| 1. |
- 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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| 2. |
- Dahl, Martin, 1984, et al.
(författare)
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Integrated Virtual Preparation and Commissioning: supporting formal methods during automation systems development
- 2016
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Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 49:12, s. 1939-1944
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Konferensbidrag (refereegranskat)abstract
- Virtual commissioning – the development and validation of industrial control systems against a simulation model – is attracting interest in the automotive industry. The main motivation for its use is that control systems can start to be integrated and tested before the construction of the physical system. In addition to this, the ability to continuously test can lead to increased reliability and enables better coping with late changes. At the same time, using formal methods during production preparation and control system design promise similar benefits. Formal methods however, are not seeing the same surge in interest – they are rarely used in the automotive industry. In this paper a framework is proposed, Integrated Virtual Preparation and Commissioning, where virtual commissioning models are used as a base for preparation and control system implementation assisted by formal methods. The extensive use of simulation in virtual commissioning allows computation results from formal methods to be continuously validated by visual inspection and using existing analysis tools (e.g. collision detection methods). The framework is applied in a case study, where the combination of a simulation model and a formal model is used as an aid in generating operation sequences for validation during production preparation. The resulting formal model can be used to study the behavior of the production system before a control system has been implemented.
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| 3. |
- Dahl, Martin, 1984, et al.
(författare)
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Sequence Planner: Supporting Integrated Virtual Preparation and Commissioning
- 2017
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Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 50:1, s. 5818-5823
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Konferensbidrag (refereegranskat)abstract
- It is essential to understand the operation sequences of a production system when designing or changing it. This paper will demonstrate how the software tool Sequence Planner (SP) not only supports this understanding by sequence visualization, but also improves the solution using optimization and verification. SP is a tool for modeling and analyzing automation systems. The tool has been developed since 2007 with an initial focus on supporting engineers when developing control code for programmable logical controllers. Today, SP is a micro-service architecture, usable in various areas like runtime control, online monitoring, energy optimization, and even emergency department patient planning. This paper presents a use case at an automotive company, where the operation sequences in a large number of automated robot stations, need to be modified. SP, together with virtual commissioning tools, automates this modification by identifying, optimizing, verifying and simulating operation sequences, and then updates the robot and control programs. This use case demonstrates the strength of SP and its architecture and how it is used for integrated virtual preparation and commissioning.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- Bergagård, Patrik, 1984, et al.
(författare)
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Derivation of placement transitions for offline calculation of restart states
- 2013
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Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - 1946-0759 .- 1946-0740.
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Konferensbidrag (refereegranskat)abstract
- This paper presents a preprocess to an existing method for offline calculation of restart states for manufacturing systems modeled by operations. In the existing method, placement transitions are used to model restart in restart states from potential error states, and supervisory control theory is used to calculate which of these transitions are valid. With the proposed preprocess, the precedence andthe alternative dependencies between the operations are exploited in order to reduce the number of such placement transitions which are required in the model used by theexisting method. With such a reduced model, the valid restart states for larger and more complex systems can be calculated.
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| 8. |
- Bergagård, Patrik, 1984
(författare)
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Modeling and analysis of restart, transport, and resource allocation in manufacturing systems using sequences of operations
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Highly automated and flexible manufacturing systems have gained industrial popularity for their ability to combine high product volumes with high product quality. However, the process planning, the process to design and plan thetasks and actions, the operations, that constitute the manufacturing process, is a complex and time consuming process. The process planning struggles with continuouslychanged requirements from the products to be produced and demands and capabilities of the manufacturing system itself.The high cost of investment of a manufacturing system in combination with many interlaced manufacturing systems in a factory, requires that the manufacturing process is running smoothly with high utilization of the resources and thatstoppages are avoided. To reach a high resource utilization, multiple products may be concurrently produced in a manufacturing system. In systems where several product routes are possible, the design of operations that combine concurrent manufacturing and high utilization is a difficult task. One major reason for stoppages is the occurrence of unforeseen errors that cause the manufacturingsystem to halt. The succeeding error recovery is often a complex and thereby time consuming process that typically requires manual involvement. To plan for restart after errors already during the process planning would therefore shorten the time the system is halted.To accomplish a useful process plan that faces the presented problems and is adaptive to (late) requirement changes, it is favorable to base the analyses and activities during the process planning on mathematically well defined methods, formal methods, well-suited for computerized calculations but heavily depended on precise models to calculate useful results.To support the process planning, this thesis presents how to use formal methods to analyze transport, resource allocation for concurrent manufacturing, and restart in manufacturing systems. To overcome the modeling issue, the required formal models are automatically generated from the operations that model the manufacturing processes and the result of the methods are given as additional operations and extensions to existing operations.
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| 9. |
- Bergagård, Patrik, 1984, et al.
(författare)
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Modeling and automatic calculation of restart states for an industrial windscreen mounting station
- 2015
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Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 48:3, s. 1030-1036
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Konferensbidrag (refereegranskat)abstract
- The production in an automated manufacturing system will not always progress as intended. A wide variety of possible faults may cause errors that lead to an unsynchronization between the control system and the physical system that consequently lead to production stoppages. The common industrial practice to deal with such non-intended progress is to extend the control system with tailor-made solutions to account for errors. This extension is both time consuming and there is no guarantee that all relevant errors are handled.This paper models the control system to enable automatic derivation of restart states applied to an existing station for automatic mounting of windscreens onto car bodies. These restart states are states in the control system where it is correct to resynchronize the control and the physical systems so that the automated production can be resumed. This aids the preparation phase by letting the developer focus on modeling the nominal production and on specifying (un-)desired behavior during the restarted production, and then automatically retrieve the restart states for all control states. The online restart process is then reduced to a semi-automatic process where an operator can be supported with instructions for how to correctly resynchronize the control and the physical systems in a selected restart state.
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| 10. |
- Bergagård, Patrik, 1984
(författare)
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On restart of automated manufacturing systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Highly automated manufacturing systems have gained industrial popularity for their ability to combine high product volumes with high product quality. The high cost of investment in combination with many linked manufacturing systems in a factory, requires that the production runs smoothly with high utilization of the resources and that stoppages are avoided. One major reason for stoppages is the occurrence of errors. A wide variety of possible faults, such as badly fixated parts, broken actuators, and teething problems in the system, may cause errors that lead to an unsynchronization between the control system and the physical system that consequently lead to production stoppages. The succeeding error recovery is often a complex and thereby time consuming process that typically requires operator involvement. To plan for restart after errors already during the development of the system would therefore greatly support the online restart process and reduce the time the production is undesirably stopped. The common industrial practice to deal with such non-intended progress is to extend the control system with tailor-made solutions to account for foreseen errors. This extension is both time consuming and there is no guarantee that all relevant errors are handled.To support both offline and online work with restart of the production, this thesis proposes a method for automatic calculation of restart states. These restart states are states in the control system from where it is correct to resynchronize the control and the physical systems so that the production can be resumed, irrespectively if the error is foreseen or unforeseen. The method aids during the development of the system by letting the developer focus on modeling the nominal production and on specifying (un-)desired behavior during the restarted production, and then automatically retrieve the correct restart states for all control states. The production can thus be designed for restart. Based on these precalculated restart states, the online restart process is reduced to a semi-automatic process where an operator can be supported with instructions for how to correctly resynchronize the control and the physical systems in a selected restart state. In addition to a thorough theoretical presentation of the supervisory control theory based method, the thesis also describes a proof of concept implementation in a lab manufacturing system and a validation on an industrial windscreen mounting station. The implementation shows that restart after unforeseen errors is enabled and exemplifies the operator support during the online restart process. From the validation it can be concluded that the underlying model is sufficient and that employment of the proposed method would have improved the restart processes after historical production stoppages.
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