M.Ing. / In this study the design of a multivariable inner loop controller for a helicopter, which is based upon pilot-in-the-Ioop considerations, is proposed. A study of previous research regarding pilot-in-the-Ioop behaviour was made. Consequently another study was conducted on previous research regarding the interaction between the pilot, helicopter and the environment. With typical pilot behaviour known, the .emphasis of the study shifted to the helicopter. The effect of speed and controller configuration changes on the dynamic behaviour of the helicopter was analysed. Design assumptions were made which are based upon the crossover model of the pilot. Standard frequency domain and time domain techniques for example a-plane analysis, root loci, pole zero contours, Bode diagrams, state space formulations and step responses were used for analysis and synthesis. Helicopter models and controller models were defined and linked in the state space to form a combined state space model. Inner loop control is the control of rotational movements of the airframe. Inner loop control is sub-divided into damping and stability augmentation control which is achieved by means of rotational rate feedback, attitude hold control which is achieved by means of attitude and rate feedback, control augmentation which is achieved by means of feedforward and additional rate feedback, de-coupling which is achieved by means of cross-feedforward and turn coordination which is achieved by means of cross-feedback. The effect of loop closure in one axis on the dynamic behaviourof the other axes was analysed by means of sequential loop closure techniques. Both the damping and stability augmentation controller and the attitude hold controller were flight tested. Conclusions made from the flight test results led to updates to the initial design assumptions. From these flight tests definite pilot preferances became clear regarding the controller configuration to be used for different flight regimes. The techniques used in this study was compared with some of the most rescent techniques used internationally. Problem areas were identified and proposals made regarding possible future research. Although many new theories exist, it was found that the s-plane is still used by many helicopter control experts. For this reason this study can be regarded as a good foundation for future research on controllers for helicopters.

This research investigated whether the same attributes that cause managers to improve performance following upward feedback also encourage subordinates to give open and honest upward feedback. By proving that these attributes encourage integrity in upward feedback, this research allows organisations to freely implement programmes to increase the desired attributes among employees without fear of jeopardising the desired integrity of the feedback.Three hundred and twenty eight employees of a prominent South African company gave an indication of the levels of self-efficacy, learning goal orientation, organisational cynicism and integrity of upward feedback in the organisation. Statistical testing carried out on the resulting data then gave an indication of the relationships between the above-mentioned attributes or variables.It was found that there is a positive relationship between self-efficacy and upward feedback integrity, a positive relationship between learning goal orientation and upward feedback integrity and a strong negative relationship between organisational cynicism and upward feedback integrity. These results confirm that organisations can promote the attributes of self-efficacy and learning goal orientation in their employees without fear of jeopardising integrity in their upward feedback process. Conversely, the amount of organisational cynicism must be reduced wherever possible as it acts against the upward feedback mechanism. / Dissertation (MBA)--University of Pretoria, 2010. / Gordon Institute of Business Science (GIBS) / unrestricted

Please read the abstract in the section, 00front, of this document Copyright 1998, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bekker, JG 1998, Modelling and control of an electric arc furnace off-gas process, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-05192008-101727 / > / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / unrestricted

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Robot control systems can be considered complex systems, the design of a controller involving the determination of the dynamic model for the system. This in itself can be a complicated task due to non-linearities, multiple axis (degrees of freedom) control and the constantly changing working environment. Problems arise when the theoretical model produced for such a system is not accurate. When developing a controller using conventional techniques a design scheme has to be produced, usually based on a model of the system. In addition kinematics equations must be derived to take into account the physical boundaries of the system. The work outlined in this thesis utilises fuzzy logic control to address these control issues. Fuzzy logic provides functional capability without the use of a system model and has characteristics suitable for capturing the approximate, vaiying values found in real world systems. Initial development of a single axis fuzzy logic control system was implemented on a Dainichi industrial five-axis robot, replacing the existing control and hardware systems with a new developmental system. The concept of fuzzy logic and its application to control highlights the potential advantages that fuzzy logic control (PLC) can provide when compared to the more conventional control methodologies. Additional new control hardware has been interfaced to an existing robot manipulator, making it possible to compare PLC and PIDVF (Proportional Integral Derivative Velocity FeedforwardlFeedback) controllers for single axis development. Average response time and overshoot for a given set point were compared for each system. The results proved that, using a basic PLC minimal overshoot and fast rise times could be achieved in comparison to the commercial PIDVF system. Further research concentrated on the development of the control software to provide multiple axis control for an industrial robot using a continuous path algorithm. The more from single axis to multiple axis control provided a much more complex control problem. A novel and innovative process for the fuzzy controller was implemented with up to three axes reaching the target point simultaneously. Control of the industrial robot was investigated using methods that were more suited to real time controL The most significant change was a reduction in the number of fuzzy rules when compared to single axis control. During robot control no adaptation of the rule base or membership functions was carried Out Ofl line; only system gain was modified in relation to link speed and joint error within predetermined design parameters. The fuzzy control system had to manage the effects of frictional and gravitational forces whilst compensating for the varying inertia components when each linkage is moving. Testing based on ISO 9283 for path accuracy and repeatability verified that real time control of three axes was achievable with values of 938tm and 864tm recorded for accuracy and repeatability respectively. The development of novel industrial robot real time multi-axis fuzzy controller has combined new control hardware with an efficient fuzzy engine addressing inverse kinematics, scaling and dynamic forces in order to provide a viable robot control system.

