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.

Queueing network-based approximation models were developed to evaluate the performance of fixed-route material-handling systems supporting a multiple workcenter manufacturing facility. In this research, we develop analytical models for fixed-route material-handling systems from two different perspectives: the workcenters?? point of view and the transporters?? point of view. The state-dependent nature of the transportation time is considered here for more accurate analytical approximation models for material-handling systems. Also, an analytical methodology is developed for analytical descriptions of the impact of several different vehicledispatching policies for material-handling systems. Two different types of vehicledispatching policies are considered. Those are workcenter-initiated vehicle dispatching rules and vehicle-initiated vehicle dispatching rules. For the workcenterinitiated vehicle dispatching rule, the Closest Transporter Allocation Rule (CTAR) was used to assign empty transporters to jobs needing to be moved between various workcenters. On the other hand, four different vehicle-initiated vehicle dispatching rules, Shortest Distance Dispatching Rule (SDR), Time Limit/Shortest DistanceDispatching Rule (TL/SDR), First-Come First-Serve Dispatching Rule (FCFSR), Longest Distance Dispatching Rule (LDR), are used to select job requests from workcenters when a transporter is available. From the models with a queue space limit of one at each workcenter and one transporter, two different types of extensions are considered. First, the queue space limit at each workcenter is increased from one to two while the number of transporters remains at one. Second, the number of transporters in the system is also increased from one to two while maintaining the queue space limit of one at each workcenter. Finally, using a simulation approach, we modified the Nearest Neighbor (NN) heuristic dispatching procedure for multi-load transporters proposed by Tanchoco and Co (1994) and tested for a fixed-route material-handling system. The effects of our modified NN and the original NN transporter dispatching procedures on the system performance measures, such as WIP or Cycle Time were investigated and we demonstrated that the modified NN heuristic dispatching procedure performs better than the original NN procedure in terms of these system performance measures.

A Generalized Cambridge Ring is a queueing system that can be used as an approximate model of some material handling systems used in modern factories. It consists of one or more vehicles that carry cargo from origins to destinations around a loop, with queues forming when cargo temporarily exceeds the capacity of the system. For some Generalized Cambridge Rings that satisfy the usual traffic conditions for stability, it is demonstrated that some nonidling scheduling polices are unstable. A good scheduling policy will increase the efficiency of these systems by reducing waiting times and by therefore also reducing work in process (WIP). Simple heuristic policies are developed which provide substantial improvements over the commonly used first-in-first-out (FIFO) policy. Variances are incorporated into previously developed fluid models that used only means to produce a more accurate partially discrete fluid mean-variance model, which is used to further reduce waiting times. Optimal policies are obtained for some simple special cases, and simulations are used to compare policies in more general cases. The methods developed may be applicable to other queueing systems. / text

Die Kosten für die Energieversorgung eines Materialflusssystems übersteigen die Investitionskosten oft schon nach wenigen Jahren. Mit steigenden Energiepreisen wird dieser Zeitraum kürzer. Bei der Bewertung der Lebenszykluskosten eines Materialflusssystems rücken deshalb die Energiekosten immer mehr in den Vordergrund. Viele Möglichkeiten zur Energieeffizienz-Steigerung sind zwar bereits bekannt, jedoch wird davon meist nur punktuell, nicht aber systematisch Gebrauch gemacht. Dies gilt insbesondere für die Ebene der Anlagen- bzw. Systemsteuerung. Die Bemühungen um eine Steigerung der Energieeffizienz in der Intralogistik fokussieren bislang auf die Optimierung fördertechnischer Komponenten (Leichtbau, Antriebe). Damit wird jedoch nur das Symptom behandelt, nicht aber die Ursache: Der energetische Aufwand für Transportvorgänge – das Symptom – muss zweifellos reduziert werden. Das geschieht auch bereits. Zugleich ist aber sicherzustellen, dass zur Lösung einer konkreten logistischen Aufgabenstellung – der Ursache – Transporte nur im tatsächlich erforderlichen Umfang und in der richtigen Weise durchgeführt werden. Dafür Sorge zu tragen, ist Aufgabe einer energieeffizienten Anlagensteuerung. Die Forschungsarbeiten an der TU Dresden verfolgen drei Ziele: (a) Der Zusammenhang zwischen der mechanischen Leistung und dem elektrischen Energieverbrauch typischer Fördertechnik-Komponenten soll allgemeingültig beschrieben werden. (b) Es sollen Routinen entwickelt werden, mit denen in der ereignisdiskreten Simulation die mechanische Leistung einer Anlage und der resultierende elektrische Energieverbrauch bestimmt wird. (c) Mithilfe der Simulation soll gezeigt werden, wie und in welchem Umfang optimierte Steuerungsstrategien die Energieeffizienz von Materialflusssystemen steigern.

