| 1. |
- Khan, Adnan, 1984, et al.
(author)
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Digital Twin for Legacy Systems: Simulation Model Testing and Validation
- 2018
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In: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. ; 2018-August, s. 421-426
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Conference paper (peer-reviewed)abstract
- In this paper, an approach to incorporate a digitaltwin for legacy production systems is presented. Hardware-in-the-loop setups are routinely used by manufacturing companiesto carry out virtual commissioning. However, manufacturingcompanies having online legacy production systems are stillstruggling to incorporate a digital twin due to the absence ofverified and validated simulation models. Companies that usevirtual commissioning as a part of their engineering tool chain,usually perform offline verification of the simulation model.This approach is typically based on visual inspection and is atedious task as each aspect of the model has to be visuallyvalidated. For legacy systems, only assessing the behaviorvisually in the absence of updated documents can result in anincorrect simulation model, i.e. simulating incorrect behaviorwith respect to the specification. Due to this, such simulationmodels cannot be incorporated in the engineering tool chain,as the simulated results can lead to improper decisions and caneven cause equipment damage. This paper presents a platformand an approach, based on model-based testing, that is a firststep for manufacturing companies to incorporate a validatedsimulation model for existing online production systems thatwill serve as a digital twin.
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| 2. |
- Khan, Adnan, 1984, et al.
(author)
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On test case reduction for testing safety properties of manufacturing systems
- 2022
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In: Journal of Manufacturing Systems. - : Elsevier BV. - 0278-6125. ; 63, s. 203-213
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Journal article (peer-reviewed)abstract
- This paper presents an approach to reduce the number of test cases, and hence testing time for the safe input-output conformance simulation relation (safe-IOCOS). The safe-IOCOS relation requires the implementation to be trace equivalent with respect to the specification only for traces composed of safety behaviors, which makes safe-IOCOS a suitable relation to test safety properties in practical settings. However, in typical manufacturing systems, multiple safety behaviors are typically associated with each nominal operation in the implementation. Thus, if safe-IOCOS is used industrially then testing for safety related faults becomes time consuming as the traces composed of same safety behaviors gets tested multiple times. This is possible either if the target states reached after the execution of traces have the same past behavior or the same future behavior. To remedy this, two reduction methods are proposed in this paper, subset construction and bisimulation equivalence. Both reduction methods preserve the traces of the system. Using both subset construction and bisimulation, a given specification can be maximally reduced and then used to implement the manufacturing system. The implementation based on a maximally reduced bisimilar specification allows the test engineer to omit test cases if the same safety behavior has already been tested. Furthermore, faults related to missing safety behaviors that are associated with multiple traces can be uncovered more efficiently compared to if the non-reduced specification is used for testing. To summarize, testing is a laborious problem, which can benefit from methods that enable reduction in testing time and makes the testing procedure efficient in terms of uncovering errors.
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| 3. |
- Khan, Adnan, 1984, et al.
(author)
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On testing and automatic mending of safety PLC code
- 2021
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In: CIRP Journal of Manufacturing Science and Technology. - : Elsevier BV. - 1755-5817 .- 1878-0016. ; 35, s. 431-440
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Journal article (peer-reviewed)abstract
- This paper presents an approach to automatically amend an erroneous model of an implementation using a safety specification as the basis to ensure safety. Industrially, safety PLCs are common to ensure safe operations. However, before its commissioning, the implemented safety code must be tested for faults caused by spurious transitions and missing safety transitions. Spurious transitions are implemented events that are not prescribed by the safety specification, while missing safety transitions are unimplemented safety events that are prescribed by the safety specification. The presence of these faults can result in material or human damage. The proposed approach requires the model of an implementation to be trace equivalent with the given safety specification only in terms of traces composed of safety events, which is captured by the notion of safe-IOCOS. If the implementation emits other than the specified safety events then the implementation is not safe-IOCOS and requires amendment. This is achieved by removing the spurious transitions and adding the missing safety events in the implementation using synthesis techniques from the supervisory control theory. The infimal controllable superlanguage is used to compute the infimal safety extension, which adds the missing safety transitions. It is shown how the resulting model of an implementation after amendment is both safe-IOCOS and controllable with respect to the specification.
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| 4. |
- Khan, Adnan, 1984, et al.
(author)
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On the Equivalence of Controllability and the Input Output Conformance Testing Relation
- 2018
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Reports (other academic/artistic)abstract
- In this paper, the relation between controllability and the IOCO testing relationis examined. Based on a natural and common notion of controllability, where uncontrollableevents are interpreted as outputs from the plant, and viewing an implementation under testas a plant, the IOCO testing relation is equivalent to controllability. Further, it is shownhow supervisor synthesis can be used to algorithmically make an implementation IOCO withrespect to its specification. This can be done either by restricting the implementation to thesupremal controllable sublanguage, or extending the specification to the infimal controllablesuperlanguage, of the implementation and the specification. Both alternatives seem to be equallyviable, and the choice between them seem strongly application dependent.
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| 5. |
- Khan, Adnan, 1984, et al.
