Notre thèse est consacrée à l’étude de la supervision des réseaux de Petri en vue de la conception de systèmes manufacturiers flexibles. L’objectif est la définition de stratégies de pilotage en ligne pour l’évitement de conflits et d’interblocages, dans le cadre de la théorie de la supervision. Le point de départ de notre travail est d’exploiterle graphe de marquage du réseau de Petri, ce qui permet en particulier d’obtenir des stratégies de commande maximalement permissive pour des problèmes d’évitement de conflits et d’interblocages. Nous avons ainsi introduit des techniques originales, manipulations d’inégalités ou réductions d’ensembles de marquages, destinées à diminuerla complexité algorithmique d’une telle méthode. Dans premier temps, nous avons focalisé sur la synthèse de superviseurs dits purs, ce qui correspond au cas particulier où l’ensemble de marquage légaux, est convexe.Cette optimisation est ensuite considérée du point de vue de la facilité de mise en oeuvre. Nous traitons ainsi de la minimisation de la structure du superviseur et de son coût d’implémentation en préservant une structure de supervision qui offre à la fois la permissivité maximale et une complexité de calcul raisonnable en vue d’utilisationsur des installations réelles. Aussi, nous avons cherché à réduire le nombre de places de contrôle nécessaires pour réaliser un superviseur maximalement permissif, pour cela nous avons formule le calcul du nombre minimal de places de contrôle en termes d’un problème de programmation linéaire. Afin d’affaiblir la complexité de ce calcul de superviseur, deux versions de l’algorithme sont proposées. Ce problème de minimisation de la taille dusuperviseur, quoique fondamental, n’est pas abordé aussi directement dans la littérature. Il s’agit là d’une première contribution.Dans u second temps, nous nous sommes intéressés aux réseaux de Petri à boucles (self-loops). Les boucles étant représentées par une variable qui s’ajoute dans la contrainte inégalité définissant l’ensemble de marquages légaux. Après avoir proposé une méthode de réduction du nombre d’inégalités ainsi que du superviseur optimalen se basant sur les approches et résultats précédents, nous avons établi une condition suffisante d’obtention d’un superviseur maximalement permissif permettant de traiter des ensembles de marquages légaux non convexes.Enfin nous proposons une méthode de synthèse de contrôleur pour une nouvelle classe de réseaux de Petri, avec des arcs inhibiteurs correspondant à des contraintes définies par des intervalles. La taille du contrôleur ainsi obtenu et défini en termes d’arcs inhibiteurs à intervalles s’en trouve réduite ainsi que par conséquent sont coût d’implémentation. / Reachability graph analysis is an important technique for deadlockcontrol, which always suffers from a state explosion problem since it requires togenerate all or a part of reachable markings.Based on this technique, an optimal or suboptimal supervisor with high behavioralpermissiveness can always be achieved. This thesis focuses on designing liveness enforcing Petri net supervisors for FMSs by considering their behavioralpermissiveness, supervisory structure, and computationnal complexity.The following research contributions are made in this thesis.1. The design of a maximally permissive liveness-enforcing supervisor for an FMSis proposed by solving integer linear programming problems (ILPPs).2. Structural complexity is also an important issue for a maximally permissivePetri net supervisor. A deadlock prevention policy for FMSs is proposed, which canobtain a maximally permissive liveness-enforcing Petri net supervisor while thenumber of control places is compressed.3. In order to overcome the computational complexity problem in MCPP and ensurethat the controlled system is maximally permissive with a simple structure, wedevelop an iterative deadlock prevention policy and a modified version.4. We consider the hardware and software costs in the stage of controlimplementation of a deadlock prevention policy, aiming to obtain a maximallypermissive Petri net supervisor with the lowest implementation cost. A supervisorconsists of a set of control places and the arcs connecting control places totransitions. We assign an implementation cost for each control place and controland observation costs for each transition. Based on reachability graph analysis,maximal permissiveness can be achieved by designing place invariants that prohibitall FBMs but no legal markings.5. Self-loops are used to design maximally permissive supervisors. A self-loop ina Petri net cannot be mathematically represented by its incidence matrix. Wepresent a mathematical method to design a maximally permissive Petri netsupervisor that is expressed by a set of control places with self-loops. A controlplace with a self-loop can be represented by a constraint and a selfloopassociated with a transition whose firing may lead to an illegal marking.