Die Kosten für die Energieversorgung eines Materialflusssystems übersteigen die Investitionskosten oft schon nach wenigen Jahren. Mit steigenden Energiepreisen wird dieser Zeitraum kürzer. Bei der Bewertung der Lebenszykluskosten eines Materialflusssystems rücken deshalb die Energiekosten immer mehr in den Vordergrund. Viele Möglichkeiten zur Energieeffizienz-Steigerung sind zwar bereits bekannt, jedoch wird davon meist nur punktuell, nicht aber systematisch Gebrauch gemacht. Dies gilt insbesondere für die Ebene der Anlagen- bzw. Systemsteuerung. Die Bemühungen um eine Steigerung der Energieeffizienz in der Intralogistik fokussieren bislang auf die Optimierung fördertechnischer Komponenten (Leichtbau, Antriebe). Damit wird jedoch nur das Symptom behandelt, nicht aber die Ursache: Der energetische Aufwand für Transportvorgänge – das Symptom – muss zweifellos reduziert werden. Das geschieht auch bereits. Zugleich ist aber sicherzustellen, dass zur Lösung einer konkreten logistischen Aufgabenstellung – der Ursache – Transporte nur im tatsächlich erforderlichen Umfang und in der richtigen Weise durchgeführt werden. Dafür Sorge zu tragen, ist Aufgabe einer energieeffizienten Anlagensteuerung. Die Forschungsarbeiten an der TU Dresden verfolgen drei Ziele: (a) Der Zusammenhang zwischen der mechanischen Leistung und dem elektrischen Energieverbrauch typischer Fördertechnik-Komponenten soll allgemeingültig beschrieben werden. (b) Es sollen Routinen entwickelt werden, mit denen in der ereignisdiskreten Simulation die mechanische Leistung einer Anlage und der resultierende elektrische Energieverbrauch bestimmt wird. (c) Mithilfe der Simulation soll gezeigt werden, wie und in welchem Umfang optimierte Steuerungsstrategien die Energieeffizienz von Materialflusssystemen steigern.

