No description available.

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.

This dissertation focuses on the material transport system design problem (MTSDP), integrating decisions of technology selection and flow network design. This research is motivated by the design of material transport systems (MTS) in manufacturing plants. The objective is to design a MTS with minimum lifetime costs, subject to service requirements, flow network restrictions, and limited resources. We characterize the MTSDP from the perspectives of task requirements, transport technology, and space utilization. A classification is proposed for transport technologies such that instances in the same class share the same properties, and a decision framework is proposed to emphasize the inter-relationships of three major decisions: task clustering, network connecting, and technology selection. We consider fixed and variable costs, arc capacities, and empty travel in our formulations. We propose two solution approaches for the MTSDP. The first is the compact formulation (CF) approach where the three major decisions are handled by a mixed integer non-linear programming (MINLP) formulation. Relaxation techniques are applied to linearize the model. The solution of the resulting linear formulation (MILP) provides a lower bound to that of MINLP. A tightened formulation reduces the computational time by a factor of 3.85. The experiment also shows that when control system costs are significant, designs with multiple-task clusters are more economical than those restricted to single-task clusters. The other approach is clustering/set partition (CSP), where the three decisions are decomposed and solved sequentially. In an example MTS design problem, three methods are compared: CSP, a GREEDY approach from the literature, and enumeration. CSP finds the optimal solution, while GREEDY results in 31% greater costs. A similar comparison with another example is made for the CF and CSP approaches. We apply the CSP approach in a case problem, using data from an auto parts manufacturer. We include flow path crossing constraints and perform experiments to determine solution quality over a range of small problem sizes. The largest difference from optimality is 3.34%, and the average is 0.98%. More importantly, based on these experiments, it seems there is no evidence that the difference percentage grows with an increase in the number of tasks.

The movement and handling of material are necessary activities, however, commonly regarded as waste. Moving and handling material more times and over longer distance than necessary is time consuming, costly and unproductive. Therefore, a suitable material handling (MH) system with appropriate facility layout is advocated. The purpose of this thesis is to explore options for material flow improvements and handling of material in production area. This comprises of a study of the material flow from storage to production areas and the handling of material in production section A. If necessary for improvements of material flow, a change in layout design will be recommended. The research approach for this thesis is a case study where data has been collected from documents, observations and interviews. The study shows that 9 % of the production time of one article is spent on manual material handling (MMH). These activities are classified as both waste and necessary, however not adding any value. The same applies for the material flow. Unnecessary distances of movements are caused by the current location of storage, operations and lack of proper structure for handling and moving material. The contribution of this study is a list of suggestions for improving the material flow and handling. Changes for improvements are, namely, availability of appropriate equipment, storing materials closer to the operations and investing in automation and vision systems with cameras of robots. The material flow and the way the material is handled can further beimproved by a change in the layout of the production area. Connecting and rearranging operations can shorter and ease the movement of material with ample space to handle the material.

No description available.

Published Article / This paper investigates the challenges of employing Van der Waals forces in micro-material handling since these forces are dominant in micro-material handling systems. The problems include the creation of a dust-free environment, accurate measurement of the micro-force, and the efficient picking and placing of micro-work pieces. The use of vacuum suction, micro-gripper's surface roughness, geometrical configuration and material type are presented as alternatives to overcome the challenges. An atomic force microscope is proposed for the accurate measurement of the Van der Waals force between the gripper and the micro-work piece.

Published Article / This paper explores the manipulation of Van der Waals' forces by geometrical parameters in a micro-material handling system. It was observed that the flat-flat interactive surfaces exerted the highest intensity of Van der Waals' forces followed by cone-flat, cylinder-flat, sphere-flat and sphere-sphere interactive surfaces, respectively. A conical micro-gripper proved to be versatile in manipulating the Van der Waals' forces efficiently in a 'picking up' and 'releasing' mechanism of micro-work parts. It was deduced that the pick-up position should be rough and spherical, and the placement position should be smooth and flat for an effective 'pick-and-place' cycle to be realised.

