In real-word manufacturing environments, finding the right job sequences and their associated schedules when resource, precedence, and timing constraints are imposed is a difficult task. For most practical problems classical scheduling easily leads to an exponential growth in the number of possible schedules. Moreover, a decision time period of hours or even minutes is too long. Good solutions are often needed in real-time. The problem becomes even more complicated if changes, such as new orders or resource breakdowns, occur within the manufacturing system. One approach to overcome the challenges of solving classical scheduling problems is the use of distributed schemes such as agent or holonic-based control architectures. This dissertation presents an innovative control architecture that uses the holonic concept, capable of delivering good solutions when applied in dynamic environments. The general holonic control framework presented in this research has specific characteristics not found in others reported so far. Using a modular approach it takes into account all the categories of hardware and software resources of a manufacturing system. Due to its modularity, the holonic control framework can be used for assigning and scheduling different task types, separately or simultaneously. Thus, it can be used not only for assigning and scheduling transport tasks, but also for finding feasible solutions to the job assignment and scheduling of processing tasks, or to better utilize the auxiliary equipment and devices in a manufacturing system. In the holonic system, under real-time constraints, a feasible schedule for the material handling resources emerges from the combination of individual holon's schedules. Internal evaluation algorithms and coordination mechanisms between the entities in the architecture form the basis for the resultant schedules. The experimental results obtained show a percentage difference between the makespan values obtained using the holonic scheduling approach and the optimal values of under seven percent. Since current control systems in use in industry lack the ability to adapt to dynamic manufacturing environments, the holonic architecture designed and the tests performed in this research could be a part in the effort to build the foundations for the control systems of the next generation manufacturing systems. / Ph. D.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: This work entails a study of the control software of transportation systems for use in recon gurable manufacturing systems (RMSs). Various control approaches are considered, with the focus on enhancing recon gurability. The work is unique in the sense that the RMS is designed to manufacture small parts/products and is meant to be used in developing countries. Manufacturing systems that can ensure product quality and delivery, are a critical need in countries where the bulk of manufacturing systems function with manual labour. RMSs and holonic manufacturing systems (HMSs) are identi ed as concepts that can potentially compete with manual manufacturing systems. The competing system must thus have a low initial adoption risk, be able to adapt to changing product functionality and demands, and have a comparable throughput rate. IEC61311-3, IEC64199 function block and agent-based control architectures are evaluated. The control software is tested on an experimental conveyor system. The thesis shows that IEC61131-3 and IEC64199 architectures are advantageous in lower levels of control. IEC64199 function blocks provide human interface and development tools and simpli es the distribution of control. The human interface and development tools of IEC64199 function blocks may prove bene cial in providing system monitoring and rapid low skilled adaptation of the control system, increasing recon gurability of systems in under-developed countries. Unfortunately, the low maturity of the development environments for IEC64199 function blocks is a limitation. It is shown that an IEC64199 function block controller becomes complex as the actuator/sensor count exceed 10. Agent-based systems o er reliable control and powerful communication tools but requires a higher level of expertise than IEC64199 function blocks. Agent-based systems are proposed for the core high level control. Complex systems can be controlled with agents and intelligence can be added to control systems in a recon gurable way. For the recon gurable control of large manufacturing systems, agent-based control was found to be superior to IEC64199 function blocks. / AFRIKAANSE OPSOMMING: Hierdie werk behels 'n studie in die beheersagteware van vervoerstelsels vir die gebruik in herkon gureerbare vervaardigingstelsels. Verskeie benaderings word oorweeg, met die fokus op die verbetering van herkon gureerbaarheid. Die werk is uniek in die sin dat die herkon gureerbare vervaardigingstelsel ontwerp is vir die vervaardiging van klein onderdele/produkte en is bedoel vir die gebruik in die ontwikkelende lande. Vervaardigingstelsels wat die kwaliteit van die produk en a ewering kan verseker, is 'n kritieke behoefte in die lande waar die grootste deel van die vervaardiging met handearbeid gedoen word. Herkon gureerbare vervaardigingstelsels en holoniese vervaardigingstelsels is geïdenti seer as konsepte wat moontlik kan meeding met die handmatige produksie-stelsels. Die mededingende stelsel moet dus 'n lae aanvanklike aannemingsrisiko hê, in staat wees om te kan aanpas by die veranderende produk funksionaliteit en aanvraag, en 'n vergelykbare deurvloeikoers kan lewer. IEC61311-3, IEC61499 funksie-blok en agent-gebaseerde beheer argitekture word geëvalueer. Die beheer sagteware is getoets op 'n eksperimentele vervoerband stelsel. Die tesis toon dat IEC61131-3 en IEC61499 argitekture voordelig is in die laër vlakke van beheer. IEC61499 funksie-blokke voorsien menslike koppelvlak en ontwikkelings-gereedskap, en vereenvoudig die verspreiding van beheer. Die menslike koppelvlak en ontwikkelings-gereedskap van die IEC61499 funksieblokke is moontlik voordelig in die voorsiening van stelselmonitering en vinnige laag-geskoolde aanpassing van die beheer stelsel. Dit mag dus moontlik die herkon gureerbaarheid van stelsels, in onder-ontwikkelde lande, verhoog. Die lae vlak van volwassenheid van die ontwikkelingsomgewings vir IEC61499 funksie-blokke verlaag hul bruikbaarheid. Daar word aangetoon dat IEC61499 funksie-blok beheerders baie kompleks raak as die hoeveelheid van aktueerders en sensors meer as 10 raak. Agent-gebaseerde stelsels bied betroubare beheer, en kragtige kommunikasie-gereedskap, maar vereis 'n hoër vlak van kundigheid as IEC61499 funksie-blokke. Agent-gebaseerde stelsels word voorgestel vir die hoëvlak beheer. Komplekse stelsels kan beheer word met agente en intelligensie kan bygevoeg word om stelsels te beheer in 'n herkon gureerbare manier. Dit was gevind dat agent-gebaseerde beheer beter is as IEC61499 funksie-blok beheer vir die herkon gureerbare beheer van groot vervaardigings stelsels.