presented. The experimental setup, as well as the equipment used, is described. Alignment processes, focal point determination and centering of the laser beam onto the optical fibre are outlined. Micromachining results are presented.
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LTI Modelling of Active Magnetic Bearings by Means of System Identification by P.A. van Vuuren, G. van Schoor and W.C. Venter
Abstract: A relatively unknown phenomenon in active magnetic bearings (AMBs) is that the frequency content of their rotor position signal can induce nonlinear behaviour in the bearings. The existence of such frequency-induced nonlinear behaviour is experimentally and theoretically confirmed. Frequency-induced nonlinearity is characterised by means of a novel graphical representation. The resultant graph is quite useful in the specification of suitable excitation signals when AMBs are to be modelled by means of system identification.
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Multivariable H∞ or Centre of Gravity PD Control for an Active Magnetic Bearing Flywheel System by S.J.M. Steyn, P.A. van Vuuren and G. van Schoor
Abstract: A state-space model with uncertainties for an active magnetic bearing energy storage flywheel system (Fly-UPS) is developed. A multivariable robust H∞ controller for the Fly-UPS is then synthesised. Different weighting schemes are explained and the additive uncertainties between the nominal simulation model and the physical model at varied rotational speeds are characterised. Furthermore, PD controllers are developed using the centre of gravity (COG) coordinate framework for decoupled parallel and conical modal control. Stability robustness is verified via the gain/phase margin stability robustness criterion. The performance robustness (disturbance attenuation) is analysed by assessing model sensitivity with the ISO/CD 14839-3 sensitivity standard. The results obtained show that H∞ control and COG coordinate PD control are not fundamentally different.
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