Thesis (PhD)--Stellenbosch University, 2012. / This doctoral dissertation focuses on the application of Van-der-Waals’ forces in micromaterial handling. A micro-material handling system consists of four main elements, which include: the micro-gripper, the micro-workpart, the picking up position and the placement position. The scientific theoretical frameworks of Van-der-Waals’ forces, presented by Van der Waals, Hamaker, London, Lifshitz, Israelachvilli, Parsegian, Rumpf and Rabinovich, are employed in exploring the extent to which these forces could be applied in a micromanufacturing situation. Engineering theoretical frameworks presented by Fearing, Bohringer, Sitti, Feddema, Arai and Fukuda, are employed in order to provide an in-depth synthesis of the application of Van-der-Waals’ forces in micro-material handling. An empirical or pragmatic methodology was adopted in the research. The Electron Beam Evaporation (e-beam) method was used in generating interactive surfaces of uniform surface roughness values. E-beam depositions of copper, aluminum and silver on silicon substrates were developed. The deposition rates were in the range of 0.6 – 1.2 Angstrom/s, at an average vacuum pressure of 2 x 10-6 mbar. The topographies were analysed and characterised using an Atomic Force Microscope and the corresponding rms surface roughness values were obtained. The Rumpf-Rabinovich equation, which gives the relationship of the exerted Van-der-Waals’ forces and the rms surface roughness values, is used to numerically model the results. In the final synthesis it is observed that the e-beam depositions of copper are generally suited for the pick-up position. Aluminum is suited for the micro-gripper and silver is suited for the placement position in an optimised micro-material handling system. Another Atomic Force Microscope was used in order to validate the numerically modelled results of the exerted Van- der-Waals’ forces. The aim was to measure the magnitude of Vander- Waals’ forces exerted by the e-beam depositions and to evaluate their applicability in micro-material handling operations. The measurements proved that Van-der-Waals’ forces exerted by the samples could be used for micro-material handling purposes on condition that they exceeded the weight of the micro-part being handled. Three fundamental parameters, ie: material type, geometrical configuration and surface topography were used to develop strategies of manipulation of micro-materials by Van-der- Waals’ forces. The first strategy was based on the material type variation of the interactive surfaces in a micro-material handling operation. This strategy hinged on the fact that materials have different Hamaker coefficients, which resulted in them experiencing a specific Van-der- Waals’ forces’ intensity during handling. The second strategy utilised variation in the geometrical configuration of the interacting surfaces. The guiding principle in this case was that, the larger the contact area was, the greater the exerted Van-der-Waals’ forces would be In the analytical modelling of Van-der-Waals’ forces with reference to geometrical configuration, a flat surface was found to exert more force than other configurations. The application of the design, for purposes of manufacturing and assembling (DFMA) criteria, also proved that flat interactive surfaces have high design efficiency. The third strategy was based on surface roughness. The rougher the topography of a given surface was, the lesser the Van-der-Waals’ forces exerted were. It was synthesised that in order for a pick-transfer-place cycle to be realised, the root-mean-square (rms) interactive surface roughness values of the micro-part (including the picking position, the micro-gripper, and the placement position) should decrease successively. Hybrid strategies were also identified in this research in order to deal with some complex cases. The hybrids combined at least two of the aforementioned strategies.

Tenhults Pressgjuteri AB is facing growth in expansion, which results in need of bigger premises. The company has bought an adjoining property to overcome this problem. This thesis givessuggestions on how the logistics of these properties should be managed, which transport system is most suitable to use, where deliveries will take place and how the stock will be set upin the new premises. To obtain relevant data and information have a description of the facts, measurements and calculations been made. Selections and ratings have been used to develop suitable alternative solutions. The payback-method has been used to calculate the investments. A specially designed evaluation chart forms the basis of which transport system to be used. Lastly, a sensivity analysishas been conducted to determine how reliable the results are. Deliveries and inventory have been determined based on the choice of transport system.The thesis shows that the choice of transport system depends on the volumes that are carried, distance and environmental conditions. The market offers both automated transport systems and systems that require a driver. The automated transport system willnot be profitable whenthe cargo volume is too small since the investment costs are significantly higher. However, the operating costs are low which makes it profitable with an increased cargo volume. Closer analysis of existing production flow could provide a more credibleresult. What also must be taken into account is thatthe costs is not preciseand may differ in reality. The costs are assumed to be so lifelike that they do not affect the result more than marginally. / Tenhults Pressgjuteri AB befinner sig i en expansionsfasoch är i behov av större lokaler. För att lösa dettahar företaget köpt upp en grannfastighet. Denna rapport ger förslag på hur logistiken mellan dessa fastigheter skall skötas,vilket transportsystem som är lämpligt att använda, var utleveranserskall ske,samt ett förslag på hurlager kan ställas uppi den nya fabriken. För att erhålla relevant data och information har nulägesbeskrivningar, mätningar och beräkningar gjorts. Urval och värderingar har använts för att ta fram lämpliga alternativ på lösningar. För att beräkna investeringskostnader har payback-metoden använts och ett specialframtaget värderingsschema ligger som grund för valet av transportsystem. Slutligen har en känslighetsanalys gjorts för att bestämma hur pålitligt resultatet är. Utleverans och lager har bestämts utifrån valet av transportsystem för att synkronisera på bästa sätt. Arbetet visar att val av transportsystem beror påvilka volymer som fraktas, avstånd och miljöförhållanden. Marknaden erbjuder både automatiserade transportsystem och system som kräver chaufför. I detta fall är fraktvolymen för litenför att ett automatiserat system skall vara lönsamt eftersominvesteringskostnaderna för ett sådant system är betydligt högre. Däremot är driftkostnaderna lågaför ett automatiserat systemoch vid en större fraktvolym sparas dessa driftkostnaderin då ingen bemanningskostnad tillkommer.Närmare undersökning av befintligt produktionsflöde kunde ge ett mer trovärdigt resultat då arbetet baseras på beräkningar från olika portar. Det som också skall tas i beaktande är att kostnaderna inte är exakta och kan komma att avvika i verkligheten. Kostnaderna antas dock vara så verklighetstrogna att de inte påverkar resultatet mer än marginellt.

