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- Andersson, Kristin, 1976, et al.
(författare)
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Coordination of Operations by Relation Extraction for Manufacturing Cell Controllers
- 2010
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Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 18:2, s. 414-429
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Tidskriftsartikel (refereegranskat)abstract
- A method for generation of the control function for flexible manufacturing cells is presented in this paper. The control function is separated from the rest of the PLC program, and partitioned into a high-level part handling the operation sequence and a low-level part defining the execution process of the operations. The program structure enables high-level supervisor synthesis, which alleviates the state-space explosion problem. Information present in earlier steps of the development process is reused and processed, to automatically generate the automata needed for supervisor synthesis. An algorithm for generating automata, from the low-level safety requirements that restrict the high-level behavior, is presented. Algorithms are also presented for extracting the relations between the operations defining the work in the cell, from the synthesized supervisor. These relations give an easy-to-read representation of the control function that makes it interpretable by machine operators and maintenance personnel, an important feature to make the method applicable in an industrial setting. Hence, the control function generated by our method combines the benefits of a traditional supervisor, namely optimality and flexibility, with simplicity and clarity.
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| 3. |
- Andersson, Kristin, 1976, et al.
(författare)
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Generation of restart states for manufacturing cell controllers
- 2011
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Ingår i: Control Engineering Practice. - : Elsevier BV. - 0967-0661. ; 19:9, s. 1014-1022
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Tidskriftsartikel (refereegranskat)abstract
- A method for restart of manufacturing systems has recently been introduced. After correction of a fault. 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 automatic generation of the restart states, using discrete event systems theory. The generation process finds all possible restart states that guarantee that the execution restrictions are fulfilled during a restart, and that the production goals can be maintained. The number of restart states is minimized to reduce the number of necessary extensions to the control program. (C) 2011 Elsevier Ltd. All rights reserved.
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| 4. |
- 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. |
- Andersson, Kristin, 1976
(författare)
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Hierarchical Control and Restart of Flexible Manufacturing Systems
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Product life-cycles are constantly shortening, and the amount of new product types increases, for example in the automotive industry. Growing demands on flexibility and ability to decrease time to market has made it increasingly important to find methods for fast and accurate development of control programs for flexible manufacturing cells. There are several means to achieve this goal. Information present in early steps of the development process, as well as already developed software, should be reused when possible. In addition, formal methods should be used to automatically generate the control functions. To enable information reuse and usage of formal methods, a suitable structure has to be defined for the control program. Also, the methods have to be adapted to industrial work procedures.This thesis presents a methodology for generation of control functions for flexible manufacturing cells. The control program is structured hierarchically and partitioned into two parts. The first part corresponds to hardware and basic cell functions that are essentially the same for different manufacturing cells, and the second part is the actual control function, i.e. the part of the control program that is specific to each cell. By structuring the control information similarly in a hierarchical way, models of the system can be produced and supervisor synthesis can be used to generate the high-level control function. Because of the hierarchical approach, the problem of state space explosion is alleviated. A method for presenting the control function in a simple and easy-to-read way has also been developed. This facilitates the use of the control function by the maintenance personnel handling the manufacturing cell.Furthermore, this thesis contains an approach to solve the restart problem in flexible manufacturing systems. When an error has been detected and solved, it is often a difficult and time-consuming task to resynchronize the controller and the cell, and restart production. Most often the entire restart must be handled manually. The method presented in this thesis analyzes the control function off-line, and synthesizes certain restart states in it, from which a restart is guaranteed to be safe. In contrast to earlier methods, the issues of not increasing the complexity of the cell more than necessary, as well as how to physically move the machines in the cell to the restart states in a safe way, are addressed.
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| 9. |
- 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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| 10. |
- 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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