| 231. |
- Miremadi, Sajed, 1983, et al.
(författare)
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Supervisor Computation and Representation: A Case Study
- 2010
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Ingår i: 10th International Workshop on Discrete Event Systems, Berlin; 30 August 2010 through 1 September 2010. - 1474-6670. - 9783902661791 ; 10:1, s. 275-280
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Konferensbidrag (refereegranskat)abstract
- When supervisory control theory is applied to industrial problems the need for a more expressive modeling formalism than plain event based automata is crucial. The models are typically built in a bottom-up structure where multiple sub-plant and sub-specifications together compose the full plant and specification, respectively. Typically, the enabling of an event in a sub-model may depend on the state of other sub-models. The standard approach is to synchronize on shared events. However, to build models of large industrial problems with complex constraints between sub-models are beyond many engineers abilities. One attempt to deal with this problem is to extend the plain automata with variables and allow guard conditions and action functions to be associated with transitions. This paper discusses the strengths and weaknesses of one such formulation that fits well together with the standard supervisory control theory. A related problem is how to represent the result after the synthesis procedure, i.e., the supervisor. In this paper we present an approach where the supervisor may be represented as extended guard conditions on the original sub-models. This allows an efficient and comprehensible representation of complex supervisors. Hence, it is preferable both from a user, as well as an implementation perspective. Both the modeling formalism based on extended finite automata and the way to represent the supervisor as extended guard conditions have been implemented in a supervisory control tool.
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| 232. |
- Miremadi, Sajed, 1983, et al.
(författare)
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Symbolic Computation of Nonblocking Control Function for Timed Discrete Event Systems
- 2012
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - 2576-2370 .- 0743-1546. ; , s. 7352-7359
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Konferensbidrag (refereegranskat)abstract
- In this paper, we symbolically compute a minimally restrictive nonblocking supervisor for timed discrete event systems, in the supervisory control theory context. The method is based on Timed Extended Finite Automata, which is an augmentation of extended finite automata (EFAs) by incorporating discrete time into the model. EFAs are ordinary automaton extended with discrete variables, guard expressions and action functions. To tackle large problems all computations are based on binary decision diagrams (BDDs). The main feature of this approach is that the BDD-based fixed-point computations is not based on “tick” models that have been commonly used in this area, leading to better performance in many cases. As a case study, we effectively computed the minimally restrictive nonblocking supervisor for a well-known production cell.
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| 233. |
- Miremadi, Sajed, 1983, et al.
(författare)
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Symbolic Computation of Reduced Guards in Supervisory Control
- 2011
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Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 8:4, s. 754-765
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Tidskriftsartikel (refereegranskat)abstract
- In the supervisory control theory, a supervisor is generated based on given plant and specification models. The supervisor restricts the plant in order to fulfill the specifications. A problem that is typically encountered in industrial applications is that the resulting supervisor is not easily comprehensible for the users. To tackle this problem, we introduce an efficient method to characterize a supervisor by tractable logic conditions, referred to as guards, generated from the models. The guards express under which conditions an event is allowed to occur to fulfill the specifications. To obtain tractable guard expressions, we reduce them by exploiting the structure of the given models. In order to be able to handle complex systems efficiently, the models are symbolically represented by binary decision diagrams and all computations are performed on these data structures. The algorithms have been implemented in a supervisory control tool and applied to an industrially relevant example.
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| 234. |
- Miremadi, Sajed, 1983, et al.
(författare)
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Symbolic On-the-Fly Synthesis in Supervisory Control Theory
- 2016
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Ingår i: IEEE Transactions on Control Systems Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6536 .- 1558-0865. ; 24:5, s. 1705-1716
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an efficient synthesis algorithm and its proof of correctness for computing the controllable, nonblocking, and minimally restrictive supervisor in the supervisory control theory. Conventional synthesis algorithms are based on backward reachability computations, where blocking and uncontrollable states are iteratively found by searching the entire state space several times until a fixed point is reached. Many unnecessary states may be visited in this kind of searching. In this paper, we present an alternative synthesis algorithm based on forward reachability, where a number of synthesis steps are performed during the reachability computations. This approach is inspired from the search techniques in Artificial Intelligence ( AI) planning. To handle large-scale problems, the algorithm performs the computations symbolically based on binary decision diagrams. The algorithm has been developed, implemented, and applied to several large-scale benchmarks. It is shown that, on average, the on-the-fly algorithm is more efficient than the conventional synthesis algorithms, in particular for problems with many uncontrollable states.
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| 235. |
- Miremadi, Sajed, 1983, et al.