(author)
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On-the-fly conformance testing of safety PLC code using QuickCheck
- 2019
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In: IEEE International Conference on Industrial Informatics (INDIN). - 1935-4576. ; 2019-July, s. 419-424
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Conference paper (peer-reviewed)abstract
- In this paper, an approach based on the IOCOS testing relation to test safety PLC code using the tool QuickCheck is presented. Testing and validation of the safety PLC code is typically carried out on a physical system using checklists. These checklists are developed by engineers using system specification. However, due to the manual nature of checklist generation and execution, certain test cases can be overlooked and can lead to human accidents. The presented approach allows on-the-fly generation and execution of test cases, which expands the scope of testing by including test cases unconceived during checklist generation. Furthermore, it is demonstrated how errors in the safety PLC code are uncovered based on the IOCOS relation.
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| 6. |
- Khan, Adnan, 1984, et al.
(author)
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On the Safe IOCOS relation for Testing Safety PLC Code
- 2019
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In: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - 1946-0759 .- 1946-0740. ; 2019-September, s. 1449-1452
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Conference paper (peer-reviewed)abstract
- In this paper, limitations of the IOCOS testing relation in regard to testing safety PLC code is examined and a modification of the current IOCOS relation, called safe-IOCOS is proposed. In the IOCOS testing relation, an implementation is IOCOS with respect to a specification, if it emits a subset of the specified outputs and a super-set of the specified inputs after the execution of each trace in the specification. However, for testing safety PLC code, the IOCOS relation is not detailed enough as the subset requirement on the respective inputs and outputs could allow some safety behaviors to go untested. These limitations of the IOCOS relation may thus pose threats to humans. So the notion of safe-IOCOS is defined, which strengthens IOCOS to require equality between the implementation and the specification in relation to the inputs and outputs, respectively. An example shows these shortcomings of IOCOS and how the proposed safe-IOCOS relation is better suited for testing safety PLC code.
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| 7. |
- Khan, Adnan, 1984, et al.
(author)
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Testing and validation of safety logic in the virtual environment
- 2019
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In: CIRP Journal of Manufacturing Science and Technology. - : Elsevier BV. - 1755-5817 .- 1878-0016. ; 26, s. 1-9
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Journal article (peer-reviewed)abstract
- This paper presents an approach for testing safety PLC logic in a virtual environment, using the IOCO testing relation as validation criteria. Manufacturing companies more and more rely on virtual commissioning to reduce the physical commissioning time by testing and debugging the PLC logic of the nominal behavior prior to physical commissioning. However, safety PLC logic testing is still carried out on real systems manually. This manual practice of safety logic validation hinders industry to exploit the full potential of virtual commissioning to reduce the physical commissioning time. The proposed approach assists manufacturing companies in the validation of safety PLC logic using a simulation model before the factory acceptance testing phase. Using the proposed approach, a simulation model can be used to test the safety PLC logic and prepare better for the factory acceptance testing phase, hence, further reduction in physical commissioning time can be achieved.
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| 8. |
- Khan, Adnan, 1984
(author)
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Towards the safe-IOCOS relation -- On testing and correction of errors in an implementation to ensure safety
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The technological advancement that has occurred at a blistering pace in the past decades has enabled manufacturing companies to conceive innovative products. However, to meet growing demands of consumers, manufacturing companies are expected to maintain a steady production rate without compromising product quality. To meet these requirements, the industrial sector is increasingly using robots and other automated machinery. Automated machines are predominantly controlled via programmable logic controllers (PLCs) to carry out the nominal tasks. For safety critical tasks, though, special devices in conjunction with safety PLCs are used to prevent material damage and accidents leading to human injuries. Before physical commissioning of a manufacturing system, the nominal PLC code is tested to uncover faults. This can be done either by running tests on the physical system or using a simulation model via virtual commissioning . However, the safety code is usually tested during the factory acceptance test phase on the actual physical system. The faults found in the safety code are corrected manually, which is time consuming and error prone. The formal methods community has developed testing relations and approaches that can be used to automatically test and amend faults in the implementation. The work presented in this thesis is based on such a testing relation and formal approach. The safe input-output conformance simulation relation (safe-IOCOS) is a testing relation that requires equality for traces composed of safety behaviors. However, in practical settings, many safety behaviors in a production system are implemented for each nominal operation. And these behaviors get tested multiple times during testing, which increases the testing time unnecessarily. To counter this problem, an approach to minimize testing time is proposed. Furthermore, an approach to automatically amend a faulty implementation to ensure safety properties with respect to a safety specification is presented. This approach uses the procedure of synthesis , from the framework of supervisory control theory, based on the infimial controllable superlanguage , which not only removes the faults from the implementation but also guarantees to make it safe-IOCOS.
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| 9. |
- Khan, Adnan, 1984, et al.
(author)
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Virtual Engineering Framework forAutomatic Generation of Control Logic including Safety
- 2017
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In: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. ; 2017-August
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Conference paper (peer-reviewed)abstract
- In this paper, a new virtual engineering framework based on clever components for automatic generation of control logic including safety is presented. Manual practices of modeling plant components and writing PLC programs is an error-prone and time-consuming task. This new virtual engineering framework enables automatic generation of control solutions based on cloud based repositories, containing clever components with formalized logic descriptions provided by vendors. Consequently, reduced time for virtual engineering and commissioning can be achieved by avoiding current manual practices. Other advantages include testing and validation of PLC logic and plant models in the engineering phase, and less human errors due to automatic generation of both plant models and logic. In addition, this framework will help in the development of more reliable and robust safety logic and assist the procedure of issuing safety certificate.
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