Methods of designing multivariable feedback control systems based on system eigenvalues and matrix diagonalization are discussed. It is shown that these methods allow single-variable graphical analysis and design techniques to be applied to multivariable systems. The experimental determination of system eigenvalues is shown to be feasible. The suitability of these methods in conjunction with simulation studies for investigation and design purposes is also shown. A simulated two-axis tracking system is used to compare the eigenvalue method and the diagonalized method. The eigenvalue method is applied to a system of four parallel-operated synchronous machines and graphical methods of stability investigation are discussed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis describes discrete robust adaptive control methods based on using slow sampling and slow adaptation. For the stability analysis, we consider that the plant model order is not exactly known and assume that the estimation model order is lower than the plant model order. A stability condition is derived with a given upper limit for the adaptation gain which is related to a strictly positive real operator. Discussion of the relation between sampling and stability condition is then given. For the robust adaptive control design, we study slow adaptation and predictive control. For the slow adaptation, the main idea is to use only good estimates and use a compensation filter. Some frequency domain information on the plant is necessary for this method. For predictive control, we discuss the relationship between the extended control horizon and the critical sampling. For a simple case, it is shown that the larger extended control horizon brings more robust adaptive control. The purpose of this thesis is to provide robust discrete adaptive controller design guidelines, especially in such cases as using slow sampling frequency, slow adaptation rate. It is true that in practice, for various discrete adaptive control algorithms, slow sampling and slow adaptation rate will bring more robustness. The use of slow sampling and slow adaptation rate is simple and economic, thus a careful choice of sampling rate and adaptation rate is highly recommended. This thesis provides such guidelines for choosing proper sampling rate and adaptation rate for robust discrete adaptive control. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

In many control, data-processing, and communication systems, sampling is an inherent part of the system. If the time-continuous input signal is nonbandlimited, and noise is introduced in the system, an unavoidable error exists between the actual reconstructed signal and the desired time-continuous output signal. This error can be reduced by the suitable choice of prefilter prior to sampling and by the suitable choice of post-filter for reconstructing the time-continuous signal from the samples. In this thesis, an algorithm for determining the jointly optimal pre and post-filters which minimize the frequency weighted mean-integral-squared error of the system is presented, and the validity of the algorithm is proved. In the analysis, no restrictions are placed on the input signal spectrum or the noise spectrum, and the cross-correlation between signal and noise is taken into account. Applications of the optimization algorithm to M-channel time-multiplexed PAM systems, PCM systems with digital channels errors, and DPCM systems are considered. Performance characteristics, showing mean-squared error and inband signal-to-noise ratio versus channel signal-to-noise ratio, are determined explicitly for optimal pre and postfiltered PAM and PCM systems with first-order Butterworth input spectrum. These characteristics are compared with those of PAM and PCM systems which use suboptimal filtering schemes and with the optimal performance theoretically attainable. Performance characteristics, showing mean-squared error versus channel capacity, are also determined for PAM, PCM, and DPCM systems when the systems parameters are optimized to yield the least mean-squared error for a given channel capacity. Because of the subjective nature of speech, the effect of pre and postfilters in PAM, PCM and DPCM communication systems for speech transmission is studied by simulation methods and evaluated with subjective tests. Weak noise pre and postfilters (WNF), which yield virtually the same performance as optimal pre and postfilters, are considered in the subjective evaluation, in addition to lowpass pre and postfilters (LPF). The digital simulation facilities and the subjective testing methods are described, and the subjective results interpreted. It was observed that no significant subjective improvement resulted when WNF were used in place of LPF in PAM and DPCM systems. In PCM systems, significant differences in WNF and LPF subjective performances could exist. Using the analytical results, an explanation for the subjective behaviour is presented. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate