| 1. |
- Alenljung, Tord, 1977, et al.
(författare)
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Formal verification of PLC controlled systems using sensor graphs
- 2009
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Ingår i: 2009 IEEE Conference on Automation Science and Engineering, CASE 2009, Bangalore, India. - 9781424445783 ; , s. 164-170
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Konferensbidrag (refereegranskat)abstract
- This paper describes how a system, consisting of a discrete controller (e.g. a PLC) that controls a physical plant/process, can be formally verified. The physical process is assumed to be modeled using Sensor Graphs, a discrete event modeling language directed at physical systems with binary and identity sensors (e.g. RFID). The formal and graphical syntaxes of Sensor Graphs are presented and exemplified. The "semitimed" semantics is defined considering a process model together with a controller model, represented as a discrete state equation. Finally, it is shown how requirements on the closedloop system, represented by a Sensor Graph and a controller model, can be verified using the model checker Cadence SMV.
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| 2. |
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| 3. |
- Alenljung, Tord, 1977, et al.
(författare)
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Semantics of sensor activation graphs
- 2006
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Ingår i: Proceedings of the 2006 IEEE Conference on Automation Science and Engineering, Shanghai, China.
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Konferensbidrag (refereegranskat)
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| 4. |
- Alenljung, Tord, 1977, et al.
(författare)
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Simplified modeling of manufacturing systems: an introduction to sensor activation graphs
- 2005
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Ingår i: Automation Science and Engineering, 2005. IEEE International Conference on. ; , s. 261- 266
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Konferensbidrag (refereegranskat)abstract
- This paper presents a graphical modeling formalism, sensor activation graphs, which simplifies the design of discrete event models for a class of physical systems common within manufacturing industry. Sensor activation graphs captures, in an intuitive way, the relations between binary sensors, the physical entities that activate them, and the actuators of the system. Models expressed as sensor activation graphs are in most cases significantly simpler than corresponding automata or Petri net models. The presented formalism support two levels of detail, one that gives the general view on the order of sensor activation, and one with full control semantics that incorporates guard conditions on transitions. In addition, an algorithm for converting sensor activation graphs into a number of small deterministic finite state automata is presented.
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| 5. |
- Andersson, Kristin, 1976, et al.
(författare)
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Generation of restart states for manufacturing systems with discarded workpieces
- 2009
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Ingår i: 2009 IEEE Conference on Automation Science and Engineering, CASE 2009, Bangalore, India. - 9781424445783 ; , s. 191-196
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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 reexecutes parts of the work schedule. In the present paper the method is extended to handle also systems where some, but not necessarily all, workpieces are discarded during the error correction preceding the restart. The restart process must then replace the discarded workpieces with new ones. The workpieces that remain in the cell may limit the possibilities of executing certain operations needed to process the new workpieces correctly, thus complicating the restart. Properties of the restart states that guarantee a correct restart are defined, typical situations that make the system impossible to restart are presented, and some suggestions are given for modifications that make the system restartable.
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| 6. |
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| 7. |
- 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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| 8. |
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| 9. |
- 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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| 10. |
- Bengtsson, Kristofer, 1979, et al.
(författare)
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Aspect-Oriented Programming for Manufacturing Automation Control Systems
- 2009
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Ingår i: 13th IFAC Symposium on Information Control Problems in Manufacturing Technology, INCOM’09, Moscow, Russia. - 1474-6670. - 9783902661432 ; :PART 1, s. 668-673
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Konferensbidrag (refereegranskat)abstract
- The languages defined by the standard IEC 6-1131 for Programm\-able Logic Controllers (PLCs), have both benefits and drawbacks compared to object-oriented programming languages. For example, the current programming approach is good for maintaining the system, since it is easy to program and comprehend for a plant floor personal with limited programming experience. The main drawbacks are reusability, code dependability and flexibility. This paper proposes an aspect-oriented programming (AOP) approach as an alternative solution, which can keep the benefits and eliminate the drawbacks. AOP is an emerging programming methodology in computer science, which helps the programmer by separating different crosscutting concerns in the program. These crosscutting concerns and tangled behavior are especially important issues in PLC programming, which makes AOP a suitable approach. The paper describes how to adapt the AOP methodology into PLC program development and how it can benefit the control design process.
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