<p>  </p> <p>High-resolution enclosed channels/fibers are highly demanded by different disciplines such as microfluidic channels for chemical synthesis, bioreactors for drug metabolism, magnetic locomotor for drug delivery, and wearable devices for motion detection. However, the current fabrication techniques for enclosed channels/fibers are restricted to a few millimeters in size. Their manufacturing often involves time and energy-consuming multi-step processes with insufficient resolution. In this work, we demonstrate a novel co-flow-enabled fabrication method to resolve the technological restrictions in the fabrication of high-resolution enclosed channels/fibers with efficient production time, controllable morphologies, and high throughput manner.</p> <p>An epoxy-based enclosed microfluidic channel was first built. A non-reactive paraffin oil and a liquid resin were pumped into a 3D-printed co-flow generator and worked as core and shell fluids, respectively. The epoxy resin was cured by external heat stimulus. As a result, the reaction region was limited between the generator wall surface and the boundary of core flow, eliminating the need for precise control over the curing system. The experiment was successfully conducted to cure build resin channel inside copper and resin tubes with good shell thickness.</p> <p>Conductive hollow hydrogel microfibers were also fabricated by this method. Sodium Alginate and Calcium Chloride were chosen as the shell and core flows, respectively. The ionic crosslinking happens at the boundary of two flows and expands outwards across the radial direction. Thus, the diameter of the hollow channel can be easily adjusted by tuning the flow rate and the size of the core flow injection needle. PEDOT: PSS, a conductive polymer, was mixed with Sodium Alginate to impart fibers with excellent electrical conductivity. The synthesized hollow microfibers have shown their functionality in stretching movement detection by serving as a fundamental building element of motion sensors. </p>

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<p>  </p> <p>Manufacturing flexibility and human-centered designs are promising approaches to face the demand for individualized products. Human-robot assembly cells still lack flexibility and adaptability (VDI, 2017) using static control architectures (Bessler et al., 2020). Autonomous adaptation to human operators in short time horizons increases the willingness to work with cobots. Besides, monotonous static assembling in manufacturing operations does not accommodate the human way of working. Therefore, Human-Robot Collaboration (HRC) workstations require a work behavior adaptation accommodating varying work behavior regarding human mental and physical conditions (Weiss et al., 2021). The thesis presents the development of a cyber-physical HRC assembly station.</p> <p>Moreover, the thesis includes an experimental study investigating the influence of a cobot’s speed on human work behavior. The Cyber-Physical System (CPS) integrates the experiment's findings with event-based software architecture and a semantic knowledge representation. Thereby, the work focuses on demonstrating the feasibility of the CPS and the semantic model, allowing the self-adaptation of the system. Finally, the conclusion identifies the need for further research in human work behavior detection and fuzzy decision models. Such detection and decision models could improve self-adaptation in human-centered assembly systems.</p>

The purpose of this study was to identify the usage level of QR technologies and to examine the relationships between the organizational characteristics and the usage level of QR technologies and QR adoption in the U.S. apparel industry. Using the usage level of QR technologies and QR adoption as the dependent variables, the selected organizational characteristics, as independent variables, were: firm size (Le., numbers of employees, dollar amounts of sales volume), organizational strategy (i.e., prospector, analyzer, reactor, defender), product characteristics (i.e., product category, fashion change, seasonal change), and perception of QR benefits. The conceptual framework for this study was based on Rogers' adoption theory (1983). A factor approach was used to examine a cross-section of firms to determine significant characteristics influencing QR adoption. A random sample of 306 apparel manufacturers without locational limitation were selected from a purchased list. The sample was stratified by firm size (i.e., number of employees) and product category (Le., men's, women's, children's/infant's wear). A mail questionnaire was pilot tested for content validity and instrument reliability, and the revised questionnaire was sent to plant managers. Adjusted response rate was 47.0% (n=103). Regression, discriminant analysis, and nonparametrics were used to test the statistical significance of hypothesized relationships. The most frequently used technologies were small lot orders, short cycle cut planning, short cycle sewing, and production planning with customer. Firm size, organizational strategy, and fashion change were significantly related to the usage level of QR technologies. Firm size, organizational strategy, product category, and perception ofQR benefits were significantly related to QR adoption. Four QR elements (i.e., production planning, flexible manufacturing, inventory control, information sharing) were significantly related to QR adoption. / Master of Science

Thesis (M. Tech. (Engineering: Electrical)) -- Central University of technology, Free State, 2013 / In the industry, automation is used to optimize production, improve product quality and increase profitability. By properly implementing automation systems, the risk of injury to workers can be minimized. Robots are used in many low-level tasks to perform repetitive, undesirable or dangerous work. Robots can perform a task with higher precision and accuracy to lower errors and waste of material. Machine Vision makes use of cameras, lighting and software to do visual inspections that a human would normally do. Machine Vision is useful in application where repeatability, high speed and accuracy are important. This study concentrates on the development of a dedicated robot vision system to automatically place components exiting from a conveyor system onto Automatic Guided Vehicles (AGV). A personal computer (PC) controls the automated system. Software modules were developed to do image processing for the Machine Vision system as well as software to control a Cartesian robot. These modules were integrated to work in a real-time system. The vision system is used to determine the parts‟ position and orientation. The orientation data are used to rotate a gripper and the position data are used by the Cartesian robot to position the gripper over the part. Hardware for the control of the gripper, pneumatics and safety systems were developed. The automated system‟s hardware was integrated by the use of the different communication protocols, namely DeviceNet (Cartesian robot), RS-232 (gripper) and Firewire (camera).