Within manufacturing organizations, the material flow is a promoted part of the supply chain to evaluate, since it often stands for a significant part of the costs. The evaluation refers to the analysis and optimization of the material flow that arise during manufacturing of products. It can focus on very different levels, such as the material flow in a region or within a company’s internal processes. However, the material flow is concerned with the transportations, operations and storages of materials. A well-organized material flow enables organizations to cutting costs and increase competitiveness, via increased effectiveness and efficiency of operating practices. Scania operates in the automotive industry and they are constantly striving to improve their supply chain in terms of productivity and lower costs, to meet the needs of the market and gain increased competitiveness. Today, Scania engine assembly in Södertälje has operations in two main buildings, approximately one km in-between. One building is the material warehouse, and the other building is the actual assembly. In the future, the two building will be joint together. Consequently, the project logistics department of Scania engine assembly has recognized a possibility to re-organize and improve the material flows. The upcoming merge between the two buildings enables a possibility to investigate how the current material flows could be more efficient, before they are applied in the future state. The purpose of this research is to investigate and improve a material flow, box flow, within an automotive environment. A box flow is concerned with smaller components that use plastic boxes as packaging material. The objective is to derive a more efficient process for the flow of supplying boxes to the assembly building. By efficiency, it is defined as shorter total lead time, higher capacity, lower time/cost per box delivered, and a maintained or improved ergonomics during manual handling operations within the box flow. To fulfil the purpose of this research interviews, observations and data collections have been used to gain an understanding of how the current situation is managed at Scania engine assembly. Conducted benchmarking and literature research have been used to gain an understanding of how other companies in the industry, as well as departments at Scania, are managing their box flows. The findings have been analysed, where the different flow of boxes have been compared with the theoretical frame of reference as well as against each other. The conclusions of the analysis are different key factors, for better logistics efficiency, when managing a box flow. These key factors are providing an increased theoretical understanding, when the aim is to make a material flow of boxes more efficient, in an assembly environment. In this research, they are utilized as guidelines, to derive a more efficient process for the flow of supplying boxes. That is, implementing the findings theoretically into a practical context. To derive a more efficient process, a Business Case have been conducted. Its outcome provides a concept of how the process of boxes should be organized. That is, how the different material handling operations and equipment should be utilized to achieve an overall increased efficiency. How the box flow should be organized are presented as recommendations, which works as guidelines and insights for Scania engine assembly. They are jointly fulfilling the purpose of this research, together with the other achieved research questions. / Inom tillverkningsorganisationer är materialflödet en prioriterad del av försörjningskedjan att utvärdera, eftersom den ofta står för en betydande del av kostnaderna. Utvärderingen avser analys och optimering av materialflödet som uppstår vid tillverkning av produkter. Den kan fokusera på många olika nivåer, som materialflödet i en region eller inom ett företags interna processer. Materialflödet berör emellertid transporten, operationerna och materiallager. Ett välorganiserat materialflöde gör det möjligt för organisationer att sänka kostnaderna och öka konkurrenskraften, genom ökad inre- och yttre effektivitet av utföranden inom företaget. Scania verkar inom bilindustrin och strävar ständigt efter att förbättra sin försörjningskedja när det gäller produktivitet och lägre kostnader, för att möta marknadens behov och öka konkurrenskraften. Idag har Scanias motormontering i Södertälje verksamheter i två huvudbyggnader, med ca en kilometer mellan varandra. Den ena byggnaden är materiallagret, och den andra byggnaden är den faktiska monteringen. I framtiden kommer de två byggnaderna att bli integrerade. Följaktligen har projektlogistikavdelningen vid Scanias motormontering bedömt en möjlighet att organisera och förbättra deras materialflöden. Den kommande integrationen mellan de två byggnaderna gör det möjligt att undersöka hur de aktuella materialflödena kan bli effektivare, innan de appliceras i det framtida tillståndet. Syftet med denna forskning är att undersöka och förbättra ett materialflöde, boxflöde, i en monteringsmiljö. Ett boxflöde behandlar mindre komponenter som använder plastlådor som förpackningsmaterial. Målet är att klarlägga en effektivare process för flödet av boxar till monteringsbyggnaden. Effektivitet definieras som ett flöde som har kortare total ledtid, högre kapacitet, lägre tid / kostnad per box levererad och en bibehållen eller förbättrad ergonomi under manuella hanteringar. För att uppfylla syftet med forskningen har olika typer av intervjuer, observationer och datasamlingar använts, för att skapa en djupare förståelse över den nuvarande situationen hos Scanias motormontering. Genomförd benchmarking och litteraturforskning har använts för att förstå hur andra företag inom branschen, även andra avdelningar på Scania, hanterar sina boxflöden. Den insamlade empirin har använts i en analys där de olika flödena av boxar har jämförts både med den teoretiska referensramen samt varandra. Konklusionerna från analysen är presenterade som nyckelfaktorer för att öka effektiviteten vid hantering av boxföden. Dessa nyckelfaktorer ger en ökad teoretisk förståelse, när syftet är att skapa ett effektivare materialflöde i form av boxar, i en monteringsmiljö. I denna forskning används nyckelfaktorerna som riktlinjer för att skapa en effektivare process för flödet av boxar. Det vill säga, att implementera nyckelfaktorerna teoretiskt i ett praktiskt sammanhang. För att ta fram en effektivare process har ett Business Case realiserats, som presenterar hur samtliga processer inom boxflödet borde organiseras på fallföretaget. Det vill säga, hur olika materialhanteringsoperationer och utrustningar borde användas för att uppnå en ökad effektivitet som helhet. Hur boxflödet ska organiseras presenteras som rekommendationer. Dessa bidrar med insikter och riktlinjer för hur Scanias motormontering borde organiseras, gällande deras interna materialflöde. Tillsammans med resterande forskningsfrågor uppfyller rekommendationerna syftet med forskningen.