| 11. |
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| 12. |
- Andersson, Kristin, 1976, et al.
(författare)
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Restarting Flexible Manufacturing Systems; Synthesis of Restart States
- 2006
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Ingår i: 2006 8th International Workshop on Discrete Event Systems. - 1424400538 ; , s. 201-206
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Konferensbidrag (refereegranskat)abstract
- A method for restart of flexible manufacturing systems is presented. Based on the execution restrictions on the operations in the control function, a number of restart states are synthesized off-line. We show that a restart from the closest preceding restart state never violates the execution restrictions. The presented method usually produces fewer restart states than an intuitive approach, and the number of paths used solely in the restart is considerably reduced, so less paths have to be updated and maintained. Instead, normal production paths are used in the restart when possible. The on-line part of the restart method can be executed by any PLC, and does not require the use of more powerful computers. The method is able to handle situations in which an error or manual intervention has lead to a machine configuration that is not consistent with any of the states in the control function
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| 13. |
- Andersson, Kristin, 1976, et al.
(författare)
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Restarting manufacturing systems; restart states and restartability
- 2010
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Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 7:3, s. 486-499
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Tidskriftsartikel (refereegranskat)abstract
- A method for restart after an error in a manufacturing system is introduced. The method is able to restart systems even after nonforeseen errors that cannot be planned for, and the online part of the restart method does not require use of more powerful computers than a standard Programmable Logic Controller. It is shown what properties the control function must have to ensure that there is at least one restart state for each controller state. Sufficient conditions to guarantee the possibility to restart a system regardless of where an error occurs are given, along with indications on how the system could otherwise be rebuilt to be restartable.
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| 14. |
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| 15. |
- Andersson, Kristin, 1976, et al.
(författare)
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Synthesis of Restart States for Manufacturing Cell Controllers
- 2009
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Ingår i: 2nd IFAC Workshop on Dependable Control of Discrete Systems, DCDS’09, Bari, Italy.
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Konferensbidrag (refereegranskat)abstract
- In earlier work we presented a method for restart of manufacturing systems. After correction of an error, the system resumes normal production by returning to a certain restart state in the control function, and from there reexecuting parts of the work schedule. The current paper concerns automatically finding (synthesizing) the restart states. The control function is modeled by finite automata, and properties of the restart states are defined. The synthesis process finds all possible restart states, guaranteeing that the execution restrictions are fulfilled during a restart, and that the production goals can be maintained. The error and the corrective actions preceding the restart need not be modeled; neither is it necessary to know the exact physical states of the machines at the time of the error. The number of restart states is finally minimized to reduce the need for extensions to the control program.
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| 16. |
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| 17. |
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| 18. |
- Bergagård, Patrik, 1984, et al.
(författare)
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Calculating Restart States for Systems Modeled by Operations Using Supervisory Control Theory
- 2013
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Ingår i: Machines. - : MDPI AG. - 2075-1702. ; 1:3, s. 116-141
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a supervisory control theory based offline method for calculating restart states in a manufacturing control system. Given these precalculated restart states, an operator can be given correct instructions for how to resynchronize the control system and the manufacturing resources during the online restart process. The proposed method enables restart after unforeseen errors. It is assumed that the control system is modeled by operations and that possible operation sequences emerge through dependencies between the operations. The paper shows how reexecution requirements may be included in the calculation to obtain a correct behavior for the restarted system. In addition, it is shown how to filter out restart states that require less effort for the operator during the online restart, and how to adapt the nominal production to always enable restart in desired restart states.
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| 19. |
- Bergagård, Patrik, 1984, et al.
(författare)
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Calculating restart states using reset transitions
- 2014
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Ingår i: Proceedings - IEEE International Conference on Robotics and Automation. - 1050-4729. ; , s. 3345-3350
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Konferensbidrag (refereegranskat)abstract
- This paper presents a supervisory control theory based offline approach for calculating restart states in a manufacturing control system. Given these precalculated restart states, an operator can be given instructions for how to correctly resynchronize the control system and the manufacturing resources during the online restart phase, as part of the error recovery process. Restarting from a restart state guarantees that all requirements on the nominal and the restarted productions are fulfilled. The paper includes an empirical comparison showing that the proposed approach enables restart states calculation for systems of sizes that could not be handled using an earlier presented approach.
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| 20. |
- Bergagård, Patrik, 1984, et al.
(författare)
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Deadlock avoidance for multi product manufacturing systems modeled as sequences of operations
- 2012
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Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. - 9781467304290 ; , s. 515 - 520
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Konferensbidrag (refereegranskat)abstract
- This paper demonstrates how industrial models of the sequential order between manufacturing operations may be connected with academic resource deadlock avoidance policies. Given a set of product types each modeled as a sequence of operations, the operations can be adapted to control concurrent manufacturing of multiple product instances, without resource deadlocks and with maximal flexibility. The given sequences of operations may contain routing flexibility, conjunctive and/or disjunctive resource requirements, and product assembly. Using a known deadlock avoidance approach, this paper presents how to transform the given operations into models required for the deadlock avoidance approach and how the calculated policy may be retransformed back into the operations.
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