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- Kobetski, Avenir, 1977
(författare)
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Optimal Coordination of Flexible Manufacturing Systems, with Automatic Generation of Collision- and Dealock-Free Working Schedule
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ever more rapidly changing markets pose high demands on the modern industry, often making it necessary to have varied and frequently updated product portfolios. As a consequence, modern industrial systems need to be easily adaptable to different kinds of products, which makes the use of flexible manufacturing systems (FMS) increasingly popular. An FMS generally contains a number of moving actors, such as production robots, conveyor belts, etc, that can be configured for different tasks. However, a big challenge with FMS is their high complexity, which makes FMS coordination a time and resource demanding undertaking. In this thesis, the challenge of FMS coordination is accepted, with the goal of developing methods for automatic and off-line generation of a correct, safe and time optimal working logic for the moving actors of a given FMS. This means that the order of operations in the studied FMS should minimize the total cycle time of the system and respect all specifications, while avoiding collisions and blocking situations between the moving actors.To represent possible and specified FMS behavior, deterministic finite automata (DFA) models are used. A method to automatically generate such models is presented, whereafter much work is laid at developing optimization methods, applicable to DFAs. While we start out with considering normal FMS behavior, a method for treating FMS that suffer from uncontrollable operations, such as machine breakdown or manually ordered product inspection, is also presented. When relating our results to the real world, we noted that the optimal control logic often induces uneven movement patterns to the FMS actors. This inconvenience is thus studied and amended.Finally, combining our results with some existing techniques, a framework for automatic generation of control code from 3D simulation models of FMS is presented. In developing this framework, functionality common to most robot simulation environments is used where possible to facilitate the portability of the approach between different simulation tools.
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- Kobetski, Avenir, 1977
(författare)
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Optimization of Manufacturing Cells Using Discrete Event Models
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the name suggests, this thesis is concerned with flexible manufacturing systems (FMS) and their way of living. More specifically, the main objective of this workis to generate working schedules for the moving objects of the manufacturing cells. These schedules should be optimal in some sense, while situations involving several moving objects blocking each other or colliding should be avoided.If such working schedules could be generated automatically and efficiently, the flexibility together with the productivity of the manufacturing cells would be affected positively. To guarantee safe FMS functionment, production cells are modeled in terms of discrete event systems (DES), whereafter supervisory control theory helps to prevent undesirable behaviour. The modeling procedure is done automatically, leaving the field open for the efficiency considerations. In this work, several methods for exploring DES in search for a time optimalworking sequence, based on the ideas of mixed integer linear programming, A* search and visibility graphs, are presented and studied with respect to their efficiency and robustness. In the final part of this work, the focus is shifted towards the reduction of the acceleration load imposed on the moving objects in a production cell. Thisleads to a decrease of strain on the manufacturing equipment, thus prolonging the productive life of the FMS. Naturally, the acceleration reduction should be, and thus is, done without compromising such qualities of the working schedule as time optimality, collision- and deadlock avoidance.
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- Kobetski, Avenir, 1977, et al.
(författare)
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Scheduling Algorithms for Optimal Robot Cell Coordination - a Comparison
- 2006
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Ingår i: Proc. of IEEE Conference on Automation Science and Engineering. - 1424403103 ; , s. 381-386
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Konferensbidrag (refereegranskat)abstract
- Flexibility is the keyword in the modern industrial world. Automatic generation of collision- and blocking free, time optimal schedules for industrial robot cells is thus motivated. While a lot of attention has been paid to the control of industrial systems, as well as to the development of general optimization algorithms, there is still a need to properly combine these two research areas. This paper discusses two scheduling algorithms, designed for industrial robot cells, in terms of performance. A novel heuristic to an A*-based algorithm, operating on Discrete Event Systems, is proposed and benchmarked against the well-known MILP algorithm.
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- Kobetski, Avenir, 1977, et al.
(författare)
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Scheduling of Discrete Event Systems Using Mixed Integer Linear Programming
- 2006
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Ingår i: 8th International Workshop on Discrete Event Systems.
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Konferensbidrag (refereegranskat)abstract
- To remain competitive, the modern industry strivefor flexibility. Recently, a method for automatic generation of control code from a 3D simulation model of a flexible manufacturing system was developed. Finite automata and Supervisory Control Theory (SCT) was used to guarantee the required behaviour of the system. This paper moves one step further. A method for automatic conversion between deterministic finite automata and Mixed Integer Linear Programming (MILP) formulation is presented. This allows to efficiently combine SCT and MILP to automatically generate time-optimal, collision-freeand non-blocking working schedules.
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- Kobetski, Avenir, 1977, et al.
(författare)
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Time-Optimal Coordination of Flexible Manufacturing Systems Using Deterministic Finite Automata and Mixed Integer Linear Programming
- 2009
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Ingår i: Discrete Event Dynamic Systems: Theory and Applications. - : Springer Science and Business Media LLC. - 0924-6703 .- 1573-7594. ; 19:3, s. 287-315
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Tidskriftsartikel (refereegranskat)abstract
- Automation and flexibility are often mentioned as key concepts in modern production industry. To increase the level of flexibility, deterministic finite automata (DFA) can be used to model, specify and verify the production systems. Often, it is also desirable to optimize some production criteria, such as for example the cycle time of a manufacturing cell. In this paper, a method for automatic conversion from DFA to a mixed integer linear programming (MILP) formulation is first presented. This conversion is developed for a number of DFA structures that have shown to be useful in practical applications. Special attention is paid to reducing the search region explored by the MILP solver. Second, a conversion from the MILP solution to a DFA supervisor is described. This allows to combine the advantages of DFA modeling with the efficiency of MILP and supervisory control theory to automatically generate time-optimal, collision-free and non-blocking working schedules for flexible manufacturing systems.
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| 8. |
- Kobetski, Avenir, 1977, et al.
(författare)
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Velocity balancing in flexible manufacturing systems
- 2008
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Ingår i: 9th International Workshop on Discrete Event Systems, WODES' 08; Goteborg; Sweden; 28 May 2008 through 30 May 2008. - 9781424425921 ; , s. 358-363
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Konferensbidrag (refereegranskat)abstract
- Practical incentives motivate the development of optimal working schedules in manufacturing environments. Most often, such development is focused on time optimality issues, without concern for how the resulting schedules are executed. In practice, this often leads to an unnecessarily high amount of acceleration during a production cycle, which affects negatively the productive life of the manufacturing equipment. In this paper, we present and compare several methods to reduce the acceleration load in a production cell by processing a given working schedule, without compromising such features of the schedule as cycle time optimality, collision- and deadlock avoidance.
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- Kobetski, Avenir, 1977, et al.
(författare)
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Velocity Balancing in Flexible Manufacturing Systems
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Practical incentives motivate the development of optimal working schedules in manufacturing environments. Most often, such development is focused on time optimality issues, without concern for how the resulting schedules are executed. In practice, this often leads to an unnecessarily high amount of acceleration during a production cycle, which affects negatively the productive life of the manufacturing equipment. In this paper, we present and compare several methods to reduce the acceleration load in a production cell by processing a given working schedule, without compromising such features of the schedule as time optimality, collision- and deadlock avoidance.
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