Syfte – Syftet med denna studie är att undersöka hur materialhantering från inleverans till förmontering i ett tillverkande företag av kundanpassade produkter kan förbättras med avseende på kvalitet. Följande två frågeställningar ska uppfyllas för att besvara syftet: 1. Vilka faktorer påverkar materialhanteringen från inleverans fram till förmontering? 2. Hur kan faktorerna förbättras för att erhålla en effektiv materialhantering från inleverans fram till förmontering? Metod – En fallstudie genomfördes på ett företag inom husvagnsindustrin för att samla in empiriskt material. Intervjuer och observationer användes under fallstudien. Vidare genomfördes en litteraturstudie för att skapa ett teoretiskt ramverk. Den insamlade datan jämfördes och analyserades gentemot det teoretiska ramverket. Resultat – Flera faktorer som påverkar materialhanteringen har identifierats. Dessa var mänskliga faktorer och av Liker’s (2009) åtta slöserier var det sex stycken som identifierades. Flera potentiella förbättringsförslag rekommenderas till att förbättra respektive faktor. Några av förslagen till en mer effektiv materialhantering är bättre kommunikation och kontroll, standardiserade arbetsmoment samt implementering av periodinspektionssystem. Genom bättre samverkan mellan anställda kan bättre förståelse till varandras processer skapas vilken kan leda till att anställdas kompetens utnyttjas. Implikationer – Studien har visat på flera olika faktorer som påverkar materialhanteringen. Förbättringsförslagen som har rekommenderats till att effektivisera materialhanteringen är utav olika karaktärer vilken gör att implementationer kan vara både enkla och svåra. Det är viktigt att företag identifierar sina egna påverkande faktorer när de ska effektivisera materialhanteringen. Begränsningar – Under datainsamlingen har en enfallsstudie med en analysenhet genomförts. Dock kan en flerfallsstudie genomföras i syfte att generalisera studiens resultat ytterligare. Vidare har fokus varit från inleverans fram till förmontering. Detta har begränsat arbetet från andra avdelningar som kan ge andra perspektiv på materialhanteringen. / Purpose – The purpose of this study is to examine how the material handling from receiving to pre-assembly of a manufacturing company of customized products can be improved in terms of quality. The following two issues must be met in order to answer the purpose: 1. What factors influence the material handling from receiving until the pre-assembly? 2. How can the factors be improved to obtain an effective material handling from receiving until the pre-assembly? Method – A case study was conducted at a company in the caravan industry in order to gather empirical material. Interviews and observations were executed during the case study. Further on, a literature study was conducted to create a theoretical framework. The collected data was compared and analyzed against the theoretical framework. Findings – Several factors that affect the material handling have been identified. These were human factors and from Liker´s (2009) eight wastes were six identified. Several potential improvement methods were suggested for each factor. Some of the proposed improvement methods for a more efficient material handling is better communication and control, standardized operations and implementation of periodic inspection system. Through better collaboration between employees, a better understanding of each other's processes can generate a better use of their expertise. Implications – The study has revealed several factors that affect the material handling. Suggestions that have been recommended for improving the efficiency of material handling are based of different nature which means that the implementations can both be easy and difficult. It is important that companies identify their own influencing factors when they are going to improve the efficiency of material handling. Limitations – During the data collection, a single-case study with one analyzing unit was performed. However, a multi-case study can be performed in order to further generalize the results from the study. Furthermore, the focus has been from receiving until the pre-assembly. This has limited the work from other departments that can provide a different perspective on material handling.