(författare)
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Symbolic Representation and Computation of Timed Discrete-Event Systems
- 2014
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Ingår i: IEEE Transactions on Automation Science and Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-3783 .- 1545-5955. ; 11:1, s. 6-19
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we symbolically represent timed discrete-event systems (TDES), which can be used to efficiently compute the supervisor in the supervisory control theory context. We model a TDES based on timed extended finite automata (TEFAs): an augmentation of extended finite automata (EFAs) by incorporating discrete time into the model. EFAs are ordinary automata extended with discrete variables, where conditional expressions and update functions can be attached to the transitions. The symbolic computations are based on binary decision diagrams (BDDs). We show how TEFAs can be represented by BDDs. The main feature of this approach is that the BDD-based fixed point computations are not based on tick models that have been commonly used in this area, leading to better performance in many cases. The approach has been implemented and applied to a simple case study and several large-scale benchmarks. Note to Practitioners-In today's industry, the control functions are implemented to a great extent manually by designing a candidate and verifying it towards different properties to ensure that the control function is satisfactory. Designing a control function manually makes it a tedious, error-prone and time consuming process. Another way is to do this process automatically, referred to as the synthesis method. In the synthesis method, the designers model the system's behavior and the desired properties and feed them to an algorithm that can automatically generate the control function. Supervisory Control Theory (SCT) provides a powerful framework for automatically synthesizing safe and flexible control functions, referred to as supervisors, that restrict the system only when it necessary. For large-scale systems, synthesis typically suffers of from the state space explosion problem, that is the required memory to represent the states of the system is more than the available memory. To handle real-time systems, in this paper, we also incorporate time in the theory and show how the supervisor can be efficiently computed for large-scale systems.
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| 236. |
- Miremadi, Sajed, 1983, et al.
(författare)
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Symbolic Supervisory Control of Timed Discrete Event Systems
- 2015
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Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 23:2, s. 584-597
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Tidskriftsartikel (refereegranskat)abstract
- We symbolically compute a nonblocking, controllable, and minimally restrictive supervisor for timed discrete event systems (TDESs), in the supervisory control theory context. We model TDES based on timed extended finite automata (TEFAs): an augmentation of extended finite automata (EFAs) by incorporating discrete time into the model. EFAs are ordinary automata extended with discrete variables, where conditional expressions and update functions can be attached to the transitions. The controllability is defined based on the corresponding tick models of the TEFAs. A tick can be considered as an event that is generated by a global digital clock. The tick models suffer from a major problem: the state size is very sensitive to the clock frequency. We show how a controllable supervisor, equivalent to the one computed based on the tick models, can be obtained by eliminating the tick events. To tackle large problems, all computations are conducted symbolically using binary decision diagrams (BDDs). We show that, based on the proposed approach, a fixed point is reached earlier in the reachability analysis and that the size of the intermediate BDDs usually becomes smaller. The framework has been applied to a real industrial application and several benchmarks.
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| 237. |
- Nia, Nima, 1975, et al.
(författare)
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Efficient geometrical simulation and virtual commissioning performed in stamping
- 2012
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Ingår i: Proceedings of 2012 IEEE 17th International Conference on Emerging Technologies & Factory Automation (ETFA 2012). - Polen : IEEE. - 9781467347372 - 9781467347365 - 9781467347358 ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- In order to perform efficient geometrical simulation and virtual commissioning in stamping, three fields are investigated namely: simulation building time, collision detection time and optimization time. Hence, reducing time is the main theme of this paper. To reduce simulation building time and optimization time, an efficient stamping simulation model is built and tested. Collision detection time is examined by a relative motion method based on 3D to 2D geometrical collision detection. The presented results mean that simulation and virtual commissioning can be performed at least ten times faster compared to standard approaches.
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| 238. |
- Nia, Nima K., et al.
(författare)
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A faster collision detection method applied on a sheet metal press line
- 2011
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Ingår i: The 4th International Swedish Production Symposium. - Lund : Swedish Production Academy. ; , s. 467-472, s. 833-840, s. 833-840
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Konferensbidrag (refereegranskat)abstract
- Geometrical collision detection is a time and resource consuming simulation task. In order to decrease time and resources, a general method applicable for 2D motions has been developed. The method is useful in simulation cases where 3D CAD data is part of an iterative method, e.g. optimization. The method is based on a transformation of a general 3D problem to a 2D problem, eliminating the need of 3D CAD models. Press Line simulations during the last decade have been accepted as a quality improvement method. Today simulations of automated press lines are done for internal collision checks in dies and external collision checks against dies and material handling equipment. If these collisions are not detected in simulations, they result in delays, in introduction of a new product in the line, so called line tryout or later when the line is ramped up to decide rate. The results of these collisions are used for pre-die design, design of grippers, maintenance and production planning. In this paper a new method, based on 2D simplifications, is developed and tested successfully in a virtual model of a press line at Volvo Car Manufacturing. Die Uppers 2 917 708 triangles and Die Lowers 602 686 triangles where reduced to 58 and 90 points. The result of the method shows substantial reduction of geometry data and considerable improvement in collision detection evaluation time over general 3D algorithms in the tested case.
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| 239. |
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| 240. |
- Noori-Hosseini, Mona, 1982, et al.
(författare)
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A survey on efficient diagnosability tests for automata and bounded Petri nets
- 2013
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Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - 1946-0759 .- 1946-0740. - 9781479908622 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- This paper presents a survey and evaluation of the efficiency of polynomial diagnosability algorithms for systems modeled by Petri nets and automata. A modified verification algorithm that reduces the state space by exploiting symmetry and abstracting unobservable transitions is also proposed. We show the importance of minimal explanations on the performance of diagnosability verifiers.Different verifiers are compared in terms of state spaceand elapsed time. It is shown that the minimal explanationnotion involved in the modified basis reachabilitygraph, a graph presented by Cabasino et al. [3] for diagnosability analysis of Petri nets, has great impact alsoon automata-based diagnosability methods. The evaluationoften shows improved computation times of a factor1000 or more when the concept of minimal explanation isincluded in the computation.
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