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M.Ing. / Fuzzy controllers are increasingly being accepted by engineers and scientists alike as a viable alternative for classical controllers. The processes involved in fuzzy controllers closely imitate human control processes. Human responses to stimuli are not governed by transfer functions and neither are those from fuzzy controllers. The fuzzy approach is of course not the answer to all problems, but it can clearly be very successful, and can also be helpful to anyone involved in developing control systems. This study however is devoted to the environmental control task within greenhouses and the fuzzy approach is proposed in order to fulfil this task. To create near optimal conditions within a greenhouse for plant growth two environmental factors are proposed to be controlled namely the temperature and relative humidity. These factors are interdependent and they make the environmental control within a greenhouse a multi-variable control problem. Furthermore, the non-linear physical phenomena governing the dynamics of temperature and relative humidity in such a process makes it very difficult to model and to control using traditional techniques. Thus, it can be said that the environmental control in greenhouses is an art, that only expert growers bring to near perfection. The central theme of this study is the development of a multi-input-single-output heuristic rule-based fuzzy logic control algorithm, for environmental control within a greenhouse. This study is intended to improve existing environmental control systems by implementing this control technique. The control algorithm is tested in an experimental greenhouse and the results obtained indicate that fuzzy logic control is viable for environmental control within greenhouses.

M.Ing. / Parts feeding devices or feeders are used in automated assembly systems to deliver correctly oriented parts to the assembly station workhead. These devices play an important operational role since feeding is one of the major operations involved in an automated assembly process. However they account for much of the cost of an automated assembly system because most of the engineering time spent to develop such a system is used to devise a means of feeding the components in the correct orientation for the assembly process. This thesis describes the implementation of an integrated and computer controlled feeding and transfer system. The system consists of a vibratory bowl feeder for selecting, orienting and feeding parts and a flat conveyor belt for transferring parts to a prescribed location. The work focusses mainly on the design and analysis of the bowl feeder, on the mechanical and information interfacing aspects of the integration problem and on the control of the system. Sensing and electronic control circuits were also built to complete the system. The system implemented is to be integrated at a later stage with an industrial robot for handling purposes. Therefore, some issues related to the handling of parts from the conveyor belt by the robot are also discussed. Experimental results show that the recommendable operating frequency for the vibratory feeder is close to the value predicted by theoretical analysis. Several concurrent activities with critical time constraints and different periods were involved in the system, making the control more difficult due to the limited control capabilities of Visual basic, an easy to learn programming language used to implement the control program and the relatively slow speed of the computer used Nevertheless, it was observed that for feed rates close to 3 parts/min, the program developed performs well regarding the random control of the flow rate of parts on the conveyor, parts position and speed profiles obtained compare satisfactorily with the corresponding theoretical profiles. Recommendations for the integration of the robot to the system are made.

A thesis submitted to the Faculty of Engineering and the Built Environment in fulfilment of the requirement for the degree Doctor of Philosophy, University of the Witwatersrand, Johannesburg, 2019 / The design of feedback stabilizing controllers is an essential component of control engineering theory and practice. A large part of the modern literature in control theory is devoted to coming up with new methods of designing feedback stabilizing controllers. This sustained interest in answering the question \how to design a feedback stabilizing controller" has not been accompanied by equal interest in the more existential and fundamental problem of \when is a system stabilizable by feedback". As such the theory of control Lyapunov functions still remains the most general framework that characterizes stabilizability as a system property. This approach however simply replaces one elusive and di cult concept (i.e stabilizability) with an equally diffcult concept, the existence of control Lyapunov functions. In this thesis we analyse control system stabilizability from the perspective of control system quotients which are generalized control system reductions, the focus being on the propagation of the stabilizability property from the lower order quotient system to the original system. For the case where the quotient system is a linear controllable system we prove that propagation of the stabilizability property to the original system is possible if the zero dynamics of the original system are stable. A novel way of constructing the zero dynamics which does not involve the solution of a system of partial differential equations is devised. More generally for analytic non-linear systems given a stabilizable quotient system, we develop a new method of constructing a control Lyapunov function for the original system, this construction involves the solution of a system of partial di erential equations. By studying the integrability conditions of this associated system of partial differential equations we are able to characterize obstructions to our proposed method of constructing control Lyapunov functions in terms of the structure of the original control system. / PH2020

The computed-torque algorithm is a popular model-based robot trajectory control scheme. Adding an adaptive mechanism to this scheme can improve the error tracking capabilities of the robot controller. This thesis describes the algorithms necessary to develop a computer simulation for the PUMA 560 robot arm. Several robot controllers are outlined with an emphasis on the computed-torque scheme. The PUMA simulation is used to analyze the error tracking capabilities of an adaptive computed-torque controller. Consideration is given to parameter mismatch, unmodeled friction, unknown loading, and path excitation. This thesis shows that even with inaccurate load knowledge the adaptive algorithm enhances the tracking capabilities of the controller.