| 11. |
- Bengtsson, Kristofer, 1979, et al.
(författare)
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Sequence Planning Using Multiple and Coordinated Sequences of Operations
- 2012
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Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 9:2, s. 308-319
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Tidskriftsartikel (refereegranskat)abstract
- The sequential behavior of a manufacturing system results from several constraints introduced during the product, manufacturing, and control logic development. This paper proposes methods and algorithms for automatically representing and visualizing this behavior from various perspectives throughout the development process. A new sequence planning approach is introduced that uses self-contained operations to model the activities and execution constraints. These operations can be represented and visualized from multiple perspectives using a graphical and formal language called Sequences of Operations (SOPs). The operations in a manufacturing system are related to each other in various ways, due to execution constraints expressed by operation pre- and post-conditions. These operation relations include parallel, sequence, arbitrary order, alternative, and hierarchy relations. Based on the SOP language, these relations are identified and visualized in various SOPs and sequences. A software tool, Sequence Planner, has been developed, for organizing the operations into SOPs that visualize only relevant operations and relations. Note to Practitioners-This paper proposes methods and algorithms for a new sequence planning approach in which sequences are automatically created based on the relations among operations instead of having to be manually constructed. Using various views, the sequences of operations related to, for example, part flow, robot operations, and operator tasks, can be visualized. The use of various views helps the user better understand the relations between cell control and mechanical design, and between product design and total system behavior.
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| 12. |
- Bengtsson, Kristofer, 1979, et al.
(författare)
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Towards Sequence Planning Based on Configurable Product and Manufacturing System Platforms
- 2010
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Ingår i: Proceedings of the 8th International Conference NordDesign 2010. - 9789163370649 ; Vol. 2, s. 467-476
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Konferensbidrag (refereegranskat)abstract
- Operation sequences are central in the interaction between product and manufacturing development. This is because the sequences create an understanding of how a product is manufactured. The high degree of complexity in managing and planning manufacturing operations during the development of a configurable product and manufacturing platform requires a new and more flexible sequence planning approach. By integrating configurable product and manufacturing system platform descriptions, product variance, manufacturing system flexibility, and product and manufacturing system complexity can all be efficiently adapted to each other by considering interrelated constraints. Such an integrated platform system also provides the information required to describe the operations needed to manufacture an instantiated product variant. This paper proposes an approach in which sequences are viewed based on the relations among self-contained operations, thus saving engineers from manually constructing sequences for each product variant. The sequences of operations related to, for example, the part flow for a specific platform configuration, robot operations or operator tasks can be automatically visualized through the use of different perspectives.
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| 13. |
- Björkenstam, Staffan C, 1981, et al.
(författare)
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Energy Efficient and Collision Free Motion of Industrial Robots using Optimal Control
- 2013
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Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089.
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Konferensbidrag (refereegranskat)abstract
- In a production plant for complex assembled products there could be up to several hundred of robots used for handling and joining operations. Thus, improvement in robot motions can have a huge impact on equipment utilization and energy consumption. These are two of the most important aspects of sustainability in a production system. Therefore, this paper presents an algorithm for generating efficient and collision free motion of industrial robots using path planning and direct transcription methods for numerical optimal control. As a measure of efficiency for moving between configurations we use a combination of the energy norm of the applied actuator torques and the cycle time. Velocity and torque limits are handled and modeled as hard constraints. However, more general problems can be solved by the same approach. Our novel algorithm solves the problem in three steps; (i) first a path planning algorithm calculates an initial collision free path, (ii) a convex optimal control problem is then formulated to follow this path, and finally (iii) a nonlinear optimal control problem is solved to iteratively improve the trajectory. The resulting trajectory is guaranteed to be collision free by restrictions in the configuration space based on a local sensitivity analysis. The algorithm has been successfully applied to several industrial cases demonstrating that the proposed method can be used effectively in practical applications.
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| 14. |
- Carlsson, Henrik, 1979-, et al.