"Fixtures form an important factor in traditional and modern flexible manufacturing systems, since fixture design directly affects manufacturing quality and productivity. Hence, it is necessary to evaluate quality of fixture design. The fixturing accessibility refers to machining feature accessibility and loading /unloading accessibility. The development of Computer Aided Fixture Design (CAFD) has simplified this task. Fixture design activities include setup planning, fixture planning and fixture configuration design. Fixture design verification comes next. Fixturing accessibility using Computer Aided Fixture Design is part of the verification process and has not received much attention till date. Machining feature accessibility analysis involves the evaluation of possible interference between fixture components and the cutting tool, which moves with pre-programmed tool path, while the loading and unloading accessibility relates to the ease with which the operator attaches/detaches the workpiece from the surrounding manufacturing environment. This research has three main focuses. The first focus is to evaluate machining feature accessibility, by integrating fixture designs in SolidWorks and the NC programming in Esprit. The main goals are evaluation of fixture design for any kind of interference between tool/workpiece/fixtures and enable Esprit to indicate interference, if any. The next step is to modify the fixture design accordingly and thus, finally obtain an interference free fixture design by reiteration. The second and third focuses deal with analysis of loading and unloading accessibility. A simulation based approach is applied to evaluate loading/unloading paths for different workpiece-fixture setups and checking interference in a dynamic mode. Then the third focus is to develop analysis method and criteria of comparisons of fixturing accessibility in different fixture designs. Thus, this research establishes methods of analysis for accessibilities in fixture design. Also, the guidelines for good fixture design will prove to be of great use to both, the beginners as well as the experienced fixture designers in this field. "

Made available in DSpace on 2015-03-05T13:56:58Z (GMT). No. of bitstreams: 0 Previous issue date: 20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho tem como objetivo a geração de um modelo de escalonamento aplicado ao Jobshop Scheduling Problem num Sistema de Manufatura Flexível que considera o tempo total de produção (makespan), o tempo total de atraso, o tempo total parado e o tempo total ocioso.O modelo proposto é composto por: (a) uma função objetivo que reflete, através de suas variáveis de decisão e seus pesos respectivos, as estratégias de otimização, e de (b) uma arquitetura que está dividida em cinco fases. O modelo utilizou o algoritmo Busca Tabu que,através de duas estratégias de geração de vizinhanças, busca a otimização da função objetivo. A arquitetura do modelo baseia-se na extração da demanda de produção, na Tecnologia de Grupo, nas Regras de Despacho, no Algoritmo Busca Tabu e na gravação do plano de produção, para tratar os Problemas de Seleção de Partes (Famílias de Partes) e do Escalonamento. Foram realizados, através de um estudo de caso, diversos experimentos que possibilitaram a comparação de estratégias de otimiza / This paper has the aim of generating a scheduling model applied to Job-shop Scheduling Problem in Flexible Manufacturing System, which considers the makespan, total tardiness time, total stop time, total idle time. The model proposed is composed for: (a) an objective function that reflects, through its variables of decision and its weights, the optimization strategies, and (b) arquitecture that is divided in five phases. The model used the Tabu Search algorithm which, through two strategies neighborhoods generation, searching the objective function optimization. The model architecture is based on extraction of production demand, in the Group Technology, in the Dispatching Rules, in the Tabu Search algorithm and save production plan, to deal the Part Selections (Part Families) and Scheduling Problems.Through a study of case, it has been realized several experiments which makes it possible the comparison of optimization strategies and real scheduling, and which proves conflicts in decision variables. For mo

Made available in DSpace on 2015-03-05T13:58:26Z (GMT). No. of bitstreams: 0 Previous issue date: 1 / Universidade do Vale do Rio dos Sinos / Neste trabalho é abordado o Problema de Escalonamento em um job shop, considerando restrições de datas de entrega, turnos de produção e tempo de setup entre operações. Considera-se um ambiente de Sistema de Manufatura flexível, que dado ao alto nível de automação, permite a previsibilidade dos processos de carregamento dos recursos à área de processamento. O problema foi modelado através de uma Função Objetivo fn composta de três variáveis de decisão. A importância da contribuição de cada variável para o valor de fn é gerida pela atribuição de valores aos pesos associados às variáveis. Na abordagem proposta, são utilizadas técnicas de Tecnologia de Grupo e Busca Tabu. O modelo implementado é uma modificação da técnica i TSAB, proposta por Nowicki e Smutnicki, a qual apresenta bons resultados no tratamento do Problema de Escalonamento em um job shop PEJS clássico. A consideração das restrições adicionais ao PEJS aumenta a complexidade do modelo implementado, porém, deixa o problema mais próximo da realidade. / In this work the Job Shop Scheduling Problem is studied, considering due dates, production turns and tooling constraints. This problem is applied in a Flexible Manufacturing System, which possesses high degree of automation, allowing previsibility in the processes of loading and unloading jobs on the machines. The problem is modeled through a objective function fn composed by three weighted decision variables. The importance of each variable in the fn final value is managed through assignment of values to the weights of these variables. In the proposed approach, it was used Group Technology and Tabu Search techniques. The implemented model is a modification of the i TSAB technique, proposed by Nowicki and Smutniki. The consideration of adicional constraints in the Job Shop Scheduling Problem increases the complexity of the implementation, otherwise, makes the problem closer to the industrial reality. The model was validated using benchmark instances, in which the data from the addional constraints were added.