(författare)
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Automated Generation of Discrete Event System Simulation Models for Flexible Automation
- 2011
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Ingår i: The 21st International Conference on Flexible Automation and Intelligent Manufacturing. - 9789868729100 ; , s. 825-832, s. 825-832
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Konferensbidrag (refereegranskat)abstract
- Flexible automation cells with rapid product changes are an important competitive advantage for industries today. These cells can increase a company’s productivity and thereby increase their profits. A flexible cell shall be able to handle different products with none or minimal changes to the cell itself. A powerful tool, which can be used to analyse and verify such cells, is discrete event system simulation. Problems such as potential bottlenecks, deadlocks, answers to "what-if" questions and the level of resource utilisation can be gathered. The drawback of discrete event system simulation is that the modelling task is both time consuming and difficult to accomplish. Furthermore, state-of-the-art discrete event system simulation tools that are used in the industry today are not suitable for flexible automation. If the production scenario is changed, e.g. introduction of a new product, the simulation and modelling has to be redone and this is both time consuming and tedious. In this paper a new approach will be presented that enables discrete event simulation models to be generated automatically. The models are generated from information retrieved from a PLM/PDM database system, which is shared among other engineering tools such as robot simulation, CAD and process planning. Hence, when the cell and the database are updated a new model can easily be generated. The database is also connected to the real cell so up-to-date data can be retrieved from the real cell. The model generator described in this paper was implemented and tested in a discrete event system simulation tool and showed promising results. With this approach it is possible to handle flexible automation cells more effectively in a process planning stage.
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| 15. |
- Carlsson, Henrik, 1979-, et al.
(författare)
-
Methods for Reliable Simulation-Based PLC Code Verification
- 2012
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Ingår i: IEEE Transactions on Industrial Informatics. - 1941-0050 .- 1551-3203. ; 8:2, s. 267-278
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Tidskriftsartikel (refereegranskat)abstract
- Simulation-based programmable logic controller (PLC) code verification is a part of virtual commissioning, where the control code is verified against a virtual prototype of an application. With today's general OPC interface, it is easy to connect a PLC to a simulation tool for, e. g., verification purposes. However, there are some problems with this approach that can lead to an unreliable verification result. In this paper, four major problems with the OPC interface are described, and two possible solutions to the problems are presented: a general IEC 61131-3-based software solution, and a new OPC standard solution.
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| 16. |
- Falkman, Petter, 1972, et al.
(författare)
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Vendor independent control database for virtual preparation and formal verification
- 2011
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Ingår i: International Conference on Information and Automation, ICIA 2011; Shenzhen; 6 June 2011 through 8 June 2011. - 9781457702686 ; , s. 851-857
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Konferensbidrag (refereegranskat)abstract
- It is very advantageous to use virtual techniques for testing and developing new hardware and software systems within a manufacturing system. It is, however, of greatest importance that the virtual model can be trusted so that the results of the development and tests can be directly transferred to a real system without any manual last minute changes. In order to trust the result, formal verification techniques can be applied and by doing that guaranteeing a correct system behavior. Today, there is a gap between how systems are modeled in simulation softwares and formal verification softwares and it is therefore hard to perform formal verification. In order to limit the risk of introducing errors it is also important that the specifications created in the simulation softwares are not manually converted into formal languages. The present paper presents a method for sharing information between the different virtual development tools and formal verification tools. A database, storing necessary control information for verification and controller synthesis, is presented.
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| 17. |
- Fasth, Åsa, 1978, et al.
(författare)
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From Task Allocation Towards Resource Allocation when Optimising Assembly Systems
- 2012
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Ingår i: Procedia CIRP - Elsevier. - 2212-8271. ; 3, s. 400-405
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Tidskriftsartikel (refereegranskat)abstract
- The article discusses the question; is it possible to reach route flexibility and system proactivity through resource allocation and task optimisation. In order to answer this, differences between three types of optimisation regarding task and resource allocation are discussed: Global Task and Resource optimisation, Task optimisation and local resource allocation, but with resource alternatives, Task optimisation and local resource allocation (optimisation), with prioritised resources, shown as a possible solution in this paper in order to increase the route flexibility and proactivity in the system planning. An example of the last approach will be shown using a logic language (SOP) with help of software tool called Sequence Planner (SP).
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| 18. |
- Fei, Zhennan, 1984, et al.
(författare)
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A Symbolic Approach to Large-Scale Discrete Event Systems Modeled as Finite Automata with Variables
- 2012
-
Ingår i: 2012 IEEE Conference on Automation Science and Engineering (CASE). - 2161-8070. - 9781467304290 ; , s. 502 - 507
-
Konferensbidrag (refereegranskat)abstract
- The state-space explosion problem, resulting from the reachability computation of the synthesis task, is one of the main obstacles preventing the supervisory control theory (SCT) from having an industrial breakthrough. To alleviate this problem, a well-known strategy is to utilize binary decision diagrams (BDDs) to compute supervisors symbolically. Based on this principle, we present in this paper an efficient reachability approach to large-scale discrete event systems modeled as finite automata with variables. By making use of the disjunctive partitioning technique, the proposed approach partitions the transition relation of a considered system into a set of partial transition relations according to included events. Then those partial transition relations are selected systematically to per- form the reachability computation. Experimental results show that more iterations might be required to compute the fixed point, but the intermediate BDDs are smaller. The approach has been implemented in the supervisory control tool Supremica and the efficiency is demonstrated on a set of industrially relevant benchmark problems.
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| 19. |
- Fei, Zhennan, 1984, et al.
(författare)
-
Efficient Symbolic Supervisor Synthesis for Extended Finite Automata
- 2014
-
Ingår i: IEEE Transactions on Control Systems Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6536 .- 1558-0865. ; 22:6, s. 2368-2375
-
Tidskriftsartikel (refereegranskat)abstract
- The state-space explosion problem, resulting from the reachability computations in controller synthesis, is one of the main obstacles preventing supervisory control theory from having an industrial breakthrough. To alleviate this problem, a strategy is to symbolically perform the synthesis procedure using binary decision diagrams. Based on this principle, the work presented in this brief develops an efficient symbolic reachability approach for discrete event systems that are modeled as finite automata with variables, referred to as extended finite automata. Using a disjunctive event partitioning technique, the proposed approach first partitions the transition relation of the considered system into a set of partial transition relations. These partial transition relations are then selected systematically to perform the reachability analysis, which is the most fundamental challenge for synthesizing supervisors. It has been shown through solving a set of benchmark supervisory control problems for EFA that the proposed approach significantly improves scalability in comparison with the previously published results.
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| 20. |
- Fei, Zhennan, 1984, et al.
(författare)
-
Efficient Symbolic Supervisory Synthesis and Guard Generation: Evaluating partitioning techniques for the state-space exploration
- 2011
-
Ingår i: ICAART 2011 - Proceedings of the 3rd International Conference on Agents and Artificial Intelligence. - 9789898425409 ; 1, s. 106-115
-
Konferensbidrag (refereegranskat)abstract
- The supervisory control theory (SCT) is a model-based framework, which automatically synthesizes a supervisor that restricts a plant to be controlled based on specifications to be fulfilled. Two main problems, typically encountered in industrial applications, prevent SCT from having a major breakthrough. First, the supervisor which is synthesized automatically from the given plant and specification models might be incomprehensible to the users. To tackle this problem, an approach was recently presented to extract compact propositional formulae (guards) from the supervisor, represented symbolically by binary decision diagrams (BDD). These guards are then attached to the original models, which results in a modular and comprehensible representation of the supervisor. However, this approach, which computes the supervisor symbolically in the conjunctive way, might lead to another problem: the state-space explosion, because of the large number of intermediate BDD nodes during computation. To alleviate this problem, we introduce in this paper an alternative approach that is based on the disjunctive partitioning technique, including a set of selection heuristics. Then this approach is adapted to the guard generation procedure. Finally, the efficiency of the presented approach is demonstrated on a set of benchmark examples.
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